chemical engineering MCQs – Page 203

Practise multiple-choice questions from chemical engineering for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

chemical engineering Mcqs
4041. Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around _____________ metres/second?
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A. 30

B. 1

C. 10

D. 20

4042. For what value of Prandtl number, the Col-burn analogy is valid ?
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A. 0.06 to 120

B. 1 to 103

C. 0.6 to 120

D. 1 to 50

4043. A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is ______________?
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A. 3.5

B. 5.6

C. 0.025

D. 0.0035

4044. A metal ball of radius 0.1 m at a uniform temperature of 90C is left in air at 30C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60C is_________________?
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A. 0.55

B. 0.15

C. 555

D. 55.5

4045. A dephlegmator is a_____________________?
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A. Vacuum evaporator

B. Double pipe heat exchanger

C. Partial condenser

D. Total condenser

4046. The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re)0.8 (Pr)0.4] cannot be used for________________?
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A. Molten metals

B. All A., B. and C.

C. Low Reynolds number

D. Very low Grashoff number

4047. Steady state one dimensional heat flow by conduction as given by Fouriers low does not assume that_______________?
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A. Material is anisotropic

B. There is no internal heat generation

C. Constant temperature gradient exists

D. Boundary surfaces are isothermal

4048. Nusselt number is the ratio of the ____________________?
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A. Heat flux at the wall to that across the entire pipe

B. Temperature gradient of the wall to that across the entire pipe

C. None of these

D. Temperature difference to the temperature gradient at the wall

4049. Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube___________________?
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A. Exit fluid temperature < wall temperature

B. Exit fluid temperature = wall temperature

C. Exit-fluid temperature > wall temperature

D. Graetz number > 100

4050. Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is________________?
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A. > 1

B. < 1

C. 1

D. 0.1
4051. Fouriers law applies to the heat transfer by__________________?
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A. Conduction

B. Radiation

C. Convection

D. All A., B. & C.

4052. The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe) ?
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A. hi/K

B. 2K/h0

C. 2hi/K

D. K/h0
4053. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (?T) between wall and outside bulk. The proportionality is given as______________?
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A. (?T)1/4

B. (?T)5/4

C. (?T)1/2

D. (?T)3/4
4054. Multiple effect evaporators are commonly used in the manufacture of P. Paper Q. Superphosphate R. Sugar S. Fats ?
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A. P and S

B. P and R

C. P and Q

D. R and S

4055. If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid_________________?
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A. Increases or decreases depending on number of shell passes

B. Remains unchanged

C. Increases

D. Decreases
4056. Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface ?
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A. Liquid viscosity

B. Hot surface temperature

C. Interfacial tension

D. Liquid density

4057. Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the________________?
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A. Surrounding temperature

B. Constant temperature equal to that of the base

C. Average temperature of the fin

D. Temperature of the fin end

4058. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the___________________?
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A. Buffer zone

B. Turbulent core

C. Both A. and B.

D. Viscous sub-layer
4059. In case of a vertical tube evaporator, with increase in the liquor level, the___________________?
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A. Capacity of the evaporator is decreased

B. Capacity of the evaporator is increased

C. True temperature drop increases

D. Both B. and C.

4060. Use of transverse baffles in a shell and tube heat exchanger is done to increase the___________________?
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A. Flow velocity

B. All A., B. and C.

C. Rate of heat transfer

D. Turbulence of shell side fluid