chemical engineering heat transfer chemical engineering Mcqs
451. The value of Stefan-Boltzmann constant in SI unit is_________________?
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A. 0.1714 10-8W/m2.K4

B. 5.6697 10-8W/m2.K4

C. 5.6697 10-8kcal/m2. K4

D. 0.1714 10-8kcal/m2. K4

452. Duhring?s rule is important in solving problems on__________________?
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A. Evaporation

B. Humidification

C. Distillation

D. Crystallisation

453. While the total emissivity of a perfect black body is unity, the same for a real body is__________________?
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A. 0

B. > 1

C. Between 0 and 1

D. 1

454. _____________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side?
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A. U-tube

B. None of these

C. Three pass, fixed tube sheet

D. Single pass, fixed tube sheet

455. Analogy between mass and heat transfer is not applicable in case of____________________?
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A. Same velocity profile or equal eddy diffusivities

B. Thermal or pressure mass diffusion

C. Viscous heating or chemical reaction

D. Both B. and C.
456. The film thickness for laminar film condensation on vertical surface _____________ from top to bottom?
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A. And the surface conductance increase

B. Cumulatively increases

C. Cumulatively decreases

D. Remain constant

457. Among liquids, water has a comparatively high value of thermal conductivity, due to its__________________?
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A. Dense structure

B. High viscosity

C. Partial ionisation

D. Low density

458. In which mode of heat transfer, the Biot number is important ?
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A. Natural convection

B. Transient heat conduction

C. Radiation

D. Forced convection

459. Increasing the liquor level in the evaporator results in the_______________?
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A. Decreased capacity

B. Decreased effect of hydrostatic head

C. Increased true temperature drop

D. Increase in liquor film co-efficient

460. The critical radius r of insulation on a pipe is given by____________________?
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A. r = h/k

B. r = k/2h

C. r = 2k/h

D. r = k/h
461. 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. Temperature of the fin end

B. Constant temperature equal to that of the base

C. Average temperature of the fin

D. Surrounding temperature

462. The heat flux in the nucleate boiling regimes is proportional to (where, ?T = excess temperature) ?
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A. (?T)4

B. (?T)2

C. (?T)3

D. ?(?T)

463. The sum of reflectivity and absorptivity for an opaque body is equal to____________________?
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A. 2

B. 0.5

C. 1

D. 0

464. Which of the following is not used as a medium for high temperature heating ?
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A. Fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)

B. Dowtherm

C. Liquid metal (e.g. molten sodium)

D. Mercury
465. Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is_________________?
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A. < 1

B. > 1

C. > 5

D. 1

466. Fouriers law of heat conduction applies to _____________ surfaces?
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A. Isothermal

B. Non-isothermal

C. Both A. and B.

D. Neither A. and B.

467. Double pipe heat exchangers are used__________________?
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A. Because it occupies less floor area

B. Because it is less costly

C. When heat transfer area required is very low, i.e. (100-200 ft2).

D. When heat transfer area required is very high

468. _______________ paint has the maximum absorption coefficient ?
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A. Grey

B. Yellow

C. White

D. Black
469. Steam side heat transfer co-efficient in an evaporator is in the range of ______________ kcal/hr.m2C?
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A. 100-500

B. 1000-1500

C. Oct-50

D. 5000-15000
470. In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient______________?
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A. May increase or decrease; depends on the feed

B. Decreases

C. Is not affected

D. Increases

471. For concentrating an aqueous solution of a material like anhydrous Na2SO4, whose solubility decreases with rise in temperature, the most suitable evaporator is a _______________ evaporator?
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A. None of these

B. High pressure

C. Vacuum

D. Backward feed

472. What is Nusselt number ?
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A. CP. ?/k

B. hD/k

C. CP. ?/h

D. h. CP/?

473. The unit of heat transfer co-efficient in SI unit is____________________?
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A. J/mK

B. W/mK

C. W/m2K

D. J/M2K

474. 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.

475. Pick out the wrong statement?
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A. Thermal conductance of a wall of thickness L, thermal conductivity k and heat flow area A is kL/A

B. Unit of thermal conductance is W/K

C. Reciprocal of the resistance to heat flow is called thermal conductance

D. None of these

476. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is_____________?
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A. Vertical heat exchanger with steam on tube side

B. Horizontal heat exchanger with steam on shell side

C. Horizontal heat exchanger with steam on tube side

D. Vertical heat exchanger with steam on shell side
477. Crystallisation of solids from a homogeneous solution is a/an ______________ process?
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A. Mildly endothermic

B. None of these

C. Exothermic

D. Highly endothermic

478. The purpose of floating head in a heat exchanger is to_________________?
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A. Avoid buckling of tubes

B. Facilitate its lengthening, if needed

C. Provide support for tubes

D. Decrease the pressure drop

479. In forced circulation, the heating element is injected_________________?
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A. Internally

B. Externally

C. Both A. and A.

D. Neither A. nor B.

480. With the increase of temperature, the Col-burn jH factor_____________________?
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A. Decreases

B. Remains unchanged

C. Increases

D. May increase or decrease; depending on temperature

481. Pick out the wrong statement ?
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A. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as

B. In case of heat transfer by purely forced convection, GR/Re 2 ? 1

C. med and detached from the heating surface

D. The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are

E. Distillation process is not the same as evaporation

F. 216;x) is equal to 4x</strong>

482. Heat transfer co-efficient (h1) for liquids increases with__________________?
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A. Increasing temperature

B. None of these

C. Decreasing temperature

D. Decreasing Reynolds number

483. Thermal diffusivity is the most important in heat transfer by__________________?
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A. Radiation

B. Natural convection

C. Condensation

D. Conduction
484. Baffles are provided in heat exchangers to increase the________________?
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A. Heat transfer co-efficient

B. Fouling factor

C. Heat transfer area

D. Heat transfer rate

485. The number of kg vaporised per kg of steam fed to the evaporator is defined as____________?
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A. Rate of evaporation

B. Capacity

C. Rate of vaporisation

D. Economy
486. For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus- Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of________________?
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A. 6.1

B. 37

C. 1.74

D. 1

487. Dropwise condensation occurs on ______________ surfaces?
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A. Contaminated cooling

B. Smooth clean

C. Polished

D. Clean and dirt free

488. Which of the following is correct ?
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A. Driving force = Rate Resistance

B. Rate = Resistance/Driving force

C. Rate = Driving force Resistance

D. Resistance = Driving force Rate

489. _____________ paint has the minimum absorption co-efficient?
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A. White lead

B. Light cream

C. Grey

D. Black

490. For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is_________________?
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A. 3

B. 0.33

C. 1.33

D. 1
491. Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by h = 0.023 (K/D) (DV?/?)0.8 (CP.?/k)0.4. This is valid for the value of NRe equal to_______________?
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A. > 10000

B. 4000

492. A dephlegmator is a_____________________?
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A. Partial condenser

B. Double pipe heat exchanger

C. Vacuum evaporator

D. Total condenser

493. Which is the most suitable for the concert-ration of highly concentrated solution ?
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A. Long tube vertical evaporator

B. None of these

C. Open pan evaporation

D. Agitated film evaporator

494. Pick out the wrong statement ?
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A. n one sequence of heating or cooling i.e., desuperheating & condensation or condensation

B. vent, then it is called a hydrate

C. p; sub-cooling

D. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted

E. al tube cross-sectional area

F. In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the

495. Pick out the wrong statement?
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A. When a vertical plate is heated in infinite air environmental under natural convection

B. ditions, the velocity profile in air, normal to the plate, exhibits a maximum

C. In process heat exchangers, saturated steam is preferred over the superheated steam

D. tted over the entire wavelength range is equal to emissivity

E. wavelength band between 3 ?m to 4 ?m. The fraction of this energy in the total energy

F. ?1. If the surface temperature is halved, the maximum in the emissive power would occur at

496. Pick out the wrong statement ?
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A. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger

B. Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number

C. Hot gases at moderate pressure are usually in the shell side of shell and tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side

D. In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2

497. Pick out the correct statement ?
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A. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity

B. 1 kcal/hr.m.C is equal to 1 BTU/hr. ft.F

C. In heat transfer by forced convection, Grashoff number is very important

D. In unsteady state heat conduction, heat flows in the direction of temperature rise

498. Pick out the wrong statement ?
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A. Value of Stefan-Boltzmann constant is 4.876 10-8 KCal/m2.hr.K4

B. Absorptivity of a body approaches unity in case of diffuse reflection

C. With change in temperature, the radiant energy emitted by a black body remains unchanged

D. Absorptivity of a perfectly black body is unity

499. Maximum heat transfer rate can be expected in case of_________?
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A. Co-current flow

B. Laminar flow

C. Heat flow rate is independent of nature of flow

D. Turbulent flow
500. Baffles are provided in heat exchangers to____________?
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A. Reduce vibrations

B. Increase heat transfer rate

C. Reduce heat transfer rate

D. Remove dirt