Heat Transfer Mock Test 10

10%

Question 1 of 10

1. The entrance length required for the flow to become fully-developed turbulent flow is dependent on
(i) Surface finish
(ii) Downstream conditions
(iii) Fluid properties
Identify the correct answer

ii and iii

i and ii

i and iii

i, ii and iii

Question 1 of 10

Question 2 of 10

2. Which one is having the lowest value of solar absorptivity?

Dull stainless steel

Concrete

White marble

Black paint

Question 2 of 10

Question 3 of 10

3. 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?

1555.78 k J/m² hr degree

1666.78 k J/m² hr degree

1777.78 k J/m² hr degree

1444.78 k J/m² hr degree

Question 3 of 10

Question 4 of 10

4. In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m² hr degree. Find the effectiveness of the heat exchanger. At the condensing pressure, stream has a saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to the water. Take specific heat of water as 4 k J/kg K

0.224

3.224

0.706

2.224

Question 4 of 10

Question 5 of 10

5. The conditions for flow beyond the boundary layer and its outer edge are

d u/d y = 0 and u = U₀

d u/d y = Infinity and u = U_INFINITY

d u/d y = 0 and u = U_INFINITY

d u/d y = 1 and u = U₀

Question 5 of 10

Question 6 of 10

6. 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

7.2

6.2

5.2

4.2

Question 6 of 10

Question 7 of 10

7. Kirk bride criterion is given by

h = 0.0067 (Re)^0.4 [k ³p² g/δ²]^1/3

h = 0.0057 (Re)^0.4 [k ³p² g/δ²]^1/3

h = 0.0077 (Re)^0.4 [k ³p² g/δ²]^1/3

h = 0.0087 (Re)^0.4 [k ³p² g/δ²]^1/3

Question 7 of 10

Question 8 of 10

8. Which one is having the lowest value of solar absorptivity?

Snow

Red brick

Aluminum foil

Polished aluminum

Question 8 of 10

Question 9 of 10

9. A copper pipe (k = 350 W/m K) having inner diameter of 1.75 cm and 2.0 cm outside diameter conveys water and the oil flows through the annular passage between this pipe and a steel pipe. On the water side, the film coefficient is 4600 W/m² K and the fouling factor is 0.00034 m² K/W. The corresponding values for the oil side are 1200 W/m²K and 0.00086 m² K/W. Estimate the overall heat transfer coefficient between the oil and water

435.16 W/m²K

335.16 W/m²K

235.16 W/m²K

535.16 W/m²K

Question 9 of 10

Question 10 of 10

10. What is the value of specific heat for asphalt in J/kg K?

720

920

820

620

Question 10 of 10

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