查看更多>>摘要：As an important component of the hypersonic combined precooling cycle aero-engine, the precooler utilizes the ultralow temperature coolant to precooling the incoming air, so that the temperature of the freestream can be significantly reduced, and the mass flow rate of the airflow can be obviously increased. However, during the process of the precooling of the freestream, the frost layer condenses on the outside of the precooler and then results in the blockage of the flow channel. Therefore, the performance of the aero-engine gradually deteriorates. In order to maintain the performance of the aero-engine, the precooler should be defrosted. In addition, during the process of the actual operation, the precooler experiences different freestream humidity environments. Therefore, it is necessary to conduct the frosting and defrosting experimental investigations on the microtubule precooler under different humidity conditions, as well as analyze the influences of the freestream humidity value on the frosting and defrosting characteristics of the microtubule precooler from the perspectives of qualitative and quantitative. Under the conditions of the flow velocity and the temperature of the mainstream are 10 m/s and 50 °C, respectively, the frosting and defrosting experiments of the microtubule precooler are conducted with two different airflow humidity (1.8 g/kg and 6.4 g/kg). As the organic solvent, the anhydrous methanol is utilized for the defrosting experimental conditions, and the mass ratio of anhydrous methanol ranges from 0.75 to 1.25. The influences of the airflow humidity on the frosting and defrosting performances of the microtubule precooler are experimentally studied. The experimental results manifest that the heat transfer rate of the precooler is actually the results of the combined action and the compromise between the wall surface temperature of the precooler tube bundles and the coverage area of the condensation. Under the frosting experimental conditions, the coverage area of the frost layer increases with the increase of the airflow humidity. However, the growth rate of the frost layer coverage area is not proportional to the growth rate of the airflow humidity. In addition, for the frosting experiments, the higher the airflow humidity value, the lower the wall surface temperature, the lower the heat transfer rate, and the greater the growth rate of the pressure loss coefficient. However, for the defrosting experimental conditions, the pressure loss coefficients obviously decrease; and the heat transfer rates gradually tend to stabilization. In the defrosting experimental conditions, the coverage area of the condensation and the pressure loss coefficients do not increase with the increase of main flow humidity, it indicates that the defrosting performance only relates to the mass ratio of anhydrous methanol. The frosting and defrosting experimental results further indicate that increasing the freestream humidity leads to the heat transfer rate of the precooler decreases. Finally, the optimal mass ratio of anhydrous methanol that to achieve the best defrosting performance should be between 1.0 and 1.2.
NSTL
Elsevier