Impact of working fluid filling ratio on the performance of a micro-channel loop heat pipe based solar PV/T heat and power system

The working fluid filling-ratio (FR) has a significant impact on the heat output of a loop heat pipe (LHP); a lower FR may lead to a faster dry-out of the LHP resulting in a reduced heat transport capacity, while a higher FR may lead to the over-charging of the working fluid, resulting in the less available evaporation surface and reduced heat transport capacity. This paper presented an experimental investigation into the impact of FR on the performance of a unique loop heat pipe (LHP) and associated PV/T system. This LHP, with a unique liquid upper-feeding header and a novel micro-channel evaporating pipes array, can effectively distribute the working fluid across the side wall of the evaporator and thus realize higher heat capacity. The thermal characteristics tests were carried out in an indoor (laboratory) space, with 4 filling mass values (0.8 kg, 0.9 kg, 1.0 kg, 1.1 kg, i.e. FR of 52.6 %, 59.2 %, 65.8 %, 72.3 %). The experimental results showed that the heat capacity and solar thermal efficiency had a same trend changing with filling mass, and the suggested optimal FR of this unique LHP should be around 59.2 % under the pre-set operational condition. While the highest value of heat capacity and solar thermal efficiency are 712.83W and 67.68 % at this optimal FR of 59.2 %. This research will contribute to wide deployment of the novel LHP PV/T system, thus leading to significant fossil fuel energy saving and carbon emission reduction on the global context.