Complex Turbulent Flow And Heat Transfer Characteristics Of Spiral Finned EGR Cooler

Exhaust gas recirculation (EGR) is the main method for reducing emissions of NOx and fine particulate matters in auto exhaust. With the environmental problems caused by exhaust gas turning increasingly serious, regulations for vehicle emission are becoming more and more stringent, which also putting higher requests forward the heat transfer capability of EGR cooler.This article detailed the basic design and calculation methods of EGR cooler as well as basic calculation principles including mean temperature difference, the temperature of the heat transfer interface and heat transfer coefficient. Also, the way to arrange and fix the heat exchange tubes on EGR cooler, the center distance of tubes and the principles of enhanced heat transfer technology were discussed. Based on the basic principles above, the effects of the width, length and screw pitch of the spiral fins on fluid heat transfer performance were analyzed through numerical simulation method. And three different groups of EGR coolers with different spiral fin widths, screw pitches and lengths were designed. To help the analysis, three dimensionless quantities, ε_Dh, ε_Lf and ε_Lp, which representing spiral fin width, length and screw pitch, were introduced for qualitative and quantitative analysis. The study of spiral fin shows that with one more screw pitch added in the same length, the pressure drop increases by 7% to 10%; When the fin length increases a half pitch, the outlet temperature declines by 6.2%; And the bigger ε_Lf is, the slower the speed of thermal property increases; ε_Dh affects little toward hydrodynamic and thermal properties, which change less than by 2% when ε_Dh changes by 1/35. In order to solve the problem that FLUENT calculation method is relatively cumbersome and time-consuming, a new calculation program for fluid thermal performance of spiral groove tube EGR cooler was designed and the calculation results were compared with FLUENT calculation to verify the reliability of the designed calculation program. Combined with genetic algorithm, the best match of four spiral fin parameters, the diameter, the center distance, the number and the thermal transfer acreage of spiral groove tube in EGR cooler, is obtained, which has important reference significance for designing spiral groove tube EGR cooler.Based on the studies above, the optimum structure of spiral finned groove tube was put forward and a comparative analysis was made among four kind of EGR coolers, which separately installed light tubes, spiral groove tubes, spiral finned light tubes and spiral finned groove tubes. Compared with the EGR cooler with spiral groove tube, the pressure drop of EGR cooler with spiral finned groove tube falls by 20%, and the outlet temperature on the tube side drops about 8 ℃, which successfully evades the drawback of enhancing heat transfer performance at the expense of hydrodynamic performance in spiral groove tube EGR cooler.