The geothermal convector: experimental and numerical results

Abstract

The Geothermal Convector (GTC) is an unconventional system that uses a two-phase closed thermosyphon for heat extraction from a geothermal aquifer without fluid withdrawal. This paper reports on the experimental tests carried out on a GTC prototype installed in a geothermal well on the island of Ischia. The GTC prototype comprises a tube bundle with a central feeding pipe as the evaporator, and a conventional shell-and-tube type condenser with cooling water flow inside the tubes. The evaporator and condenser are connected using flexible ducts. The GTC is equipped with an annular convection promoter. This paper describes the prototype, the experimental plant and the tests carried out on the experimental apparatus, and reports the results, thereby illustrating the device performance. The experimental tests indicate that there is a limit to the heat obtained by the GTC; this limit arises from the thermal and fluid dynamic interaction between the well and the aquifer. In particular, the heat flow is due to a short-circuit effect in the aquifer between cold and warm fluids, respectively, leaving and entering the well. An estimate of this short-circuit effect for the Ischia aquifer is obtained from the two-dimensional (2D) thermal and flow fields determined using the Finite Element Method.