Design and simulations of refrigerated sea water chillers with CO2 ejector pumps for marine applications in hot climates.

Various system configurations and control strategies were developed in order to improve performance of R744 systems in hot ambient conditions. However, stationary land applications are characterised by negligible limits of space for system equipment as in the case of marine industry, i.e. fishing vessels. CO2 refrigeration system for fishing vessels are developed by Kuldeteknisk AS. Namely, Refrigerated Sea Water Chillers operation at Norwegian coast confirmed successful application of this approach. In this study, modified layouts are evaluated for operation in warmer climates without the need for an additional compressor unit, to maintain the compactness of the unit. The flash gas valve-, parallel compression- and multi-ejector system was numerically investigated. Moreover, each system was equipped in the liquid ejector section enabling a flooded operation of the evaporator. Sea water temperatures as occurring in Mediterranean and East-Asian waters were investigated. Both the optimal high-pressure as well as the pressure level in an intermediate pressure receiver are controlled to achieve low energy consumptions. Finally, up to 70% of performance improvement was obtained in the case of the most advanced installation working in warm East-Asian waters. The obtained results showed that the proper design of the system should ensure no necessity of an additional compressor in warmer climates still maintaining the designed cooling capacity.

为改善热环境下R744（二氧化碳制冷剂）系统的运行性能，已有多种系统构型与控制策略被开发出来。不过固定式陆地应用的系统设备空间限制可忽略不计（即无需追求装置紧凑性），而海洋产业（如渔船）则恰恰相反。由Kuldeteknisk AS开发的渔船用二氧化碳制冷系统，其在挪威海岸运行的海水冷藏冷却器应用已证实该方案的成功落地。本研究针对温暖气候下的运行工况，评估了无需额外压缩机组即可保持装置紧凑性的改进型系统布局。研究对闪发气体阀（flash gas valve）系统、并联压缩系统及多喷射器系统开展了数值仿真研究。此外，每套系统均配备了液体喷射器组件，可实现蒸发器的满液式运行。研究还针对地中海与东亚海域的海水温度工况展开了分析。为实现低能耗运行，研究对最优高压侧压力与中间压力储液器（intermediate pressure receiver）内的压力水平均进行了调控。最终，在东亚温暖海域运行的最先进系统构型中，性能提升幅度可达70%。研究结果表明，合理设计的系统可在温暖气候下无需额外压缩机组，同时保持设计制冷量。