Parameters that determine a critical heat flux (CHF) inside a biporous evaporator (wick) for a closed loop heat pipe have been studied. In a present work, a biporous wick structure was sintered from copper powder 53–63μm diameter into clusters 500–710μm diameter; the clusters were then sintered into 20mm long and 3mm wide wicks with different wick thickness on copper bases with three different lengths (5mm, 7.5mm and 10mm). Total of six wicks were made and tested. Copper base(mm) to wick thickness(mm) ratios of the wicks tested are: 5/5, 7.5/5, 10/5, 5/3, 7.5/3 and 10/1.5. Narrow (3mm) wicks with different copper base lengths allowed sidewise observation of the boiling inside the wick at different heat loads. Best-performed 10/1.5 wick, second best was 5/3 and then following 7.5/3, 5/5, 7.5/5, 10/5. Tests were run at atmospheric pressure and absolute ethanol as working fluid.

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