Study On The Performance Of Helical Tube Heat Exchanger For Engine Exhaust Heat Utilization

A large part of the combustion heat of the fuel vehicle engines is discharged with the exhaust gas,which causes a great exhaust.Recycling the exhaust heat of the engine exhaust gas can improve the overall thermal efficiency of the engine,reduce the fuel consumption rate,and it is also an important way to reduce the carbon of the traditional fuel engines.The spiral tube heat exchanger has the advantages of high heat transfer efficiency,compact structure and small volume,which is suitable for heat recovery in the engine exhaust heat recovery system.This paper studies the spiral tube heat exchanger in the engine exhaust heat recovery system,explores the heat transfer performance of different forms of spiral tube heat exchanger,and carries out the intensive heat transfer research of the spiral tube heat exchanger.Based on the requirements of automotive engines,optimizing the enhanced heat transfer spiral tube heat exchanger designed in this article.Firstly,geometric modeling,grid partitioning,and grid independence verification were performed on the spiral tube heat exchanger,and the correctness of the model was verified.A numerical simulation method was used to simulate and analyze a fixed curvature spiral tube heat exchanger with inner baffles,outer baffles,as well as inner and outer baffles.The results show that compared to the situation where separate baffles are installed on the inside or outside of the spiral tube,setting baffles on both sides of the spiral tube can achieve better heat transfer efficiency,among them,heat transfer coefficient of the b heat exchanger is the highest,and the comprehensive performance of a heat exchanger is the best.In addition,the constant curvature of the spiral tube heat exchanger with different diameter guide column on the inside of the spiral tube is analyzed.The results show that with the increasing diameter of the guide column,the comprehensive heat transfer performance of the heat exchanger is first improved and then reduced.When the diameter of the guide column is 40 mm,the comprehensive performance of the heat exchanger is the best.In conclusion,for the constant curvature spiral tube heat exchanger,setting around the fluid on the inside of the spiral tube can better improve the performance of the heat exchanger.Secondly,simulation studies are conducted on the simplest types of variable curvature spiral tubes,namely expanded and contracted,and on the slightly more complex types of variable curvature spiral tube heat exchangers,namely expanded-contracted and contracted-expanded.The results show that the comprehensive heat transfer performance of the expanded spiral tube heat exchanger is superior to that of the contracted type.The expanded-contracted type spiral tube has higher heat transfer performance,while the contracted-expanded type spiral tube has a smaller pressure difference between the inlet and outlet.Furthermore,by adding a conical fluid guide at the inner center of the tail of the contracted-expanded type spiral tube,a heat transfer enhancement study is conducted on the contracted-expanded type spiral tube heat exchanger.The results show that adding a fluid guide cannot effectively enhance its comprehensive heat transfer performance.In addition,spindle shaped fluid guides of different lengths are installed in the inner center of the expanded-contracted spiral tube for simulation.The results show that as the length of the guide body increases,the pressure difference between the inlet and outlet of the heat exchanger gradually decreases and the heat transfer coefficient gradually increases.When the length of the conductive fluid is 240 mm,the pressure difference between the inlet and outlet of the heat exchanger is low,the surface heat transfer coefficient is high,and the PEC value is the highest,resulting in the best comprehensive heat transfer performance.In summary,for variable curvature spiral tube heat exchangers,the expanded-contracted type spiral tube has great heat transfer performance,and adding a spindle shaped guide fluid inside it can effectively improve heat transfer performance.The contracted-expanded type spiral tube has the smallest inlet and outlet pressure difference,but adding a guide fluid is difficult to improve heat transfer performance.Finally,analyzing the requirements of vehicle engines for heat exchangers in exhaust heat recovery systems.Based on the aforementioned research,a double expanded-contracted spiral tube heat exchanger is designed and its heat transfer performance is studied through numerical simulation.Based on the requirements of automotive engines,the effect of reducing the shell diameter of the heat exchanger on heat transfer performance is studied to explore its applicability in automotive engines.The results show that the double expanded-contracted spiral tube heat exchanger designed in this article has better heat transfer performance.Compared with the originally designed 300 mm shell diameter heat exchanger,the heat transfer performance is better when the shell diameter is reduced to 280 mm.This not only improves the comprehensive heat transfer performance of the heat exchanger,but also reduces the volume of the heat exchange system and makes it more suitable for the automotive engine field.