气体组分变化对热式质量流量计测量精度的影响

Effect of gas composition change on the measurement accuracy of thermal mass flowmeter

混合气体组分变化会造成其物性参数变化,进而对热式气体质量流量计测量精度产生影响。结合混合气体物性参数计算与误差传递理论对气体组分变化或组分设定不准确时流量测量精度的影响进行了研究与分析,给出了由物性参数变化引起质量流量误差的定量计算公式。以最常见的混合气体——空气为例进行了实例计算,并采用热式气体质量流量计在气体流量标准装置上进行实流测试,在300~3 000 kg/h流量范围内,空气组分设定变化1%、5%、10%时对热式流量测量依次产生0.56%、3.19%、4.94%的误差,与定量计算公式得到的结果相比具有很好的一致性,且在组分变化较大时,由组分变化造成对质量流量的误差不可忽略,并找到了组分变化不可忽略的临界值约为3%~5%,为实际应用提供参考。

The change of the mixed gas composition will cause the change of its physical property parameters, which will affect the measurement accuracy of the thermal gas mass flowmeter. Combining the physical property parameter calculation of the mixed gas and the error transfer theory, the influence of the gas composition change or the inaccurate composition setting on the flow measurement accuracy is studied and analyzed, and the quantitative calculation formula of the mass flow error caused by the physical property parameter change is given. Taking the most common mixed gas-air as an example, calculation is conducted, and real flow test is performed using a thermal gas mass flowmeter on the gas flow standard device. When the air composition setting changes by 1%, 5% and 10% within the flow range of 300~3 000 kg/h, the thermal flow measurement will produce errors of 0.56%, 3.19%, and 4.94%, respectively. Compared with the results obtained from the quantitative calculation formula, the results have good consistency. When the composition changes greatly, the mass flow rate error caused by the composition change cannot be ignored. It is found that the critical value of the non-negligible composition change is about 3%~5%, which provides a reference for practical applications.