Study Of High-precision Thermal Conductivity Measuring Apparatus By Guarded Heat Flow Meter Technique

With the development of sustained economy, the energy crisis becomesmore seriously, and energy conservation has gradually become an importanttopic throughout whole world. One important way for dealing with energycrisis is to use and to develop more energy-saving materials. Thermalconductivity is the main parameter of the thermal properties of materials,accurate assessment of thermal conductivity has major significance for thedevelopment and production of energy-saving insulation materials. Theguarded heat flow meter method is able to measure samples of small sizes orfilms, and with a larger range. Instruments developed by developed countriesbased on this method have high accuracy, good repeatability, widetemperature and thermal conductivity range. However, domestic instrumenthas low accuracy and repeatability, and measurement range is relatively small.For this reason, the study of thermal conductivity measuring instrument basedon this technique is very important.According to the current situation and based on the already-existingguarded heat flow meter instrument prototype, the influence of contactresistance was carefully analyzed and several improvements and relatedalgorithms have been conducted and designed. Furthermore, calibrationsystem of the instrument system was established. Through the experimentalresults, the instrument achieves the expected purpose.The major work of this thesis is as following:1. The basic theory of heat transfer and various thermal conductivitymeasurement methods and principles were described, with an overview ofguarded heat flow meter instrument of domestic and abroad. The drawbacksand current situation of domestic instrument have been described.2. The measurement principle of the guarded heat flow meter techn iquewas introduced. On the basis of the mechanical structure and electricalsystems of laboratory prototype, the measurement error factors were analyzed.3. The mechanism of thermal contact resistance influence on the guardedheat flow meter instrument was introduced. Then a calibration method whichcan reduce thermal contact resistance effects was proposed. This method makes use of a pair of samples that have large difference in thickness tocalibrate the instrument. With this method, it is able to improve the accuracyand repeatability of the instrument by reducing the influence of the thermalcontact resistance and.4. Calibration methods of the instrument were established, includingthermocouple calibration, different thermal resistance range calibration, thinspecimen calibration, different average temperature calibration. M easurementsoftware and its process have been introduced, with some key subroutines andalgorithms.5. Experiments were designed and conducted to test various aspects ofthe instrument performance. The experimental results show that the accuracyand repeatability of the instrument have been improved and the measurementrange has been increased.