The first experiment for the Downhole Coaxial Heat Exchanger (DCHE, see Fig. 1) was carried out successfully at the HGP-A well on the island of Hawaii using an interval from the surface down to a depth of 876.5m. The temperature at the bottom of the DCHE before the onset of the experiment was 110°C. The observed highest hot water temperature during the experiment was 98°C, and the maximum gross and net thermal outputs were 540 kW and 370 kW, respectively. The experiment proceeded smoothly and excellent agreement between measured values and computed values was obtained in the analysis (Morita et a/., 1992). Thus, the concept of the DCHE was proved to be sound
