Passive downward heat transport: experimental results of a technical unit

A bench scale model for passive downward transport of heat has been built and tested. The heat is transported by evaporation of a fluid in an evaporator at a higher level and condensation at a lower level. The condensate is returned to the evaporator by the periodic operation of a self-actuated float valve without disconnectding the heat delivery to the evaporator. The cost of lifting the liquid back to the evaporator is a temperature difference of a few degrees centigrade between the evaporator and the heat store. The unit works under moderate pressure (a maximum of 9 bar at 85°C). The actual vertical distance between heat source and heat store is about 1 m; a pressure difference equivalent to a vertical distance of 15 m was introduced by two spring-loaded check valves; in these conditions the ΔT between heat source and heat store is about 10°C. This ΔT is comparable to that occurring in the condenser to promote heat transfer to the heat store medium. Most of the components of the 1000 W model are similar to those used in conventional refrigerators or heat pumps. The system can easily be integrated with a solar heat collector working with a 2-phase fluid.