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高温下全辐射系数的测定,一般用辐射法(相对法)和能量法(绝对法)。能量法是研究材料热辐射性能最准确的方法之一,它基于测量试样的辐射热能和辐射表面的绝对温度。热交换过程中对流和辐射往往同时进行并相互影响,所以应在真空(10~(-3)mmHg)中进行测量。试样作成薄壁管(壁厚0.5mm),夹在通有冷却水的铜制夹头中,通电加热。为了补偿高温下的热膨胀,下端夹头是可动的。试样安装在真空室的轴心位置上,设备见图1。试样与真空室两个表面间的辐射热交换表示如下:
Determination of total emissivity at high temperatures, the general method of radiation (relative method) and energy method (absolute method). The energy method is one of the most accurate methods to study the thermal radiation performance of a material. It is based on measuring the radiant thermal energy of the specimen and the absolute temperature of the radiant surface. Convection and radiation during heat exchange often occur simultaneously and affect each other, so measurements should be made in a vacuum (10 -3 mmHg). The sample was made into a thin-walled tube (wall thickness: 0.5 mm) and sandwiched between copper chucks with cooling water and electrified. To compensate for thermal expansion at high temperatures, the lower collet is movable. The sample is installed in the axis of the vacuum chamber, the device shown in Figure 1. Radiation heat exchange between the two surfaces of the sample and the vacuum chamber is expressed as follows: