Heat Transfer Mock Test 3

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Question 1 of 10

1. The figure shows a 5 cm diameter rod, 90 cm long, which is having its lower face grinded smooth. The remainder of the rod is exposed to 32 degree Celsius room air and a surface coefficient heat transfer equal to 6.8 W/m² degree exists between the rod surface and the room air. The grinder dissipates mechanical energy at the rate of 35 W. If thermal conductivity of rod material is 41.5 W/m degree, find the temperature of the rod at the point where the grinding is taking place

161.45 degree celsius

141.45 degree celsius

131.45 degree celsius

151.45 degree celsius

Question 1 of 10

Question 2 of 10

2. Find the heat transfer rate from a hot surface for 6 fins of 10 cm length? The base temperature of the fin is maintained at 200 degree Celsius and the film is exposed to a convection environment at 15 degree Celsius with convective coefficient 25W/square m K. Each fin has cross-sectional area 2.5 square centimeter and is made of a material having thermal conductivity 250W/m K

145.46W

130.18W

165.43W

120.34W

Question 2 of 10

Question 3 of 10

3. A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for junction diameter needed for the thermocouple to have thermal time constant of one second. Assume the thermos-physical properties as given below
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³

0.756 mm

0.556 mm

0.856 mm

0.656 mm

Question 3 of 10

Question 4 of 10

4. The rate of heat transfer in case of infinitely long fin is given by

(h P k A) ^1/2 (t₀– t_a)

(P k A) ^1/2 (t₀– t_a)

(h k A) ^1/2 (t₀– t_a)

(h P A) ^1/2 (t₀– t_a)

Question 4 of 10

Question 5 of 10

5. Which one is true regarding parabolic fin?

It dissipates the maximum amount of heat at a maximum material cost

It dissipates the minimum amount of heat at a maximum material cost

It dissipates the maximum amount of heat at a minimum material cost

It dissipates the minimum amount of heat at a minimum material cost

Question 5 of 10

Question 6 of 10

6. “The response of a thermocouple is defined as the time required for the thermocouple to reach the surrounding temperature when it is exposed to it”.

False

True

Question 6 of 10

Question 7 of 10

7. In heat dissipation from an infinitely long fin, the boundary conditions are

t = t₀ at x = infinity and t = t_a at x = 0

t = t₀ at x = 0 and t = t_a at x = 0

t = t₀ at x = 0 and t = t_a at x = infinity

t = t₀ at x = infinity and t = t_a at x = infinity

Question 7 of 10

Question 8 of 10

8. Suppose there are two reservoirs A and B. Let T_Aand T_Bbe the temperatures of respective reservoirs. At any instant say T_A = T_B. In this case, maximum temperature occurs at

Right

Left

All over the rod

Middle

Question 8 of 10

Question 9 of 10

9. The utility of fin in dissipating a given quantity of heat is generally assessed on the basic of how many parameters?

Question 9 of 10

Question 10 of 10

10. A fin protrudes from a surface which is held at a temperature higher than that of its environment. The heat transferred away from the fin is

Sum of heat conducted along the fin length and that convected from the surface

Convective heat transfer from the fin surface

Heat escaping from the tip of the fin

Heat conducted along the fin length

Question 10 of 10

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