Development And Application Of A High Temperature Thermal Conductivity Measuring Instrument Based On The Guarded Hot Plate Method

With the development of the industry and consumption of resources, the world isfacing more and more serious energy crisis. Nowadays，energy conservationand emissions reduction have become a world-wide concern in thedevelopment of the economy, science and society. One of the effective ways ofenergy saving and emission reduction is to use and to develop moreenergy-saving materials. Thermal conductivity is one of the main parametersof thermal properties of materials. Accurate assessment of thermalconductivity is of great significance for the development and production ofenergy-saving insulation materials. The guarded hot plate method is aninternational standard method and has high accuracy, good repeatability, widetemperature range and thermal conductivity range, etc. At present, most of thethermal conductivity measuring apparatuses are designed forroom-temperature test. As the demand of the high temperature insulationmaterial become increasingly significant, it is necessary to know the thermalconductivity of the insulation materials at high temperature ranges. Therefore,the development of high temperature thermal conductivity measuringapparatus is of great significance for the development and application ofthermal insulation material.This thesis aims to development a new high temperature thermalconductivity measuring instrument based on the guarded hot plate method.The instrument consists of single-plate device and intelligent control module,and can realize the measurement of thermal insulation material in hightemperature stage, measuring range from100℃to800℃. The instrument iscontrolled by a computer, and has the advantages of automation, easyoperation, and short measure time.The main contents of this thesis are:1. The basic theory of heat transfer and various thermal conductivitymeasurement methods and principles were described. With an overview ofhigh temperature thermal conductivity measuring instruments of domestic and abroad, especially the drawbacks and current situation of domestic instrumenthave been described.2. The measurement principle of the guarded hot plate method wasintroduced and the measurement error factors were analyzed. The thermalinsulation structure of the system was improved and the mechanical drawingshave been designed.3. An overall scheme of the instrument has been designed, includingselection and installation of sensors, the signal measurement circuit design,control, the design of control circuit and protection circuit.4. Principle of PID control algorithm was analyzed, and the PID controltechnology was used in the temperature control of the instrument. Themeasurement and control software based on LabVIEW platform has beendesigned, with the flow chart and some key subroutines and algorithms weredescribed.5. Calibration methods of the instrument were established, mainlyincluding temperature sensor calibration, displacement sensor calibration,heating wire resistance correction and coefficient of thermal conductivitycalibration.6. Experiments were conducted to test various aspects of the instrumentperformance. The experimental results showed that the repeatability andaccuracy of the instrument have reached the design objectives in the fulltemperature range.