Molecular Physics | Thermodynamics Answers

An exterior wall of a house may be approximated by a 0.1 m layer of

common brick (k = 0.7 W/m°C) followed by a 0.04 m layer of gypsum plaster (k = 0.48 W/m°C).

What thickness of loosely packed rock wool insulation (k = 0.065 W/m°C) should be added to

reduce the heat loss or (gain) through the wall by 80 per cent?

. A mild steel tank of wall thickness 12 mm contains water at 95°C. The

thermal conductivity of mild steel is 50 W/m°C, and the heat transfer coefficients for the inside

and outside the tank are 2850 and 10 W/m2°C, respectively. If the atmospheric temperature is

15°C, calculate :

(i) The rate of heat loss per m2 of the tank surface area ;

(ii) The temperature of the outside surface of the tank

A thick walled tube of stainless steel with 20 mm inner diameter and

40 mm outer diameter is covered with a 30

mm layer of asbestos insulation (k = 0.2 W/

m°C). If the inside wall temperature of the pipe

is maintained at 600°C and the outside

insulation at 1000°C, calculate the heat loss

per metre of length.

Hot air at a temperature of 65°C is flowing through a steel pipe of 120 mm

diameter. The pipe is covered with two layers of different insulating materials of thickness 60 mm

and 40 mm, and their corresponding thermal conductivities are 0.24 and 0.4 W/m°C. The inside

and outside heat transfer coefficients are 60 and 12 W/m°C. The atmosphere is at 20°C. Find the

rate of heat loss from 60 m length of pipe

Hot air at a temperature of 65°C is flowing through a steel pipe of 120 mm

diameter. The pipe is covered with two layers of different insulating materials of thickness 60 mm

and 40 mm, and their corresponding thermal conductivities are 0.24 and 0.4 W/m°C. The inside

and outside heat transfer coefficients are 60 and 12 W/m°C. The atmosphere is at 20°C. Find the

rate of heat loss from 60 m length of pipe.

A 150 mm steam pipe has inside dimater of 120 mm and outside diam￾eter of 160 mm. It is insulated at the outside with asbestos. The steam temperature is 150°C and

the air temperature is 20°C. h (steam side) = 100 W/m2°C, h (air side) = 30 W/m2°C, k (asbestos)

= 0.8 W/m°C and k (steel) = 42 W/m°C. How thick should the asbestos be provided in order to

limit the heat losses to 2.1 kW/m2 ?

. A spherical shaped vessel of 1.4 m diameter is 90 mm thick. Find the rate

of heat leakage, if the temperature difference between the inner and outer surfaces is 220°C.

Thermal conductivity of the material of the sphere is 0.083 W/m°C.