| There are many applications in aerospace,weaponry,and industrial production where transient high temperature testing is required,such as rocket nozzle jet temperatures,explosive blast temperatures,and aircraft head cone surface temperatures.In these scenarios,a large number of hot components are subjected to high velocity airflow,high pressure,strong vibration,and transient high temperatures,which can easily be damaged.However,common armored thermocouples’ low structural strength and slow response time cannot meet the demand for rapid temperature measurement in hot environments.Therefore,in order to test the surface temperature of hot components in extreme environments there is an urgent need to develop high strength fast response thermocouple probes with high structural strength,shock resistance,and fast response time.In this paper,high structural strength,fast response,and high accuracy thermocouple probes are designed and prepared using thin strips of Ni Cr/Ni Si metal thermocouples of micron thickness as sensitive materials,the details of the paper are as follows:Firstly,the structure of the thermocouple probe was designed.The thermocouple probe consists of a 30 mm × 3 mm × 0.07 mm thin strip of nickel-chromium alloy,a 30 mm ×2.5 mm × 0.07 mm thin strip of nickel-silicon alloy,an alumina insulation layer,a Ni Cr/Ni Si thermocouple wire,a wedge-shaped ceramic piece,a two-hole ceramic tube,and a stainless steel housing.Thin strips of Ni Cr/Ni Si alloy are used as the material for the positive and negative poles of the thermocouple probe respectively.The aluminium oxide insulation layer is deposited on the surface of the thin strip of alloy to act as electrical insulation between the two poles.Thermocouple wires are used as leads to connect the thermocouple probe to the plug.A wedge-shaped ceramic piece serves to hold the alloy strip in place.The two-hole ceramic sleeve ensures electrical insulation between the two thermocouple wires.The stainless steel housing serves as a mounting and support structure for the thermocouple probe.The internal slit of the thermocouple probe is filled with high-temperature insulating rubber.Secondly,the effects of material type,laser energy,and thermocouple probe structure size on the dynamic characteristics of the thermocouple probe were simulated using COMSOL multi-physics field finite element analysis software.The results show that for the same structure size of Ni Cr/Ni Si,WRe5/WRe26,and Pt/Pt Rh thermocouple probes,the response time of Pt/Pt Rh thermocouple is the shortest under the same excitation,which is due to the smaller specific heat capacity of Pt/Pt Rh and the fastest heating rate under the same laser;the laser energy does not affect the dynamic response performance of the thermocouple probe.The pulsed laser energy does not affect the dynamic response performance of the probe.As the thickness of the thin strip increases,the heat capacity increases with the thickness of the strip,resulting in a lower heating rate and a higher response time for the thermocouple under the same excitation.Thirdly,using reactive magnetron sputtering and atomic layer deposition techniques,an alumina insulation layer with a thickness of approximately 700 nm was deposited on the surface of the Ni Cr/Ni Si alloy strip.The two alloy strips were joined to each other by spot welding with thermocouple wires of the same composition.The insulating side of the two strips is overlapped and the two strips are clamped with wedges of ceramic and inserted into the front of the stainless steel housing in a tight fit.The gap between the two wedge-shaped ceramic sheets is filled with high temperature insulating adhesive and cured at room temperature for 24 h,then at 80 °C and 150 °C for 2 h.The thermocouple wire is passed through the double-hole ceramic sleeve and the metal housing is then welded to the front and back of the thermocouple probe.The Ni Cr/Ni Si thermocouple wires were connected to the two poles of the plug to prepare the thermocouple probe samples.The hot junction of the thermocouple was polished to create a weak connection conduction between the thin strips of Ni Cr/Ni Si alloy.Finally,the performance of the prepared thermocouple probe samples was calibrated.The results show that the average Seebeck coefficient of the thermocouple probe reaches about 42 μV/°C in the test temperature range,which is close to that of a standard K-type thermocouple,with good linearity between the output thermopotential and the temperature change,and good stability,with the upper limit of temperature measurement reaching 1200 °C.The average response time of the thermocouple probe is about 0.265 ms and has good repeatability. |
