1. what is the difference between heat transfer and Thermodynamics? 2. Derive the relationship between the effectiveness and the number of transfer units for a counter flow heat exchanger.       3.Explain  the following :  Capacity ratio,  Heat  exchanger effectiveness,  Number  of transfer units

1. HEAT TRANSFER
ASSIGNMENT
By AMIT KUMAR
IVth Semester, 1902003, 19030520003
PRODUCTION ENGG.

2. 1. what is the difference between
heat transfer and
Thermodynamics?
QUESTION

3. Answer :
"Heat Transfer" deals with the rate of energy transfer thus, it gives idea of how long a heat transfer
will occur? Heat transfer deals with time and non equilibrium phenomena. Heat can only transfer
when there is a temperature gradient exists in a body and which is indication of non equilibrium
phenomena.
if we cover Thermodynamics, it is more of a phenomena which studies the spontaneity of a
thermodynamic process, the process parameters at certain state points etc. whereas heat transfer
deals with so many other parameters, like flow behaviour, material properties, temperature gradient.
In thermodynamics, time of reaction doesn't play any role, whereas heat transfer can help us
determine the exact time and quantity based parameters involving in the process. How the heat
flows from body to body, where it looses uniformity etc.

4. Answer :
If you look at the laws involved in computation of thermodynamics, they can
be listed as follows:
● Zeroth Law of Thermodynamics (defines temperature)
● First law of Thermodynamics (defines internal energy)
● Second Law of Thermodynamics (defines entropy)
● Third Law of Thermodynamics (limits the lowest temperature
attainable)

5. Answer :
Observe the process parameters which are given importance in this kind of process, whereas, heat
transfer has following laws for its process variable computation:
● Fourier's Law (Heat conduction)
● Newton's Law of Cooling (Heat convection)
● Planck's Law (Thermal Radiation)
● Stefan Boltzmann's Law (Thermal Radiation)
● Wien's Law (Thermal Radiation)
● Kirchoff's Law (Thermal Radiation)
● Lambert's Law (Thermal Radiation)

6. Answer :
Heat transfer is slightly more broader than Thermodynamics, and goes a bit more specific into a process as
a whole. Considering the type of material, its geometry, the fluid flow, the temperature gradient and many
other parameters are taken into account while obtaining or analyzing the variables that involve heat transfer
problems in real life.
Though, heat transfer won't consider the computation of process end points, but it won't be wrong if we
formalize the equation which says:
Heat transfer=Thermodynamics+Material Science+Fluid Mechanics
Though, it's not like going into hundred percent depth of these topics which will be involved in computing
heat transfer problems in real life, but some segments of all these subjects are somewhere involved when it
comes to compute those problems which involve heat transfer.

7. In Conclusion, we can say that :
Thermodynamics is process descriptor and tells us about the amount of heat, energy, work,
dissipations etc. as total and doesn't involve individual states (until and unless properly
defined by the process parameters) whereas heat transfer is the study of computation of non
equilibrium states and the entire process at various steps, looking for uniformity, material
properties, distortions, thermal stresses etc. Heat transfer is actually a study of rate of
transfer of these physical variables like energy and material properties.

8. Question
2. Derive the relationship between
the effectiveness and the number of
transfer units for a counter flow
heat exchanger.

9. WRITTEN ON PAPER IN NEXT
PAGE:
Solution

11. Question
3.Explain the following :
● Capacity ratio,
● Heat exchanger effectiveness,
● Number of transfer units

12. Capacity ratio (C): It is defined as ratio of minimum to
maximum capacity rate of fluids being used in a heat
exchanger. The fluid with lower heat capacity rate will
undergo greater change in temperature as compared
to fluid with higher heat capacity rate.
Capacity Ratio :
as cmin
= mh
cph
and cmax
= mc
cpc
The fluid with lower heat capacity rate will undergo greater
change in temperature as compared to fluid with higher heat
capacity rate.

13. A heat exchanger is an equipment which facilitates the flow of
thermal energy between two or more fluids at different
temperatures. Heat exchangers are employed in a variety of
domestic, commercial, and industrial applications, such as
power generation, refrigeration, air conditioning, process
industry, manufacturing industry etc
Heat Exchanger :

14. Parallel flow heat exchanger In a parallel flow heat
exchanger, the two fluid streams (hot and cold) flow through
the heat exchanger in the same direction. The two fluid
streams enter at one end of the heat exchanger and leave at
the other end. The schematic and the temperature profile of
the fluid streams in parallel flow heat exchanger are shown in
From the temperature profile ,it is clear that the temperature
difference between the fluid streams decreases from the inlet
to the outlet of the heat exchanger. Parallel flow heat
exchangers are rarely employed due to their requirement of
large surface area for heat transfer.
Examples:Oil heaters, oil coolers, water heater
Parallel flow
Heat Exchanger :

15. In a counter flow heat exchanger, the two fluid streams flow in
relatively opposite directions. The fluid streams enter at
opposite ends. The temperature difference between the two
fluid streams remains nearly constant. Counter flow heat
exchangers provide the maximum heat transfer rate for a
given surface area. Hence, they are the most widely used
heat exchangers.
Temperature Difference(θ1) = th1 − tc2 … (4)
Temperature Difference(θ2) = th2 − tc1 … (5) Log mean
temperature difference (LMTD) = θ1 − θ2 ln θ1 − θ2
Counter flow
heat exchanger :

16. In a counter flow heat exchanger, the two fluid streams flow in
relatively opposite directions. The fluid streams enter at
opposite ends. The temperature difference between the two
fluid streams remains nearly constant. Counter flow heat
exchangers provide the maximum heat transfer rate for a
given surface area. Hence, they are the most widely used
heat exchangers.
Temperature Difference(θ1) = th1 − tc2 … (4)
Temperature Difference(θ2) = th2 − tc1 … (5)
Log mean temperature difference (LMTD) = θ1 − θ2 ln θ1 −
θ2
Counter flow
heat exchanger :

17. In a cross-flow heat exchanger, the paths of the two fluid
streams through the heat exchanger are usually at right
angles to each other. The cross flow heat exchanger in our
laboratory is of finned type and the cooling media used is air.
Cross flow heat
exchanger :

18. This type of heat exchangers has a bundle of tubes enclosed
in a shell, usually cylindrical. The tubes are arranged parallel
to the shell axis. One fluid stream is passed through the
bundle of tubes, while the other fluid stream is flows through
the shell over the tubes . Overall heat transfer between the
fluid streams is enhanced by the use of multiple shell & tube
passes. With the use of baffles, the shell-side fluid stream is
re-routed and made to flow back-and-forth over the tube
Shell & tube heat
exchanger :

19. Plate heat exchangers consist of a number of thin corrugated
metal plates arranged together. The fluid streams enter the
heat exchanger through frame connections and are then
distributed to the plates. The two fluid streams pass through
alternate spaces formed between the successive plates.
Thanks to the corrugations on the metal plates and the small
spacing between the plates, the fluid flow is essentially
turbulent which improves the overall heat transfer between
the fluid streams. Also, the eddies generated in the flow clean
the heat exchanger surface, thus minimizing fouling. Plate
heat exchangers are widely used in industries due to their low
cost, easy maintenance, and high thermal efficiency.
Plate heat
exchanger :

20. The number of transfer units (NTU = UA/(mcp
)) itself is a
combination of overall heat transfer coefficients,
transfer area, fluid flow rate and heat capacity. It
summarizes these dimensional parameters into one
dimensionless parameter. The performance becomes a
monotone function of this dimensionless parameter.
Number of
Transfer units :

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THANK -
19030520003