Thermal diffusivity of a material __________________?

Related Mcqs:

1. The ratio of momentum diffusivity to thermal diffusivity is the ______________ number?

   A. Prandtl
   B. Nusselt
   C. Stanton
   D. Grashoff

2. Thermal diffusivity is given by__________________?

   A. k/ρCp
   B. ρCp/k
   C. μCp/a
   D. μ/hCp

3. Thermal diffusivity is the most important in heat transfer by__________________?

   A. Conduction
   B. Radiation
   C. Condensation
   D. Natural convection

4. The ratio of kinematic viscosity to thermal diffusivity is called the _______________ number?

   A. Peclet
   B. Prandtl
   C. Stanton
   D. Nusselt

5. 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

6. 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

7. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?

   A. 2000
   B. 4000
   C. 5000
   D. 6000

8. 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

9. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of ‘a’ in SI system will be________________?

   A. W/m.k
   B. W/m
   C. W/m.k2
   D. None, ‘a’ is just a number

10. 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