霜层非均匀成长加速风冷冰箱蒸发器性能衰减机理及其增效研究

Frost-free refrigerator evaporator has the frost maldistribution caused by non-uniform temperature/humidity distribution. The local frost blocking phenomenon restrains the potential heat transfer capacity of downstream heat exchanger parts. The increasing frost thickness reduces the airflow rate of evaporator fan. The evaporator heat transfer performance deteriorates under non-uniform frosting conditions. First, this project first conducts experiments and measures the local temperature/humidity distribution of inlet air by thermocouple grids and humidity sensors. The frost thickness is measured by high resolution CCD camera. Second, the quasi-static 3-2-1-1 frosting evaporator model is bulit based on the 3D evaporator structure, 2D temperature/humidity distribution of inlte air, 1D frost growth and non-uniform fin spacing. The coupling of the temperature/humidity distribution and air volocity redistribution is included in the numerical model. The coupling mechanism of the many kinds of factors affecting the frosting evaporator performance will be studied and provied. The reasons that the frost maldistribution deteriorates the evaporator heat transfer performance will be revealed. Third, the new technology of face-to-face jet flow of two streams of refrigerating return-air is used to improve the transversal direction of non-uniform frost growth. And the new evaporator structure of enlarging funnel section is applied to improve the longitudinal direction of non-uniform frost growth. Then, the evaporator heat transfer performance will be improved with the improvement of non-uniform frost growth. Based on these, theoretical basis and technical support for the solution to the heat transfer deterioration of the evaporator under non-uniform frosting conditions and defrost heat transfer loss during defrost cycles can be provided.

风冷冰箱翅片管蒸发器存在来流温/湿度不均匀分布导致的非均匀结霜现象，霜层局部堵塞抑制了蒸发器下游换热潜力发挥，导致风机流量非线性减小，加剧蒸发器性能衰减，开展相关研究意义重大。本项目拟通过迎风面热电偶网格和湿度传感器测量来流温/湿度分布，使用多工位高分辨率CCD相机动态监测霜层厚度分布；考虑霜层局部堵塞诱发的来流速度再分布与不均匀来流的耦合，构建包含蒸发器3D结构、来流温/湿度2D分布、速度1D再分布、霜层1D生长和不等间距翅片的准静态3-2-1-1蒸发器结霜性能仿真模型，研究影响霜层非均匀成长过程的多因素耦合机制，揭示霜层非均匀成长加速蒸发器性能衰减的机理。在此基础上提出冷藏回风内凹斜对射新技术和蒸发器漏斗渐阔截面新结构，改善霜层成长的非均匀性，实现蒸发器性能的显著增效。研究成果可为周期性结霜/除霜蒸发器的传热强化和性能评价提供理论指导，提高除霜效率，具有重要的学术意义和工程应用价值。

风冷冰箱翅片管蒸发器存在来流温/湿度不均匀分布导致的非均匀结霜现象，霜层局部堵塞抑制了蒸发器下游换热潜力发挥，导致风机流量非线性减小，加剧蒸发器性能衰减。.项目研究了来流温湿度不均匀分布和来流速度再分布影响霜层非均匀成长过程的耦合作用机制，从机理层面对蒸发器冷表面结霜过程分解建模，对液核形成、液滴生长、液滴冻结、霜晶生长、霜层完全生长等各个子过程分别进行理论分析和模型构建，实现了冷表面结霜全过程的仿真重现；针对风冷冰箱翅片管蒸发器的结霜过程进行了二维CFD仿真，分析了翅片和圆管表面局部霜层生长的特征规律；基于非均匀来流对蒸发器进行子区域划分，构建了包含蒸发器3D结构、来流温/湿度2D分布、速度1D再分布、霜层1D生长和不等间距翅片的准静态3-2-1-1蒸发器结霜性能仿真模型，研究了霜层非均匀生长对蒸发器性能衰减的作用机制。为改善霜层成长的非均匀性，实现蒸发器性能增效的作用机制，对非均匀结霜下风冷冰箱蒸发器的翅片分布进行再设计，提出了基于“压降等速增加”的优化方法，进行了宽工况下的鲁棒性分析，并开展了初始无霜条件下的等效实施。.研究成果可为周期性结霜/除霜蒸发器的传热强化和性能评价提供理论指导。