Research On Measurement Method Of Solid Thermal Conductivity Induced By Dual Wavelength Laser

Thermal conductivity is an important thermophysical parameter to characterize the thermal conductivity of materials.In the fields of metrology,advanced industries and new energy,In the fields of metrology,advanced industry and new energy,it is increasingly important to measure the thermal conductivity of materials at high temperatures in an isotropic,in situ and non-invasive manner.Therefore,this paper investigates the method of measuring the thermal conductivity of solids by dual wavelength laser induction.The measurement of the thermal conductivity of a target in an same direction,in-situ,nonintrusive manner in the target temperature field is achieved.The main work and results are as follows:1.A measurement model for dual wavelength laser induced in situ measurement of thermal conductivity of solids was developed.(1)Based on the principle of inverse sequence wavelength detection of photothermal effect of dual-wavelength infrared laser,the theoretical model of measuring solid thermal conductivity by dual wavelength infrared laser is carried out;(2)On the basis of the traditional effective wavelength theory,the theoretical model of the first-order effective wavelength is proposed;(3)The factors influencing the correction factor in the theoretical model were analyzed.The results show that when the temperature difference between the two samples varies within1 K,the correction factor varies by about 2%;2.An experimental system for dual wavelength laser induced measurement of thermal conductivity of solids was designed and built.(1)A dual wavelength laser induced thermal conductivity measurement system is designed and built.The thermal conductivity of different materials can be measured in the same direction in the temperature range(873.15 ～ 1173.15)K;(2)The experimental system consists of sample heating module,laser light source module,photoelectric detection and signal acquisition module.(3)The wavelength range of the laser source is selected to be in the near infrared band.two filter radiometers corresponding to the laser wavelength were designed.A single channel alternating shutter method is used to shield the reflected laser radiation,and a low noise amplifier is used to amplify the weak AC radiation temperature rise signal.3.Research on the characteristics of the temperature field distribution of the target to be measured.(1)For the acquisition of the surface temperature of the samples used in the experimental system,Fluent was used to simulate and experimentally validate the temperature fields of high-temperature alloys,low-emissivity coated samples and Si C samples,respectively.The reliability of simulation is verified;(2)The internal temperature fields of the three different samples are approximately onedimensional steady state temperature conductivity,with the temperature distribution showing an approximately centrosymmetric distribution;The temperature field on the front surface has an approximately centrosymmetric distribution,with low temperatures at the centre and high temperatures at the edges,and a tendency for the temperature to rise rapidly from the centre to the edges,followed by a slow rise in the radius direction;(3)The temperature uniformity of the front surface of the sample was analysed over the range of the laser spot used in the experiment.The results show that the samples were at a temperature of 1173.15 K.The relative standard deviations of the temperature at each point on the surfaces of the high-temperature alloy,low-hair coating samples and Si C samples were0.06%,0.04% and 0.03%,respectively,within the range of the laser spot used for the experiments,with good temperature uniformity.4.Experimental study of dual wavelength laser induced measurement of thermal conductivity of solids.(1)Stability analysis of an experimental system for measuring the thermal conductivity of solids with dual wavelength laser.The results show that the experimental system built for dual wavelength laser induced measurement of thermal conductivity of high temperature solids is stable within 10% over the temperature range(873.15 to 1173.15)K;(2)The effect of the temperature difference between the surface of the reference sample and the sample to be measured on the measurement results was analysed.The results show that when the temperature difference between the two samples is within 2K,the effect of whether or not to consider the temperature difference on the measurement results is within approximately 4%.Even small differences in temperature between the two samples can have a significant effect on the results of the measurement;(3)Thermal conductivity measurements were carried out at(873.15～1173.15)K on different materials(high temperature alloys,silicon samples,304 stainless steel).The relative deviations from the reference values were less than 24%,22% and 24% respectively.This is comparable to the current international measurement level of 25% at the National Physical Laboratory.5.Assessment of measurement uncertainty.(1)The uncertainty of the thermal conductivity measurement results in the temperature range(873.15 to 1173.15)K was evaluated for the selected high temperature alloy samples.The results show that the standard uncertainty is better than 17%.The results show that the dual wavelength laser technique for measuring the thermal conductivity of solids studied in this paper can achieve thermal conductivity measurements of high-temperature materials,and has the unique advantage of same direction,in-situ,noninvasive measurements.