ABSTRACT
A heat pipe is a device with very high effective thermal conductivity that is capable of transferring large quantities of heat over considerable distances without an appreciable temperature gradient. The high effective thermal conductance of the heat pipe maintains the vapor core temperature at an almost uniform temperature while transferring heat, making it capable of being used also as a “heat spreader.”As described by Peterson (1994), a heat pipe operates in a closed two-phase cycle in which heat added to the evaporator region causes the working fluid to vaporize and move to the cooler condenser region, where the vapor condenses, giving up its latent heat of vaporization. In traditional heat pipes, the capillary forces existing in a wicking structure pump the liquid back to the evaporator. While the concept of utilizing a wicking structure as part of a device capable of transferring large quantities of heat with a minimal temperature drop was first introduced by Gaugler (1944), it was not until much more recently that the concept of combining phase change heat transfer and microscale fabrication techniques (i.e., MEMS devices for the dissipation and removal of heat), was first proposed by Cotter (1984). This initial introduction envisioned a series of very small “micro” heat pipes incorporated as an integral part of semiconductor devices. While no experimental results or prototype designs were presented, the term micro heat pipe was first defined as a heat pipe “so small that the mean curvature of the liquid-vapor interface is necessarily comparable in magnitude to the
reciprocal of the hydraulic radius of the total flow channel” [Babin et al., 1990]. Early proposed applications of these devices included the removal of heat from laser diodes [Mrácek, 1988] and other small localized heat generating devices [Peterson, 1988a, 1988b]; the thermal control of photovoltaic cells [Peterson, 1987a, 1987b]; the removal or dissipation of heat from the leading edge of hypersonic aircraft [Camarda et al., 1997]; applications involving the nonsurgical treatment of cancerous tissue through either hyper-or hypothermia [Anon., 1989; Fletcher and Peterson, 1994]; and space applications in which heat pipes are embedded in silicon radiator panels to dissipate the large amounts of waste heat generated [Badran et al., 1993].
