Heat and Mass Transfer
Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of

0.16736111111111
0.043055555555556
0.084027777777778
0.042361111111111

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Heat and Mass Transfer
Film coefficient is defined as the ratio of

Thermal conductivity to the equivalent thickness of the film of fluid
Thickness of film of fluid to the temperature drop through the films of fluids
Thickness of film of fluid to the thermal conductivity
Temperature drop through the films of fluids to the thickness of film of fluids

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Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

All of these
Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C
Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

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