Whilst the efficiency of reverse electrodialysis (RED) for thermal-to-electrical conversion has been theoretically demonstrated for low-grade waste heat, the specific configuration and salinity required to manage power generation has been less well described. This study demonstrates that operating RED by recycling feed solutions provides the most suitable configuration for energy recovery from a fixed solution volume, providing a minimum unitary cost for energy production. For a fixed membrane area, recycling feeds achieves energy efficiency seven times higher than single pass (conventional operation), and with an improved power density. However, ionic transport, water flux and concentration polarisation introduce complex temporal effects when concentrated brines are recirculated, that are not ordinarily encountered in single pass systems. Regeneration of the concentration gradient at around 80% energy dissipation was deemed most economically pragmatic, due to the increased resistance to mass transport beyond this threshold. However, this leads to significant exergy destruction that could be improved by interventions to better control ionic build up in the dilute feed. Further improvements to energy efficiency were fostered through optimising current density for each brine concentration independently. Whilst energy efficiency was greatest at lower brine concentrations, the work produced from a fixed volume of feed solution was greatest at higher saline concentrations. Since the thermal-to-electrical conversion proposed is governed by volumetric heat utilisation (distillation to reset the concentration gradient), higher brine concentrations are therefore recommended to improve total system efficiency. Importantly, this study provides new evidence for the configuration and boundary conditions required to realise RED as a practical solution for application to sources of low-grade waste heat in industry.

中文翻译：

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管理闭环反向电渗析中的功耗以最大限度地提高热电转换过程中的能量回收

虽然逆电渗析 (RED) 的热电转换效率已在理论上证明用于低品位废热，但管理发电所需的特定配置和盐度尚未得到很好的描述。该研究表明，通过回收进料溶液运行 RED 为从固定溶液体积中回收能量提供了最合适的配置，从而为能源生产提供了最低的单一成本。对于固定的膜面积，循环进料的能效比单程（常规操作）高 7 倍，并具有更高的功率密度。然而，当浓缩盐水再循环时，离子传输、水通量和浓差极化会引入复杂的时间效应，这在单程系统中通常不会遇到。由于超过此阈值对质量传输的阻力增加，因此在大约 80% 能量耗散时再生浓度梯度被认为是最经济实用的。然而，这会导致显着的火用破坏，这可以通过干预来改善，以更好地控制稀释进料中的离子积聚。通过独立优化每种盐水浓度的电流密度，进一步提高了能源效率。虽然在较低盐水浓度下能量效率最高，但在较高盐水浓度下由固定体积的进料溶液产生的功最大。由于所提出的热电转换受体积热利用（蒸馏以重置浓度梯度）控制，因此，建议使用更高的盐水浓度来提高系统总效率。重要的是，这项研究为实现 RED 作为应用于工业低品位废热源的实用解决方案所需的配置和边界条件提供了新的证据。