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Unformatted text preview: ation of water.
10–28E Repeat Problem 10–27E for a platinum-plated heating element.
10–29E Reconsider Problem 10–27E. Using EES (or
other) software, investigate the effect of surface temperature of the heating element on the boiling heat
transfer coefficient, the electric power, and the rate of evaporation of water. Let the surface temperature vary from 260°F to
300°F. Plot the boiling heat transfer coefficient, the electric
power consumption, and the rate of evaporation of water as a
function of the surface temperature, and discuss the results.
10–30 Cold water enters a steam generator at 15°C and
leaves as saturated steam at 100°C. Determine the fraction of
heat used to preheat the liquid water from 15°C to the saturation temperature of 100°C in the steam generator.
Answer: 13.6 percent 10–31 Cold water enters a steam generator at 20°C and
leaves as saturated steam at the boiler pressure. At what pressure will the amount of heat needed to preheat the water to saturation temperature be equal to the heat needed to vaporize the
liquid at the boiler pressure?
10–32 Reconsider Problem 10–31. Using EES (or
other) software, plot the boiler pressure as a
function of the cold water temperature as the
temperature varies from 0°C to 30°C, and discuss the results.
10–33 A 50-cm-long, 2-mm-diameter electric resistance
wire submerged in water is used to determine the boiling
heat transfer coefficient in water at 1 atm experimentally. The
wire temperature is measured to be 130°C when a wattmeter cen58933_ch10.qxd 9/4/2002 12:38 PM Page 556 556
HEAT TRANSFER will the average heat transfer coefficient for the entire stack of
tubes be equal to half of what it is for a single horizontal tube? 1 atm
3.8 kW 130°C FIGURE P10–33
indicates the electric power consumed to be 3.8 kW. Using
Newton’s law of cooling, determine the boiling heat transfer
coefficient. Answer: 16 10–44 Saturated steam at 1 atm condenses on a 3-m-high and
5-m-wide vertical plate that is mainta...
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- Spring '10