This dissertation describes the complete development of a very novel micro loop heat pipe. The activities described include the proof of concept research and convenes at the transition into commercial development. The proof of concept devices consisted of a small 1x1 cm. MEMS (micro electro mechanical systems) based silicon LHP cell that was developed and tested, which is intended as a pre-prototype for arbitrary lateral planar expansion in multiple cells for cooling electronic chips and other systems, in terrestrial and space applications (e.g. solar cell farms for energy beaming back to earth). The author as a member of a team of MEMS researchers and thermal science researchers, concentrated mainly on physical development, and measurement issues.
The micro loop heat pipe is unique in that the wick is planar, is made of semiconductor grade silicon and is fabricated by the unique application of a photon pumped electrochemical etching (developed elsewhere for other applications but refined in this lab), locally referred to as “coherent porous silicon”. The resulting micro-capillary arrays were in the low micron range, with up to several million such through-capillaries per square centimeter. Also “quartz wool” has been demonstrated to serve well as a secondary or even primary wick with multi-micron effective pore size and porosity in the range of 95 percent.
The author’s major research contribution to this work was the refinement of the coherent porous silicon fabrication. A number of cps wicks were fabricated to act as the central component of the aforementioned LHP systems. The author also reveled and resolved multiple materials issues associated with the controlled micropatterening of the CPS wicks. This controlled micropatterening made it possible to carry out micro bonding of thermal pads/rails necessary for proper device operation.
Cooling has been demonstrated up to about 60Watts/cm2, while maintaining top cap temperatures well below military specifications for microelectronics. Calculated cooling of over 500 °F has been achieved in this passive device which requires no pumps or external power. However it is believed that improvements are possible to give a five fold increase in performance.