Performance Characteristics of Vapor Chambers with Boiling Enhanced Multi-Wick Structures

Thermal management remains an important reliability factor in electronic components/systems, and quite a bit of effort has been devoted both in terms of lowering the heat dissipation and increasing the overall efficiency of heat removal devices. In terms of the former, the industry has leveraged on altering the semiconductor technology as well as the basic chip design (i.e. multi-core), and in terms of the latter, the market is increasingly seeking more heat removal devices with content and embedded heatpipes. While these combined efforts have largely increased the safety margin in desktop computer systems, low-profile systems (i.e. notebooks, graphic cards, blade severs) are still largely constrained by the efficiency of the heat removal devices. In addition, whether and how long it will take for the desktop systems to outgrow the "improved" thermal solutions remains an important and unclear question. Clearly, continual R&D in cooling technology is necessary, and the present investigation represents one such effort. Among the many competing cooling technologies, the present work focuses on the characteristics of vapor chambers. As is well known in the heat transfer community, the vapor chamber operates on a heatpipe principle and thus, cooling devices utilizing vapor chambers could potentially achieve a significant increase in efficiency relative to solid heat sinks. However, as this technology is relatively new, there is a critical shortage of data. In this sense, one objective of the present work is to provide quantitative data for the references of fellow researchers. The focus of the present work is on the performance advantage of a boiling enhanced multi-wick structure, which is patent pending (filed in the U.S. in 2005) and based on an earlier patent application on the multi-wick structure (filed in the U.S. in 2002). Utilizing the BTX type II configuration, vapor chambers were built using groove type wicks (Type-1), boiling enhanced (Type-2) and boiling- enhanced multi-wick structures (Type-3). Measurements are presented for these vapor chambers in gravity-assist, anti-gravity orientations, different flow rates and varying heating power (25mm times 25mm heat source). The results indicate the Type-1 chamber to undergo dry-out at around 100W, while Type-2 and Type-3 chambers were functional even up to 330W. Under identical heating and airflow conditions, the chamber resistance for the Type-3 chamber was found to be the lowest at 0.03degC/W under a heat flow of 330W.