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

**UNSTEADY STATE HEAT CONDUCTION**

**MULTIPLE CHOICE QUESTIONS **

**(MCQ) WITH ANSWERS **

### MCQ makes a topic very clear. It

### increases the depth of understanding. It

### is easy to apply it in real life applications.

### Unsteady state heat conduction exist

### everywhere. It is exponential time

### dependent. Newtonian cooling / heating

### is unsteady state heat conduction. There

### are three possibilities with unsteady state

### heat conduction. These are Bi <0.1, Bi=1

### to 100 and Bi →infinity.

**Fig. Temperature variation during heating & cooling during unsteady state heat conduction**

**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

- Firstly Time and space
- Secondly Temperature & time
- Thirdly Time, temperature & space
- None

ANS: (a)

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

- Firstly Periodic
- Secondly Non-periodic
- Thirdly Periodic & non-periodic
- None

ANS: (c )

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

- Firstly Fixed time interval
- Secondly Any time interval
- Thirdly All time intervals
- None

ANS: (a)

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

- Piston angle
- Crank angle
- Both piston & crank angle
- None

ANS: (b)

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

- Firstly After a fixed time interval
- Secondly After any time interval
- Can’t say
- None

ANS: (b)

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

- Firstly Time
- Secondly Space
- Thirdly Time & space
- None

ANS: (a)

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

- Firstly Linear
- Secondly Parabolic
- Thirdly Linear & parabolic
- None

### ANS: (d)

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

(a)Firstly ρV/h A

(b)Secondly ρV/C_{p }h A

(c )Thirdly ρVCp/h A

(d) None

ANS: (c )

### 13. Characteristic length of a solid is

- Firstly Surface area/volume
- Secondly Surface area/volume
^{2} - Volume/surface area
- None

### ANS: (c )

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

- Firstly Heating effect
- Secondly Cooling effect
- Thirdly Heating or cooling effect
- None

ANS: (c )

### 15. Fourier number is

- Firstly α/τl
^{2} - Secondly ατ/l
^{2} - Thirdly αl
^{2}/τ - None

ANS: (b)

### 16. Biot number is

- Firstly h k/l
- Secondly kl/h
- Thirdly hl/k
- 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

- Firstly > 0.1
- Secondly < 0.1
- Thirdly > 0.1 & < 0.1
- None

ANS: (b)

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

- Firstly R
- Secondly R/2
- Thirdly R/3
- None

ANS: (c )

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

- Firstly R
- Secondly R/2
- Thirdly R/3
- None

ANS: (b)

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

- Firstly l/2
- Secondly L/3
- Thirdly L/6
- None

ANS: (c )

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

- Firstly Q
_{i}=-h A(t_{i}-t_{a}) exp(-hAτ/ρVC_{p}) - Secondly Q
_{i}=-h A(t_{i}-t_{a}) exp(-hAτ/ρV) - Thirdly Q
_{i}=-h A(ti-ta) exp(-hAτ/V C_{p}) - None

### ANS: (a)

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

- Firstly Q
_{t}=ρVC_{p}(t_{i}-t_{a}) exp[(-hAτ/ρVC_{p})-2] - Secondly Q
_{t}= ρVC_{p}(t_{i}-t_{a}) exp[(-hAτ/ρVC_{p})-1] - Thirdly Q
_{t}= ρVC_{p}(t_{i}-t_{a}) exp[(-hAτ/ρVC_{p})-3] - None

ANS: (b)

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

(a) large value of h A/ρVC_{p}

(b) Small value of h A/ρVC_{p}

(c) Both large & small values of h A/ρVC_{p}

(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 d^{2}t/dx^{2} = α dt/dτ

(b) Secondly d^{2}t/dx^{2} = α^{2} dt/dτ

(c) Thirdly d^{2}t/dx^{2} = (1/α) dt/dτ

(d) None

ANS: (c )

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

- Firstly Gaussian Error function
- Secondly Heisler Charts
- Thirdly Gaussian Error function & Heisler charts
- 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)

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