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Circumferentially grooved heat pipe evaporators have been proposed as an alternative solution to obtain high capillary pressure and large liquid cross sections to reduce the viscous pressure losses in the liquid flow. Such evaporators have been employed in a capillary pumped two-phase loop and first results have been reported for loop operation in the mechanical pump assisted mode. Additional tests have been carried out in order to determine the performance of the loop also in the capillary pumped mode. Using freon 11 as the working fluid, heat fluxes up to 12 kW/m2 have been measured. For ammonia, the corresponding value is estimated to be about 78 kW/m2. A theoretical analysis is also presented in order to understand differing performances of the individual capillary pumps.