Concerning the inner pipe the results
Fig. 1. Wellbore heat exchanger. Cross section and schematic.Figure optionsDownload full-size imageDownload as PowerPoint slide
The produced thermal energy can be used in district heating plants or can be converted into electricity using an Organic Ranking Cycle (ORC) plant (Fig. 2) as discussed in previous works . Other researchers ,  and  have focused on a direct power generation system to convert the thermal energy into electricity. Instead the proposed system is a binary (S)-CPW 399 plant: there are two steps of heat exchange: in the first step a working fluid is circulated in the double-pipe exchanger and amniote egg acquires heat from the rock; in the second step the working fluid exchanges the heat with the low-boiling point fluid of the ORC machine. In order to evaluate the conversion capacity of the ORC plant a thermodynamic model has been build. Having selected the working fluid, the produced electrical power has been compared to that one evaluated using the relationship, based on data from actual ORC plants, between thermal efficiency and fluid temperature .