A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large ?

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Pick out the wrong statement ?

A. In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2 B. Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number C. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt … Pick out the wrong statement ?Read More...

In forced convection, the Nusselt number is a function of ____________________?

A. Re and Pr B. Re and Gr C. Pr and Gr D. Re and Sc...

Pick out the correct statement ?

A. Higher is the temperature of the radiating body, higher is the wavelength of radiation B. Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder C. The wavelength corresponding to maximum mono-chromatic emissive power increases with rise in temperature D. Solid angle subtended by the finite surface at … Pick out the correct statement ?Read More...

In forced convection, the heat transfer depends on _______________?

A. Re, Pr B. Re, Gr C. Mainly Gr D. Re only...

A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?

A. Greater than that for un-insulated steam pipe B. Less than that of the un-insulated steam pipe C. Equal to that of the un-insulated steam pipe D. Less than the steam pipe with 5 cms insulation...