Particle Deposition Characteristics Of Finned Tube Heat Exchangers And Analysis For Influence Of Particles On Pressure Drop And Heat Transfer Performance

The air-side performance of finned tube heat exchanger will decrease due to the coverage of dust particles after long-term running.Particle deposition characteristics on heat exchanger under dry conditions are different from that under dehumidifying conditions,and the effect of dry particles on heat exchanger performance is obviously different from the effect of wet particles.In order to improve the long-term performance of heat exchanger,it is necessary to experimentally investigate the particle deposition characteristics on finned tube heat exchanger both under dry conditions and under dehumidifying conditions,and analyze the effect of deposited particles on the air-side performance of heat exchanger.In order to determine the consistents of artificial dust used for dust deposition experiments,the actual dust samples on outdoor unit of air-conditioners in several typical cities were collected and the physical properties of these dust samples were analyzed.The results show that the components of dust samples include particles and fibers;the main constituents of deposited particles are 41% for silicon dioxide,23.1% for calcium compounds,19.5% for alumina and other salts,respectively;the median diameter of deposited particles is 15?m.An visualization experimental rig was designed and set up to investigate the particle deposition characteristics on finned tube heat exchanger under dry conditions,and the influences of dust injection conditions(including air velocity and particle concentration)and heat exchanger structures(including fin type,fin pitch and tube row number)on the air-side performance were analyzed.The results show that,abundant dry particles concentrate on the leading edge of fins as well as the front part of tubes.For the dust injection conditions,high particle concentration and high air velocity contribute to dust deposition and may increase pressure drop.For the heat exchanger structures,louver fin is the most beneficial to particle deposition compared with wavy fin and plate fin,and the increment of pressure drop is the most serious for louver fin;small fin pitch can promote particle deposition and increase pressure drop;the increase of tube row number is prone to dust deposition and pressure drop.In order to investigate the wet particle deposition characteristics on finned tube heat exchanger under dehumidifying conditions,another visual test section was designed to accomplish the dehumidification process of moist air based on the above experimental rig.The influences of heat exchanger structures(including fin type,fin pitch and tube row number)on wet particle deposition as well as air-side performance of heat exchanger were analyzed.The results show that,overwhelming wet particles concentrate on the windward side of fins,and the degree of wet particle deposition is more obvious than the degree of dry particle deposition;the maximum particle deposition weight on plate-fin typed,wavy-fin typed and louver-fin typed heat exchanger under dehumidifying conditions is 7.3 times,5.9 times and 5.1 times,respectively,of that under dry conditions.Louver fin is the most beneficial to wet particle deposition compared with wavy fin and plate fin,and the deterioration of airside performance is the most serious for louver fin;small fin pitch is prone to wet particle deposition,and lead to more severe deterioration of heat transfer and pressure drop performance;high tube row number can promote particle deposition,thus significantly decrease air-side performance.