Measurements of the thermal conductivity of n-hexane in the supercritical region
Introduction
The goal of this work is to report new set of data and to provide wide-scale correlations for the thermal conductivity of n-hexane that are valid over an extended pressure-temperature-density domain covering the supercritical conditions. This work complements our previous measurements and correlations of the thermal conductivity of gaseous and liquid n-hexane reported in Ref. [1]. To our knowledge, no self-consistent measurements of the thermal conductivity of n-hexane were reported in such a large compressed fluid state. In particular, we have noted that the reference correlation for the thermal conductivity of n-hexane over a large range of temperature and pressure reported by Assael et al. [2] was constructed without any extended validation from experimental data obtained in the surrounding domain of the n-hexane critical point.
Section snippets
Experimental set UP
The present thermal conductivity measurements of n-hexane were carried on as a function of temperature between and and pressures up to 10 MPa, in the homogeneous supercritical region, using vertical coaxial cylinders, operating in the steady-state mode. is the critical temperature of n-hexane. This method of measurement and the applied corrections were described in several papers [[3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]].
We briefly recall that
Experimental results
Our new experimental results (1321 data) are reported in column 3 of Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10 for the dense fluid state characterized by the pressure (column 1) - density (column 2) values along 10 isotherms at 508.17 K (93), 508.92K (193), 509.85 K (133), 510.36 K (127), 511.55 K (145), 511.79 K (147), 513.09 K (167), 515.56 K (141), 525.42 K (106), and 553.00 K (69), respectively. The numbers of data per isotherm are indicated
Background correlations
The two first contributions of Eq. (1) represent the background thermal conductivity:The formulations of Eq. (4) were obtained from our previous measurements of the thermal conductivity of gaseous and liquid n-hexane, as detailed in Ref. [1] and briefly recalled below.
The thermal conductivity for the zero-density limit was expressed by the following polynomial form:where and T were expressed in mW⋅m−1⋅K−1and K, respectively. The values of the
Critical enhancement correlations
The values of were estimated by subtracting the background thermal conductivity calculated using Eqs. (4)–(6), from the measured data reported in column 4 of Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10, i.e.,The resulting data are reported in column 5 of Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10. Even though was a calculated
Thermal conductivity calculated from Eq. (1)
The total thermal conductivity λ(T,ρ) estimated from Eq. (1), with , are reported in column 6 of Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10 The residuals are shown (open red circles) in Fig. 15. The evaluations of the correlation of Eq. (1) are reported in Table 15 for each isotherm and for all the 1321 data measurements in supercritical n-hexane. The standard deviation is 1.152%. Due to the large
Conclusion
New measurements of the thermal conductivity of n-hexane are presented in the supercritical region, at temperatures from 508.17 to 553.00 K along ten isotherms and at pressures up to 10 MPa with an estimated uncertainty lower than 4% (95 level of confidence). Their careful analysis is based on the (background + critical enhancement) additive form of the thermal conductivity data. The temperature and density dependences of the background term have been already determined from previous
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2021, Russian Journal of Physical Chemistry B