R134a Contact Angle Measurements
have been recently made and reported. This data is the first known data of the contact angle R134a makes with copper and aluminum and give values of roughly five to seven degrees, for copper and aluminum, respectively. These results show that R143a has very favorable wetting onto these two common metals and hence is a viable candidate working fluid for low temperature heat pipe applications.
Metal Felt Wick Heat Pipes have been made and tested. To the best knowledge, these heat pipes are the first such devices reported in the open literature.
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Copper-water, copper-R134a, and aluminum-R134a heat pipes have been successfully made. Tests on the copper-water heat pipe have shown a conductance equal to fifty five times that of a copper. This is quite remarkable in that copper has a conductance of roughly 390 W/m-K, whereas diamond, which is the best known solid conductor know to man, has a copper equivalence of five.
Micro Channel Array Heat Pipes in silicon using DRIE and wet etch techniques are under study and development. Shown to the right are 100 micron micro channel heat pipes in silicon. Current efforts are focused into a commercialization of etching, filling, and sealing micro heat pipe arrays directly into silicon wafers.
Bendable Heat Pipes have been recently demonstrated to continue their high heat transport performance even after contorting the pipe in angles beyond 60 degrees. This bendable heat pipe behavior is due to the wicks being constructed out of microfibrous metal felt wicks.
It is the metal felt advantage that makes these heat pipes work much better than wrapped screen wick heat pipes, which are the only other bendable heat pipes available.
Micro-Fibrous Metal Felt porous media characterization has been under study for several years. Many different felts have been used to measure permeability, IPA bubble point, and pore size distribution using flow porometry.
