# Heat Transfer Test Questions - Set 7

1)   What is effectiveness of fin?

a. the ratio of actual heat transferred from fin area to the heat which would be transferred if entire fin area was at base temperature
b. the heat which would be transferred if entire fin area was at base temperature to the ratio of actual heat transferred from fin area
c. the heat which would be transferred if entire fin area was at minimum temperature to the ratio of actual heat transferred from fin area
d. the ratio of actual heat transferred from fin area to the heat which would be transferred if entire fin area was at minimum temperature
 Answer  Explanation  Related Ques ANSWER: the ratio of actual heat transferred from fin area to the heat which would be transferred if entire fin area was at base temperature Explanation: No explanation is available for this question!

2)   What is the effect of thermal conductivity k on fin effectiveness?

a. fin is effective for smaller value of thermal conductivity k
b. fin is effective for larger value of thermal conductivity k
c. thermal conductivity k does not affect the fin effectiveness
d. cannot say
 Answer  Explanation  Related Ques ANSWER: fin is effective for larger value of thermal conductivity k Explanation: No explanation is available for this question!

3)   What is the effect of convective heat transfer coefficient h on fin effectiveness?

a. fin is effective if the value of convective heat transfer coefficient h is small
b. fin is effective if the value of convective heat transfer coefficient h is large
c. fin effectiveness does not affected by the value of convective heat transfer coefficient h
d. none of the above
 Answer  Explanation  Related Ques ANSWER: fin is effective if the value of convective heat transfer coefficient h is small Explanation: No explanation is available for this question!

4)   Which medium of surrounding is better for fin effectiveness?

a. gas medium
b. liquid medium
c. fins have same effectiveness in both the gas and liquid mediums
d. none of the above
 Answer  Explanation  Related Ques ANSWER: gas medium Explanation: No explanation is available for this question!

5)   For effective working of fins, the thickness of the fines should be

a. large
b. small
c. thickness of fin does not affect the fin effectiveness
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: small Explanation: No explanation is available for this question!

6)   A fin of uniform cross-section A and perimeter P has a base temperature Ts and it is exposed to fluid having temperature T How is the temperature distribution in the fin given?

Where,
m = √(hP/kA)
h = convective heat transfer coefficient
k = thermal conductivity of fin
T = Temperature of the fin at the distance x from the base of fine
and the constants C1 and C2 depend on the boundary conditions

a. T – T = C1emx – C2e– mx
b. T – T = C1emx + C2e– mx
c. T + T = C1emx – C2e– mx
d. T + T = C1emx + C2e– mx
 Answer  Explanation  Related Ques ANSWER: T – T∞ = C1emx + C2e– mx Explanation: No explanation is available for this question!

7)   What is the correct formula for the temperature distribution in infinitely long fin?
Where,
m = √(hP/kA)
h = convective heat transfer coefficient
P = perimeter of the fin
k = thermal conductivity of fin
A = cross-sectional area of the fin
T = Temperature of the fin at the distance x from the base of fine
and the constants C1 and C2 depend on the boundary conditions
Ts = Base temperature of the fin
T = Temperature of surrounding fluid

a. (Ts – T) / (T – T) = C2emx
b. (Ts – T) / (T – T) = C2e– mx
c. (T – T) / (Ts – T) = C2emx
d. (T – T) / (Ts – T) = C2e– mx
 Answer  Explanation  Related Ques ANSWER: (T – T∞) / (Ts – T∞) = C2e– mx Explanation: No explanation is available for this question!

8)   How is the rate of heat transfer from the fin given?
h = convective heat transfer coefficient
P = perimeter of the fin
k = thermal conductivity of fin
A = cross-sectional area of the fin
Ts= Base temperature of the fin
T = Temperature of surrounding fluid

a. q = h P k A (Ts – T)
b. q = √(h P k A (Ts – T))
c. q = √(hPkA) (Ts – T)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: q = √(hPkA) (Ts – T∞) Explanation: No explanation is available for this question!

9)   The parameters of a fin are given below.Diameter of the fin d = 2 cm
Thermal conductivity k = 200 W/mK
Convective heat transfer coefficient h = 12 W/m2K
Base temperature of the fin Ts =  500 0C
The air temperature
T8 =  50 0C

Calculate the rate of heat transfer from the fin.

a. 119.7 W
b. 97.93 W
c. 57.7 W
d. 4.62 W
 Answer  Explanation  Related Ques ANSWER: 97.93 W Explanation: No explanation is available for this question!

10)   Aluminum is used as a fin material because

a. it has higher convection heat transfer coefficient
b. it has higher thermal conductivity
c. it has lower convection heat transfer coefficient
d. it has lower thermal conductivity
 Answer  Explanation  Related Ques ANSWER: it has higher thermal conductivity Explanation: No explanation is available for this question!

11)   Which of the following arrangements of fins is more effective for the same base area?

1. Large number of closely spaced fins

2. Small number of thick fins

a. Arrangement 1
b. Arrangement 2
c. both the arrangements 1 and 2 are similarly effective
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: Arrangement 1 Explanation: No explanation is available for this question!

12)   Consider an element with finite dimensions. In general which among the following equations is correct for change in energy of element during a time span dt?

a. [Heat generated in the element during time dt] + [Heat flow into the element during time dt] + [Heat flow out of the element during time dt]
b. [Heat generated in the element during time dt] + [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]
c. [Heat generated in the element during time dt] – [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]
d. none of the above
 Answer  Explanation  Related Ques ANSWER: [Heat generated in the element during time dt] + [Heat flow into the element during time dt] – [Heat flow out of the element during time dt] Explanation: No explanation is available for this question!

13)   What is the general heat conduction equation which gives the temperature distribution and conduction heat flow in an isotropic solid?
Where,
= rate of heat generation
k = thermal conductivity
α = (k/ρc) thermal diffusivity
ρ = density of the element
c = specific heat of the element

a. (∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) = (∂T/∂t)
b. (∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) = (1/α)(∂T/∂t)
c. (∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) + (q̇/k) = (∂T/∂t)
d. (∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) + (q̇/k) = (1/α)(∂T/∂t)
 Answer  Explanation  Related Ques ANSWER: (∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) + (q̇/k) = (1/α)(∂T/∂t) Explanation: No explanation is available for this question!

14)   If the body or element does not produce heat, then the general heat conduction equation which gives the temperature distribution and conduction heat flow in an isotropic solid reduces to(∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) = (1/α)(∂T/∂t)this equation is known as

a. Laplace equation
b. Fourier equation
c. Poisson equation
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Fourier equation Explanation: No explanation is available for this question!

15)   If the body or element is in steady-state but has heat generation then the general heat conduction equation which gives the temperature distribution and conduction heat flow in an isotropic solid reduces to(∂T/∂x2) + (∂T/∂y2) + (∂T/∂z2) + (q̇/k) = 0. This equation is known as

a. Laplace equation
b. Fourier equation
c. Poisson equation
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Poisson equation Explanation: No explanation is available for this question!

16)   When does the general heat conduction equation which gives the temperature distribution and conduction heat flow in an isotropic solid reduce to Laplace equation?

a. if the body or element is in unsteady-state with heat generation
b. if the body or element is in steady-state with heat generation
c. if the body or element is in unsteady-state with no heat generation
d. if the body or element is in steady-state with no heat generation
 Answer  Explanation  Related Ques ANSWER: if the body or element is in steady-state with no heat generation Explanation: No explanation is available for this question!

17)   Generally the external thermal resistance between the surface of the body and the environment is

a. less than the internal conduction resistance in the body
b. more than the internal conduction resistance in the body
c. same as the internal conduction resistance in the body
d. none of the above
 Answer  Explanation  Related Ques ANSWER: more than the internal conduction resistance in the body Explanation: No explanation is available for this question!

18)   Suppose that a hot metal ball is immersed in cold water, then temperature distribution in the body depends upon

a. thermal conductivity of the body
b. convective heat transfer from the body surface to water
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

19)   Suppose that a hot metal ball is suddenly immersed in cold water. What is the condition for the ball to maintain it at a uniform temperature?

a. the conduction resistance in a ball should be very large compared to the convection resistance for heat transfer from surface of ball to water
b. the conduction resistance in a ball should be very small compared to the convection resistance for heat transfer from surface of ball to water
c. the conduction resistance in a ball should be equal to the convection resistance for heat transfer from surface of ball to water
d. cannot say
 Answer  Explanation  Related Ques ANSWER: the conduction resistance in a ball should be very small compared to the convection resistance for heat transfer from surface of ball to water Explanation: No explanation is available for this question!

20)   What is lumped heat capacity analysis?

a. the analysis of a system in which it is assumed to be at no uniform temperature
b. the analysis of a system in which it is assumed to be at uniform temperature
c. the analysis of a system in which it is assumed to be at either uniform or no uniform temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the analysis of a system in which it is assumed to be at uniform temperature Explanation: No explanation is available for this question!

21)   The Biot number or Biot modulus is given by

a. the ratio of external convection resistance to the internal conduction resistance
b. the ratio of internal conduction resistance to the external convection resistance
c. multiplying internal conduction resistance and external convection resistance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the ratio of internal conduction resistance to the external convection resistance Explanation: No explanation is available for this question!

22)   What is the correct formula for The Biot number?

a. hl/k
b. k/hl
c. l/hk
d. hk/l
 Answer  Explanation  Related Ques ANSWER: hl/k Explanation: No explanation is available for this question!

23)   What should be the Biot number to assume the body at uniform temperature?

a. the Biot number should be less than 0.1
b. the Biot number should be more than 0.1
c. the Biot number should be equal to 0.1
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the Biot number should be less than 0.1 Explanation: No explanation is available for this question!

24)   The cooling of a metal ball of volume V, in large quantity of fluid is analogous to

a. discharging of battery in an electric system
b. discharging of capacitor in an electric system
c. generation of heat in resistor in an electrical system
d. none of the above
 Answer  Explanation  Related Ques ANSWER: discharging of capacitor in an electric system Explanation: No explanation is available for this question!

25)   Which of the following condition is correct for natural convection?

a. (Gr / Re2) = 1
b. (Gr / Re2) << 1
c. (Gr / Re2) >> 1
d. none of the above
 Answer  Explanation  Related Ques ANSWER: (Gr / Re2) >> 1 Explanation: No explanation is available for this question!

26)   If there are no externally induced flow velocities, then the Nusselt number (Nu) does not depend upon

a. Prandtl number (Pr)
b. Reynolds number (Re)
c. Grashof number (Gr)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Reynolds number (Re) Explanation: No explanation is available for this question!

27)   The Grashof number in natural convection plays same role as

a. Prandtl number (Pr) in forced convection
b. Reynolds number (Re) in forced convection
c. Nusselt number (Nu) in forced convection
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Reynolds number (Re) in forced convection Explanation: No explanation is available for this question!

28)   When is the arithmetic mean temperature difference of heat exchanger used instead of LMTD?

a. when the temperature profiles of two fluids of heat exchanger are sloping downward with curve
b. when the temperature profiles of two fluids of heat exchanger are sloping upward with curve
c. when the temperature profiles of two fluids of heat exchanger are straight
d. none of the above
 Answer  Explanation  Related Ques ANSWER: when the temperature profiles of two fluids of heat exchanger are straight Explanation: No explanation is available for this question!

29)   How can the arithmetic mean temperature difference and LMTD of a same heat exchanger be compared?

a. the arithmetic mean temperature difference is less than LMTD of a same heat exchanger
b. the arithmetic mean temperature difference is more than LMTD of a same heat exchanger
c. the arithmetic mean temperature difference and LMTD of a same heat exchanger are equal
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the arithmetic mean temperature difference is more than LMTD of a same heat exchanger Explanation: No explanation is available for this question!

30)   Which of the following temperature difference is safer than other to consider in designing of heat exchangers?

a. Arithmetic Mean Temperature Difference (ΔTam)
b. Logarithmic Mean Temperature Difference (LMTD)
c. Both have nothing to do with safety
d. Other
 Answer  Explanation  Related Ques ANSWER: Logarithmic Mean Temperature Difference (LMTD) Explanation: No explanation is available for this question!

31)   For the same inlet and exit temperatures of two fluids, the LMTD for counterflow is always

a. smaller than LMTD for parallel flow
b. greater than LMTD for parallel flow
c. same as LMTD for parallel flow
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: greater than LMTD for parallel flow Explanation: No explanation is available for this question!

32)   For the same heat transfer Q and same overall heat transfer coefficient Uo, surface area required for parallel flow operation is always

a. less than LMTD for counter flow
b. more than LMTD for counter flow
c. same as LMTD for counter flow
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: more than LMTD for counter flow Explanation: No explanation is available for this question!

33)   In parallel flow heat exchangers,

a. the exit temperature of hot fluid is always equal to the exit temperature of cold fluid
b. the exit temperature of hot fluid is always less than the exit temperature of cold fluid
c. the exit temperature of hot fluid is always more than the exit temperature of cold fluid
d. we cannot predict comparison between exit temperatures of hot fluid and cold fluid
 Answer  Explanation  Related Ques ANSWER: the exit temperature of hot fluid is always more than the exit temperature of cold fluid Explanation: No explanation is available for this question!

34)   For the same heat transfer Q and same overall heat transfer coefficient Uo, surface area required for cross flow operation is always

a. less than LMTD for parallel flow
b. more than LMTD for parallel flow
c. same as LMTD for parallel flow
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: less than LMTD for parallel flow Explanation: No explanation is available for this question!