Thermal insulation of roofs can be obtained by covering the top exposed surface of the roof with                  

Related MCQs

• Presence of moisture in the thermal insulating material increases thermal insulation while the presence of air spaces decreases thermal insulation.
• A water-heater is covered up with insulation boards over a total surface area of 3 m2. The inside board surface is at 75°C and the outside surface is at 20°C and the board material has a conductivity of 0.08 W/m K. How thick a board should it be to limit the heat transfer loss to 200 W ?
• A composite wall is made of two layers of thickness δ1 and δ2 having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?
• A water-heater is covered with insulation boards over a total surface area of 3 m2. The inside board surface is at 75°C and the outside being at 20°C and the conductivity of material being 0.08 W/m K. Find the thickness of board to limit the heat transfer loss to 200 W ?
• Thermal insulation keeps the room cool in winters and hot in summers.
• According to Indian Standards, it is recommended that the overall thermal transmittance of a roof should not be more than                kcal/m2 h deg C.
• Which of the following is the correct relationship between thermal resistance and thermal conductivity?
• Which of the following is the correct relation between thermal transmittance and thermal time constant?
• A simple pendulum is attached to the roof of a lift. If the time period of oscillation, when the lift is stationary is T, then the frequency of oscillation when the lift falls freely, will be                        
• The black grille on the back of a refrigerator has a surface temperature of 35°C with a surface area of 1 m2. Heat transfer to the room air at 20°C takes place with convective heat transfer coefficient of 15 W/Km^2. How much energy is removed during 15 minutes of operation?