Multi-stage rotary liquid-piston compression for hightemperature heat pumps
A crucial and often overlooked source of emissions is industrial production, especially the generation of process heat. This heat is used for many critical processes such as drying, melting, and chemical transformations. Electrification of this heat supply, powered by renewables, can be a promising means to decarbonize the supply chain. However, for it to be cost-competitive, the heat provided needs to be efficiently delivered. To this end, we can use heat pumps, which use one unit of energy to deliver multiple units of heat. Unfortunately, typical vapour compression heat pump designs have several limitations that prevent them from functioning at high temperatures. For such designs, typical compressors cannot deliver the required high pressure ratios, and their lubricant breaks down above certain temperatures. This work presents a new heat pump design, which avoids using a compressor: instead, a conventional pump is used to pressurize a liquid, which then exchanges its pressure with the working fluid by means of a rotary liquid piston device. This process is repeated over multiple stages to achieve a high isentropic compression efficiency. As the active mechanical elements (e.g. impeller, vanes) are isolated from the suction fluid, there is potential to both achieve higher temperatures and design cycles that rely on wet compression. This work details the overall architecture of the cycles and explains its working principle. Thermodynamic correlations are used to calculate the performance of the pressure exchanger. Finally, the coefficient of performance (COP) of the heat pump is estimated and design considerations are explored.