Enrico Maria Latrofa

Gravity Heat Pipes as Geothermal Convectors

ABSTRACT Gravity heat pipes may be used as devices to extract heat from hot acquifers such as those of low enthalpy geothermal fields: under such conditions heat pipes have been called geothermal convectors (GTC). The Authors describe the design and tests of a pipe able to transmit up to 25 kW thermal power from a surface acquifer, located in a volcanic area. The acquifer temperature is 65°C and the cooling water temperature leaving the condenser is set at a value of 40°C or more. GTC features an evaporator made of an array of 65 stain less steel AISI 316 pipes with a 17,2 mm outer diameter and 2500 mm length. The overall pipe lenght is 7,00 m; it maybe increased by adding longer adiabatic sections by means of flanges. R-11 has been selected as working fluid and the average working pressure is 3 bar. The experimented GTC is expected to work with other fluids without difficulties. In the present work the Authors describe: – preliminary laboratory tests carried on a single pipe immersed in a thermostat reproducing water speed up to 0.1 m/s; in such tests the overall pipe conductance has been determined in order to design the final device. – final design and construction of a full scale device.

Geothermal Convector Design: Solutions, Design Criteria, and Calculation Methods

Abstract The geothermal convector (GTC) is an unconventional system for heat extraction from a geothermal aquifer without fluid withdrawal. In this system a special two-phase thermosyphon is used. This device works with a downhole evaporator and with a condenser at the ground level. The system shares advantages and disadvantages with other downhole heat exchanger plants; for instance, a second well to return geothermal water to the aquifier is not required. Because of the limitations of the natural heal flow in the hot aquifer, however, the device is most suitable for small-to moderate-size applications. In this article, the fundamental elements required to determine the device performance and the thermal design criteria are reported and a GTC prototype is described. Designed for 70°C temperature of the geothermal water and 3 m length of the evaporator, this prototype was recently installed in a geothermal well on the island of Ischia. In this article the results of the first experimental tests are reported.