chemical engineering heat transfer chemical engineering Mcqs
351. A body is called grey if the monochromatic emissivity of the body is___________________?
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A. Unity

B. Different for all wavelengths

C. Zero

D. Same for all wavelengths
352. For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is _________________?
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A. Forward

B. Backward

C. None of these

D. Parallel

353. In natural convection heat transfer, the correlating parameter is the_______________________?
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A. Eckert number

B. Grashoff number

C. Bond number

D. Graetz number

354. Prandtl number is the ratio of________________?
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A. Thermal diffusivity to mass diffusivity

B. Momentum diffusivity to thermal diffusivity

C. Mass diffusivity to thermal diffusivity

D. Thermal diffusivity to momentum diffusivity

355. Which of the following is not concerned with the heat transfer ?
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A. Peclet number

B. Stanton number

C. Brinkman number

D. Schmidt number
356. In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side ______________ the heat transfer rate?
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A. Decreases

B. Does not affect

C. Increases

D. May increase or decrease, depends on the type of baffle

357. Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by____________________?
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A. Enhancing the fluid pumping rate

B. Keeping the heat transfer surface clean

C. Increasing the tube length

D. None of these

358. In a multiple effect evaporator, the effect of boiling point elevation is to______________________?
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A. Increase the economy

B. Reduce the economy

C. Reduce the capacity

D. None of these

359. The separation of liquid droplets from the vapor is done by a/an _____________ in the evaporators?
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A. Entrainment separator

B. Vacuum pump

C. Steam ejector

D. Compressor

360. Fouling factor used in the design of a multipass shell and tube heat exchanger is a_____________________?
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A. None of these

B. Conversion factor for individual film heat transfer co-efficient to overall heat transfer coefficient

C. Factor of safety

D. Non-dimensional factor

361. In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell) ?
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A. D/2 and 2 D

B. D/5 and D

C. D/4 and 2 D

D. D and 2 D

362. What is the absorptivity of a black body?
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A. 1

B. 0

C. 0.78

D. 0.95

363. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?
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A. 1

B. 1

C. None of these

364. A _____________ surface has the maximum thermal emissivity out of the following ?
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A. White & smooth

B. White & rough

C. Black & smooth

D. Black & rough
365. Boiling point elevation of a solution of NaOH _____________________?
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A. Increases rapidly with temperature rise

B. Is almost independent of temperature

C. Is almost independent of pressure

D. Both B. and C
366. Heat transfer by natural convection is enhanced in system with__________________?
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A. Low density change with temperature

B. High viscosity

C. High co-efficient of thermal expansion

D. Low temperature gradients

367. Sensible heat of hot industrial flue gases cannot be recovered by a/an________________?
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A. Ceramic recuperator

B. Regenerator

C. None of these

D. Economiser

368. Which of the following is generally considered as opaque surface towards radiations ?
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A. Gases

B. Solids

C. Liquids

D. Both B. and C.
369. 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. Liquid density

C. Hot surface temperature

D. Interfacial tension
370. In a forward feed multiple effect, the pressure build up will be____________________?
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A. Least at the inlet of the first effect

B. Highest at the inlet of the last effect

C. Least at the outlet of the last effect

D. Highest at the outlet of the last effect

371. 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_________________?
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A. 4

B. 1

C. 2-Jan

D. 2
372. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell) ?
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A. 0.50 D

B. 0.75 D

C. None of these

D. 0.25 D

373. Removal of ______________ heat is involved in the condensation of a vapor under saturated conditions?
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A. Super

B. Sensible

C. Latent

D. Both B. & C.

374. Reynolds analogy states that (where, St = Stanton number f = friction factor) ?
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A. St = f/4

B. St = f1/2

C. St = 4f

D. St = f/2
375. Log mean temperature difference (LMTD) cannot be used, if ___________________?
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A. Heat transfer co-efficient over the entire heat exchanger is not constant

B. The heat capacity is not constant and there is a phase change

C. None of these

D. There exists an unsteady state

376. Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be_________________?
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A. 0.55

B. 0.45

C. 0.85

D. 0.35

377. Harmonic mean temperature difference is given by_________________?
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A. 2 (?T1 . ?T2)/(?T1 ?T2)

B. 2 (?T1 . ?T2)/(?T1 + ?T2)

C. ?(?T1 . ?T2)

D. (?T1 ?T2)/(?T1 . ?T2)

378. The ratio of momentum diffusivity to thermal diffusivity is the ______________ number?
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A. Prandtl

B. Nusselt

C. Stanton

D. Grashoff

379. A 2-4 heat exchanger involves__________________?
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A. Only counter-flow of fluids

B. Only parallel-flow of fluids

C. Both counter and parallel-flow of the fluids

D. Smaller pressure drop compared to 1-2 exchanger

380. In a single effect evaporator, the economy is________________?
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A. < 1

B. > 1

C. None of these

D. 1

381. Shell side pressure drop in a shell and tube heat exchanger does not depend upon the_________________?
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A. Baffle spacing & shell diameter

B. None of these

C. Tube diameter & pitch

D. Viscosity, density & mass velocity of shell side fluid

382. 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)1/2

B. (?T)5/4

C. (?T)3/4

D. (?T)1/4

383. A 10 cm dia steam pipe, carrying steam at 180C, is covered with an insulation (conductivity = 0.6 W/m.C). It losses heat to the surroundings at 30C. Assume a heat transfer co-efficient of 0.8 W/m2.C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?
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A. Less than the steam pipe with 5 cms insulation

B. Equal to that of the un-insulated steam pipe

C. Less than that of the un-insulated steam pipe

D. Greater than that for un-insulated steam pipe

384. When vaporisation takes place directly at the heating surface, it is called________________?
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A. Vapour binding

B. Film boiling

C. None of these

D. Nucleate boiling
385. The ratio of total radiating power to the absorptivity of the body depends upon the _____________ as per Kirchoff?s law?
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A. None of these

B. Wavelength of radiation

C. Temperature of the body

D. Nature of the body

386. For a given ambient air temperature with increase in the thickness of insulation of a hot cylindrical pipe, the rate of heat loss from the surface would ?
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A. First decrease and then increase

B. Decrease

C. First increase and then decrease

D. Increase

387. ____________ chart is known as transient heat conduction chart?
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A. Cox

B. Heislers

C. Molliers

D. Dirhings
388. Heat transfer by radiation between two bodies at T1 & T2 and in an ambient temperature of TaC depends on_____________?
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A. T2 Ta

B. T1 T2

C. T1 Ta

D. None of these
389. In case of _____________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid?
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A. None of these

B. Pool

C. Low pressure

D. Nucleate

390. Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low___________________?
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A. Hardness

B. All A., B. and C.

C. Suspended solids content

D. Dissolved solids content

391. The purpose of providing bleed points in the evaporator is to__________________?
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A. Remove the product

B. Create vacuum

C. Admit the feed

D. Facilitate removal of non-condensable gases
392. 1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is__________________?
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A. 200

B. 520

C. 500

D. 400
393. Nusselt number (for forced convection heat transfer) is a function of the _____________ number?
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A. Prandtl

B. Reynolds

C. Both A. & B.

D. Neither A. nor B.

394. Heat waves_____________________?
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A. Cannot pass through vacuum

B. Travel in straight line

C. Can be reflected by a mirror

D. Both B. and C.
395. As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient ?
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A. Goes through a maximum

B. Continues to decrease

C. Continues to increase

D. Goes through a minimum
396. The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by ______________ times, when the number of tube passes is increased to 8?
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A. 40.4

B. 40.8

C. 20.8

D. 20.4

397. Economy of an evaporator is influenced by the_____________________?
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A. Steam pressure

B. Feed temperature

C. Number of effect

D. Both B. & C.
398. Heat flux is the time rate of heat transfer per unit_______________?
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A. Area

B. None of these

C. Length

D. Volume

399. Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80C and leaves at 50C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20C. The log mean temperature difference in C is approximately ?
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A. 32

B. 45

C. 50

D. 37

400. Steam traps are provided in steam carrying pipelines to_________________?
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A. Condense steam

B. Remove condensate and inert gases

C. Release excess steam pressure by bleeding steam

D. None of these