Study On Heat Transfer Enhancement Of Immersed Heat Exchanger Based On Ultrasonic Technology

The heat transfer enhancement of heat exchanger has always been the key research point in heat and mass transfer industry.Due to its high efficiency,safety,energy concentration and other advantages,ultrasonic wave,which has been widely applied in various industries,has broad prospects in development and application.The liquid which has been given the ultrasonic wave will produce the cavitation effect.In this text,ultrasonic cavitation is used to study the heat transfer enhancement of immersion condensing coil.First,on the basis of ultrasonic heat transfer enhancement,by establishing related physical and mathematical model of equal diameter and non-equal diameter coil,the influence to heat transfer on the coils with different power was simulated in the ultrasonic wave frequency of 20 kHz,25 kHz and 28 kHz by using Fluent software.Through the comparison of simulations,the influence of ultrasonic wave to unequal diameter coil is higher than the equal diameter coil in the condition of the same frequency and power.Then,the text contrasts the velocity field distribution in the condition of non-ultrasonic wave and ultrasonic wave.For the case of same frequency,with the increasing of ultrasonic wave power,the turbulence of water will be strengthened.Due to the increased pressure on the cavitation bubble,it promotes the generation of cavitation bubbles in water.The generated pressure wave impacts the boundary layer and reduces the thickness of boundary layer and the heat transfer resistance.It changes the water flow state,and then enhances the heat transfer.At last,the experiment verifies the heat transfer effect of ultrasonic wave by using the piezoelectric transducer in the frequency of 28 kHz and power of 180 W.In the experiment,the water in the tank is heated by static state method which means there is no water outflow.The result of experiment shows that it has an obvious effect of ultrasonic cavitation in promoting natural convection outside the tube.When the ultrasonic effect is applied,the temperature rise of water in the tank is faster,and the temperature of the condenser is reduced and the time of water heating in the tank is shortened.