Thermal diffusivity is given by__________________?

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 the most important in heat transfer by__________________?

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

3. 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

4. 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.

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

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

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. Prandtl number is given by__________________?

   A. CP μ/a
   B. hD/k
   C. CP μ/k
   D. μ/h CP

9. Graetz number is given by__________________?

   A. mCp/kL
   B. kL/mCp
   C. mCp/kμ
   D. kμ/mCp

10. The rate of heat transfer through a pipe wall is given by, q = 2π k (Ti – T0)/ln (ri/r0). For cylinder of very thin wall, q can be approximated by__________________?

    A. q = [2π k (Ti + T0)/2]/ln (ri/r0)
    B. q = 2π ri k (Ti – T0)/(r0/ri)
    C. q = 2π k (Ti – T0)/(r0/ri)
    D. q = 2π k (Ti – T0)/[(r0 + ri)/2]