| Facing the serious energy and environmental situation, urban sewage source heat pump system has been one of the important technologies and effective ways to develop and utilize the city sewage, various countries are promoting the application and development of this technology actively. But the scaling problems on the sewage heat exchanger lead to the development bottleneck. The ultrasonic anti-descaling technology has great superiority because of its high efficiency and high cleanness. At present this technology has had some certain theoretical basis and the application in the areas of oil, electricity has been approved.The paper studies some key problems during the process of water heat transfer around the current sewage-source heat pump system, by discussing the formation mechanism of the dirt, and then introducing the ultrasonic cavitation technology in the sewage heat exchanger. The paper studies the scale removal effect and the strengthen heat transfer effect of the ultrasonic technology. The mainly study works and results are presented as follows:(1) On the basis of existing literatures, the paper studies the present anti blocking and decontamination methods of sewage heat exchanger, and summarizes the applications of acoustic cavitation technology in the field of descaling and strengthen heat transfer, according to the mechanism of the ultrasonic, the paper designs and builds experiments on descale and strengthening heat transfer in the sewage side of the sewage-source heat pump system with acoustic cavitationg. after the acoustic cavitation technology workes on heat exchange pipeline, by calculating the descaling rate to verify its effect.(2) The scaling regular pattern of the heat exchange tube under different flow rate and viscosity is studied. The experiments have proved that when the wastewater contained a certain amount of grease, the velocity is smaller, the scale amount difference is more significant. The dirt thickness decreases with the increase of flow velocity, when the flow velocity is0.5m/s and after96h,the stable scale amount is10.6g, at this time the dirt thickness is5.35mm after calculated, thermal resistance is9.81×10-4m2·K/W. Experiments confirm that in the heat exchange tube is soft dirt mainly.(3) Experimental researched the effect and influencing factors of the ultrasonic scaling. Within10mins-60mins, by changing the water flow velocity in the heat exchange tube, the paper analysises ultrasonic descaling regular pattern and draws the effect curve. When the velocity is constant, the longer ultrasonic action time, higher the removal rate is, but after40mins or50mins it begins to decrease. In the same action time, bigger the flow velocity is, the descaling effect is better, but when after the velocity exceeds a certain value, the effect is also reduced. The experiment also studies the influence of different pipe material and the function of ultrasonic distance. When the velocity is1.36m/s, carbon steel tube inner surface descaling rate is80%.Copper tube outer surface descaling rate is83.3%.(4) In combination with the experimental results, and the paper analyzes the influence regular pattern of strengthening heat transfer under different moisture content and action time and velocity, the analyzed effect when the ultrasonic technology can reduce the heat transfer area35.7%which is applied on a heat pumps, the heat transfer coefficient is increased by48%. Author designes a new and high efficient heat exchanger, describes the operation scheme and matters needing attention.In short, results has showed that ultrasonic descaling technology has obvious descaling effect and strengthen the heat transfer performance, but the influence factors are lots. Through the experiment research and analysis, this paper discusses the sewage dirt removal and the new method of sewage heat exchanger strengthening heat transfer, lay the theoretical basis for development and application research of new the descaling technology. The conclusion has a guiding significance to system design and operation. |
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