chemical engineering heat transfer chemical engineering Mcqs
401. The rate of heat transfer through a pipe wall is given by, q = 2? k (Ti T0)/ln (ri/r0). For cylinder of very thin wall, q can be approximated by__________________?
comments icon0

A. q = 2? k (Ti T0)/(r0/ri)

B. q = 2? ri k (Ti T0)/(r0/ri)

C. q = [2? k (Ti + T0)/2]/ln (ri/r0)

D. q = 2? k (Ti T0)/[(r0 + ri)/2]
402. A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case ?
comments icon0

A. The cooling rate will be the same for the two spheres and hence the two spheres will have

B. al temperatures at any instant

C. Both the spheres will emit equal amount of radiation per unit time in the beginning

D. Both will absorb equal amount of radiation from the surrounding in the beginning

E. Both B. & C.
403. Radiant energy received by a body is proportional to (where, d = the distance between the object emitting radiation and that receiving it.) ?
comments icon0

A. ?d

B. d1.5

C. d

D. d2
404. Heat transfer in the laminar sub-layer in case of a liquid flowing through a pipe, is mostly by__________________?
comments icon0
A. Conduction

B. Eddies current

C. Convection

D. None of these

405. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the___________________?
comments icon0

A. Buffer zone

B. Turbulent core

C. Both A. and B.

D. Viscous sub-layer
406. 1 BTU/hr.ft.F is equal to _____________ kcal/hr. m.C?
comments icon0

A. None of these

B. 1

C. 4.88

D. 1.49
407. Baffle spacing ____________________?
comments icon0

A. Should be less than one fifth the diameter of the shell

B. Should be less than the inside diameter of the shell

C. None of these

D. Is not the same as baffle pitch

408. The ratio of kinematic viscosity to thermal diffusivity is called the _______________ number?
comments icon0

A. Peclet

B. Nusselt

C. Stanton

D. Prandtl
409. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is______________?
comments icon0

A. Dependent on NRe only

B. 3.66

C. 88.66

D. 1.66

410. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface) ?
comments icon0

A. h0/2K

B. K/h0

C. 2K/h0

D. h0/K

411. Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is __________________?
comments icon0

A. None of these

B. Uniformly distributed throughout the fluid

C. In the central core of the fluid

D. Mainly confined to a thin film of fluid near the surface
412. Pick out the wrong statement?
comments icon0

A. Steam jet ejector is used for vapor compression in a thermal recompression evaporator

B. Heat sensitive materials should be concentrated in high pressure evaporators

C. The capacity of an evaporator is reduced by the boiling point elevation

D. Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger

413. Heat transfer occurs by natural convection because change in temperature causes difference in__________________?
comments icon0

A. Thermal conductivity

B. Viscosity

C. Heat capacity

D. Density
414. The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2. The approximate surface temperature (K) is (Stefan-Boltzmann constant = 5.67 10-8 W/m2.K4) ?
comments icon0

A. 800

B. 1000

C. 727

D. 1200

415. The type of liquor circulation system to be employed in evaporators (viz. natural or forced circulation) is determined mainly by the ______________ of the liquid?
comments icon0
A. Viscosity

B. Thermal conductivity

C. Corrosive nature

D. Density

416. The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by__________________?
comments icon0

A. Painting the surface black

B. Giving the surface a mirror finish

C. Roughening the surface

D. Painting the surface white (with aluminium paint)
417. In an extended surface heat exchanger, fluid having lower co-efficient________________?
comments icon0

A. Should not be used as it gives very high pressure drop

B. Flows outside the tubes

C. Can flow either inside or outside the tubes

D. Flows through the tube

418. In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is_________________?
comments icon0
A. Infinity

B. Same as average heat transfer co-efficient for tube side

C. None of these

D. Zero

419. Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively) ?
comments icon0

A. E/C

B. C/E

C. 1/CE

D. CE

420. Thermal diffusivity is given by__________________?
comments icon0

A. ?Cp/a

B. k/?Cp

C. ?/hCp

D. ?Cp/k

421. Economy of a multiple effect evaporator is not influenced much by the_______________________?
comments icon0

A. Ratio of the weight of the thin liquor to thick liquor

B. Rate of heat transfer

C. Boiling point elevations

D. Temperature of the feed

422. For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in_____________________?
comments icon0
A. Increased economy

B. Decreased economy

C. No effect on economy

D. Lower capacity

423. The advantage of backward feed multiple effect evaporators over forward feed units is that___________________?
comments icon0

A. Heat sensitive material can be handled

B. Most concentrated liquid is at highest temperature

C. Equal heat transfer co-efficients exist in various effects

D. There is no additional cost of pumping

424. Reynolds analogy states that_________________?
comments icon0

A. NRe ? f

B. NNu ? f

C. Nst ? f

D. Nst ? NRe

425. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally ?
comments icon0

A. Remains unchanged

B. Decreases

C. Increases exponentially

D. Increases

426. Dittus-Boelter equation cannot be used for molten metals mainly due to its very low_____________________?
comments icon0

A. Thermal conductivity

B. Prandtl number

C. Viscosity

D. Grashoff number

427. Fouriers law applies to the heat transfer by__________________?
comments icon0

A. Radiation

B. All A., B. & C.

C. Conduction

D. Convection

428. In case of evaporators, liquid entrainment results primarily due to_________________?
comments icon0

A. High evaporation rate

B. High vacuum in the evaporator

C. Foaming of the solution

D. High heat transfer rate

429. With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer ?
comments icon0

A. Remain unaffected

B. Increases exponentially

C. Increases

D. Decreases
430. Electromagnetic radiations propagate in vacuum with a velocity of _______________ metre/second?
comments icon0

A. 3 1012

B. 3 1010

C. 3 108

D. 3 105

431. A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is__________________?
comments icon0

A. 6000

B. 48000

C. 60000

D. 24000
432. Circulation pump is located below the evaporator to___________________?
comments icon0

A. Avoid cavitation

B. None of these

C. Avoid frequent priming

D. Create more suction head
433. Baffles in the shell side of a shell and tube heat exchanger ?
comments icon0

A. Decrease the shell side heat transfer co-efficient

B. Force the liquid to flow parallel to the bank

C. Increase the shell side heat transfer co-efficient

D. Increase the cross-section of the shell side liquid

434. Multiple effect evaporators ar used to___________________?
comments icon0

A. Increase the steam economy & decrease the capacity

B. Decrease the steam economy & increase the capacity

C. Decrease the steam economy & the capacity

D. Increase the steam economy & the capacity
435. If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?
comments icon0

A. ha = hl

B. ha = 0.5 hl

C. ha = 2hl

D. ha = 0.75 hl

436. In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of___________________?
comments icon0

A. Chemical potentials

B. Activity co-efficients

C. Mass transfer co-efficients

D. Concentrations
437. In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always__________________?
comments icon0

A. > 1

B. ?

C. 1

D. < 1
438. Steam is routed through the tube in case of a ______________ evaporator?
comments icon0

A. Long tube vertical

B. Short tube vertical

C. Basket type

D. Horizontal tube
439. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for_________________?
comments icon0

A. Equal for all the three

B. Cylinder

C. Cube

D. Sphere

440. Air is best heated with steam in a heat exchanger of__________________?
comments icon0

A. Double pipe type with fin on steam side

B. Shell and tube type

C. Double pipe type with fin on air side

D. Plate type

441. Which of the following has the minimum thermal conductivity ?
comments icon0

A. Carbon black

B. Nitrogen

C. Steel

D. Tar

442. In a heat exchanger, floating head is provided to____________________?
comments icon0

A. Facilitate cleaning of the exchanger

B. Increase the heat transfer area

C. Increase log mean temperature gradient

D. Relieve stresses caused by thermal expansion
443. Vacuum is generally maintained in the vapour space of an evaporator mainly to__________________?
comments icon0

A. Achieve very high concentration of the final product

B. Concentrate heat sensitive materials

C. Get economical temperature difference by using moderate pressure steam

D. Facilitate forward feeding in multiple effect evaporation

444. For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then__________________?
comments icon0

A. hf > hd

B. hf = hd

C. hf < hd

D. hf could be greater or smaller than hd

445. What is the steam economy in case of a single effect evaporator system ?
comments icon0

A. > 1

B. 1

C. < 1

D. 0.1

446. Value of Prandtl number for water ranges from_________________?
comments icon0

A. 1 to 2

B. 5 to 10

C. 100 to 500

D. 1000 to 2000

447. In the equation Q = UA?t; ?t is_________________________?
comments icon0

A. The difference of average bulk temperatures of hot and cold fluids

B. Logarithmic mean temperature difference

C. Arithmetic mean temperature difference

D. Geometric mean temperature difference

448. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is_________________?
comments icon0

A. Minimum

B. Zero

C. Maximum

D. Infinity

449. Graetz number is given by__________________?
comments icon0

A. mCp/k?

B. k?/mCp

C. mCp/kL

D. kL/mCp

450. The actual temperature drop across the heating surface in an evaporator depends on the_________________?
comments icon0

A. Feed

B. Pressure difference between steam chest and vapour space

C. All A., B. and C.

D. Depth of liquid over heating surface