Elsevier

Fluid Phase Equilibria

Volume 453, 15 December 2017, Pages 46-57
Fluid Phase Equilibria

Viscosity and density measurements on liquid n-tetradecane at moderately high pressures

https://doi.org/10.1016/j.fluid.2017.08.025Get rights and content

Abstract

The main aim of the work is to study the viscosity and density of compressed normal tetradecane in the region of pressures from saturation to 10 MPa, where the available literature data are scarce. New measurements of the viscosity of n-tetradecane (n-C14) along eight isotherms in the range (283–358) K and at pressures up to 70 MPa, have been performed using the vibrating wire technique in the forced mode of operation. Density measurements have also been performed along nine isotherms in the temperature range from (283 to 373) K and pressures from (0.1 to 70) MPa. The vibrating wire viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square (rms) deviation of the data from the correlation is less than 0.32% and the maximum absolute relative deviation is less than 1.0%. The expanded uncertainty of the present viscosity data is estimated as ±1.5% at a 95% confidence level. The density results were correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density data is estimated as ±0.2% at a 95% confidence level. The isothermal compressibility and the isobaric thermal expansion were calculated by differentiation of the modified Tait equation. The uncertainties of isothermal compressibility and the isobaric thermal expansion are estimated to be less than ±1.7% and ±1.1%, respectively, at a 95% confidence level. The results are compared with the available literature data.

Introduction

Thermal energy storage systems are very important to achieve significant energy savings in order to get sustainability in its environmental, economic and social aspects. The storage of energy in adequate forms is a present day challenge to engineers and scientists. In particular, storing thermal energy is presently requiring further research in order to enable its large scale application. Among the materials in use for storing thermal energy, phase change materials (PCMs) are particularly interesting. Paraffins and their mixtures are a group of substances with potential for use as phase change materials (PCM) [1], [2] near room temperature. Having in view large-scale applications of potential PCMs, namely involving the use of solar energy [3], the knowledge of their physical properties assumes an obvious relevance. Normal tetradecane (n-C14) has a melting point near 6 °C [4] which makes it suitable for some “low temperature” energy storage applications, like v.g., cold water tanks. The development of models for the description of energy charge and discharge of PCMs, eventually contained in solid structures (v.g., capsules), require thermophysical properties of both the solid and liquid phases of the PCMs. Among other applications, the development of two-phase, moving boundary models, may require accurate data on the thermophysical properties of the PCM's, namely, their density, viscosity, and thermal conductivity, possibly at pressures above atmospheric pressure, v.g., in the case of containment in capsules.

The thermal conductivity of n-alkanes, including n-C14, have been subject of rigorous measurements since, at least, the 1980's (vd., for instance Calado et al. [5]). However, this might eventually not be the case of viscosity and density measurements at moderately high pressures. In particular, the available viscosity results covering the range from (0.1–10) MPa, which is of great importance for many applications, are restricted to just one set of measurements [6]. In fact, as far as the authors are aware, only one set of viscosity values could be found in that pressure interval [6]. The present article has therefore a definite goal to provide information on the viscosity and density of n-C14 at moderately high pressures, where measurement results are scarce. Ultimately it is aimed to develop a reference viscosity correlation with density for n-C14, which may prove useful for the development of estimation techniques for the properties of paraffin mixtures in use for thermal energy storage. It is believed that this goal is consistent with work that is being developed in the International Association for Transport Properties (IATP).

The present article follows the lines discussed in several recently published works regarding the strategy, the type of property correlation methods [7], [8], [9], [10], [11], [12] and the experimental measurement technique mainly used by the present authors, namely, the vibrating wire method [13], [14], [15], [16].

Section snippets

Materials

The vibrating wire sensor was calibrated with toluene, supplied by Sigma Aldrich, having a nominal purity of 99.8%, without further treatment, except for drying to a water content of ca. 14 mg∙kg−1 and degassing by helium spraying.

The n-C14 sample was obtained from Merck KGaA, batch S7150867 (normal tetradecane GR for synthesis), with a minimum purity of 99%, used without further treatment except for drying to a water content less than 13 mg∙kg−1 and degassing by helium spraying. Drying of both

Density measurements

The results of the measurements of the density, ρ, of n-C14 in our laboratory obtained with an Anton Paar DMA HP densimeter, performed at pressures up to 70 MPa, and at nine temperatures from (283 to 373) K are shown in Table 2. The measurements have an estimated uncertainty of ±0.2% at a 95% confidence level. It should be noted that the (283, 288 and 293) K isotherms contain a restricted range of pressures, due to the low freezing pressures of n-C14 at these temperatures.

Density correlation with temperature and pressure

Since the proposed

Experimental results

In the present work, experimental measurements of the viscosity, η, for n-C14 along eight isotherms between (283 and 358) K and pressures up to 70 MPa, have been performed. The measurements at high pressures were carried out using the vibrating wire technique. The density data needed to compute the vibrating wire viscosity results from the raw data were obtained from Eqs. (1)–(3). All high-pressure viscosity data are presented in the Supporting Information. The viscosity results were correlated

Conclusions

The density and viscosity of n-C14 have been measured in the ranges (283–373) K and (283–358) K, respectively, and at pressures up to 70 MPa. The importance of n-alkanes in general and normal tetradecane in particular call for the establishment of reference values for both properties. This is especially clear for viscosity, which has a significant lack of experimental data, in particular for temperatures lower than 293 K and at pressures greater than 0.1 MPa and lower than 100 MPa. Moreover, a

Acknowledgements and funding

This work was supported by the Strategic Project PEst-OE/QUI/UI0100/2013 funded by Fundação para a Ciência e a Tecnologia (FCT, Portugal). The authors are grateful to FCT (Portugal) for its support.

References (54)

  • M.A. Hernández-Galván et al.

    Liquid viscosities of benzene, n-tetradecane, and benzene+n-tetradecane from 313 to 393K and pressures up to 60MPa: experiment and modeling

    Fluid Phase Equilib.

    (2007)
  • N.B. Vargaftik

    Tables of the Thermophysical Properties of Gases and Liquids

    (1977)
  • J.C.G. Calado et al.

    Thermal conductivity of five hydrocarbons along the saturation line

    Int. J. Thermophys.

    (1983)
  • W.A. Wakeham et al.

    Thermophysical property measurements: the journey from accuracy to fitness for purpose

    Int. J. Thermophys.

    (2007)
  • C.A. Nieto de Castro et al.

    Metrology of viscosity: have we learned enough?

    J. Chem. Eng. Data

    (2009)
  • H.M.N.T. Avelino et al.

    Viscosity measurements of compressed liquid refrigerant blend R-507A, using a vibrating-wire technique

    J. Chem. Eng. Data

    (2008)
  • F.J.P. Caetano et al.

    An industrial reference fluid for moderately high viscosity

    J. Chem. Eng. Data

    (2008)
  • M.J. Assael et al.

    Reference correlation for the viscosity of liquid toluene from 213 to 373 K at pressures to 250 MPa

    Int. J. Thermophys.

    (2001)
  • M. Dix et al.

    A vibrating-wire densimeter for measurements in fluids at high pressures

    Int. J. Thermophys.

    (1991)
  • A.A.H. Padua et al.

    Validation of an accurate vibrating-wire densimeter: density and viscosity of liquids over wide ranges of temperature and pressure

    Int. J. Thermophys.

    (1996)
  • F.J.P. Caetano et al.

    Viscosity measurements of liquid toluene at low temperatures using a dual vibrating-wire technique

    Int. J.Thermophysics

    (2004)
  • F.J.P. Caetano et al.

    Validation of a vibrating-wire viscometer: measurements in the range of 0. 5 to 135 mPa·s

    J. Chem. Eng. Data

    (2005)
  • S. Brito e Abreu et al.

    Density of diisodecyl phthalate at temperatures from (283.15 to 363.15) K and pressures from (0.1 to 65) MPa

    J. Chem. Eng. Data

    (2010)
  • W. Wagner et al.

    The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use

    J. Phys. Chem. Ref. Data

    (2002)
  • A.A.H. Pádua et al.

    Density and viscosity measurements of 2,2,4-trimethylpentane (isooctane) from 198 K to 348 K and up to 100 MPa

    J. Chem. Eng. Data

    (1996)
  • J.C.F. Diogo et al.

    Viscosity measurements of the ionic liquid trihexyl(tetradecyl)phosphonium dicyanamide [P 6,6,6,14 ][dca] using the vibrating wire technique

    J. Chem. Eng. Data

    (2012)
  • F.J.P. Caetano et al.

    Viscosity of di-isodecylphthalate: a potential standard of moderate viscosity

    Int. J. Thermophys.

    (2004)
  • Cited by (0)

    View full text