Which of the following phenomenon will exhibit the minimum heat transfer ?

Related Mcqs:

1. A steam pipe is intended to be insulated with two layers of insulating materials of different thermal conductivities. For minimum heat transfer to take place_________________?

   A. The better insulation material should be put just next to pipe (i.e., inside)
   B. The better insulating material should be put outside
   C. Either of the insulating material could be put on either side
   D. Steam temperature is considered before deciding as to which insulating material is to be put
   inside (i.e., just next to the pipe)

2. A reduction in thermal resistance during heat transfer does not occur in the___________________?

   A. Convection heat transfer by stirring the fluid and cleaning the heating surface
   B. Conduction heat transfer by reduction in the material thickness and increase in the thermal
   conductivity
   C. Radiation heat transfer by increasing the temperature and reducing the emissivity
   D. None of these

3. Transition from laminar to turbulent zone in free convection heat transfer is governed by the critical value of ?

   A. Grashoff number
   B. Grashoff number & Reynolds number
   C. Reynolds number
   D. Grashoff number & Prandtl number

4. Heat transfer to the water wall in a high pressure water wall type boiler furnace is mainly by_________________?

   A. Conduction
   B. Convection
   C. Radiation
   D. Both A. & B.

5. What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively ?

   A. 2
   B. 8
   C. 10
   D. 40

6. A thin, flat & square plate measuring 2 m × 2 m is freely hanging in ambient air at 25°C. It is exposed to the solar radiation falling on one side of the plate at the rate of 500 W/m2. The plate temperature will remain constant at 30°C, if the convective heat transfer co-efficient is ________________ W/m2 °C ?

   A. 50
   B. 100
   C. 150
   D. 200

7. In a furnace with heating element temperature at 1700°C, the dominant mechanism of heat transfer will be__________________?

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

8. Heat transfer by ______________ is almost absent in case of fluidised bed drying operation?

   A. Radiation
   B. Conduction
   C. Convection
   D. Both B. & C.

9. The efficiency of a Carnot heat engine operating between absolute temperatures T1 and T2 (when, T1 > T2) is given by (T1 – T2)/T1. The co-efficient of performance (CO.P.) of a Carnot heat pump operating between T1 and T2 is given by_________________?

   A. T1/(T1-T2)
   B. T2/(T1-T2)
   C. T1/T2
   D. T2/T1

10. Which of the following phenomenon/ phenomena is/are diffusion controlled ?

    A. Dislocation climb
    B. Cross-slip
    C. Twinning
    D. Recrystallisation