Research On Measurement Technology Of Thermal Parameters Of Plate Specimen Under Heat Loss

Thermal parameters such as thermal conductivity,heat transfer coefficient and boundary shape play an important role in aerospace thermal protection,engine heat dissipation and nuclear power plant safety.Its accurate measurement is of great significance to the safe operation and thermal protection design.However,due to the poor working conditions or space,it cannot be obtained directly by measurement.The heat conduction inverse problem method provides an effective way to measure such parameters.The measurement of thermal parameters has a great influence on the heat loss,so the research on the measurement technology to improve the measurement accuracy of thermal parameters under the condition of heat loss has very important scientific value and practical significance.It is easier to measure the temperature in the heat exchange or heat transfer equipment.It is an indirect measurement technology to identify the thermal parameters based on the temperature information of the measuri ng points at a certain moment or period of time.This technology has no special requirements for the target,has wide application fields,and is easy to operate.It is especially suitable for the measurement of thermal parameters of equipment with limited space,complex structure or working conditions.In this paper,the indirect measurement technology based on temperature is used to solve the thermal conductivity,heat transfer coefficient and unknown boundary shape.The purpose is to explore the construction of thermal conductivity measurement model based on the second kind of boundary conditions with heat loss,and solve the problem of large error in the traditional model based on the measured data;to study the construction of thermal conductivity measurement model based on the third kind of boundary conditions with heat loss In order to solve the problem that the temperature difference is too large when using the results of traditional model to construct the temperature field,a new algorithm of boundary shape inversion measurement is studied to solve the problem that the inversion results of current traditional algorithm are easily affected by the initial value and the number of measurement points.The inversion device of thermal conductivity and heat transfer coefficient is developed to solve the problem of lack of experimental verification.Based on the above purpose,this paper studies the measurement technology of thermal conductivity,heat transfer coefficient and boundary shapeIn order to solve the problem of large error in traditional thermal conductivity measurement model based on measured temperature,a thermal conductivity measurement model based on the second kind of boundary conditions under heat loss,virtual thin plate,is constructed.The problem of large error caused by the lack of estimation of heat loss term in traditional models is summarized.Considering the heat loss,the relationship between the heat loss and the temperature field of the model is studied by derivation,and the realization method of the thermal conductivity measurement model with loss is proposed.The simulation results show that,compared with the traditional model,the inversion results of the virtual thin plate are not affected by the heat loss,and the measurement a ccuracy is improved.In order to solve the problem of large temperature deviation in the construction of temperature field by using the traditional heat transfer coefficient measurement method in engineering application,a local heat transfer coefficient m easurement model based on the third kind of boundary conditions with heat loss is constructed.According to the location of heat loss in engineering problems,the influence of heat loss on measurement model is deduced,and the relationship between heat los s and temperature of measurement point is constructed,which realizes the inclusion of heat loss in measurement solution.The simulation results with loss show that the local model overcomes the influence of heat loss of traditional model,and reduces the relative error of measurement value from-7.12% to less than 0.5%.In view of the fact that the accuracy of traditional optimization algorithms is easily affected by the number of measuring points,a new boundary shape inversion algorithm based on the third kind of boundary conditions is proposed.The inherent law between the temperature of the measuring point and the position of the boundary to be solved is studied,and the algorithm solving model between the temperature of the measuring point and the position of the boundary is established.The algorithm avoids the gradient solving step of the objective function,and provides a new idea for solving the shape of the boundary.The simulation results show that,compared with the mainstream conjugate gradient method,the new algorithm reduces the average relative error of inversion results from 20.1% to 1.6%when the number of measurement points is less,and improves the accuracy of inversion measurement when the number of measurement points is less.In order to solve the problem of lack of engineering verification in thermal conductivity measurement,an experimental device for thermal conductivity measurement based on the second boundary condition is developed.According to the requirements of the actual solution,the temperature control system,mechanical system and application program of the experimental device are designed.Compared with the traditional inversion model,the new model reduces the relative error from-14.76% to-4.67%.In order to solve the problem that the inverse measurement of heat transfer coefficient is lack of engineering verification,an unsteady heat transfer coefficient experimental device based on the third kind of boundary conditions is developed.The heating system,thermal protection device,mechanical system and application program are designed.The experimental results show that compared with the traditional model,the local model reduces the deviation between the measured temperature field and the actual temperature from-0.30 ? to ±0.02?.