Current Developments in Heat Pipes: An Overview

Heat transfer is one of the most difficult tasks in thermal management of electronic components and directly influences cost, reliability and performances. Heat pipes are efficient heat transfer devices used in many applications, e.g. electronic systems, spacecrafts thermal control, energy collectors, power generation, chemical engineering, air conditioning, engine cooling and others. At normal operating temperatures all heat pipes have heat transfer limits imposed by the capillary transport capabilities in presence of high heat fluxes. Typical wick or capillary structures and common working fluids show advantages in some aspects and disadvantages in others. After a general introduction and a short description of the history of heat pipes developments, an overview of the current intellectual property environment and market is presented to identify trends for future developments. Then an overview of recent patents related to heat pipes technology is presented, with particular reference to: flat heat pipes, flexible heat pipes, innovative wick structures, phase change materials, innovative working fluids. Concerning flat and flexible heat pipes, a number of patents are shown that are characterized by different geometries and materials and, differently from usual cylindrical heat pipes, are particularly suited for use in microelectronics applications. Patents related to innovative wick structures are shown that are aimed to overcome some limitations associated with usual wick structures (woven mesh or sintered powder). Patented heat pipes architectures are also described that are designed to enlarge the operating temperature range by using appropriate phase change materials. In addition, recent patents are shown that exploit the use of binary mixtures as working fluids to improve the heat pipes efficiency compared to conventional pure working fluids. Keywords: Heat pipes, flat heat pipes, flexible heat pipes, wick structures, working fluids