The aims of the work are as follows:

— to develop a simple self-acting device that will transfer heat downward up to a depth above 10 m. The temperature difference between the warm and cold branches would be only a few degrees, and

— to test the performance of the device under laboratory conditions and when integrated with a solar installation.

The proposed device operates cyclically, is self-controlled, has a simple design and has no

mechanical moving elements except flaps of check valves.

The principles of action are shown in Fig. 1. The cycle of action include two stages [2], [3], [4]:

— heating the upper part of warm branch and pushing warm liquid downward. It will cause rising of level of liquid in the cold branch (see Fig. 1a),

—

opening the upper path in the flow circuit, equalising vapour pressure in both branches, pouring off the surplus of cold liquid through the intermediate canal to upper part of warm branch gravity (see Fig. 1b).

The upper parts of each branch have to be made wider. It will cause the pumping of a greater portion of liquid during each cycle. The directions of liquid flow in the main part of the circuit and intermediate canal are maintained by placing non-return valves. A special control valve has to be used for periodical opening and closing of the upper path of the flow circuit.