| The paper studied mainly fouling and descaling ultrasorlic influence heat convection of pace synergism in convection heat exchange, and the factors which affects ultrasonic anti descaling effect and the question of descaling effective evaluation based on principles of field synergy and ultrasonic theory.Firstly, analyzing the characteristics of fouling and it affects heat transfer and heat convection of pace synergism.Secondly, according to the Doppler frequency shift principle, in order to improve the ultrasonic anti-descaling effect, establishing the spread of mathematical model of ultrasonic in flowing liquid to find out the analytical solution for distribution of sound pressure. The propagation characteristic of ultrasonic in all kinds of tube type was acquired by using numerical simulation software. It was concluded that the distribution of sound pressure and frequency response characteristics, and analyzing the factors that affect the propagation characteristic of descaling ultrasonic and cavitation, then, for further study, the ultrasonic cavitation effect on the velocity and heat flow of field synergy heat exchange tube. In order to optimize the operation of the ultrasonic anti-descaling instrument, the author put forward real-time online evaluation method of anti-descaling effect and defines the evaluation index for the first time. Finally, the numerical simulation results validated by experiment, and according to the research results, the paper puts forward optimizing instrument design and operation of conception for ultrasonic anti descaling, and pointed out the direction for follow-up research.According to the principles of field synergy, heat transfer process was affected by different tubes which scale CaCO3dirt by using numerical simulation method, and the results of calculation made a detailed analysis and objective evaluation. The result of calculation indicates that the velocity vector and the temperature gradient of the synergy degree were affected by different tube. The collaborative angle B of corrugated pipe decreased with the increases of dirt thickness, and the bellows tube heat exchange capacity and the heat exchange capacity of corrugated pipe increased in the fouling state. However, the collaborative angle β for other type tube increased with the thickness of fouling and the synergy degree become poor. The synergy Angle θ of velocity and pressure gradient increased with fouling thickness and the loss of pressure for all types of tube. Although the collaborative angle B of speed and temperature gradient for alternating axis tubes was smaller than other heat exchange tube, the heat transfer effect was stronger than other tube type and the collaborative angle θ of velocity and pressure gradient were less influenced by fouling. From the view of integrated heat transfer coefficient performance alternating axis tubes, the performance of comprehensive heat exchange coefficient was highest. Alternating axis tubes had great prospects on the high efficiency and low resistance enhanced heat transfer area.According to the Doppler frequency shift principle, wave equation on the stationary was improved, then established spreading mathematical model of ultrasonic flow in liquid and viscous liquid, and calculated the analytic solution. The results showed that acoustic attenuation amplitude was relatively small when the heat transfer medium flow rate was relatively small. When the flow velocity increased, the energy density per unit volume will be smaller and anti-scaling effect will be weaker. Liquid viscosity is the main reason for ultrasonic attenuation in heating medium. Viscosity increasing made the increase of absorption coefficient and the speed of ultrasonic absorption, and made the reduction of ultrasonic wave propagation distance and ultrasonic anti-fouling effect. Using numerical simulation software, the ultrasonic propagation characteristics in a variety of tube were numerically simulated that the distribution of sound pressure and the effect of enhanced tube of ultrasonic anti-fouling can get.We can get cavitation effect on velocity and temperature of field synergy in the heat exchanger by using numerical simulation. Simulation results showed that cavitation coefficient was different while difference of structure forms pipe. Cavitation coefficient of round tube was maximum, transverse tube’s coefficient was greater than the bellow, and coefficient was minimum for transversely ridged tube. Field synergy coefficient and cavitation coefficient existed a corresponding function that synergy coefficient in the fluid field increased with increase of cavitation coefficient. Field synergy coefficient of fluid velocity and temperature gradient after ultrasonic cavitation was smaller than the untreated.The thesis proposes the method that can realize real-time online evaluation for ultrasonic anti-fouling effect combined heat transfer theory, and defined the evaluation index. Evaluation indexes which were analyzed and modified made the coefficient can use to online evaluation of the descaling effect when heat exchanger worked in variable conditions.The ultrasonic anti-fouling experimental station is established. In the ultrasonic antifouling experiment station, the effect of temperature is studied on ultrasonic propagation character of descaling.The results show that the best temperature is55℃, ultrasonic wave propagation in the water.And ultrasonic effective action range is2m in heat exchanger. |
