The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
A. (COP)R = (COP)HP = 0.6
B. (COP)R = 2.5; (COP)HP = 1.5
C. (COP)R = 1.5; (COP)HP = 2.5
D. (COP)R = (COP)HP = 2.5
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Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the
A. Maximum resistance in the series
B. Sum of all resistances
C. Average of all resistances
D. Minimum resistance presents in the series
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In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is
A. Infinity
B. Zero
C. Same as average heat transfer co-efficient for tube side
D. None of these
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Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place
A. Between two bodies in physical contact with each other
B. Between two bodies not in physical contact with each other
C. From one part of a body to the another part of the same body
D. Both B & C
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At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical?
A. 1
B. < 1
C. > 1
D. None of these
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Pick out the wrong statement.
A. The controlling resistance in case of heating of air by condensing steam is in the air film
B. The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant temperature
C. In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs
D. Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature
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A body is called grey if the monochromatic emissivity of the body is
A. Zero
B. Unity
C. Same for all wavelengths
D. Different for all wavelengths
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Rate of crystallisation does not depend upon the
A. Extent of supersaturation
B. Turbulence within the solution
C. Number and active surface area of the crystals
D. None of these
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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. Kirchoffs
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Stefan-Boltzman law applies to __________ body.
A. Black
B. White
C. Grey
D. Any colour
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__________ paint has the maximum absorption coefficient.
A. Black
B. Yellow
C. White
D. Grey
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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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The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emis-sivities ε x ε y
A. ε x + ε y
B. ε x ⋅ ε y
C. ε x 1 + ε y 1
D. ε x + ε y − ε x ⋅ ε y ε x + ε y
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Heat transfer co-efficient (h1 ) for liquids increases with
A. Increasing temperature
B. Decreasing temperature
C. Decreasing Reynolds number
D. None of these
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Baffle spacing
A. Is not the same as baffle pitch
B. Should be less than one fifth the diameter of the shell
C. Should be less than the inside diameter of the shell
D. None of these
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In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid.
A. Nucleate
B. Pool
C. Low pressure
D. None of these
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The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium. This is __________ law.
A. Kirchoffs
B. Planck's
C. Wien's displacement
D. Stefan-Boltzman
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Solid angle subtended by the finite surface at the radiating element is
A. Called the view factor
B. Called the angle of vision
C. Proportional to the square of the distance between surfaces
D. Expressed in terms of radians
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Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called
A. Radiation
B. Natural convection
C. Forced convection
D. Conduction
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Agitated film evaporator is suitable for concentrating __________ liquids.
A. Foaming
B. Viscous
C. Very thin
D. Corrosive
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