Abstract
Low-temperature thermal energy conversions down to exergy zero to electric power must contribute energy sustainability. That is to say, reinforcements of power harvesting technologies from extremely low temperatures less than 373 K might be at least one of minimum roles for the current generations. Then, piezoelectric power harvesting process for recovering low-temperature heats was invented by using a unique biphasic operating medium of an underlying water-insoluble/low-boiling-point medium (i.e. NOVEC manufactured by 3M Japan Ltd.) in small quantity and upper-layered water in large quantity. The higher piezoelectric power harvesting densities were naturally revealed with an increase in heating temperatures. Excessive cooling of the operating medium deteriorated the power harvesting efficiency. The denser operating medium was surpassingly helpful to the higher piezoelectric power harvesting density. Concretely, only about 5% density increase of main operating medium (i.e. water with dissolving alum at 0.10 mol/dm3) came to the champion piezoelectric power harvesting density of 92.6 pW/dm2 in this study, which was about 1.4 times compared to that with the original biphasic medium of pure water together with a small quantity of NOVEC.
Highlights
Thermodynamic interests are to approach Carnot efficiencies in any thermal energy converting processes, thermal energy conversions down to exergy zero and practical power generators operated under extremely low temperatures, especially less than 373 K
Piezoelectric power harvesting process for recovering low-temperature heats was invented by using a unique biphasic operating medium of an underlying water-insoluble/low-boiling-point medium (i.e. NOVEC manufactured by 3M Japan Ltd.) in small quantity and upper-layered water in large quantity
This paper provides experimental evidences of the piezoelectric power harvesting densities from a prototype apparatus under various heating/cooling temperatures
Summary
Thermodynamic interests are to approach Carnot efficiencies in any thermal energy converting processes, thermal energy conversions down to exergy zero and practical power generators operated under extremely low temperatures, especially less than 373 K. One vessel is an evaporator containing a small amount of an operating medium possessing a low-boiling-point less than 373 K, such as pentane, methanol and ethanol. As described both in the preceding paragraph and, the primal PEG requires power consuming devices of the electromagnetic valve and diaphragm micro pump since it is dichotomous system composed of the evaporator and power generator where the operating medium is traversed. Characteristics of primal PEG dichotomous system (evaporator and power generator) utilizations of devices consuming electricity slightly (electromagnetic valve and diaphragm micro pump) low vapor pressure impressing frequency (< 1 Hz) dominated by mass transfers intermittent/sequential operations. All the data are discussed in details, and future strategies for improving the prototype piezoelectric power harvesting apparatus are declared throughout this paper [20]
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