Heat Transfer - Study Mode

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[#251] The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U 0 = 400 W/m 2 .K. The fouling factor after one year of operation is found to be h d0 = 2000 W/m 2 .K. The overall heat transfer co-efficient at this time is

(A) 1200 W/m 2 .K

(B) 894 W/m 2 .K

(C) 333 W/m 2 .K

(D) 287 W/m 2 .K

Correct Answer

(C) 333 W/m 2 .K

[#252] Forced circulation evaporators are normally used for concentrating liquids having

(A) Scaling characteristics

(B) High viscosity

(C) Both A & B

(D) Neither A nor B

Correct Answer

(C) Both A & B

[#253] If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is

(A) 1

(B) 2

(C) $$frac{1}{2}$$

(D) 4

Correct Answer

(B) 2

[#254] Temperature profile in steady state heat transfer is

(A) Asymptotic

(B) Hyperbolic

(C) Parabolic

(D) Linear

Correct Answer

(D) Linear

[#255] The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m -1 .°C -1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m -2 .°C -1 . The rate of heat loss from the outer surface in W.m -2 is

(A) 165.4

(B) 167.5

(C) 172.5

(D) 175

Correct Answer

(A) 165.4