Downhole heat exchangers (DHE) eliminate the problem of geothermal fluid disposal because only heat is taken from the well. To design DHEs, it is necessary to know how aquifer fluid interacts with well fluid Experimental tests carried out by the authors indicate that there is a limit to the heat flux that can be obtained by a DHE in a well: this limit arises only from the thermal and fluid dynamic interaction between the well and aquifer The two-dimensional thermal and flowfields in the aquifer were also determined using the finite element method. It was found that the heat flux limit is due to the short circuit effect in the aquifer between cold and warm fluids, respectively, leaving and entering the well. A characteristic parameter, termed the "short circuit factor" was introduced to a simple model with lumped parameters. This factor depends on the average temperatures of the well inlet and outlet fluid and on the unperturbed aquifer temperature. A simplified model developed by the authors allowed the maximum heat flux obtained by the DHE in the well to be determined using knowledge of the short-circuit factor as the starting point.
AN AQUIFER-WELL THERMAL AND FLUID DYNAMIC MODEL TO DESIGN A DOWNHOLE HEAT EXCHANGER
CASAROSA, CLAUDIO;
1998-01-01
Abstract
Downhole heat exchangers (DHE) eliminate the problem of geothermal fluid disposal because only heat is taken from the well. To design DHEs, it is necessary to know how aquifer fluid interacts with well fluid Experimental tests carried out by the authors indicate that there is a limit to the heat flux that can be obtained by a DHE in a well: this limit arises only from the thermal and fluid dynamic interaction between the well and aquifer The two-dimensional thermal and flowfields in the aquifer were also determined using the finite element method. It was found that the heat flux limit is due to the short circuit effect in the aquifer between cold and warm fluids, respectively, leaving and entering the well. A characteristic parameter, termed the "short circuit factor" was introduced to a simple model with lumped parameters. This factor depends on the average temperatures of the well inlet and outlet fluid and on the unperturbed aquifer temperature. A simplified model developed by the authors allowed the maximum heat flux obtained by the DHE in the well to be determined using knowledge of the short-circuit factor as the starting point.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
