Measurement Of Specific Heat Of Thermal Insulation Materials And Analysis Of Influencing Factors

As a kind of material with low density and low leading coefficient,thermal insulation material plays an important role in aerospace,thermal equipment and construction.In order to better understand the thermal properties of thermal insulation materials,it is essential to study their thermal properties.As a basic physical property parameter to characterize the heat absorption capacity of materials,specific heat is very important for the study of the performance of thermal insulation materials,and it can also provide a basis for the measurement of other physical properties.Differential scanning calorimetry(DSC)is a widely used method to measure specific heat due to its advantages of less consumption,short measurement time and convenient operation.Therefore,this paper focuses on the measurement of specific heat of thermal insulation materials by differential scanning calorimetry,carries out the experimental measurement and numerical simulation work,and studies the influence of different factors on the comparative heat measurement results.In the experiment,the DSC 404F3 instrument was used to calibrate the instrument after temperature correction and sensitivity correction.Based on the basic principle of DSC specific heat measurement,the specific heat tests of two kinds of insulation materials,silica aerogels and heat insulation cotton felt,were carried out,and the measurement results were analyzed.The results show that the repeatability of specific heat measurement of thermal insulation materials is very poor.In order to study the cause of this problem,the baseline and sample heat flow curve were measured for many times.It was found that the sensitivity of DSC is very high,but the amount of sample is very small.Therefore,the baseline may have uncontrollable difference when the sample is put back after each sample crucible is filled,This will lead to significant differences in heat flow curves of samples,resulting in poor repeatability of specific heat measurement.Then,the specific heat of pure copper is measured by DSC.The results show that the instrument has good accuracy at low temperature,and the measurement results become worse with the increase of temperature.According to the structure of the measuring instrument furnace,a three-dimensional model is constructed,and the mathematical model and physical model of the internal heat transfer process are defined.The commercial software FLUENT is used for numerical simulation,and the grid independence is verified.On this basis,the heat transfer process of pure copper and a thermal insulation material under different heating rate,purge gas rate,sample thickness and sample emissivity was simulated.The results show that the thermal lag time of different materials is almost the same,but it changes with the change of heating rate,purge gas rate and sample thickness,which provides the initial temperature at which the effective specific heat value can be obtained.The results show that the heating rate and purge gas rate have almost no effect on the thermal measurement results,and the sample thickness has a certain impact on the specific heat measurement results.However,in the simulation of changing the emissivity of the sample,an important discovery is obtained.The radiation has little effect on the specific heat measurement results of pure copper at low temperature,but with the increase of temperature,the effect of radiation will be more and more obvious.For the heat insulation materials,the effect of radiation will have a very big impact,which makes the specific heat measurement results very unreliable.In this paper,combined with experimental measurement and numerical simulation,the availability of DSC to measure the specific heat of thermal insulation materials is analyzed.It is proved that DSC has good reliability to measure the specific heat of metal materials at low temperature,and the error of measuring the specific heat of thermal insulation materials and metal materials at high temperature is very large.