The geothermal convector: experimental and numerical results

The Geothermal Convector (GTC) is an unconventional system that uses a two- phase closed thermosyphon for heat extraction from a geothermal aquifer wit hout fluid withdrawal. This paper reports on the experimental tests carried out on a GTC prototype installed in a geothermal well on the island of Isc hia. The GTC prototype comprises a tube bundle with a central feeding pipe as the evaporator, and a conventional shell-and-tube type condenser with co oling water flow inside the tubes. The evaporator and condenser are connect ed using flexible ducts. The GTC is equipped with an annular convection pro moter. This paper describes the prototype, the experimental plant and the t ests carried out on the experimental apparatus, and reports the results, th ereby illustrating the device performance. The experimental tests indicate that there is a limit to the heat obtained by the GTC; this limit arises fr om the thermal and fluid dynamic interaction between the well and the aquif er. In particular, the heat flow is due to a short-circuit effect in the aq uifer between cold and warm fluids, respectively, leaving and entering the well. An estimate of this short-circuit effect for the Ischia aquifer is ob tained from the two-dimensional (2D) thermal and flow fields determined usi ng the Finite Element Method. (C) 1998 Elsevier Science Ltd. All rights res erved.