Research On Sapphire Ultrasonic Temperature Sensor And Laser Heating Calibration System

The temperature measurement for a long-working time and at the original position may provide references for the improvement of engine design and performance priority.In order to realize the engine measurement in harsh temperature environments,a new temperature sensor with better performance is need to be designed.The appearance of ultrasonic temperature measurement sensor provides a new method for this problem.Sapphire with the characteristics of high melting point and anti-oxidation performance is an excellent heat-resistant material.Moreover,it is necessary to conduct a number of experiments to verify the rationality and reliability of the sensor design.A high power laser provides the possibility of static and dynamic calibration of the temperature sensor.The static and dynamic calibration of the temperature sensor can ensure the accuracy of temperature operation under various harsh conditions.Therefore,this article presents the design and manufacture of a sapphire ultrasonic temperature sensor as well as the construction and experiment of a high power laser heating calibration system.This paper studies the following contents:(1)The design and implementation of the sapphire ultrasonic temperature sensor are as follows.According to the temperature measurement principle of ultrasonic guided wave,the characteristics of the sapphire ultrasonic waveguide were simulated and analyzed.The sensor with a length of 300 mm,a diameter of 0.7mm,a groove diameter of 0.5mm and a sensitive length of 28 mm was designed.The dispersion feature of sapphire ultrasonic waveguide were studied and the L(0,1)was selected as the mode of wave guide.The thermodynamics simulation and the transient dynamics simulation under 20?~1800? of sapphire ultrasonic waveguide were performed.The results showed that the delay time of sapphire ultrasonic waveguide was increased with the increasing of temperature,but the amplitude of signal was constant.(2)The calibration scheme of ultrasonic temperature sensor with the high power semiconductor laser heating technology was researched.The structure of calibration system was designed to meet the requirements of static and dynamic calibration of sensors.According to the basic principle of heat transfer,a model of the soaking block in calibration system was established.The thermal characteristics,temperature distribution characteristics and thermal equilibrium temperature in the process of heating the soaking block had been studied.A thermometer was used to test the temperature of the soaking block which acting as the simulated black body cavity with an emission ratio of 0.99.The COMSOL Multiphysics software was adopted to simulate the heating curve of soaking blocks with cuboid,cylinder and slab shapes.The optimal heating curves from 20? to 2600? of different soaking blocks were obtained.(3)The surface absorptivity of the soaking block is increased by femtosecond laser induction.The micro and nanostructure of metal surfaces were studied regarding the near field of light bondage and field strength increase effects.The absorption of the soaking block was increased to 93%,reducing the requirement of laser power and producing the high temperature environment up to 2600?.The method of Finite Difference Time Domain(FDTD)was used to analyze the causes of increased absorption of the surface microstructure and the improved absorption characteristics of surface micro-nano structure.The absorption efficiency of soaking blocks with the micro-nano structure surface and a polished surface were compared by laser heating.The maximum temperature of the soaking block with micro-nano structure is 88°C higher and 25 s faster than the block with the polished surface.(4)The construction and experiment of ultrasonic temperature sensor calibration system with laser heating were performed.The tungsten-graphite composite structure was prepared to complete the construction of high temperature system and test the system performance.The 2600? temperature condition was obtained.The temperature of soaking block was measured with a thermometer.The result was given to a controller to adjust the temperature in a closedloop feedback way.The thermometer is calibrated with the standard thermometer.The dynamic calibration of sensor was traced to the standard source.The static and dynamic calibration method of temperature sensor were also studied.The sapphire ultrasonic temperature sensor was calibrated from 20? to 1800?,obtaining the static characteristic curve.The time constant of sensor is 2.7s in dynamic calibration.In a simulated aircraft engine system,the temperature of combustion chamber exit has been measured by the sapphire ultrasonic temperature sensor.This result has laid the foundation for the practical application of the ultrasonic temperature sensor.The temperature of a plasma source has been measured with this sensor and the highest measured temperature is up to 1966?.