Development Of A Novel Intelligent Guarded Hot Plate Apparatus For Thermal Conductivity Measurement

The main method to achieve building energy saving is to develop and promote the application of insulation materials.Thermal conductivity is one of the main thermophysical parameters for evaluating the insulation performance of materials,so the accurate measurement of thermal conductivity is very important to continuously promote building energy saving.Guarded hot plate(GHP)is a widely accepted and arbitration method for measuring the thermal conductivity of insulation materials.However,the temperature-imbalance sensors used in the traditional GHP apparatus have the drawbacks of complicated mechanical structure and electronics,difficulty in assembly and online calibration,which make it very expensive.In addition,compared with the foreign well-developed GHP apparatus,the level of the intelligence of the domestic apparatus lags behind a lot,including electronics,PID parameters tuning and its calibration.In response to the above problems,a novel intelligent GHP apparatus without temperature-imbalance sensors is developed.The main tasks completed are as the followings:1.Firstly,combined with the relationship among thermal conductivity,insulation materials and building energy saving,the background and significance of the research are discussed.Then,the problems of the temperature-imbalance sensors in the GHP apparatus and the intelligent technologies of the domestic GHP apparatus are analyzed.Finally,the goal and main contents of the research are clarified.2.For the scheme of the GHP apparatus without temperature-imbalance sensors,starting from the ideal state of zero heat exchange between the hot-plate and guard-plate,a function expression between the guard-plate temperature offset and the hot-plate temperature,the ambient temperature as well as the cold-plate temperature is established,and a calibration method based on the standard reference material and applying an offset to the guard-plate temperature is further proposed.3.The old electronics of the GHP apparatus developed in our laboratory that utilizes Pt100 sensors for the temperature measurement of the each plate and measures the power of the hot-plate through the heater current is optimized,mainly including temperature measurement part,power control and measurement part,communication part and power supply part,etc.4.For the multivariable temperature control system of the GHP apparatus,a method for the self-tuning of PID parameters based on the relay feedback method and the RGA(Relative Gain Matrix)offset factor method is proposed.5.The PC software of the GHP apparatus including the self-tuning of PID parameters and self-calibration functions is developed.6.The reliability and effectiveness of the above-mentioned technologies are verified by a series of experiments;the overall evaluation results show that the accuracy,repeatability and efficiency of the novel GHP apparatus are significantly improved.7.The main achievements are summarized and the future tasks are suggested.