| Nowadays,society of China and economy are developing rapidly,and the industrial development is especially rapid,and the demand for energy has also increased greatly.With this,the shortage of non-renewable resources and environmental pollution have become increasingly serious.The state has adopted a series of measures and local regulations to improve engine exhaust emission standards,and engine emission performance has become an important indicator in automobile design.The temperature of the pressurized air rises sharply,and the combustion of high-temperature gas reduces the output power of the engine,which affects the efficiency of the engine.In severe cases,knocking may occur.In addition,experiments have shown that the higher the intake air temperature,the higher the NOx content in the exhaust.Therefore,the research on intercooler has important practical significance.Based on the structure improvement of the Z170 high-speed marine diesel engine intercooler produced by Zichai Machinery Co.,Ltd.,the structure of the intercooler with better performance and suitable for the Z160 diesel engine is designed.Firstly,the prototype is appropriately simplified,the heat dissipation unit model is established,and the results are analyzed.The changes in the temperature field,pressure field,and speed field inside the heat dissipation unit under the engine’s full load conditions and the changes in each of the five operating conditions are compared.The temperature difference and pressure drop between the inlet and outlet of the unit,the change of the Nusselt number at different air inlet speeds,the heat transfer factor j,the friction factor f,and the comprehensive performance factor j/f are calculated.The specific conclusions are as follows:First,analyze the heat transfer performance of the cooling unit.Cooling tubes of different structures will affect the heat transfer performance of the cooling unit.In the study of the cross-sectional shape of the cooling tube,it is found that the heat transfer performance of the square tube is good,and then the round tube and the ellipse are in turn.Compared with round tubes,the Nusselt number of square tubes is increased by 1.5% on average,and the j factor is increased by 1.83% on average;the larger the tube longitudinal distance,the Nu and j factors of the heat dissipation unit will gradually decrease,when the tube longitudinal distance is 25 mm,compared with the original heat dissipation unit,Nu is increased by 2.26% on average,and the j factor is increased by 4.38%.Through the study of the fin structure,it is found that as the thickness of the fin increases,the heat transfer performance of the heat dissipation unit is better.When the thickness of the fin is 3mm,the Nusselt number and heat transfer factor f are respectively improved on average compared with the original heat dissipation unit.7.92%,and7.84%;the heat transfer performance of the heat sink unit increases with the increase of the fin height.When the fin height is 21 mm,compared with the original heat sink unit,Nu is increased by an average of 6.57% and j increased by an average of 7.4%;As the fin spacing increases,the heat transfer performance gradually becomes weaker.When the fin spacing is 10 mm,the Nusselt number increases by 2.31% on average,and the heat transfer factor increases by 3.66%on average.Secondly,the flow characteristics of the heat dissipation unit are analyzed.Because the elliptical tube has small resistance to the supercharged air and good flow performance,the f factor is reduced by 0.09 on average compared with the round tube;the pressure drop is reduced by 2.4k Pa on average;the greater the tube longitudinal distance,The thermal fluid flow space of the heat dissipation unit is larger,and the flow performance is better.When the tube longitudinal distance is 35 mm,the f factor is reduced by 7.64% on average,and the ΔP is reduced by 5.1% on average.For the fin structure,the greater the thickness and height of the fin and the smaller the fin spacing,the greater the retarding and disturbing effect on the thermal fluid,and the worse the flow characteristics.When the fin thickness is 1.8mm,compared with the original model The f factor is reduced by 7.25% on average,and the ΔP is reduced by1.7k Pa on average;when the fin height is 12 mm,the friction factor is reduced by 8.1% on average,and the pressure drop is reduced by 2.27 k Pa on average.Compared with the model,the f factor is reduced by 8.54% on average,and the inlet and outlet pressure drops are reduced by 2.47 k Pa on average.Finally,the comprehensive performance of the heat dissipation unit is analyzed,and the ratio of the heat transfer factor j to the resistance factor f is obtained to obtain the comprehensive performance factor j/f under each working condition of the heat dissipation unit.Finally,it is found that the longitudinal distance of the tube is 25 mm and the rear of the fin is1.8mm.Because the elliptical tube has small resistance to the supercharged air and good flow performance,the f factor is reduced by 0.09 on average compared with the round tube.The overall performance is optimal when the height is 18 mm and the spacing is 14 mm.For the cooling tube structure,the overall performance factor of the oval tube is increased by 0.139,and the outlet temperature is reduced by 7.5K;when the tube longitudinal distance is 25 mm,the overall performance is increased by 0.142,and the outlet temperature is reduced by 7.7K.For the fin structure,when the fin thickness is 1.8mm,j/f is increased by 0.145,and the outlet temperature is reduced by 9.1K;when the fin height is 18 mm,j/f is increased by 0.22,and the outlet temperature is reduced by 11.4K;the fin spacing is 14 mm When j/f increased by 0.254,the outlet temperature decreased by 12.6K.The comprehensive performance of the improved cooling unit is 33.8% higher than that of the original model,and the outlet temperature is reduced by 3.2K on average under five working conditions. |
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