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

Related Mcqs:

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

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

2. Thermal diffusivity of a material __________________?

   A. Has the unit m2 /sec
   B. Is defined as K/ρ . Cp
   C. Is the ratio of thermal conductivity to thermal capacity
   D. All A., B. and C.

3. Thermal diffusivity is given by__________________?

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

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

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

5. 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

6. 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

7. 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

8. 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

9. A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is ______________?

   A. 5.6
   B. 0.025
   C. 3.5
   D. 0.0035

10. “The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium”. This is ______________ law?

    A. Kirchoff’s
    B. Planck’s
    C. Wien’s displacement
    D. Stefan-Boltzmann