Dust Accumulation Experiments For Long-term Performance And Anti-dust Structure Design Of Finned Tube Heat Exchangers For Air Conditioner

A large amount of dust will accumulate on the surfaces of finned tube heat exchanger of air-conditioner after long-term operation.The accumulated dust may reduce the air flow area and increase the air-side thermal resistance of heat exchanger,leading to the performance degradation of air-conditioner.In order to reduce the performance degradation of air-conditioner,it is necessary to study the influence of dust on air-side performance of heat exchanger.In the actual condition,the dust concentration is very low,resulting in the slow process of dust accumulation.Therefore,an accelerated test method of dust accumulation on heat exchanger should be developed to investigate the influence of dust on air-side performance of heat exchanger.The purpose of this paper is to develop an accelerated test method of dust accumulation and establish an experimental rig to carry out the experiments of dust accumulation on heat exchanger test samples,and analyze the influence of geometric factors of heat exchangers on air-side heat transfer capacity and pressure drop.Meanwhile,anti-dust structure is designed for the plate-fin tubed heat exchanger,and the effects of anti-dust structures on dust deposition rate were analyzed.The detailed research contents are shown as follows:An experimental method has been developed to improve the repeatability of the accelerated dust accumulation test of heat exchangers.The equivalent relationship between accelerated dust accumulation time and actual operating time of heat exchanger is analyzed and deduced,providing a theoretical basis to determine the time condition of accelerated dust accumulation.The experimental principle is developed for both accelerated dust accumulation test and heat transfer test,which can improve the repeatability of experimental rig.A room-typed experimental rig has been established for accelerated dust accumulation test and heat transfer test of heat exchangers.The key component of dust feeder is designed to stably and accurately control the dust concentration in dust environment.The room-type experimental rig is established for accelerated dust accumulation test and heat transfer test of heat exchangers,and some experiments of performance degradation have been carried out to validate the repeatability of experimental rig.The validation results show that the experimental rig has good repeatability.Dust accumulation experiments of long-term performance are carried out on different heat exchangers.The results show that,the dust accumulated on the bend side is more obvious than that on the windward side and lateral side.For the heat exchanger fin types,louver fin is the most beneficial to dust accumulation compared with plate fin and wavy fin;the attenuation rate of heat transfer capacity is 16.4%,and the pressure drop is increased by 16.3%.For tube row number,the 2-tube row heat exchanger is easier to dust accumulation compared with the 1-tube row heat exchanger.The attenuation rate of heat transfer capacity and the increase rate of pressure drop in the 2-tube row heat exchanger are 4.75%and 2.6% respectively.For the heat exchanger structure parameters,the increase of tube diameter and the number of 1-tube row holes are prone to dust accumulation;meanwhile,the decrease of fin pitch and longitudinal tube pitch may cause more particle deposition.The anti-dust structures on the windward side of the plate fin heat exchanger with the fin pitch range of 1.2-1.6 mm were designed and validated by the numerical simulation method.The results show that,the interval-cut fin structure of the 1-tube row heat exchanger is conducive to reduce dust accumulation,and the dust deposition rate on the heat exchanger with fin pitch of 1.2mm was 16.42% less than that on the heat exchanger with fin pitch of 1.6mm.The optimized structures with large fin pitch in the windward and small fin pitch in the backward were designed for the 2-tube row heat exchangers with fin pitch of 1.2 mm and 1.4 mm.The results show that,the dust deposition rate on heat exchanger whose fin pitch increases from 1.2 mm to 1.6 mm was 7.81% less than that on heat exchanger whose fin pitch increases from 1.4 mm to 1.6 mm,meaning that these optimized structures are helpful to reduce the dust accumulation.