Helena Avelino Avelino - Academia.edu (original) (raw)

Papers by Helena Avelino Avelino

Research paper thumbnail of Simultaneous viscosity and density measurement of supercritical CO2-saturated PEG 400

The Journal of Supercritical Fluids, 1998

In order to analyse the effect of supercritical fluid (SCF) addition on polymer viscosity we have... more In order to analyse the effect of supercritical fluid (SCF) addition on polymer viscosity we have used, for the first time, a high precision vibrating wire instrument, for the simultaneous measurement of viscosities and densities of a SCF-saturated polymer. For the density measurements, this technique makes use of the buoyancy force exerted by a fluid on a solid sinker, detected

Research paper thumbnail of Density Measurements of Compressed Dipropyl, Dibutyl, Bis(2-ethylhexyl) Adipates from (293 to 373K) at pressures up to about 68MPa

Fluid Phase Equilibria, 2014

ABSTRACT The article reports density measurements of dipropyl (DPA), dibutyl (DBA) and bis(2-ethy... more ABSTRACT The article reports density measurements of dipropyl (DPA), dibutyl (DBA) and bis(2-ethylhexyl) (DEHA) adipates, using a vibrating U-tube densimeter, model DMA HP, from Anton Paar GmbH. The measurements were performed in the temperature range (293 to 373) K and at pressures up to about 68 MPa, except for DPA for which the upper limits were 363 K and 65 MPa, respectively. The density data for each liquid was correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density results is estimated as ±0.2% at a 95% confidence level. No literature density data at pressures higher than 0.1 MPa could be found. DEHA literature data at atmospheric pressure agree with the correlation of the present measurements, in the corresponding temperature range, within ±0.11%. The isothermal compressibility and the isobaric thermal expansion were calculated by differentiation of the modified Tait correlation equation. These two parameters were also calculated for dimethyl adipate (DMA), from density data reported in a previous work. 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. Literature data of isothermal compressibility and isobaric thermal expansivity for DMA have an agreement within ±1% and ±2.4%, respectively, with results calculated in this work.

Research paper thumbnail of Saccharification of tomato pomace for the production of biomass

Bioresource Technology, 1997

... Duc0 and DN5A we 0aed fr0m MeL Darma, 6erman M0n05acchar1de pr0 e5 were dermed 6y HPLC u59 a ... more ... Duc0 and DN5A we 0aed fr0m MeL Darma, 6erman M0n05acchar1de pr0 e5 were dermed 6y HPLC u59 a 5u9aPak (W M11f0rd, M5 ... AM Elshafei, JL Vega, KT Klassom, EC Clausen and JLGaddy, The saccharification of corn stover by cellulase from Penicillium funiculosum. ...

Research paper thumbnail of Density and Rheology of Tris(2-ethylhexyl) Trimellitate (TOTM)

Journal of Chemical & Engineering Data

Research paper thumbnail of Viscosity and Self-Diffusion Coefficients of Dialkyl Adipates: A Correlation Scheme with Predictive Capabilities

Journal of Chemical & Engineering Data, 2015

Research paper thumbnail of Viscosity Measurements of Compressed Liquid Dipropyl and Dibutyl Adipates

Fluid Phase Equilibria, 2015

ABSTRACT The paper reports viscosity measurements of compressed liquid dipropyl (DPA) and dibutyl... more ABSTRACT The paper reports viscosity measurements of compressed liquid dipropyl (DPA) and dibutyl (DBA) adipates obtained with two vibrating wire sensors developed in our group. The vibrating wire instruments were operated in the forced oscillation, or steady-state mode. The viscosity measurements of DPA were carried out in a range of pressures up to 18 MPa and temperatures from (303 to 333) K, and DBA up to 65 MPa and temperature from (303 to 373) K, covering a total range of viscosities from (1.3 to 8.3) mPa s. The required density data of the liquid samples were obtained in our laboratory using an Anton Paar vibrating tube densimeter and were reported in a previous paper. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is less than (0.21 and 0.32)% and the maximum absolute relative deviations are within (0.43 and 0.81)%, for DPA and DBA respectively.

Research paper thumbnail of Tris(2-ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part I: Viscosity measurements at temperatures from (303 to 373)K and pressures up to 65MPa, using a novel vibrating-wire instrument

Fluid Phase Equilibria, 2014

The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate o... more The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate or 1,2,4-Benzenetricarboxylic acid, tris(2-ethylhexyl) ester (TOTM) which is an important plasticizer in the polymer industry and has wide applications as a lubricant. Nevertheless, the main motivation for the present work is to propose TOTM as a plausible candidate for an industrial viscosity reference fluid for high viscosity, high pressure and high temperature. This kind of reference fluid is presently on demand by oil industries and the International Association for Transport Properties is developing efforts aiming to select appropriate candidates and to establish the corresponding reference data. The viscosity measurements were performed with a novel vibrating wire sensor. The new instrument was designed for operation at high pressures (up to 100 MPa) and temperatures up to 373 K. The present measurements were obtained using the vibrating wire sensor in the forced oscillation or steady-state mode of operation. The viscosity measurements were carried out up to 65 MPa and at six temperatures from (303 to 373) K. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is 0.53% and the maximum absolute relative deviation was less than 1.7%. The expanded uncertainty of the present viscosity results, at a 95% confidence level, is estimated to be less than AE2% for viscosities up to 68 mPa s, less than AE2.6% for viscosities between (69 and 268) mPa s and less than AE3% for higher viscosities. The TOTM density data necessary to compute the viscosity results were measured using a vibrating Utube densimeter, model DMA HP and are described in part II of the present work. No literature data above atmospheric pressure could be found for the viscosity of TOTM. As a consequence, the present viscosity results could only be compared upon extrapolation of the vibrating wire data to 0.1 MPa. Independent viscosity measurements were performed, at atmospheric pressure, using an Ubbelohde capillary in order to compare with the vibrating wire results, extrapolated by means of the above mentioned correlation. The two data sets agree within AE1%, which is commensurate with the mutual uncertainty of the experimental methods. Comparisons of the literature data obtained at atmospheric pressure with the present extrapolated vibrating-wire viscosity measurements have shown an agreement within AE2% for temperatures up to 339 K and within AE3.3% for temperatures up to 368 K.

Research paper thumbnail of Density of Diisodecyl Phthalate at Temperatures from (283.15 to 363.15) K and Pressures from (0.1 to 65) MPa

Journal of Chemical & Engineering Data, 2010

Diisodecyl phthalate (DIDP) has recently been proposed to be an industrial reference fluid for mo... more Diisodecyl phthalate (DIDP) has recently been proposed to be an industrial reference fluid for moderately high viscosity at atmospheric pressure. Moreover, some results of the viscosity and also of the density of DIDP at high pressures have been reported recently. ...

Research paper thumbnail of Viscosity Measurements of Compressed Liquid Refrigerant Blend R-507A, Using a Vibrating-Wire Technique

Journal of Chemical & Engineering Data, 2008

The refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydr... more The refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydrofluorocarbon refrigerants, 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125). The paper reports viscosity measurements, performed with a vibrating-wire viscometer, of the refrigerant blend R-507A, at five temperatures in the range (253 to 293) K. The measurements were carried out at pressures from slightly above saturation up to 10 MPa, except for the isotherms at 253.26 K where the maximum pressure was 7.52 MPa and at 263.23 K where the maximum pressure was 7.09 MPa. The overall uncertainty of these measurements is estimated to be (1.0 %. The data obtained were correlated by means of a modified hard-sphere based correlation technique. The root-mean-square deviation, rmsd, of the experimental results from the correlation equations is 0.23 %, and their bias is not significant. This correlation method has also been used to interpolate and extrapolate the present results to enable comparisons with measurements performed by other authors of the viscosity of liquid R-507A at different temperatures and pressures.

Research paper thumbnail of Viscosity of Compressed Liquid 1,1,1-Trifluoroethane (HFC-143a) and Pentafluoroethane (HFC-125)

Journal of Chemical & Engineering Data, 2006

ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethan... more ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125) has been measured with a vibrating-wire viscometer at five temperatures between (254 and 293) K. The measurements were performed at pressures from above saturation up to 10 MPa, although for the isotherms at about 254 K the maximum pressure was approximately 5 MPa for HFC-143a and 7.4 MPa for HFC-125. For the isotherm at about 263 K, the highest pressure for HFC-143a was of the order of 7.5 MPa. The overall uncertainty of these results has been estimated to be less than ± 1.0 %. The measurements have been correlated using a scheme based on a hard-spheres model. The root mean square deviation of the experimental results from the correlations for HFC-143a and HFC-125 is ± 0.24 % and ± 0.25 %, respectively. The correlation scheme has been used to perform the small extrapolations of the present data to the saturation line to enable comparison with literature results at saturation pressure.

Research paper thumbnail of Viscosity of Compressed Liquid 1,1,1-Trifluoroethane (HFC143a) and Pentafluoroethane (HFC125)

Journal of Chemical and Engineering Data - J CHEM ENG DATA, 2006

ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethan... more ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125) has been measured with a vibrating-wire viscometer at five temperatures between (254 and 293) K. The measurements were performed at pressures from above saturation up to 10 MPa, although for the isotherms at about 254 K the maximum pressure was approximately 5 MPa for HFC-143a and 7.4 MPa for HFC-125. For the isotherm at about 263 K, the highest pressure for HFC-143a was of the order of 7.5 MPa. The overall uncertainty of these results has been estimated to be less than ± 1.0 %. The measurements have been correlated using a scheme based on a hard-spheres model. The root mean square deviation of the experimental results from the correlations for HFC-143a and HFC-125 is ± 0.24 % and ± 0.25 %, respectively. The correlation scheme has been used to perform the small extrapolations of the present data to the saturation line to enable comparison with literature results at saturation pressure.

Research paper thumbnail of Simultaneous viscosity and density measurement of supercritical CO2-saturated PEG 400

The Journal of Supercritical Fluids, 1998

In order to analyse the effect of supercritical fluid (SCF) addition on polymer viscosity we have... more In order to analyse the effect of supercritical fluid (SCF) addition on polymer viscosity we have used, for the first time, a high precision vibrating wire instrument, for the simultaneous measurement of viscosities and densities of a SCF-saturated polymer. For the density measurements, this technique makes use of the buoyancy force exerted by a fluid on a solid sinker, detected

Research paper thumbnail of Density Measurements of Compressed Dipropyl, Dibutyl, Bis(2-ethylhexyl) Adipates from (293 to 373K) at pressures up to about 68MPa

Fluid Phase Equilibria, 2014

ABSTRACT The article reports density measurements of dipropyl (DPA), dibutyl (DBA) and bis(2-ethy... more ABSTRACT The article reports density measurements of dipropyl (DPA), dibutyl (DBA) and bis(2-ethylhexyl) (DEHA) adipates, using a vibrating U-tube densimeter, model DMA HP, from Anton Paar GmbH. The measurements were performed in the temperature range (293 to 373) K and at pressures up to about 68 MPa, except for DPA for which the upper limits were 363 K and 65 MPa, respectively. The density data for each liquid was correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density results is estimated as ±0.2% at a 95% confidence level. No literature density data at pressures higher than 0.1 MPa could be found. DEHA literature data at atmospheric pressure agree with the correlation of the present measurements, in the corresponding temperature range, within ±0.11%. The isothermal compressibility and the isobaric thermal expansion were calculated by differentiation of the modified Tait correlation equation. These two parameters were also calculated for dimethyl adipate (DMA), from density data reported in a previous work. 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. Literature data of isothermal compressibility and isobaric thermal expansivity for DMA have an agreement within ±1% and ±2.4%, respectively, with results calculated in this work.

Research paper thumbnail of Saccharification of tomato pomace for the production of biomass

Bioresource Technology, 1997

... Duc0 and DN5A we 0aed fr0m MeL Darma, 6erman M0n05acchar1de pr0 e5 were dermed 6y HPLC u59 a ... more ... Duc0 and DN5A we 0aed fr0m MeL Darma, 6erman M0n05acchar1de pr0 e5 were dermed 6y HPLC u59 a 5u9aPak (W M11f0rd, M5 ... AM Elshafei, JL Vega, KT Klassom, EC Clausen and JLGaddy, The saccharification of corn stover by cellulase from Penicillium funiculosum. ...

Research paper thumbnail of Density and Rheology of Tris(2-ethylhexyl) Trimellitate (TOTM)

Journal of Chemical & Engineering Data

Research paper thumbnail of Viscosity and Self-Diffusion Coefficients of Dialkyl Adipates: A Correlation Scheme with Predictive Capabilities

Journal of Chemical & Engineering Data, 2015

Research paper thumbnail of Viscosity Measurements of Compressed Liquid Dipropyl and Dibutyl Adipates

Fluid Phase Equilibria, 2015

ABSTRACT The paper reports viscosity measurements of compressed liquid dipropyl (DPA) and dibutyl... more ABSTRACT The paper reports viscosity measurements of compressed liquid dipropyl (DPA) and dibutyl (DBA) adipates obtained with two vibrating wire sensors developed in our group. The vibrating wire instruments were operated in the forced oscillation, or steady-state mode. The viscosity measurements of DPA were carried out in a range of pressures up to 18 MPa and temperatures from (303 to 333) K, and DBA up to 65 MPa and temperature from (303 to 373) K, covering a total range of viscosities from (1.3 to 8.3) mPa s. The required density data of the liquid samples were obtained in our laboratory using an Anton Paar vibrating tube densimeter and were reported in a previous paper. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is less than (0.21 and 0.32)% and the maximum absolute relative deviations are within (0.43 and 0.81)%, for DPA and DBA respectively.

Research paper thumbnail of Tris(2-ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part I: Viscosity measurements at temperatures from (303 to 373)K and pressures up to 65MPa, using a novel vibrating-wire instrument

Fluid Phase Equilibria, 2014

The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate o... more The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate or 1,2,4-Benzenetricarboxylic acid, tris(2-ethylhexyl) ester (TOTM) which is an important plasticizer in the polymer industry and has wide applications as a lubricant. Nevertheless, the main motivation for the present work is to propose TOTM as a plausible candidate for an industrial viscosity reference fluid for high viscosity, high pressure and high temperature. This kind of reference fluid is presently on demand by oil industries and the International Association for Transport Properties is developing efforts aiming to select appropriate candidates and to establish the corresponding reference data. The viscosity measurements were performed with a novel vibrating wire sensor. The new instrument was designed for operation at high pressures (up to 100 MPa) and temperatures up to 373 K. The present measurements were obtained using the vibrating wire sensor in the forced oscillation or steady-state mode of operation. The viscosity measurements were carried out up to 65 MPa and at six temperatures from (303 to 373) K. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is 0.53% and the maximum absolute relative deviation was less than 1.7%. The expanded uncertainty of the present viscosity results, at a 95% confidence level, is estimated to be less than AE2% for viscosities up to 68 mPa s, less than AE2.6% for viscosities between (69 and 268) mPa s and less than AE3% for higher viscosities. The TOTM density data necessary to compute the viscosity results were measured using a vibrating Utube densimeter, model DMA HP and are described in part II of the present work. No literature data above atmospheric pressure could be found for the viscosity of TOTM. As a consequence, the present viscosity results could only be compared upon extrapolation of the vibrating wire data to 0.1 MPa. Independent viscosity measurements were performed, at atmospheric pressure, using an Ubbelohde capillary in order to compare with the vibrating wire results, extrapolated by means of the above mentioned correlation. The two data sets agree within AE1%, which is commensurate with the mutual uncertainty of the experimental methods. Comparisons of the literature data obtained at atmospheric pressure with the present extrapolated vibrating-wire viscosity measurements have shown an agreement within AE2% for temperatures up to 339 K and within AE3.3% for temperatures up to 368 K.

Research paper thumbnail of Density of Diisodecyl Phthalate at Temperatures from (283.15 to 363.15) K and Pressures from (0.1 to 65) MPa

Journal of Chemical & Engineering Data, 2010

Diisodecyl phthalate (DIDP) has recently been proposed to be an industrial reference fluid for mo... more Diisodecyl phthalate (DIDP) has recently been proposed to be an industrial reference fluid for moderately high viscosity at atmospheric pressure. Moreover, some results of the viscosity and also of the density of DIDP at high pressures have been reported recently. ...

Research paper thumbnail of Viscosity Measurements of Compressed Liquid Refrigerant Blend R-507A, Using a Vibrating-Wire Technique

Journal of Chemical & Engineering Data, 2008

The refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydr... more The refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydrofluorocarbon refrigerants, 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125). The paper reports viscosity measurements, performed with a vibrating-wire viscometer, of the refrigerant blend R-507A, at five temperatures in the range (253 to 293) K. The measurements were carried out at pressures from slightly above saturation up to 10 MPa, except for the isotherms at 253.26 K where the maximum pressure was 7.52 MPa and at 263.23 K where the maximum pressure was 7.09 MPa. The overall uncertainty of these measurements is estimated to be (1.0 %. The data obtained were correlated by means of a modified hard-sphere based correlation technique. The root-mean-square deviation, rmsd, of the experimental results from the correlation equations is 0.23 %, and their bias is not significant. This correlation method has also been used to interpolate and extrapolate the present results to enable comparisons with measurements performed by other authors of the viscosity of liquid R-507A at different temperatures and pressures.

Research paper thumbnail of Viscosity of Compressed Liquid 1,1,1-Trifluoroethane (HFC-143a) and Pentafluoroethane (HFC-125)

Journal of Chemical & Engineering Data, 2006

ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethan... more ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125) has been measured with a vibrating-wire viscometer at five temperatures between (254 and 293) K. The measurements were performed at pressures from above saturation up to 10 MPa, although for the isotherms at about 254 K the maximum pressure was approximately 5 MPa for HFC-143a and 7.4 MPa for HFC-125. For the isotherm at about 263 K, the highest pressure for HFC-143a was of the order of 7.5 MPa. The overall uncertainty of these results has been estimated to be less than ± 1.0 %. The measurements have been correlated using a scheme based on a hard-spheres model. The root mean square deviation of the experimental results from the correlations for HFC-143a and HFC-125 is ± 0.24 % and ± 0.25 %, respectively. The correlation scheme has been used to perform the small extrapolations of the present data to the saturation line to enable comparison with literature results at saturation pressure.

Research paper thumbnail of Viscosity of Compressed Liquid 1,1,1-Trifluoroethane (HFC143a) and Pentafluoroethane (HFC125)

Journal of Chemical and Engineering Data - J CHEM ENG DATA, 2006

ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethan... more ABSTRACT The viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125) has been measured with a vibrating-wire viscometer at five temperatures between (254 and 293) K. The measurements were performed at pressures from above saturation up to 10 MPa, although for the isotherms at about 254 K the maximum pressure was approximately 5 MPa for HFC-143a and 7.4 MPa for HFC-125. For the isotherm at about 263 K, the highest pressure for HFC-143a was of the order of 7.5 MPa. The overall uncertainty of these results has been estimated to be less than ± 1.0 %. The measurements have been correlated using a scheme based on a hard-spheres model. The root mean square deviation of the experimental results from the correlations for HFC-143a and HFC-125 is ± 0.24 % and ± 0.25 %, respectively. The correlation scheme has been used to perform the small extrapolations of the present data to the saturation line to enable comparison with literature results at saturation pressure.