| Compact air pre-cooler has the advantages of low mass,high heat exchange efficiency,and superior comprehensive heat transfer performances,which shows great potential in the application of combined cycle engines.In order to further explore the heat transfer mechanisms and resistance performances of the special-shaped air precooler,a new type of air precooler is proposed.In the present study,the calculation of pre-cooler structure parameters is carried out.Besides,the pre-cooler design method is elaborated.The structural design and optimization are carried out.Additionally,a pre-cooling test system is built,which is used for air pre-cooling test verification and heat transfer characteristics investigation.Moreover,the thermal-fluid-solid coupling simulation analysis is conducted to analyze the structure of the pre-cooler numerically.The optimized design and its heat transfer performance have been evaluated.In terms of the air precooler design,a highly reliable method for calculating the cross-sectional area of the air flow is proposed,the corresponding error between the calculated result and the actual data is within ±5%.Then,a single-phase design procedure of the air precooler based on Dittus-Boelter formula is proposed.The error between the designed precooler length and the experimental data is within 20%.Furthermore,a phase change-based air pre-cooler design method is proposed.The design method divides the phase change process of the coolant into three processes.The weighted average of the amount of heat exchange gives the average temperature difference between the cold and hot fluids before and after the phase change.This method solves the problem of calculating and solving the average temperature difference in the design process of the air precooler based on phase change.The corresponding relationship between the air outlet temperature and the coolant flow rate under the specified air flow condition is also clarified.Based on the proposed methods,three pre-cooler configurations are designed,i.e.the reference configuration(No.1pre-cooler),the No.2 pre-cooler which is waved in the air channel on the basis of the No.1 pre-cooler,and the No.3 pre-cooler which is on the basis of the No.2 precooler with waved circumferential fins.In the air pre-cooling experimental study,the air pre-cooling test system is designed and built,and the experimental operation procedure is documented.The reliability verification and key parameter error analysis of the test system are carried out,and the shortcomings of the test system are summarized.Using this test system,the impacts of air flow rate on air temperature drop are studied.The influence of air flow temperature on air temperature drop,heat transfer factor,friction factor and comprehensive heat transfer performance is explored.In addition,the influence of the pre-cooler configuration on the air temperature drop,heat transfer coefficient,friction factor and the comprehensive heat transfer performance is analyzed.It is found that,compared with No.1 precooler,the thermal efficiency of the No.2 pre-cooler increases by 49%～56%.The thermal efficiency of the No.3 pre-cooler increases by about60%～66%.However,the No.2 precooler exhibits better comprehensive heat transfer performance.In terms of numerical simulation,the fluid-heat-solid mechanics coupling simulation is conducted in the present study.The temperature distribution,flow field distribution and thermal deformation of the three pre-cooler configurations are quantitatively analyzed.Numerical results show that the No.2 precooler has much outstanding comprehensive heat transfer performances than No.1 and No.3 precoolers.Moreover,the No.2 pre-cooler also avoids the problem of excessive local thermal deformation in terms of thermal deformation of the pre-cooler structure. |
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