温室冷却除湿用翅片管换热器空气侧的性能

为探究温室环境对冷却除湿系统中亲水翅片管换热器空气侧性能的影响机理，在风洞营造的温室环境下(温湿度分别为285～308 K和60%～90%)，对带有厚度为0.8 μm亲水涂层的铝翅片管换热器进行了空气侧性能试验，与无亲水涂层翅片管换热器空气侧的性能对比；分析了进口条件对翅片管换热器热质传递及阻力特性的影响，并对现有无亲水涂层翅片的性能预测关联式进行了修正，确保修正后的关联式适用于温室及相似环境下带亲水涂层的翅片管换热器。试验结果表明，带亲水涂层翅片的传热因子、传质因子及摩擦因子均小于无亲水涂层翅片；带亲水涂层翅片的传热因子、传质因子及摩擦因子随空气侧雷诺数和制冷剂进口温度的增加而减小，随相对湿度的增加而增加；修正后传热因子、传质因子和摩擦因子的关联式能够在±10%的误差范围内涵盖92.9%、96.4%和96.4%的试验数据，3种因子的平均误差分别为5.1%、5.9%、4.7%。该研究可为温室及相似环境下冷却除湿系统中亲水翅片管换热器的设计与应用提供参考。

Airside performance of fin-tube heat exchangers for cooling dehumidification in greenhouses

Cooling-dehumidification technology is gradually applied to the semi-closed structure of the greenhouse. The reason can be that the indoor air humidity is usually higher than the suitable growth range of the planted crops. Among them, the airside performance of the fin-tube heat exchangers directly dominates the efficiency of the cooling-dehumidification system. In this study, a systematic investigation was made to clarify the influence mechanism of the greenhouse environment on the airside performance of the aluminum fin-tube heat exchangers with the hydrophilic coating (thickness 0.8 μm). An airside performance experiment was then conducted on the greenhouse environment created by a wind tunnel, in which the air temperature was 285 to 308 K and the relative humidity was 60% to 90%. The experimental platform of the wind tunnel consisted of the airflow rate measurement, the air temperature and humidity treatment, the fin-tube heat exchanger test, and the refrigerant circulation circuit, according to the American Society of Heating Refrigerating and Air conditioning Engineer (ASHRAE) standards. A comparison was made on the airside performance of the exchanger with and without hydrophilic coating. The correlation analysis was carried out between the predicted and experimental data, in terms of the heat transfer, mass transfer, and friction factor for those without hydrophilic fins. It was found that the predicted values deviated significantly from the experimental data. By contrast, multiple nonlinear regression was utilized to add the correction factors of temperature and relative humidity into the correlations of the fin-tube heat exchanger without hydrophilic coating. The new correlation was then applied to the fin-tube heat exchangers with the hydrophilic coating in the greenhouse environment. The results showed that the hydrophilic coating dominated the airside performance of the fin-tube heat exchanger in the greenhouse environment. The heat transfer factor, mass transfer factor, and friction factor of the fins with the hydrophilic coating were smaller than that of those without hydrophilic coating, in which the hydrophilic coating posed the most significant effect on the friction factor. The maximum difference in the friction factor of fin-tube heat exchangers with and without hydrophilic coating was 53.9%, indicating that the fins with the hydrophilic coating effectively promoted the discharge of condensate. The heat transfer factor, mass transfer factor, and friction factors of the fins with the hydrophilic coating decreased with the increase of airside Reynolds number and refrigerant inlet temperature, but increased with the rise of relative humidity. The mass transfer factor was more sensitive to the inlet relative humidity. Once the inlet temperature of refrigerant was 285 K, the inlet air relative humidity was 80%, and the air inlet temperature increased to 300 K, indicating the maximum heat transfer factor. There was no influence of the air inlet temperature on the heat transfer performance of the airside in this case. The predicted values of the selected correlation of the smallest deviation were larger than the experimental data. The maximum deviation reached 52.5%, 219.6%, and 71.1% for the heat transfer factor, mass transfer factor, and friction factor, respectively. The new correlations for the corrected heat transfer factor, mass transfer factor, and friction factor were 92.9%, 96.4%, and 96.4% of the experimental data within ±10%, after the correction factors were introduced for the temperature and relative humidity into the selected correlations. The mean deviation of the heat transfer factor, mass transfer factor, and friction factor were 5.1%, 5.9%, and 4.7%, respectively. The finding can provide a strong reference for the thermal design and application of fin-tube heat exchangers with the hydrophilic coating in the cooling-dehumidification systems of the greenhouse.