AN AQUIFER-WELL THERMAL AND FLUID DYNAMIC-MODEL FOR DOWNHOLE HEAT-EXCHANGERS WITH A NATURAL-CONVECTION PROMOTER

Downhole heat exchangers (DHE) eliminate the problem of geothermal flu id disposal, since only hear is taken from the well. For this reason, as well as their low cost and simple installation, they are frequently used in geothermal plants. In the last few years DHEs have been provi ded with a natural convection promoter to improve the heat and mass tr ansfer of geothermal fluid between the aquifer and the well. Knowledge of the interaction between the fluid in the aquifer, in the well and in the promoter is necessary for DHE design. The authors experimentall y verified the existence of a limit in the heat how obtained by the DH E, which is connected only to the aquifer-well-promoter interaction. T his heat how limit is due to the short-circuit effect in the aquifer b etween cold and warm fluids, respectively leaving and entering the wel l, The authors propose a simplified model developed to determine the m ain lumped parameters characterizing the heat and mass transfer betwee n aquifer, well and natural convection promoter. (C) 1997 Elsevier Sci ence.