Engineering research on positive displacement gas expanders. Phase I technical report

A research, design, and development program related to positive displacement gas expanders is reported. The objective of this program is to develop and demonstrate a more cost effective gas expander for use in those waste heat recovery systems which utilize an Organic Rankine Cycle. To provide a lower cost machine, the gas expander uses a positive displacement concept, rather than a turbine as currently used. Several positive displacement machine concepts were examined, and various performance measures have been developed for each of the concepts. The machine concepts were: single and multiple cylinder reciprocators, radial piston, roller piston, sliding vane, trochoidal, helical screw, and lobed rotor. For each of the concepts, designs were generated for machines operating with three different sets of operating conditions. These designs were then used to develop measures of efficiency and cost, and to examine other characteristics of the machines, such as development risk and ability to operate with different flow, pressure, and temperature levels. Based upon an evaluation of these characteristics, a specific concept was selected for further development. This concept is a double acting, single cylinder reciprocating machine with crossheads and ceramic liners