【作者】 浦晖；

【导师】 丁国良；

【作者基本信息】 上海交通大学 ， 制冷及低温工程， 2009， 博士

【摘要】 采用翅片管换热器作为蒸发器是空调器的重要部件,研究者对于提高其性能已经做了大量研究,包括采用强化管提高制冷剂侧换热性能,采用强化翅片提高空气侧换热性能,以及改变管路连接方式等。但是,随着空调器使用时间的增加,蒸发器的效率会逐渐降低,其能耗也相应的提高。蒸发器的长期性能变化已经得到越来越多的重视,其长效传热和压降特性已经成为重要的研究课题。影响空气侧长效性的因素包括空调的翅片表面沉积的污垢、翅片表面生长的微生物、间歇运行和盐雾腐蚀等。其中,翅片表面沉积的污垢的影响已经得到广泛的研究;而间歇运行、翅片表面生长的微生物和盐雾腐蚀等因素对蒸发器的影响机理和定量分析的研究却很少。因此,这方面的研究具有很强的迫切性和必要性。本文的主要目的是对铝翅片铜管换热器和铜翅片铜管换热器在析湿工况下,分别考虑间歇运行、微生物生长和盐雾腐蚀等影响因素,测试蒸发器的空气侧传热和压降特性。取得了以下几方面的成果:1)开发了湿工况污垢翅片翅片效率求解模型。通过该模型计算可知:当翅片在部分湿工况时,无污垢翅片效率模型与有污垢翅片效率模型计算结果相差很小;但当翅片在全湿工况时,无污垢翅片效率模型的计算值明显小于有污垢翅片效率模型的计算值,且随着空气入口相对湿度的增大,两个模型计算的结果相差会增大。2)模拟实际空调蒸发器经过长期运行并经过间歇运行、翅片表面霉变和盐雾腐蚀等因素影响,设计能够快速实现上述三种因素对蒸发器影响的方法。该方法可使翅片管换热器每次间歇运行实验(包括高低温循环和干湿循环)的时间控制在约4分钟,可通过人工加速微生物生长方法,使翅片管换热器翅片表面较快地生长微生物,以及可通过人工加速盐雾腐蚀方法,使翅片管换热器在实验室中较快地腐蚀。3)对1个铝翅片铜管换热器和1个铜翅片铜管换热器进行间歇运行实验,每300次间歇运行后进行空气侧传热和压降特性测试实验,根据实验数据分析间歇运行对翅片管蒸发器空气侧长效传热和压降特性的影响,并开发了析湿工况下反应翅片材料和间歇运行次数的传热和压降特性关联式。开发的传热关联式的平均误差为3.1%,压降关联式的平均误差为1.6%。4)对3个铝翅片铜管换热器和3个铜翅片铜管换热器进行微生物加速生长,对经过翅片表面生长微生物的换热器进行性能测试,并与未翅片表面未生长微生物的换热器进行对比,根据实验数据分析微生物污垢对翅片管蒸发器的空气侧传热和压降特性的影响。研究发现少量的微生物污垢会增强空气侧传热特性,而大量的微生物污垢会弱化传热,微生物污垢会使蒸发器空气侧压降增大。实验结果表明:当风速为0.5～2.0m/s时,微生物污垢会使翅片管蒸发器空气侧传热系数变化-16.0%～12.7%,使空气侧压降增多1.1%～43%。5)对3个铝翅片铜管换热器和3个铜翅片铜管换热器进行人工加速盐雾腐蚀,对经过腐蚀的翅片管换热器进行性能测试,并与未腐蚀的换热器进行对比,根据实验数据分析盐雾腐蚀对翅片管蒸发器的亲水性、空气侧传热和压降特性的影响。实验结果表明:随着盐雾腐蚀时间的增加,附带亲水层的铝翅片和不带亲水层的铜翅片,静态接触角、动态前进接触角和动态后退接触角均随腐蚀时间的增加而增大。说明随着盐雾腐蚀时间的增加,蒸发器的亲水性逐渐衰减。当风速为0.5～2.0 m/s时,盐雾腐蚀会使铝翅片管蒸发器空气侧传热系数变化-20.5%～36.8%,压降增大0%～21.6%。最后,简要阐述由于时间关系本文尚没有深入研究的问题,以及将来应重点关注的相关研究方向。更多还原

【Abstract】 Fined tube heat exchangers are widely used in air-conditioners operating as evaporator, a large amount of investigations have been carried out for improving the performance of evaporator, e.g. enhanced tubes are used to enhance the tube-side heat transfer performance, enhanced fins are used to enhance the air-side heat transfer performance, and optimization on refrigerant circuitry for improving the overall heat transfer performance. However, with the increase of operation duration, the heat transfer efficiency of evaporator degrades gradually, and the energy consumption increases correspondingly. More and more researchers focus their studies on the performance of evaporator after long time operations. Therefore, the long-term heat transfer and pressure drop performance becomes an important research topic. The effect on the long-term performance including fouling deposited on the fin surfaces, microorganism growth on the fin surfaces, intermittent operation and salt spray corrosion, and so on. Compare with the study on effect of fouling deposited on the fin surfaces, the effects of intermittent operation, microorganism growth and salt spray corrosion on the evaporator are limited. As a result, to give the reply to these issues is necessary and important for investigating the long-term air-side heat transfer and pressure drop performance.The purpose of this study is to investigate the heat transfer and pressure drop performance for aluminum-fin heat exchangers and copper-fin heat exchangers under wet conditions, considering the influence of intermittent operations, biofouling and salt spray corrosion. Based on the above purposes, this dissertation realized the following work:1) The fouled fin efficiency model under wet conditions was developed. The following conclusions can be obtained. When the fin is under partial wet conditions, the difference of calculation results between the clean fin efficiency model and the fouled fin efficiency model is limited. When the fin is under full wet conditions, the efficiency of clean fin is larger than that of fouled fin. Moreover, the difference of calculation results between the two models getting much larger with the increase of inlet air relative humidity.2) In order to simulate the operation condition of actual air-conditioner under intermittent operation condition, biofouled condition and corrosion condition, a method for realizing the above operation condition were developed. The method can realize a single intermittent operation (include dry/wet cycles and high/low temperature cycles) in four minutes, realize the microorganism growth on the fin surface in a short period, and realize the fin of finned tube heat exchanger corroded in a short period.3) Conduct the experiments for an aluminum-fin heat exchanger and a copper-fin heat exchanger under intermittent operation conditions. The heat transfer and pressure drop performance were measured each 300 repetitions. The effects of intermittent operation on air-side heat transfer and pressure drop performance were analyzed according to the experimental results. New models, which reflect the difference of fin material and repetitions, were developed to predict the heat transfer and pressure drop performance of finned tube heat exchanger. The average deviation is within 3.1% for heat transfer model, and 1.6% for pressure drop model.4) Conduct the experiments for three biofouled aluminum-fin heat exchangers and three biofouled copper-fin heat exchangers. The heat transfer and pressure drop performance were measured. The effects of intermittent operation on air-side heat transfer and pressure drop performance were analyzed according to the experimental results. In order to compare with the air-side performance of clean heat exchangers, the heat transfer and pressure drop performance were measured for the biofouled heat exchangers. According to the experimental results, fewer biofouling particles can enhance the air-side heat transfer performance, while a large quantity of biofouling particles deposit on the fin surface can degrade the air-side heat transfer performance. The experimental results shows that biofouling can cause the air-side heat transfer coefficient changing with the range of -16.0%~12.7%, and pressure drop changing with the range of 1.1%~43% when the air velocity is 0.5~2.0 m/s.5) Conduct the experiments for three corroded aluminum-fin heat exchangers and three corroded copper-fin heat exchangers. The heat transfer and pressure drop performance were measured. The effects of salt spray corrosion on hydrophilicity, air-side heat transfer and pressure drop performance were analyzed according to the experimental results. According to the experimental results, the static contact angle, the advancing and receding dynamic contact angle increase with the increase of salt spray corrosion hours for aluminum-fin evaporators with hydrophilic coating and copper-fin evaporators without hydrophilic coating. This results show that the hydrophilicity of fins degrade. Corrosion can cause he air-side heat transfer coefficient changing with the range of -20.5%~36.8%, and pressure drop changing with the range of 0%~21.6% when the air velocity is 0.5~2.0 m/s.At the end of this dissertation, the author presented the main weakness and further key points should be focused on in the near future.更多还原