大尺寸活塞-厚壁圆筒式固体传压高温三轴压力室的温度标定

Temperature Calibration for the Solid Confining Media Vessel of Large-Size and Thick-Walled Piston-Cylinder Apparatus under High Temperature and Triaxial Pressure

"600℃、20MN伺服控制高温高压岩体三轴试验机"的高温三轴压力室,采用活塞-厚壁圆筒式结构,内、外径分别达到300mm和1 060mm,高1 100mm,岩石试件尺寸达200mm×400mm,采用低电压高电流内加热方式。为了对高温压力室进行温度标定,在试样内、外布设9个测温点,观测试样在加热和保温过程中各测点的温度变化,研究试样内的温度分布特征及其与试样外控制点温度的关系。实验结果表明,试样中部盐环与外层云母板交界处的温度数据稳定可靠,与试样内部的温度具有良好的线性关系,可作为加热过程的温度控制点。在同一横截面上,试样内部的温度高于试样外盐环与外层云母板交界处的温度,且两者的中部温度均高于两端;试样轴向温度对称于试样中部分布,中间高于两端,温差随加热温度的上升不断增大,最大温度梯度为0.85℃/mm;试样径向温度随着离中心点距离的增加近似呈线性增大,表面温度最高,最大温度梯度约0.5℃/mm。同时,试样轴心温度、离轴心40和80mm点的温度,以及试样表面的温度,分别比控制点高21%、27%、28%和29%,而试样上、下端温度只比控制点温度低1.5%。试验机加热方式合理,温度控制精度高,试样温度分布较均匀。

The pressure chamber of ＂600 ℃ and 20 MN servo-controlled triaxial rock testing system with high temperature and high pressure＂ has adopted the piston- thick-walled cylinder structure. Compared with normal pressure chamber, the inner diameter rises to 300 mm,the outside diameter be- comes 1060 mm and the height grows to 1 100 mm. The size of test specimen also amounts to φ5200 min× 400 mm. The calibration test applies internal heating type and electronic heating approach with low voltage and high current. Before the system is put into use,the reference temperature point should be calibrated. Thus,nine thermocouples were placed in and outside the specimen to observe the temperature variation at these observation points, and to study temperature field characteristics inside of specimen, as well as its relationship with reference point temperature. The calibration experiment results indicate that, the temperature data collected from the middle of the junction of NaC1 and mican- ite paper are stable and reliable,and are in a favorable linear relationship with the inner temperature. Therefore, the place is qualified to be the reference temperature point in the heating process. The test results show that the inner temperatures of the specimen are higher than the temperatures of the junc- tion of NaC1 and micanite paper in the same cross section,the middle temperatures of whom are higher than those on both ends. In the inner axial direction, the upper end and the bottom temperature are symmetric to the middle of the specimen whose temperature is higher than either of those of the both ends. The disparity from middle to end grows bigger as the heating temperature increases, the maxi- mum gradient is 0.85 ~C/mm. In the radial direction,the larger distance from the central point,the greater trend of linear temperature distribution. While the central temperature is the lowest, the sur- face temperature is the highest. The biggest temperature gradient is about 0.5 ℃/mm. The tempera- ture at the central point,40 mm from the central point,80 mm from the central point and on the sur- face of the specimen are respectively larger than the reference temperature by 21% ,27% ,28G and 29%. Whereas,in the inner axial direction,the upper end temperature and the bottom temperature are close,only 1.5% lower than the reference temperature. It is testified that the heating approach is rea- sonable, and the accuracy of temperature control is high and the temperature of test specimen is well- distributed.