Fouling Dynamic Characteristics of River Water Source Heat Pump Heat Exchanger and Its Study on the Effects
|Course||Heating,Gas Supply, Ventilation and Air Conditioning Engineering|
|Keywords||River water-source heat pump Water quality Fouling Fouling resistance Flow and heat transfer characteristics|
River water-source heat pump is the promotion of renewable energy technology. In the conditions of water quality better circumstances, open-type system are widely used because of the energy utilization efficiency in the engineering applications.But in certain conditions of water quality, fouling, wear, corrosion , biological sludge due to microbial continuous reproduction and and other issues may be produced, which will cause many problems such as pipeline is blockaged, energy consumption is incre-ased, the normal operation of the turbine is affectd, the refrigerating and heating effect is reduced and the service life of the equipment is reduced . Therefore, when in use, attention should be paid to the requirement of water quality and treatment to prevent the emergence of heat exchanger, pipeline corrosion problems and soJ on. Meanwhile, it must be considerd that the long-term operation may reduce influence of heat exchange efficiency on system. Therefore, fouling formation mechanism research on unit heat exchanger of water source heat pump system of open-type system and reserch on its effect on flow and heat transfer characteristics are important basisof water source heat pump technology popularization and application. his research is based on the Chongqing river water source heat pump heat exchanger.The pape includes fouling causes and time-varying regularity, and its effect on the heat exchanger of flo-wand heat transfer characteristics of impact studies, and the conclusion is obtained.The variation rule of water quality indexes is obtained by mean of the river water quality testing and analysis. By comparing the actual water quality status and current standards of water quality requirements, key treatment objects are put forward when annual water is used.Because the river water quality and groundwater quality is differ-ent, the index limit of the proposal COD, conductivity and dissolved oxygen of water quality should be increased into river water quality standard on source heat pump. Through the influence factor analysis of river water source heat pump heat exchanger fouling,it is found that the key factor is the sediment concentration and turbidity, and causing scaling factor does not include the role of algae.With reference to the sediment particle size distribution of the river in last few years, after 31 groups different sedi-ment concentration and turbidity of water are respectively prepard, the relationship of the river sediment concentration and turbidity is obtainde by experimental analysis. The test system of heat exchanger fouling includes drying calcination loss analysis, EDS spectrum scanning analysis and scanning electron microscope analysis.The resu-lts show that fouling of the heat exchange pipe mainly includes sediment particles of fouling.The fouling is dense and hard texture and its main component is small particle diameter silt.Experiment platform on heat exchanger fouling of river water source heat pump was built on segment cruise ship in Jialing River Ciqikou ,Chongqing.The experiment includes the thermal resistance method for monitoring fouling in pipes first growth characteristic experiment and dirt cleaning again after the experimental research on growth characteristics. Study found that when the first growth, flow rate on heat exch-ange tube water was 0.6m/s, 1.0m/s and 1.5m/s and the fouling induction period of its corresponds was 55h, 74h and 86h. And corresponding stable thermal resistance we-re 10×10-5（m2·k）/w,6×10-5（m2·k）/w and 5×10-5（m2·k）/w.The induction period and velocity is directly proportional, and stable thermal resistance and velocity is inversel-y proportional.For the flow rate of 0.6m/s, 1.5m/s of tube heat exchanger fouling, the cleaning methods included using double flow backwashi-ng and nylon brush cleaning.The results showed cleaning effect of water source heat pump heat exchanger fouling is relatively good.New heat exchange tube within the conduit （ induction period of growth charact-eristics of fouling in neglect ） appears first exponential function type slow growth and exponential asymptotic characteristic again fast growth. And after scale removal gro-wth characteristics of fouling in pipes only presents exponential asymptotic growth process.Research shows that, fouling layer within the tube is made of grass hard to get rid of and the easy cleaning attachment layer.The linear slow growth characteristics of fouling reflect the fouling grass growth process. During the late exponential asym-ptotic growth characteristics reflect the fouling layer forming process. To the new heat exchange tube, first fouling growth is the basic form, and it is difficult to remove the adhesive layer formation. For the heat exchange tube after decontamination, process of fouling again growth is the main adhesive layer formation.Through time-varying characteristics analysis of the actual river water source heat pump heat exchanger fouling, based on the asymptotic growth model proposed by Zubair and Sheikh, inside the tube flow rate of 1.0m/s and 1.5m/s in two different conditions, Study suggests including asymptotic growth phase for the first time,temporary equilibrium stage, asym-ptotic growth stage again and again equilibrium stage model for prediction of fouling.And the prediction of fouling model has been validated and analysised.Stabilizing fouling thermal resistance on the heat exchanger tube flow rate of 0.6m/s, 1.0m/s and 1.5m/s is analysised.Stability of fouling thermal resistance of water source heat pump in Chongqing Jalingjiang can be valued 5.5×10-5（m2·k）/w. Through exgery analysis,the results showed that under certain conditions of constant temperature and under different flow rate changes, velocity between the 1.0m/s1.5m/s value is appropriate by the analysis of three exegry coefficients associated with fouling.Heat exchanger fouling of water source heat pump in practical applications are considered. The two currently-used methods of water source heat pump heat exchang-er cleaning are comparatively analysised by the test.The methods are nylon brush to clean and powerful rotation of small water flushing.The results showed that the meth-od of nylon brush to clean has problems of not completely withdrawn from circulation. And the method of small water, strong rotation processing is confined to single-tube and double-tube shell and tube heat. So more reasonable and new technology are needed to be introduced. In the flood peak of the river, fouling resistance of tube heat exchanger can achieve the stable value in a very short period of time.Therefore, cleaning after the flood peak is needed. When the river water quality is good, before or after the flood comes, water only general filter can be directly into the unit.Water quality testing and analysis of air conditioning and refrigeration and heati-ng period in Chongqing jialing River and Yangtze River have been done.Experiment platform on water source heat pump heat exchanger fouling research has been set up. Thermal resistance method for monitoring fouling in pipes first growth characteristic experiment and dirt cleaning again after the experimental research on growth charact-eristics have been done.Key treatment indexs of water quality have been put forward. Key factors that affect river water source heat pump heat exchanger fouling have beendetimered. Relationship between river sediment concentration and turbidity have been identified. Tube fouling layer and corresponding fouling prediction model have been put forward. The increased limit of water quality index on river water source heat pu-mp have been dertimered. Fouling composition, fouling thermal resistance under different velocity stability, the growth characteristics of fouling in new heat exchanger tube pipe, recommended velocity values of river water source heat pump the water side heat transfer tube and the cleaning cycle on unit has been obtained by experimentand analysis.The conclusion of the study laid the foundation for further study of water source heat pump fouling, provides the basis for formulation of related standards, and also is as a reference in practical engineering application.