基于低温制冷机的低温流体电容式密度测量

Capacitive density measurement of cryogenic fluids based on a G-M cryocooler

设计并搭建了一套基于G-M低温制冷机的电容式密度测量实验装置,由平行板电容器、样品流体测试腔、充排气体管路、低温制冷机、温度测量与控制单元、压力测量单元、真空绝热保护腔以及高真空排气系统八个部分组成。该系统适用温度测量范围为15—300 K,压力测量范围0.01—0.3 MPa。实验中的低温液体由常温气体经低温制冷机冷却液化得到,并蓄存在装有平行板电容器的样品测试腔内。该测试腔上开有视窗,可用于观察冷却过程中低温液体的形成及其液位。对受控压力及温度下的液氮、液氩两种低温流体的密度进行了测量,所得数据与文献实验值及美国NIST标准数据吻合良好,液相区相对偏差小于±0.5%。该密度测量系统今后可用于测量其他流体(包括混合物)在低温下的p-ρ-T数据,还有望经过改进和集成化设计后实现LNG和空分等工业领域的低温流体密度在线实时监测。

An experimental setup for density measurement of cryogenic fluids by capacitance method has been designed and fabricated to measure the density of deuterium and oxygen, with a single-stage G-M cryocooler as the cold source. It consists of a parallel plate capacitor, a sample fluid test cell, a gas char- ging and discharging pipeline, a cryocooler, a temperature measurement and control unit, a pressure meas- urement and control unit, a vacuum chamber and a high vacuum pumping unit. The system is applicable for the temperature range of 15--300 K, and the pressure range of 0.01--0.3 MPa. Cryogenic liquid is ob- tained through liquefaction of the gas by the cryocooler and then stored in the sample fluid test cell, in which the parallel plate capacitor is positioned. The test cell is embedded with an optical window, which can be used to observe the formation of liquid and its level during the cooling process. The densities of liq- uid nitrogen and liquid argon under controlled pressure and temperature have been measured, with agreewith the experimental data in literature ment system could be used to measure even for on-line monitoring of LNG or and the NIST reference data within p-p-T data of other fluids （ including air product density in next step. ± 0.5%. The density measure- mixtures） at low temperature,