The migration and redistribution of refrigerant are critical factors that affect the refrigeration system performance. To improve the defrosting and start-up heating performance, it is essential to investigate the transient distribution characteristics of refrigerant mass. However, quantitative studies on the transient distribution of refrigerant during defrosting and start-up heating stages in heat pump systems are scarce. The dynamic characteristics of defrosting and start-up heating cannot be deeply understood from the perspective of refrigerant migration. Therefore, the purpose of this paper is to experimentally study the transient distribution characteristics of refrigerants during defrosting and start-up heating stages for different defrosting strategies. Based on the refrigerant-side dynamic characteristics, the defrosting cycle is divided into three stages for the defrosting strategy with the indoor fan off, the indoor coil charging stage, accumulator charging stage, and wet compression stage. Additionally, for the defrosting strategy with the indoor fan on, it is divided into two stages: the indoor coil charging stage and the outdoor coil discharging stage. For the defrosting strategy with the indoor fan off, the wet compression phenomenon occurs at 240 s, which poses significant challenges to the stability of the compressor. At the end of defrosting, the accumulator retains the most refrigerant for both defrosting strategies. From the perspective of refrigerant transient distribution, the start-up heating stage is the process of refrigerant migration from the accumulator to indoor and outdoor coils. The two main factors that affect start-up heating performance are heating the indoor coil metal, and vaporizing the liquid refrigerant in the accumulator. For the defrosting strategy with indoor fan on, the energy consumption of heating the indoor coil and vaporizing the liquid refrigerant is reduced by 45.7 % and 48.9 % during start-up heating. Based on the transient refrigerant distribution experiment, some methods to improve defrosting and start-up heating are also proposed. This study can provide useful insights into the transient distribution of refrigerants and provide guidance for defrosting optimization.

中文翻译：

---

不同逆循环除霜策略下微通道换热器热泵系统的瞬态制冷剂分布


制冷剂的迁移和再分布是影响制冷系统性能的关键因素。为了提高除霜和启动制热性能，有必要研究制冷剂质量的瞬态分布特性。然而，对热泵系统除霜和启动加热阶段制冷剂瞬态分布的定量研究很少。从制冷剂迁移角度无法深入理解除霜和启动制热的动态特性。因此，本文的目的是实验研究不同除霜策略下除霜和启动制热阶段制冷剂的瞬态分布特性。根据制冷剂侧动态特性，室内风扇关闭除霜策略将除霜循环分为三个阶段：室内盘管充液阶段、蓄能器充液阶段和湿压缩阶段。另外，对于室内风扇打开的除霜策略，分为两个阶段：室内盘管充电阶段和室外盘管放电阶段。对于室内风机关闭的除霜策略，在240 s时出现湿压缩现象，这对压缩机的稳定性提出了重大挑战。除霜结束时，蓄能器保留两种除霜策略的大部分制冷剂。从制冷剂瞬态分布来看，启动制热阶段是制冷剂从蓄能器向室内外盘管迁移的过程。影响启动加热性能的两个主要因素是室内盘管金属的加热和蓄能器中液体制冷剂的汽化。 采用室内风扇开启除霜策略，启动制热时室内盘管加热和液体制冷剂汽化能耗分别降低45.7%和48.9%。基于瞬态制冷剂分布实验，还提出了一些改善除霜和启动加热的方法。这项研究可以为制冷剂的瞬态分布提供有用的见解，并为除霜优化提供指导。