Accelerating-particle-deposition, Long-term performance, Heat exchanger, Air conditioner, Accelerating factor
Fin-and-tube heat exchanger is the most commonly used heat exchanger type in air-conditioning systems. In the actual operation of air-conditioning systems, the dust particles involved in the air may partly deposit and form particulate fouling on fins and tubes when the dusty air flows through the heat exchangers. The deposited particles may gradually block the passageway of air flow and occupy the heat transfer area, which results in the continuous increase of air side thermal resistance and the significant deterioration of the heat transfer capacity of heat exchangers during the long-term operation. In order to quickly evaluate the long-term performance of fin-and-tube heat exchangers, an accelerating-particle-deposition method, which is capable of implementing the particle deposition process on the long-running heat exchangers in a short time, is proposed in this study. The idea of the accelerating-particle-deposition method is to employ high concentration dusty air flow through heat exchangers in the accelerated test, and to quickly form the particulate fouling with the same weight as that on long-running heat exchangers under the actual operating environment with low particle concentration. The accelerating factor, which is defined as the ratio of the actual running time to the accelerated testing time, is calculated based on the deposition weight of dust particles. The deposition weight is calculated by the relationship of the impact frequency and deposition probability of dust particles with the particle concentration of dusty air. An experimental apparatus for accelerating the particle deposition process and testing the heat transfer capacity of fin-and-tube heat exchangers is designed. The predicted long-term performances of heat exchangers based on the proposed accelerating-particle-deposition method are compared with the actual performance data of heat exchangers after 5-8 years’ operation published by China Quality Certification Center. The comparison results show that, the predicted results agree well with the actual operation data, and the mean deviation of the heat transfer capacity is within 10%.