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 ?

Related Mcqs:

1. 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

2. Upto the critical radius of insulation, added insulation, will____________________?

   A. Increase the heat loss
   B. Decrease heat loss and will have no effect beyond that
   C. Decrease heat flux
   D. Reduce convection heat loss compared to conduction heat less

3. A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of thermal conductivity 0.14 W/m.K and thickness ______________ metre?

   A. 0.01
   B. 0.1
   C. 0.25
   D. 0.5

4. Thermal diffusivity of a substance is proportional to (where, k = Thermal conductivity) ____________________?

   A. 1/k
   B. k
   C. k2
   D. 1/k2

5. _______________ number determines whether the fluid flow in an open channel is super-critical, critical or sub-critical ?

   A. Mach
   B. Reynolds
   C. Froude
   D. Weber

6. Heat flow across a hollow sphere of inner radius ‘r1’ and outer radius ‘r2’ is directly proportional to__________________?

   A. (r2 – r1)/r1. r2
   B. r1. r2/(r2 – r1)
   C. (r2 + r1)/r1. r2
   D. r1. r2/(r2 + r1)

7. Thermal conductivity of a material does not depend upon its_____________________?

   A. Mass
   B. Volume
   C. Surface area
   D. All A, C & C

8. One face of a furnace wall is at 1030°C and the other face is exposed to room temperature (30°C). If the thermal conductivity of furnace wall is 3 W. m-1. k-1 and the wall thickness is 0.3 m, the maximum heat loss (in W/m) is____________________?

   A. 100
   B. 900
   C. 9000
   D. 10000

9. In the formation of cermets, the ratio of ceramic material to metallic material is usually 80:20. Which of the following is a cermet ?

   A. Zirconia
   B. Alumina
   C. Bakelite
   D. Tungsten carbide

10. 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