ME6502 Heat and Mass Transfer question bank

This post covers the unit wise 2 marks questions with answers repeatedly asking from Anna University, Chennai, for the subject ME6502- Heat and Mass Transfer which is the one of the important subjects of Mechanical Engineering students whom were studying V semester.

                    Unit I    Conduction

            Part- A (2 Marks with Answers)

Click :Unit II Convection 2 Marks with Answers

Click:Unit III Phase change Heat Transfer and Heat exchangers 2 Marks with Answers   

Click: Unit IV Radiation 2 Marks with Answers

Click: Unit V Mass Transfer 2 Marks with Answers

1. State Fourier’s Law of Heat Conduction.

       The rate of heat conduction is proportional to the area measured normal to the direction of heat flow and to the temperature gradient in that direction.

Q α –A (dT/dx)

Q= -KA (dT/dx)

Where A-Area in m²

   (dT/dx)-Temperature gradient in K/m

             k- Thermal conductivity in W/mK

2. Define thermal conductivity and list out the factors affecting the thermal conductivity.

Thermal Conductivity:

       It is defined as the ability of a substance to conduct the heat.

Factors affecting the thermal conductivity:

(i) Moisture

(ii) Density of material

(iii) Pressure

(iv)Temperature

(v) Structure of material

3. State Newton’s law of cooling or State Newton’s law of convection.

       Heat transfer by convection is given by Newton’s law of cooling

                           Q= hA (T_s-T_∞ )

Where A-Area exposed to heat transfer in m²

            h- Heat transfer coefficient in W/m²K

            T_s - Temperature of the surface in K

            T_∞ - Temperature of the fluid in K

4. Define Overall heat transfer coefficient.

       The overall heat transfer by combined mode is usually expressed in terms of an overall conductance or overall heat transfer coefficient “U”

                           Q = UA ΔT

Q- Heat transfer in Watts

U- Overall heat transfer coefficient in W/m²K

ΔT – Temperature difference in K

5. What are the modes of heat transfer?

(i) Conduction

Heat transfer within the same medium (Solid to Solid)

Ex: Heating a steel rod

(ii) Convection

Heat transfer from one medium to another medium (Solid to liquid)

Ex: Heating of a pan which is full of water

(iii) Radiation

Heat transfer from one medium to another without any transmitting medium.

Ex: Sun light direct to the earth

6. What is critical radius of insulation or critical thickness?

Addition of insulating material on a surface does not reduce the amount of heat transfer rate always.

Infact under certain circumstances it actually increases the heat loss up to certain thickness of insulation.

“The radius of insulation for which the heat transfer is maximum is called critical radius of insulation” and the corresponding thickness is called “critical thickness”.

7. Define fins or extended surfaces.

       It is impossible to increase the heat transfer rate by increasing the surface of heat transfer.

       The surfaces used for increasing heat transfer are called “Extended surfaces” or sometimes known as “fins”.

8. State the applications of fins.

       (i) Cooling of electronic components

       (ii) Cooling of motor cycle engines

       (iii) Cooling of transformers

       (iv) Cooling of small capacity compressors

9. Define fin efficiency and fin effectiveness.

Fin efficiency:

It is the ratio of actual heat transferred to the maximum possible heat transferred by the fin.

              Ŋ _fin = Q_{fin /} Q _max

Fin effectiveness:

It is the ratio of heat transfer with fin to the heat transfer without fin.

                           € _fin = Q_{with fin /} Q_{without fin}

10. Differentiate steady state and unsteady (Transient) heat conduction.

Steady state heat conduction:

       If the temperature of a body does not vary with time, it is said to be in a steady state and that type of conduction is known as “steady state heat conduction”.

Unsteady state heat conduction:

       If the temperature of a body varies with time, it is said to be in a Unsteady state and that type of conduction is known as “Unsteady state heat conduction or transient heat conduction”.

11. What is meant by lumped heat analysis?

       In a Newtonian heating or cooling process the temperature throughout the solid is considered to be uniform at a given time.

       Such an analysis is called “Lumped heat analysis”.

              Here Bi always less than 1. (Bi < 1)

Click :Unit II Convection 2 Marks with Answers

12. What is meant by semi- infinite solid?

       In a semi infinite solid, at any instant of time, there is always a point where the effect of heating or cooling at one of its boundaries is not felt at all.

       At this point the temperature remains unchanged.

       The biot number value is ∞

12. What is meant by infinite solid?

       A solid which extends itself infinitely in all directions of space is known as infinite solid.

       Here the biot number value is in between 0.1 and 100.

 i.e, 0.1 < Bi < 100

13. Define Biot number and mention its significance.

       It is defined as the ratio of the internal conductive resistance to the surface convective resistance.

       

               

                              Bi = hL_c / K

Significance:

       It is used to find Lumped heat analysis, Semi infinite solids and infinite solids.

14. What are Heisler chart.

       In Heisler chart, the solutions for the temperature distributions and heat flows in a plane walls, long cylinders and spheres with finite internal and surface resistance are presented.

       It is the analytical solutions in the form of graphs.

      

Click: DME Unit 1 Question Bank

Click : DME Unit 2 Question Bank
Click: DME Unit 3 Question bank
Click: DME Unit 4 Question Bank
Click: DME Unit 5 Question Bank

Click :Unit II Convection 2 Marks with Answers

Click: Unit III Phase change heat transfer and heat exchangers 2 Marks with Answers