Geometry: shape, size, aspect ratio and orientation Flow Type: forced, natural, laminar, turbulent, internal, external Boundary: isothermal (Tw = constant) or isoflux (q̇w = constant) Fluid Type: viscous oil, water, gases or liquid metals Properties: all properties determined at film temperature Tf = (Tw + T∞)/2 Note: ρ and ν ∝ 1/Patm ⇒ see Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: μ, (N · s/m) kinematic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K) thermal diffusivity: α, ≡ k/(ρ · Cp) (m/s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K)

Convection Heat Transfer

An experimental investigation was conducted to determine the thermal behavior of arrays of micro heat pipes fabricated in silicon wafers. Two types of micro heat pipe arrays were evaluated, one that utilized machined rectangular channels and the other that used an anisotropic etching process to produce triangular channels. Once fabricated, a clear pyrex cover plate was bonded to the top surface of each wafer using an ultraviolet bonding technique to form the micro heat pipe array. These micro heat pipe arrays were then evacuated and charged with a predetermined amount of methanol. Using an infrared thermal imaging unit, the temperature gradients and maximum localized temperatures were measured and an effective thermal conductivity was computed. The experimental results were compared with those obtained for a plain silicon wafer

Experimental Investigation of Micro HeatPipes Fabricated in Silicon Wafers

A system and method is disclosed for fabricating a heat spreader system, including providing a plurality of bottom microporous wicks recessed in a bottom substrate, bonding a center substrate to the bottom substrate, and bonding a top substrate having a top chamber portion to the center substrate to establish a first vapor chamber with said plurality of bottom microporous wicks.

Heat spreader with high heat flux and high thermal conductivity

The miniaturization and improving performance of electronic devices has lead to increasing power densities in electronic systems. Consequently, the thermal environment has become a main issue in their performance and reliability. The use of flat miniature heat pipes has been investigated for transferring the heat over distances or to spread it over a larger surface area to avoid hot spots on the device. The interest of silicon etching techniques for heat pipe manufacturing is that such heat pipes can be very compact, very light and have better heat transfer capacities than metallic heat pipes. In this paper the structure of a flat radial structure silicon heat pipe is presented. A one dimensional two-phase flow model has been developed in order to optimize the performances of the radial grooved silicon heat pipe. Then an experimental study investigates the thermal performance of a realized prototype. The thermal transfer capacities achieved are in the range 50-70 W depending on the working temperature

Design, fabrication and test of silicon heat pipes with radial microcapillary grooves

An experimental study is realized in order to verify the Mini Heat Pipe (MHP) concept for cooling high power dissipation electronic components and determines the potential advantages of constructing mini channels as an integrated part of a flat heat pipe. A Flat Mini Heat Pipe (FMHP) prototype including a capillary structure composed of parallel rectangular microchannels is manufactured and a filling apparatus is developed in order to charge the FMHP. The heat transfer improvement obtained by comparing the heat pipe thermal resistance to the heat conduction thermal resistance of a copper plate having the same dimensions as the tested FMHP is demonstrated for different heat input flux rates. Moreover, the heat transfer in the evaporator and condenser sections are analyzed, and heat transfer laws are proposed. In the theoretical part of this work, a detailed mathematical model of a FMHP with axial microchannels is developed in which the fluid flow is considered along with the heat and mass transfer processes during evaporation and condensation. The model is based on the equations for the mass, momentum and energy conservation, which are written for the evaporator, adiabatic, and condenser zones. The model, which permits to simulate several shapes of microchannels, can predict the maximum heat transfer capacity of FMHP, the optimal fluid mass, and the flow and thermal parameters along the FMHP. The comparison between experimental and model results shows the good ability of the numerical model to predict the axial temperature distribution along the FMHP.

/pdf/flat-miniature-heat-pipes-for-electronics-cooling-state-of-50neic82cr.pdf

Flat Miniature Heat Pipes for Electronics Cooling: State of the Art, Experimental and Theoretical Analysis

The miniaturization and improving performance of electronic devices lead to increasing power densities. Consequently, the thermal environment has become a main issue in their performance and reliability. The use of flat miniature heat pipes is investigated to conduct the heat over distances or to spread it over a larger surface area avoiding hot spots on the device The interest of silicon etching techniques for heat pipe manufacturing is that such heat pipes can be very compact, very light and have a better hydraulic behavior than metallic heat pipes. In this paper the structure of a flat silicon grooved heat pipe is presented. Then an experimental study investigates power limitations of a realized prototype. The capillary limit is in the range 20-30 W depending on the working temperature.

Thermal characterization of flat silicon heat pipes

Currently the thermal losses of power electronic devices are increasing. At the same time, their sizes are decreasing. Consequently heat sinks have to dissipate very large heat flux densities. Heat pipes are very effective heat transfer devices and can be used to raise the thermal conductive path in order to spread a concentrated heat source over a much larger surface area. As a result, the high heat flux at the heat source can be reduced to a much smaller and manageable level that can be dissipated through conventional cooling methods. At the first part of this paper we present the silicon heat spreader structure. Then an analytical model of heat pipe limits is described and finally an experimental study and test results are presented in order to show the interests of heat pipes in power electronics cooling.

Realization and thermal analysis of silicon thermal spreaders used in power electronics cooling

https://www.j3ea.org/articles/j3ea/pdf/2003/03/j3ea2003610.pdf

C. Gillot

Papers

Thermal characterization of flat silicon heat pipes

Realization and thermal analysis of silicon thermal spreaders used in power electronics cooling

Apport de la microthermie pour le refroidissement des systèmes