Design And Development Of A New Type Tube For Shell-and-tube EGR Cooler

Plate-fin type heat exchangers are widely used for exhaust gas recirculation(EGR)system due to its good heat transfer performance.However,with the increased thermal load,there are some problems of the plate-fin structure,such as the gas fins crack and drop after being sensitized at high temperature,and other failures caused by the insuffient brazing between tubes and fins.Shell-and-tube heat exhangers will not appeare issues mentioned above because there is no fins inserted in the tube,and it also has the advantages of low weight and low fouling risk,thus it has great application prospects.However,shell-and-tube heat exchangers are seldom used in EGR system for vehicle,because of its poor heat exchange ability.In this case,it needs to be enhanced and the purpose of this paper is to make the heat transfer performance of shell-and-tube heat exchangers close to plate-fin type EGR coolers.In this paper,based on the geometric boundary and heat transfer performance of plate-fin EGR cooler which used for 13 L engine meeting China 6 emissions standards,and the literature review and field synergy principle,in view of the operation characteristics of EGR cooler,a shell-and-tube structure proposal based on discrete double-inclined ribs tube with small diameter is proposed,and a new tube is developed.Firstly,confirme the structure of shell-and-tube heat exchanger and the design value of tube based on the dimension and performance of plate-fin type EGR cooler.Then,choose the inclined ribs as the characteristics of tube based on field synergy principle.Next,analysis the reason of heat transfer enhancement of inner-ribs tube by the numerical calculation.Moreover,the monofactor analysis of the sructure of inner-ribs tube is carried out and this work provide the reference basis for the confirmation of the response factors and factor levels which used for multi-objective optimization of inner-ribs tube in Chapter 4.Meanwhile,the field synergy angle is calculated.Then,according to the development process which includes desigin of experiment(DOE),numerical calculation and multi-objective genetic algorithm,confirm the machining dimension of inner-ribs tube based on the result of multi-objective optimization.Finally,produce a sample and do the performance test.The main conclusions are as follows:(1)In the tube with small diameter,the inclined ribs can also induce multi-longitudinal vortexes,which make the temperature field and velocity field of the fluid more cooperative,thus enhancing the heat transfer in the tube.(2)The results of monofactor analysis show that,in the scope of the study,the influence of geometric parameters on the heat transfer performance of fluid is in the order of rib depth,rib quantity,rib angle,rib distance,rib axial length and rib width.The Nusselt number and friction factor are positively correlated with rib depth,rib quantity,rib angle,rib axial length and rib width,and inversely correlated with rib distance.The performance evaluation criteria(PEC)are positively correlated with rib depth,rib quantity and rib axial length,and inversely correlated with rib distance and rib width.Moreover,there is an inflection point on the curve of PEC with rib angle,and the angle of inflection point decreases with the increase of Reynolds number.In addition,the changing trend of Nusselt number and synergy angle accords with the field synergy principle.(3)Compared with the plate-fin type EGR cooler as the baseline,the gas outlet temperature of the shell-and-tube EGR cooler is 2-4℃ lower,which reachs the expected target;meanwhile,the total weight is reduced by 15%.