Modeling Heat Flow in Measuring Cell of Differential Scanning Calorimeter as a Control Object with Distributed Parameters

摘要

Modern differential scanning calorimeter (DSC) is a complex information-measuring system used to obtain different temperature and thermal characteristics of the investigated substances. The main subsystem of DSC is a heat block including heaters, measuring cells, and heat conducting elements. Measuring cells in the thermal block are often located symmetrically in relation to the center. However, the heat flow coming from the main heater affects them unevenly. At different overall parameters of reference and test substances uneven cells heating leads to measurement error increase. Since the defining of thermal characteristics of materials using DSC is carried out in a dynamic mode it is necessary to take into account not only the dependence of measuring cell parameters on time, but also the spatial distribution of the external thermal impact affecting it. Measuring cell DSC mathematical model is given as a block with a distributed input and concentrated output effect. The model takes into account the uneven spatial distribution of the thermal field in the thermal block, as well as heat removal from the substrate through the sensing elements considered to be inertial links. A structural model of the heat flow control system in a heat block DSC was constructed on the basis of the measurement cell mathematical model. The model shows the following: basic elements and their relationships, radiation influence on heat flow formation reaching the measuring cell and additional heat formation from micro aggregates, its influence on the measuring cell. After a number of experiments, a computer model of the automatic heat flow control system in the measuring cell of the differential scanning calorimeter DSC-500 was built as a control object with distributed parameters. This model serves as the basis for numerical experiments required to adjust the regulators parameters of the main and additional heaters in the thermal block of the DSC at different modes of this information-measuring system.