1. CH2043
Heat Transfer Processes and Equipment
CC01, CC02, CC03, CC04
Wan Zaireen Nisa Yahya and Shafirah Samsuri 2022
English Program
Ho Chi Minh City University of Technology

2. PRINCIPLES OF THERMODYNAMICS
▪ Thermodynamics and Heat Transfer
▪ The First Law of Thermodynamics
▪ The Second Law of Thermodynamics

3. Thermodynamics and Heat Transfer
Stream Temperature Profiles
3
▪ Heat Duties
60.1oC 150oC Heat Exchanger Duty,
Q = 2529 kW
T
Streams
need
cooling
Q
Q = DH
T
Streams
need
heating
Q
Q = DH
Hot Streams Cold Streams
▪ Stream profile on temperature (T) – heat (Q) diagram

4. 4
T
Q
Hot Streams
Cold Streams
DT1
DT2
Thermodynamics and Heat Transfer
Stream profile for a heat exchanger
4

5. ▪ Heat is the form of energy that can be transferred from one
systemto another due to temperature difference.
▪ Heat transfer deals with the determination of the rates of
such energy transfers as well as variation of temperature.
▪ Thermodynamics is concerned with the amount of heat
transfer as a system undergoes a process from one
equilibrium state to another. Does not give information
about how long the process will take.
5
Definitions:
Thermodynamics and Heat Transfer
5

6. Thermodynamics and Heat Transfer
▪ Object 1 at higher temperature than Object 2.
▪ When the two objects are connected, heat flows from object 1
to Object 2.
▪ Heat flows continue until both objects at thermal equilibrium. 6

7. • Thermodynamics deals with equilibrium states and changes from one
equilibrium state to another.
• Heat Transfer deals with systems that lack thermal equilibrium, and
thus, it is non-equilibrium phenomenon
Thermodynamics and Heat Transfer
Definitions:
7

8. ▪ The quantity of heat that flows from object 1 to object 2, including heat
flow to the surroundings, must be accounted. This is because heat energy
is always a conserved quantity.
▪ Heat flow is always from the higher-temperature medium to the lower-
temperature one (temperature difference).
▪ Heat transfer stops when the two mediums reach the same temperature.
▪ The larger the temperature gradient/difference, the higher the rate of heat
transfer.
8
2nd Law Thermodynamics
Q DT
1st Law Thermodynamics
Thermodynamics and Heat Transfer

9. 9
The First law of Thermodynamics
▪ The conservation of energy principle
▪ Energy can neither be created nor destroyed
▪ Energy can only change forms.
▪ In steady operation, the rate of energy
transfer to a system is equal to the rate of
energy transfer from the system.
Heat Transfer Process

10. Systems

11. 11
The First law of Thermodynamics
Thermodynamic Systems
Closed System:
Energy flows in and
out of the system
boundary but not
mass.
Mass flow
Energy Flow
DU
Open System:
Mass and Energy
flows in and out of the
system boundary
Mass flow
Energy Flow
DH
Isolated System:
No Mass or Energy
flows across the
system boundary.
Mass flow
Energy Flow
DU=0

12. 12
The First law of Thermodynamics
▪ The net change (increase or decrease) in the total energy of the
system during a process is equal to the difference between the
total energy entering and the total energy leaving the system
during that process.
Statement of the First Law of Thermodynamics

13. 13
Solutions:
Two tanks are connected by a valve. One tank contains 2 kg of CO2 at 77°C and 0.7 bar.
The other tank has 8 kg of the same gas at 27°C and 1.2 bar. The valve is opened and
gases are allowed to mix while receiving energy by heat transfer from the surroundings.
The final equilibrium temperature is 42°C. Using ideal gas model, determine the heat
transfer for the process.
Assumptions:
1. The total amount of CO2 remains constant(closed system).
2. Ideal gas with constantCv.
3. The initial and final statesin the tanks are equilibrium. No work transfer.
Example 1: Equilibrium gas chambers
The First law of Thermodynamics

14. 14
Writing the energy balance:
ΔU = Q – W
Since W = 0, then Q = ΔU = Uf - Ui
where:
initial internal energy is: Ui= mA u(TA) + mB u(TB)
and final internal energy is: Uf = (mA + mB) u(Tf)
Q = mA [u(Tf) – u(TA)] + mB [u(Tf) – u(TB)]
and u(T) = cvT where cv = 0.745 kJ/kg.K (constant)
Example 1: Equilibrium gas chambers
The First law of Thermodynamics

15. 15
Then energy balance becomes:
Q = mA cv [Tf – T A] + mB cv [Tf – TB]
Q = (2 kg)(0.745 kJ/kg.K) [315 – 350]K + (8 kg)(0.745 kJ/kg.K) [315 – 300]K
= 37.2 kJ
Example 1: Equilibrium gas chambers
The First law of Thermodynamics
#answer

16. 16
Solutions:
A hot continuous AISI 304 stainless steel sheet is being conveyed at a constant
speed of 1 cm/s into a chamber to be cooled. The stainless steel sheet is 5 mm thick
and 2 m wide, and it enters and exits the chamber at 500 K and 300 K, respectively.
Determine the rate of heat loss from the stainless steel sheet inside the chamber.
Given: ss sheet 5 mm thick and 2 m wide
Tin = 500 K and Tout = 300 K
V = 1 cm/s
To be found: The rate of heat loss from a stainless steel sheet being conveyed
Missing information: mass of the object
Example 2: Cooling of Stainless Steel Sheets
The First law of Thermodynamics

17. 17
Assumptions: 1 Steady operating conditions exist.
2 The density of stainless steel sheet is constant.
3 Changes in potential and kinetic energy are negligible.
The mass of the stainless steel sheet being conveyed enters and exits the
chamber at a rate of:
Example 2: Cooling of Stainless Steel Sheets
The First law of Thermodynamics
m = rV×width × thickness
= (7900 kg/m3)(0.01 m/s)(2 m)(0.005 m)
= 0.79 kg/s
The rate of heat removed from the stainless steel sheet in the chamber:
Q = m×cp × (Tin – Tout)
= (0.79 kg/s)(515 J/kg·K)(500 - 300)K
= 81.4 kW #answer

18. 18
2 major observation:
▪ The real world is in disorder (entropy, s = Q/T)
▪ Certain processes are spontaneousand irreversible.
The Second law of Thermodynamics
Observe the spontaneous processes:
Processes occur in a certain
direction, and not in the
reverse direction.
A process must satisfyboth
the first and second laws of
thermodynamics to proceed.

19. 19
“No process is possible whose sole result is the transfer of heat from
a cooler to a hotter body.”
Clausius’s statement of the second 2nd law
Heat transfer is always in the direction of:
Hot to cold
High Temperature to Low Temperature.
The Second law of Thermodynamics
Statement of the Second Law of Thermodynamics
30oC 70oC
Q

20. 20
“It is impossible to construct a device which operates on a cycle and
produces no other effect than the production of work and the
transfer of heat from a single body”.
Kelvin-Planck Statement of the second 2nd law
The Second law of Thermodynamics
Statement of the Second Law of Thermodynamics
Heat
Engine
TH
W Heat
Pump
TH
TC

21. Determine the direction of heat transfer in the figures below:
The Second law of Thermodynamics
21

22. Increasing
Temperature
Increasing
Enthalpy
The Temperature-Entropydiagram
The Second law of Thermodynamics
Fluid Properties
22
Increasing Entropy

23. 23
The properties table for saturated fluid x
The Second law of Thermodynamics
Fluid Properties

24. 24
The properties table for superheated fluid x
The Second law of Thermodynamics
Fluid Properties

25. 25
Solutions:
Fluid x at 0.15 kg/s, 35oC, 0.5 bar is to be heated to 65oC by saturated steam at 1 bar.
Determine the flowrate of steam required for the heating process at steady-state.
Given: mc = 0.15 kg/s
Pc = 0.5 bar
Tc,i = 35oC and Tc,f = 65oC
Ph = 1 bar
To be found: The flow rate of saturated steam, mh.
Example 3: Steam Heating
The Second law of Thermodynamics

26. 26
For the cold stream at Pc = 0.5 bar
at Tc,i = 35oC , hc,i = 146.8 kJ/kg …(by interpolation)
and at Tc,f = 65oC, hc,f = 271.7 kJ/kg …(by interpolation)
Then Qc = 18.7 kW.
For the hot stream at Ph = 1 bar, hfg = 2258 kJ/kg
From energy balance, Qh = Qc = 18.7 kW,
Then mh = 28.7 kg/h.
Example 3: Steam Heating
The Second law of Thermodynamics
#answer

27. Summary
27
▪ Thermodynamics and Heat Transfer
▪ The First Law of Thermodynamics
▪ The Second Law of Thermodynamics