In Biot number, the characteristic length used is the ratio of the _______________ of the solid?

Related Mcqs:

1. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?

   A. 0.5
   B. 0.05
   C. 0.1
   D. 0.15

2. 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

3. In which mode of heat transfer, the Biot number is important ?

   A. Transient heat conduction
   B. Natural convection
   C. Forced convection
   D. Radiation

4. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for_________________?

   A. Cube
   B. Cylinder
   C. Sphere
   D. Equal for all the three

5. Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the _____________ zone?

   A. Laminar
   B. Transition
   C. Both A & B
   D. Highly turbulent

6. When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is _______________?

   A. Free convection
   B. Entry length problem in laminar forced conduction (developing thermal boundary layer)
   C. Mixed convection (both free and forced)
   D. Forced convection

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

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

8. In case of a super-cooled solution, which is on the verge of crystallisation, the free energy of the solution as compared to that of the solid is ________________?

   A. More
   B. Less
   C. Same
   D. More or less; depends on the nature of solution

9. Thermal conductivity of a conducting solid material depends upon its_______________?

   A. Temperature
   B. Porosity
   C. Both A. & B.
   D. Neither A. nor B.

10. Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface ?

    A. Liquid density
    B. Liquid viscosity
    C. Hot surface temperature
    D. Interfacial tension