The thermal diffusivities for gases are generally_____________________?

Related Mcqs:

1. The thermal diffusivities for solids are generally__________________?

   A. less than those for gases
   B. jess than those for liquids
   C. more than those for liquids and gases
   D. more or less same as for liquids and gases
   E. zerci

2. Heat transfer in liquid and gases takes place by_____________________?

   A. conduction
   B. convection
   C. radiation
   D. conduction and convection
   E. convection and radiation

3. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by___________________?

   A. convection
   B. radiation
   C. conduction
   D. both convection and conduction
   E. none of the above

4. Unit of thermal conductivity in M.K.S. units is ___________________?

   A. kcal/kg m2 °C
   B. kcal-m/hr m2 °C
   C. kcal/hr m2 °C
   D. kcal-m/hr °C
   E. kcal-m/m2 °C

5. Thermal conductivity of solid metals with rise in temperature normally___________________?

   A. increases
   B. decreases
   C. remains constant
   D. may increase or decrease depending on temperature
   E. unpredictable

6. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of__________________?

   A. 0.002
   B. 0.02
   C. 0.01
   D. 0.1
   E. 0.5

7. Thermal conductivity of air with rise in temperature__________________?

   A. increases
   B. decreases
   C. remains constant
   D. may increase or decrease depending on temperature
   E. none of the above

8. Thermal conductivity of a material may be defined as the________________?

   A. quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
   B. quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
   C. heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
   D. all of the above
   E. none of the above

9. Thermal diffusivity is ____________________?

   A. a dimensionless parameter
   B. function of temperature
   C. used as mathematical model
   D. a physical property of the material
   E. useful in case of heat transfer by radiation

10. Thermal diffusivity of a substance is __________________?

    A. directly proportional to thermal con¬ductivity
    B. inversely proportional to density of substance
    C. inversely proportional to specific heat
    D. all of the above
    E. none of the above