Physical mechanisms involved in grooved flat heat pipes: Experimental and numerical analyses

Abstract

An experimental database, obtained with flat plate heat pipes (FPHP) with longitudinal grooves is presented. The capillary pressure measured by confocal microscopy and the temperature field in the wall are presented in various experimental conditions (vapour space thickness, filing ratio, heat transfer rate, tilt angle, fluid). Coupled hydrodynamic and thermal models are developed. Experimental results are compared to results of numerical models. Physical mechanisms involved in grooved heat pipes are discussed, including the boiling limit and the effect of the interfacial shear stress. Finally, recommendations for future experimental and theoretical research to increase the knowledge on FPHP are discussed.

Flat Plate Heat Pipes: From Observations to the Modeling of the Capillary Structure

“…Unexpectedly, this phenomenon does not prevent the working of the system and conversely increases its thermal performance. An experiment conducted in non horizontal orientation (Lips et al, 2011) showed that the presence of nucleate boiling in the system does not constitute a limit as it is generally stated in the literature. In all cases, dryout of the evaporator is due to the capillary limit.…”

“…Fig. 11 presents the comparison between this database and a hydrodynamic model based on the balance equations and the YoungLaplace law (Lips et al, 2011). To facilitate and reduce the presentation of the hydrodynamic measurements, the experimental results obtained by confocal microscopy are presented in the form of the mean capillary pressure gradient ΔP cap /Δx in the adiabatic zone.…”

“…Comparison between experimental and numerical hydrodynamic results (Lips et al, 2011) Confocal microscopy is well adapted to characterize FPHP but visual observations are sufficient to describe different physical phenomena of high importance to understand how FPHP works. For example, nucleate boiling (Fig.…”

The length and bending angle effects on the cooling performance of flat plate heat pipes

“…Moreover, the liquid-vapor interface should be accurately assessed [12]. Lips et al [13] and Lefevre et al [14] established a database for the FPHPs developed by their group, including the vapor space thickness, filling ratio, and tilt angle, and suggested that new laws are required to better describe both the permeability and the equivalent thermal conductivity of the capillary structures involved. Chen and Chou [15] showed that the optimum liquid filling ratio was 25% for their Al extruded FPHP and the minimum thermal resistance was 0.254 K/W.…”

3-D numerical and experimental models for flat and embedded heat pipes applied in high-end VGA card cooling system

“…It is known from the above description that, a thermal module in which a two-phase flow heat transfer module (heat pipes, vapor chamber or flat heat pipes) is used as the based plate represent a better thermal performance than traditional solid metal thermal modules (copper and aluminum based plates) because it can effectively reduce the based plate thermal resistance. The vapor chamber can reduce the thermal spreading resistances sufficiently by its excellent lateral spreading effect [18][19][20][21][22]. In conclusion, the next generation VGA thermal module is the flat heat pipe/vapor chamber thermal modules.…”