1. Classical thermodynamics states that absolute zero can never be reached by compressing and expanding a gas, as temperature can only be lowered to a fraction of the original value through this process.
2. Techniques like evaporative cooling and using lasers to slow atoms allow temperatures below 1 Kelvin to be achieved.
3. While absolute zero can theoretically never be reached, these techniques get closer to it with each improvement.
The document discusses the properties and behavior of gases, liquids, and solids from a microscopic perspective. It explains that gases have particles with empty space between them allowing the particles to move freely, while liquids have particles close together allowing them to flow but slide past one another, and solids have particles locked in a fixed structure. The document also covers gas laws, phase changes, types of solids based on bonding, and heating curves. It provides a concise overview of the states of matter and changes between states from a molecular level.
Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. It relates to the evaporation rate of a liquid and is affected by factors like temperature, composition of mixtures, and presence of solids or liquids. Vapor pressure increases non-linearly with temperature and the boiling point of a liquid is reached when its vapor pressure equals atmospheric pressure. It plays an important role in cloud formation through processes like condensation, supersaturation, and Raoult's law governing vapor pressures in mixtures.
1. Gases obey Boyle's law, Charles' law, and Gay-Lussac's law, collectively known as the gas laws.
2. The ideal gas law combines these and states that for an ideal gas, pressure × volume divided by temperature is a constant (PV/T = nRT).
3. Dalton's law of partial pressures states that in a gas mixture, the total pressure is equal to the sum of the partial pressures of the individual gases.
States of Matter and properties of matter: State of matter, changes in the state of matter, latent heats, vapour pressure, sublimation critical point, eutectic mixtures, gases, aerosols – inhalers, relative humidity, liquid complexes, liquid crystals, glassy states, solid- crystalline, amorphous & polymorphism.
Physicochemical properties of drug molecules: Refractive index, optical rotation, dielectric constant, dipole moment, dissociation constant, determinations and applications
Vapour pressure is the pressure exerted by a vapour in equilibrium with its condensed phases at a given temperature. It is a measure of how easily a substance transitions into a gas. The Antoine equation relates vapour pressure to temperature using substance-specific coefficients, and allows one to calculate vapour pressure. Water boils when its vapour pressure equals atmospheric pressure, which occurs at 100°C according to the Antoine equation for water. Understanding vapour pressure helps explain physics concepts related to changes of state.
1) Boyle's law states that the pressure and volume of a gas are inversely proportional at constant temperature. Charles' law states that the volume of a gas is directly proportional to its temperature at constant pressure.
2) A refrigerant is a substance used in refrigeration to absorb heat from the space being refrigerated and release it elsewhere. Common refrigerants like Freon gas are used in refrigerators.
3) A refrigerator uses a vapor-compression cycle to cool its interior. Freon gas is compressed, condenses while releasing heat outside, then evaporates in the interior, absorbing heat and cooling the refrigerator. This cycle repeats continuously.
All matter is made of atoms. The ideal gas law relates the volume, pressure, temperature, and amount of a gas. One mole of a substance contains Avogadro's number of atoms or molecules. The average kinetic energy of gas molecules is directly proportional to temperature according to kinetic theory.
The document discusses vapor pressure and boiling points. It explains that vapor pressure increases with temperature as more liquid molecules escape into the gas phase, creating pressure above the liquid. Boiling occurs when vapor pressure equals atmospheric pressure. Boiling point depends on the strength of molecular attractions, with stronger attractions yielding higher boiling points. Boiling points change with pressure, with lower pressure resulting in lower boiling points and higher pressure yielding higher boiling points.
The document discusses the properties and behavior of gases, liquids, and solids from a microscopic perspective. It explains that gases have particles with empty space between them allowing the particles to move freely, while liquids have particles close together allowing them to flow but slide past one another, and solids have particles locked in a fixed structure. The document also covers gas laws, phase changes, types of solids based on bonding, and heating curves. It provides a concise overview of the states of matter and changes between states from a molecular level.
Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. It relates to the evaporation rate of a liquid and is affected by factors like temperature, composition of mixtures, and presence of solids or liquids. Vapor pressure increases non-linearly with temperature and the boiling point of a liquid is reached when its vapor pressure equals atmospheric pressure. It plays an important role in cloud formation through processes like condensation, supersaturation, and Raoult's law governing vapor pressures in mixtures.
1. Gases obey Boyle's law, Charles' law, and Gay-Lussac's law, collectively known as the gas laws.
2. The ideal gas law combines these and states that for an ideal gas, pressure × volume divided by temperature is a constant (PV/T = nRT).
3. Dalton's law of partial pressures states that in a gas mixture, the total pressure is equal to the sum of the partial pressures of the individual gases.
States of Matter and properties of matter: State of matter, changes in the state of matter, latent heats, vapour pressure, sublimation critical point, eutectic mixtures, gases, aerosols – inhalers, relative humidity, liquid complexes, liquid crystals, glassy states, solid- crystalline, amorphous & polymorphism.
Physicochemical properties of drug molecules: Refractive index, optical rotation, dielectric constant, dipole moment, dissociation constant, determinations and applications
Vapour pressure is the pressure exerted by a vapour in equilibrium with its condensed phases at a given temperature. It is a measure of how easily a substance transitions into a gas. The Antoine equation relates vapour pressure to temperature using substance-specific coefficients, and allows one to calculate vapour pressure. Water boils when its vapour pressure equals atmospheric pressure, which occurs at 100°C according to the Antoine equation for water. Understanding vapour pressure helps explain physics concepts related to changes of state.
1) Boyle's law states that the pressure and volume of a gas are inversely proportional at constant temperature. Charles' law states that the volume of a gas is directly proportional to its temperature at constant pressure.
2) A refrigerant is a substance used in refrigeration to absorb heat from the space being refrigerated and release it elsewhere. Common refrigerants like Freon gas are used in refrigerators.
3) A refrigerator uses a vapor-compression cycle to cool its interior. Freon gas is compressed, condenses while releasing heat outside, then evaporates in the interior, absorbing heat and cooling the refrigerator. This cycle repeats continuously.
All matter is made of atoms. The ideal gas law relates the volume, pressure, temperature, and amount of a gas. One mole of a substance contains Avogadro's number of atoms or molecules. The average kinetic energy of gas molecules is directly proportional to temperature according to kinetic theory.
The document discusses vapor pressure and boiling points. It explains that vapor pressure increases with temperature as more liquid molecules escape into the gas phase, creating pressure above the liquid. Boiling occurs when vapor pressure equals atmospheric pressure. Boiling point depends on the strength of molecular attractions, with stronger attractions yielding higher boiling points. Boiling points change with pressure, with lower pressure resulting in lower boiling points and higher pressure yielding higher boiling points.
This document discusses properties of pure substances and provides an example problem. It defines key concepts like sensible heat, latent heat, enthalpy, and uses a steam table to find properties of water and steam at specific temperatures and pressures. The example problem asks the reader to calculate several properties for a vessel containing a mixture of saturated water and steam at 250°C, given the volume of the vessel is 0.04m3 and mass of liquid is 9kg. Data is collected from the steam table to solve the problem.
The document discusses the kinetic theory as it applies to gases and the nature of liquids. It describes three basic assumptions of kinetic theory for gases: gases are composed of particles in random motion that undergo perfectly elastic collisions. Gas pressure results from particle collisions. It also discusses how temperature relates to average kinetic energy of particles. The document then covers how liquids are similar to gases in that their particles are in motion, but they are more dense due to intermolecular attractions. It defines vaporization, evaporation, boiling points, and the relationship between vapor pressure and temperature.
There are five states of matter: solid, liquid, gas, plasma, and Bose-Einstein condensate (BEC). Plasma is common among stars but not on Earth, while BEC only forms at extremely low temperatures near absolute zero when atoms lose kinetic energy and clump together. Gases are characterized by diffusion, the movement from high to low concentration, and effusion, movement through a small pore. Several gas laws describe gas behavior, including Boyle's law relating pressure and volume, Charles' law relating volume and temperature, Avogadro's law of equal volumes containing equal molecules, and Dalton's law of partial pressures. Real gases deviate from the ideal gas model due to intermolecular forces
The van der Waals gas model takes into account intermolecular interactions that the ideal gas model neglects. It explains the liquid-gas phase transition through a critical point, where the vapor and liquid phases become indistinguishable. The model approximates molecules as rigid spheres that experience short-range repulsion and long-range attraction. It derives an equation of state relating pressure, volume, and temperature. This equation reduces to the ideal gas law under conditions of high temperature or low density.
This document discusses the properties and behavior of gases. It states that gases have no fixed shape or volume, their molecules are far apart with little attraction and high freedom of movement. Gases exert pressure on their containers from molecular collisions. Their volume depends on the space and container available. Gases can be liquefied by increasing pressure or decreasing temperature, as seen with common liquefied gases like ammonia, nitrogen, oxygen and LPG. The document also outlines Boyle's, Charles's and Avogadro's laws which describe the relationships between a gas's pressure, volume, temperature and number of molecules.
The document discusses several gas laws including Boyle's law, Charles' law, Gay-Lussac's law, Avogadro's law, the combined gas law, and the ideal gas law. It provides definitions of these laws and examples of calculations using each one. The key relationships covered are: the inverse relationship between pressure and volume at constant temperature (Boyle's law), the direct relationship between volume and temperature at constant pressure (Charles' law), the direct relationship between pressure and temperature at constant volume (Gay-Lussac's law), the relationship between volume and amount of gas at constant pressure and temperature (Avogadro's law), and the ideal gas law which relates pressure, volume, temperature,
The document discusses gas laws and provides examples of how they apply in everyday life. Boyle's law states that the pressure and volume of a gas are inversely proportional at constant temperature. Examples given include shaking a soda bottle and spraying aerosol cans. Charles' law explains how the volume of a gas increases with temperature. Examples are helium balloons and dented ping pong balls. Gay-Lussac's law says gas pressure rises proportionally with increasing temperature at constant volume, illustrated by firing bullets and burning tires. Avogadro's law concerns the direct relationship between gas volume and number of gas particles. Examples include projectiles, balloons, breathing, and baked goods rising.
- Gay-Lussac's Law states that the pressure of a gas at constant volume is directly proportional to its temperature in Kelvin. As temperature increases, pressure increases; as temperature decreases, pressure decreases.
- The law is expressed through an equation relating pressure (P), temperature (T), and a proportionality constant.
- Sample problems demonstrate using the law to calculate changes in pressure when temperature is varied for a constant volume of gas.
The document discusses the kinetic molecular theory and several gas laws including Boyle's law, Charles' law, Guy-Lussac's law, and the combined gas law. It explains that according to kinetic theory, gas particles are in constant random motion and their interactions are dominated by collisions. Boyle's law states that pressure and volume are inversely proportional at constant temperature. Charles' law specifies that volume and temperature are directly proportional at constant pressure. The combined gas law incorporates both Boyle's and Charles' laws.
1) Gases expand to fill their containers, are highly compressible, and have low densities due to the large distances between molecules. Their physical properties are similar regardless of chemical properties.
2) Pressure is caused by molecular collisions with surfaces. It increases with more frequent or forceful collisions. Temperature increases collision frequency and force. Pressure also rises with increased amount or decreased volume of gas.
3) Kinetic molecular theory explains gas behavior by modeling gases as particles in random motion, where temperature corresponds to average kinetic energy. This enables understanding of gas laws and pressure in terms of molecular collisions.
The document discusses the ideal gas law, which relates the pressure, volume, temperature, and number of moles of a gas. It describes how the ideal gas law was developed by combining Boyle's law, Charles' law, and Avogadro's law. The ideal gas law equation is PV=nRT, where P is pressure, V is volume, n is moles of gas, R is the gas constant, and T is temperature in Kelvin. An example problem demonstrates how to use the ideal gas law to calculate the moles of gas produced in a chemical reaction.
Chemistry - Chp 13 - States of Matter - NotesMr. Walajtys
The document discusses the kinetic theory description of gases and liquids, explaining that gas particles move rapidly in straight lines and collisions between them result in gas pressure, while liquid particles are able to flow but interact strongly and have less space between them than gas particles. It also covers evaporation as the process where some liquid particles gain enough kinetic energy to overcome attractive forces and enter the gas phase, and how heating increases the rate of evaporation by raising the average kinetic energy of particles.
The document discusses the characteristics and properties of gases. It defines the gaseous state as the state where intermolecular forces are at a minimum. Some key characteristics of gases include having low density, high compressibility, diffusibility, and filling their container uniformly. The document also discusses various gas laws including Boyle's law, Charles' law, Gay-Lussac's law, Avogadro's law, and the ideal gas equation. It provides the mathematical relationships and graphical representations for each gas law.
The document discusses the gas laws and properties of gases. It begins by describing the composition of Earth's atmosphere, which is primarily nitrogen and oxygen. It then discusses that gases have mass and low densities compared to liquids and solids. The document outlines four variables that describe gases - pressure, volume, temperature, and amount. It explains concepts such as gas compressibility, units of measurement for gases, and the kinetic molecular theory which describes gas particles as being in constant random motion.
1. The document discusses properties of pure substances and phase changes that occur in pure substances like water. It defines terms like saturated liquid, saturated vapor, quality, and superheated vapor.
2. Key points covered include the constant pressure process that water undergoes when heated from liquid to vapor, involving processes like boiling and vaporization. Phase change occurs at the saturation temperature for a given pressure.
3. The document also discusses the temperature-volume and pressure-volume diagrams for pure substances and identifies important points like the triple point and critical point on these diagrams.
This document summarizes several important laws of fluids and gases:
- Pascal's principle states that pressure applied to any part of a confined fluid is transmitted equally throughout the fluid.
- Boyle's law states that for a gas at constant temperature, the product of pressure and volume is a constant.
- Charles's law describes how the volume of a gas increases or decreases as temperature increases or decreases at constant pressure.
A conceptual description of the van der Waals equation for real gases. Discussion of van der Waals constants a and b, plus conceptual example. Does not assume that intermolcular forces have been learned previously. General Chemistry
The document discusses properties of pure substances and provides data on saturated water properties. It defines key terms like pure substance, homogeneous substance, and simple system. It describes water's phase diagram and how it can exist as a solid, liquid, or gas. Tables A-4 and A-5 show saturated water properties like temperature, pressure, internal energy, enthalpy and entropy at different states along the saturation line from the triple point to the critical point.
This document provides an overview of refrigeration concepts and components. It defines key terms like temperature, pressure, heat, latent heat and refrigerants. It describes the basic refrigeration circuit, including the evaporator, compressor, condenser and expansion process. It explains how refrigerants absorb heat during evaporation to produce cooling, and how the compressor pressurizes the refrigerant to drive the process.
The document discusses phase transitions in substances as they are heated or cooled. It explains:
- When a solid is heated, it absorbs heat until it reaches its melting point, at which temperature the solid melts and absorbs a large amount of heat called the latent heat of fusion.
- Amorphous solids undergo a glass transition rather than a first-order phase transition like melting. At the glass transition temperature Tg, the heat capacity increases but there is no latent heat absorbed.
- Sublimation is when a solid transitions directly to a gas without passing through the liquid phase, such as when dry ice (solid CO2) turns to gas.
- The vapor pressure of
Propiedades termodinámicas de las sustancias purasNorman Rivera
1. Thermodynamics properties of pure substances include phases (solid, liquid, gas), phase change processes, and property diagrams.
2. Key points in the phase change of water include compressed liquid, saturated liquid, saturated liquid-vapor mixture, saturated vapor, and superheated vapor.
3. Important thermodynamic concepts are saturation temperature and pressure, which define the conditions for phase changes, and the critical point where liquid and gas phases cannot be distinguished.
This document discusses properties of pure substances and provides an example problem. It defines key concepts like sensible heat, latent heat, enthalpy, and uses a steam table to find properties of water and steam at specific temperatures and pressures. The example problem asks the reader to calculate several properties for a vessel containing a mixture of saturated water and steam at 250°C, given the volume of the vessel is 0.04m3 and mass of liquid is 9kg. Data is collected from the steam table to solve the problem.
The document discusses the kinetic theory as it applies to gases and the nature of liquids. It describes three basic assumptions of kinetic theory for gases: gases are composed of particles in random motion that undergo perfectly elastic collisions. Gas pressure results from particle collisions. It also discusses how temperature relates to average kinetic energy of particles. The document then covers how liquids are similar to gases in that their particles are in motion, but they are more dense due to intermolecular attractions. It defines vaporization, evaporation, boiling points, and the relationship between vapor pressure and temperature.
There are five states of matter: solid, liquid, gas, plasma, and Bose-Einstein condensate (BEC). Plasma is common among stars but not on Earth, while BEC only forms at extremely low temperatures near absolute zero when atoms lose kinetic energy and clump together. Gases are characterized by diffusion, the movement from high to low concentration, and effusion, movement through a small pore. Several gas laws describe gas behavior, including Boyle's law relating pressure and volume, Charles' law relating volume and temperature, Avogadro's law of equal volumes containing equal molecules, and Dalton's law of partial pressures. Real gases deviate from the ideal gas model due to intermolecular forces
The van der Waals gas model takes into account intermolecular interactions that the ideal gas model neglects. It explains the liquid-gas phase transition through a critical point, where the vapor and liquid phases become indistinguishable. The model approximates molecules as rigid spheres that experience short-range repulsion and long-range attraction. It derives an equation of state relating pressure, volume, and temperature. This equation reduces to the ideal gas law under conditions of high temperature or low density.
This document discusses the properties and behavior of gases. It states that gases have no fixed shape or volume, their molecules are far apart with little attraction and high freedom of movement. Gases exert pressure on their containers from molecular collisions. Their volume depends on the space and container available. Gases can be liquefied by increasing pressure or decreasing temperature, as seen with common liquefied gases like ammonia, nitrogen, oxygen and LPG. The document also outlines Boyle's, Charles's and Avogadro's laws which describe the relationships between a gas's pressure, volume, temperature and number of molecules.
The document discusses several gas laws including Boyle's law, Charles' law, Gay-Lussac's law, Avogadro's law, the combined gas law, and the ideal gas law. It provides definitions of these laws and examples of calculations using each one. The key relationships covered are: the inverse relationship between pressure and volume at constant temperature (Boyle's law), the direct relationship between volume and temperature at constant pressure (Charles' law), the direct relationship between pressure and temperature at constant volume (Gay-Lussac's law), the relationship between volume and amount of gas at constant pressure and temperature (Avogadro's law), and the ideal gas law which relates pressure, volume, temperature,
The document discusses gas laws and provides examples of how they apply in everyday life. Boyle's law states that the pressure and volume of a gas are inversely proportional at constant temperature. Examples given include shaking a soda bottle and spraying aerosol cans. Charles' law explains how the volume of a gas increases with temperature. Examples are helium balloons and dented ping pong balls. Gay-Lussac's law says gas pressure rises proportionally with increasing temperature at constant volume, illustrated by firing bullets and burning tires. Avogadro's law concerns the direct relationship between gas volume and number of gas particles. Examples include projectiles, balloons, breathing, and baked goods rising.
- Gay-Lussac's Law states that the pressure of a gas at constant volume is directly proportional to its temperature in Kelvin. As temperature increases, pressure increases; as temperature decreases, pressure decreases.
- The law is expressed through an equation relating pressure (P), temperature (T), and a proportionality constant.
- Sample problems demonstrate using the law to calculate changes in pressure when temperature is varied for a constant volume of gas.
The document discusses the kinetic molecular theory and several gas laws including Boyle's law, Charles' law, Guy-Lussac's law, and the combined gas law. It explains that according to kinetic theory, gas particles are in constant random motion and their interactions are dominated by collisions. Boyle's law states that pressure and volume are inversely proportional at constant temperature. Charles' law specifies that volume and temperature are directly proportional at constant pressure. The combined gas law incorporates both Boyle's and Charles' laws.
1) Gases expand to fill their containers, are highly compressible, and have low densities due to the large distances between molecules. Their physical properties are similar regardless of chemical properties.
2) Pressure is caused by molecular collisions with surfaces. It increases with more frequent or forceful collisions. Temperature increases collision frequency and force. Pressure also rises with increased amount or decreased volume of gas.
3) Kinetic molecular theory explains gas behavior by modeling gases as particles in random motion, where temperature corresponds to average kinetic energy. This enables understanding of gas laws and pressure in terms of molecular collisions.
The document discusses the ideal gas law, which relates the pressure, volume, temperature, and number of moles of a gas. It describes how the ideal gas law was developed by combining Boyle's law, Charles' law, and Avogadro's law. The ideal gas law equation is PV=nRT, where P is pressure, V is volume, n is moles of gas, R is the gas constant, and T is temperature in Kelvin. An example problem demonstrates how to use the ideal gas law to calculate the moles of gas produced in a chemical reaction.
Chemistry - Chp 13 - States of Matter - NotesMr. Walajtys
The document discusses the kinetic theory description of gases and liquids, explaining that gas particles move rapidly in straight lines and collisions between them result in gas pressure, while liquid particles are able to flow but interact strongly and have less space between them than gas particles. It also covers evaporation as the process where some liquid particles gain enough kinetic energy to overcome attractive forces and enter the gas phase, and how heating increases the rate of evaporation by raising the average kinetic energy of particles.
The document discusses the characteristics and properties of gases. It defines the gaseous state as the state where intermolecular forces are at a minimum. Some key characteristics of gases include having low density, high compressibility, diffusibility, and filling their container uniformly. The document also discusses various gas laws including Boyle's law, Charles' law, Gay-Lussac's law, Avogadro's law, and the ideal gas equation. It provides the mathematical relationships and graphical representations for each gas law.
The document discusses the gas laws and properties of gases. It begins by describing the composition of Earth's atmosphere, which is primarily nitrogen and oxygen. It then discusses that gases have mass and low densities compared to liquids and solids. The document outlines four variables that describe gases - pressure, volume, temperature, and amount. It explains concepts such as gas compressibility, units of measurement for gases, and the kinetic molecular theory which describes gas particles as being in constant random motion.
1. The document discusses properties of pure substances and phase changes that occur in pure substances like water. It defines terms like saturated liquid, saturated vapor, quality, and superheated vapor.
2. Key points covered include the constant pressure process that water undergoes when heated from liquid to vapor, involving processes like boiling and vaporization. Phase change occurs at the saturation temperature for a given pressure.
3. The document also discusses the temperature-volume and pressure-volume diagrams for pure substances and identifies important points like the triple point and critical point on these diagrams.
This document summarizes several important laws of fluids and gases:
- Pascal's principle states that pressure applied to any part of a confined fluid is transmitted equally throughout the fluid.
- Boyle's law states that for a gas at constant temperature, the product of pressure and volume is a constant.
- Charles's law describes how the volume of a gas increases or decreases as temperature increases or decreases at constant pressure.
A conceptual description of the van der Waals equation for real gases. Discussion of van der Waals constants a and b, plus conceptual example. Does not assume that intermolcular forces have been learned previously. General Chemistry
The document discusses properties of pure substances and provides data on saturated water properties. It defines key terms like pure substance, homogeneous substance, and simple system. It describes water's phase diagram and how it can exist as a solid, liquid, or gas. Tables A-4 and A-5 show saturated water properties like temperature, pressure, internal energy, enthalpy and entropy at different states along the saturation line from the triple point to the critical point.
This document provides an overview of refrigeration concepts and components. It defines key terms like temperature, pressure, heat, latent heat and refrigerants. It describes the basic refrigeration circuit, including the evaporator, compressor, condenser and expansion process. It explains how refrigerants absorb heat during evaporation to produce cooling, and how the compressor pressurizes the refrigerant to drive the process.
The document discusses phase transitions in substances as they are heated or cooled. It explains:
- When a solid is heated, it absorbs heat until it reaches its melting point, at which temperature the solid melts and absorbs a large amount of heat called the latent heat of fusion.
- Amorphous solids undergo a glass transition rather than a first-order phase transition like melting. At the glass transition temperature Tg, the heat capacity increases but there is no latent heat absorbed.
- Sublimation is when a solid transitions directly to a gas without passing through the liquid phase, such as when dry ice (solid CO2) turns to gas.
- The vapor pressure of
Propiedades termodinámicas de las sustancias purasNorman Rivera
1. Thermodynamics properties of pure substances include phases (solid, liquid, gas), phase change processes, and property diagrams.
2. Key points in the phase change of water include compressed liquid, saturated liquid, saturated liquid-vapor mixture, saturated vapor, and superheated vapor.
3. Important thermodynamic concepts are saturation temperature and pressure, which define the conditions for phase changes, and the critical point where liquid and gas phases cannot be distinguished.
The document discusses heat and thermodynamics, specifically:
1. The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another.
2. The second law states that it is impossible to convert all heat into work, some heat must be wasted.
3. Heat transfer occurs through conduction, convection, or radiation, depending on whether the transfer is through a material, moving fluids, or electromagnetic waves.
Thermal expansion occurs when the temperature of an object increases, causing its particles to vibrate with more amplitude and increasing the average distance between particles. There are two types of expansion observed when heating a liquid in a container: apparent expansion, which does not account for expansion of the container, and real expansion, which is the apparent expansion plus the expansion of the container. The rate of real expansion is always slightly higher than the apparent rate. Steam can be classified as wet, dry saturated, or superheated depending on its moisture content and whether it has absorbed its full latent heat. Increasing pressure raises the boiling point and melting point of substances.
The document discusses heat and thermodynamics, specifically:
1) The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another.
2) The second law states that it is impossible to convert all heat into work, some heat must be wasted.
3) Heat transfer occurs through conduction, convection, or radiation, moving from warmer to cooler bodies until equilibrium is reached.
the content in this ppt pdf of properties of pure substances gives the idea of Pv, Tv, PT etc diagram and calculation of enthalpy in various region helps in dealing with Rankine and different other cycle. asy to understand about the saturation temperature and pressure.
Thermal physics concepts are introduced including temperature, thermal equilibrium, and thermometers. Temperature is defined at the macroscopic level as a measure of hotness/coldness and at the microscopic level as related to the average kinetic energy of particles. Thermal equilibrium occurs when two bodies in contact reach the same temperature. Thermometers use the expansion/contraction of liquids to measure temperature changes.
Steam and its properties and steam tableSACHINNikam39
Steam is water in its gaseous phase that is formed when water boils. There are three main types of steam: wet steam containing water droplets, dry saturated steam containing no water, and superheated steam which is heated above the saturation temperature. The properties of steam such as temperature, pressure, specific volume, enthalpy, and entropy vary depending on whether it is saturated, wet, or superheated steam. Steam tables contain values of these key thermodynamic properties at different pressures and are used for analyzing steam systems and cycles.
This document discusses refrigeration systems and how they transfer heat rather than cool. It explains that refrigeration systems lower the temperature of a space through a heat transfer process where heat is moved from the refrigerated space to the refrigerant and then to the ambient air or water. The document then provides definitions related to refrigeration and heat transfer processes. It uses a pressure-enthalpy chart to illustrate the ideal cycle of a refrigeration system as the refrigerant moves through the evaporator, compressor, condenser and expansion valve.
The document defines different phases of steam:
1) Wet steam is a mixture of liquid and vapor at saturation temperature;
2) Saturated steam is all vapor at saturation temperature;
3) Superheated steam is vapor with temperature above saturation.
Heat is a form of energy that is transferred between objects in contact with each other or at different temperatures. There are three main mechanisms of heat transfer: conduction, convection, and radiation. Conduction requires physical contact, convection occurs through the motion of fluids, and radiation can occur through empty space. Temperature is a measure of the average kinetic energy of molecular motion and is measured using thermometers on standardized scales like Celsius and Kelvin. The amount of heat required to change the temperature of a substance depends on its specific heat. Architectural design can influence heat transfer through a building's envelope and systems.
THERMODYNAMICS-I PROPERTIES OF PURE SUBSTACES MUHAMMADOKASHA3
- A pure substance can exist as a compressed liquid, saturated liquid, saturated vapor, or superheated vapor depending on its temperature and pressure.
- The boiling point of a liquid increases with pressure. At the critical point, the saturated liquid and vapor phases become indistinguishable.
- On a pressure-volume (P-V) diagram, the boiling points form a sloping saturated liquid line, while points of complete vaporization form the saturated vapor line. These lines join at the critical point to form a dome-shaped region.
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes
Physics 2.2 - Simple kinetic molecular model of matter - 2.pptxSamanyuSharma2
This document discusses evaporation and pressure changes using a kinetic molecular model of matter. It describes evaporation as the escape of more energetic molecules from the surface of a liquid, which cools the liquid. It explains how increasing temperature, surface area, or airflow can increase evaporation rate. Pressure changes are also summarized: increasing gas temperature at constant volume increases pressure, while decreasing gas volume at constant temperature increases pressure. Qualitative relationships between pressure, temperature and volume are provided based on the kinetic model.
States of Matter and properties of matter: State of matter, changes in the state of matter, latent heats, vapour pressure, sublimation critical point, eutectic mixtures, gases, aerosols – inhalers, relative humidity, liquid complexes, liquid crystals, glassy states, solid- crystalline, amorphous & polymorphism.
Physicochemical properties of drug molecules: Refractive index, optical rotation, dielectric constant, dipole moment, dissociation constant, determinations and applications
Refrigeration involves removing heat from one substance and transferring it to another. Heat naturally flows from hot to cold substances. Refrigerants are substances that absorb and transfer heat through a phase change process. Common refrigerants include pure ice, dry ice, and chemical refrigerants like R-22, each of which absorbs heat and changes phase at different fixed temperatures, allowing them to be used for cooling below the melting point of ice. Understanding the phase change properties of refrigerants is important for efficient refrigeration.
Heat is the total kinetic energy of molecules. It depends on the mass and energy of particles. Heat flows from hot to cold until equilibrium is reached, which is called when heat no longer flows. Heat can be measured in calories, joules, or BTUs. Heat causes substances to expand in volume and become less dense. The three states of matter are solid, liquid, and gas, with solids having the defined shape and volume and gases having no defined shape or volume. Heat is transferred through conduction, convection, and radiation.
There are three main methods for liquefying gases:
1. Applying sufficient pressure to gases below their critical temperature to cause liquefaction. For example, liquefying carbon dioxide which has a critical temperature of 304K.
2. Making gases do work against an external force, such as in a steam engine, causing them to lose energy and lower in temperature.
3. Forcing gases through a nozzle or porous plug, making them do work against their own internal forces and lose energy, potentially reaching liquefaction after multiple repetitions of expanding through restrictions.
The document provides an overview of kinetic theory and the states of matter. It discusses the following key points:
- Kinetic theory states that all matter is made of tiny particles in constant motion. The behavior of solids, liquids, and gases can be understood through this model.
- There are five states of matter: solid, liquid, gas, plasma, and Bose-Einstein condensate. Solids have tightly packed particles that don't move much. Liquids have spread particles that move slowly. Gases have very far apart particles that move very fast.
- Phase changes between states, such as melting, boiling, and condensation, occur when sufficient thermal energy is added to or
Understanding Inductive Bias in Machine LearningSUTEJAS
This presentation explores the concept of inductive bias in machine learning. It explains how algorithms come with built-in assumptions and preferences that guide the learning process. You'll learn about the different types of inductive bias and how they can impact the performance and generalizability of machine learning models.
The presentation also covers the positive and negative aspects of inductive bias, along with strategies for mitigating potential drawbacks. We'll explore examples of how bias manifests in algorithms like neural networks and decision trees.
By understanding inductive bias, you can gain valuable insights into how machine learning models work and make informed decisions when building and deploying them.
ACEP Magazine edition 4th launched on 05.06.2024Rahul
This document provides information about the third edition of the magazine "Sthapatya" published by the Association of Civil Engineers (Practicing) Aurangabad. It includes messages from current and past presidents of ACEP, memories and photos from past ACEP events, information on life time achievement awards given by ACEP, and a technical article on concrete maintenance, repairs and strengthening. The document highlights activities of ACEP and provides a technical educational article for members.
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The rivalry between prominent international actors for dominance over Central Asia's hydrocarbon
reserves and the ancient silk trade route, along with China's diplomatic endeavours in the area, has been
referred to as the "New Great Game." This research centres on the power struggle, considering
geopolitical, geostrategic, and geoeconomic variables. Topics including trade, political hegemony, oil
politics, and conventional and nontraditional security are all explored and explained by the researcher.
Using Mackinder's Heartland, Spykman Rimland, and Hegemonic Stability theories, examines China's role
in Central Asia. This study adheres to the empirical epistemological method and has taken care of
objectivity. This study analyze primary and secondary research documents critically to elaborate role of
china’s geo economic outreach in central Asian countries and its future prospect. China is thriving in trade,
pipeline politics, and winning states, according to this study, thanks to important instruments like the
Shanghai Cooperation Organisation and the Belt and Road Economic Initiative. According to this study,
China is seeing significant success in commerce, pipeline politics, and gaining influence on other
governments. This success may be attributed to the effective utilisation of key tools such as the Shanghai
Cooperation Organisation and the Belt and Road Economic Initiative.
A SYSTEMATIC RISK ASSESSMENT APPROACH FOR SECURING THE SMART IRRIGATION SYSTEMSIJNSA Journal
The smart irrigation system represents an innovative approach to optimize water usage in agricultural and landscaping practices. The integration of cutting-edge technologies, including sensors, actuators, and data analysis, empowers this system to provide accurate monitoring and control of irrigation processes by leveraging real-time environmental conditions. The main objective of a smart irrigation system is to optimize water efficiency, minimize expenses, and foster the adoption of sustainable water management methods. This paper conducts a systematic risk assessment by exploring the key components/assets and their functionalities in the smart irrigation system. The crucial role of sensors in gathering data on soil moisture, weather patterns, and plant well-being is emphasized in this system. These sensors enable intelligent decision-making in irrigation scheduling and water distribution, leading to enhanced water efficiency and sustainable water management practices. Actuators enable automated control of irrigation devices, ensuring precise and targeted water delivery to plants. Additionally, the paper addresses the potential threat and vulnerabilities associated with smart irrigation systems. It discusses limitations of the system, such as power constraints and computational capabilities, and calculates the potential security risks. The paper suggests possible risk treatment methods for effective secure system operation. In conclusion, the paper emphasizes the significant benefits of implementing smart irrigation systems, including improved water conservation, increased crop yield, and reduced environmental impact. Additionally, based on the security analysis conducted, the paper recommends the implementation of countermeasures and security approaches to address vulnerabilities and ensure the integrity and reliability of the system. By incorporating these measures, smart irrigation technology can revolutionize water management practices in agriculture, promoting sustainability, resource efficiency, and safeguarding against potential security threats.
Introduction- e - waste – definition - sources of e-waste– hazardous substances in e-waste - effects of e-waste on environment and human health- need for e-waste management– e-waste handling rules - waste minimization techniques for managing e-waste – recycling of e-waste - disposal treatment methods of e- waste – mechanism of extraction of precious metal from leaching solution-global Scenario of E-waste – E-waste in India- case studies.
6th International Conference on Machine Learning & Applications (CMLA 2024)ClaraZara1
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Advanced control scheme of doubly fed induction generator for wind turbine us...IJECEIAES
This paper describes a speed control device for generating electrical energy on an electricity network based on the doubly fed induction generator (DFIG) used for wind power conversion systems. At first, a double-fed induction generator model was constructed. A control law is formulated to govern the flow of energy between the stator of a DFIG and the energy network using three types of controllers: proportional integral (PI), sliding mode controller (SMC) and second order sliding mode controller (SOSMC). Their different results in terms of power reference tracking, reaction to unexpected speed fluctuations, sensitivity to perturbations, and resilience against machine parameter alterations are compared. MATLAB/Simulink was used to conduct the simulations for the preceding study. Multiple simulations have shown very satisfying results, and the investigations demonstrate the efficacy and power-enhancing capabilities of the suggested control system.
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
As digital technology becomes more deeply embedded in power systems, protecting the communication
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Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
Harnessing WebAssembly for Real-time Stateless Streaming PipelinesChristina Lin
Traditionally, dealing with real-time data pipelines has involved significant overhead, even for straightforward tasks like data transformation or masking. However, in this talk, we’ll venture into the dynamic realm of WebAssembly (WASM) and discover how it can revolutionize the creation of stateless streaming pipelines within a Kafka (Redpanda) broker. These pipelines are adept at managing low-latency, high-data-volume scenarios.
New techniques for characterising damage in rock slopes.pdf
Refrigeration
1. Refrigeration – Cengel and Boles + NPTEL(Condensed)
Can an object never be cooled to absolute zero because the thermal energy has to go somewhere
colder?
From a purely classical standpoint this is absolutely right. The classical way to cool a gas is to
compress it, in which case, according to the Ideal Gas Law (PV=nRT), it will heat up (as Pressure
rises Temperature must rise). We then put this gas through some type of heat exchanger, and
since it has a higher temperature than the cooling medium, heat flows from it into the cooling
medium. With the gas cooler now, it is allowed to expand (and depressurize), which according to
the Ideal Gas Law will cause the temperature to lower.
I pretty much just described how a refrigerator works, except in a refrigerator the gas gets so cold
that it condenses into liquid. This method alone should suffice to get you down into the single
digits of the Kelvin range. This is basically how you make Liquid Hydrogen (20 K boiling point) and
Liquid Nitrogen (77 K) or even Liquid Helium (4 K).
To get down into the sub Kelvin region requires some different techniques, and this is where
classical thermodynamics starts to break down. Classical Thermodynamics is based in the Zeroth
Law, which is so named because, though it is more fundamental than the First Law (energy neither
created nor destroyed), it was conceived of later than the First Law. It pretty much states that if
you have something in thermal equilibrium (read, same temperature) as two other things, then
those two things are in thermal equilibrium with each other. In symbolic terms, if you have body
A at temperature T(A), body B at T(B), and body C at T(C), and T(C) = T(A) and T(C) = T(B), then T(A)
= T(B). It's basically the Transitive Property for thermodynamics.
Theoretically, of course, you can use the technique I described above (compression ==>heat
exchanger ==> expansion) to get as cold as you want, but never reach zero (just as the asker
originally stated). Each time you compress your gas (cooling it with Liquid Helium, presumably),
you then expand it further and further. If you cooled your gas to 4K and then expanded it to double
its original volume, then the temperature would be 2 K (as long as you kept the pressure the same).
Quadruple the volume and you lower the temperature to 1 K, and so on and so on. But the problem
begins would you start getting to this low density, you begin to run into issues. And this is where
classical thermo really starts to break down. At some point the gas stops behaving like a gas, and
starts behaving like a group of individual atoms. CT is not designed to handle such things, and it's
fortunate that Statistical Mechanics came along to help describe what is going on. It turns out that
a better way to cool something down into the sub-kelvin range is to slowly bleed of some of the
gas, in a technique that is known as evaporative cooling. Your skin is cooled by evaporative cooling
2. when your sweat evaporates and carries heat away from your skin on a hot day. The same thing
can be done with really cold vapors, by bleeding of some of the hottest (fastest moving) atoms of
the vapor and letting it carry away some of the heat. Beyond this you need lasers to actually slow
down the atoms even more, by the simple (hahaha) technique of using the coherent photons in
the laser beam to slam into the atoms and stop them dead in their tracks (or as close as we can
get). This is not that different from two billiard balls running into each other at high speed and
then slowly drifting away from the collision. You can even use magnets to hold the atoms in place,
by exploiting the different charge of the proton and electron.
None of this answers the original question, though. By using the
compression/cooling/expansion technique (modern refrigeration), you can theoretically get as
cold as you want. But of course, this is basically Zeno's Paradox in temperature. You can only lower
the temperature to some fraction of the original temperature, and as long as it is a fraction you'll
never get to zero. So the original question wasn't entirely right, but it had a great insight, and that
makes it worthy of consideration. So no, we'll never get to absolute zero, but we're getting closer
every day.
PROPERTIES OF PURE SUBSTANCES
A pure substance does not have to be of a single chemical element or compound, however. A
mixture of various chemical elements or compounds also qualifies as a pure substance as long as
the mixture is homogeneous. Air, for example, is a mixture of several gases, but it is often
considered to be a pure substance because it has a uniform chemical composition. However, a
mixture of oil and water is not a pure substance. Since oil is not soluble in water, it will collect on
top of the water, forming two chemically dissimilar regions.
A mixture of two or more phases of a pure substance is still a pure substance as long as the
chemical composition of all phases is the same (Fig. 3–2). A mixture of ice and liquid water, for
example, is a pure substance because both phases have the same chemical composition. A mixture
of liquid air and gaseous air, however, is not a pure substance since the composition of liquid air
is different from the composition of gaseous air, and thus the mixture is no longer chemically
homogeneous. This is due to different components in air condensing at different temperatures at
a specified pressure.
3. Compressed Liquid and Saturated Liquid
Consider a piston–cylinder device containing liquid water at 20°C and 1 atm pressure (state 1, Fig.
3–5). Under these conditions, water exists in the liquid phase, and it is called a compressed liquid,
or a subcooled liquid, meaning that it is not about to vaporize. Heat is now transferred to the water
until its temperature rises to, say, 40°C. As the temperature rises, the liquid water expands slightly,
and so its specific volume increases. To accommodate this expansion, the piston moves up slightly.
The pressure in the cylinder remains constant at 1 atm during this process since it depends on the
outside barometric pressure and the weight of the piston, both of which are constant. Water is
still a compressed liquid at this state since it has not started to vaporize. As more heat is
transferred, the temperature keeps rising until it reaches 100°C (state 2, Fig. 3–6). At this point
water is still a liquid, but any heat addition will cause some of the liquid to vaporize. That is, a
phase-change process from liquid to vapor is about to take place. A liquid that is about to vaporize
is called a saturated liquid. Therefore, state 2 is a saturated liquid state.
Saturated Vapor and Superheated Vapor
Once boiling starts, the temperature stops rising until the liquid is completely vaporized. That is,
the temperature will remain constant during the entire phase-change process if the pressure is
held constant. At sea level (P = 1 atm), the thermometer will always read 100°C if the pan is
uncovered or covered with a light lid. During a boiling process, the only change we will observe is
a large increase in the volume and a steady decline in the liquid level as a result of more liquid
4. turning to vapor. Midway about the vaporization line (state 3, Fig. 3–7), the cylinder contains equal
amounts of liquid and vapor. As we continue transferring heat, the vaporization process continues
until the last drop of liquid is vaporized (state 4, Fig. 3–8). At this point, the entire cylinder is filled
with vapor that is on the borderline of the liquid phase. Any heat loss from this vapor will cause
some of the vapor to condense (phase change from vapor to liquid). A vapor that is about to
condense is called a saturated vapor. Therefore, state 4 is a saturated vapor state. A substance at
states between 2 and 4 is referred to as a saturated liquid–vapor mixture since the liquid and vapor
phases coexist in equilibrium at these states.
One the phase-change process is completed, we are back to a single phase region again (this time
vapor), and further transfer of heat results in an increase in both the temperature and the specific
volume (Fig. 3–9). At state 5, the temperature of the vapor is, let us say, 300°C; and if we transfer
some heat from the vapor, the temperature may drop somewhat but no condensation will take
place as long as the temperature remains above 100°C (for P = 1 atm). A vapor that is not about
to condense (i.e., not a saturated vapor) is called a superheated vapor. Therefore, water at state 5
is a superheated vapor.
5. The only reason water started boiling at 100°C was because we held the pressure constant at 1
atm (101.325 kPa). If the pressure inside the cylinder were raised to 500 kPa by adding weights on
top of the piston, water would start boiling at 151.8°C. That is, the temperature at which water
starts boiling depends on the pressure; therefore, if the pressure is fixed, so is the boiling
temperature.
At a given pressure, the temperature at which a pure substance changes phase is called the
saturation temperature Tsat. Likewise, at a given temperature, the pressure at which a pure
substance changes phase is called the saturation pressure Psat
Consequences of Tsat and Psat Dependence
Consider a sealed can of liquid refrigerant-134a in a room at 25°C. If the can has been in the room
long enough, the temperature of the refrigerant in the can is also 25°C. Now, if the lid is opened
slowly and some refrigerant is allowed to escape, the pressure in the can will start dropping until
it reaches the atmospheric pressure. If you are holding the can, you will notice its temperature
dropping rapidly, and even ice forming outside the can if the air is humid. A thermometer inserted
in the can will register -26°C when the pressure drops to 1 atm, which is the saturation
temperature of refrigerant-134a at that pressure. The temperature of the liquid refrigerant will
remain at -26°C until the last drop of it vaporizes.
6. Diagram
Add weights on top of the piston until the pressure inside the cylinder reaches 1 MPa. At this
pressure, water has a somewhat smaller specific volume than it does at 1 atm pressure. As heat is
transferred to the water at this new pressure, the process follows a path that looks very much like
the process path at 1 atm pressure, as shown in Fig. 3–15, but there are some noticeable
differences. First, water starts boiling at a much higher temperature (179.98C) at this pressure.
Second, the specific volume of the saturated liquid is larger (liquid being incompressible has left
effect of pressure on it) and the specific volume of the saturated vapor is smaller than the
corresponding values at 1 atm pressure. That is, the horizontal line that connects the saturated
liquid and saturated vapor states is much shorter. As the pressure is increased further, this
saturation line continues to shrink, as shown in Fig. 3–15, and it becomes a point when the
pressure reaches 22.06 MPa for the case of water. This point is called the critical point, and it is
defined as the point at which the saturated liquid and saturated vapor states are identical.
7. A piston–cylinder device that contains liquid water at 1 MPa and 150°C. Water at this state exists
as a compressed liquid. Now the weights on top of the piston are removed one by one so that the
pressure inside the cylinder decreases gradually (Fig. 3–18).
The water is allowed to exchange heat with the
surroundings so its temperature remains constant. As the pressure decreases, the volume of the
8. water increases slightly. When the pressure reaches the saturation-pressure value at the specified
temperature (0.4762 MPa), the water starts to boil. During this vaporization process, both the
temperature and the pressure remain constant, but the specific volume increases. Once the last
drop of liquid is vaporized, further reduction in pressure results in a further increase in specific
volume. Notice that during the phase-change process, we did not remove any weights. Doing so
would cause the pressure and therefore the temperature to drop [since Tsat =f(Psat)], and the
process would no longer be isothermal.
9. On P-v or T-v diagrams, these triple-phase states form a line called the triple line. The states on
the triple line of a substance have the same pressure and temperature but different specific
volumes. The triple line appears as a point on the P-T diagrams and, therefore, is often called the
triple point. For water, the triple-point temperature and pressure are 0.01°C and 0.6117 kPa,
respectively. That is, all three phases of water coexist in equilibrium only if the temperature and
pressure have precisely these values.
11. But unlike superheated vapor, the compressed liquid properties are not much different from the
corresponding saturated liquid values.
THE JOULE-THOMSON COEFFICIENT
The temperature behavior of a fluid during a throttling (h = constant) process is described by the
Joule-Thomson coefficient, defined as
12. A careful look at its defining equation reveals that the Joule-Thomson coefficient represents the
slope of h = constant lines on a T-P diagram.
Some constant-enthalpy lines on the T-P diagram pass through a point of zero slope or zero Joule-
Thomson coefficient. The line that passes through these points is called the inversion line, and the
temperature at a point where a constant-enthalpy line intersects the inversion line is called the
inversion temperature. The temperature at the intersection of the P = 0 line (ordinate) and the
upper part of the inversion line is called the maximum inversion temperature. Notice that the
slopes of the h = constant lines are negative (μJT < 0) at states to the right of the inversion line and
positive (μJT > 0) to the left of the inversion line.
A throttling process proceeds along a constant-enthalpy line in the direction of decreasing
pressure, that is, from right to left. Therefore, the temperature of a fluid increases during a
throttling process that takes place on the right-hand side of the inversion line. However, the fluid
temperature decreases during a throttling process that takes place on the left-hand side of the
inversion line. It is clear from this diagram that a cooling effect cannot be achieved by throttling
unless the fluid is below its maximum inversion temperature. This presents a problem for
substances whose maximum inversion temperature is well below room temperature. For
13. hydrogen, for example, the maximum inversion temperature is -68°C. Thus hydrogen must be
cooled below this temperature if any further cooling is to be achieved by throttling.
REFRIGERATORS AND HEAT PUMPS
14. Schematic of a Carnot refrigerator and T-s diagram of the reversed Carnot cycle.
THE IDEAL VAPOR-COMPRESSION REFRIGERATION CYCLE
1-2 Isentropic compression in a compressor
2-3 Constant-pressure heat rejection in a condenser
3-4 Throttling in an expansion device
4-1 Constant-pressure heat absorption in an evaporator
15. A rule of thumb is that the COP improves by 2 to 4 percent for each °C the evaporating temperature
is raised or the condensing temperature is lowered.
The condenser and the evaporator do not involve any work, and the compressor can be
approximated as adiabatic. Then the COPs of refrigerators and heat pumps operating on the vapor
compression refrigeration cycle can be expressed as
16. ACTUAL VAPOR-COMPRESSION REFRIGERATION CYCLE
Two common sources of irreversibilities are fluid friction (causes pressure drops) and heat transfer
to or from the surroundings.
In the ideal cycle, the refrigerant leaves the evaporator and enters the compressor as saturated
vapor. But it may not be possible to control the state of the refrigerant so precisely. Instead, it is
easier to design the system so that the refrigerant is slightly superheated at the compressor inlet.
This slight overdesign ensures that the refrigerant is completely vaporized when it enters the
compressor. Also, the line connecting the evaporator to the compressor is usually very long; thus
the pressure drop caused by fluid friction and heat transfer from the surroundings to the
refrigerant can be very significant. The result of superheating, heat gain in the connecting line, and
pressure drops in the evaporator and the connecting line is an increase in the specific volume,
thus an increase in the power input requirements to the compressor since steady-flow work is
proportional to the specific volume.
The compression process in the ideal cycle is internally reversible and adiabatic, and thus
isentropic. The actual compression process, however, involves frictional effects, which increase
the entropy, and heat transfer, which may increase or decrease the entropy.
17. In the ideal case, the refrigerant is assumed to leave the condenser as saturated liquid at the
compressor exit pressure. In reality, however, it is unavoidable to have some pressure drop in the
condenser as well as in the lines connecting the condenser to the compressor and to the throttling
valve. Also, it is not easy to execute the condensation process with such precision that the
refrigerant is a saturated liquid at the end, and it is undesirable to route the refrigerant to the
throttling valve before the refrigerant is completely condensed. Therefore, the refrigerant is sub-
cooled somewhat before it enters the throttling valve. We do not mind this at all, however, since
the refrigerant in this case enters the evaporator with a lower enthalpy and thus can absorb more
heat from the refrigerated space. The throttling valve and the evaporator are usually located very
close to each other, so the pressure drop in the connecting line is small.
GAS REFRIGERATION CYCLES
The reversed Brayton cycle, better known as the gas refrigeration cycle.
Despite their relatively low COPs, the gas refrigeration cycles have two desirable characteristics:
They involve simple, lighter components, which make them suitable for aircraft cooling, and they
can incorporate regeneration, which makes them suitable for liquefaction of gases and cryogenic
applications.
18. Vapour refrigeration system is based on phase change principle (cooling effect).
Gas refrigeration is mainly based on sensible cooling.
For pure substance boiling point coincides with dew point temperature, similarly the freezing point
and melting point also coincides. (why not for impure substance)
1. Constant volume process: heating & cooling of a gas stored in a rigid vessel (non-flow process)
2. Constant pressure process: Heating/cooling of a gas in a piston cylinder assembly (non-flow
process)
3. Constant temperature process: Compression/expansion of a gas with heat transfer (non flow
process)
4. Adiabatic process: compression and expansion of a gas under perfectly insulated conditions.
5. Polytropic process: compression/expansion with heat transfer.
19. METHODS OF PRODUCING LOW TEMPERATURES
Sensible cooling
Endothermic mixing
Phase change processes
Expansion of liquids
Expansion of gases
Thermoelectric methods
Magnetic methods
20.
21.
22.
23. Temperature drop is same whether we use throttling process or use a turbine; because of the initial
state of the working fluid.
Expansion in the subcooled region. Throttling gives lower temperature drop for the same pressure drop.
Also both the process gives lower temperature drop compared to expansion from saturated initial state.
24.
25.
26.
27.
28. Cold air assumptions won’t work for throttling process because if it would have been ideal gas there is
no reduction in the temperature as enthalpy is only function of temperature for ideal gas. Taking gas as
real gas we can explain throttling well.
29. Isothermal processes of reverse Carnot’s cycle is replaced by two isobaric processes in Reverse Brayton
cycle. Also here shaft is joined between turbine and the compressor. Part of work output is being
utilized within the cycle.
30.
31.
32. Closed systems can use dense air that is good volumetric efficiency reducing the sizes of compressor and
turbine, heat exchangers etc. Also in closed system we can use alternative for air also.
33.
34. PSYCHROMETRY
At 50°C, the saturation pressure of water is 12.3 kPa. At pressures below this value, water vapor
can be treated as an ideal gas, even when it is a saturated vapor. Therefore, water vapor in air
behaves as if it existed alone and obeys the ideal-gas relation Pv = RT. Then the atmospheric air
can be treated as an ideal-gas mixture whose pressure is the sum of the partial pressure of dry
air* Pa and that of water vapor Pv:
The partial pressure of water vapor is usually referred to as the vapor pressure. It is the pressure
water vapor would exert if it existed alone at the temperature and volume of atmospheric air.
35. Since water vapor is an ideal gas, the enthalpy of water vapor is a function of temperature only,
that is, h = h(T). This can also be observed from the T-s diagram of water where the constant
enthalpy lines coincide with constant-temperature lines at temperatures below 50°C. Therefore,
the enthalpy of water vapor in air can be taken to be equal to the enthalpy of saturated vapor at
the same temperature.
Relative Humidity
36.
37. As the air cools at constant pressure, the vapor pressure Pv remains constant. Therefore, the vapor
in the air (state 1) undergoes a constant-pressure cooling process until it strikes the saturated
vapor line (state 2). The temperature at this point is Tdp, and if the temperature drops any further,
some vapor condenses out. As a result, the amount of vapor in the air decreases, which results in
a decrease in Pv. The air remains saturated during the condensation process and thus follows a
path of 100 percent relative humidity (the saturated vapor line). The ordinary temperature and
the dew-point temperature of saturated air are identical.
The dew-point temperature of room air can be determined easily by cooling some water in a metal
cup by adding small amounts of ice and stirring. The temperature of the outer surface of the cup
when dew starts to form on the surface is the dew-point temperature of the air.
Knowing the dew-point temperature, we can determine the vapor pressure Pv and thus the
relative humidity. Another way of determining the absolute or relative humidity is related to an
adiabatic saturation process. The system consists of a long insulated channel that contains a pool
of water. A steady stream of unsaturated air that has a specific humidity of ω1 (unknown) and a
temperature of T1 is passed through this channel. As the air flows over the water, some water
evaporates and mixes with the airstream. The moisture content of air increases during this
process, and its temperature decreases, since part of the latent heat of vaporization of the water
that evaporates comes from the air. If the channel is long enough, the airstream exits as saturated
air (Φ = 100 percent) at temperature T2, which is called the adiabatic saturation temperature.
If makeup water is supplied to the channel at the rate of evaporation at temperature T2, the
adiabatic saturation process described above can be analyzed as a steady-flow process. The
process involves no heat or work interactions, and the kinetic and potential energy changes can
be neglected. Then the conservation of mass and conservation of energy relations for this two
inlet, one-exit steady-flow system reduces to the following:
40. A more practical approach is to use a thermometer whose bulb is covered with a cotton wick
saturated with water and to blow air over the wick. The temperature measured in this manner is
called the wet-bulb temperature Twb.
The basic principle involved is similar to that in adiabatic saturation. When unsaturated air
passes over the wet wick, some of the water in the wick evaporates. As a result, the temperature
of the water drops, creating a temperature difference (which is the driving force for heat transfer)
between the air and the water. After a while, the heat loss from the water by evaporation equals
the heat gain from the air, and the water temperature stabilizes. The thermometer reading at this
point is the wet-bulb temperature.
In general, the adiabatic saturation temperature and the wet-bulb temperature are not
the same. However, for air–water vapor mixtures at atmospheric pressure, the wet-bulb
temperature happens to be approximately equal to the adiabatic saturation temperature.
Therefore, the wet-bulb temperature Twb can be used in Eq. 14–14 in place of T2 to determine the
specific humidity of air.
The state of the atmospheric air at a specified pressure is completely specified by two independent
intensive properties. The rest of the properties can be calculated easily from the previous
relations. The constant wet- bulb-temperature lines are used as constant-enthalpy lines in some
charts. For saturated air, the dry-bulb, wet-bulb, and dew-point temperatures are identical.
Therefore, the dew-point temperature of atmospheric air at any point on the chart can be
41. determined by drawing a horizontal line (a line of ω = constant or Pv = constant) from the point to
the saturated curve. The temperature value at the intersection point is the dew-point
temperature.
The comfort of the human body depends primarily on three factors: the (dry-bulb) temperature,
relative humidity, and air motion.
The relative humidity of air decreases during a heating process even if the specific humidity ω
remains constant. This is because the relative humidity is the ratio of the moisture content to the
moisture capacity of air at the same temperature, and moisture capacity increases with
temperature. Mass of air and water remains constant and work transfer is also zero we have
Heating with Humidification
If steam is introduced in the humidification section, this will result in humidification with
additional heating (T3 > T2). If humidification is accomplished by spraying water into the airstream
42. instead, part of the latent heat of vaporization comes from the air, which results in the cooling of
the heated airstream (T3 < T2). Air should be heated to a higher temperature in the heating section
in this case to make up for the cooling effect during the humidification process.
Cooling with Dehumidification
The specific humidity of air remains constant during a simple cooling process, but its relative
humidity increases. If the relative humidity reaches undesirably high levels, it may be necessary to
remove some moisture from the air, that is, to dehumidify it. This requires cooling the air below
its dew-point temperature.
43. Evaporative Cooling
Evaporative cooling is based on a simple principle: As water evaporates, the latent heat of
vaporization is absorbed from the water body and the surrounding air. As a result, both the water
and the air are cooled during the process.
A porous jug or pitcher filled with water is left in an open, shaded area. A small amount of
water leaks out through the porous holes, and the pitcher “sweats.” In a dry environment, this
water evaporates and cools the remaining water in the pitcher
44. The evaporative cooling process is essentially identical to the adiabatic saturation process since
the heat transfer between the airstream and the surroundings is usually negligible. Therefore, the
evaporative cooling process follows a line of constant wet-bulb temperature on the psychrometric
chart. (Note that this will not exactly be the case if the liquid water is supplied at a temperature
different from the exit temperature of the airstream.)
Adiabatic Mixing of Airstreams