Convection - C. Calculate the rate of formation of ice (in...

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Convection Heat transfer by convection occurs when a fluid, such as air or water, is in contact with an object whose temperature is higher than the temperature of its surroundings. The temperature of the fluid increases and (in most cases) the fluid expands. Being less dense than the surrounding cooler fluid, it rises because of buoyant forces. The surrounding cooler fluid falls to take the place of the rising warmer fluid and a convective circulation is set up. 17.5.3. Radiation Every object emits electromagnetic radiation. The energy spectrum of the radiation emitted depends on the temperature of the object; the average energy increases with increasing temperature. Problem 57P A container of water has been outdoors in cold weather until a 5.0 cm-thick slab of ice has formed on its surface. The air above the ice is at -10
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Unformatted text preview: C. Calculate the rate of formation of ice (in centimeters per hour) on the bottom surface of the ice slab. Take the thermal conductivity of ice to be 0.0040 cal/s . cm . C and the density to be 0.92 g/cm3. The water at the boundary between the water and the ice will be at a temperature of 0 C. The heat transported through 5 cm of ice is equal to This heat is released when water is transformed into ice. The heat of transformation of this process is 79.5 cal/g. Suppose a mass m of water is transformed each second into ice. This produces a total heat equal to H = 79.5 m cal/s This must be equal to the heat flow through the ice: 79.5 m = 0.0080 A A mass m of ice (covering an area A) will have a thickness d, where d is given by Combining the last two expression we obtain for the rate of ice formation:...
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This document was uploaded on 11/25/2011.

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