# UNSTEADY STATE HEAT CONDUCTION MULTIPLE CHOICE QUESTIONS (MCQ) WITH ANSWERS

## (MCQ) WITH ANSWERS

### to 100 and Bi →infinity. ##### Fig. Temperature variation during heating & cooling during unsteady state heat conduction
1. During unsteady state heat conduction

(a) Firstly Temperature gradient is equal to zero

(b) Secondly Temperature difference is equal to zero

(c) Rate of temperature change is not equal to zero

(d) None

(Ans: c)

### 2. Newtonian heating/cooling of solids refers to

(a) Firstly Biot number > 0.1

(b) Secondly Biot number =0.1

(c) Thirdly Biot number < 0.1

(d) None

(Ans: c)

### 3. Biot number deals with

(a) Firstly       Steady state of heat transfer

(b) Secondly  Unsteady state of heat transfer

(c) Thirdly      Steady & unsteady rate of heat transfer

(d) None

(Ans: b)

### 4. Biot number

(a)  Firstly      Linearly varies with Time

(b)Secondly   Linearly varies with conductivity k

(c) Varies inversely with k

(d) None

(Ans: c)

### 5. Transient heat conduction depends upon

1. Firstly       Time and space
2.  Secondly  Temperature & time
3. Thirdly       Time, temperature & space
4. None

ANS: (a)

### 6.  Unsteady state heat conduction has temperature variations as

1. Firstly        Periodic
2. Secondly   Non-periodic
3. Thirdly       Periodic & non-periodic
4. None

ANS: (c )

### 7. Periodic temperature variation in unsteady heat conduction is after

1.  Firstly Fixed time interval
2.  Secondly Any time interval
3. Thirdly All time intervals
4. None

ANS: (a)

### 8. Temperature wave in transient heat conduction depends upon

1. Piston angle
2. Crank angle
3. Both piston & crank angle
4. None

ANS: (b)

### 9. Non-Periodic temperature variation in unsteady state conduction is

1. Firstly After a fixed time interval
2. Secondly After any time interval
3. Can’t say
4. None

ANS: (b)

### 10. Temperature variation in transient heat conduction in solids of infinite conductivity depends upon

1. Firstly          Time
2. Secondly     Space
3.  Thirdly        Time & space
4. None

ANS: (a)

### 11. Temperature varies in transient heat conduction in solids of infinite conductivity

1. Firstly           Linear
2. Secondly     Parabolic
3. Thirdly        Linear & parabolic
4. None

### 12.Thermal time constant in unsteady heat conduction is

(a)Firstly           ρV/h A

(b)Secondly       ρV/Cp h A

(c )Thirdly           ρVCp/h A

(d) None

ANS: (c )

### 13. Characteristic length of a solid is

1. Firstly          Surface area/volume
2. Secondly      Surface area/volume2
3. Volume/surface area
4. None

### 14. Fourier number signifies degree of penetration of

1. Firstly            Heating effect
2. Secondly      Cooling effect
3. Thirdly          Heating or cooling effect
4. None

ANS: (c )

### 15. Fourier number is

1. Firstly          α/τl2
2. Secondly      ατ/l2
3. Thirdly          αl2
4. None

ANS: (b)

### 16. Biot number is

1. Firstly         h k/l
2. Secondly    kl/h
3. Thirdly        hl/k
4. None

ANS: (c )

### 17. Lumped parameter analysis considers no

(a) Firstly           Internal resistance

(b)  Secondly    External resistance

(c ) Thirdly          Internal & external resistances

(d) None

ANS: (a)

### 18. Lumped parameter analysis is applicable with Biot number as

1. Firstly           > 0.1
2. Secondly      < 0.1
3. Thirdly          > 0.1 & < 0.1
4. None

ANS: (b)

### 19. Characteristic length for a spherical body is equal to

1. Firstly          R
2. Secondly     R/2
3. Thirdly         R/3
4. None

ANS: (c )

### 20. Characteristic length for a cylindrical body is

1. Firstly R
2. Secondly R/2
3. Thirdly R/3
4. None

ANS: (b)

### 21. Characteristic length of a cube is equal to

1. Firstly l/2
2. Secondly L/3
3. Thirdly L/6
4. None

ANS: (c )

### 22. Instantaneous rate of heat transfer when Bi <0.1 is

1. Firstly      Qi =-h A(ti-ta) exp(-hAτ/ρVCp)
2. Secondly Qi =-h A(ti-ta) exp(-hAτ/ρV)
3. Thirdly     Qi =-h A(ti-ta) exp(-hAτ/V Cp)
4. None

### 23. Total rate of heat transfer when Bi <0.1

1. Firstly Q t =ρVCp(ti-ta) exp[(-hAτ/ρVCp)-2]
2. Secondly Q t= ρVCp (ti-ta) exp[(-hAτ/ρVCp)-1]
3. Thirdly Q t = ρVCp(ti-ta) exp[(-hAτ/ρVCp)-3]
4. None

ANS: (b)

### 24. Response of a thermocouple is fast when

(a) large value of h A/ρVCp

(b) Small value of h A/ρVCp

(c) Both large & small values of  h A/ρVCp

(d) None

ANS: (a)

### 25. Time constant of a thermocouple is to be

(a) Firstly          Fast

(b) Secondly     Slow

(c) Thirdly         Fast & slow

(d) None

ANS: (a)

### 26. Time constant of a thermocouple represents

(a) Two times the speed of response

(b) Three times the speed of response

(c) Speed of response

(d) None

ANS: (c )

27. Response time of thermocouples is between

(a) Firstly 0.04 to 1.5 second

(b) Secondly 0.04 to 3.5 seconds

(c) Thirdly 0.04 to 2.5 seconds

(d) None

ANS: (c )

### 28. One dimensional equation of transient heat conduction is

(a) Firstly d2t/dx2 = α dt/dτ

(b) Secondly d2t/dx2 = α2 dt/dτ

(c) Thirdly d2t/dx2 = (1/α) dt/dτ

(d) None

ANS: (c )

### 29. Unsteady state conduction with Biot number between 0.01 and 100 uses

1. Firstly          Gaussian Error function
2. Secondly      Heisler Charts
3. Thirdly         Gaussian Error function & Heisler charts
4. None

ANS: (b)

### 30. Unsteady state heat conduction in solids having Biot tending to infinity uses

(a) Gaussian Error function

(b) Heisler Charts

(c ) Both Gaussian Error function & Heisler charts

(d) None

ANS: (a)