Ideal-gas heat capacities of dimethylsiloxanes from speed-of-sound measurements and ab initio calculations

Nannan, N.R.; Colonna, Piero; Tracy, C.M.; Rowley, Richard L.; Hurly, John J.

doi:10.1016/j.fluid.2007.04.028

Cited by 29 publications

(24 citation statements)

References 20 publications

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“…͑4͒ to data reported in Ref. 41, which were obtained from speed-of-sound measurements and ab initio calculations. The ideal-gas isobaric heat capacity correlation is valid for temperatures between 273 and 673 K. Note that extrapolation outside this temperature range leads to inaccurate results.…”

Section: A Multiparameter Eos For Siloxanesmentioning

confidence: 96%

“…Figures 2͑a͒-2͑c͒ show the geometry of three exemplary siloxanes as computed by recent ab initio calculations performed to determine the isobaric specific heat in the ideal-gas state. 41 Table I, relevant thermophysical properties of linear and cyclic siloxanes are reported. In principle, these siloxanes can all be used as working fluids in organic Rankine cycle turbines depending on the power level: the optimization of the cycle for the working fluid points to molecules with higher complexity for lower power output and vice versa.…”

Section: Siloxanesmentioning

confidence: 99%

“…These data were determined from ab initio calculations, as treated in Ref. 41. The computed lowest frequency of vibration for all the siloxanes considered here is lower than 40 cm −1 .…”

Section: A Rarefaction Shock Wave In Fluid Dmentioning

confidence: 99%

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Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids

2007

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This paper presents a new class of Bethe-Zel'dovich-Thompson fluids, which are expected to exhibit nonclassical gasdynamic behavior in the single-phase vapor region. These are the linear and cyclic siloxanes, light silicon oils currently employed as working fluids in organic Rankine cycle turbines. State-of-the-art multiparameter equations of state are used to describe the thermodynamic properties of siloxanes and to compute the value of the fundamental derivative of gasdynamics ⌫, whose negative sign is the herald of nonclassical gasdynamics. Siloxane fluids starting from D 6 and cyclic siloxanes of greater complexity, and MD 3 M and linear siloxanes of greater complexity are predicted to exhibit a thermodynamic region in which ⌫ is negative and hence nonclassical wavefields are admissible. As an exemplary case, a nonclassical rarefaction shock wave propagating in fluid D 6 is studied to demonstrate the possibility of using siloxane fluids in nonclassical gasdynamic applications and to experimentally verify the existence of nonclassical wavefields in the vapor phase. The sensitivity of the present results to the considered thermodynamic model of the fluid is also briefly discussed.

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Section: A Multiparameter Eos For Siloxanesmentioning

confidence: 96%

Section: Siloxanesmentioning

confidence: 99%

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Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids

2007

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“…These complex equations, whose accuracy in computing the value of Γ has been discussed by Colonna et al (under review), have been applied to the selected linear and cyclic siloxane and perfluorocabons fluids listed in table 1, where relevant thermophysical properties are also reported for the reader's convenience. Additional information on the thermophysical properties of these fluids and their gasdynamic behaviour can be found in Nannan et al (2007) and Colonna et al ( , 2008b for siloxanes and Lambrakis & Thompson (1972), Cramer (1989Cramer ( , 1991 and Guardone & Argrow (2005) for perfluorocarbons. The minimum value of Γ obtained from the three thermodynamic models is also reported.…”

Section: Results For Selected Siloxanes and Perfluorocarbonsmentioning

confidence: 99%

“…These complex models include various thermophysical parameters, such as the acentric factor ω, in their functional forms, and therefore the number of active degrees of freedom, N, no longer represents molecular complexity, as discussed by Guardone & Argrow (2005). Therefore, the minimum value of the fundamental derivative in the vapour phase, Γ min , which occurs at a state point along the VLE line, is used in the following Stewart, Jacobsen & Penocello (1969), Lambrakis & Thompson (1972), Cramer (1989Cramer ( , 1991, Guardone & Argrow (2005), Nannan et al (2007) and Colonna et al ( , 2008b.…”

Section: Results For Selected Siloxanes and Perfluorocarbonsmentioning

confidence: 99%

Maximum intensity of rarefaction shock waves for dense gases

2009

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Modern thermodynamic models indicate that fluids consisting of complex molecules may display non-classical gasdynamic phenomena such as rarefaction shock waves (RSWs) in the vapour phase. Since the thermodynamic region in which non-classical phenomena are physically admissible is finite in terms of pressure, density and temperature intervals, the intensity of RSWs is expected to exhibit a maximum for any given fluid. The identification of the operating conditions leading to the RSW with maximum intensity is of paramount importance for the experimental verification of the existence of non-classical phenomena in the vapour phase and for technical applications taking advantage of the peculiarities of the non-classical regime. This study investigates the conditions resulting in an RSW with maximum intensity in terms of pressure jump, wave Mach number and shock strength. The upstream state of the RSW with maximum pressure drop is found to be located along the double-sonic locus formed by the thermodynamic states associated with an RSW having both pre-and post-shock sonic conditions. Correspondingly, the maximumMach thermodynamic and maximum-strength loci locate the pre-shock states from which the RSW with the maximum wave Mach number and shock strength can originate. The qualitative results obtained with the simple van der Waals model are confirmed with the more complex Stryjek-Vera-Peng-Robinson, Martin-Hou and Span-Wagner equations of state for selected siloxane and perfluorocarbon fluids. Among siloxanes, which are arguably the best fluids for experiments aimed at the generation and measurement of an RSW, the state-of-the-art Span-Wagner multiparameter equation of state predicts a maximum wave Mach number close to 1.026 for D 6 (dodecamethylcyclohexasiloxane, [O-Si-(CH 3 ) 2 ] 6 ). Such value is well within the capacity of the measurement system of a newly built experimental set-up aimed at the first-ever demonstration of the existence of RSWs in dense vapours.

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The flexible asymmetric shock tube (FAST): a Ludwieg tube facility for wave propagation measurements in high-temperature vapours of organic fluids

et al. 2015

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(2) the process start-up time of the valve has been found to be between 2.1 and 9.0 ms, (3) preliminary rarefaction wave experiments in the dense vapour of siloxane D 6 (dodecamethylcyclohexasiloxane, an organic fluid) were successfully accomplished up to temperatures of 300 • C, and (4) a method for the estimation of the speed of sound from wave propagation experiments is proposed. Results are found to be within 2.1 % of accurate model predictions for various gases. The method is then applied to estimate the speed of sound of D 6 in the NICFD regime. List of symbols cSpeed of sound The set-up is equipped with a special fast-opening valve, separating the high-pressure charge tube from the lowpressure plenum. When the valve is opened, a wave propagates into the charge tube. The wave speed is measured using a time-of-flight technique employing four pressure transducers placed at known distances from each other. The first tests led to the following results: (1) the leakage rate of 5 × 10 −4 mbar l s −1 for subatmospheric and 5 × 10 −2 mbar l s −1 for a superatmospheric pressure is compatible with the purpose of the conceived experiments,

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Ideal-gas heat capacities of dimethylsiloxanes from speed-of-sound measurements and ab initio calculations

Cited by 29 publications

References 20 publications

Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids

Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids

Maximum intensity of rarefaction shock waves for dense gases

The flexible asymmetric shock tube (FAST): a Ludwieg tube facility for wave propagation measurements in high-temperature vapours of organic fluids

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