International Journal of Thermophysics, May 1, 2014
ABSTRACT The aim of this paper is to examine the application of a hard-sphere scheme to the corre... more ABSTRACT The aim of this paper is to examine the application of a hard-sphere scheme to the correlation and prediction of the viscosity and thermal conductivity of ionic liquids. Ionic liquids present an excellent case, because of their high viscosity. It was found that, regardless of the fact that the scheme had to be extended by orders of magnitude, it was still an excellent scheme for the correlation and prediction of the properties of these liquids; this fact is attributed to its theoretical basis. A database of 461 viscosity and 170 thermal-conductivity measurements for 19 ionic liquids was considered. The average absolute deviationwas 2.31%for the viscosity and 3.15% for the thermal conductivity, while the expanded uncertainty at the 95% confidence level was 4.6% and 6.3%, respectively. Moreover, if the thermal-conductivity roughness factor is allowed to be temperature dependent, then the average absolute deviation was reduced to 0.91% for the thermal conductivity, and the expanded uncertainty at the 95% confidence level to 1.82%. As the scheme requires knowledge of the density, 1070 measurements of density were employed to derive a Tait-type equation for every ionic liquid considered.
This paper contains new, representative reference equations for the thermal conductivity of n-hep... more This paper contains new, representative reference equations for the thermal conductivity of n-heptane. The equations are based in part upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory whenever possible.Inthecase ofthedilute-gas thermal conductivity,atheoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, inthecriticalregion,theexperimentally observedenhancementofthethermalconductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 600 K and pressures up to 250 MPa. The overall uncertainty (considered to be estimates of a combined expanded uncertainty with a coverage factor of 2) of the proposed correlation is estimated, for pressures less than 250 MPa and temperatures less than 600 K, to be less than 4%. 2013 by the U...
Ο σκοπός της παρούσας εργασίας ήταν ο σχεδιασμός και η κατασκευή ενός ιξωδομέτρου ταλαντευόμενου ... more Ο σκοπός της παρούσας εργασίας ήταν ο σχεδιασμός και η κατασκευή ενός ιξωδομέτρου ταλαντευόμενου σύρματος που θα μπορούσε να μετρήσει το ιξώδες Νευτώνειων υγρών υψηλού ιξώδους με πολύ μικρή αβεβαιότητα και σε απόλυτη βάση. Επιπλέον, οι μετρήσεις που έγιναν με το νέο ιξωδόμετρο χρησιμοποιήθηκαν για την επιλογή των νέων υγρών αναφοράς υψηλού ιξώδους, και την ανάπτυξη νέων εξισώσεων αναφοράς στη συγκεκριμένη περιοχή ιξώδους. Πιο αναλυτικά, παρουσιάζονται εν συντομία τα ιξωδόμετρα που χρησιμοποιούνται για να μετρηθεί το ιξώδες Νευτώνειων ρευστών σε μια ευρεία περιοχή θερμοκρασιών και πιέσεων, δείχνοντας ξεκάθαρα τα πλεονεκτήματα των συσκευών ταλαντευόμενου σύρματος. Επιπλέον, γίνεται αναφορά στις εξισώσεις συσχετίσεων αναφοράς των ρευστών υψηλού ιξώδους κι αναδεικνύεται το κενό που υπάρχει σε αυτή την περιοχή ρευστών. Στη συνέχεια, περιγράφεται λεπτομερώς η θεωρία της μεθόδου του ταλαντευόμενου σύρματος. Έτσι, προκύπτουν οι εξισώσεις λειτουργίας του ιξωδομέτρου και τα σχεδιαστικά κριτήρ...
Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant... more Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant and hydraulic fluid applications [1]. The physical properties of PFPEs that make them excellent lubricants at extreme conditions include their thermal and chemical stabilities and very good cold flow properties [2]. In this work the viscous behaviour of Krytox GPL102 a perfluoropolyether F-(CF(CF3)-CF2-O)n-CF2CF3 (with an average n = 9.5 and molar mass 1720 g/mol) has been analysed. A coordinated attempt is being made by several laboratories to measure viscosities on the same sample using six different high pressure instruments: three falling body, one vibrating wire, one rotational and one capillary viscometer. This enables us to check the validity of the different calibration procedures used for measurements of viscous liquids with falling body viscometers. We provide new experimental high pressure viscosities (obtained between 273 and 373, at pressures up to 225 MPa with a maximum vi...
New measurements of the viscosity of a round-robin sample of Krytox GPL102 oil are presented in t... more New measurements of the viscosity of a round-robin sample of Krytox GPL102 oil are presented in the temperature range (282 to 364) K and up to 20 MPa. The measurements were performed in a vibrating-wire instrument with an uncertainty of 2 % (at the 95 % confidence level). The Newtonian behavior of Krytox GPL102 oil was confirmed by examining the relationship between shear stress and strain. Finally, a scheme based on considerations of the hard-sphere theory of the liquid state was employed successfully to correlate all of the present measurements within 2.5 % (at the 95 % confidence level).
A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of s... more A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2$$\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$W·m-1·K-1 to $$4\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$4W·m-1·K-1 is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to $$\times $$×120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.
Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant... more Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant and hydraulic fluid applications [1]. The physical properties of PFPEs that make them excellent lubricants at extreme conditions include their thermal and chemical stabilities and very good cold flow properties [2]. In this work the viscous behaviour of Krytox GPL102 a perfluoropolyether F-(CF(CF3)-CF2-O)n-CF2CF3 (with an average n = 9.5 and molar mass 1720 g/mol) has been analysed. A coordinated attempt is being made by several laboratories to measure viscosities on the same sample using six different high pressure instruments: three falling body, one vibrating wire, one rotational and one capillary viscometer. This enables us to check the validity of the different calibration procedures used for measurements of viscous liquids with falling body viscometers. We provide new experimental high pressure viscosities (obtained between 273 and 373, at pressures up to 225 MPa with a maximum viscosity of 4170 mPa·s). This study also reports high-temperature, high-pressure density data from 278.15 to 398.15 K and pressures to 120 MPa. The viscosity and density data were satisfactorily fitted to empirical equations, which can be used to interpolate them within the experimental conditions investigated in this study.
International Journal of Thermophysics, May 1, 2014
ABSTRACT The aim of this paper is to examine the application of a hard-sphere scheme to the corre... more ABSTRACT The aim of this paper is to examine the application of a hard-sphere scheme to the correlation and prediction of the viscosity and thermal conductivity of ionic liquids. Ionic liquids present an excellent case, because of their high viscosity. It was found that, regardless of the fact that the scheme had to be extended by orders of magnitude, it was still an excellent scheme for the correlation and prediction of the properties of these liquids; this fact is attributed to its theoretical basis. A database of 461 viscosity and 170 thermal-conductivity measurements for 19 ionic liquids was considered. The average absolute deviationwas 2.31%for the viscosity and 3.15% for the thermal conductivity, while the expanded uncertainty at the 95% confidence level was 4.6% and 6.3%, respectively. Moreover, if the thermal-conductivity roughness factor is allowed to be temperature dependent, then the average absolute deviation was reduced to 0.91% for the thermal conductivity, and the expanded uncertainty at the 95% confidence level to 1.82%. As the scheme requires knowledge of the density, 1070 measurements of density were employed to derive a Tait-type equation for every ionic liquid considered.
This paper contains new, representative reference equations for the thermal conductivity of n-hep... more This paper contains new, representative reference equations for the thermal conductivity of n-heptane. The equations are based in part upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory whenever possible.Inthecase ofthedilute-gas thermal conductivity,atheoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, inthecriticalregion,theexperimentally observedenhancementofthethermalconductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 600 K and pressures up to 250 MPa. The overall uncertainty (considered to be estimates of a combined expanded uncertainty with a coverage factor of 2) of the proposed correlation is estimated, for pressures less than 250 MPa and temperatures less than 600 K, to be less than 4%. 2013 by the U...
Ο σκοπός της παρούσας εργασίας ήταν ο σχεδιασμός και η κατασκευή ενός ιξωδομέτρου ταλαντευόμενου ... more Ο σκοπός της παρούσας εργασίας ήταν ο σχεδιασμός και η κατασκευή ενός ιξωδομέτρου ταλαντευόμενου σύρματος που θα μπορούσε να μετρήσει το ιξώδες Νευτώνειων υγρών υψηλού ιξώδους με πολύ μικρή αβεβαιότητα και σε απόλυτη βάση. Επιπλέον, οι μετρήσεις που έγιναν με το νέο ιξωδόμετρο χρησιμοποιήθηκαν για την επιλογή των νέων υγρών αναφοράς υψηλού ιξώδους, και την ανάπτυξη νέων εξισώσεων αναφοράς στη συγκεκριμένη περιοχή ιξώδους. Πιο αναλυτικά, παρουσιάζονται εν συντομία τα ιξωδόμετρα που χρησιμοποιούνται για να μετρηθεί το ιξώδες Νευτώνειων ρευστών σε μια ευρεία περιοχή θερμοκρασιών και πιέσεων, δείχνοντας ξεκάθαρα τα πλεονεκτήματα των συσκευών ταλαντευόμενου σύρματος. Επιπλέον, γίνεται αναφορά στις εξισώσεις συσχετίσεων αναφοράς των ρευστών υψηλού ιξώδους κι αναδεικνύεται το κενό που υπάρχει σε αυτή την περιοχή ρευστών. Στη συνέχεια, περιγράφεται λεπτομερώς η θεωρία της μεθόδου του ταλαντευόμενου σύρματος. Έτσι, προκύπτουν οι εξισώσεις λειτουργίας του ιξωδομέτρου και τα σχεδιαστικά κριτήρ...
Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant... more Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant and hydraulic fluid applications [1]. The physical properties of PFPEs that make them excellent lubricants at extreme conditions include their thermal and chemical stabilities and very good cold flow properties [2]. In this work the viscous behaviour of Krytox GPL102 a perfluoropolyether F-(CF(CF3)-CF2-O)n-CF2CF3 (with an average n = 9.5 and molar mass 1720 g/mol) has been analysed. A coordinated attempt is being made by several laboratories to measure viscosities on the same sample using six different high pressure instruments: three falling body, one vibrating wire, one rotational and one capillary viscometer. This enables us to check the validity of the different calibration procedures used for measurements of viscous liquids with falling body viscometers. We provide new experimental high pressure viscosities (obtained between 273 and 373, at pressures up to 225 MPa with a maximum vi...
New measurements of the viscosity of a round-robin sample of Krytox GPL102 oil are presented in t... more New measurements of the viscosity of a round-robin sample of Krytox GPL102 oil are presented in the temperature range (282 to 364) K and up to 20 MPa. The measurements were performed in a vibrating-wire instrument with an uncertainty of 2 % (at the 95 % confidence level). The Newtonian behavior of Krytox GPL102 oil was confirmed by examining the relationship between shear stress and strain. Finally, a scheme based on considerations of the hard-sphere theory of the liquid state was employed successfully to correlate all of the present measurements within 2.5 % (at the 95 % confidence level).
A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of s... more A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2$$\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$W·m-1·K-1 to $$4\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$4W·m-1·K-1 is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to $$\times $$×120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.
Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant... more Perfluoropolyethers are a class of synthetic oils used in a variety of high-temperature lubricant and hydraulic fluid applications [1]. The physical properties of PFPEs that make them excellent lubricants at extreme conditions include their thermal and chemical stabilities and very good cold flow properties [2]. In this work the viscous behaviour of Krytox GPL102 a perfluoropolyether F-(CF(CF3)-CF2-O)n-CF2CF3 (with an average n = 9.5 and molar mass 1720 g/mol) has been analysed. A coordinated attempt is being made by several laboratories to measure viscosities on the same sample using six different high pressure instruments: three falling body, one vibrating wire, one rotational and one capillary viscometer. This enables us to check the validity of the different calibration procedures used for measurements of viscous liquids with falling body viscometers. We provide new experimental high pressure viscosities (obtained between 273 and 373, at pressures up to 225 MPa with a maximum viscosity of 4170 mPa·s). This study also reports high-temperature, high-pressure density data from 278.15 to 398.15 K and pressures to 120 MPa. The viscosity and density data were satisfactorily fitted to empirical equations, which can be used to interpolate them within the experimental conditions investigated in this study.
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