Fabrication and evaluation of a copper flat micro heat pipe working under adverse-gravity orientation

Abstract

The fabrication of a prototype flat micro heat pipe (FMHP) of a size appropriate for mobile electronics and its performance test results are reported. To ensure reliable operation under repeated thermal loads and to enhance the heat transport capacity, copper is selected as the packaging material considering its high thermal conductivity and good strength. The wick structure of the FMHP consists of fan-shaped microgrooves with a width and depth of about 100 and 200 μm, respectively. The fabrication of microgrooves was done using a laser micromachining technique and water was used as the working fluid. Fan-shaped microgrooves were found to induce a greater capillary pressure than triangular microgrooves of a similar size. Subsequent test results confirmed that despite its small size, 56 mm (L) × 8 mm (W) × 1.5 mm (H), the FMHP had a high heat transport capacity; the maximum heat transfer rate was 8 W under stable operation conditions and 13 W at the dryout point. In addition, the FMHP worked under adverse-gravity conditions with little change in cooling capacity, a key advantage for application in modern mobile electronics.

Laser Beam Machining, Laser Beam Hybrid Machining, and Micro-channels Applications and Fabrication Techniques

“…Also, since the main heat source in an electronic device is a chip, and the sides of most chips are flat, the flat micro flat heat pipes are designed in a flat rectangular shape with a thickness of 1.5 mm. Recently, Lim et al [214] developed a micro heat pipe with a microchannel groove wick structure using laser micro-machining technology. The structure of the microchannel grooves of a micro flat heat pipe is shown in Fig.…”

Theoretical and Experimental Analysis of Flows and Heat Transfer Within Flat Mini Heat Pipe Including Grooved Capillary Structures

“…More recently, laser-assisted wet etching technique was used in order to machine fan-shaped microgrooves (Lim et al, 2008). A literature survey of the micromachining techniques and capillary structures that have been used in metallic materials are reported in table 1.…”

“…It can be seen from this overview that three types of grooved metallic FMHP are developed: i. Type I: FMHPs with only axial rectangular, triangular or trapezoidal grooves (Murakami et al, 1987;Plesh et al, 1991;Sun and Wang, 1994;Ogushi and Yamanaka., 1994;Cao et al, 1997;Hopkins et al, 1999;Schneider et al, 1999aSchneider et al, , 1999bSchneider et al, , 2000Avenas et al, 2001, Cao and Gao, 2002, Lin et al, 2002Chien et al, 2003;Moon et al, 2003Moon et al, , 2004Soo Yong and Joon Hong, 2003;Lin et al, 2004;Romestant et al, 2004;Zhang et al, 2004;Popova et al, 2006;Lefevre et al, 2008;Lim et al, 2008;Tao et al, 2008, Zhang et al, 2009Xiaowu et al, 2009). These FMHPs allow for high heat fluxes for horizontal or thermosyphon positions (up to 150 W/cm²).…”

Experimental investigation of copper-grooved micro heat pipes (MHPs)

“…Mahmood R. S. Shirazy et al [22] studied the capillary and wetting characteristics of copper metal foam which was used as a wick in flat heat pipes. Lim H. T, et al [23] fabricated a copper MHP that worked under adverse-gravity conditions. The wick structure of the flat MHP consisted of fan-shaped microgrooves with a width and depth of about 100 μm and 200 μm, respectively.…”