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


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.

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Figure 1: Working principle of the thermo-osmotic energy conversion system.
Figure 2: Demonstration of power generation using a vapour-gap membrane.
Figure 3: Water flux across a membrane driven by a temperature gradient.
Figure 4: Efficiency of a closed-loop system with heat recovery.


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We acknowledge the National Science Foundation Graduate Research Fellowship DGE-1122492 awarded to A.P.S.

Author information




A.P.S., N.Y.Y., S.L., J.L. and M.E. participated in developing the process and designing the experiments. A.P.S. performed the experiments and analysed the data. A.P.S. and S.L. conducted the system modelling. A.P.S. and M.E. co-wrote the paper. All authors contributed to data analysis, discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Menachem Elimelech.

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The authors declare no competing financial interests.

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Supplementary Notes 1–8, Supplementary Figures 1–23, Supplementary Tables 1, Supplementary References. (PDF 1081 kb)

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Straub, A., Yip, N., Lin, S. et al. Harvesting low-grade heat energy using thermo-osmotic vapour transport through nanoporous membranes. Nat Energy 1, 16090 (2016). https://doi.org/10.1038/nenergy.2016.90

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