| Title | NUMERICAL SIMULATION OF HEAT EXTRACTION IN THE GEOTHERMAL PART OF THE EXCHANGER IN ONE-HOLE SYSTEM |
|---|---|
| Authors | Tomasz KUJAWA, W?adys?aw NOWAK |
| Year | 2001 |
| Conference | Geothermal Energy in Underground Mines, Ustron, Poland |
| Keywords | downhole heat exchanger |
| Abstract | Geothermal plants and power stations can work as one-hole systems with an injection and production well, or as two-hole systems. The one-hole system operates using a vertical geothermal probe. It is an exchanger that has two parts. One part is immersed in a geothermal deposit, where the heat extraction medium takes heat from geothermal water. The other part of the exchanger, a double-pipe exchanger, is located in the impermeable rock massif. The extraction medium is conducted through a rig-shaped channel to the geothermal part of the exchanger, where its temperature rises. The heat extraction medium flows up to the ground through the inner pipe. However, the heat exchange takes place in both parts of the exchanger, and the part of the exchanger located in the geothermal deposit has a considerable impact on the amount of geothermal energy gained. The type of exchanger also influences the amount of heat extracted. The results of exchanger calculations on heat extraction for two types of exchanger (Field's * exchanger and a spiral-tube exchanger) are presented. The calculations were carried out using two computational models. In the first model it was assumed that the temperature field and the overall heat transfer coefficient were known. In the second, the exchanger was considered to be a cross-counter-flow heat exchanger with a single non-mixing fluid. It was also assumed that the temperature field and the overall heat transfer coefficient were known in this case too. In both cases, it was assumed that the temperature field in a geothermal deposit changes linearly in a vertical direction, as is the case in a rock massif. To simplify the calculations, in all the cases the same conditions for the double-pipe heat exchanger part were taken into account. Also, it was assumed that the inner pipe was perfectly insulated. Comparisons of the results of the heat extraction calculations for the Field exchanger and the spiraltube exchanger, obtained using both computational models, are presented as graphs. The graphs illustrate the impact of the overall heat transfer coefficients and heat extraction rates. |