High Heat Flux Two-Phase Thermal Control System using Non-Uniform Capillary Evaporator

A two-phase flow with an external forced fluid flow, i.e., flow boiling, offers a high heat flux thermal control system. However, a technical barrier of a conventional flow boiling system, i.e., a plain surface, is a premature surface dryout, resulting in a rapid surface temperature rise or Heat Transfer Coefficient (HTC) drop, leading to a system burnout, i.e., Critical Heat Flux (CHF). As miniaturized power conversion and electronic systems are expected to exceed the CHF of the conventional flow boiling system, it requires a breakthrough technology to manage such a high heat dissipation. Approaching the CHF, the excessive vapors produce and develop wavy vapor layers with wetting fronts, while the liquid is locally supplied to the surface through the wetting fronts and liquid film. Due to the nature of the fluid flow, the produced vapors “accumulate” toward downstream to increase vapor layer thickness, and excessive vapor upward momentum at the downstream triggers the liquid-vapor interfacial lift-off at the critical wavelength, lambda_cr, i.e., hydrodynamic-instability wavelength. To tailor the hydrodynamic-instability wavelength for the enhanced CHF, the non-uniform capillary evaporator is employed. Using the modified lift-off hydrodynamic model, the increased CHF is predicted up to 4 time compared to the plain surface. The detailed controlled hydrodynamic-instability wavelength mechanisms are discussed. Also, the possible experimental validations with the non-uniform wick fabrications are also discussed. The non-uniform wick structure provides in-depth insights into the advanced two-phase thermal control systems for the space technologies.