A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is________________?

Related Mcqs:

1. A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is ______________ °C?

   A. 6
   B. 12
   C. 18
   D. 24

2. A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when_________________?

   A. CPA > CPB
   B. CPA < CPB
   C. kA < 0.5 kB
   D. kA >2 kB

3. The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K = 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is – 5°C. The outside wall temperature is___________________?

   A. 25°C
   B. 30°C
   C. 35°C
   D. 40°C

4. Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade ?

   A. 35.5
   B. 43.75
   C. 81.25
   D. 48.25

5. The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C- 1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat loss from the outer surface in W.m-2is__________________?

   A. 165.4
   B. 167.5
   C. 172.5
   D. 175

6. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows _____________ law?

   A. Parabolic
   B. Hyperbolic
   C. Linear
   D. Logarithmic

7. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows ____________ law?

   A. Hyperbolic
   B. Parabolic
   C. Linear
   D. Logarithmic

8. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of ‘a’ in SI system will be________________?

   A. W/m.k
   B. W/m
   C. W/m.k2
   D. None, ‘a’ is just a number

9. Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of ____________ °C?

   A. 40
   B. 95
   C. 70
   D. 50

10. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally ?

    A. Decreases
    B. Increases
    C. Remains unchanged
    D. Increases exponentially