Research On Heat Transfer And Flow Resistance Characteristics Of Oil Cooler With Aluminum Fins

As a water-cooled heat transfer equipment, oil cooler with aluminum fins has compact structure, large heat transfer area, strong corrosion resistance and many other advantages, is more widely applied in the field of construction machinery. In this paper, the heat transfer and flow resistance characteristics of oil cooler with aluminum fins are explored by the means of numerical simulation and experimental study. Firstly, numerical analysis is adopted to research the flow field characteristics and the influence of its comprehensive heat transfer performance with the change of baffle structure parameters. Secondly, by experimental study to analyze the pros and cons of the heat transfer and resistance performance compared with different structures oil cooler, and explore the impact of the cooling water parameters on its performance. Finally, on the basis of oil cooler with flat fins, a new type of dimpled fin is proposed to enhance its heat transfer rate. Through the changes of velocity, streamlines, temperature and local nusselt number in the flow field to analyze the mechanism of heat transfer enhancement. And the effect of different geometry size of dimpled fin surfaces about the comprehensive heat transfer performance is extensively studied. The main work and conclusions of this study are as follows:(1) The shell flow field of oil cooler with aluminum fins has confirmed the existence of import and export instability stage and full development stage. In the clearance of aluminum fins, the direction of fluid flow are perpendicular to the tube bundle, and are more close to the ideal cross-flow. The shell-side heat transfer performance and resistance coefficients will be improved with the baffle spacing decreases. And when the baffle spacing is smaller, it has better comprehensive heat transfer performance. The baffle gap height has little effect on heat transfer and pressure drop performance.(2) Contrast test results of aluminum fins, low-finned spiral baffle plate oil cooler and arched smooth tube oil cooler show that oil cooler with aluminum fins has more significant advantage of heat transfer rate, and has minimal irreversibility of heat exchanger. And comparison with low-finned spiral baffle plate oil cooler and arched smooth tube oil cooler,its heat transfer is on average improved by 82% and 175%, at the same time, the shell-side pressure drop is on average increased by 26% and 77%.(3) The inlet temperature of cooling water can influence the heat transfer to a larger content and has little impact of the flow resistance. Experiment tests find a 500-950 W increase in heat transfer for every 2°C decrease in the inlet temperature of cooling water. And the inlet flow of cooling water has little influence on heat transfer and flow resistance characteristics.(4) The heat transfer enhancement mechanism of oil cooler with dimpled fins analysis show that when the hydraulic oil flow through dimpled fin, it will appear flow separation at the leading edge of dimple, form longitudinal vortex in the depths of the dimple, and then pour out of the dimple with high speed after it attachs again at the ending edge of dimple. Then the thickness of the flow boundary layer will be thinned and the heat transfer performance of the downstream will be intensified. At the same time, back-flow region will be formed in the leeward side of convex surface, and vortex of symmetry about center will be developed in the rear of it.In conclusion, above phenomena will enhance the disturbing extent of the fluid.(5) The comparative analysis of oil cooler with dimpled fins and oil cooler with flat fins about heat transfer and resistance performance show that the heat transfer of the dimpled fins promotes 26.6%-31%, the resistance factor only increases 10.3%-17.2%, the comprehensive heat transfer performance rises 20%-25% under the same pump power. The analysis of field synergy indicates that the dimpled fins can improve the synergy degree of temperature and velocity field effectively. In addition, the influence of geometric parameters on the comprehensive heat transfer performance is discussed, such as the height, the radius, and the longitudinal spacing of the dimpled fins. The results of single factor analysis show that the dimpled fins have better comprehensive heat transfer performance when the height is 0.9mm, the radius is 1.7mm, and the longitudinal spacing is 7.2mm.