共查询到20条相似文献,搜索用时 140 毫秒
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《热能动力工程》2016,31(11)
在高空低气压环境下模拟舱内对开缝翅片管换热器在湿工况下的换热特性进行了实验研究,分析了不同环境压力对空气侧换热特性的影响,包括显热换热、潜热换热和努赛尔数的变化规律。实验结果表明,当干球温度和相对湿度不变时,湿工况下空气侧显热换热量、潜热换热量和空气侧传热系数均随着环境压力的降低而减小;而单位质量潜热换热量几乎不变,潜热换热所占比例略微增大。同一个环境压力下,入口空气的相对湿度对换热器的显热换热量影响不大,而对潜热换热量影响显著。当相对湿度分别为40%、60%和80%时,显热换热量差异小于5%;而潜热换热量当相对湿度为80%时,是相对湿度为40%时的5.9~6.8倍。 相似文献
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《可再生能源》2016,(10)
文章针对日光温室环境下土壤空气换热器的换热特性进行了研究。首先通过监测土壤空气换热器沿程空气温度的全天变化,分析了试验工况下土壤空气换热器的动态换热过程及系统性能变化规律。研究结果表明,在试验工况下,土壤空气换热器系统的性能系数(COP)可高达24.1。在此基础上,通过建立土壤空气换热器的非稳态换热模型,模拟研究不同的入口风速对土壤空气换热器换热性能的影响。研究结果表明,当换热管入口空气温度相同时,随着入口风速的增加,土壤空气换热器进出口空气温度差逐渐减小,出口处空气温度与土壤温度差值逐渐增大,这意味着土壤空气换热器有效换热长度逐渐变长。在此过程中,土壤空气换热器系统的换热量和COP随着入口空气风速的增加呈现出先增后减的规律。通过模拟结果可知,当入口风速达到5.5 m/s时,土壤空气换热器系统的换热量与COP均达到最大值。 相似文献
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为探究相变温度对相变材料回填地埋管换热器传热性能的影响,建立管内流体换热、回填区域相变换热及土壤换热的三维耦合传热数值模型,利用焓-多孔介质模型对相变区域相变问题进行处理,研究夏季间歇运行工况下不同相变温度回填材料对埋管换热器传热性能的影响。结果表明:添加PCM,可有效提高换热量,短期内缓解埋管周围热积聚,利用相变温度18℃的PCM回填,单位井深换热量至少比普通材料回填提高49.54%;在间歇运行初期,换热量随相变温度的升高逐渐减小,低相变温度的PCM可明显改善埋管换热量,但随着时间的进行,较高相变温度PCM回填对换热器换热量的改善效果优于前期低相变温度。此外,在运行期间,不同相变温度的PCM表现出不同的熔化、凝固特性,当PCM的熔化、凝固过程交替进行时,可减缓土壤温度在运行期间内波动幅度。 相似文献
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建立了管内流体流动及周围土壤热渗耦合传热的垂直U型地埋管换热数理模型,采用数值方法对有渗流和无渗流工况下的土壤温度场分布、埋管出口温度、不同渗流速度下的单位井深换热量进行了模拟计算分析。结果表明,地下水渗流作用能减小埋管出口升温幅度,在埋管入口平均温度为33℃时,有渗流工况下的埋管出口平均温度为29.91℃,无渗流工况下的埋管出口平均温度为30.85℃。单位井深换热量随渗流速度的增大而增加,当地下水渗流速度为10 m/a和400 m/a时,与无渗流工况相比,单位井深换热量分别增大了约6.33%和71.33%。 相似文献
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This paper presents a theoretical analysis and an experimental test on a shell‐and‐tube latent heat storage exchanger. The heat exchanger is used to recover high‐temperature waste heat from industrial furnaces and off‐peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase‐change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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运用平板太阳能集热器热迁移因子FR的表达式,研究集热器管间距W和管外径Do对FR的影响规律。研究发现,随着W的减小,FR逐渐增大,当W趋近于Do时,FR趋近最大,此时集热管导热系数对FR影响甚微,即可采用非金属材料替代金属材料制作集热管;随着Do增大,FR先增加而后逐渐下降。研制了非金属管式平板太阳能集热器,建立了其性能试验测量系统。试验结果表明,当工质流量为0.165 kg/s时,FR为0.738,平均集热效率为54%。运用BP神经网络算法,建立了非金属管式平板太阳能集热器出口热流体温度的预测模型,并将预测结果与试验结果进行了比较。 相似文献
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运用平板太阳能集热器热迁移因子FR的表达式,研究集热器管间距W和管外径Do对FR的影响规律。研究发现,随着W的减小,FR逐渐增大,当W趋近于Do时,FR趋近最大,此时集热管导热系数对FR影响甚微,即可采用非金属材料替代金属材料制作集热管;随着Do增大,FR先增加而后逐渐下降。研制了非金属管式平板太阳能集热器,建立了其性能试验测量系统。试验结果表明,当工质流量为0.165 kg/s时,FR为0.738,平均集热效率为54%。运用BP神经网络算法,建立了非金属管式平板太阳能集热器出口热流体温度的预测模型,并将预测结果与试验结果进行了比较。 相似文献
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叙述了利用FLUENT6.3软件中的组分输运模型及多相流模型,对置于温室外的空气—土壤换热器(SHESS)进行三维动态模拟,采用典型时段的气象参数,分析换热器在输入环境空气时出口温度和含湿量随时间的变化趋势。指出,埋管深4m的换热器,最大可将输入空气的温度降低10.9℃,平均可降低9.2℃;最大减少含湿量8.14g/kg.干,平均可减少3.86g/kg.干,得出,空气—土壤换热器在北方地区夏季对温室具有明显的降温除湿效果的结论。 相似文献
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Prediction of the air temperature and humidity at the outlet of a cooling coil using neural networks
《International Communications in Heat and Mass Transfer》2006,33(7):898-907
The main objective of this study is to predict air temperature and humidity at the outlet of a wire-on-tube type heat exchanger using neural networks. For this purpose, initially the heat exchanger was coupled to a refrigeration unit and placed in a wind tunnel. Afterwards, its performance was tested under various experimental conditions. We measured nine input parameters, namely, temperature and humidity of the air entering the coil, air velocity, frost weight, the temperature at the coil surface, mass flow rate of the heat transfer fluid and its temperatures at the inlet and outlet of the coil along with ambient temperature. Additionally, we measured temperature and humidity of the air leaving the coil as the output parameters. Then, a feed-forward neural network based on backpropagation algorithm was developed to model the thermal performance of the coil. The artificial neural network (ANN) was trained using the experimental data to predict the air conditions at the outlet of the coil. The predicted values are found to be in good agreement with the actual values from the experiments with mean relative errors less than 1% for outlet air temperature and 2% for outlet humidity. This demonstrates that the neural network presented can help the manufacturer predict the performance of cooling coils in air-conditioning systems under various operating conditions. 相似文献
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针对光伏发电功率预测精度低的问题,以澳大利亚爱丽丝泉地区某200kW的光伏电站为例,选用遗传算法(GA)优化BP神经网络,采用相关性分析法(CA)确定太阳辐照度、温度、湿度为影响光伏发电功率的主要因子,结合经样本熵(SE)量化的天气类型作为模型输入量,提出CA-SE-GA-BP神经网络的光伏发电功率预测模型。结果表明,多云天气下CA-SE-GA-BP神经网络均方根误差、平均绝对百分比误差分别为4.48%、2.27%,晴天、雾霾、雨天三种天气类型下的预测误差也基本上不超过10%,相较于SE-GA-BP、CA-GA-BP、GA-BP神经网络,CA-SE-GA-BP神经网络预测误差降低,为解决光伏系统发电功率预测提供了一种高效准确可行的方法。 相似文献
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Akiyoshi Ohira Michio Yanadori Kunihiko Iwabuchi Toshikatsu Kimura Yuji Tsubota 《亚洲传热研究》2001,30(2):95-113
This paper deals with the cold energy release characteristics of an ice/air direct contact heat exchanger. Characteristics of the outlet temperature, humidity, and time history of heat release are examined when the initial height of the ice‐cube‐packed bed in the heat exchanger is changed. The following results were obtained in these experiments: (1) Inlet air of 30 °C is lowered to about 0 °C when passed through the heat exchanger, and the absolute humidity of the outlet air is reduced to about a quarter of that of the inlet air. (2) There is an optimum height of the ice‐cube‐packed bed to maximize the amount of cold energy release. (3) This heat exchange method can supply about twice as much cold energy as is released by an ordinary fin‐tube‐type heat exchanger even if the air velocity in the heat exchanger is reduced to about 0.38 times that of the fin‐tube‐type heat exchanger. (4) A nondimensional correlation equation for predicting the time taken for the ice‐cube‐packed bed to completely melt is derived. © 2001 Scripta Technica, Heat Trans Asian Res, 30(2): 95–113, 2001 相似文献