This document discusses thermodynamic processes and the laws of thermodynamics. It provides definitions and explanations of key concepts in thermodynamics including:
- Thermodynamics deals with the conversion of heat into mechanical energy and vice versa.
- The first law of thermodynamics states that the change in internal energy of a system equals the heat supplied plus work done.
- The second law of thermodynamics states that there is a limit to the amount of work that can be extracted from a heat source. Not all heat can be completely converted to work.
- A thermodynamic cycle consists of a series of thermodynamic processes that return a system to its initial state. Common cycles used in engines are described.
This document discusses pure substances and the phases of pure substances. Some key points include:
- A pure substance has a fixed chemical composition throughout and can exist in different phases like solid, liquid, and gas.
- Pure substances can undergo phase changes through processes like melting, vaporization, and condensation.
- The properties of a pure substance depend on its phase and conditions like temperature and pressure.
- Mixtures of substances qualify as pure substances as long as they are homogeneous. Examples include liquid water and water vapor mixtures.
The document then discusses concepts like saturation, latent heat, quality, and moisture content which are important for understanding phase equilibria of pure substances.
The document discusses key concepts in thermodynamics including:
1. Thermodynamics is the study of heat and its transformation into mechanical energy. It describes the relationship between heat and work.
2. The first law of thermodynamics states that energy cannot be created or destroyed, and that whenever heat is added to a system, it transforms into an equal amount of internal energy or external work done by the system.
3. Thermodynamic processes can be represented on pressure-volume diagrams, which show how properties change as a system undergoes different thermodynamic processes like expansion or compression.
The document summarizes the four laws of thermodynamics:
1) The first law states that energy cannot be created or destroyed, only changed in form.
2) The second law states that the entropy of an isolated system always increases.
3) The third law states that the entropy of a system approaches a minimum, zero, as the temperature approaches absolute zero.
4) There is no universally accepted fourth law, but some proposals include the Onsager reciprocal relations regarding heat and matter flow parameters.
This document discusses concepts related to the second law of thermodynamics and entropy. It defines entropy as a measure of randomness or disorder in a system. Examples are given of processes that increase entropy, such as a solid becoming a liquid or gas, and those that decrease it, like gases condensing into liquids. The mixing of hot and cold water is used to demonstrate how entropy changes in both the hot and cold portions. Formulas are provided for calculating changes in entropy. The four-stage Carnot cycle is described as a reversible heat engine process. Equations show the changes in entropy and heat transfers in each stage. The Carnot theorem on efficiency is stated. Finally, the document discusses entropy changes for van der Waals gases
Thermodynamics is the study of heat and temperature and their relation to energy and work. It defines macroscopic variables like internal energy, entropy, and pressure that describe systems. Refrigerators, freezers, air conditioners, and evaporative coolers all use thermodynamic processes like compression, expansion, and heat transfer to remove heat from one area and release it to another area. They circulate refrigerants that change state from gas to liquid and back through cycles, absorbing heat inside and releasing it outside. This allows them to lower the temperature of the area being cooled.
This document discusses spontaneous processes and the driving forces behind them in thermodynamics. It explains that spontaneous processes are driven by a decrease in enthalpy or an increase in entropy. While enthalpy change alone cannot predict spontaneity, the introduction of entropy and Gibbs free energy allows better determination of spontaneous processes. The document also discusses how temperature, entropy change, and the relationship between Gibbs free energy and equilibrium constant can be used to analyze spontaneity.
This document provides an overview of chemical thermodynamics, including:
- The first law of thermodynamics which states that change in internal energy equals heat added plus work done.
- The second law of thermodynamics which states that the entropy of the universe increases for spontaneous processes.
- How changes in entropy and free energy determine whether processes are spontaneous, with spontaneous processes favoring higher entropy and more negative free energy.
The document discusses key concepts in thermodynamics including:
1. Thermal energy and temperature, which is a measure of hotness or coldness.
2. Heat is the transfer of thermal energy between objects of different temperatures.
3. There are various instruments for measuring temperature like thermometers, which use thermal sensors and temperature scales.
4. Materials expand when heated as thermal energy increases, and contract when cooled as thermal energy decreases.
This document discusses pure substances and the phases of pure substances. Some key points include:
- A pure substance has a fixed chemical composition throughout and can exist in different phases like solid, liquid, and gas.
- Pure substances can undergo phase changes through processes like melting, vaporization, and condensation.
- The properties of a pure substance depend on its phase and conditions like temperature and pressure.
- Mixtures of substances qualify as pure substances as long as they are homogeneous. Examples include liquid water and water vapor mixtures.
The document then discusses concepts like saturation, latent heat, quality, and moisture content which are important for understanding phase equilibria of pure substances.
The document discusses key concepts in thermodynamics including:
1. Thermodynamics is the study of heat and its transformation into mechanical energy. It describes the relationship between heat and work.
2. The first law of thermodynamics states that energy cannot be created or destroyed, and that whenever heat is added to a system, it transforms into an equal amount of internal energy or external work done by the system.
3. Thermodynamic processes can be represented on pressure-volume diagrams, which show how properties change as a system undergoes different thermodynamic processes like expansion or compression.
The document summarizes the four laws of thermodynamics:
1) The first law states that energy cannot be created or destroyed, only changed in form.
2) The second law states that the entropy of an isolated system always increases.
3) The third law states that the entropy of a system approaches a minimum, zero, as the temperature approaches absolute zero.
4) There is no universally accepted fourth law, but some proposals include the Onsager reciprocal relations regarding heat and matter flow parameters.
This document discusses concepts related to the second law of thermodynamics and entropy. It defines entropy as a measure of randomness or disorder in a system. Examples are given of processes that increase entropy, such as a solid becoming a liquid or gas, and those that decrease it, like gases condensing into liquids. The mixing of hot and cold water is used to demonstrate how entropy changes in both the hot and cold portions. Formulas are provided for calculating changes in entropy. The four-stage Carnot cycle is described as a reversible heat engine process. Equations show the changes in entropy and heat transfers in each stage. The Carnot theorem on efficiency is stated. Finally, the document discusses entropy changes for van der Waals gases
Thermodynamics is the study of heat and temperature and their relation to energy and work. It defines macroscopic variables like internal energy, entropy, and pressure that describe systems. Refrigerators, freezers, air conditioners, and evaporative coolers all use thermodynamic processes like compression, expansion, and heat transfer to remove heat from one area and release it to another area. They circulate refrigerants that change state from gas to liquid and back through cycles, absorbing heat inside and releasing it outside. This allows them to lower the temperature of the area being cooled.
This document discusses spontaneous processes and the driving forces behind them in thermodynamics. It explains that spontaneous processes are driven by a decrease in enthalpy or an increase in entropy. While enthalpy change alone cannot predict spontaneity, the introduction of entropy and Gibbs free energy allows better determination of spontaneous processes. The document also discusses how temperature, entropy change, and the relationship between Gibbs free energy and equilibrium constant can be used to analyze spontaneity.
This document provides an overview of chemical thermodynamics, including:
- The first law of thermodynamics which states that change in internal energy equals heat added plus work done.
- The second law of thermodynamics which states that the entropy of the universe increases for spontaneous processes.
- How changes in entropy and free energy determine whether processes are spontaneous, with spontaneous processes favoring higher entropy and more negative free energy.
The document discusses key concepts in thermodynamics including:
1. Thermal energy and temperature, which is a measure of hotness or coldness.
2. Heat is the transfer of thermal energy between objects of different temperatures.
3. There are various instruments for measuring temperature like thermometers, which use thermal sensors and temperature scales.
4. Materials expand when heated as thermal energy increases, and contract when cooled as thermal energy decreases.
This document provides an overview of thermodynamics basics. It discusses that thermodynamics is concerned with how energy is stored and transformed through heat and work. The first law of thermodynamics states that energy is conserved and cannot be created or destroyed. A thermodynamic system and its boundary with the surroundings are defined. Various thermodynamic processes like isothermal, adiabatic, and isobaric processes are also summarized. Key concepts like thermal energy, temperature, heat transfer methods, and the second law of thermodynamics are briefly explained.
This document discusses key concepts in chemical thermodynamics including the first, second, and third laws of thermodynamics. It describes how energy, entropy, enthalpy, and Gibbs free energy relate to spontaneous processes and equilibrium. Spontaneous processes are irreversible and result in an increase in entropy of the universe according to the second law. The third law states that the entropy of a pure crystalline substance is 0 at absolute zero. Gibbs free energy can be used to predict spontaneity based on its sign and relationship to the reaction quotient and equilibrium constant.
The document summarizes an adiabatic process and the adiabatic law of compression and expansion. It then discusses:
1. An adiabatic process is one where no heat is transferred to or from the system. It can occur when a system is well insulated or a process is very fast.
2. According to the adiabatic law, a gas will cool during free expansion and heat during compression without external energy transfer.
3. The Carnot cycle consists of two reversible adiabatic processes and two reversible isothermal processes, resulting in no net transfer of heat or work.
This document provides an overview of key concepts in thermodynamics. It begins with contact information for the instructor, Dr. Sabar D. Hutagalung, and lists the main topics to be covered, including the four laws of thermodynamics. It then provides more detailed explanations of these topics, such as definitions of the zeroth, first, and second laws. It also explains concepts like heat, work, internal energy, and processes involving gases like isobaric, isothermal, and adiabatic. In addition, it discusses mechanisms of heat transfer including conduction, convection, and radiation, and defines important related terms.
This document discusses key concepts in thermodynamics including:
1. Thermodynamics deals with the stability of systems and describes overall system properties like temperature and pressure, rather than interactions at the particle level.
2. The four main laws of thermodynamics are universal and apply across all disciplines of science and engineering.
3. Thermodynamics considers how energy in the form of heat or work can be transferred to or from a system, and the different types of processes this can occur under such as isothermal, isobaric, or adiabatic processes.
This presentation contains about the history of the thermodynamics and the scientist who has invented these laws and the year of their invention. This presentation will help you to know about the laws and scientist and their laws of invention. You can get more idea about the history of thermodynamics by this presentation.
This slide will completely describes you about thermodynamics. The basics of thermo is explained in this slide. Intensive and Extensive Propeties are exolained in this properties.
The document discusses the zeroth law of thermodynamics. It states that the zeroth law is the basis for temperature measurement and defines thermal equilibrium. It explains that temperature relates to the ability to differentiate between hot and cold. The zeroth law states that if two bodies A and B are in thermal equilibrium with each other, and body A is also in thermal equilibrium with a third body C, then B and C must be in thermal equilibrium as well. This allows for a common temperature scale. The document also discusses temperature measurement procedures and the use of fixed points and gas as the standard thermometric substance.
1) The document discusses different forms and modes of energy transfer including heat, work, internal energy, and kinetic and potential energy at both the macroscopic and microscopic levels.
2) Heat is defined as the random motion of particles and is identified as energy crossing system boundaries, while work involves a direct transfer of energy between a system and its surroundings.
3) The specific heat of a material is the amount of heat required to change its temperature by one degree, while heat of transformation (latent heat) is the energy required for phase changes like melting or vaporization.
The document provides an overview of basic thermodynamics concepts and the three laws of thermodynamics. It then discusses several thermodynamic processes including reversible and irreversible processes. It concludes with an explanation of the Rankine vapor power cycle, including its thermal efficiency calculation using the first law of thermodynamics.
ME6301 ENGINEERING THERMODYNAMICS SHORT QUESTIONS AND ANSWERS - UNIT IVBIBIN CHIDAMBARANATHAN
This document contains a compilation of concepts related to ideal gases, real gases, and thermodynamic relations for a Mechanical Engineering course. It defines ideal gases as having no intermolecular forces and real gases as having small intermolecular forces at high temperatures and low pressures. Key concepts summarized include the gas laws, equations of state, reduced properties, partial pressures, compressibility factor, and thermodynamic properties.
Heat and thermodynamics - Preliminary / Dr. Mathivanan VelumaniMathivanan Velumani
The document discusses key concepts in thermodynamics including:
1. Thermodynamic states are characterized by macroscopic properties like temperature, pressure, and volume that determine a system's internal state and interaction with external bodies.
2. Thermal equilibrium exists when temperature is uniform throughout a system, as stated by the zeroth law of thermodynamics.
3. Internal energy (U) is the energy associated with the random, disordered motion of molecules within a system.
the branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.
Heat & Mass Transfer Chap 1 (FE-509) Food Engineering UAFAown Rizvi
This chapter introduces key concepts of heat transfer and thermodynamics. It defines heat transfer as energy transferred due to a temperature difference and discusses the three mechanisms of heat transfer: conduction, convection, and radiation. Conduction involves energy transfer through direct contact of particles. Convection combines conduction and bulk fluid motion. Radiation transfers energy via electromagnetic waves. The chapter establishes relationships like Fourier's law of conduction and Newton's law of cooling and introduces concepts such as thermal conductivity and heat transfer coefficients.
In this PPT have have covered
1. Basic thermodynamics definition
2. Thermodynamics law
3. Properties , cycle, Process
4. Derivation of the Process
5.Formula for the numericals.
This topic is use full for those students who want to study basic thermodynamics as a part of their University syllabus.
Most of the university having basic Mechanical engineering as a subject and in this subject Thermodynamics is a topic so by this PPT our aim is to give presentable knowledge of the subject
The document discusses various topics related to heat and thermodynamics including:
1) Heat is a form of energy transferred between objects due to a temperature difference, not a substance that flows.
2) The internal energy of a substance is the total energy of all its molecules. Temperature measures average kinetic energy.
3) Specific heat is a property that determines how much heat is required to change an object's temperature.
A donut contains a significant amount of calories, fat, and sugar. A plain cake donut has 226 calories, while a frosted donut has 303 calories and a glazed chocolate donut has 250 calories. Yeast donuts also contain a lot of calories, fat, and sugar, with a glazed yeast donut having 269 calories. Thermodynamics concepts discussed include the first law of thermodynamics regarding conservation of energy, the second law placing constraints on heat transfer and limiting efficiencies, and the Carnot cycle representing the most efficient possible heat engine cycle.
The document discusses different types of thermodynamic systems and their characteristics. It defines closed, open, and isolated systems based on whether they allow for mass and/or energy transfer with their surroundings. An adiabatic system exchanges work but not heat, while a homogeneous system consists of a single phase and a heterogeneous system consists of multiple phases. Any process that returns a system to its initial state is considered a cycle. Reversible processes occur through continuous equilibrium states while irreversible processes occur through non-equilibrium states. Temperature is proportional to the average molecular kinetic energy. Work is the product of a force and distance of displacement, and heat is something that flows due to a temperature difference between a system and its surroundings.
engineering physics- unit 3- thermal physics- thermodynamics- laws of thermodynamics- heat engine- carnot cycle- otto and diesel engine- forbes and lees disc method.
This document provides an introduction to thermodynamics, including definitions of key concepts and summaries of important laws and principles. It begins with an overview of the course content, which covers topics like the definitions of thermodynamics, heat, work, and systems. It then discusses the significance of thermodynamics in applications ranging from household appliances to power plants. The document proceeds to define fundamental concepts like temperature, pressure, energy and power. It also explains the first and second laws of thermodynamics. In its concluding sections, it summarizes processes, criteria for reversibility, and the specific thermodynamic laws of Boyle and Charles.
Thermodynamics is the branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. It explains interactions of variables in an system in terms of conservation of energy. The four main concepts are heat, temperature, entropy, and the laws of thermodynamics. Heat is energy transferred between objects at different temperatures. Temperature is a measure of average kinetic energy. Entropy represents disorder and waste heat. The laws govern energy transfer and conservation.
This document provides an overview of thermodynamics basics. It discusses that thermodynamics is concerned with how energy is stored and transformed through heat and work. The first law of thermodynamics states that energy is conserved and cannot be created or destroyed. A thermodynamic system and its boundary with the surroundings are defined. Various thermodynamic processes like isothermal, adiabatic, and isobaric processes are also summarized. Key concepts like thermal energy, temperature, heat transfer methods, and the second law of thermodynamics are briefly explained.
This document discusses key concepts in chemical thermodynamics including the first, second, and third laws of thermodynamics. It describes how energy, entropy, enthalpy, and Gibbs free energy relate to spontaneous processes and equilibrium. Spontaneous processes are irreversible and result in an increase in entropy of the universe according to the second law. The third law states that the entropy of a pure crystalline substance is 0 at absolute zero. Gibbs free energy can be used to predict spontaneity based on its sign and relationship to the reaction quotient and equilibrium constant.
The document summarizes an adiabatic process and the adiabatic law of compression and expansion. It then discusses:
1. An adiabatic process is one where no heat is transferred to or from the system. It can occur when a system is well insulated or a process is very fast.
2. According to the adiabatic law, a gas will cool during free expansion and heat during compression without external energy transfer.
3. The Carnot cycle consists of two reversible adiabatic processes and two reversible isothermal processes, resulting in no net transfer of heat or work.
This document provides an overview of key concepts in thermodynamics. It begins with contact information for the instructor, Dr. Sabar D. Hutagalung, and lists the main topics to be covered, including the four laws of thermodynamics. It then provides more detailed explanations of these topics, such as definitions of the zeroth, first, and second laws. It also explains concepts like heat, work, internal energy, and processes involving gases like isobaric, isothermal, and adiabatic. In addition, it discusses mechanisms of heat transfer including conduction, convection, and radiation, and defines important related terms.
This document discusses key concepts in thermodynamics including:
1. Thermodynamics deals with the stability of systems and describes overall system properties like temperature and pressure, rather than interactions at the particle level.
2. The four main laws of thermodynamics are universal and apply across all disciplines of science and engineering.
3. Thermodynamics considers how energy in the form of heat or work can be transferred to or from a system, and the different types of processes this can occur under such as isothermal, isobaric, or adiabatic processes.
This presentation contains about the history of the thermodynamics and the scientist who has invented these laws and the year of their invention. This presentation will help you to know about the laws and scientist and their laws of invention. You can get more idea about the history of thermodynamics by this presentation.
This slide will completely describes you about thermodynamics. The basics of thermo is explained in this slide. Intensive and Extensive Propeties are exolained in this properties.
The document discusses the zeroth law of thermodynamics. It states that the zeroth law is the basis for temperature measurement and defines thermal equilibrium. It explains that temperature relates to the ability to differentiate between hot and cold. The zeroth law states that if two bodies A and B are in thermal equilibrium with each other, and body A is also in thermal equilibrium with a third body C, then B and C must be in thermal equilibrium as well. This allows for a common temperature scale. The document also discusses temperature measurement procedures and the use of fixed points and gas as the standard thermometric substance.
1) The document discusses different forms and modes of energy transfer including heat, work, internal energy, and kinetic and potential energy at both the macroscopic and microscopic levels.
2) Heat is defined as the random motion of particles and is identified as energy crossing system boundaries, while work involves a direct transfer of energy between a system and its surroundings.
3) The specific heat of a material is the amount of heat required to change its temperature by one degree, while heat of transformation (latent heat) is the energy required for phase changes like melting or vaporization.
The document provides an overview of basic thermodynamics concepts and the three laws of thermodynamics. It then discusses several thermodynamic processes including reversible and irreversible processes. It concludes with an explanation of the Rankine vapor power cycle, including its thermal efficiency calculation using the first law of thermodynamics.
ME6301 ENGINEERING THERMODYNAMICS SHORT QUESTIONS AND ANSWERS - UNIT IVBIBIN CHIDAMBARANATHAN
This document contains a compilation of concepts related to ideal gases, real gases, and thermodynamic relations for a Mechanical Engineering course. It defines ideal gases as having no intermolecular forces and real gases as having small intermolecular forces at high temperatures and low pressures. Key concepts summarized include the gas laws, equations of state, reduced properties, partial pressures, compressibility factor, and thermodynamic properties.
Heat and thermodynamics - Preliminary / Dr. Mathivanan VelumaniMathivanan Velumani
The document discusses key concepts in thermodynamics including:
1. Thermodynamic states are characterized by macroscopic properties like temperature, pressure, and volume that determine a system's internal state and interaction with external bodies.
2. Thermal equilibrium exists when temperature is uniform throughout a system, as stated by the zeroth law of thermodynamics.
3. Internal energy (U) is the energy associated with the random, disordered motion of molecules within a system.
the branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.
Heat & Mass Transfer Chap 1 (FE-509) Food Engineering UAFAown Rizvi
This chapter introduces key concepts of heat transfer and thermodynamics. It defines heat transfer as energy transferred due to a temperature difference and discusses the three mechanisms of heat transfer: conduction, convection, and radiation. Conduction involves energy transfer through direct contact of particles. Convection combines conduction and bulk fluid motion. Radiation transfers energy via electromagnetic waves. The chapter establishes relationships like Fourier's law of conduction and Newton's law of cooling and introduces concepts such as thermal conductivity and heat transfer coefficients.
In this PPT have have covered
1. Basic thermodynamics definition
2. Thermodynamics law
3. Properties , cycle, Process
4. Derivation of the Process
5.Formula for the numericals.
This topic is use full for those students who want to study basic thermodynamics as a part of their University syllabus.
Most of the university having basic Mechanical engineering as a subject and in this subject Thermodynamics is a topic so by this PPT our aim is to give presentable knowledge of the subject
The document discusses various topics related to heat and thermodynamics including:
1) Heat is a form of energy transferred between objects due to a temperature difference, not a substance that flows.
2) The internal energy of a substance is the total energy of all its molecules. Temperature measures average kinetic energy.
3) Specific heat is a property that determines how much heat is required to change an object's temperature.
A donut contains a significant amount of calories, fat, and sugar. A plain cake donut has 226 calories, while a frosted donut has 303 calories and a glazed chocolate donut has 250 calories. Yeast donuts also contain a lot of calories, fat, and sugar, with a glazed yeast donut having 269 calories. Thermodynamics concepts discussed include the first law of thermodynamics regarding conservation of energy, the second law placing constraints on heat transfer and limiting efficiencies, and the Carnot cycle representing the most efficient possible heat engine cycle.
The document discusses different types of thermodynamic systems and their characteristics. It defines closed, open, and isolated systems based on whether they allow for mass and/or energy transfer with their surroundings. An adiabatic system exchanges work but not heat, while a homogeneous system consists of a single phase and a heterogeneous system consists of multiple phases. Any process that returns a system to its initial state is considered a cycle. Reversible processes occur through continuous equilibrium states while irreversible processes occur through non-equilibrium states. Temperature is proportional to the average molecular kinetic energy. Work is the product of a force and distance of displacement, and heat is something that flows due to a temperature difference between a system and its surroundings.
engineering physics- unit 3- thermal physics- thermodynamics- laws of thermodynamics- heat engine- carnot cycle- otto and diesel engine- forbes and lees disc method.
This document provides an introduction to thermodynamics, including definitions of key concepts and summaries of important laws and principles. It begins with an overview of the course content, which covers topics like the definitions of thermodynamics, heat, work, and systems. It then discusses the significance of thermodynamics in applications ranging from household appliances to power plants. The document proceeds to define fundamental concepts like temperature, pressure, energy and power. It also explains the first and second laws of thermodynamics. In its concluding sections, it summarizes processes, criteria for reversibility, and the specific thermodynamic laws of Boyle and Charles.
Thermodynamics is the branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. It explains interactions of variables in an system in terms of conservation of energy. The four main concepts are heat, temperature, entropy, and the laws of thermodynamics. Heat is energy transferred between objects at different temperatures. Temperature is a measure of average kinetic energy. Entropy represents disorder and waste heat. The laws govern energy transfer and conservation.
Thermodynamics is the branch of physics that deals with heat and other forms of energy. The first law of thermodynamics states that the total energy of a system remains constant, such that any increase in one form of energy (such as heat) results in an equal decrease in another form (such as work). The second law states that heat cannot spontaneously flow from a colder body to a hotter body without an input of work. The third law states that the entropy of a perfect crystal approaches zero as the temperature approaches absolute zero.
This document discusses key concepts in thermodynamics including:
1. Thermodynamics is concerned with energy relationships involving heat, mechanical energy, and other aspects of energy transfer between systems and their surroundings. Temperature is a measure of an object's hotness or coldness.
2. The zeroth law of thermodynamics allows the definition of temperature and states that if two bodies are in thermal equilibrium with a third body, they are in thermal equilibrium with each other.
3. An ideal gas is a theoretical gas that follows the ideal gas law (PV=nRT) and behaves similarly to real gases at high temperatures and low pressures. The ideal gas law relates the pressure, volume, temperature, and amount
This document discusses key concepts in thermodynamics including:
1. Thermodynamics is concerned with energy relationships involving heat, mechanical energy, and other aspects of energy transfer between systems and their surroundings. Temperature is a measure of an object's hotness or coldness.
2. The zeroth law of thermodynamics allows the definition of temperature and states that if two bodies are in thermal equilibrium with a third body, they are in thermal equilibrium with each other.
3. An ideal gas is a theoretical gas that follows the ideal gas law (PV=nRT) and behaves similarly to real gases at high temperatures and low pressures. The ideal gas law relates the pressure, volume, temperature, and amount
This document provides an introduction to thermodynamics, including:
- A definition of thermodynamics as the study of energy and energy transformations between a system and its surroundings.
- A brief history of thermodynamics beginning with Otto von Guericke's vacuum pump in 1650 and the formulation of Boyle's Law by Robert Boyle and Robert Hooke.
- Explanations of key thermodynamics concepts and terminology like system, boundary, properties, and the zeroth, first, and second laws of thermodynamics.
- Summaries of processes involving perfect gases like isobaric, isochoric, and adiabatic processes, as well as thermodynamic cycles like the Carnot,
FINAL_201 Thursday A-3 Convective and Radiant Heat TransferKaylene Kowalski
This document describes an experiment on heat transfer through various modes. Thermocouples measured the temperature of a heated cylinder surface and surrounding air temperature. The experiment determined heat loss coefficients and amounts due to radiation, natural convection, and forced convection by varying voltage, temperature, and air velocity. Total heat loss was calculated from individual heat losses to understand heat transfer under different conditions.
Thermodynamics describes systems and their ability to transfer and transform energy. A closed system does not allow mass transfer across its boundary, while an open system does. The zeroth law establishes thermal equilibrium, while the first law concerns energy conservation. The second law establishes that entropy always increases and heat naturally transfers from hot to cold bodies. Heat engines like steam power plants operate between a heat source and sink in a cycle to convert some heat into work, with efficiency limited by exhausting waste heat. The Carnot cycle achieves the highest possible efficiency between two temperatures. Real cycles like Rankine approximate Carnot but have additional practical considerations.
Group E of Sanskar Public School completed a physics project on thermodynamics during the 2018-2019 academic year. The project was led by Sawarni Tiwari and included group members Manjeet Kumar, Shreya Tiwari, Mahwish, and Abhishek Singh. The project covered topics such as the laws of thermodynamics, heat and internal energy, state variables, processes like isothermal and adiabatic processes, and the work done in different processes. The principal and physics teacher certified that the project was the work of Group E and praised their initiative, cooperation, and the quality of their content and analysis.
Group E of Sanskar Public School completed a physics project on thermodynamics during the 2018-2019 academic year. The project was led by Sawarni Tiwari and included group members Manjeet Kumar, Shreya Tiwari, Mahwish, and Abhishek Singh. The project covered various topics in thermodynamics including the zeroth law, different types of processes, and the first and second laws of thermodynamics. The group thanked their teacher and principal for guidance and support in completing the successful project.
This document is the preface to a textbook on engineering thermodynamics. It discusses the history and updates that have been made to the fifth edition of the textbook. The preface emphasizes that concepts of engineering thermodynamics are important for modern industrial society's energy needs. It also notes that better resource management will be needed for sustainability in the future. The textbook is intended to cover basic engineering thermodynamics concepts required by most related curriculums.
These slides cover detailed information about laws of thermodynamics.It include 1st law definition and then its limitation and then entropy etc.Once you read this you will get know about detailed concept of thermodynamics and its laws with examples.
Thermodynamics: Thermodynamics system (open, close, and isolated), Thermodynamic Properties:
Definition and Units of -Temperature, Pressure (atmospheric, absolute and gauge). Volume. Internal
energy, Enthalpy, Concept of Mechanical work, Thermodynamics Laws with example- Zeroth Law, First
Law, Limitations of first law. Concept of heat Sink. Source, heat engine, heat pump,
refrigeration engine. 2nd Law of Thermodynamics statements (Kelvin Plank, Claussius), Numerical
on 2" law only.
Measurement: Measurement of Temperature (Thermocouple - Type according to temperature range
and application), Measurement of Pressure (Barometer, Bourdon pressure gauge, Simple U tube
Manometer with numerical).
The document discusses the second law of thermodynamics. It begins by describing some limitations of the first law, such as not predicting whether processes are possible or specifying direction. It then defines the second law as "heat cannot flow itself from a colder body to a hotter body." The second law introduces the concept of entropy as a measure of system disorder. It also helps determine the preferred direction of processes and states that entropy always increases for irreversible processes in closed systems. The document provides examples of reversible and irreversible processes.
The document discusses the second law of thermodynamics. It begins by describing some limitations of the first law, such as not predicting whether processes are possible or specifying direction. It then defines the second law as "heat cannot flow itself from a colder body to a hotter body." The second law introduces the concept of entropy as a measure of system disorder. It also helps determine the preferred direction of processes and states that entropy always increases for irreversible processes in closed systems. The document provides examples of reversible and irreversible processes.
Liquefied Natural Gas (LNG) is produced by cooling natural gas into a liquid form at liquefaction plants. It is then stored or transported as a liquid and regasified at regasification plants before being used. Understanding the thermodynamics of LNG plants is important for analyzing and evaluating the processes involved. The document discusses key thermodynamic concepts like the first and second laws of thermodynamics, entropy, enthalpy, latent and sensible heat, and different refrigeration cycles used in LNG plants. It provides explanations of these concepts and their relevance to analyzing energy transfers and processes in LNG plants.
The document discusses the three laws of thermodynamics:
1. Zeroth law defines temperature and thermal equilibrium. It allows for temperature measurement.
2. First law states that energy is conserved and can change forms but not be created or destroyed. It defines heat, work, and internal energy. Heat engines and refrigerators are discussed.
3. Second law introduces the concept of entropy and establishes limits on heat engine efficiency below 100% and prohibits converting heat to work without temperature difference. Carnot cycle and Carnot efficiency are introduced.
The laws establish fundamental thermodynamic principles and define key concepts like heat, work, efficiency. Processes must obey both the first and second laws or would create impossible
Ivanolegov thermodynamics serbian 4th edition test bank 1Ivan Olegov
Thermal energy is the energy a compound or system has due to its temperature, i.e., the power of moving or shaking molecules, according to the Power Education web site of the Texas Education Company. Thermodynamics involves determining this energy, which can be "exceptionally complicated," according to David McKee, a teacher of physics at Missouri Southern State University. Commonly this is idealized as the mass of the system, the stress of the system, and the quantity of the system, or some various other comparable set of numbers.
This document provides an overview of key concepts in chemical thermodynamics, including:
1. Systems, surroundings, boundaries, open vs closed vs isolated systems, and extensive vs intensive properties are introduced.
2. The three laws of thermodynamics - first law regarding energy conservation, second law regarding entropy, and third law regarding unattainability of zero kelvin - are briefly outlined.
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Module No. 33
1. 1
Module # 33
Thermodynamic Processes
Thermodynamics
It deals with the conversion of heat energy into mechanical
energy and vice versa. Thus, thermodynamics is the branch of
science that deals with the relation between heat and mechanical
energy. It is mainly concerned with the transformation of heat into
mechanical work and vice versa. The structure of
thermodynamics rests upon two simple laws known as the First
and Second Laws of Thermodynamics.
Alternatively, the field of Science, which deals with energies
possessed by gases and vapors, their conversion in terms of heat
and work, and their relationship with properties of system, is
called thermodynamics.
Automobile technology is based on the principle of
thermodynamics.
First Law of Thermodynamics
The first law of thermodynamics is that,
Change in internal energy of any system = Heat in flow + Work
done on the system.
2. 2
The heat and mechanical work are inter-convertible. According to
this law a definite amount of mechanical work is needed to
produce a definite amount of heat and vice versa.
If W is the amount of mechanical work converted from heat
energy Q, then
W Q
OR
W = JQ
Where J is constant and is called Joule's mechanical equivalent
of heat. It is defined as the amount of work done to produce unit
quantity of heat.
Second Law of Thermodynamics
This law states, there is a definite limit to the amount of
mechanical energy, which can be obtained from a given quantity
of hat energy.
This law of thermodynamics has been enunciated by clausius in a
lightly different form as "it is impossible for a self-acting machine
working in a cyclic process, to transfer heat from a body at a
lower temperature to a body at a higher temperature without the
aid of on external agency”. Or, in other words, the heat cannot
flow itself from a cold body to hot body without the help of an
3. 3
external agency.
This law has also been stated by Kelvin Planck as "It is
impossible to construct an engine working on a cyclic process,
whose sole purpose is to convert heat energy into work". In other
words, no actual heat engine, working on a cyclic process, can
convert the heat energy supplied to it into mechanical work. It
means that there is a degradation of energy in the process of
producing mechanical work from heat. According to this
statement, the second law of thermodynamics is sometimes
called as law of degradation of energy.
The second law of thermodynamics was given by Kelvin.
Thermodynamic Cycle
A thermodynamic cycle consists of a series of thermodynamic
operation (processes) which take place in a certain order and the
initial conditions are restored at the end of processes.
The study of various thermodynamic cycles is very essential for
power developing system (such as petrol engine, diesel engine,
gas turbine etc.). These engines use a mixture of fuel and air for
their operations. Since the mass of fuel used as compared to
mass of air is very small, therefore, the mixture may be assumed
to obey the properties of perfect gases.
4. 4
Assumptions in Thermodynamic Cycle
The analysis of all thermodynamic cycles is based on the
following assumptions.
1 The gas in the engine cylinder is a perfect gas, i.e. it obeys
the gas laws and constant specific heats.
2 The physical constants of the gas in the engine cylinder are
same as those of air at moderate temperature.
3 All the compression and expansion processes are adiabatic
and they take place without any internal friction.
4 Heat is supplied by bringing a hot body in contact with the
cylinder at appropriate points during the process. Similarly, heat is
rejected by bringing a cold body in contact with the cylinder at
these points.
5 The cycle is considered to be a closed one and the same air
is used again and again to repeat the cycle.
6 No chemical reaction whatsoever takes place in the engine
cylinder.
Types of Thermodynamic Cycles
The following are the important types of thermodynamic cycles.
1. Carnot cycle
5. 5
2. Stirling cycle
3. Ericsson cycle
4. Joule cycle
5. Otto cycle
6. Diesel cycle
7. Dual combustion cycle.
Thermodynamic Process
The process of heating and expanding of a gas may broadly be
defined as thermodynamic process. It has been observed that as
a result of flow of energy, change takes place in various
properties of the gas such as pressure, volume, temperature,
specific energy, specific enthalpy etc. The thermodynamic
process may be performed in innumerable ways, but the following
are important from the subject point of view:
1. Constant volume process
2. Constant pressure process
3. Hyperbolic process
4. Isothermal process
5. Adiabatic process or isentropic process
6. Polytropic process
6. 6
7. Free Expansion
8. Throttling process
Constant Volume Process
When a gas is heated at a constant volume, its temperature and
pressure will increase. Since there is no change in its volume, no
external work is done by the gas. The whole of the heat supplied
will be stored in the form of internal energy.
Constant Pressure Process
When a gas is heated at constant pressure its temperature and
volume will increase. Since there is a change in its volume, the
heat supplied is utilized in increasing the internal energy of the
gas, and for doing external work.
Constant Temperature Process
OR
Isothermal Process
When heat is supplied to a gas such that its temperature remains
constant, then such an expansion is called "Isothermal
Expansion". In this case, the whole of the heat supplied to the gas
will be used up in doing external work. Since Boyle's law assumes
constant temperature of the gas, therefore, expansion according
to Boyle's law is isothermal.
7. 7
Notes:
1. Thermodynamic processes are also applicable to the cooling
and
compression of gases. Cooling is regarded as negative heating
and compression as negative expansion.
2. In a thermodynamic process, apart from other details, we are
interested to find out the amount of work done during the process.
Low Temperature Physics
It is concerned with the study of the production and effects of very
low temperatures. It includes superconductivity and super fluidity
which take place in the very low range temperature. It is also
called cryophysics.
Brownian Motion
The phenomenon of molecular motion was first observed by
Robert Brown in 1827. He observed movement of pollen grains
suspended in water with a microscope and found that they were
constantly moving in a zig zag path. After many years, scientists
realized that this was due to collisions between the water
molecules and pollen grains. This random motion of tiny particles
is known as Brownian motion.
8. 8
This motion can also be seen in tiny graphite particles suspended
in water. These particles in water are illuminated by a strong
beam of light and are then seen with the help of a microscope.
These particles are also found to be moving in zig zag paths.
According to the molecular theory of matter, the water molecules
are always in motion and, hence, they collide with the graphite
particles and push them in some directions where they collide
with other water molecules and are pushed in some other
directions and this process continues.
This shows that molecules always remain in random motion either
vibratory or translatory.
Throttling Process
This type of expansion occurs when a gas or vapor is expanded
through an orifice or aperture of minute dimension like a valve,
which is very slightly opened, or a narrow throat. Fluid under
pressure is forced through that aperture but the velocity of fluid
flowing out is reduced to a negligible amount by the high
resistance offered by the friction between the fluid and the walls of
aperture. Hence, the kinetic energy of the fluid flowing out of
aperture is very small. In fact, the kinetic energy of the fluid has
been converted into heat, which warms up the fluid to an initial
temperature. Thus, no heat is supplied from or rejected to an
9. 9
external source and there is no external work done. Also there is
no change in temperature in case of perfect gas. In the throttling
process also,
W = 0, Q = 0 and ΔU = 0
Linear Thermal Expansion
When a metal rod is heated, its length increases. This expansion
in length is called linear thermal expansion.
Suppose the temperature of a metal rod of length L is raised by
an amount T. If L is the increase in its length, then,
L L T
OR
L = L T ______ [1]
Where, is the coefficient of linear expansion. Its value depends
upon the nature of the material of the rod. Its unit is 1/°c or 1/k.
Eq. [1] can also be written as
L2 – L1 = L1 T
OR
L2 = L1 (1 + T)
Where, L1 and L2 are the initial and final lengths of the rod.
10. 10
From Eq. [1], we get,
= L/L T
The coefficient of linear expansion can, therefore, be defined as
"The fractional change in length per unit change in temperature.’’
Atmosphere
The relations between various units of pressure are given below:
1 atmosphere = 14.7 lb/in2
= 760 mm of Hg
= 76 cm of Hg =1.01325 bar
Barometer
A device for measuring the atmospheric pressure is called a
barometer. OR
The instrument used for measuring the unknown pressure with
respect to the atmospheric pressure is called barometer.
There are two types of barometers. These are (1) = Mercury
Barometer (2) = Aneroid Barometer
Mercury Barometer
Atmospheric pressure is measured in a laboratory by a device
called a mercury barometer. A barometer consists of a thick
walled glass tube one meter in length which is opened at one end
11. 11
and closed from the other side. This glass tube is filled with
mercury. The open end is firmly covered with a thumb and then
carefully inverted in a vessel containing mercury. When the open
end is completely immersed in mercury, the thumb is removed.
Some of the mercury from the mercury column in the tube drops
in the vessel leaving a space at the closed end. This space
contains no air and is nearly a vacuum. If the mercury column in
the tube is measured, it is found to be approximately 760 mm
above the surface of mercury in the vessel. This length of 760 mm
always remains the same even if tubes of different diameters are
taken. The column of the mercury (the mercury column in the
tube) does not fall as the atmospheric pressure exerted on the
surface of mercury in the vessel is balanced by the pressure of
the mercury column in the tube. The length of the mercury column
in the tube is referred to as the atmospheric pressure since it is a
convenient measurement and is directly proportional to the
pressure. At sea level, the normal atmospheric pressure is 760
mm of mercury. It is often used as unit of pressure and is
abbreviated as 1 atm. Therefore, 1 atm. = 760 mm (mercury).
The fact that the atmosphere exerts pressure has been put into
use in several devices such as siphons, pumps and syringes. We
live at the bottom of a deep sea of air called the atmosphere. The
air, which is a mixture of hydrogen, oxygen and many other gases
12. 12
in our atmosphere, exerts pressure. The density of air varies from
sea level to different altitudes. It is more dense at sea level, its
density decreases with increase of height above sea level.
At sea level, the pressure of air is about 100000 Pa. We do not
normally feel atmospheric pressure as the pressure inside our
bodies is almost the same as that outside.
Pressure Law
The pressure of a fixed mass of gas at constant volume is
proportional to its thermodynamic temperature.
p
----------- = constant
T
Where p is the pressure and T is the absolute temperature.
"The pressure of a given mass of a gas is directly proportional to
its absolute temperature, provided the volume of the gas is kept
constant". This is known as pressure law and can be expressed
as:
P T
OR
P/T = a constant
13. 13
Graphical representation of this law is shown in the figure. It is
clear that as the temperature is decreased, the pressure of the
gas also decreases. At -273°C pressure becomes zero, because
at this temperature all molecular motion ceases and, therefore,
the gas does not exert any pressure on the walls of the container.
P
Fig: (1) Temperature Pressure Graph
Pressure
Force per unit area is called pressure.
Mathematically:
Pressure = Force / Area
P = F / A
OR
Pressure is defined as the force acting normally per unit area.
14. 14
Thrust
Pressure = -------------
Area
The SI unit of pressure is 1 newton per metre2
(N/m2
). It is called
the Pascal (Pa). High pressure is usually expressed in kilo pascal.
(1 k Pa = 1000 Pa)
Pressure in Liquids
Water contained in a glass has weight. As the weight is a force
which acts downward, therefore, the water exerts a pressure on
the bottom of the glass. This pressure is equal to the force per
unit area. The pressure at any point in a liquid depends on the
density and the depth in the liquid. Let us calculate the pressure
at the bottom of a liquid. Imagine a circle of area A at the bottom
of the liquid. This area lies at a depth h below the surface of the
liquid. Now the liquid which exerts pressure on this area is
contained in a cylinder whose bottom has an area A and whose
height is h. The volume of the liquid in this imaginary cylinder is
Ah. If is the density of the liquid, then mass of the liquid above
the area A will be Ah and its weight will be Ahg (where g is the
acceleration due to gravity).
15. 15
Therefore, the pressure of the liquid on the area A is given by
Force Ahg
Pressure = ----------- = --------- = hg
Area A
It is evident that the pressure at a point inside the liquid depends
on the height of the liquid above this point and the density of the
liquid. Persons who dive into a swimming pool experience an
increase in pressure as they descend below the surface of water.
If a beaker is filled with water and another similar beaker is filled
with a liquid whose density is higher than the density of water,
such as saline water, then pressure at a point in saline water will
be greater than the pressure at a point in ordinary water although
both the points are taken at the same level. Liquids also exert a
pressure on the vertical walls of the container. Internal stresses
are set up in the liquids by external forces, and these allow the
pressure in a liquid to be transmitted in all directions. The solid
surface needed to contain a liquid must exert a force on that
liquid. This force is equal and opposite to the force exerted by the
liquid on the containing surface.
Pressure in Gases
It is hard to believe that air possesses mass. However, when our
body feels the blow in a wind storm, then it is the mass of air
16. 16
which gives a push to our body. We can weigh the mass of air by
weighing a balloon inflated with air, then, allowing its air to escape
and weighing it again. We will note that there will be a loss in
weight when the air has escaped from the balloon. All gases exert
force due to their weight and hence exert pressure. The kinetic
theory enables us to account for the pressure a gas exerts on the
walls of its container. When a moving molecule strikes the walls of
its container, a force is exerted on the walls during the impact.
The continuous bombardment of molecules striking the walls
accounts for the pressure of the gas.
Vacuum Pressure
Vacuum pressure means pressure below atmospheric pressure. If
vacuum pressure is given, absolute pressure may be obtained
from the following relation.
Absolute pressure =Atmospheric pressure - vacuum pressure.
Absolute Pressure
All the pressure gauges read the difference between the actual
pressure in any system and the atmospheric pressure. The
reading of the pressure gauge is known as gauge pressure, while
the actual pressure is called absolute pressure.
Mathematically:
17. 17
Absolute pressure = Gauge pressure + Atmosphere pressure.
Atmospheric Pressure
We live at the bottom of a deep sea of air called the atmosphere.
The air, which is a mixture of nitrogen, oxygen and many other
gases in our atmosphere, exerts pressure. The density of air
changes from sea level to different altitudes. It is most dense at
sea level and its density decreases with increase of height above
the sea level. The density of air at sea level is about 1.2g per liter.
At an altitude of 2000 m, it is about 1g per liter and at 10000 m; it
is about 0.4 g per liter.
The atmosphere, because of its weight exerts pressure on the
surface of the earth and on everything on the earth including
ourselves. This pressure is called atmosphere pressure. At sea
level, the pressure of air is about 100,000 Pa. We do not normally
feel atmospheric pressure as the pressure inside our bodies is
almost the same as that outside.
The existence of atmospheric pressure was first demonstrated by
a German scientist Von Guericke. He took two hollow metallic
hemispheres which were made to fit with each other tightly. Air
inside the hemispheres was removed through a small hole by
means of an air pump. It was found that the hemispheres could
not be pulled apart when the air had been removed. The force
18. 18
keeping the hemispheres together was the air pressure acting
from outside. The hemispheres were so tightly held that it took
two teams each of eight horses to separate them. This
experiment was first performed in the city of Magdeburg.
Therefore, the experiment is called the Magdeburg hemisphere
experiment.
Fig: Magdeburg Hemisphere Apparatus
Pascal (1623-1662)
Pascal gave us law of fluid pressure.
Pascal's Law
Liquids transmit pressure equally in all directions. This is known
as Pascal's Law.
Thermometer
The device (or instrument) which is used for the exact or
quantitative measurement of temperature is called as
thermometer. Common thermometers use the expansion of liquid
to show change of temperature.
19. 19
Principle of Thermometer
When an object is heated, then, it undergoes various changes
e.g. change in length of the object, change in color or increase in
the resistance. Any one of these changes may be utilized to
construct a thermometer.
Construction of a Mercury Thermometer
An ordinary mercury thermometer is made up of a long glass
capillary tube having a uniform bore. One end of the tube is
closed while the other end is provided with a glass bulb filled with
mercury as a thermometric substance.
Working of the Mercury Thermometer
As bulb of the thermometer is placed in contact with a hot body,
then, the mercury expands and rises higher in the capillary tube.
This, height of the mercury in the capillary tube can be used as a
measurement of the temperature of the body.
Thermometric Substance
The substance (mercury, alcohol etc.) used in thermometer is
called thermometric substance.
20. 20
Mercury is usually used as thermometric substance because of its
following qualities.
(1) Pure mercury can be easily obtained i.e. it is easily available.
(2) It remains liquid over a fairly wide range of temperature i.e.
does not change its physical state within a wide range of
temperature variation.
(3) Over a wide range of temperature, its expansion is quite a
linear function of the temperature and its expansion is directly
proportional to the temperature.
(4) Being practically non-volatile, it is affected very little by its
vapor pressure.
(5) It has a low specific heat so that it does not remove much of
the heat of the body whose temperature is to be measured.
(6) On account of its high conductivity, it quickly assumes the
temperature of the body with which it is in contact.
(7) Being an opaque and shining liquid, it can be easily seen
through glass.
(8) It does not wet the glass walls of tube of thermometer and
does not stick to the glass walls.
21. 21
Thermometry
The branch of physics which deals with the measurement of
temperature is called as thermometry. The basic principle of
thermometry is that two bodies in contact and in thermal
equilibrium have the same temperature.
Thermos Flask
Thermos flask is a pot designed to prevent heat loss from the fluid
inside it due to all of the three modes of heat transfer (i.e.
conduction, convection and radiation). It also prevents the heat
present outside the flask from getting into the flask. Any hot or
cold drink contained in the thermos flask remains hot or cold for a
relatively long time.
Thermostat
Thermostats are devices which control temperature in a certain
region.
Kinetic Theory
The molecules of all the substances are not at rest. In liquids and
gases, the molecules move with different velocities and have
kinetic energies of translation. In solids, the molecules vibrate and
rotate and thus have vibrational and rotational energies. When the
energies of the molecules increase, they can transfer their
22. 22
energies to other bodies by collision. The energy transferred is
called the heat.
Kinetic Theory of Matter
OR
Molecular Theory of Matter
The kinetic theory of matter says that anything that moves does a
certain amount of work and possesses some energy.
British Thermal Unit (B.T.U)
It is defined as the amount of heat required to raise the
temperature of one pound of water by 1°F.
1 B.T.U = 252 calorie
1 calorie = 4.18 J
1 K Cal = 1000 calorie
1 B.T.U = 252 Calorie = 1055.06 J
Dew Point
The dew point is defined as the temperature at which the water
vapor present in the air is just sufficient to saturate it.
23. 23
Evaporation
The phenomenon of changing liquids into vapors without boiling is
called evaporation.
For example, when wet clothes are hung on the cord, they get
dry. Water present in clothes changes into vapors and disappears
into atmosphere.
Factors Upon Which Evaporation Depends
Fig: Evaporation depends upon Surface Area
Experiments have shown that evaporation of liquids depends on
the following factors.
1. Nature of Liquid:
The liquids having low boiling points evaporate more easily e.g.
Alcohol, ether, etc.
2. Temperature of Liquid:
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Evaporation process increases with the increase of temperature,
e.g., under hot iron wet clothes dry out quickly as the water
evaporates quickly.
3. Surface Area of the Liquid:
The more the surface area of liquid, the more will be the rate of
evaporation.
4. Dryness of Air:
The dryer the air, the quicker is the rate of evaporation. In the
rainy season, the clothes take much longer to dry.
5. Wind Speed:
The higher the wind speed, the greater is the rate of evaporation.
6. Air Pressure on the Surface of Liquid:
If the pressure on the surface of liquid is lowered, then, its rate of
evaporation is increased.
Cooling Through Evaporation
According to the kinetic theory, the molecules of a liquid move
freely. Some of the molecules have more kinetic energy while
some have less kinetic energy. Some of the molecules having
more kinetic energy and moving towards the surface overcome
the forces of attraction.
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When the molecules having more kinetic energy leave a liquid
surface, the average kinetic energy of the molecules left behind
becomes low and causes decrease of temperature of liquid. The
liquid, thus, cools down.
Example
If a person sits under a fan with wet clothes, his body feels
cooling because under the fan air, the water in the clothes
evaporates quickly. Here, each gram of water on evaporation
takes away 4.2J of heat from the body. Rapid evaporation thus
cools the body rapidly.
Experiment
Place some spirit in a beaker. Put the beaker on a wooden block
on which some water has been spilled. A thin layer of water is
formed between the beaker and block. By blowing on the spirit
through a glass tube, bubbles will start appearing in spirit, i.e. the
rate of evaporation of spirit increases.
As the molecules of spirit escape from the surface, the
temperature of spirit will fall. More and more molecules of spirit
turn into vapor and at one stage the temperature of spirit
becomes less than 0°C. This cools the water under the beaker to
0°C and it freezes.