Dynamic characterization of a slug calorimeter via transfer function modeling

In order to quantify the dynamic characteristics of the slug calorimeter, based on the linear time-invariant system theory, the heat conduction process and temperature measurement subsystem of the sensitive element are modeled, respectively, and the dynamic response characteristics of the calorimeter are characterized by the frequency characteristics of the transfer function. The heat conduction differential equation of the sensitive element under the input of step heat flux density is established, and the analytical solution of the time domain response of the rear wall temperature is derived. Then, the transfer function between heat flux input and rear wall temperature output is obtained by using the unit impulse response method. On this basis, the transfer function of the complete measurement system is constructed by connecting the transfer functions of the temperature measurement system in series. A prototype calorimeter is developed, and the sensitivity calibration experiment is completed on the laser heat flux calibration system, which verifies the correctness of theoretical analysis. The research results show that the passband width of the sensitive element is proportional to the thermal conductivity of the material and inversely proportional to the square of the thickness. The dynamic characteristics of the temperature measurement system have a significant impact on the overall frequency response. This study provides a theoretical basis for the optimal design of heat capacity calorimeter with high dynamic response.