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1) Nusselt number is the ratio of the ____________________? a. Temperature gradient of the wall to that across the entire pipe b. Temperature difference to the temperature gradient at the wall c. Heat flux at the wall to that across the entire pipe d. None of these
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2) Heat transfer by ____________ may not necessarily require the presence of a medium? a. Conduction b. Natural convection c. Forced convection d. Radiation
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3) Which of the following situations can be approximated to a steady state heat transfer system ? a. A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmospheric air at 35°C b. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C c. Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C d. A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C
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4) Use of transverse baffles in a shell and tube heat exchanger is done to increase the___________________? a. Rate of heat transfer b. Flow velocity c. Turbulence of shell side fluid d. All A., B. and C.
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5) Evaporation by thermo compression results in the _________________________? a. Saving of steam b. Realisation of multiple effect economy in a single effect c. Both A. and B. d. None of these
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6) The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of ‘n’ is exactly 4 for__________________? a. Black painted bodies only b. All bodies c. Polished bodies only d. A black body
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7) Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of ____________ °C? a. 40 b. 95 c. 70 d. 50
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8) A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun ? a. Yellow paint b. White paint c. Black paint d. Grey paint
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9) Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around _____________ metres/second? a. 1 b. 10 c. 20 d. 30
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10) Temperature profile in steady state heat transfer is________________? a. Asymptotic b. Hyperbolic c. Parabolic d. Linear
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11) A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is ______________ °C? a. 6 b. 12 c. 18 d. 24
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12) Economy of a multiple effect evaporator depends upon the _____________________? a. Heat balance consideration b. Rate of heat transfer c. Both A. and B. d. Neither A. nor B.
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13) Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is ________________ law? a. Stefan’s b. Dalton’s c. Wien’s d. Kirchoff’s
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14) Trap is used to remove ________________ from steam pipe lines? a. Steam b. Condensate c. Non-condensable d. None of these
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15) Prandtl number is given by__________________? a. CP μ/a b. hD/k c. CP μ/k d. μ/h CP
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16) Prandtl number is the ratio of________________? a. Momentum diffusivity to mass diffusivity b. Momentum diffusivity to thermal diffusivity c. Thermal diffusivity to mass diffusivity d. Thermal diffusivity to momentum diffusivity
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17) In the free convection regime of pool boiling, the heat flux is proportional to__________________? a. Δt1/2 b. Δt2 c. Δt5/4 d. Δt
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18) Radiation heat losses from satisfactorily insulated high pressure boiler may be about _____________ percent? a. 1 b. 7 c. 18 d. 26
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19) In SI units, fouling factor is expressed in __________________? a. m2°K/W b. W/m2°K c. m2°K d. m°K/W
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20) Kg of liquid evaporated per hour in an evaporator is defined as its_________________? a. Capacity b. Economy c. Steam load d. None of these
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21) In forced convection, the heat transfer depends on _______________? a. Re, Pr b. Re, Gr c. Mainly Gr d. Re only
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22) A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is________________? a. 125 b. 133 c. 150 d. 160
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23) The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2. The flux, when the element temperature is increased to 1000°C for the same furnace temperature is_____________________? a. 11.2 kW/m2 b. 12.0 kW/m2 c. 14.6 kW/m2 d. 16.5 kW/m2
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24) The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re)0.8 (Pr)0.4] cannot be used for________________? a. Low Reynold’s number b. Very low Grashoff number c. Molten metals d. All A., B. and C.
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25) Kirchoff’s law is applicable to________________? a. Monochromatic radiation only b. Total radiation only c. Both A. and B. d. Only volumes and not to surfaces
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26) Agitated film evaporator is suitable for concentrating _____________ liquids? a. Foaming b. Viscous c. Very thin d. Corrosive
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27) The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m2.K. At steady state, the temperature of the right face in °C is____________________? a. 77.2 b. 71.2 c. 63.8 d. 48.7
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28) When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as ___________________ boiling? a. Pool b. Nucleate c. Transition d. Film
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29) The main purpose of providing fins on heat transfer surface is to increase the_________________? a. Temperature gradient b. Mechanical strength of the equipment c. Heat transfer area d. Heat transfer co-efficient
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30) Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is__________________? a. 0.5 b. 2 c. 10 d. 100
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