Study Of Heat Convection Enhancement By Vibration For Ribbon-tubular Radiator

Ribbon-tubular radiator is widely used in vehicle engine cooling system, it can ensure engine reliable work in an ideal temperature range through the rational matching radiator and engine power. The heat convection efficiency of radiator determine its energy and resource consumption, therefore, how to use the heat transfer enhancement technology to improve the heat convection efficiency of radiator is the focus of attention. This paper combines with the vibration heat transfer enhancement method and radiator, carried on systematic research on the mechanism and effect of heat transfer enhancement by vibration for radiator through numerical simulation and wind tunnel experiments.Mathematical models of flat tube and louvered fin were established by CFD method, expounded the governing equation discretization with unstructured grid and the corresponding SIMPLEC algorithm. Fluent was used to simulate the flow and temperature field distribution of flat tube and fin under different vibration conditions, and discussed the influence of amplitude and frequency. Simulation results of flat,tube show that:Vibration can disturb flow field and obviously increases the turbulence of boundary layer, which is conducive to enhance the heat convection of radiator. HCEV effect increases with amplitude, but less affected by frequency. Nu can be improved by14.07%to67.78%for increase amplitude and4.64%to26.03%for increase frequency. Effects of vibration on heat transfer decreases with wind speed. Results of fin show that: Vibration will change the path of flow particles, force the flow is louver-directed which can improves the flow efficiency and increases the turbulence in boundary layer. Inter-fin interference thermal wake or lighter intra-fin interference thermal wake caused by vibration, which reduce fin channel average temperature, significantly improves heat convection efficiency. Heat flux (q) increase with the vibration intensity and wind speed, and the effect of frequency is greater than amplitude, q maximum increase of22.92% for increase amplitude, but51.50%with increase frequency. Disturbance from vibration decrease with air velocity, but the effect of vibration on heat transfer enhancement increase first and then decrease with air velocity.The field synergy number and field synergy angle distribution were used to field synergy analysis on flat tube and fin models, which in-depth revealed the internal mechanism of HCEV for radiator. Field synergy analysis shows that:Vibration can obviously change the field synergy angle distribution near flat tube and fin wall, and the change along the direction departure from90°, which bring to a better synergy between temperature gradient field and velocity field. The field coordination increases with vibration strength, and decreases with wind speed. Flat tube and fin simulation results show that vibration can improve the heat convection rate, and field synergy analysis shows that vibration improved the coordination of convective heat transfer. Therefore, the inner reason for vibration-disturbed enhancement of heat convention is the increases of heat convention coordination. Field synergy principle well reveals the mechanism of HCEV.A wind tunnel experiment platform for radiator has been set up under vibration condition, through which the experimental study to question of HCEV for radiator has been carried on. Thermal-hydraulic performance was discussed by j/f1/3. Results show that:Vibration can effectively improve the total heat transfer (Ua) coefficient and air side heat transfer coefficient (ha) of radiator, within the scope of the experiment, the Ua can be most increased by11.71%, and the ha can be increased by16.82%. It confirmed air side heat resistance of radiator is the key factor that hinder the convective heat transfer, so improve air side heat convection performance by vibration, especially under low Reynolds number, is very effective. However, vibration also increases the pressure loss, the pressure drops can be increased maximumly by40.48%. On vibration conditions, the percentage of pressure loss decreases with wind speed, which indicates that HCEV under high air speed is a better method that has more advantages in pressure loss compared with other forms of heat convection strengthening methods. Pressure loss get big proportion of increase under low wind speed, but the increment is small, so the extra power consumption is not big. Heat transfer factor ja and resistance factor fa both increase with the vibration intensity, define B=(jv/j0)/(fv/f0)1/3to describe the effectiveness of HCEV. Results show that B>1, namely the salutary effect brought by HCEV is greater than the price of pressure loss, which proof HCEV method is effective. The effectiveness of HCEV increases with the vibration intensity, and on the rise with the increases of Reynolds number.