The Heat Pipe Exchanger's Conceptual Research Of Using The High Pressure Gas To Heat The High Pressure Pure Air

The supersonic air tunnel ground-testing system for ramjet needs high temperature and high pressure air supply to simulate the real air current. A heat-pipe heat exchanger scheme that uses high temperature and high pressure gas to heat the high pressure air is studied in this paper.The computation model of heat pipe is built for a high temperature and high pressure heat exchanger. The heat-transfer characteristics of circular heat pipe, elliptical heat pipe and finned heat pipe are calculated and analyzed with the mean temperature difference method. Comparing the three heat pipes, the conclusions are as follows: the heat transfer characteristics of elliptical heat pipe in duct is better than that of the circular heat pipe, and the mean heat transfer coefficient of the ellipse heat pipe is about 20% higher than that of the circular heat pipe in the same air current velocity. Under the same resistance, increasing the velocity of secondary air current can enhance the heat-transfer effect of the elliptical heat pipe.Design scheme of heat-pipe heat exchanger for ground-testing system is put forward. Design values of ellipse heat pipe and circular heat pipe are selected for the case of 2.5MPa pressure and 300K～1020K temperature. The strength calculation of the two pipes is carried out with FEM software Patran/Nastran, and the structural parameters of each heat pipe are modified and confirmed. The structural reliability of heat pipe is analyzed. With the mean temperature difference method, the mean heat-transfer coefficients under different working conditions are calculated. Comparing the heat transfer performance of the two pipes in high temperature and high pressure, the merit which the ellipse pipe is selected as the heat-transfer element is analysed.Basing on the demand of the ground-testing system, specific schemes of the two heat-pipe heat exchangers are designed. The amount and length of heat pipe in different temperature areas of the heat exchanger are determined with the mean temperature difference method. The suitable thickness of barrel wall is chosen through mechanical analyses. According to the working characteristics of gas generator, the heat exchanger requires an expanding head and a contracting-expanding nozzle. By Patran/Nastran, the strength of each parts of the exchanger is checked, the design parameters are modified, and the major structure is confirmed. The heat-transfer capability of the exchanger is checked by validity-number of heat transfer units method. Analyse the feasibility of the exchanger. Comparing the two heat-exchanger schemes, the one of horizontally flowing through heat pipes is chosen as the air supply scheme for the ground-testing system.