chemical engineering heat transfer chemical engineering Mcqs
301. A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the _______________ number?
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A. Condensation

B. Grashoff

C. Stanton

D. Brinkman
302. Prandtl and Reynolds analogies are identical for Prandtl number value of__________________?
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A. 0

B. 1

C. 5

D. 0.5

303. According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor) ?
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A. f/4

B. f/2

C. f

D. 2f

304. Evaporation of 1kg of water from a solution in a single effect evaporator requires about ________________ kg of steam?
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A. 1-1.3

B. 2 2.4

C. 1.8-2

D. 0.4 0.6

305. For an ideal black body______________________?
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A. Transmissivity = 1

B. Absorptivity = 1

C. Reflectivity = 1

D. Emissivity = 0

306. What is the thermal conductivity of a perfect heat insulator ?
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A. ?

B. Between 0 and ?

C. One

D. Zero
307. The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the___________________?
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A. Heating volume

B. None of these

C. Heat transfer area

D. Nusselt number

308. Kirchoff?s law applies to _____________ radiation?
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A. Total

B. Monochromatic

C. Both A. & B.

D. Neither A. nor B.

309. Crystal size in a continuous crystalliser depends upon the___________________?
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A. Rate of heat transfer

B. All A., B. and C

C. Degree of super-saturation

D. Degree of turbulence

310. The energy radiated from a surface Q at absolute temperature T is related as__________________?
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A. None of these

B. Q ? T3

C. Q ? T4

D. Q ? T2

311. Film boiling is usually not desired in commercial equipments, because____________________?
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A. None of these

B. It is difficult to maintain

C. The heat transfer rate is low in view of the large temperature drop

D. It is not economic

312. The main function of baffles provided in a shell and tube heat exchanger is to______________?
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A. All A , B & C

B. Hold the tubes in position

C. Enhance turbulence

D. Facilitate the cleaning of outer tube surface

313. Double pipe heat exchangers are preferably useful, when____________________?
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A. Overall heat transfer co-efficient is very high

B. Requirement of heat transfer area is low

C. High viscosity liquid is to be cooled

D. A corrosive liquid is to be heated

314. For small temperature difference, the heat transfer rate as per Newtons law of cooling is proportional to (where, ?t = excess temperature) ?
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A. ?t2

B. ?t3

C. ?t

D. ?(?t)

315. A long iron rod initially at a temperature of 20C has one end dipped in boiling water (100C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?
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A. t = 283 s

B. t = 400 s

C. t = 356 s

D. t = 800 s
316. Pick out the wrong statement ?
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A. Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube

B. In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles

C. Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient

D. S.I. unit of fouling factor is Watt/m2.K
317. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area___________________?
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A. Decreases

B. Increases

C. Passes through a maxima

D. Remain constant

318. Latent heat absorbed by 1 lb of water at 212F, when it is changed to steam at 212F, may be around ______________ BTU?
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A. None of these

B. 180

C. 3.97

D. 970

319. Radiation heat transfer rates does not depend upon the_________________?
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A. Type of absorbing surface

B. Surface area and temperature of the heat source

C. None of these

D. Distance between the heat source and the object receiving the heat

320. Rate of heat transfer by vaporisation from pools of water is affected by the ____________________?
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A. Surface tension of water

B. Viscosity of water

C. All A., B. and C.

D. Nature of heating surface and distribution of bubbles

321. 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. Remains unchanged

B. Increases

C. Increases or decreases depending on number of shell passes

D. Decreases
322. Boiling point elevation of an ideal solution_______________?
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A. Increases rapidly with temperature rise

B. Decreases rapidly with temperature rise

C. In independent of pressure

D. Both B. and C.

323. Heat produced when a steady state current, I passes through an electrical conductor having resistance, R is___________________?
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A. IR

B. IR2

C. I2R

D. I2R2

324. Small scale evaporation is done in a_________________?
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A. Steam jacketed kettle

B. Multiple effect evaporator

C. Heat exchanger

D. Condenser

325. Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the____________________?
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A. Sum of all resistances

B. Average of all resistances

C. Maximum resistance in the series

D. Minimum resistance presents in the series

326. Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity ?
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A. Aluminium foil

B. Refractory bricks

C. Coke breeze

D. Iron plate

327. Pick out the wrong statement ?
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A. The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same

B. Propagation velocity for travel of heat radiation through vacuum is equal to the velocity of the light

C. Heat transfer by radiation cannot occur across an absolute volume

D. In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bundle between baffles

328. For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and pressure drop are__________________?
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A. Same

B. Different

C. Linearly related

D. Never different

329. Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid ?
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A. Bleed point

B. Catchall

C. Baffle

D. Vent

330. _____________ equation relates the thermal conductivity of a solid to its temperature ?
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A. Antoine

B. 217;s

C. Lees

D. Kistyakowsky

331. The statement that maximum wavelength of radiation is inversely proportional to the temperature is ______________ law?
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A. Stefan-Boltzmanns

B. None of these

C. Wiens displacement

D. Plancks

332. In a boiling curve, the peak heat flux is called the _____________ point?
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A. Nusselt

B. Burnout

C. Leidenfrost

D. Boiling

333. The purpose of providing a catchall in the vapor line of an evaporator is to__________________?
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A. Create vacuum

B. Regulate the vapor flow

C. Arrest the entrained liquid

D. Vent the non-condensable gases

334. Unsteady state heat conduction occurs, when_______________?
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A. Temperature distribution is dependent on time

B. Heat flows in one direction only

C. Three dimensional heat flow is concerned

D. Temperature distribution is independent of time

335. Which of the following has the highest thermal conductivity ?
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A. Silver

B. Water

C. Air

D. Brick

336. In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred_________________?
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A. By heating an intermediate material (like chequor bricks) and then heating the air from this

B. By direct contact of hot flue gas with air

C. material</strong>

D. None of these

E. Through a metallic wall

337. Heat flux through several resistances in series in analogous to the current flowing through several_____________________?
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A. Capacitors in series

B. Resistances in series

C. Resistances in parallel

D. None of these

338. Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is ____________________?
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A. Thin walled having the value of Ao Ai/< 2

B. Thick walled

C. Having the value of Ao/Ai > 2

D. Both B. and C.

339. With increase in porosity, the thermal conductivity of a solid substance__________________?
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A. Decreases

B. May increase or decrease; depends on the solid

C. Increases

D. Remains unchanged

340. Choose the most important factor on which the heat conducted through a wall in a unit time will depend on ?
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A. Material of the wall

B. Temperature difference between the two surfaces of the wall

C. Area of the wall perpendicular to heat flow

D. Thickness of the wall

341. If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer co-efficient is________________?
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A. Always higher than h2

B. Always between h1 and h2

C. Always less than h1

D. Dependent on metal resistance

342. The equivalent diameter for pressure drop is ________________ that for heat transfer?
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A. Smaller than

B. Greater than

C. Equal to

D. Not related with

343. Low thermal conductivity of heat insulating materials is due to its_________________?
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A. High specific heat

B. Dense structure

C. High proportion of air space

D. None of these

344. Steady state one dimensional heat flow by conduction as given by Fouriers low does not assume that_______________?
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A. Constant temperature gradient exists

B. Boundary surfaces are isothermal

C. There is no internal heat generation

D. Material is anisotropic
345. Mechanical recompression evaporation is used in the production of____________________?
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A. Distilled water

B. Fruits jam

C. Alcohol

D. Salt

346. Heat exchangers operating, when the asymptotic range is reached, ?
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A. None of these

B. Results in making part of the heating surface inactive

C. Provide very large heat transfer co-efficient

D. Results in abruptly increased velocity

347. In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to _____________ the velocity head?
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A. Square root of

B. Twice

C. Square of

D. Four times
348. A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides __________________?
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A. Higher economy

B. Lower capacity

C. Both A. & B.

D. Lower economy

349. Which of the following is concerned with both heat and mass transfer ?
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A. Froude number

B. Kutateladze number

C. Nusselt number

D. Lewis relationship
350. 1000 Kg of liquid at 30C in a well stirred vessel has to be heated to 120C, using immersed coils carrying condensing steam at 150C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.C, the time taken for the liquid to reach desired temperature will be__________________?
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A. 44 min

B. 15 min

C. 51 min

D. 22 min