Evaluation of Pressure Drop Performance During Enhanced Flow Boiling in Open Microchannels With Tapered Manifolds

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling applications. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with micro-channels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and low critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above-mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. The effect of tapered manifold block with varied dimension is investigated with distilled, degassed water at atmospheric pressure. Heat transfer coefficient and pressure drop results for uniform and tapered manifolds with plain and micro-channel chips are presented. The OMM configuration yielded a CHF of over 500 W/cm(2) in our earlier work. In the current work, a heat transfer coefficient of 277.8 kW/m(2) degrees C was obtained using an OMM design with an inlet gap of 127 mu m and an exit gap of 727 mu m over a 10mm flow length. The OMM geometry also resulted in a dramatic reduction in pressure drop from 158.4 kPa for a plain chip and 62.1 kPa for a microchannel chip with a uniform manifold, to less than 10 kPa with the tapered OMM design. A tapered manifold (inlet and exit manifold heights of 127 and 727 mu m, respectively) with microchannel provided the lowest pressure drop of 3.3 kPa.