空气源热泵逆循环除霜优化研究现状与发展趋势

Research Status and Trends on Reverse Cycle Defrosting for Air Source Heat Pump Units

空气源热泵在低温高湿环境下运行制热工况时,存在其室外空气侧翅片管换热器表面结霜这一难题,无数国内外学者投身于热泵除霜研究,尤其针对具有改造简单、除霜效率高、不需外加辅助热源等诸多优点的逆循环除霜.文中围绕性能优化对比实验研究、性能优化数值模拟研究、控制策略优化研究等三方面,对既有空气源热泵逆循环除霜的前沿研究成果进行了综述.结果表明,相变蓄能逆循环除霜方法因解决了除霜时能量不足的根本性问题,成为性能优化对比实验研究部分的重点;针对竖置式多环路换热器除霜过程的阶段划分、化霜水流动对除霜过程的负面影响、逆循环初始阶段换热器间金属蓄热量的迁移、除霜过程数理建模的验证与外推等,成为性能优化数值模拟研究方面的重点;为优化逆循环除霜起始与结束阶段的控制策略而对霜层厚度与结霜总量的精密测量,以及对四种典型误除霜现象的消除等成为控制策略优化方面的研究重点.最后,对空气源热泵逆循环除霜的未来研究进行了展望,尤其指出需加强对热泵结霜前期竖置翅片表面微小冷凝水滴的粒径与分布等生长状态,水滴形变、滑移、破裂、凝并、撞击等动力学行为变化规律,及水滴成核与相变时内部温度场分布等热力学行为变化规律的综合研究.本综述旨在为空气源热泵逆循环除霜领域的系统设计优化与结霜除霜机理研究提供借鉴与参考.

When an air source heat pump operating at heating mode in low temperature and high relative humidity environment,the frosting on its outdoor heat exchanger surface is a big problem.This attracts more and more attentions from global scholars,especially around the reverse cycle defrosting due to its advantages of simple adjustment,high defrosting efficiency,unnecessary additional heating source,etc.This review work is divided into three main sections,experimental study,numerical study and control strategies.Results show that,the phase change energy storage reverse cycle defrosting is a trend due to the fundamental problem of energy shortage during defrosting is solved.More numerical studies are around the divisions of defrosting stages,the negative effects of flowing melted frost on defrosting,the energy transfer process in the metal of heat exchangers at start of defrosting,the validation and extension of defrosting models.For the optimization of defrosting start control storage,the accuracy measurement of frost layer thickness and total mass should be explored,and the four classical mal-defrosting phenomena should be eliminated.Finally,the outlook for the defrosting study is given.It is especially pointed out that it is necessary to strengthen the comprehensive research on the growth state of the tiny condensate water droplets on the surface of vertical fins in the early stage of frost formation,the dynamic behavior of water droplets such as deformation,slip,rupture,coalescence and impact,and the thermodynamic behaviors,such as the distribution of internal temperature field during the nucleation and phase transition of water droplets.This work makes contributions to guiding the optimization and design of ASHP system,and mechanism investigation of frosting and defrosting.