共查询到17条相似文献,搜索用时 171 毫秒
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采用多孔介质法,构建了低温圆管壁面结霜的非稳态数学模型,对低温圆管壁面霜层的生长过程进行了数值模拟,研究了结霜过程的非稳态传热特性,并对壁面温度、管径以及相对湿度、气流速度等影响因素进行了分析,获得了霜层厚度、换热热流密度与霜层表面温度与各影响参数之间的依赖关系。结果表明:霜层厚度与密度的预测值与文献实验数据吻合良好;对流换热在结霜过程中起主导作用,总的热流密度随着霜层厚度的增加而减小;圆管壁面温度越低,圆管直径越大,相对湿度越高,霜层厚度越大;与强制对流条件相比,自然对流条件下形成的霜层更厚,表面温度更低。 相似文献
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本文针对铝基波纹翅片换热器广泛应用及结霜问题,基于相变驱动力分析结霜机理,实验研究了在不同冷表面温度(-5~-15℃)、空气温度(11~17℃)、空气流速(1.5~2.5 m/s)等工况下,铝基裸铝波纹表面的结霜情况,观察了铝基波纹表面上霜层生长过程中的微观形貌,并采用田口实验法分析了环境因素对表面结霜情况的影响。结果表明:环境因素的改变会对铝基波纹表面结霜产生不同程度的影响,以波纹角度11.3°为例,结霜60 min时,与冷表面温度为-5℃相比,冷表面温度为-10℃和-15℃时结霜量分别增长12.20%和31.28%,霜层厚度分别增长19.95%和47.24%。田口实验法分析表明:相比湿空气温度和空气流速,冷表面温度和湿空气相对湿度对波纹表面结霜特性影响相对较大,对波纹表面结霜量的贡献率分别为37.3%和31.8%,对霜层厚度的贡献率分别为61.1%和22.6%。空气流速对结霜量的贡献率为22.6%,而对结霜层厚度的贡献率仅为4.2%,表明空气流速对霜层的致密化作用较大。 相似文献
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两级压缩空气源热泵结霜性能试验研究 总被引:2,自引:0,他引:2
虽然空气源热泵得到了广泛的应用,但是空气源热泵机组在冬季低温环境下运行,其蒸发器表面结霜,会严重影响效率。本文研究了两级压缩空气源热泵在低温工况下一些参数变化对风冷热泵结霜的影响,以及结霜条件下热泵机组性能参数的变化。研究表明:在0℃以下,结霜量以及结霜速度随着温度的升高而增多和加快,在进风温度在0℃左右的时候结霜最严重。温度在3℃的时候,结霜却不如前者严重。而当温度达到-7℃以下时,结霜不是很明显,特别是在相对湿度为90%,温度为-12℃时几乎不结霜。当蒸发器壁面的温度与空气的露点温度比较接近,而且空气含湿量大时,结霜速度最快。在保持进风温度一定,相对湿度越大,换热器风侧表面结霜量也就越多。相对湿度变化对结霜量的影响比温度要大,因此环境相对湿度是影响空气源热泵机组结霜、除霜特性的主要因素。同时,机组在结霜条件下运行时,机组的制热量和COP降低,综合性能下降。这一研究对翅片管式蒸发器除霜具有指导意义。 相似文献
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室外环境参数对空气源热泵翅片管蒸发器动态结霜特性的影响 总被引:7,自引:0,他引:7
对一台空气源热泵空调器在不同环境条件下室外换热器的动态结霜性能进行了实验研究,分析了进风温、湿度对热泵空调器结霜量及霜层厚度的影响。实验中考虑了结霜引起的热泵系统蒸发温度及风机流量的变化,采用显微照相法测量翅片表面霜层厚度,结霜量则通过测量蒸发器进出口含湿量的方法来获得。实验结果表明,室外换热器结霜量随时间线性增长,而翅片表面霜层厚度则分为初始段、匀速增长段和快速增长段三个阶段;在结霜循环的最后20%~30%的快速增长段内霜层生长速率大大加快,可达匀速生长段霜层生长速率的2.4,3.3倍。对于不同的工况,蒸发器均在进风温度0~3℃附近时结霜最为严重,且相对湿度对霜层厚度的影响要大于对结霜量的影响。 相似文献
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Deniz Seker Hakan Karatas Nilufer Egrican 《International Journal of Refrigeration》2004,27(4):367-374
In this study, the heat and mass transfer characteristics of heat exchangers during frost formation process are analyzed numerically. Unsteady heat and mass transfer coefficients of the air side, heat transfer coefficient of the refrigerant side, air-frost layer interface temperature, the surface efficiency of the heat exchanger and the mass flow rate of the frost accumulated on the heat exchanger surface are calculated. The total conductivity (UA) and pressure drop of the heat exchanger are reported for different air inlet temperature, relative humidity, air mass flow rate and the refrigerant temperature. 相似文献
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This paper proposes a mathematical model to predict the frost properties and heat and mass transfer within the frost layer formed on a cold plate. Laminar flow equations for moist air and empirical correlations for local frost properties are employed to predict the frost layer growth. Correlations for local frost density and effective thermal conductivity of the frost layer, derived from various experimental data, are expressed as a function of the various frosting parameters: the Reynolds number, frost surface temperature, absolute humidity and temperature of the moist air, cooling plate temperature, and frost density. The numerical results are compared with experimental data to validate the proposed model, and those agree well with the experimental data within a maximum error of 10%. Heat and mass transfer coefficients obtained from the numerical analyses are also presented. The results show that the model for the frost growth using the correlation of the heat transfer coefficient without considering the air flow has a limitation in its application. 相似文献
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This study presents a mathematical model to predict the frosting behavior on a cold surface under turbulent flow. The model consists of the standard κ–ε model for turbulent flow and the diffusion equation for the frost layer. The numerical results show that turbulent flow promotes the growth of the frost layer on the cold surface, compared to the laminar flow. Increase in air velocity has little effect on mass transfer under turbulent flow, while frost growth under laminar flow is influenced by the air velocity. With constant air humidity, the frost layer thickness increases with decreasing air temperature, while the relationship for the frost density is reversed. The effect of the air temperature on the mass flux is negligible, compared to the other frosting parameters. 相似文献
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Processes involving the transfer of heat from a humid air stream in laminar flow to a horizontal plate with the simultaneous deposition of frost is of importance in a variety of refrigeration equipment. The accumulating frost layer impedes the heat flow to the cooling surface. The present study is carried out to determine both theoretically and experimentally the factors that influence, frost formation on a cold surface and to correlate the Nusselt and Sherwood numbers with these factors.Experiments were conducted on a 600 mm long, flat horizontal plate, the Reynolds number and the relative humidity of the impinging air stream were varied from 30 000 to 140 000 and from 40% to 60% respectively, while the average surface temperature was near - 18°C. Empirical correlations of the Nusselt number and Sherwood number are presented. 相似文献
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Processes involving the transfer of heat from a humid air stream in laminar flow to a horizontal plate with the simultaneous deposition of frost is of importance in a variety of refrigeration equipment. The accumulating frost layer impedes the heat flow to the cooling surface. The present study is carried out to determine both theoretically and experimentally the factors that influence, frost formation on a cold surface and to correlate the Nusselt and Sherwood numbers with these factors.Experiments were conducted on a 600 mm long, flat horizontal plate, the Reynolds number and the relative humidity of the impinging air stream were varied from 30 000 to 140 000 and from 40% to 60% respectively, while the average surface temperature was near - 18°C. Empirical correlations of the Nusselt number and Sherwood number are presented. 相似文献
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霜层生长初期冰晶体分布状况实验研究 总被引:3,自引:0,他引:3
研究霜层的结构对于理解结霜现象有着重要的意义。利用自行研制的图像放大及采集系统,对霜层生长初期冰晶体的形态进行显微观测,得到了不同生长条件下冰晶体的图像。随后采用数字图像处理方法,将原图像转换为二值图。通过对图像的分析,发现霜层的生长初期冰晶体的分布与充分生长的霜层有所不同,此时霜层靠近冷表面固含率最大;随着高度的增长,固含率以近似线性的方式减小。实验还发现,对霜层生长初期影响最大的两个因素是冷表面的温度和空气的相对湿度。随着冷表面温度的降低,霜层的高度明显增长,冰晶体沉积量增加,而平均密度的变化则不明显;随着空气相对湿度的增加,霜层的高度、平均密度以及冰晶体总的沉积量都有所增加。空气温度对霜层生长的影响不明显。 相似文献