Analytical Study of the Thermal Performance of a Novel Loop Heat Pipe Solar Heating System

A novel loop heat pipe (LHP) array was designed for use in solar hot water heating and an analytical model was developed to investigate its thermal performance and determine five major limits to heat transport capacity of this system, i.e., capillary, entrainment, boiling, sonic, viscous limits. Relations among the limits and several associated parameters, i.e., the heat pipe operating temperature, heat pipe diameter, and height difference between the evaporator pipe array and condenser, were established through the comprehensive analyses. It was found that the levels of capillary, entrainment, sonic, viscous limits increased with the temperature increasing; however, the boiling limit was in the adverse trend. Larger pipe diameters would lead to higher heat transport limits except for sonic and viscous limits. The sonic limit was maintained and the viscous limit increased first and was constant then. The height difference between the evaporator pipe array and condenser was the most important factor impacting on heat transfer capacities of the system, and was largely affecting the capillary limit of the system. The governing limit of the system was capillary limit and the relation between the capillary limit and the above addressed parameters was analysed.