Unformatted text preview: ube as a function of the temperature of the saturated R-134a vapor as the temperature
varies from 25°C to 50°C, and discuss the results. Special Topic: Heat Pipes 10–61C A heat pipe with water as the working fluid is said to
have an effective thermal conductivity of 100,000 W/m · °C,
which is more than 100,000 times the conductivity of water.
How can this happen? P = 4.25 kPa n = 100
tubes 10–55 10–60C What is a heat pipe? How does it operate? Does it
have any moving parts? Saturated
steam N = 10 long and have an outer diameter of 3 cm. If the tube surfaces
are at 20°C, determine (a) the rate of heat transfer from the
steam to the cooling water and (b) the rate of condensation of
steam in the condenser.
Answers: (a) 3678 kW, (b) 1.496 kg/s 10–62C What is the effect of a small amount of noncondensable gas such as air on the performance of a heat pipe?
10–63C Why do water-based heat pipes used in the cooling
of electronic equipment operate below atmospheric pressure?
10–64C What happens when the wick of a heat pipe is too
coarse or too fine?
10–65C Does the orientation of a heat pipe affect its performance? Does it matter if the evaporator end of the heat pipe is
up or down? Explain. FIGURE P10–54 10–66C How can the liquid in a heat pipe move up against
gravity without a pump? For heat pipes that work against gravity, is it better to have coarse or fine wicks? Why? cen58933_ch10.qxd 9/4/2002 12:38 PM Page 558 558
HEAT TRANSFER 10–67C What are the important considerations in the design
and manufacture of heat pipes? coefficient, (b) the rate of heat transfer, and (c) the rate of condensation of ammonia. 10–68C What is the major cause for the premature degradation of the performance of some heat pipes? 10–74 Saturated isobutane vapor in a binary geothermal
power plant is to be condensed outside an array of eight horizontal tubes. Determine the ratio of the condensation rate for
the cases of the tubes being arranged in a horizontal tier versus
in a vertical tier of horizontal tubes. 10–69 A 4...
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