Using ab initio "data" to accurately determine the fourth density virial coefficient of helium
Using ab initio "data" to accurately determine the fourth density virial coefficient of helium
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DOI：
10.1016/j.jct.2010.02.015
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发表时间：
2010-10-01
影响因子：
2.6
通讯作者：
McLinden, Mark O.
中科院分区：
文献类型：
--
作者：
Moldover, Michael R.;McLinden, Mark O.
我们结合联合收割机精确的从头计算的第二和第三密度维里系数。（4）He的B（T）和C（T），并测量其（p-rho-T）行为以确定第四密度维里系数D（7）用双沉降器磁悬浮密度计在高达38 MPa的压力下进行测量。T = 223 K至T = 323 K等温线的测量结果已发表;这里给出了从T = 323 K到T = 500 K的新测量值。在每个等温线上，维里膨胀的回归被约束到B（T）和C（T）的从头算值，回归确定D（T）以及补偿测量中的系统误差的两个依赖于设备的参数。D（T）的不确定度从T = 223 K时的2.6%到T = 400 K时的95%到T = 500 K时的247%，其中，这些不确定度是扩展不确定度，覆盖因子k = 2，对应于95%置信区间。这些不确定度是在没有B（T）和C（T）从头算值的情况下获得的不确定度的1/6。依赖于仪器的参数可用于校准密度计，这将降低使用这种双沉降器密度计进行的其他测量的不确定性。D（T）的新值将在精确的气体计量中找到应用，例如基于氦（C）折射率的主要压力标准2010 Elsevier Ltd.保留所有权利。
We combine accurate ab initio calculations of the second and third density virial coefficients. B(T) and C(T), of (4)He with measurements of its (p-rho-T) behavior to determine the fourth density virial coefficient D(7) The measurements were made with a two-sinker, magnetic-suspension densimeter at pressures up to 38 MPa. The measurements on isotherms from T = 223 K to T = 323 K were previously published; new measurements from T = 323 K to T = 500 K are presented here On each isotherm, a regression of the virial expansion was constrained to the ab initio values of B(T) and C(T), the regression determined D(T) as well as two apparatus-dependent parameters that compensated for systematic errors in the measurements. The percentage uncertainties of D(T) ranged from 2.6% at T = 223 K to 95% at T = 400 K to 24 7% at T = 500 K, where these uncertainties are expanded uncertainties with coverage factor of k = 2 corresponding to a 95% confidence interval These uncertainties are 1/6th of the uncertainty obtained without the ab initio values of B(T) and C(T) The apparatus-dependent parameters can be used to calibrate the densimeter, and this will reduce the uncertainty of other measurements made with this two-sinker densimeter The new values of D(T) will find applications in accurate gas metrology, such as a primary pressure standard based on the refractive index of helium (C) 2010 Elsevier Ltd. All rights reserved.