ME6502 Heat and Mass Transfer university questions

This post covers the unit wise 2 marks questions with answers of Unit 2 Convection, 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.

Click: Unit I Conduction 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

                Unit II    Convection

Part- A (2 Marks with Answers)

1. What is meant by free or natural convection? Give examples.

      If the fluid motion is produced due to change in density resulting from temperature gradients, the mode of heat transfer is said to be free or natural convection.

Ex: (i) Ice Melting

(Heat move to the ice from air-This causes the melting from a solid to liquid)

      (ii) Steaming cup of hot tea

(The steam is showing heat being transferred in the air)

2. What is forced convection? Give examples.

     

     If the fluid motion is artificially created by means of an external force like a blower or fan, that type of heat transfer is known as forced convection.

Ex: Steam turbines, Air conditioning, Heat exchangers, Car radiator using fluid

3. What are the dimensionless parameters used in forced convection.

      (i) Reynolds number (Re)

      (ii) Nusselt number (Nu)

      (iii) Prandtl number (Pr)

4. What are the dimensionless parameters used in free convection.

      (i) Grashof number (Gr)

      (ii) Nusselt number (Nu)

      (iii) Prandtl number (Pr)

5. Indicate the concept or significance of boundary layer.

      (i) A thin region near the body called the boundary layer where the velocity and the temperature gradients are large.

      (ii) The region outside the boundary layer where the velocity and the temperature gradients are very nearly equal to their free stream values.

Click: Unit I Conduction 2 Marks with Answers

6. Define critical Reynolds number. What is the typical value for flow over a flat plate and flow through a pipe?

      The Reynolds number at which flow changes from laminar to turbulent is called critical Reynolds number.

      For plate, it is 5 * 10⁵

      For Pipe it is 2300.

7. What is hydrodynamic and thermal boundary layer?

      The velocity of the fluid is less than 99% of free stream velocity, it is said to be “hydro dynamic boundary layer”.

      The temperature of the fluid is less than 99% of free stream temperature, it is said to be “thermal boundary layer”.

8. Define Reynolds number & Prandtl number.

       

     Reynolds number (Re) is defined as the ratio of inertia force to the viscous force.

      Prandtl number (Pr) is defined as the ratio of the momentum diffusivity to the thermal diffusivity.

9. Define Nussselt number & Groshof number.

Nusselt number (Nu) is defined as the ration of the heat flow by convection process under an unit temperature gradient to the heat flow rate by conduction under an unit temperature gradient through a stationary thickness (L) of mater.

Groshof number (Gr) is defined as the ratio of product of inertia force and buyoncy force to the square of the viscous force.

10. How does laminar flow differ from turbulent flow?

      Laminar flow

Laminar flow sometimes called stream line flow.

      In this type of flow, the fluid moves in a layers and each fluid particle follows a smooth continuous path.

      The fluid particles in each layer remain in orderly sequence without mixing with each other.

Turbulent flow

      In addition to the laminar type of flow a distinct irregular flow is frequently observed in nature.

      This type of flow is called turbulent flow.

     The path of any individual particle is zig-zag and irregular.

     

Click: Unit I Conduction 2 Marks with Answers

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

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

ME6301 Engineering Thermodynamics 2 marks with answers

This post covers the repeated 2 marks questions asking from the Anna University for the subject, ME6301 Engineering Thermodynamics. Here unit wise repeated 2 marks with answers given for the benefits of Mechanical Engineering students.

 Click here Previous Anna University questions May 2014

Click here Previous Anna University questions Dec 2014

Clich here Previous Anna University questions May 2015

Click here Anna University questions Nov/Dec 2012

ME6301-Engineering Thermodynamics

Unit I BASIC CONCEPTS AND FIRST LAW

Part-A (2 Marks with Answers)

1. What is meant by thermodynamic system? How do you classify it?

(AU Dec' 12)

It is defined as any space or matter or group of matter where the energy transfer or energy conversions are studied. It is classified into 3 types as follows

(i)              Open System

(ii)           Closed system

(iii)        Isolated System

2. Distinguish open system and closed systems. (AU Dec' 10)

S.No	Open system	Closed system
1	Mass transfer takes place	There is no mass transfer
2	In addition to the heat and work transfer	Only heat and work will transfer
3	System boundary may or may not change.	System boundary is fixed one
4	Ex: wind mill, Air Compressor, Boiler	Ex: Mixture of ice and water in a metal container, Piston and cylinder arrangement, Thermal Power plant

3. Define an Isolated system. (AU May' 12)

          In this system, total energy remains constant. There is no heat, work and mass transfer takes place. Isolated system is not affected by surroundings.

Ex: Entire Universe

4. Define specific capacity at constant volume. (AU Dec' 09)

          It is defined as the amount of heat energy required raising or lowering the temperature of unit mass of the substance through one degree when the volume kept constant. It is denoted by C_v.

5. Define specific capacity at constant pressure. (AU Dec' 11)

          It is defined as the amount of heat energy required raising or lowering the temperature of unit mass of the substance through one degree when the pressure kept constant. It is denoted by C_p.

6. Define intensive and extensive properties. (AU Dec' 12)

Intensive properties:

The properties which are independent of the mass of the system are called intensive properties.

Ex: Pressure, Temperature, Specific volume etc.,

Extensive properties:

The properties which are dependent of the mass of the system are called extensive properties.

Ex: Total energy, total volume, weight etc.,

7. What do you understand by equilibrium of a system?(AU Dec' 13)

          When a system remains in equilibrium state, it should not undergo any changes on its own accord.

8. When a system is said to be in “Thermodynamic equilibrium”? 

(AU May' 12)

          When a system is in thermodynamic equilibrium, it should satisfy the following three conditions.

(i)                          Mechanical Equilibrium- Pressure remains constant

(ii)                       Thermal Equilibrium- Temperature remains constant

(iii)                    Chemical Equilibrium- There is no chemical reaction

9. State zeroth law of thermodynamics. (AU Dec' 14)

          It states that when two systems are separately in thermal equilibrium with a third system, then they themselves is in thermal equilibrium with each other.

10. State first law of thermodynamics. (AU Dec' 12)

          It states that “when a system undergoes a cyclic process, then the net heat transfer is equal to the net work transfer”.

          It may be stated, “The heat and work are mutually convertible”.

 Click here Previous Anna University questions May 2014

Click here Previous Anna University questions Dec 2014

Clich here Previous Anna University questions May 2015

Click here Anna University questions Nov/Dec 2012

11. Compare microscopic and macroscopic approaches. (AU May' 13)

S.No	Microscopic Approach	Macroscopic Approach
1.	Many coordinates are required to describe the system properly.	A few coordinates are enough to describe the system properly.
2.	The properties of matter of the individual molecule at a given instant or at a particular time are studied.	The behavior of the total system in terms of properties is studied.
3.	Special assumptions are required for describing the matter in microscopic coordinates.	No need of Special assumptions is required for describing the matter in macroscopic coordinates.
4.	More complex mathematical equations are used for the analysis.	It requires far fewer mathematical complications.

12. List the limitations of first law of thermodynamics. (AU Nov' 12)

(i) It does not specify the direction of flow of heat and work.

(ii) The heat and work are mutually convertible. The work can be converted fully into heat energy but heat cannot be converted fully into mechanical work.

(iii)   Perpetual Motion Machine (PMM-1) is a machine which delivers work continuously without any input. Thus, the machine violates first law of thermodynamics.

13. What is meant by reversible and irreversible process? (AU Dec' 13)

                    A process is said to be reversible, it should trace the same path in the reverse direction when the process is reversed, and it is possible only when the system passes through a continuous series of equilibrium state.

          If a system does not pass through continuous equilibrium state, then the process is said to be irreversible.

14. Differentiate Path function and Point function. (AU June' 14)

S.No	Path function	Point function
1.	The quantity which is dependent on the process or path followed by the system	The quantity which is independent on the process or path followed by the system
2.	Ex: Heat transfer, Work transfer	Ex: Pressure, Volume, Temperature
3.	It considers the direction of processes.	It does not considers the direction of processes.
4.	The cyclic integral of a path function is non zero.	The cyclic integral of a point function is zero.

15. What is Quasi-static process? (AU Nov' 12, AU May '14)

           The process is said to be quasi-static, if it proceeds infinitesimally slow and follows continuous series of equilibrium states. Therefore, it may b a reversible process.

  

16. Define the term enthalpy. (AU Dec' 11)

          The combination of internal energy and flow energy is known as enthalpy of the system

Mathematically, Enthalpy (H)=U + pV

Where U be the internal energy in kJ

              P be the pressure in kPa

              V be the volume in m³             

17. What are the conditions for steady flow process? (AU May' 13)

          (i) The streams of material crossing the control surface must not change their state or flow rate with time.

          (ii) Each point within the control volume must not change its state with time or only cyclic state variation occurs.

(iii)The heat and work transfer rates must not change with time or the mean rates in this case of cyclic behavior must not change.

18. Identify any four reasons for irreversibility in a process. (AU April' 12)

          (i) Lack of equilibrium

          (ii) Free expansion

          (iii) Heat transfer through a finite temperature difference.

          (iv)  Dissipative effects

          (v) Lack of pressure equilibrium within the interior of the system.

Click here Previous Anna University questions May 2014

Click here Previous Anna University questions Dec 2014

Clich here Previous Anna University questions May 2015

For more question bank with answers, Lecture notes, Previous years Anna University questions were uploaded in annaunivstudymaterials.blogspot.com