Study On The Effect Of Ultrasonic Cavitation On The Enhancement Of Heat Transfer

Ultrasound has the characteristics of high efficiency, cleanness, environmental protection,and has been widely used in many aspects of social life. This article, based on the previous research, mainly studies the effect of ultrasonic cavitation on heat transfer in the heat exchanger,and the synergy degree between velocity field and temperature field in the heat transfer tubes is analyzed by using field synergy theory. At the same time, comprehensive evaluation of heat transfer effect of each heat transfer tube is carried out by using comprehensive performance coefficient index.First of all, we establish the physical model and the mathematical model, namely, circular tube, horizontal tube, corrugated tube and bellows tube. The advantages and disadvantages of the standard k-? model, the RNG k-? model and the Realizable k-? model are analyzed and compared. According to the specific conditions of fluid flow in heat transfer tubes, we point out that the standard k-? turbulence model is much better than others and the numerical calculation is carried out by using the finite difference method.Secondly, the effect of heat transfer in the heat transfer tubes is simulated under different working conditions by using the Flunet software, and we calculate the relationship of each heat transfer tube’s Nusselt number, field synergy number, comprehensive performance coefficient and Reynolds number. Furthermore we calculate the changing situation of Nusselt number and field synergy number along with the tube length. Through the comparative analysis, we find that Nusselt number, field synergy number, comprehensive performance coefficient of the various tubes increase with Reynolds number without ultrasonic wave. On heat transfer, horizontal tube is much better than others, followed by bellows tube and circular tube is worst. Moreover, the temperature field and the velocity field’s synergy degree and comprehensive performance coefficient index are much better in horizontal tube.Finally, a brief introduction is made on the mechanism of ultrasonic cavitation, the ultrasonic cavitation dynamics model, the concept of cavitation number and the physical meaning, the highest temperature and the maximum pressure of the cavitation bubble collapse,and the key to simulate the influence of ultrasonic cavitation effect of each heat exchanger tubes.We study on the influence of ultrasonic frequency, ultrasonic pressure amplitude and cavitation bubble number on the heat transfer effect, and the results are analyzed from theoretical aspects applying ultrasonic cavitation-related knowledge, besides, we compare the variation of heat transfer with and without ultrasonic cavitation. Results indicate that when the ultrasonic cavitation occurs in the heat exchange tube, the heat transfer ability of the heat exchange tube isenhanced. If the ultrasonic frequency is smaller and the acoustic pressure amplitude is larger and the number of cavitation bubbles is increased, the effect of the heat transfer is more obvious.When the pressure amplitude is greater and cavitation number is smaller, the field synergy number is larger, so the synergy degree of the temperature field and the velocity field is much better. Circular tube’s and bellows tube’s comprehensive performance coefficient is greater than1, while the comprehensive performance coefficient of the horizontal tube and the corrugated tube is less than 1, so circular tube and bellows tube are more suitable for heat transfer enhancement in accordance with the relationship between heat transfer and fluid drag reduction.