The effect of working fluid properties on the performance of a miniature free piston expander for waste heat harvesting
Burugupally, Sindhu Preetham
Depcik, Christopher David
MetadataShow full item record
Burugupally, Sindhu Preetham; Weiss, Leland; Depcik, Christopher David. 2019. The effect of working fluid properties on the performance of a miniature free piston expander for waste heat harvesting. Applied Thermal Engineering, vol. 151:pp 431-438
Power generation from waste heat sources at the miniature length scales may be generated by using phase change working fluids (liquid-to-vapor) in a traditional boiler-expander-condenser-pump system. This paper builds on our prior work of boiler and expander design by investigating the effects of working fluid properties on an expander unit based on a Free Piston (FPE) architecture. Here, using first principles, a lumped-parameter model of the FPE is derived by idealizing the FPE as a linear spring-mass-damper system. Moreover, a linear-generator model is incorporated to study the effects on useful power output from the FPE directly. As a result, insight into the thermodynamic processes within the FPE are detailed and general recommendations for working fluid selection are established. They include: (1) to achieve a higher FPE efficiency, it is desirable for a working fluid to have high specific heat ratio, and (2) a peak output voltage of about 20 V AC and peak output power of around 2 W can be generated by coupling a centimeter-scale electromagnetic energy converter to the FPE. Overall, this effort shows the promise of reliable miniature thermal power generation from low temperature waste heat sources.
Click on the DOI link to access the article (may not be free).