This Small Business Innovation Research (SBIR) Phase I project will develop critical measurements necessary for eventually producing a high efficiency Thermal Engine with Metastable Power Extraction Step (TEMPES). The TEMPES thermodynamic power cycle is designed primarily for low-temperature power generation and waste heat recovery. The basic operating principle of the TEMPES engine is a closed 2-cycle cylinder piston assembly that converts heat energy in a working fluid to mechanical energy using an innovative thermodynamic power cycle. The method of conversion from heat energy to work is accomplished via formation of metastable non-equilibrium states in a portion of the thermodynamic cycle. Unlike states that are thermodynamically equilibrated, metastable states incorporate a temporal component and history required for fixing the state. Metastable state formation and state trajectories have been previously demonstrated in our lab providing a means for conducting a preliminary analysis of a theoretical TEMPES power cycle. The awarded research work will expand this knowledge base by producing an experimental set-up more closely tailored to closed cycle configurations for ultimate power generation. This experimental configuration will allow detailed characterizations of metastable states and the mechanisms by which these states form and collapse back into equilibrated thermodynamics states.
The broader impact/commercial potential of this project is related to the vast supply of low grade waste heat that could be converted into useful energy. The TEMPES technology can be the core of a scalable electricity generation system using low-grade waste heat as its primary energy source. Recovery of low-grade waste heat can potentially reclaim trillions of BTUs annually from industrial waste heat sources, concentrating solar plants, geothermal plants, and waste-water treatment facilities and convert this energy back into useful work. Low temperature power conversion technology at temperatures <350 C is enabling for waste heat recovery power generation, solar trough power generation, and geothermal power generation at both consumer level and large grid scale energy applications.
to convert low-temperature (<350°C) heat to power at efficiencies greater than Organic Rankine or Kalina Cycle technologies. The TEMPES thermal engine incorporates a new, game-changing thermodynamic power cycle optimized for low temperature heat sources. The TEMPES cycle incorporates a power extraction step that operates a portion of the cycle at a rate much faster than the rate with which the working fluid can thermodynamically equilibrate thereby producing a metastable thermodynamic state from which additional useful work may be extracted. For our Phase I effort, we built a miniature, single-cylinder TEMPES engine testbed with a motor-driven piston assembly and ground support test and control equipment. This single piston design uses a ceramic cylinder and piston head for maximal thermal insulation and structural stability. The testbed is outfitted with control electronics and data acquisition equipment that can measure pressure, position, and temperature anywhere in the piston’s cycle. With this testbed, we can alter the starting parameters to adjust our location in the phase diagram, and make a set of pv curves that show net work from a variable heat source. We verified the formation of metastable states with our testbed, and their ability to perform useful work. We also performed two types of theoretical modeling. A thermal and structural analysis using finite element modeling and 3D analytic structural modeling informs our mechanical design. The results of this thermal analysis showed that we needed sufficiently thick ceramic cylinder walls to maintain thermal isolation of the working fluid in the TEMPES cycle. We also developed an analytical model of the kinetics of the metastable states in the two-phase working fluid of the TEMPES cycle. With our model, we have compared 39 candidate working fluids for their isentropic expansion properties and suitability for forming metastable states. From our experience building a single-cylinder TEMPES engine, we have designed a 6-cylinder, free standing and full-scale TEMPES engine that incorporates all our lessons learned in manufacturing, cycle speed, pressure and scaling properties. Eventually, this design will become an operational unit that demonstrates the TEMPES cycle ability to convert low temperature heat to useful work.
