Heat Transfer Test

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Heat Transfer Test - 7

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Weekly Quiz Competition

Question 1
4 / -1

Which of the following is having the lowest value of overall heat transfer coefficient?

A
Feed water heaters

B
Air condensers

C
Air to low viscosity liquids

D
Steam condensers

Solution

Overall heat transfer coefficient for air condensers is 780 W/m²K while that of steam condensers, air to low viscosity liquids and feed water heaters are 5000 W/m²K, 600 W/m²K and 8500 W/m²K.
Question 2
4 / -1

A cross-flow type air heater has an area of 50 cm². The overall heat transfer coefficient is 100 W/m²K and the heat capacity of both hot and cold streams is 1000 W/m K. The value of NTU is

A
0.2

B
6

C
1000

D
5

Solution

NTU = A U/C _MIN = 5.
Question 3
4 / -1

An oil cooler in a high-performance engine has an outside surface area 0.12 m² and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m ² K. Find out the heat transfer rate?

A
564.98 W

B
324.67 W

C
190.68 W

D
768.43 W

Solution

Q = (T₂– T₁) A h = 0.12 (65-30) 45.4 = 190.68 W.
Question 4
4 / -1

Which of the following statement is incorrect according to heat transfer?

A
Heat flow doesn’t depend on temperature

B
A material medium is not necessary for heat transmission

C
The process of heat transfer is an irreversible process

D
For heat exchange, a temperature gradient must exist

Solution

Heat flows from higher to lower temperature.
Question 5
4 / -1

Consider a convective heat flow to water at 75 degree Celsius from a cylindrical nuclear reactor fuel rod of 50 mm diameter. The rate of heat generatioN is 50000000 W/m³ and convective heat transfer coefficient is I kW/m² K. The outer surface temperature of the fuel element would be

A
400 degree Celsius

B
625 degree Celsius

C
700 degree Celsius

D
550 degree Celsius

Solution

t _w = t _a + q _g R/ 2h.
Question 6
4 / -1

For a cylindrical rod with uniformly distributed heat sources, the thermal gradient at half the radius location will be

A
One half

B
One fourth

C
Four times

D
Twice

Solution

t = t _w+ q _g (R² – r²)/4k. (d t /d r) _{r = R/2} = 1/2(d t/d r) _{r = R}.
Question 7
4 / -1

Water (specific heat = 4 k J/kg K) enters a cross flow exchanger (both fluids unmixed) at 15 degree Celsius and flows at the rate of 7.5 kg/s. It cools air (C _P= 1 k J/kg K) flowing at the rate of 10 kg/s from an inlet temperature of 120 degree Celsius. For an overall heat transfer coefficient of 780 k J/m² hr degree and the surface area is 240 m², determine the NTU

A
1.2

B
8.2

C
6.2

D
5.2

Solution

NTU = U A/C _MIN= 5.2.
Question 8
4 / -1

A heat exchanger to preheat oil for a furnace was designed without considering the possibility of scale formation, and the overall heat transfer coefficient based on the fuel oil side was 3200 k J/m² hr degree. What would be the corrected coefficient of heat transfer if a fouling factor of 0.00025 m² hr degree/k J for the fuel oil is taken into account?

A
1222.78 k J/m² hr degree

B
1555.78 k J/m² hr degree

C
1777.78 k J/m² hr degree

D
1233.78 k J/m² hr degree

Solution

U = 1/ (R + 1/h _S).
Question 9
4 / -1

Which of the following is the value of fouling factor for engine exhaust?

A
0.001 m²K/W

B
0.002 m²K/W

C
0.003 m²K/W

D
0.004 m²K/W

Solution

Its unit is m² hr K/kcal and it represents the reciprocal of the scale coefficient i.e. heat transfer.
Question 10
4 / -1

The value of fouling factor for industrial liquids is ______

A
0.0002 m²K/W

B
0.0001 m²K/W

C
0.0003 m²K/W

D
0.0004 m²K/W

Solution

Its unit is m² hr K/kcal and it represents the reciprocal of the scale coefficient i.e. heat transfer.

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Re-Attempt Weekly Quiz Competition

Heat Transfer Test - 7

Result

Heat Transfer Test - 7

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SHARING IS CARING

Question 1

Feed water heaters

Air condensers

Air to low viscosity liquids

Steam condensers

Solution

Question 2

0.2

6

1000

5

Solution

Question 3

564.98 W

324.67 W

190.68 W

768.43 W

Solution

Question 4

Heat flow doesn’t depend on temperature

A material medium is not necessary for heat transmission

The process of heat transfer is an irreversible process

For heat exchange, a temperature gradient must exist

Solution

Question 5

400 degree Celsius

625 degree Celsius

700 degree Celsius

550 degree Celsius

Solution

Question 6

One half

One fourth

Four times

Twice

Solution

Question 7

1.2

8.2

6.2

5.2

Solution

Question 8

1222.78 k J/m2 hr degree

1555.78 k J/m2 hr degree

1777.78 k J/m2 hr degree

1233.78 k J/m2 hr degree

Solution

Question 9

0.001 m2 K/W

0.002 m2 K/W

0.003 m2 K/W

0.004 m2 K/W

Solution

Question 10

0.0002 m2 K/W

0.0001 m2 K/W

0.0003 m2 K/W

0.0004 m2 K/W

Solution

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1222.78 k J/m² hr degree

1555.78 k J/m² hr degree

1777.78 k J/m² hr degree

1233.78 k J/m² hr degree

0.001 m²K/W

0.002 m²K/W

0.003 m²K/W

0.004 m²K/W

0.0002 m²K/W

0.0001 m²K/W

0.0003 m²K/W

0.0004 m²K/W