Introduction

1. Dr. Vishal Patil
Associate Professor
Department of Mechanical Engineering
1
Sharad Institute of Technology, College of
Engineering, Yadrav- Ichalkarnji
Department of Mechanical Engineering
Lecture 0:
Fundamental Concepts and Definitions
Heat Transfer

2. 2
Content
1. Heat transfer
2. Objectives of heat transfer
3. Applications of heat transfer
4. Conduction
5. Applications of conduction
6. Radiation Wave theory or classical theory
7. Radiation Quantum Theory or Planck's Theory
8. Characteristics of radiation
9. Convection
10. Newton's law of cooling

3. 3
1. Heat Transfer
The Heat transfer deals with the study of different ways (modes) and
estimation of the rates of such energy in transit
Modes of Heat transfer:
1.Conduction
2. Radiation
3. Convention
Ref: https://earthhow.com/solar-radiation-electromagnetic/

4. 4
2. Objectives of Heat Transfer
1. Quantifies the rate at which a system gains/looses thermal energy
2. Identifies the mode by which the energy is transported
3. Predicts the temperature distribution throughout a body
4. Develops the methods to accelerate or retard the rate of heat flow as per
requirement.
5. Provides the analysis of various heat transfer equipment such as heat
exchangers, evaporators, condensers etc.

5. 5
3. Applications Heat transfer
1. The sciences like metabolism, Human comfort etc. primarily deals with heat
transfer
2. Cooling of sensitive electronic components in computers, the rockets used for
launching satellites, HVAC systems, microwaves, underground water pipes etc.
are several areas where heat transfer must be addressed
3. Houses and buildings using air conditioning systems. The heating and chilling
chamber required in food processing units.
4. The process like evaporation, distillation, crystallization etc.
5. Cylinder of I. C. engine must be cooled for proper functioning.
6. Melting of metals and plastics for melting process.
7. Equipments those generate steam (like boilers) and the devices which utilize the
steam to perform work use almost all the theorems deducted in this subject.

6. 6
4. Conduction
Conduction is the mode of heat transfer in which the flow of energy through
a substance take place with out any appreciable movement of an individual
molecule.
Mechanism modes:
1. Lattice Vibrations
2. Flow of Free Electrons
Ref: http://ecoursesonline.iasri.res.in/mod/page/view.php?id=2339

7. 7
5. Applications of Conduction
1. In boiler the heat flow from the flue gases to the water, takes places
across the tubes by conduction.
2. In cooling of IC engine, the flow from the combustion gases to the
atmospheric air or the cooling water, take place across the cylinder walls
by conduction
3. When steam flows through a pipeline then the energy loss from the
steam to the atmospheric air across the pipe wall, by condition
4. Flow of energy from the cold chamber into the liquid refrigerant flowing
through evaporator tubes take place by conduction
5. The heat loss from the furnace to the atmospheric air across the
insulated furnace wall takes place by conduction

8. 8
6. Radiation
Every surface continuously emits energy in all possible directions. This way of
flow of energy in the form of electromagnetic emissions is know as radiation.
Wave theory or classical theory

9. 9
7. Radiation
Quantum Theory or Planck's Theory
This theory is developed by Max Plank. It states that the emissions are in the
form of series of particles known as Quanta or Photons. Hence radiations are
also termed as Photon gas flow. Each quanta possess certain amount of
energy which is proportional to the frequency of emission. The energy
content per quanta is given by,
e = h × v
Where,
e- Energy content by each quanta
v- Frequency of emission
h- Plank’s constant = 6.6261 × 10-34 [J-Sec]

10. 10
8. Characteristics of Radiation
1. All objects at all temperature emit radiation.
2. The distinction between one form of radiation from another lies only in its frequency and
wavelength which is related by, C (Speed of light) = λ ( Wave length) × f (frequency)
3. A body at a higher temperature emits more radiation of higher frequency. Higher the frequency,
more is the amount of energy possessed. Hence, a body at a higher temperature emits radiation at a
greater rate than a body at a lower temperature.
4. Conduction is a mode of heat transfer through substance. Hence, we can say that medium is
essential for this mode. On the contrary, medium is not required for the flow energy by radiation. It
is observed that, in space the rate of radiation increases.
5. In conduction, the heat flow take place from the high temperature to the low temperature, While
in radiation, the heat flow continually takes place in both directions. A body radiating heat,
simultaneously receives heat from other bodies as incident radiation.
6. Conduction mode of heat of heat transfer primarily depends on the temperature gradient (δT/ δx),
while the convection mode of heat transfer primarily depends on the temperature difference (ΔT).
7. In conduction mode, the intermediate temperatures with in the system are decided by the surface
temperature and thermal conductivity of material.

11. 11
9. Convection
The process of heat transfer between the surface and surrounding fluid is known as
convection. In this process, the flow of energy is primarily due to the movement of
fluid molecules.
Convection
Single Phase System Two Phase System
Forced Convection Natural Convection Condensation Boiling

12. 12
10. Newton's Law of Cooling
Rate of heat flow in convection process can be estimated using Newton's
law of cooling.
q = h A (T –Tf)
Where-
h- Average heat transfer coefficient (W/m2 K)
A- Surface area (m2)
T- Average temperature of surface [°C]
Tf- Average temperature of surrounding fluid [°C]

13. 13
Reference: Heat transfer, Prof. D. S. Pavaskar and Prof. S. H. Choudhari (Text book), Nishant Prakashan, Pune
This video is prepared for academic use only.