Multiple Choice Questions on Heat and Temperature with Answers pdf - Set 31 - ObjectiveBooks

# Practice Test: Question Set - 31

1. Heat flux through several resistances in series in analogous to the current flowing through several
(A) Resistances in parallel
(B) Capacitors in series
(C) Resistances in series
(D) None of these

2. Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by
(A) Keeping the heat transfer surface clean
(B) Enhancing the fluid pumping rate
(C) Increasing the tube length
(D) None of these

3. For a counter current heat exchanger with Tih = 80°C, T°c = 60°C, T°h = 50°C and Tic = 30°C, and the temperature difference between the two streams being the same everywhere along Z, the direction of flow of hot fluid. The temperature profile should satisfy
(A) d2T/dZ2 > 0
(B) d2T/dZ2 = 0
(C) d2T/dZ2 < 0
(D) dT/dZ = 0

4. Which is the most suitable for the concert-ration of highly concentrated solution?
(A) Open pan evaporation
(B) Long tube vertical evaporator
(C) Agitated film evaporator
(D) None of these

5. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally
(A) Decreases
(B) Increases
(C) Remains unchanged
(D) Increases exponentially

6. 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
(A) Ellipse
(B) Straight line
(C) Parabola
(D) Circular arc

7. With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer
(A) Decreases
(B) Increases
(C) Increases exponentially
(D) Remain unaffected

8. Prandtl number is the ratio of
(A) Mass diffusivity to thermal diffusivity
(B) Momentum diffusivity to thermal diffusivity
(C) Thermal diffusivity to mass diffusivity
(D) Thermal diffusivity to momentum diffusivity

9. Double pipe heat exchangers are preferably useful, when
(A) High viscosity liquid is to be cooled
(B) Requirement of heat transfer area is low
(C) Overall heat transfer co-efficient is very high
(D) A corrosive liquid is to be heated

10. A hot body will radiate heat most rapidly, if its surface is
(A) White & rough
(B) Black & rough
(C) White & polished
(D) Black & polished

11. Rate of heat transfer by vaporization from pools of water is affected by the
(A) Nature of heating surface and distribution of bubbles
(B) Surface tension of water
(C) Viscosity of water
(D) All (a), (b) and (c)

12. Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is
(A) 1
(B) < 1
(C) > 1
(D) > 5

13. The purpose of providing bleed points in the evaporator is to
(B) Remove the product
(C) Facilitate removal of non-condensable gases
(D) Create vacuum

14. Choose the most important factor on which the heat conducted through a wall in a unit time will depend on?
(A) Thickness of the wall
(B) Area of the wall perpendicular to heat flow
(C) Material of the wall
(D) Temperature difference between the two surfaces of the wall

15. With increase in temperature, the thermal conductivity of steel
(A) Increases
(B) Decreases
(C) Remains unchanged
(D) Increases exponentially

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