逆流湿式冷却塔宏观预测耦合模型及其热力性能研究

提出了一种同时考虑喷淋区与填料区的湿式冷却塔性能预测模型,通过对喷淋区和填料区分别建立数学模型,将两个区域耦合求解,从而计算出最终的出口参数,分析在不同入口空气相对湿度下液滴初始直径和液滴初始速度对冷却塔换热能力的影响。结果表明,耦合模型的结果相比于忽略喷淋区和雨区的模型更接近实验结果,预测误差最大可减少1.51%;降低入口空气相对湿度、减少液滴初始直径可以强化换热,冷却水出口温度降低,而初始液滴速度对冷却水出口温度的影响则可忽略不计。     

横向风对湿式冷却塔热力特性影响数值研究

基于CFD软件和湿冷塔相关理论,建立了基于Poppe理论的填料区数值求解模型,对喷淋区和雨区采用离散相模型计算.模拟了横向风对冷却塔热力特性和飘水损失的影响;提出了沿塔周设置回流槽的措施,以减少飘水损失.结果表明:横向风对出塔水温影响很大;无风时,出塔水温最低,随着风速的增加,出塔水温先升高后降低,并且,随着环境温度、湿度的不同,在横向风速为5m/s～7m/s间取得极大值.     

基于焓差理论的带填料逆流闭塔热力性能分析

为了分析不同风量和喷淋水量对填料逆流闭式冷却塔热力性能的影响,建立和验证了带填料逆流闭式冷却塔热质交换的数学模型,基于焓差理论对模型计算的结果进行分析。结果表明：加入填料相当于对盘管区进口的喷淋水进行预冷,降低了喷淋水的平均温度,使带填料闭式冷却塔的冷却性能优于纯盘管闭式冷却塔;风量的增加可以提高带填料逆流闭式冷却塔和纯盘管逆流闭式冷却塔的热力性能,两种塔的冷却性能随风量增加的提升速率相同;喷淋水量的增加对纯盘管逆流闭式冷却塔的热力性能的影响较小,却可以较大幅度提高带填料逆流闭式冷却塔的热力性能。     

空气物理参数对电厂风量测量的影响

针对火电厂风量测量问题,研究温度、压力和相对湿度对电厂风量测量的影响.结合云南某电厂300 MW锅炉的风烟系统,计算了各测点的温度、压力修正系数以及冷热风混合不均对磨入口风量造成的最大偏差值,分析了不引入相对湿度修正对于冷、热风流量测量可能造成的偏差.结果表明,准确测量风量需要合理引入温度、压力及相对湿度修正.当风温不高于50 ℃时,不引入相对湿度修正将使云南该厂风量测量产生0～3%的偏差.     

太阳能驱动的中空纤维膜液体除湿系统分析

建立太阳能驱动的中空纤维膜液体除湿系统的分析模型,对系统各部件进行分析,分析空气、冷水进口参数和溶液流量对系统性能的影响.结果显示:1)影响系统效率较大的因素是空气进口含湿量、空气流量、冷水温度和冷水流量;2)整个系统中太阳能集热器部件的损最大,可见提高太阳能集热器的性能是提高系统效率的关键.     

基于填料蒸发预冷原理的自然通风干式冷却塔夏天运行效率的优化

针对自然通风干式冷却塔夏天运行效率低的问题,提出填料蒸发预冷塔的入口空气的优化措施。填料蒸发预冷一方面引入预冷,可以起到改善干式冷却塔夏天热交换的作用。另一方面,填料也引入了额外的压损,从而减小流经空冷散热器的空气流量,继而会阻碍冷却塔的热交换。对于填料蒸发预冷自然通风冷却塔,存在蒸发预冷所带来的益处与额外压损引入的弊端的权衡,此权衡与蒸发冷却用的填料密切相关。为此,该文分别对2种代表性填料(薄膜式和点滴薄膜式)蒸发预冷的自然通风干式冷却塔进行模拟研究。模拟发现,就蒸发预冷与额外压损的权衡而言,薄膜式填料的性能优于点滴薄膜式填料。该文模拟的120 m高的冷却塔,在高温低湿条件下,经蒸发预冷后的换热效果最高可提升104%。     

冷水相变能热泵系统的性能系数与经济性分析

冷水相变能热泵系统是一种清洁能源供热供冷系统,性能系数和经济性是冷水相变能热泵系统的主要问题。根据冷水相变能热泵系统的运行原理,采用控制变量法实验分析了冰层厚度、冷水流量以及蒸发冷凝温度对系统能效比的影响,提出了一种冷水相变能热泵系统的运行调控方案并计算其经济性。研究表明：结冰厚度为8 mm时,系统有效能效比最大;系统制热量为744 kW时,相变机结冰期冷水流量应控制在70 t/h,排冰期冷水流量应控制在80 t/h;根据不同时间段的冷热负荷进行系统运行调控,与传统运行方式相比,冬季运行成本降低了4.72%,夏季运行成本降低了29.96%,系统能效比提高了5.6%;系统投资回报率为15.27%,投资回收期为7.67年,具有良好的经济性与节能性。     

高炉鼓风除湿热质交换性能理论与实验研究

基于Whitman理论以及热质平衡理论建立高炉鼓风除湿器理论模型,设计并搭建1∶200高炉鼓风除湿模化实验台,对高温高湿环境下鼓风除湿性能进行实测。结果表明:除湿量理论值与实验值偏差在0.67%～8.53%内,数据差异小,说明理论模型适应性好,可将此理论模型用于大高炉鼓风除湿器设计计算;在高温高湿环境下,鼓风空气入口干球温度为43.5℃、含湿量为58.54 g/m~3时,溶液喷淋浓度为40%,喷淋温度为21.2℃,气液质量流量比为0.7时,除湿效果最优,除湿后鼓风空气含湿量降低44.79 g/m~3,鼓风湿度低至13.75 g/m~3,高炉鼓风风温可提升268.74℃。     

直接空冷机组喷淋冷却系统的数值模拟和性能分析

以国产某300 MW直接空冷机组为例,建立了空冷单元喷淋冷却系统的数值分析模型,设计了3种不同型式的喷淋冷却系统,并采用Fluent软件对喷淋冷却系统的性能进行了数值模拟,得到了空冷单元内部及出口的温度场.结果表明:喷淋后空冷单元的出口空气平均温度比喷淋前降低了2～5 K,其中加装喷淋系统C后的空冷单元出口空气平均温度降低了5 K,排汽压力降低了6.7 kPa;喷淋系统的喷雾越均匀,雾滴覆盖范围越大,喷淋冷却系统的性能越好,排汽压力的降幅越大,经济性越好;对于国产某300 MW机组,当除盐水量充足时,采用喷淋系统C是最佳方案,如除盐水量有限,则应选择喷淋系统B.     

填料式饱和器稳态和动态特性的试验研究

对填料式饱和器进行了稳态及动态特性试验研究,分析了进水流量、进气流量、进水温度对空气加热加湿过程的影响,主要考察了出水温度、出气温度、进出口空气含湿量差、填料段压降和持液量等性能参数的变化规律.结果表明：在相同进水流量下,提高水气比和进水温度,可显著提高加热加湿性能;当气相速度升高时,进出口空气含湿量差减小,填料段压降及持液量升高;在动态工况下,当进口参数发生扰动时,持液量及出水温度比压降需要更长的时间才能达到新的稳定点.     

Cold energy release characteristics of an ice/air direct contact heat exchanger

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     

Numerical investigation of heat transfer and pressure drop characteristics of tube–fin heat exchangers in ice slurry HVAC system

This paper analyzes the heat transfer and pressure drop characteristics of a tube–fin heat exchanger in ice slurry HVAC system. Ice slurry is a suspension of crystallized water based - ice solution with a freezing point depressant like ethylene glycol. The ice- slurry is pumpable, hence it is also called pumpable ice. The composition of ice slurry considered for analysis is 14% ice fraction, 16% ethylene glycol, and 70% water by volume. It is deduced that the ice slurry HVAC system results in 7.4% increase in temperature drop over the conventional chilled water system The latent heat absorbed by ice slurry on melting makes it an attractive choice for achieving high degree of cooling. The numerical analysis was conducted by simulating the ice slurry tube flow region and air flow region of tube–fin heat exchanger in the air-handling unit of HVAC system. For the simulation six different louver patterns with 10 to 55 louver angle were considered. The design of the tube–fin heat exchanger for optimal heat transfer and pressure drop characteristics was also determined with the optimization parameter like louver angle, fin pitch, and ice slurry flow velocity.     

Thermodynamic performance experiment and cooling number calculation of a counter-flow spray humidifier in the HAT cycle

An experimental investigation of the thermodynamic performance of a counter-flow spray humidifier was conducted on the basis of theoretical analysis of the heat and mass transfer mechanism inside the humidifier. Critical parameters such as the temperature and relative humidity of air and the temperature of water at the inlet and outlet were measured. The influence of every measured parameter on the thermal performance of the humidifier was obtained under different experimental conditions. The cooling number, whose variation was also obtained, was calculated according to the measured data. The experimental results show that both the temperature and the temperature increment of outlet humid air and the temperature of outlet water increase with an increase of the water-gas ratio, whereas the cooling number decreases. Under all experimental conditions, the outlet humid air reaches or is close to the saturation level. The lower cooling number is favorable for the system, but it has an optimal value for a certain humidifier.     

Prediction of the air temperature and humidity at the outlet of a cooling coil using neural networks

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.     

HAT循环逆流式湿化器的热力性能实验研究及冷却数计算

在理论分析湿化器内部传热传质机理的基础上，进行了湿化器总体热力性能试验，得出了在不同实验工况下，各测量参数对湿化器热力性能的影响规律，同时计算了冷却数，得出了其变化规律。结果表明：随水气质量比的增大，湿化器出口湿空气的温度、温升和出口水温都增大，而冷却数减少。在同一水气质量比下，随进口水温升高，出口湿空气温度、温升和出口水温都增大，冷却数减少。在各实验工况下，湿化器的出口湿空气都具有很高的相对湿度，达到或接近饱和状态。冷却数降低对系统有利，但不是越低越好，应该优化选择最佳值。     

An experimental study of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been installed and experiments were carried out for a period of nine months covering rainy, cold, and hot seasons in a hot and humid climate (Thailand). A heat exchanger was used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The evaporation rate at the regeneration process was always greater than the moisture removal rate at the dehumidification process indicating that the concentration of the desiccant in the system would not decrease and so the performance would not drop during continuous operation. The system could reduce the temperature of the delivered air by about 1.2 °C while the humidity ratio was reduced by 0.0042 kg_w/kg_da equivalent to 11.1% relative humidity reduction. The experimental results were also compared with models in literature.     

Thermodynamic performance experiment and cooling number calculation of a counter-flow spray humidifier in the HAT cycle

An experimental investigation of the thermodynamic performance of a counter-flow spray humidifier was conducted on the basis of theoretical analysis of the heat and mass transfer mechanism inside the humidifier. Critical parameters such as the temperature and relative humidity of air and the temperature of water at the inlet and outlet were measured. The influence of every measured parameter on the thermal performance of the humidifier was obtained under different experimental conditions. The cooling number, whose variation was also obtained, was calculated according to the measured data. The experimental results show that both the temperature and the temperature increment of outlet humid air and the temperature of outlet water increase with an increase of the water-gas ratio, whereas the cooling number decreases. Under all experimental conditions, the outlet humid air reaches or is close to the saturation level. The lower cooling number is favorable for the system, but it has an optimal value for a certain humidifier. __________ Translated from Journal of Power Engineering, 2006, 40(9): 1263–1267 [译自: 动力工程]     

Heat Transfer Enhancement of Spray Cooling on Flat Aluminum Tube Heat Exchanger

This study provides an experimental analysis on the heat transfer performance of a flat aluminum tube microchannel heat exchanger with spray cooling. The effects of water spraying rate, airflow rate, and relative humidity were investigated. The test results show that the heat transfer performance increased with increasing the water spraying rate but without the penalty of increased flow resistance at low spray conditions. This effect is further enhanced by increasing the water spraying rate. However, when the spraying rate is high, part of the nonevaporated drops attached to the fin surface and formed a liquid film, which caused the flow passage to become narrower. Further increase in the spraying rate resulted in part of the flow passages being blocked by the nonevaporated water drops and caused a region of poor heat transfer. The friction coefficient jumped drastically at this condition. This phenomenon deceased gradually with increasing airflow rate. High inlet air humidity resulted in the water accumulation phenomenon appearing at lower water spraying rates. The evaporative cooling effect decreased and flow friction increased. The test results just described show that the water spray is able to significantly improve the air-side heat transfer performance. The optimum spray rate for each airflow rate must be carefully determined.     

利用空气—土壤换热系统对温室降温除湿的分析

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。     

Heat and mass transfer analysis of a wavy fin-and-tube heat exchanger under fully and partially wet surface conditions

In this study a mathematical model of heat and mass transfer performance of a wavy fin-and-tube heat exchanger under wet surface condition is presented. The heat exchanger is a counterflow heat exchanger in which humid air and liquid are flowing in opposite direction. A water film that causes evaporative cooling of the humid air is circulated on the humid air side. The heat and mass transfer equations are first derived for fully wet heat exchanger and then by defining a wettability parameter, these equations are obtained for partially wet heat exchanger. In modeling, values of Lewis number and wettability parameter are not necessarily specified as unity. The temperature distributions of humid air, liquid and water film, and relative humidity distribution of humid air are obtained numerically. The theoretical results are found to be in good agreement with the available experimental measurements.