| Title | A novel multi-tube heat exchanger applicable for a geothermal power plant |
|---|---|
| Authors | Hsieh, Guo, Lee, Liu, Cheng, Wang |
| Year | 2013 |
| Conference | European Geothermal Conference |
| Keywords | Downhole heat exchanger, Geothermal, Organic Rankine Cycle, Shell and Tube heat exchanger |
| Abstract | In this study, the present authors had proposed a novel multi-tube heat exchanger (NMTHE) to retrieve geothermal energy as the heat source for ORC. The NMTHE was designed to be placed in the well and it features the shell and tube heat exchanger configuration. The tube-side fluid flow has been divided into 40 small tubes (small tubes with outer diameter 12.7 mm and inner diameter 10.7 mm). The 40 small tubes are designed at manifold to improve flow uniformity in the well. The NMTHE was designed subject to natural convection in the shell-side and forced convection on the tube-side. The total manifold length of the heat exchanger is 11 meters and the effective heat exchange area is 17.22 m².The inlet temperature of the heat exchanger tube-side is 100.4 °C, the outlet temperature is 130 °C, flow rate is 10 tons/hr and the estimated heat capacity is 250 kW, which is used as the heat input into the ORC system to generate electricity. Through this design, we can improve the effective heat capacity within limited space in the well. The preliminary experiment showed that by increasing the flow rate of pure water to 13 ton/hr, the heat transfer rate would be as large as 700 kW. The inlet and the outlet temperature of the heat exchanger shell-side is around 80~85 °C and 120~130 °C, respectively. Test results also shows that the shell-side heat transfer coefficient peaks at 1600 W/m2 K when the inlet pressure is 1.5bar at the flow rate 7.4 CMH and is decreased to 800 W/m2K 2.57bar at 6.6 CMH. It is noted that the pressure of the hot water from the geothermal well affects the heat transfer coefficient due to the effects of vapour quality and dissolved carbon dioxide. Moreover, heat transfer coefficient is increased with the high flow rate for geothermal water. The novel multi-tube heat exchanger associated with an ORC system has been successfully operated with a maximum capacity of 60 kWh. |