热源非均布诱发多支路蒸发器过热度振荡及其传热衰减机理

The multi-circuit evaporator is widely used in large and middle scale refrigeration systems, but inevitably suffers from the problem of heat source maldistribution due to complicated factors, such as narrow tortuous air ducts and non-uniform water flow resistance. This project aims at investigating the mechanism of heat source maldistribution inducing the superheat oscillation and its resultant heat transfer deterioration in multi-circuit evaporators. The microscopic characteristics of refrigerant and their variation modes induced by heat source maldistribution would be identified at the outlets of all circuits, including flow regime. Then, the thermophysical process in the transient mixing behavior of non-equilibrium state refrigerant at the overall outlet would be uncovered, especially the entrained liquid refrigerant droplets’ evaporation, oscillation, and hitting onto the tube wall, which significantly affects the superheat stability at the overall outlet. Next, the regulation and re-allocation mode of refrigerant supply from the throttling device which is based on the superheat degree at the overall outlet would be described, as well as the resultant re-influence on the overall outlet superheat. Moreover, the secondary deterioration in the heat transfer performance of the multi-circuit evaporator caused by the periodically variation in refrigerant supply after hunting occurs in the superheat feedback control would be analyzed. Finally, the dynamic model coupling superheat stability and heat transfer performance of the multi-circuit evaporators would be constructed, which could realize the complete simulation process from heat source maldistribution to the superheat stability, and then to the heat transfer performance variation of multi-circuit evaporators. The expected results of this project would provide theoretical basis and methodological support for the superheat control stabilization and heat transfer enhancement of multi-circuit evaporators.

多支路蒸发器广泛应用于大、中型制冷系统中，因风道狭小曲折、水流路阻力不均等原因，热源非均布难以避免，项目旨在研究由热源非均布诱发的多支路蒸发器过热度振荡行为及其传热性能衰减的机理。识别热源非均布诱发蒸发器各支路出口制冷剂的流型、流态等微观特征及其演化规律；揭示非平衡状态制冷剂在总出口处瞬态掺混行为的热物理过程，尤其掺混液滴的蒸发、振荡及其与管壁的随机碰撞模式对总出口过热度稳定性的影响机制；描述节流机构基于蒸发器总出口过热度反馈控制的流量调节与再分配特性，及其对蒸发器出口过热度的逆向影响；分析过热度反馈振荡诱发的周期性波动供液对多支路蒸发器传热性能的“二次恶化”机理；建立热源非均布多支路蒸发器过热度稳定性和传热性能耦合的动态仿真模型，实现由“热源非均布→过热度控制稳定性→蒸发器传热性能”的完整的仿真过程。预期研究结果将为多支路蒸发器过热度控制稳定性及传热性能提升提供理论依据与技术支持。

多支路蒸发器广泛应用于大、中型制冷系统中，因风道狭小曲折、水流路阻力不均等原因，热源非均布难以避免。.项目研究了由热源非均布诱发的多支路蒸发器过热度振荡行为及其传热性能衰减的机理，发现热源非均布引起非平衡状态制冷剂在总出口处瞬态掺混行为，其中裹挟制冷剂液滴与管壁的随机碰撞并蒸发吸热是过热度振荡的根本原因；而基于蒸发器总出口过热度反馈控制的流量调节与再分配特性，会放大过热度振荡幅度，使系统进入反复超调的状态；此外，过热度反馈振荡诱发的周期性波动供液，时均供液量大幅降低，对多支路蒸发器传热性能产生“二次恶化”；建立了热源非均布多支路蒸发器过热度稳定性和传热性能耦合的动态仿真模型，实现由“热源非均布→过热度控制稳定性→蒸发器传热性能”的完整的仿真过程。.针对制冷空调领域普遍存在的翅片管换热器风速非均匀分布情形，设计新式非等宽翅片C型整体式换热器，并提炼出其过热度控制及传热性能提升的设计准则，即“C型换热器+最速曲线轮廓+优选翅片强化处理”，基于翅片与风速非均匀相似协同强化原则设计C型换热器及其翅片，显著提升过热度稳定性及其传热特性；借鉴“最速曲线”设计C型翅片轮廓提升其排水性能，仿真和实验研究了新式C型翅片的排水特性，从而提升了湿和结霜工况下翅片管换热器的流动与传热特性；③采用Taguchi优化确定了C型翅片表面结构设计方案，仿真和实验研究了不同强化方案的传热和排水性能。.研究结果将为多支路蒸发器过热度控制稳定性及传热性能提升提供理论依据与技术支持。