Harvesting low-grade heat energy using thermo-osmotic vapour transport through nanoporous membranes

• Published in: Nature energy Vol. 1; no. 7; p. 16090
• Main Authors: Straub, Anthony P., Yip, Ngai Yin, Lin, Shihong, Lee, Jongho, Elimelech, Menachem
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 27.06.2016; Nature Publishing Group
• Subjects: 639/4077/4072/4062; Economics and Management; Energy; Energy harvesting; Energy Policy; Energy Storage; Energy Systems; Heat; Heat sinks; Heat sources; Hydrophobicity; Low temperature; Membranes; Renewable and Green Energy; Reservoirs; Temperature gradients
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/nenergy.2016.90

Low-grade heat from sources below 100  ∘ C offers a vast quantity of energy. The ability to extract this energy, however, is limited with existing technologies as they are not well-suited to harvest energy from sources with variable heat output or with a small temperature difference between the source and the environment. Here, we present a process for extracting energy from low-grade heat sources utilizing hydrophobic, nanoporous membranes that trap air within their pores when submerged in a liquid. By driving a thermo-osmotic vapour flux across the membrane from a hot reservoir to a pressurized cold reservoir, heat energy can be converted to mechanical work. We demonstrate operation of air-trapping membranes under hydraulic pressures up to 13 bar, show that power densities as high as 3.53 ± 0.29 W m −2 are achievable with a 60  ∘ C heat source and a 20  ∘ C heat sink, and estimate the efficiency of a full-scale system. The results demonstrate a promising process to harvest energy from low-temperature differences (<40  ∘ C) and fluctuating heat sources. Heat recovery from sources with temperatures below 100  ∘ C can provide a significant amount of energy, but it is difficult to achieve with current technologies. Straub  et al.  devise a thermo-osmotic energy conversion process that can generate power from heat sources at temperatures as low as 40  ∘ C.