1) The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________? a. (ΔT)1/4 b. (ΔT)1/2 c. (ΔT)5/4 d. (ΔT)3/4
|
||||
2) 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________________? a. ha = hl b. ha = 2hl c. ha = 0.5 hl d. ha = 0.75 hl
|
||||
3) Harmonic mean temperature difference is given by_________________? a. √(ΔT1 . ΔT2) b. 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2) c. 2 (ΔT1 . ΔT2)/(ΔT1 – ΔT2) d. (ΔT1 – ΔT2)/(ΔT1 . ΔT2)
|
||||
4) 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)? a. 0.5 b. 0.05 c. 0.1 d. 0.15
|
||||
5) Fourier’s law of heat conduction applies to _____________ surfaces? a. Isothermal b. Non-isothermal c. Both A. and B. d. Neither A. and B.
|
||||
6) Which of the following is generally considered as opaque surface towards radiations ? a. Gases b. Solids c. Liquids d. Both B. and C.
|
||||
7) 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_____________? a. Vertical heat exchanger with steam on tube side b. Vertical heat exchanger with steam on shell side c. Horizontal heat exchanger with steam on tube side d. Horizontal heat exchanger with steam on shell side
|
||||
8) The steam ejector is used to__________________? a. Remove condensate from the steam pipelines b. Create vacuum c. Superheat the steam d. None of these
|
||||
9) Heat flux is the time rate of heat transfer per unit_______________? a. Length b. Area c. Volume d. None of these
|
||||
10) The actual temperature drop across the heating surface in an evaporator depends on the_________________? a. Feed b. Depth of liquid over heating surface c. Pressure difference between steam chest and vapour space d. All A., B. and C.
|
||||
11) 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________________? a. Surrounding temperature b. Average temperature of the fin c. Temperature of the fin end d. Constant temperature equal to that of the base
|
||||
12) Thermal conductivity of a conducting solid material depends upon its_______________? a. Temperature b. Porosity c. Both A. & B. d. Neither A. nor B.
|
||||
13) When vaporisation takes place directly at the heating surface, it is called________________? a. Film boiling b. Nucleate boiling c. Vapour binding d. None of these
|
||||
14) As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the_______________? a. Temperature of the body only b. Wavelength of monochromatic radiation c. Both A. and B. d. Nature of material of body
|
||||
15) Fourier’s law applies to the heat transfer by__________________? a. Convection b. Radiation c. Conduction d. All A., B. & C.
|
||||
16) 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__________________? a. Painting the surface black b. Painting the surface white (with aluminium paint) c. Giving the surface a mirror finish d. Roughening the surface
|
||||
17) Heat produced when a steady state current, I passes through an electrical conductor having resistance, ‘R’ is___________________? a. IR b. I2R c. IR2 d. I2R2
|
||||
18) In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to _____________ the velocity head? a. Twice b. Four times c. Square root of d. Square of
|
||||
19) The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K = 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is – 5°C. The outside wall temperature is___________________? a. 25°C b. 30°C c. 35°C d. 40°C
|
||||
20) Dittus-Boelter equation cannot be used for molten metals mainly due to its very low_____________________? a. Prandtl number b. Grashoff number c. Thermal conductivity d. Viscosity
|
||||
21) Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively) ? a. C/E b. E/C c. CE d. 1/CE
|
||||
22) Which of the following is unimportant in forced convection ? a. Reynolds number b. Prandtl number c. Grashoff number d. None of these
|
||||
23) 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? a. Laminar b. Transition c. Both A & B d. Highly turbulent
|
||||
24) The number of kg vaporised per kg of steam fed to the evaporator is defined as____________? a. Capacity b. Rate of evaporation c. Economy d. Rate of vaporisation
|
||||
25) Vacuum is generally maintained in the vapour space of an evaporator mainly to__________________? a. Get economical temperature difference by using moderate pressure steam b. Facilitate forward feeding in multiple effect evaporation c. Concentrate heat sensitive materials d. Achieve very high concentration of the final product
|
||||
26) With increase in porosity, the thermal conductivity of a solid substance__________________? a. Increases b. Decreases c. Remains unchanged d. May increase or decrease; depends on the solid
|
||||
27) Which type of heat exchanger is preferred for heavy heat loads ? a. Double pipe b. Plate fine c. Series and parallel set of shell and tube d. None of these
|
||||
28) The unit of heat transfer co-efficient in SI unit is____________________? a. J/M2°K b. W/m2°K c. W/m°K d. J/m°K
|
||||
29) If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid_________________? a. Remains unchanged b. Increases c. Increases or decreases depending on number of shell passes d. Decreases
|
||||
30) Fouling factor_____________________? a. Is a dimensionless quantity b. Does not provide a safety factor for design c. Accounts for additional resistances to heat flow d. None of these
|