Industrial waste heat and geothermal energy represent abundant and widely available clean energy sources that are currently underutilized. However, most of the industrial waste heat streams are at low temperatures (below 130 °C), while the temperature of accessible geothermal energy is constrained by the prohibitively high cost of drilling deep wells. The relatively low temperatures of the obtainable waste heat and geothermal energy thus pose considerable technical challenges for utilization by existing technologies. Recently, low-grade heat utilization by vapor transport though a hydrophobic membrane against a pressure difference was demonstrated. The pioneering study shows the promising potential of directly utilizing environmentally available heat resources below 80 °C for high power-density energy generation. A schematic of the process is depicted below. This study further investigates the impact of membrane chemistry and structural parameters on mass and heat transfer in vapor-pressure-driven (VPD) membrane processes. Membrane materials with different surface hydrophobicity and transport structures are studied. Power density and water flux performance is examined over a range of temperature differences and operating pressures, and the effect of membrane properties on the tradeoff between vapor permeability and thermal insulation is analyzed. A figure of merit parameter, b<sub>m</sub>, is proposed for characterizing VPD membranes. The findings of this study will enhance understanding of the fundamental principles of the novel VPD membrane technology, and the insights can inform the development of greater conversion efficiency and higher power-density clean energy generation.

Low-temperature heat utilization with vapor pressure-driven (VPD) membrane technology: Impact of membrane chemistry and structure

254th National Meeting (2017)

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