Heat generated by electric components has become larger and larger and electric components have been installed at higher density. In these situations, aluminum flat heat pipes are expected to be very useful for electronic components cooling because thin, light and bendable ones are possible. However, there is a problem that suitable working fluid is not found for aluminum heat pipes. Conventionally used freons that include not only CFCs but also HCFCs and HFCs are not harmless to global environment, and hence should be substituted by other materials, Water that is usually used in copper heat pipes causes non-condensing gas generation in aluminum container, and hence is not available. As to other materials, ammonia and hydrocarbon are listed, however, both are not safe to people. But, recently hydrocarbon has been reconsidered in other technologies that have used freons conventionally. Considering that an amount of fluid in a heat pipe is too small to cause explosion in flammable fluid leakage, the application of hydrocarbon to heat pipes also should be reconsidered. In this paper, cyclopentane application to aluminum heat pipes is discussed. First, thermal resistance in aluminum-cyclopentane heat pipes was evaluated as compared with aluminum-HCFC123 heat pipes, which is the one of conventional materials used in aluminum heat pipes. Secondary, long time reliability in aluminum-cyclopentane heat pipes was evaluated as compared with aluminum-HCFC123 heat pipes. These evaluations resulted in showing the possibility of substitution for HCFC123 by cyclopentane and gave one answer to the working fluid problem in aluminum heat pipes.
