This document provides an overview of heat transfer mechanisms and concepts. It discusses the three main mechanisms of heat transfer: conduction, convection, and radiation. Conduction involves the transfer of energy between adjacent particles due to collisions. Convection refers to heat transfer between a surface and a moving fluid. Radiation involves the emission and absorption of electromagnetic waves. Key equations for each mechanism are presented, including Fourier's law of conduction and Newton's law of cooling for convection. Common ranges of thermal properties are also listed.
Very useful for the beginners in the field of heat and the mass transfer field. It also gives the idea about the different modes of heat transfer and the measurement of energy transfer rate.
Very useful for the beginners in the field of heat and the mass transfer field. It also gives the idea about the different modes of heat transfer and the measurement of energy transfer rate.
As companies examine their total cost of operations, energy usage and heat recovery deliver cost savings through increased energy utilization and efficiency. Heat exchangers offer companies the opportunity to reuse energy generated for a specific purpose instead of venting that energy to the atmosphere. Shell and tube heat exchangers are in wide use throughout the Food, Dairy, Beverage, Pharmaceutical, Chemicals, Petroleum Refining, and Utility industries. This paper briefly explores three modes of heat transfer and basic designs found in shell and tube heat exchangers. Also included are several case studies from different industries where
Enerquip’s heat exchangers have saved the operators energy and money.
Introduction
Mechanism of Heat Flow
Conduction
Heat Flow through a Cylinder-Conduction
Conduction through fluids
Convection
Film type condensation
Cold liquid-boiling of liquids
Modes of Feed-Heat Transfer
Thermal Radiation
Black Body
Grey body
Equipments
References
2.1 Heat
Heat is a form of energy. According to the principle of thermodynamics whenever a physical or chemical transformation occurs heat flow into or leaves the system.
A number of sources of heat are used for industrial scale operations steam and electric power is the chief sources to transfer heat. It is essential to cover steam without any loses to the apparatus in which it is used. The study of heat transfer processes helps in be signing the plant efficiently and economically
2.2 Heat Transfer:-
Work is one of the basic modes of energy transfer in machines the action of force on a moving body is identified as work. The work is done by a force as it acts upon a body moving in the direction of the force.
Work transfer is considered as occurring between the system and the surroundings work is said to be done by a system is the sole effect on things external to the system can be reduced to the raising of a weight.
If a system has a non-adiabatic boundary its temperature is not independent of the temperature of the surroundings and for the system between the states 1 and 2 the work w depends on path and the differential d-w is inexact. The work depends on the terminal state 1 and 2 as well as non-adiabatic path connecting them. For consistency with the principle of conservation of energy. Some type of energy transfer must have occurred because of the temperature difference between the system and its surroundings and it is identified as heat thus when an effect in a system occurs solely as result of temperature difference between the system and some other system the process in which the effect occur shall be called a transfer of heat from the system at the higher temperature to the system at the lower temperature.
1.1 Evaporation
1.2 Distillation
1.3 Drying
1.4 Crystallization
1.5 Sterilization
Application of Heat Transfer in Pharmaceuticals Industries
As companies examine their total cost of operations, energy usage and heat recovery deliver cost savings through increased energy utilization and efficiency. Heat exchangers offer companies the opportunity to reuse energy generated for a specific purpose instead of venting that energy to the atmosphere. Shell and tube heat exchangers are in wide use throughout the Food, Dairy, Beverage, Pharmaceutical, Chemicals, Petroleum Refining, and Utility industries. This paper briefly explores three modes of heat transfer and basic designs found in shell and tube heat exchangers. Also included are several case studies from different industries where
Enerquip’s heat exchangers have saved the operators energy and money.
Introduction
Mechanism of Heat Flow
Conduction
Heat Flow through a Cylinder-Conduction
Conduction through fluids
Convection
Film type condensation
Cold liquid-boiling of liquids
Modes of Feed-Heat Transfer
Thermal Radiation
Black Body
Grey body
Equipments
References
2.1 Heat
Heat is a form of energy. According to the principle of thermodynamics whenever a physical or chemical transformation occurs heat flow into or leaves the system.
A number of sources of heat are used for industrial scale operations steam and electric power is the chief sources to transfer heat. It is essential to cover steam without any loses to the apparatus in which it is used. The study of heat transfer processes helps in be signing the plant efficiently and economically
2.2 Heat Transfer:-
Work is one of the basic modes of energy transfer in machines the action of force on a moving body is identified as work. The work is done by a force as it acts upon a body moving in the direction of the force.
Work transfer is considered as occurring between the system and the surroundings work is said to be done by a system is the sole effect on things external to the system can be reduced to the raising of a weight.
If a system has a non-adiabatic boundary its temperature is not independent of the temperature of the surroundings and for the system between the states 1 and 2 the work w depends on path and the differential d-w is inexact. The work depends on the terminal state 1 and 2 as well as non-adiabatic path connecting them. For consistency with the principle of conservation of energy. Some type of energy transfer must have occurred because of the temperature difference between the system and its surroundings and it is identified as heat thus when an effect in a system occurs solely as result of temperature difference between the system and some other system the process in which the effect occur shall be called a transfer of heat from the system at the higher temperature to the system at the lower temperature.
1.1 Evaporation
1.2 Distillation
1.3 Drying
1.4 Crystallization
1.5 Sterilization
Application of Heat Transfer in Pharmaceuticals Industries
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
HEAP SORT ILLUSTRATED WITH HEAPIFY, BUILD HEAP FOR DYNAMIC ARRAYS.
Heap sort is a comparison-based sorting technique based on Binary Heap data structure. It is similar to the selection sort where we first find the minimum element and place the minimum element at the beginning. Repeat the same process for the remaining elements.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
NUMERICAL SIMULATIONS OF HEAT AND MASS TRANSFER IN CONDENSING HEAT EXCHANGERS...ssuser7dcef0
Power plants release a large amount of water vapor into the
atmosphere through the stack. The flue gas can be a potential
source for obtaining much needed cooling water for a power
plant. If a power plant could recover and reuse a portion of this
moisture, it could reduce its total cooling water intake
requirement. One of the most practical way to recover water
from flue gas is to use a condensing heat exchanger. The power
plant could also recover latent heat due to condensation as well
as sensible heat due to lowering the flue gas exit temperature.
Additionally, harmful acids released from the stack can be
reduced in a condensing heat exchanger by acid condensation. reduced in a condensing heat exchanger by acid condensation.
Condensation of vapors in flue gas is a complicated
phenomenon since heat and mass transfer of water vapor and
various acids simultaneously occur in the presence of noncondensable
gases such as nitrogen and oxygen. Design of a
condenser depends on the knowledge and understanding of the
heat and mass transfer processes. A computer program for
numerical simulations of water (H2O) and sulfuric acid (H2SO4)
condensation in a flue gas condensing heat exchanger was
developed using MATLAB. Governing equations based on
mass and energy balances for the system were derived to
predict variables such as flue gas exit temperature, cooling
water outlet temperature, mole fraction and condensation rates
of water and sulfuric acid vapors. The equations were solved
using an iterative solution technique with calculations of heat
and mass transfer coefficients and physical properties.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
5. What is heat transfer?
Heat is a form of energy that can be transferred from one
system to another as a result of temperature difference.
The science that deals with the determination of the rates of
such energy transfer is heat transfer.
In practice we are more concerned about the rate of heat
tranfer (heat tranfer per unit time) than the amount of heat
transfer, e.g.
Heat treatment of metals: (a) quenching and (b) annealing.
5
Lecture 1
7. MECHANISMS OF HEAT TRANSFER
Heat can be transferred in three
different ways: conduction,
convection, and radiation.
All modes of heat transfer require
the existence of a temperature
difference, and all modes of heat
transfer are from the high-
temperature medium to a lower
temperature one.
7
Lecture 1
8. Conduction, Convection & Thermal Radiation
Conduction refers to the transport of energy in a medium due to
a temperature gradient.
In contrast, the convection refers to heat transfer that occurs
between a surface and a fluid (at rest or in motion) when they
are at different temperatures.
Thermal radiation refers
to the heat transfer that
occurs between two
surfaces at different
temperatures. It results
from the energy emitted
by any surface in the form
of electromagnetic waves.
8
Lecture 1
10. Physical Mechanism of Conduction
Temperature is a measure of the kinetic energies of the molecules.
In a liquid or gas, the kinetic energy of the molecules is due to the
random motion of the molecules as well as the vibrational and
rotational motions.
When two molecules possessing different kinetic energies collide,
part of the kinetic energy of the more energetic (higher
temperature) molecule is transferred to the less energetic (lower
temperature) particle,
In solids, heat conduction is due to two effects: the lattice
vibrational waves induced by the vibrational motions of the
molecules positioned at relatively fixed position in a periodic manner
called a lattice, and the energy transported via the free flow of
electrons in the solid.
The thermal conductivity of a solid is obtained by adding the lattice
and the electronic components.
The thermal conductivity of pure metals is primarily due to the
electronic component, whereas the thermal conductivity of
nonmetals is primarily due to the lattice component.
10
Lecture 1
11. The lattice component of thermal conductivity strongly depends
on the way the molecules are arranged.
For example, the thermal conductivity of diamond, which is a
highly ordered crystalline solid, is much higher than the thermal
conductivities of pure metals, as can be seen from Table 1-1.
11
Lecture 1
12. Conduction
is the transfer of energy from the
more energetic particles of a
substance to the adjacent less
energetic ones as a result of
interactions between the particles.
Conduction can take place in solids,
liquids, or gases.
In gases and liquids, conduction is
due to the collisions of the molecules
during their random motion.
In solids, it is due to the combination
of vibrations of molecules in a lattice
and the energy transport by free
electrons.
A cold canned drink in a warm room
eventually warms up to the room
temperature as a result of heat
transfer from the room to the drink
through the aluminum can by
conduction
12
Lecture 1
13. Conduction
It is observed that the rate of heat conduction
through a layer of constant thickness Δx is
proportional to the temperature difference ΔT
across the layer and the area A normal to the
direction of heat transfer, and is inversely
proportional to the thickness of the layer, Δx .
where the constant of proportionality kt is the thermal conductivity
of the material, which is a measure of the ability of a material to
conduct heat (Table 1-1).
Materials such as copper and silver, which are good electric
conductors, are also good heat conductors, and therefore have high
kt values.
Materials such as rubber, wood, and styrofoam are poor conductors
of heat, and therefore have low kt values.
13
16. In the limiting case of x → 0,
the equation above reduces to
the differential form
x
hot wall cold wall
dx
dT
temperature
profile
which is known as Fourier’s law of heat conduction.
It indicates that the rate of heat conduction in a direction is
proportional to the temperature gradient in that direction.
Heat is conducted in the direction of decreasing temperature,
and the temperature gradient becomes negative when
temperature decreases with increasing x. Therefore, a
negative sign is added in the Eq. to make heat transfer in the
positive x direction a positive quantity.
16
Lecture 1
17. Example:
The Cost of Heat Loss through a Roof
The roof of an electrically heated home is 6 m long, 8 m wide, and
0.25 m thick, and is made of a flat layer of concrete whose thermal
conductivity is k 0.8 W/m · °C . The temperatures of the inner and
the outer surfaces of the roof one night are measured to be 25°C
and 0°C, respectively, for a period of 10 hours.
Determine:
(a) the rate of heat loss through the roof that night and
(b) the cost of that heat loss to the home owner if the cost of
electricity is $0.2/kWh.
17
Lecture 1
25 C
0 C
18. Solution:
(a) Noting that heat transfer through the roof is by conduction and
the area of the roof is:
A= 6 m×8 m=48 m2.
The steady rate of heat transfer through the roof is determined
to be
Q·=kA(T1-T2)/L= (0.8)(48 )(25-0)/0.25= 3840 W= 3.84 kW
(b) The amount of heat lost through the roof during a 10-hour
period and its cost are determined from
Q = Q·t =(3.84 kW)(10 h) = 38.4 kWh
Cost/day = (Amount of energy)(Unit cost of energy)
= (38.4 kWh)($0.2/kWh) =$7.68
Cost/month = (cost/day)×(30day/month)= $7.68×30=$230.4
Why is the
bill so high?
18
Lecture 1
19. Thermal Diffusivity
The thermal diffusivity is a
measure of how quickly a material
can carry heat away from a hot
source.
Since material does not just
transmit heat but must be warmed
by it as well, involves both the
conductivity, k, and the volumetric
heat capacity, ρ cp.
s
m
J
K
kg
kg
m
K
s
m
J
stored
Heat
conducted
Heat
C
k
p
2
3
.
.
19
Lecture 1
21. Convection
Convection is the mode of energy transfer between a solid surface
and the adjacent liquid or gas that is in motion, and it involves the
combined effects of conduction and fluid motion.
The faster the fluid motion, the greater the convection heat
transfer. In the absence of any bulk fluid motion, heat transfer
between a solid surface and the adjacent fluid is by pure
conduction.
The presence of bulk motion of the fluid enhances the heat
transfer between the solid surface and the fluid, but it also
complicates the determination of heat transfer rates.
Consider the cooling of a hot block by blowing of cool air over its
top surface. Energy is first transferred to the air layer adjacent
to the surface of the block by conduction. This energy is then
carried away from the surface by convection; that is, by the
combined effects of conduction within the air and the motion of
the air, which removes the heated air near the surface and
replaces it by the cooler air.
21
Lecture 1
22. Forced and Free Convection
Convection is called forced convection if the
fluid is forced to flow in a tube or over a
surface by external means such as a fan,
pump, or the wind.
In contrast, convection is called free (or
natural) convection if the fluid motion is
caused by buoyancy forces induced by density
differences due to the variation of
temperature in the fluid.
For example, in the absence of a fan, heat
transfer from the surface of the hot egg will
be by natural convection since any motion in
the air in this case will be due to the rise of
the warmer (and thus lighter) air near the
surface and the fall of the cooler (and thus
heavier) air to fill its place.
22
Lecture 1
23. Forced and Free Convection
The cooling of a boiled egg by forced and natural convection.
23
Lecture 1
24. Newton’s law of cooling
The rate of heat transfer by convection is determined from
Newton’s law of cooling, expressed as
where h is the convection heat transfer coefficient,
A is the surface area through which heat transfer takes place,
Ts is the surface temperature, and
Tf is bulk fluid temperature away from the surface.
The convection heat transfer coefficient h is not a property of the
fluid.
It is an experimentally determined parameter whose value depends on
all the variables that influence convection such as:
the surface geometry,
the nature of fluid motion,
the properties of the fluid, and the bulk fluid velocity.
24
Lecture 1
25. Convection
Typical values of h, in
W/m2·K, are in the range
of 2–25 W/m2·K for the
free convection of gases,
50–1000 W/m2·K for the
free convection of
liquids,
25–250 W/m2·K for the
forced convection of
gases, 50–20,000
W/m2·K for the forced
convection of liquids,
and 2500–100,000
W/m2·K for convection
in boiling and
condensation processes.
25
Lecture 1
26. Unlike conduction and convection, heat transfer by radiation can occur
between two bodies, even when they are separated by a medium colder
than both of them.
Radiation
26
Lecture 1
27. Radiation
Radiation is the energy emitted by matter in the form of
electromagnetic waves as a result of the changes in the
electronic configurations of the atoms or molecules.
Unlike conduction and convection, the transfer of energy by
radiation does not require the presence of an intervening
medium. In fact, energy transfer by radiation is fastest (at the
speed of light) in a vacuum. This is exactly how the energy of
the sun reaches the earth.
In heat transfer studies, we are interested in thermal radiation,
which is the form of radiation emitted by bodies because of
their temperature. It differs from other forms of
electromagnetic radiation such as X-rays, gamma rays,
microwaves, radio waves, and television waves that are not
related to temperature.
All bodies at a temperature above absolute zero emit thermal
radiation.
27
Lecture 1
28. Radiation is a volumetric phenomenon, and all solids, liquids, and
gases emit, absorb, or transmit radiation of varying degrees.
However, radiation is usually considered to be a surface
phenomenon for solids that are opaque to thermal radiation such
as metals, wood, and rocks since the radiation emitted by the
interior regions of such material can never reach the surface,
and the radiation incident on such bodies is usually absorbed
within a few microns from the surface.
The maximum rate of radiation that can be emitted from a
surface at an absolute temperature Ts is given by the Stefan–
Boltzmann law as
where A is the surface area and = 5.67 * 10-8 W/m2 · K4 is the
Stefan–Boltzmann constant.
The idealized surface that emits radiation at this maximum rate
is called a blackbody, and the radiation emitted by a blackbody
is called blackbody radiation. 28
29. Emissivity,
The radiation emitted by all real surfaces is less than the
radiation emitted by a blackbody at the same temperatures and
is expressed as
where is the emissivity of the surface.
The property emissivity, whose value is in the range 0 1, is
a measure of how closely a surface approximates a blackbody
for which = 1.
29
Lecture 1
31. Another important radiation property of a surface is its
absorptivity, , which is the fraction of the radiation energy
incident on a surface that is absorbed by the surface. Its value is
in the range 0 1.
A blackbody absorbs the entire radiation incident on it. That is, a
blackbody is a perfect absorber ( = 1) as well as a perfect
emitter ( = 1).
In general, both and of a surface depend on the temperature
and the wavelength of the radiation.
Kirchhoff’s law of radiation states that the emissivity and the
absorptivity of a surface are equal at the same temperature and
wavelength.
In most practical applications, the dependence of and on the
temperature and wavelength is ignored, and the average
absorptivity of a surface is taken to be equal to its average
emissivity. =
Absorptivity,
31
Lecture 1
32. Absorpitivity
The rate at which a surface absorbs radiation is determined
from
where Qinc is the rate at which radiation is incident on the
surface and is the absorptivity of the surface.
For opaque (nontransparent) surfaces, the portion of incident
radiation that is not absorbed by the surface is reflected back.
32
Lecture 1
33. Absorption and Emission of Radiation
Energy out = Energy in
Emitted energy/Incident energy = Emissivity = . 33
34. Black Bodies
Summer clothing: white
reflects radiant energy
better than black.
Until equilibrium is
reached, white stripes on
roads are at a
lower temperature than
unpainted asphalt.
Wrap an ice-cube in black
cloth and another in
aluminum foil and place
both in the sunshine. What
will happen?
34
Lecture 1
35. The difference between the rates of radiation emitted by the
surface and the radiation absorbed is the net radiation heat
transfer.
If the rate of radiation absorption is greater than the rate of
radiation emission, the surface is said to be gaining energy by
radiation. Otherwise, the surface is said to be losing energy by
radiation.
In general, the determination of the net rate of heat transfer
by radiation between two surfaces is a complicated matter since
it depends on the properties of the surfaces, their orientation
relative to each other, and the interaction of the medium
between the surfaces with radiation.
35
Lecture 1
36. However, in the special case of a relatively small surface of
emissivity and surface area A at absolute temperature Ts that
is completely enclosed by a much larger surface at absolute
temperature Tsurr separated by a gas (such as air) that does not
intervene with radiation (i.e., the amount of radiation emitted,
absorbed, or scattered by the medium is negligible), the net
rate of radiation heat transfer between these two surfaces is
determined from
In this special case, the
emissivity and the surface
area of the surrounding
surface do not have any
effect on the net radiation
heat transfer.
36
Lecture 1
37. Not all three can exist simultaneously in a
medium. For example, heat transfer is only
by conduction in opaque solids, but by
conduction and radiation in
semitransparent solids. Thus, a solid may
involve conduction and radiation but not
convection.
However, a solid may involve heat transfer
by convection and/or radiation on its
surfaces exposed to a fluid or other
surfaces. For example, the outer surfaces
of a cold piece of rock will warm up in a
warmer environment as a result of heat
gain by convection (from the air) and
radiation (from the sun). But the inner
parts of the rock will warm up by
conduction.
Simultaneous Heat Transfer Mechanisms
37
Lecture 1
38. Heat transfer is by conduction and
possibly by radiation in a still fluid and
by convection and radiation in a flowing
fluid.
In absence of radiation, heat transfer
through a fluid is either by conduction
or convection, depending on the
presence of any bulk fluid motion.
Convection can be viewed as combined
conduction and fluid motion
Thus, when we deal with heat transfer
through a fluid, we have either
conduction or convection, but not both.
Also, gases are practically transparent
to radiation, except that some gases are
known to absorb radiation strongly at
certain wavelengths.
Liquids, on the other hand, are usually
strong absorbers of radiation.
Combined Heat
transfer coefficient:
Q total = hcomb (Ts – T)
38
Lecture 1
39. Example :
Consider a person standing in a breezy
room at 20°C. Determine the total rate of
heat transfer from this person if the
exposed surface area and the average
outer surface temperature of the person
are 1.6 m2 and 29°C, respectively, and the
convection heat transfer coefficient is 6
W/m2 · °C . Convection can be viewed as
combined conduction and fluid motion.
Solution :
Heat is transfered from the person by convection and radiation. From
the above table the emissivity of human skin is 0.95,
Q
·
conv
=hAs(Ts -T)=
Q
·
rad
W
4
.
86
C
)
20
29
(
m
6
.
1
C
m
W
6 2
2
W
7
.
81
K
)
393
302
(
m
6
.
1
K
m
W
10
67
.
5
95
.
0
)
T
T
(
A
εσ
4
4
4
2
4
2
8
4
surr
4
s
s
39