Effectiveness of Fins - MCQs with Answers

Effectiveness of Fins – MCQs with Answers

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

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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

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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

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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

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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

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6. A fin of uniform cross-section A and perimeter P has a base temperature T_s and it is exposed to fluid having temperature T_∞ How is the temperature distribution in the fin given?

a. T – T_∞ = C₁e^mx – C₂e^{– mx}
b. T – T_∞ = C₁e^mx + C₂e^{– mx}
c. T + T_∞ = C₁e^mx – C₂e^{– mx}
d. T + T_∞ = C₁e^mx + C₂e^{– mx}

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

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7. What is the correct formula for the temperature distribution in infinitely long fin?

a. (T_s – T_∞) / (T – T_∞) = C₂e^mx
b. (T_s – T_∞) / (T – T_∞) = C₂e^{– mx}
c. (T – T_∞) / (T_s – T_∞) = C₂e^mx
d. (T – T_∞) / (T_s – T_∞) = C₂e^{– mx}

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
T_s = Base temperature of the fin
T_∞ = Temperature of surrounding fluid

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8. How is the rate of heat transfer from the fin given?

a. q = h P k A (T_s – T_∞)
b. q = √(h P k A (T_s – T_∞))
c. q = √(hPkA) (T_s – T_∞)
d. none of the above

h = convective heat transfer coefficient
P = perimeter of the fin
k = thermal conductivity of fin
A = cross-sectional area of the fin
T_s= Base temperature of the fin
T_∞ = Temperature of surrounding fluid

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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 T_s = 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

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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

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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

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