The heat pipes are passive heat transport devices generally using in electronic cooling. Thermal performance enhancement of heat pipe is essential for better thermal management. The present investigation attempts the effect of thin layer copper coating over the inner surface of the wickless heat pipe (WHP) to improve the heat transfer characteristics and compared with uncoated WHP using R134a, R290 and R600a as working fluids. The influence of fluid fill ratio (in the range between 30% and 80%), at three positions (0°, 45° and 90°) and heat inputs (in the range between 25 and 200 W) on the thermal performance of coated and uncoated WHPs are investigated. Moreover, the significance of Bond, Webber, Kutateladze and condensation numbers on heat transfer performance of coated and uncoated WHPs are investigated. The fill ratio was optimised to 50% (by volume). The results showed that the coated WHP at 45° inclination has improved thermal performance than uncoated WHP. The R600a was identified as a good working fluid because of its favourable thermo-physical properties, which results in low thermal resistance and improved heat transfer coefficients.
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