Theoretical And Experimental Research Of Heat Transfer Enhancement For Wastewater Heat Exchanger In Wastewater Source Heat Pump

Municipal sewage can be used as a low-level heat source for heat pumps to play an important role in the field of sewage source heat pumps,alleviating the current situation of water shortage in China,municipal sewage has the advantages of stability,reliability,heat storage,economy,environmental protection,etc.Compared with other heat pumps,sewage source heat pumps have many advantages,not only save energy consumption,but also recover municipal sewage heat energy,which is conducive to China's sustainable development concept.In the case of long-term use of sewage,the generation of dirt is inevitable,so the following aspects are mainly considered when selecting the sewage heat exchanger: heat exchange capacity of the heat exchanger,convenient maintenance of the later maintenance,anti-corrosion ability,descaling Scale inhibition ability,etc.The heat transfer capacity of heat exchangers is fundamental to the study,and energy conservation and environmental protection measures must be taken on the premise of improving heat transfer efficiency;The convenience of post-cleaning can save a lot of manpower and material resources,etc;In order to prevent system abnormalities caused by corrosion of sewage heat exchanger tubes,anti-corrosion pipes must be used;The automatic descaling capacity and scale inhibition capacity of the sewage heat exchanger are also considered.In this paper,a shell-and-tube heat exchanger with interpolated spirals was designed and its heat transfer performance was studied.In order to solve the problems of descaling and scale inhibition under the premise of improving heat exchange efficiency,this paper heat exchange tube is inserted into the rotatable spiral to enhance heat transfer technology,among them,the spiral has two kinds of helical line and screw slice.Inserting a rotatable spiral in the heat exchange tube can enhance fluid disturbance in the tube and increase fluid turbulence to enhance heat transfer,when the spiral in the tube rotates,it also has a scratching effect on the tube wall,which can reduce and prevent the generation of dirt to a certain extent.In order to meet the actual working conditions,this paper builds a horizontal singletube interpolating rotatable spiral test bench,the heat transfer coefficients of the two interpolated spiral horizontal tubes at different pitch or rotational speed conditions are obtained,and compared with the obtained traditional tube heat transfer coefficient,using Fluent software for numerical simulation and theoretical analysis,and the accuracy of the experimental results is verified by the combination of theory and practice.The experimental results are analyzed as follows:(1)When the rotation speed is constant,only the influence of the pitch is considered,the heat transfer effect of the interpolated helical line and screw slice heat exchange tube is enhanced with the decrease of the pitch.Compared with the traditional tube,at a speed of 10 rad/s,the helical line with a pitch of 10 mm has the best heat transfer enhancement performance,and the highest rate of heat transfer coefficient is 38.72%;the screw slice with a pitch of 10 mm has the best heat transfer enhancement performance,and the highest rate of heat transfer coefficient is 104.22%,finally,an interpolating spiral heat exchange tube with a rotational pitch of 10 mm is preferred;(2)When the pitch is constant,only the influence of the rotation speed is considered,the heat transfer effect of the interpolated helical line and screw slice heat exchange tube is enhanced with the increase of the rotational speed.Compared with the traditional tube,at a pitch of 10 mm,the helical line with a speed of 10 rad/s has the best heat transfer enhancement performance,and the highest rate of heat transfer coefficient is 54.07%;the screw slice with a speed of 10 rad/s has the best heat transfer enhancement performance,and the highest rate of heat transfer coefficient is 135.96%;Although the heat transfer coefficient improvement rate of the helical line and the screw slice is optimal under the condition of 40 rad/s,the comprehensive operation cost,the heat transfer coefficient increase,and the expected heat transfer enhancement effect are considered,finally,an interpolating spiral heat exchange tube with a rotational speed of 10 rad/s is preferred.By optimizing the heat exchange tubes,this paper not only enhances heat transfer,but also effectively inhibits the generation of dirt.It has a great role in promoting the effective use of resources and also has a protective effect on the environment.