Flow Boiling Heat Transfer Over Open Microchannels With Tapered Manifold

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling application. It can dissipate large quantities of heat while maintaining a low surface temperature to fluid difference. Flow boiling with microchannels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and early critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design based on a mechanistic approach is taken to overcome the above mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with tapered manifold (OMM) to provide stable and efficient operation. The tapered manifold above the microchannels provides an increasing cross-sectional area in the flow direction. The extra flow cross-sectional area allows bubbles to emerge from the microchannels and expand in the manifold along the flow direction. Using a 6% taper and a moderately high inlet liquid flow Reynolds number of 1095, a CHF of 1.07 kW/cm^2 with a heat transfer coefficient of 295 kW/m^2°C and a pressure drop of 30 kPa was recorded. Baseline test with uniform manifold were conducted and compared with tapered geometry. The experimental data was substantiated with pressure drop modeling for the new geometry. High speed visualization was also conducted to understand the underlying mechanism in the tapered configuration