Open Microchannel Manifold (OMM) with taper has been effective in enhancing heat transfer performance during flow boiling with low pressure drop. This makes it very attractive in low pressure drop systems like a thermosiphon loop. A gravity-driven flow boiling system was used to generate the performance data using ethanol at low flow rates. Based on the pressure drop and heat transfer data, a two-phase thermosiphon loop with a small ethanol head of 0.2 m was developed and tested with OMM configuration. A maximum heat flux of 136 W/cm(2) was "recorded at a wall superheat of 42 degrees C resulting in a highest heat transfer coefficient of 34,100 W/m(2)K with 6% taper manifold. The thermosiphon loop provided a maximum flow rate of approximately 35 mL/min. Pressure drop data showed stable thermosiphon operation and a very low pressure drop of only 4 kPa near CHF. The heat transfer performance was independent of the orientation of the test section as the horizontal and the vertical upflow configurations yielding similar values of heat transfer. (C) 2016 Elsevier Ltd. All rights reserved.