Thermal stability of hexamethyldisiloxane (MM) as a working fluid for organic Rankine cycle

Abstract

Summary The high temperature organic Rankine cycle (ORC) has recently attracted much interest for its excellent performance in renewable energy utilization and industrial waste heat recovery. The thermal stability of working fluids is the important property for fluid selection studies because of the possible decomposition at high temperatures. Siloxanes are good selections for high temperature ORCs in previous studies. However, study on the thermal stability of siloxanes for high temperature ORCs is scant. This paper studied the thermal stability of siloxanes, using hexamethyldisiloxane (MM) as a representative fluid. An experimental method with two test systems was designed to identify the compositions of decomposition products. Linear siloxanes, such as octamethyltrisiloxane (MDM), were found to be the main decomposition products of MM. The influences of pressure, temperature, and time on the decomposition were then determined experimentally. The decomposition mechanism of MM and the influences of the decomposition on ORCs were also analyzed based on the experimental results.

Numerical and experimental study of a looped travelling‐wave thermoacoustic electric generator for low‐grade heat recovery

“…In order to utilize the abundant low‐grade heat source, a variety of ways have been developed to convert low‐grade heat into electricity over last few decades. Among them, organic Rankine cycle (ORC) has already been implemented in some industrial applications . Systems using ORC can convert the heat at low temperature into electricity with a careful selection of the organic and high molecular mass working fluids.…”

“…However, these working fluids are generally flammable and toxic by nature, posing potential environmental and safety hazards. In addition, some organic fluids are not thermally stable, causing potential degradation during the long‐time operation, which can lead to significant deterioration in thermodynamic properties . A better thermal match in the evaporator with less irreversibility can be achieved when the supercritical fluid is adopted in ORC, because the thermodynamic process does not need to pass through the two‐phase region .…”

“…Among them, organic Rankine cycle (ORC) has already been implemented in some industrial applications. 2 Systems using ORC can convert the heat at low temperature into electricity with a careful selection of the organic and high molecular mass working fluids. However, these working fluids are generally flammable and toxic by nature, posing potential environmental and safety hazards.…”

“…In addition, some organic fluids are not thermally stable, causing potential degradation during the long-time operation, which can lead to significant deterioration in thermodynamic properties. 2 A better thermal match in the evaporator with less irreversibility can be achieved when the supercritical fluid is adopted in ORC, because the thermodynamic process does not need to pass through the twophase region. 3 However, the critical temperature of the working fluid is too low for condensation process, and the operating pressure of 6 to 16 MPa brings about more safety concerns.…”

Performance comparison of looped thermoacoustic electric generators with various thermoacoustic stages

“…1,2 Moreover, the existing technologies (such as ORC, 3 supercritical ORC, 4 Kalina cycle, 5 and Goswami cycle 6 ) are more or less troubled with safety hazards, environmental problems, high cost, or low efficiency. The abundant low-grade heat sources, including but not limited to geothermal energy, industrial waste heat, and solar thermal energy, show potential in responding to this challenge.…”