Miniature Loop Heat Pipe With Flat Evaporator for Cooling Computer CPU

Abstract

This paper presents an experimental investigation on a copper miniature loop heat pipe (mLHP) with a flat disk shaped evaporator, 30 mm in diameter and 10-mm thick, designed for thermal control of computer microprocessors. Tests were conducted with water as the heat transfer fluid. The device was capable of transferring a heat load of 70 W through a distance up to 150 mm using 2-mm diameter transport lines. For a range of power applied to the evaporator, the system demonstrated very reliable startup and was able to achieve steady state without any symptoms of wick dry-out. Unlike cylindrical evaporators, flat evaporators are easy to attach to the heat source without need of any cylinder-to-plane reducer material at the interface and thus offer very low thermal resistance to the heat acquisition process. In the horizontal configuration, under air cooling, the minimum value for the mLHP thermal resistance is 0.17 C/W with the corresponding evaporator thermal resistance of 0.06 C/W. It is concluded from the outcomes of the current study that a mLHP with flat evaporator geometry can be effectively used for the thermal control of electronic equipment including notebooks with limited space and high heat flux chipsets. The results also confirm the superior heat transfer characteristics of the copper-water configuration in mLHPs.Index Terms-CPU cooling, flat evaporator, miniature loop heat pipe (mLHP), thermal control.

Experimental tests of a stainless steel loop heat pipe with flat evaporator

“…2 (favourable configuration). The study conducted is very close to that successfully performed by Singh et al [5,7,18] on a similar miniature device, with the loop made of copper and the wick of nickel. The space layout, the design details and the locations of the thermocouples are shown in Fig.…”

“…The transient and steady thermal hydraulic response following a given supply heat load for starting the device is affected by many parameters, some of them are reported hereunder. It is important to emphasize that this description refers to some literature reviews [2,3] and to some other authors' works [5,7,14], the analysis and explanations of which are mentioned for some of the conditions affecting also the start-up behaviour of the LHP presented in this paper.…”

“…Many efforts are directed to the improvement of the design of miniature loop heat pipes (mLHPs) being easier fitting them inside very small and compact electronic equipment [4,5]. A great advantage for loop systems with respect to conventional heat pipes, is their wide flexibility in the design of the evaporator and condenser sections.…”

Thermal Analysis and Flow Visualization of a Flat Loop Heat Pipe

“…Now LHP is successfully used in cooling of laptops and desktops (Kim et al, 2003). They are also used effectively for thermal management of electronic system (Singh et al, 2007). Miniature cylindrical LHP has been developed for electronic cooling applications (Maydanik et al, 2005).…”

Operational characteristics of the miniature loop heat pipe with non-condensable gases

“…Due to the space and weight constraints in electronics, compact and lightweight designs of LHP, similar to conventional heat pipes, are required. Miniature loop heat pipes (mLHPs) with cylindrical evaporators 6-8 mm in diameter [7,8] and flat evaporators 5-15 mm in thickness [9][10][11] have been successfully tested for high powered electronic equipments. These mLHP devices were capable of transferring maximum heat loads within 50-200 W and possess total thermal resistance in the range 1-4°C/W.…”