A Thermosiphon Loop for High Heat Flux Removal using Flow Boiling of Ethanol in Open Microchannel Manifold (OMM) with Taper

Open Microchannel Manifold (OMM) with taper has proved instrumental in enhancing heat transfer performance in flow boiling while keep the pressure drop to a minimum. This makes it applicable in developing a low pressure drop system like a thermosiphon loop. To this end, a gravity-driven flow boiling system developed earlier was tested at low flow rates using ethanol. Based on the pressure drop and heat transfer data, a two-phase thermosiphon loop with a small ethanol head below 0.2 m was developed and tested with OMM configuration. A maximum heat flux of 136 W/cm2 was recorded at a wall superheat of 42 °C. Pressure drop data showed stable thermosiphon operation with lesser flow and pressure fluctuations over the microchannels with increase in heat flux. Stable operation was complimented with tremendously low pressure drop below 4 kPa near Critical Heat Flux (CHF). Investigations were also carried out on the effect of flow orientation on flow boiling performance in the gravity-driven flow boiling system by varying the orientations as horizontal flow (0°), vertical upflow (90°) and vertical downflow (-90°) flow. Flow couldn’t be sustained in the vertical upflow orientation, however, the system performed best in the horizontal flow orientation. The heat transfer performance of the thermosiphon loop was independent of the orientation of the test section with the horizontal and the vertical upflow configurations giving similar heat transfer performances