Enhanced Geothermal Systems – Promises and Challenges

Geothermal energy plays a very important role in the energy basket of the world. However, understanding the geothermal hotspots and exploiting the same from deep reservoirs, by using advanced drilling technologies, is a key challenge. This study focuses on reservoirs at a depth greater than 3 km and temperatures more than 150°C. These resources are qualified as Enhanced Geothermal System (EGS). Artificially induced technologies are employed to enhance the reservoir permeability and fluid saturation. The present study concentrates on EGS resources, their types, technologies employed to extract energy and their applications in improving power generation. Studies on fracture stimulation using hydraulic fracturing and hydro shearing are also evaluated. The associated micro-seismic events and control measures for the same are discussed in this study. Various simulators for reservoir characterization and description are also analyzed and presented. Controlled fluid injection and super critical CO2 as heat transmission fluid are described for the benefit of the readers. The advantages of using CO2 over water and its role in reducing the carbon footprint are brought out in this paper for further studies.

Connecting volume effects on dynamics of pneumatic pressure measurement systems

The pressure sensors are often placed at a certain distance from the measured object. Beside the properties of the transmission fluid, dynamic characteristics of such a measurement system depends on the geometry and dimensions of the connecting elements. So far made research works have shown that the internal volume of the pressure sensor can have a large influence on the dynamic response. This paper is focused on theoretical analysis of the effects of the sensor volume on characteristic parameters of both the frequency and the time response of the system under discussion with a gas medium.

Evaluation of thermo-oxidized Jatropha bio-oil in lubrication of actual wet clutch materials

In this work, an assessment of the performance of thermo-oxidated Jatropha oil as a lubricant for actual wet clutch materials was performed and compared with a commercial automatic transmission fluid. For this, Jatropha oil, a commercial automatic transmission fluid and a blend of 20 vol% Jatropha oil–80 vol% automatic transmission fluid were subjected to thermo-oxidative aging at 26 °C and 100 °C, followed by a pin-on-disk testing with disk samples from an actual wet clutch. Evaluation of the film thickness at the sliding interface resulted in a boundary lubrication regime for all the tests. The changes in oxidation, viscosity, and a viscosity index of the samples were evaluated along with friction coefficients at various sliding speeds. Jatropha oil was the most sensitive to thermo-oxidation. Jatropha oil and the blend showed a higher viscosity increase than automatic transmission fluid with thermo-oxidation, while the viscosity index of all oils was decreased considerably, Jatropha oil and the blend being the most reduced. Finally, the anti-shudder property, as measured by the change in the friction coefficient with a sliding speed, of Jatropha oil and automatic transmission fluid was improved by thermo-oxidation at 26 °C but worsened at 100 °C, meanwhile it was barely affected in the blend. Therefore, these results indicate that using pure Jatropha oil as automatic transmission fluid would be unsuitable, but blending it with automatic transmission fluids in specific proportions may be apposite for improving the friction properties of wet clutches even under thermo-oxidative conditions.

Surface Temperature Effect on Convective Heat Transfer Coefficients for Jet Impingement Cooling of Electric Machines With Automatic Transmission Fluid

In this study, the results of NREL’s continued work on experimental characterization of the thermal performance of free-surface jets of automatic transmission fluid impinged on a heated target surface are presented. The measured heat transfer coefficients are useful for understanding factors influencing performance of driveline fluid-based cooling systems for electric machines and help designers in developing high-performance, power-dense and reliable machines. Experiments were carried out for different fluid and target surface temperatures (50°C, 70°C, and 90°C for the fluid and 90°C, 100°C, 110°C, and 120°C for the target surface). Impinging jet velocities (0.5 m/s to 7.5 m/s) and the jet position on the target surface (center versus edge) were also varied. The impinging angle was kept at 90° relative to the target surface. It was found that higher target surface temperature increased heat transfer coefficients, namely, increasing surface temperature from 90°C to 120°C enhanced heat transfer coefficient values at higher impinged jet velocities (7.5 m/s) by up to 15%.