Research On The Effect Of Ultrasonic Descaling Technology On Fouling In Sewage Heat Exchange Tubes

Sewage source heat pump is an efficient air conditioning system that extracts the low-level heat energy in sewage through heat exchange technology to heat buildings.Sewage heat exchanger is an important part of sewage source heat pump system.Because there are a large number of impurities in the sewage,it is very easy to generate dirt in the heat exchange tube during the flow process.Dirt will increase the thermal resistance of the sewage heat exchange tube and affect the heat exchange capacity of the heat exchanger and the operation efficiency of the sewage source heat pump.Therefore,it is one of the important methods to improve the heat exchange capacity and maintain the long-term stable operation of the heat exchanger to study how to descale the heat exchanger tubes economically and effectively.At present,the common descaling technologies usually use mechanical and chemical means to remove the scale.Although these two methods can effectively remove the scale,sometimes chemical pollutants will be generated in the descaling process,and sometimes the heat exchange equipment needs to be shut down,affecting the normal operation of the system.Ultrasonic descaling technology uses physical means for descaling,which has the advantages of high efficiency,low cost and no pollution,and has attracted the attention of relevant personnel.Under the action of ultrasonic wave,a large number of cavitation bubbles will be generated in the fluid,and the cavitation bubbles will produce strong pulse stress when they break,which speeds up the process of dirt falling off from the pipe wall and plays a descaling effect.In this paper,the process of ultrasonic descaling is studied by numerical simulation.Taking the ultrasonic parameters and fluid parameters that affect the effect of ultrasonic descaling as variables,the rules of ultrasonic descaling under different working conditions are studied.The main research contents of this thesis are as follows:Firstly,the classification of fouling and the growth process of fouling in the pipeline are introduced;The common descaling technologies in the market are studied,the principles of various descaling technologies are introduced,and their advantages and disadvantages are analyzed;The cavitation model and other mathematical models used in the numerical simulation of ultrasonic descaling are summarized.On this basis,the mathematical model of ultrasonic sound pressure and the physical model of heat exchange tube are established,and the grid independence is verified.Secondly,ultrasonic parameters such as ultrasonic power,ultrasonic frequency,action time and cavitation effect are selected as variables,and the sewage heat exchange straight pipe is taken as the research object to study the effect of ultrasonic descaling,and the particle fouling deposition data and wall erosion data in the descaling process are recorded in real time.After calculation,the relationship curve between ultrasonic parameters and descaling rate and the transformation curve of fouling thermal resistance with time under different working conditions are obtained,By analyzing the data,the best power,time and frequency of ultrasonic descaling were obtained.Finally,the influence of fluid parameters on ultrasonic descaling process is studied,such as fluid flow rate,fluid temperature,fluid viscosity,particle size,and so on.It is concluded that viscosity,particle size,and concentration have a greater impact on ultrasonic descaling,while particle concentration and temperature have a smaller impact on ultrasonic descaling,and there is an optimal descaling fluid flow rate of 1.2m/s.