Study On Heat Transfer Enhancement Of Wastewater Heat Exchanger In Wastewater Source Heat Pump System

Facing the global energy crisis and the deterioration of the environment, in order to make the human society healthy and sustainable development, we must accelerate the optimization of energy structure and reduce the use of mineral energy to shift the focus of energy structure to the new energy and renewable energy. With the development of science and technology, heat pump technology makes the development and utilization of waste heat in city wastewater has become possible. The use of wastewater source heat pump has become the most effective way of urban wastewater recycling. It is an energy efficient and environmentally friendly way and it just satisfies the need of strategy of sustainable development.The focus and difficulty of the application of wastewater heat pump is the choice of the proper wastewater heat exchanger. Because of the specificity of wastewater water quality, the wastewater heat exchanger should not only be high in heat transfer coefficient, but also be with a characteristic that insusceptibility to scaling, corrosion resistant and easy to clean. The traditional heat transfer tube is mainly light tube or metal tube with rough surface treatment. It can’t effectively improve the heat transfer efficiency of the heat exchanger and the impurities in the wastewater are easily deposited on the inner wall of the pipe. The development of the fouling layer, which affects the life of the heat exchanger, reduces the heat transfer coefficient.In view of the fact that the traditional heat exchanger can’t meet the above requirements, the structure of the heat exchanger of indirect sewage source heat pump is modified in this paper. This paper adds a rotatable flexible screw rod in heat exchange tube to drive the helical flow of fluid in the pipe, in this way it can improve the turbulence of fluid, break the development of interference boundary layer and enhance the mixture of hot and cold fluids. This kind of tube can improve the heat transfer coefficients and inhibit impurity precipitation and scaling.This paper uses the numerical simulation to calculate the modified model of heat exchanger. It can accurately simulate the movement of fluid and heat transfer process in the simulation physical model. The movement of the fluid in the heat exchange tube is mainly influenced by the rotating speed and the structure of the screw,so this paper mainly discuss this two factors on the influence of heat transfer of heat exchange tube and the ability about restraint of scale format. Through the simulation, it found that the heat transfer efficiency of the heat exchanger increased with the increase of the rotating speed of the screw rod and decrease of the screw thread pitch. Therefore, the actual project should be based on the actual situation to determine the screw rod speed and the size of the pitch.