chemical engineering heat transfer chemical engineering Mcqs
251. A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an___________________?
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A. Circular arc

B. Straight line

C. Parabola

D. Ellipse

252. Fouling factor_____________________?
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A. None of these

B. Is a dimensionless quantity

C. Does not provide a safety factor for design

D. Accounts for additional resistances to heat flow
253. Film boiling occurs at ________________ pressure?
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A. Sub-atmospheric

B. Very high

C. Negative

D. Atmospheric

254. 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. Graetz number > 100

C. Exit fluid temperature < wall temperature

D. Exit fluid temperature = wall temperature
255. Black liquor generated during paper manufacture is concentrated in a___________________?
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A. Single effect evaporator followed by a crystalliser

B. Multiple effect evaporator

C. Multiple effect evaporators followed by a crystalliser

D. Single effect evaporator

256. In a backward feed multiple effect evaporator ___________________ ?
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A. Feed is introduced in the first effect

B. Feed flows from low pressure to high pressure

C. No pumps are required between successive effects

D. None of these

257. Film condensation is promoted on a/an _______________________ surface?
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A. Oily

B. Clean & smooth

C. Coated

D. Dirty

258. With increase in temperature, the thermal conductivity of steel___________________?
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A. Increases exponentially

B. Increases

C. Remains unchanged

D. Decreases
259. In counter flow compared to parallel flow, ?
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A. LMTD is greater

B. Less surface area is required for a given heat transfer rate

C. Both A. and B.

D. More surface area is required for a given heat transfer rate

260. Thermal conductivity of a conducting solid material depends upon its_______________?
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A. Temperature

B. Porosity

C. Both A. & B.

D. Neither A. nor B.

261. In evaporators, lowering the feed temperature_______________?
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A. Increases the heating area required

B. Reduces the economy

C. Both A. and B.

D. Decreases the heating area required

262. 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. 0.1

C. < 1

D. 1

263. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?
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A. 0.5

B. 0.15

C. 0.05

D. 0.1
264. A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter d. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to_____________________?
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A. d0.8

B. d-0.2

C. d-1

D. d-1.8

265. jH factor for heat transfer is not a function of the _______________ number?
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A. Reynolds

B. Nusselt

C. Grashoff

D. Both B. & C.
266. The most conducive surface for dropwise condensation to occur is the _____________ surface?
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A. Oily

B. Smooth

C. Coated

D. Glazed & polished

267. A hot body will radiate heat most rapidly, if its surface is___________________?
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A. Black & polished

B. Black & rough

C. White & rough

D. White & polished

268. Convective heat transfer, in which heat is transferred by movement of warmed matter is described by___________________?
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A. Ficks law

B. Fouriers law

C. None of these

D. Newtons law of cooling
269. Intermittent tube cleaning is possible to be done in case of a _____________ evaporator?
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A. Basket type

B. Calandria

C. Horizontal tube

270. If air (a non-condensing gas) is present in a condensing vapor stream, it will ______________ the condensation rate of vapor?
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A. Increase the condensing film co-efficient as well as

B. Increase

C. Not affect

D. Decrease
271. Which type of heat exchanger is preferred for heavy heat loads ?
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A. Series and parallel set of shell and tube

B. Plate fine

C. None of these

D. Double pipe

272. Controlling heat transfer film co-efficient is the one, which offers ______________ resistance to heat transfer?
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A. Lower

B. The largest

C. No

D. The least

273. Multiple effect evaporation is generally recommended, when the______________________?
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A. Large scale evaporation of liquor is needed

B. Fuel is cheaply available

C. Evaporation on small scale is to be done

D. Corrosive liquids are to be concentrated

274. Overall heat transfer co-efficient for cooling of hydrocarbons by water is about_________________?
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A. 50 -100 Kcal/hr.m2.C

B. 1000 1500 BTU/hr. ft.2F

C. 50 -100 BTU/hr. ft.2F

D. 50 -100 W/m2.K

275. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50C in industrial practice mainly to avoid_________________?
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A. Excessive corrosion

B. Its evaporation loss

C. Decrease in heat exchanger efficiency

D. Uneconomic LMTD

276. An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is___________________?
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A. 9000

B. 4600

C. 4000

D. 3000

277. Mode of heat transfer involved in the cooling of air cooled internal combustion engine is_________________?
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A. Natural convection

B. Conduction

C. None of these

D. Forced convection

278. Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called_______________?
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A. Conduction

B. Forced convection

C. Radiation

D. Natural convection

279. 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. 555

B. 0.55

C. 55.5

D. 0.15
280. Pick out the wrong statement?
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A. The liquor left after the removal of crystals from a solution is called mother liquor

B. Swenson-Walker crystalliser is a batch crystalliser

C. Super saturation of the solution is the driving potential for a crystal growth

D. The first stage of crystal formation is called nucleation

281. For specified tube outside diameter, higher BWG means higher___________________?
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A. Tube thickness

B. Weight per unit length

C. Cross-sectional area

D. None of these

282. Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger ?
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A. Fouling characteristic

B. Corrosiveness

C. None of these

D. Viscosity

283. If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will ________________?
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A. Increase by 216

B. Decrease by 22

C. Increase by 1.8 times

D. Remain unchanged

284. Leidenfrost point is a term concerned with the____________________?
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A. Boiling of a liquid on a hot surface

B. Condensation of the saturated vapor on a cold surface

C. Concentration of a corrosive solution by evaporation

D. Heat transfer between two highly viscous liquids

285. As per Kirchoff?s law, the ratio of the total radiating power to the absorptivity of a body depends on the_______________?
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A. Temperature of the body only

B. Wavelength of monochromatic radiation

C. Both A. and B.

D. Nature of material of body

286. The Fourier number (defined as a.t/L2) is used in the analysis of problem involving heat transfer by_______________?
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A. Transient conduction

B. Natural convection

C. Steady state conduction

D. Forced convection

287. Vibrations in the tubes of a shell and tube heat exchanger is induced due to the _________________?
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A. Vibrations transmitted through piping and/or supports due to external reasons

B. Flow of fluid on the tube and shell sides

C. All A., B. and C.

D. Oscillations in the flow of shell/tube sides fluid

288. Which of the following is unimportant in forced convection ?
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A. Prandtl number

B. None of these

C. Reynolds number

D. Grashoff number
289. Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids ?
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A. Nusselt equation

B. None of these

C. Sieder-Tate equation

D. Dittus-Boelter equation

290. Thermal conductivities of most of the liquids _______________ with rise in temperature?
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A. Remains unchanged

B. Decreases

C. Increases

D. May increase or decrease; depends on the liquid

291. Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the _____________ zone?
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A. Laminar

B. Transition

C. Both A & B

D. Highly turbulent
292. LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is __________________?
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A. < 1

B. > 1

C. 0

D. 1

293. In a heat exchanger, one transfer unit means___________________?
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A. A section of the exchanger in which change in temperature of one stream equals the average

B. ving force in the section</strong>

C. The size of the exchanger in which heat transfer rate is 1 kcal/hr

D. Both A. and B.

E. None of these

294. Correction is applied to LMTD for __________ flow?
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A. Parallel

B. None of these

C. Cross

D. Counter

295. Which of the following has the minimum absorptivity ?
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A. Aluminium foil

B. Coal dust

C. Refractory bricks

D. Iron plates

296. 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. 5.6

B. 0.0035

C. 0.025

D. 3.5

297. Low thermal conductivity of heat insulating materials is due to its_______________?
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A. High specific heat

B. Dense structure

C. None of these

D. High proportion of air space
298. The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness) _________________?
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A. Independent of t

B. ? 1/t

C. ? t

D. ? ?t

299. A diathermanous substance _______________ the thermal radiation completely?
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A. Absorbs

B. Reflects

C. None of these

D. Transmits
300. In case of a vertical tube evaporator, with increase in the liquor level, the ____________ is increased?
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A. Velocity of circulation

B. Liquor-film co-efficient

C. Both A. and B.

D. Neither A. and B.