Experimental study on thermal characteristics of ammonia three-dimensional oscillating heat pipes with different filling ratios

A three-dimensional oscillating heat pipe (3DOHP) transfers heat through both latent heat and sensible heat and features good temperature uniformity, compact channels, and high thermal conductivity. In this work, an ammonia-charged 3DOHP with channels gradually contracting from the condenser toward the evaporator is used to heat dissipate under a heat load of 1000W and a heat flux of 111.1 W/cm 2 . The effects of filling ratios (20%-80%) and heating power (50-1000W) on the flow pattern and thermal characteristics of the 3DOHP were experimentally studied. The results show that the establishment of unidirectional flow in the ammonia-charged 3DOHP can remarkably improve its thermal characteristics. When there is a small amount working fluid inventory, the flow pattern is oscillating motion and the evaporator temperature uniformity is poor. Meanwhile, for the 3DOHP with a larger filling ratio, a unidirectional flow is more likely to form, but as the filling ratio increases, its thermal performance gradually decreases. Moreover, the optimal filling ratio of the 3DOHP varies with heating power. For a heat load exceeding 600W, the optimal filling ratio is 50%. When the power reaches 1000W, the 3DOHP exhibits a thermal resistance of 0.04424 °C/W, a temperature difference of 44.24 °C, and an effective thermal conductivity of 15489 W/(m·K). This research offers a viable approach to addressing the thermal management challenges encountered by electronic devices operating at high power levels and generating substantial heat fluxes.