Enhanced Flow Boiling Over Open Microchannels With Uniform and Tapered Gap Manifolds

Abstract

Flow boiling in microchannels has been extensively studied in the past decade. Instabilities, low critical heat flux (CHF) values, and low heat transfer coefficients have been identified as the major shortcomings preventing its implementation in practical high heat flux removal systems. A novel open microchannel design with uniform and tapered manifolds (OMM) is presented to provide stable and highly enhanced heat transfer performance. The effects of the gap height and flow rate on the heat transfer performance have been experimentally studied with water. The critical heat fluxes (CHFs) and heat transfer coefficients obtained with the OMM are significantly higher than the values reported by previous researchers for flow boiling with water in microchannels. A record heat flux of 506 Wlcrr? with a wall superheat of 26.2 °C was obtained for a gap size of 0.127 mm. The CHF was not reached due to heater power ¡imitation in the current design. A maximum effective heat transfer coefficient of 290,000Wlm^°C was obtained at an intermediate heat flux of 319Wlcm^ with a gap of 0.254 mm at 225mLlmin. The flow boiling heat transfer was found to be insensitive to flow rates between 40-333 mLlmin and gap sizes between 0.127-1.016mm, indicating the dominance of nucleate boiling. The OMM geometry is promising to provide exceptional performance that is particularly attractive in meeting the challenges of high heat flux removal in electronics cooling applications.

Electronics Thermal Management in Information and Communications Technologies: Challenges and Future Directions

“…Several geometric enhancements have been proposed to suppress instabilities, such as inlet restrictions [101], channel tapering [102] and the use of surface roughness [103]. Recent work at Stanford has focused on vapor/liquid phase separation, i.e., vapor extraction from a microchannel flow using permeable membrane surfaces [104] or heat pipeinspired separation using phase-separator coatings on a porous medium which keeps liquid contained within structure by surface forces, yet allows evaporation at the boundaries.…”

Experimental and theoretical studies of critical heat flux of flow boiling in microchannels with microbubble-excited high-frequency two-phase oscillations

“…Pros * Cons * Inlet restriction [4,5] CHF+ and HTC+ DP+ Reentrant cavity [6,7] CHF+ DP$ and HTC$ Tapered manifod [17] CHF+, HTC+ and DPÀ Micro/minijet [15,16,23] CHF+, HTC+ and DPÀ Micromixer [18] CHF+ and HTC+ DP+ Nanofluid [8,24,25] CHF+ DP+ and HTC$ Surfactant [14] CHF+ and HTC+ DP$ Solution [19,20] CHF+ and HTC+ DP$…”

“…Meanwhile, surfactant can enhance CHF by reducing surface tension of fluids [14]. In addition, techniques, such as micro/mini-jets [15,16], tapered manifod [17], micromixer [18] and solution (e.g., aqueous n-butanol, TSP and boric acid solutions) [19,20] can enhance CHF as well. However, some enhancement techniques are at the cost of pressure drop.…”

Flow patterns and heat transfer mechanisms during flow boiling over open microchannels in tapered manifold (OMM)

“…Further details on these techniques that provide enhanced heat transfer and reduced flow instability have been addressed in a previous publication by the authors [14]. The open microchannel with manifold (OMM) geometry was introduced by Kandlikar et al [15] to provide a stable, low pressure drop and high performance system. This geometry provides additional flow area over the microchannel (manifold region) which assists in removing the generated vapor without an excessive pressure drop.…”