DESIGN AND ANALYSIS OF A HIGH POWER DENSITY, LOW TEMPERATURE WASTE HEAT RECOVERY SYSTEM USING AN OIL-FREE TURBOALTERNATOR

In this paper the authors will present the design and preliminary test results for a distributed electric generating system that uses renewable energy sources for economical load-following and peak-shaving capability in an oil-free, highspeed micro-turboalternator system using compliant foil bearings and a permanent magnet alternator. Test results achieved with the prototype system operating to full speed and under power generating mode will be presented. A comparison between predicted and measured electrical output will also be presented up to a power generating level of 25 kWe at approximately 55,000 rpm. The excellent correlation between design and test provides the basis for scale up to larger power levels. Based upon the turboaltemator test results a thermodynamic cycle analysis of a system using low grade waste heat water at approximately 100 C will be reviewed. The tradeoff study results for a series of environmentally friendly refrigerant working fluids will also be presented including sensitivity to vaporization and condensing temperatures. Based on the cycle and pinch point analyses predicted maximum output power was determined. Finally a preliminary turbine design for the selected R134a working fluid was completed. The results of this study show that a net output power level of greater than 40 kW is possible for approximately 240 1/m flow of water at 100C is possible.