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Thermally regenerative batteries (TRBs) is an emerging platform for extracting electrical energy from low-grade waste heat (T < 130 °C). TRBs using an ammonia-copper redox couple can store waste-heat energy in a chemical form that can be later discharged to electrical energy upon demand. Previous thermally regenerative ammonia battery (TRAB) demonstrations suffered from poor heat to electrical energy conversion efficiency when benchmarked against thermoelectric generators (TEGs). In this work, we report the highest power density to date for a TRAB (280 W m −2 at 55 °C) with a 5.7× improvement in power density over conventional TRAB designs. Notably, the TRAB was configured similar to a redox flow battery setup, which is termed here an ammonia flow battery (AFB). The substantial improvement in the AFB power density translated to thermal efficiency (η th ) values as high as 2.99% and 37.9% relative to the Carnot efficiency (η th/C ). These values correspond to an 87.6% improvement in η th value over conventional TRAB designs and the highest reported η th/C for low-grade waste heat recovery using TRABs. The excellent performance of the AFB was ascribed to a zero gap design, deploying a low-resistant, inexpensive anion exchange membrane (AEM), and implementing a copper ion selective ionomer coating on the copper mesh electrodes. The high-power AFB in this report represents a significant milestone in harvesting low-grade waste heat.

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Two measurement methods which are multiwave ultrasonic pulsed Doppler (multiwave UVP) method and wire mesh tomography (WMT) have been applied to the measurement of bubbly two-phase flow. Velocity profiles of bubbles and liquid have been measured using multiwave UVP. Simultaneously, cross-sectional void fraction distribution has been measured using WMT. As the result, a combination method has been set up. The measured parameters are indispensable in order to obtain detailed structures of two-phase flow. Multiwave UVP method exploits two basic ultrasonic frequencies which are 2 MHz and 8 MHz. Simultaneous measurement of velocity profiles of bubbles (using 2 MHz frequency) and those of liquid (using 8 MHz frequency), at the same position, is enabled. A multiwave ultrasonic transducer (multiwave TDX) which is able to emit and receive the two ultrasonic frequencies along the measurement line at the same time has been applied. The signal processing is based on the pulsed Doppler method. Using the combination method, first, instantaneous velocity profiles and void fraction distribution have been measured simultaneously for air-water counter-current bubbly flow in a vertical pipe. Flow structure has been clarified. Effect of initial condition on void fraction distribution has been confirmed. Next, measurements have been carried out for subcooled boiling bubbly flow in a vertical pipe. For measurement of subcooled boiling flow, a high temperature wire mesh sensor (WMS) has been developed. A method for separation of velocity profiles of bubbles with different sizes and velocities has been suggested.

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