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?

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. 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

3. The laminar boundary layer thickness in zero pressure gradient flow over a flat plate along the x-direction varies as x0.5 while the thickness of turbulent boundary layer varies as (where, x = distance from the leading edge) ?

   A. x1.5
   B. x0.8
   C. x-1.5
   D. x-0.8

4. The refractory brick which has good thermal shock resistance at high temperature but cracks on cooling below 400°C is__________________?

   A. Magnesite
   B. Chrome
   C. Silica
   D. Fireclay

5. The ratio of thermal & electrical conductivity is same for all the metals at the same temperature; and at around room temperature, this ratio is proportional to(where, T = absolute temperature, °K) ?

   A. T
   B. 1/T
   C. T2
   D. 1/T2

6. 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.

7. Temperature of hot gases flowing in a pipe is measured by a thermocouple inserted in the thermal well. The thermal well made of ______________ will facilitate the most accurate measurement of the temperature ?

   A. Copper
   B. Steel
   C. Aluminium
   D. Brass

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. In a boundary layer developed along the flow, the pressure decreases in the downstream direction. The boundary layer thickness in this case will _______________?

   A. Decrease gradually
   B. Increase gradually
   C. Increase rapidly
   D. Remain constant

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

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