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 co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?

Heat Transfer
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 co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?

81.25

43.75

48.25

35.5

81.25

43.75

48.25

35.5

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Heat Transfer
Log mean temperature difference (LMTD) cannot be used, if

the heat capacity is not constant and there is a phase change.

there exists an unsteady state

heat transfer co-efficient over the entire heat exchanger is not constant

none of the listed here

the heat capacity is not constant and there is a phase change.

there exists an unsteady state

heat transfer co-efficient over the entire heat exchanger is not constant

none of the listed here

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Heat Transfer
1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m² and the overall heat transfer co-efficient to the liquid is 1500 W/m².°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be

44 min

22 min

51 min

15 min

44 min

22 min

51 min

15 min

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Heat Transfer
The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

Giving the surface a mirror finish

Painting the surface white (with aluminium paint)

Painting the surface black

Roughening the surface

Giving the surface a mirror finish

Painting the surface white (with aluminium paint)

Painting the surface black

Roughening the surface

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Heat Transfer
Steam traps are provided in steam carrying pipelines to

none of the listed here

condense steam

remove condensate and inert gases

release excess steam pressure by bleeding steam.

none of the listed here

condense steam

remove condensate and inert gases

release excess steam pressure by bleeding steam.

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Heat Transfer
The critical radius 'r' of insulation on a pipe is given by

r = k/h

r = 2k/h

r = k/2h

r = h/k

r = k/h

r = 2k/h

r = k/2h

r = h/k

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Heat Transfer

Heat Transfer Log mean temperature difference (LMTD) cannot be used, if

Heat Transfer The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

Heat Transfer Steam traps are provided in steam carrying pipelines to

Heat Transfer The critical radius 'r' of insulation on a pipe is given by

Heat Transfer
Log mean temperature difference (LMTD) cannot be used, if

Heat Transfer
The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

Heat Transfer
Steam traps are provided in steam carrying pipelines to

Heat Transfer
The critical radius 'r' of insulation on a pipe is given by