It has been proposed that the very hot air trapped

Chapter 10, Problem 10.77

(choose chapter or problem)

It has been proposed that the very hot air trapped insidethe attic of a house in the summer may be used as theenergy source for a passivewater heater installed in theattic. Energy costs associated with heating the coolwater and air conditioning the house are both reduced.Ten thermosyphons, similar to that of 10.73,are inserted in the bottom of a well-insulated water heater. Each thermosyphon has a condensing sectionthat is Lc?50 mm long, an insulated section that is oflength Li?40 mm, and a boiling section that isLb?30 mm long. The diameter of each thermosyphonis D?20 mm. The working fluid within the thermo-syphons is water at a pressure of p?0.047 bars. (a) Determine the heating rate delivered by the 10thermosyphons when boiling occurs at 25% of theCHF. What are the mean temperatures of the boil-ing and condensing sections?(b) At night the attic air temperature drops below thetemperature of the water. Estimate the heat lossfrom the hot water tank to the cool attic, assuminglosses through the tank insulation are negligibleand the stainless steel tube wall thickness of eachthermosyphon is very small.