Research On The Combined Cooling Method Of Super High Speed Optical Head Cover

In the development of hypersonic vehicle,the thermal protection of structures which directly exposed to high heat flux is a challenging problem.In particular,the head position of the aircraft is the position facing the high-temperature and high-speed flow and the maximum heat flow.It needs reliable cooling system to cool it.The head is generally resistant to high heat flow with ablative materials.Few suitable cooling methods are applied to the head.Although a lot of experiments have been carried out on the transpiration cooling scheme of the head made of porous materials,it is almost difficult to be used in the head of high-speed aircraft.In this paper,a new type of head cooling system for high-speed aircraft is proposed.The heat transfer inner channel model of the ball head is designed by using superalloy steel,and the performance of the cooling system is experimented on a test bench.Firstly,the common cooling methods used in high-speed flight are introduced in detail,and the newer one is transpiration cooling.Many people begin to study phase change in transpiration cooling.Its cooling effect is better.A model of heat transfer channel of ball head is designed.The equipment used in the experiment and the test system of pressure sensor,temperature sensor,schlieren and infrared camera are introduced.A set of cooling system experiment platform is built by using liquid nitrogen tank,various pipelines and models.The schlieren test system was introduced.The errors of various test systems and the correctness of the experiment were analyzed.Then through the data of temperature sensor and pressure sensor of liquid nitrogen flowing through the inlet and outlet of the ball head heat exchange channel,combined with the images of the visualized glass tube under different experimental conditions,the vaporization effect of different heating gear and different liquid nitrogen supply pressure conditions is obtained.It is found that under these experimental conditions,liquid nitrogen can completely vaporize through the heat exchange channel,and the infrared characteristics of the ball part heating and liquid nitrogen injection process are photographed by the infrared camera to verify the safety of the cooling scheme carried on the weapon.The results show that in the heating process,the brightness of the surface of the ball head will increase with the increase of temperature,but when liquid nitrogen is injected,the ball head will immediately darken.As liquid nitrogen is continuously injected,the ball head will gradually darken from the stagnation point upward,which is the temperature drop caused by liquid nitrogen injection.Furthermore,the pressure and temperature of heated liquid nitrogen under different experimental conditions were studied.It is found that liquid nitrogen can completely vaporize under the existing experimental conditions,and the total temperature of vaporized nitrogen is above 140 K,which can be used as the supply gas for jet cooling,and also make the imaging guidance missile carry small liquid nitrogen bottles to realize the cooling of the ball head and optical window.However,when the external heating heat flow is constant,with the increase of liquid nitrogen supply pressure,at a certain liquid nitrogen pressure value,liquid nitrogen flowing through the heated head will not be completely vaporized.Finally,the thermal resistance of the spherical head heat exchanger is analyzed,which shows that its heat dissipation performance is very good.At the same time,the convective heat transfer coefficients of liquid nitrogen under different experimental conditions are obtained,and the effects of different liquid nitrogen supply pressure and different heating heat flow on the convective heat transfer coefficients are studied.It is found that the liquid nitrogen heat transfer coefficients increase with the increase of liquid nitrogen supply pressure and the heating heat flow density of the outer wall.At the same time,the cooling effect under different experimental conditions is analyzed.It is considered that only when the coolant supply pressure rises to the rated pressure in a short period of time can the cooling effect be better,and at the same time,the coolant supply pressure should be stable as much as possible.When the external heat flow is constant,the cooling effect becomes better with the increase of pressure.In the case of high heat flow,the cooling effect is more violent with the decrease of coolant pressure than in the case of low heat load,and the higher the heat flow is,the better the cooling effect is generally when the maximum pressure of liquid nitrogen supply is the same.