A review of the capabilities of high heat flux removal by porous materials, microchannels and spray cooling techniques

• Three direct cooling techniques are presented and compared in detail.
• The thermal and flow parameters which have influence on performances are investigated.
• The spray cooling technique is characterized by the most promising thermal performances.

Most advanced, high power technologies require a large amount of heat to be dissipated from the limited surface area or space. Solutions to such problems are vital, among others, in the field of computer microchips, where promising designs of future high power processing components can reach heat fluxes up to 500 W cm−2 in the background or even 1000 W cm−2 at the hot-spots. Such high requirements can be satisfied by so-called Direct Cooling Techniques, which are heat removal techniques that apply porous media, microchannel heat sinks and spray cooling. The paper presents an exhaustive comparison of the aforementioned techniques with respect to the media type, operating fluids and flow character, maximal achievable heat flux dissipation and heat transfer coefficient, pressure drop, the Reynolds number, other selected thermal and/or flow parameters. Special attention is paid to the spray cooling technique, which is the most effective direct cooling technology. For that reason, several parameters, such as: spray and fluid types, maximum achieved heat flux, heat transfer coefficient, the Sauter Mean Diameter and flow rate are studied and compared in detail.