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为实现吸热型碳氢燃料的低温密度在线测量,基于计数率模式下的gamma(伽马)射线衰减原理,设计一套适用于高压、低温的碳氢燃料密度测量系统,温度测量范围:233~333 K,最高压力达到10 MPa,合成相对标准不确定度为:0.13%~1.46%。分别通过正己烷和质量比1∶1正庚烷-正辛烷二元混合物对测试系统测量精度进行验证,实验结果表明:密度测量的最大相对误差控制在0.67%,相对误差绝对平均值分别为0.22%、0.07%。在此基础上,对碳氢燃料A在压力:0.7、3和6 MPa,温度:234.15~323.45 K时的密度进行测量,并计算碳氢燃料A等压热膨胀系数,结果表明,燃料A在三种压力下,等压热膨胀系数αp随着测试温度的升高而增加;低温下,高压不利于热量在流体中的扩散。实验中还发现,当温度接近230.65 K时,碳氢燃料在预冷管路中逐渐由液相变为固相,系统工作压力急剧升高。此套密度测量系统为开展吸热型碳氢燃料低温密度的测量创造了条件。
In order to realize the low temperature density online measurement of endothermic hydrocarbon fuel, a set of hydrocarbon fuel density measurement system suitable for high pressure and low temperature is designed based on the principle of γ (gamma ray) attenuation in counting rate mode. The measurement range of temperature is 233 ~ 333 K, the maximum pressure reached 10 MPa, the synthetic relative standard uncertainty: 0.13% ~ 1.46%. The measurement accuracy of the test system was verified by n-hexane and n-heptane-n-octane binary mixtures with mass ratio of 1: 1 respectively. The experimental results showed that the maximum relative error of density measurement was controlled at 0.67%, and the absolute relative error was 0.22%, 0.07%. On this basis, the density of hydrocarbon fuel A at pressures of 0.7, 3 and 6 MPa and temperatures of 234.15 to 323.45 K were measured, and the isobaric thermal expansion coefficient of hydrocarbon fuel A was calculated. The results showed that the fuel A was in three Under the pressure, the isobaric thermal expansion coefficient αp increases with the increase of the test temperature; under low temperature, the high pressure is not conducive to the heat diffusion in the fluid. The experiment also found that when the temperature is close to 230.65 K, the hydrocarbon fuel gradually changes from liquid phase to solid phase in the precooling pipe, and the working pressure of the system rises sharply. This set of density measurement system to carry out low-temperature endothermic hydrocarbon fuel density to create the conditions for the measurement.