A small scroll expander has been incorporated into a power cycle for performance evaluation. Using heat from a circulating hot oil supply, a working fluid (R123) was vapourized under pressure and fed to the inlet of the expander. Power generated was measured by a torque/rotation rate sensor as the power was delivered to a compressor. The exhausted working fluid was then sent through a regenerator to recover thermal energy, and then to an air-cooled condensation heat exchanger. To complete the cycle, the working fluid passed through a pump and was fed back to the boiler by way of the regenerator. The major components of the power cycle were monitored for performance, and from these values, overall cycle efficiency was determined. A model of the system was also developed in order to validate system state points and allow follow-on projections of cycle performance with better component efficiencies. Depending on the operating state points during testing, the power output from the cycle ranged from 187 to 256 W. At nominal ambient outside temperatures (22.5 °C), the system efficiency was 7.2 per cent. The critical component limiting the overall system efficiency was the expander. Operating within the power cycle, expander efficiency was measured at levels between 45 and 50 per cent, based on the isentropic ideal. The obvious path forward is to improve the efficiency of the scroll expander.

A small-scale scroll expander was developed and tested. The expander was based on a compliant scroll compressor having a displacement of ∼6.8 cm3. A test loop was also developed for determining expander performance parameters. The loop employed a compressor to pressurize the working fluid up to 2758 kPa and a heat exchanger to create the expander inlet conditions that would characterize an operating power cycle. The expander was tested with R134a as the working fluid. For power output measurements, a dynamometer was used where torque and rotational rate were measured. An important feature in adapting a scroll compressor to expander duty was the lubrication of the scroll wraps during operation and the lubrication required by the journal bearings within the expander housing. The approach used in this study was to dissolve a compatible oil into the circulating working fluid to lubricate the wraps, while a pump was employed to deliver pressurized oil to the bearings. The pressurized oil supply was also used to generate a controlled force to the upper stationary scroll wrap through a sealed piston assembly. This force maintained axial contact between the upper and lower scroll wraps during operation. After expansion, the R134a vapour passed through an orifice flow meter and then to a liquid-cooled heat exchanger. It then enters a compressor and heat exchanger to complete the flow loop. A series of performance tests were conducted on the expander at various expander rotational speeds, inlet and outlet pressures, and scroll sealing pressures. Test results show consistent isentropic efficiencies of over 70 per cent for the expander at its maximum efficiency operating points. The expander performance, however, is a function of speed, pressure ratio, and scroll sealing pressure.

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