Maximum heat dissipation occurs from a steel wire (k = 0.5 W/m. k) of 15 mm diameter exposed to air (h = 20W/m2 .k), when the insulation thickness is ________________ mm?

Related Mcqs:

1. 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

2. 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

3. 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

4. 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

5. 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

6. The heat treatment to which the steel wire containing > 0.25% carbon is subjected to is___________________?

   A. Full annealing
   B. Bright annealing
   C. Patenting
   D. None of these

7. Coating thickness in case of galvanising of steel sheet generally corresponds to the deposition of _______________ gms of zinc per m2 of steel strip ?

   A. 5-10
   B. 1000-1500
   C. 120-500
   D. 1500-3000

8. Out of the following, maximum temperature drop for a given heat flow & for the same thickness will be in the case of________________?

   A. Steel
   B. Glass wood
   C. Copper
   D. Fireclay bricks

9. Maximum change in the hardness of martensite occurs in the carbon content range of _____________ percent in steel?

   A. 0.01 to 0.10
   B. 0.2 to 0.4
   C. 0.5 to 0.7
   D. 0.8 to 1.0

10. In case of water (Prandtl number ≈ 6) flowing over a flat plate heated over the entire length, the thermal boundary layer thickness as compared to hydrodynamic boundary layer thickness is ?

    A. Less
    B. More
    C. Equal
    D. Unpredictable