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Mechanical Engineering :: Heat and Mass Transfer

  1. Film coefficient is defined as the ratio of

  2. A.

     Thermal conductivity to the equivalent thickness of the film of fluid

    B.

     Temperature drop through the films of fluids to the thickness of film of fluids

    C.

     Thickness of film of fluid to the thermal conductivity

    D.

     Thickness of film of fluid to the temperature drop through the films of fluids


  3. The highest thermal diffusivity is of

  4. A.

     Iron

    B.

     Lead

    C.

     Concrete

    D.

     Wood


  5. The rate of energy transferred by convection to that by conduction is called

  6. A.

     Stanton number

    B.

     Nusselt number

    C.

     Biot number

    D.

     Peclet number


  7. Thermal conductivity of water _________ with rise in temperature.

  8. A.

     Remain same

    B.

     Decreases

    C.

     Increases

    D.

     May increase or decrease depending upon temperature


  9. Which of the following property of air does not increase with rise in temperature?

  10. A.

     Thermal conductivity

    B.

     Thermal diffusivity

    C.

     Density

    D.

     Dynamic viscosity


  11. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of

  12. A.

     1:1

    B.

     2: 1

    C.

     1: 2

    D.

     4: 1


  13. Thermal conductivity of glass wool varies from sample to sample because of variation in

  14. A.

     Composition

    B.

     Density

    C.

     Porosity

    D.

     All of the above


  15. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

  16. A.

     Convection

    B.

     Radiation

    C.

     Forced convection

    D.

     Free convection


  17. According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

  18. A.

     Absolute temperature

    B.

     Square of temperature

    C.

     Fourth power of absolute temperature

    D.

     Fourth power of temperature


  19. The critical radius is the insulation radius at which the resistance to heat flow is

  20. A.

     Maximum

    B.

     Minimum

    C.

     Zero

    D.

     None of these