三排变片距翅片盘管换热器结霜特性实验研究

为改善空气源热泵室外翅片盘管换热器在低环境温度下沿空气流动方向结霜不均匀、首排结霜量较大进而导致热泵除霜间隔较短、制热能力下降等问题,对不同翅片片距组合的变片距翅片盘管换热器在低环温工况下运行及结霜的情况进行实验研究。结果表明：变片距翅片盘管换热器在低环温条件下可有效延长迎风面管排发生结霜堵塞的时间、对于结霜生长速度和结霜质量也有抑制作用。变片距翅片盘管换热器在结霜中后期阶段换热功率更高,在合理的翅片间距组合下,变片距翅片盘管换热器可以在不损失过多换热功率的情况下延长换热器迎风面管排结霜堵塞的时间,如样品4的平均换热功率比样品1低6.02%,而除霜间隔延长了37 min。     

热泵热水器除霜方法的研究

阐述了空气源热泵热水器的结霜特性,分析了热泵热水器化霜时与空调器不同的特征,提出了采用检测冷凝器温度与水温的差值来判断室外蒸发器是否结霜、检测室外热交换器盘管温度来判断除霜是否完成的两器盘管温度综合判断除霜法。     

空气热源热泵动态结霜过程研究

建立了空气热源热泵动态结霜过程的物理模型,对热泵机组在结霜工况下的供热特性和霜在空气盘管翅片表面的集聚过程进行了动态模拟,分析了环境温湿度,翅片间距,管排数对结霜特性和机组供热性能的影响。     

空气热源热泵冬季结霜特性研究

本文主要研究空气热源热泵机组冬季供热工况空气盘管表面湿空气结霜、结露及干冷却特性，得出了不同迎面风速条件下热泵机组结霜曲线，针对我国冬季气候特点进行了具体分析。     

空气温湿度对空气源螺杆热泵机组除霜性能的影响

试验研究了空气温湿度变化对风冷热泵机组的除霜性能的影响,采用实时数据分析方法研究了在多次除霜周期和除霜间隔周期内翅片温度、过冷度和过热度的变化规律和特点,为寻求优化的除霜控制方法提供了大量试验依据.定量分析了空气温湿度的变化对制热恢复时间、制热衰减时间、稳定制热时间以及除霜间隔时间的影响.研究表明,在不同的温湿度工况下,均出现了盘管出口温度变化率突变以及温度的周期性震荡,这一时刻,制热量开始快速衰减,霜层开始形成并快速生长.当相对湿度从75%提高到90%时,这一突变的温度变化率提高了2倍,制热衰减时间减少了约70%.蒸发盘管出口温度的变化率以及周期性震荡间接反映了蒸发盘管的翅片表面的结霜状态,并呈规律性变化,这一温度参数可以作为重要的除霜循环的控制参数.     

复叠式空气源热泵翅片管换热器的结霜因子研究

空气源热泵在冬季结霜会对机组的运行产生较大影响。本文实验机组为一台复叠式空气源热泵,室外侧换热器采用带亲水膜的翅片,在焓差实验室中进行室外温度在-18℃~6℃区间、相对湿度在70%~90%区间内的实验,研究空气源热泵的翅片管换热器的结霜量。实验结果显示:结霜量随时间增加而增加,并且接近线性关系;室外温度在-3℃~3℃时的结霜量最高,随着室外温度的下降,结霜量下降;室外湿度对结霜量的影响较大,在70%的相对湿度下,结霜量远小于80%~90%的结霜量;本文根据结霜时间、换热面积和盘管表面温度与空气露点温度与结霜量之间的关系,提出了结霜因子的概念,并得到结霜因子的范围为1.69~2.67×10-3kg/(m2·℃·h),其平均值为2.22×10-3kg/(m2·℃·h)。     

美国专家圣斯伯雷在广州学术交流的谈话记录

美国冷库专家,顾问工程师圣斯伯雷先生一九八二年十一月廿八日在广州市广东科学馆与广东制冷科技工作者就冷库技术等问题进行了学术交流。下面就是他对11个问题的回答:1、0℃库蒸发器传热面积及传热系数的计算如何考虑结霜的影响因素?请举计算实例。答:干式翅片盘管的显热传热系数(循环的制冷剂是氨)是在25～28Watt/m~2·℃     

风源热泵模糊自修正除霜技术应用研究

在对热泵运行时结霜和除霜过程进行深入研究的基础上,提出了能适应环境温湿度变化的"变温差"模糊自修正除霜技术.该技术具有在线辩识和修正控制参数的功能,可根据热泵运行时蒸发温度与室外温度的差值和温差的变化率判断除霜的切入点,依据除霜时间和除霜结束时盘管的温度参数评估除霜质量,实时修正控制参数以获取最佳的制热效果.实验和应用研究表明:采用该技术的空调器在较宽的气候变化范围工作可靠,能适时把握除霜切入点和退出点,除霜干净.     

选择带湿膜加湿器风机盘管的研讨

为解决北方地区高档建筑冬天室内加湿问题,国内企业研究开发出了带湿膜加湿器的风机盘管机组,本文就该类型设备在使用时可能出现的一些问题作了试验和分析,指出随着排风量的减少,盘管热效率降低,在选用时应充分考虑.     

空气源热泵除霜研究

空气源热泵的结霜问题已经成为影响空气源热泵机组可靠性的关键,提出了解决问题的三个方法:延缓结霜、除霜方法改进和除霜控制技术。增加风量、改进换热器形式等可以有效延缓结霜,并降低结霜的程度;采用蓄能除霜法可以减少除霜时间,室内恢复供热更快;模糊控制等控制方式可以使除霜更加智能化,从而达到良好的除霜效果。     

Heat and mass transfer on a cylinder surface in cross flow under supersaturated frosting conditions

In this paper a semi-empirical model describing heat and mass transfer on a cylinder surface in humid air cross flow under supersaturated frosting conditions is presented. The lack of psychrometric data in the supersaturated zone of the psychrometric chart has historically impeded the ability of researchers to accurately predict heat and mass transfer in supersaturated air. The work described in this paper has been partially made possible by developing a systematic procedure to compute the properties of supersaturated moist air, especially in the low temperature zone of the psychrometric chart. Development of such a capability will allow us to predict the amount of frost collected on a coil, the frost deposition and coil heat transfer rates, frost thickness and frost surface temperature, and other important coil frost parameters under supersaturated conditions.     

Modeling non-uniform frost growth on a fin-and-tube heat exchanger

A semi-empirical model that predicts non-uniform frost growth on heat exchangers is developed and experimentally validated. The model is based on a scaling approach that uses the average frost layer properties to predict growth in a quasi-steady state, heat and mass balance based segment-by-segment coil simulation. The air redistribution algorithm in the model improved frost thickness predictions by 20%-50% and coil capacity predictions by 42% compared to the same model without air redistribution. The model along with an empirical frost delay predicted the frost thickness for different inlet refrigerant temperatures, air relative humidities and air velocities under non-uniform frosting with a root mean square error of 3.7%, 9.8% and 5.2% respectively.     

Dynamic behavior of a direct expansion evaporator under frosting condition. Part I. Distributed model

A general distributed model with two-phase flow for refrigerant coupled with a frost model is developed for studying the dynamic behavior of an evaporator. The equations are derived in non-steady-state manner for the refrigerant and a quasi-steady state model with permeation for the frost. The complex flow and geometry of the finned tube evaporator lead to uneven wall and air temperature distributions, which in turn affect the rate of frost growth and densification along the coil depth. Results include frost accumulation and its effect on energy transfer, air off-coil temperature, refrigerant liquid dry-out position and propagation of frost formation along the coil.     

Comparison of parallel- and counter-flow circuiting in an industrial evaporator under frosting conditions

This paper describes a theoretical model of a large-scale, ammonia-fed evaporator coil used in an industrial refrigeration system and operating under low temperature air and refrigerant conditions that are typically encountered in refrigerated storage spaces. The model is used to simulate the performance of counter-flow and parallel-flow circuited evaporator coil designs under frosting conditions. The counter-flow frost model is validated using in situ data obtained from a field-installed evaporator coil. The performance of an evaporator in a parallel-flow circuit arrangement is simulated and compared to counter-flow circuiting. The effects of coil circuiting are evaluated in terms of the frost distribution across the evaporator coil and the associated reduction in cooling capacity during operation.     

冻藏间冷却排管霜层传热效应的研究

本文实地凋研了冻结物冷藏间冷却排管的结霜速度和相应的霜层密度及影响结霜速度的主要因素.在此基础上进一步研究分析了:(1)在蒸发温度不变条件下霜层厚度与传热系数的关系.(2)在保证排管冷量不变和库温恒定的条件下,蒸发温度、传热系数和制冷系统COP等重要性能指标随霜层厚度的变化关系.分析计算结果表明:冻藏间的冷却排管霜层厚度的过度增加会严重地影响排管本身的传热性能和制冷能力,降低制冷系统的COP.     

洁净空调机组防冻保护自动控制装置的改进

通过对典型的洁净空调系统中带防冻保护自动控制装置的空调机组盘管层流结冰冻裂事故的分析,提出增加小容量电加热器保护装置的改进方法来达到有效的防冻保护,降低财产损失.     

Experimental investigation of the performance of industrial evaporator coils operating under frosting conditions

This paper describes a field experimental investigation of the effects of frost formation on the performance of a low-temperature large-scale evaporator coil used in industrial refrigeration systems. A series of experiments were conducted to determine the in situ coil cooling capacity of the evaporator over time as frost builds on its surfaces. Field-measured quantities include inlet and outlet air temperatures, inlet and outlet air relative humidity, and air volume flow rate. These measurements provide a baseline set of experimental data that can be used to validate numerical models of industrial evaporators operating under frosting conditions.     

冻干机冷阱传热性能实验研究

对影响冻干机冷阱传热性能的两个因素(冷阱盘管壁面温度和结霜厚度)进行了实验研究。实验研究表明冷阱壁面温度越低则冷阱捕集效率越高；随着霜层厚度的不断增加，传热性能将不断下降。对影响冷阱传热的另一个因素-真空度，进行了理论分析，认为随着冷阱真空度的提高，换热强度不断降低，直至可以不考虑换热。     

翅片类型对热泵空调结霜特性的影响

通过实验研究了室外换热器采用平直、波纹、波纹/开缝翅片对热泵空调器动态结霜性能的影响。结果表明,在结霜工况下,平直、波纹、波纹/开缝三种翅片类型的系统制热量、COP和压缩机功率的峰值、平均值依次增大,其中,波纹/开缝翅片的各项平均值比平直翅片分别减小了14.57%、8.26%和7.11%。波纹/开缝翅片的性能参数最早开始衰减且衰减幅度也最大,其次是波纹翅片,平直翅片最晚开始衰减且幅度最小。结霜时,水蒸气变为霜的相变过程对传热具有强化作用,同时霜层减小了翅片间隙使风阻增大、室外风机流量减小,这对传热具有恶化作用。结霜时性能参数的曲线存在上升段和衰减段,与霜层微观成长特性一致:结霜初期,冰晶由粒状变为柱状,尚未显著阻塞翅片间隙,对传热的强化作用较显著,曲线处于上升段;结霜中后期,冰晶先沿半径成长,后又在柱状晶间隙堆垛,对传热的恶化作用较显著,曲线处于衰减段。     

Experimental investigation of the surface temperature and water retention effects on the frosting performance of a compact microchannel heat exchanger for heat pump systems

Frost formation on a louvered fin microchannel heat exchanger was experimentally investigated in this paper with the aim of determining the dominant factors affecting the time of frosting and frost growth rate. A novel methodology was developed to measure frost thickness and frost weight at intervals during the frosting period. Frost mass and thickness growth rates, corresponding coil heat transfer, capacity degradations and air pressure drop are measured and discussed. The experimental data showed that at a given air dry bulb temperature, the fin surface temperature and air humidity are the primary parameters that influence the frost growth rates. Water retention and air velocity had a secondary impact on the frosting performance. From digital images of the frost growth it was observed that frost does not nucleate from the water droplets retained in between fins but it developed from the leading edges of the fins.