Friday, February 22, 2019

Heat Transfer (Objective Questions With Answers)

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01. Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around __________ metres/second.
(A) 1
(B) 10
(C) 20
(D) 30
Answer: Option A

02. For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it
(A) Decreases the pressure drop
(B) Decreases the outlet temperature of cooling medium
(C) Increases the overall heat transfer coefficient
(D) None of these
Answer: Option C

03. A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun?
(A) Yellow paint
(B) White paint
(C) Black paint
(D) Grey paint
Answer: Option C

04. Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?
(A) 35.5
(B) 43.75
(C) 81.25
(D) 48.25
Answer: Option C

05. Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60
kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C
and 100°C respectively. The interface between B and C will be at a temperature of __________ °C.
(A) 40
(B) 95
(C) 70
(D) 50
Answer: Option C

06. A graph between __________ is called Wilson plot.
(A) (1/U) Vs. (1/v0.8)
(B) (1/v0.8) Vs. U
(C) v0.8 Vs . U
(D) (1/U) Vs. (1/V)
Answer: Option A

07. The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of 'n' is exactly 4 for
(A) Black painted bodies only
(B) All bodies
(C) Polished bodies only
(D) A black body
Answer: Option B

08. For a laminar flow of fluid in a circular tube, 'h1' is the convective heat transfer co-efficient at velocity 'V1'. If the velocity is reduced by half and assuming the fluid properties are constant,
the new convective heat transfer co-efficient is
(A) 1.26 h1
(B) 0.794 h1
(C) 0.574 h1
(D) 1.741 h1
Answer: Option B

09. Pick out the correct statement.
(A) 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F
(B) In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity
(C) In unsteady state heat conduction, heat flows in the direction of temperature rise
(D) In heat transfer by forced convection, Grashoff number is very important
Answer: Option B

10. Evaporation by thermo compression results in the
(A) Saving of steam
(B) Realisation of multiple effect economy in a single effect
(C) Both (A) and (B)
(D) None of these
Answer: Option C

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