Imperial College London

Dr Saif Z. S. Al Ghafri

Faculty of EngineeringDepartment of Chemical Engineering

Honorary Research Fellow
 
 
 
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Contact

 

+44 (0)20 7594 1227saif.al-ghafri06

 
 
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Location

 

231ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

68 results found

Sadaghiani MS, Siahvashi A, Arami-Niya A, Tsuji T, Yukumoto A, Seiki Y, Al Ghafri SZS, Stanwix PL, May EFet al., 2023, Cryogenic Solid Solubility Measurements for HFC-32+CO<sub>2</sub> Binary Mixtures at Temperatures Between (132 and 217) K, INTERNATIONAL JOURNAL OF THERMOPHYSICS, Vol: 44, ISSN: 0195-928X

Journal article

Dhakal S, Al Ghafri SZS, Rowland D, May EF, Trusler JPM, Stanwix PLet al., 2023, Speeds of sound in binary mixtures of water and carbon dioxide at temperatures from 273 K to 313 K and at pressures up to 50 MPa, International Journal of Thermophysics, Vol: 44, Pages: 1-29, ISSN: 0195-928X

Knowledge of thermodynamic properties of aqueous solutions of CO2 is crucial for various applications including climate science, carbon capture, utilisation and storage (CCUS), and seawater desalination. However, there is a lack of reliable experimental data, and the equation of state (EOS) predictions are not reliable, particularly for sound speeds in low CO2 concentrations typical of water resources. For this reason, we have measured speeds of sound in three different aqueous solutions containing CO2. We report speeds of sound in the single-phase liquid region for binary mixtures of water and CO2 for mole fractions of CO2 of 0.0118, 0.0066 and 0.0015 at temperatures from 273.15 K to 313.15 K and at pressures up to 50 MPa, measured using a dual-path pulse-echo apparatus. The relative standard uncertainties of the sound speeds are 0.05 %, 0.03 % and 0.01 % at 0.0118, 0.0066 and 0.0015 CO2 mole fractions, respectively. The change in sound speeds as functions of composition, pressure and temperature are analysed in this study. We find that dissolution of CO2 in water increases its sound speeds at all conditions, with the greatest increase occurring at the highest mole fractions of CO2. Our sound speed data agree well with the limited available experimental data in the literature but deviate from the EOS-CG of Gernert and Span by up to 7 % at the lowest temperatures, highest pressures, and highest CO2 mole fraction. The new low-uncertainty sound speed data presented in this work could provide a basis for development of an improved EOS and in establishing reliable predictions of the change in thermodynamic properties of seawater-like mixtures due to absorption of CO2 gas.

Journal article

Xiao X, Kim D, Jiao F, Yang X, Al Ghafri S, Siahvashi A, Tsuji T, Yukumoto A, Seiki Y, Stanwix PL, May EFet al., 2023, Viscosity, thermal conductivity, and interfacial tension study of CO<inf>2</inf> + difluoromethane (R32), International Journal of Refrigeration, Vol: 152, Pages: 331-342, ISSN: 0140-7007

Reliable understanding of viscosity (η), thermal conductivity (λ), and interfacial tension (γ) are demanded in the refrigeration process, especially in the heat, mass and momentum transfer calculations. In this work, measurements of these thermophysical properties for (CO2 + R32) have been conducted by vibrating wire viscometry, transient hot-wire technique, and differential capillary rise approach. The experimental condition ranges from (208.4 to 344.4) K and pressures up to 7.58 MPa at x(CO2) = 0.7, 0.8 and 0.9, including those in the single-phase and near the melting curves. The standard uncertainties (k = 1) are between (0.21 and 6.80) μPa·s, (0.00012 and 0.00290) W·m–1·K–1, and (0.13 and 0.67) mN·m–1 for viscosity, thermal conductivity, and interfacial tension, respectively. The achieved results and the literature data (if applicable) were utilised to regress the extended corresponding states correlation and Parachor approach implemented in REFPROP 10.0. With the regressed models, most viscosity and thermal conductivity results can be described within 4%. The determined data and improved model provided here should contribute significantly to the design margin minimisation in the refrigeration cycle.

Journal article

Xiao X, Tenardi LD, Sadaghiani MS, Sadeghi Pouya E, Yang X, Al Ghafri S, Siahvashi A, Tsuji T, Yukumoto A, Seiki Y, Stanwix PL, May EFet al., 2023, Thermodynamic property measurements and modelling of CO<inf>2</inf> + difluoromethane (R32): Density, heat capacity, and vapour-liquid equilibrium, International Journal of Refrigeration, Vol: 149, Pages: 260-273, ISSN: 0140-7007

Accurate thermodynamic property data and models are demanded to reduce the design margins of industrial processes based on these fluids. In this work, measurements of density (ρ), heat capacity (cp), and vapour-liquid equilibrium (VLE) for CO2 + difluoromethane (R32) have been performed by the vibrating tube densimeter and the magnetic suspension balance densimeter, the visual cell and gas chromatograph, and the differential scanning calorimeter, respectively. Experiments were conducted over the temperatures ranging from (208.3 to 334.3) K and pressures reaching 10.04 MPa at CO2 concentrations of 0.7, 0.8 and 0.9. The measured data, together with the results reported in literature where applicable, were subsequently applied to regress the binary interaction parameters utilised in the mixture functions of Helmholtz energy model from REFPROP 10 software package. Noticeable improvements have been achieved for the model's ability to represent thermodynamic property data. The most significant achievement exists in density description: compared with the default parameters, the root-mean-square (RMS) deviation has been decreased by half.

Journal article

Ghafri SZSA, Revell C, Di Lorenzo M, Xiao G, Buckley CE, May EF, Johns Met al., 2023, Techno-economic and environmental assessment of LNG export for hydrogen production, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 48, Pages: 8343-8369, ISSN: 0360-3199

Journal article

O'Neill KT, Al Ghafri S, Falcao BDS, Tang L, Kozielski K, Johns MLet al., 2023, Hydrogen ortho-para conversion: process sensitivities and optimisation, CHEMICAL ENGINEERING AND PROCESSING-PROCESS INTENSIFICATION, Vol: 184, ISSN: 0255-2701

Journal article

Jiao F, Al Ghafri SZ, Seneviratne KN, Akhfash M, Hughes TJ, Johns ML, May EFet al., 2022, Interfacial tension measurements of methane plus propane binary and methane plus propane plus <i>n</i>-heptane ternary mixtures at low temperatures, JOURNAL OF CHEMICAL THERMODYNAMICS, Vol: 171, ISSN: 0021-9614

Journal article

Sadaghiani MS, Siahvashi A, Norris BWE, Al Ghafri SZS, Arami-Niya A, May EFet al., 2022, Prediction of solid formation conditions in mixed refrigerants with iso-pentane and methane at high pressures and cryogenic temperatures, ENERGY, Vol: 250, ISSN: 0360-5442

Journal article

Li M, Lim VWS, Ghafri SZSA, Ling N, Adebayo AR, May EF, Johns MLet al., 2022, Minimum miscibility pressure of CO2 and oil evaluated using MRI and NMR measurements, JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING, Vol: 214, ISSN: 0920-4105

Journal article

Xiao X, Trusler JPM, Yang X, Thol M, Al Ghafri SZS, Rowland D, May EFet al., 2022, Erratum: “Equation of state for solid benzene valid for temperatures up to 470 K and pressures up to 1800 MPa” [J. Phys. Chem. Ref. Data 50, 043104 (2021)], Journal of Physical and Chemical Reference Data, Vol: 51, Pages: 1-11, ISSN: 0047-2689

Journal article

Al Ghafri SZS, Munro S, Cardella U, Funke T, Notardonato W, Trusler JPM, Leachman J, Span R, Kamiya S, Pearce G, Swanger A, Rodriguez ED, Bajada P, Jiao F, Peng K, Siahvashi A, Johns ML, May EFet al., 2022, Hydrogen liquefaction: a review of the fundamental physics, engineering practice and future opportunities, Energy and Environmental Science, Vol: 15, ISSN: 1754-5692

Hydrogen is emerging as one of the most promising energy carriers for a decarbonised global energy system. Transportation and storage of hydrogen are critical to its large-scale adoption and to these ends liquid hydrogen is being widely considered. The liquefaction and storage processes must, however, be both safe and efficient for liquid hydrogen to be viable as an energy carrier. Identifying the most promising liquefaction processes and associated transport and storage technologies is therefore crucial; these need to be considered in terms of a range of interconnected parameters ranging from energy consumption and appropriate materials usage to considerations of unique liquid-hydrogen physics (in the form of ortho–para hydrogen conversion) and boil-off gas handling. This study presents the current state of liquid hydrogen technology across the entire value chain whilst detailing both the relevant underpinning science (e.g. the quantum behaviour of hydrogen at cryogenic temperatures) and current liquefaction process routes including relevant unit operation design and efficiency. Cognisant of the challenges associated with a projected hydrogen liquefaction plant capacity scale-up from the current 32 tonnes per day to greater than 100 tonnes per day to meet projected hydrogen demand, this study also reflects on the next-generation of liquid-hydrogen technologies and the scientific research and development priorities needed to enable them.

Journal article

Al Ghafri SZS, Swanger A, Jusko V, Siahvashi A, Perez F, Johns ML, May EFet al., 2022, Modelling of Liquid Hydrogen Boil-Off, ENERGIES, Vol: 15

Journal article

Al Ghafri SZS, Swanger A, Park KH, Jusko V, Ryu Y, Kim S, Kim SG, Zhang D, Seo Y, Johns ML, May EFet al., 2022, Advanced boil-off gas studies of liquefied natural gas used for the space and energy industries, ACTA ASTRONAUTICA, Vol: 190, Pages: 444-454, ISSN: 0094-5765

Journal article

Al Ghafri SZS, Akhfash M, Hughes TJ, Xiao X, Yang X, May EFet al., 2021, High pressure viscosity measurements of ternary (methane plus propane plus heptane) mixtures, FUEL PROCESSING TECHNOLOGY, Vol: 223, ISSN: 0378-3820

Journal article

Dhakal S, Tay WJ, Al Ghafri SZS, Rowland D, Mullins SP, May EF, Trusler JPM, Stanwix PLet al., 2021, Thermodynamic properties of liquid toluene from speed-of-sound measurements at temperatures from 283.15 K to 473.15 K and at pressures up to 390 MPa, International Journal of Thermophysics, Vol: 42, Pages: 1-40, ISSN: 0195-928X

We report the speeds of sound in liquid toluene (methylbenzene) measured using double-path pulse-echo apparatus independently at The University of Western Australia (UWA) and Imperial College London (ICL). The UWA data were measured at temperatures between (306 and 423) K and at pressures up to 65 MPa with standard uncertainties of between (0.02 and 0.04)%. At ICL, measurements were made at temperatures between (283.15 and 473.15) K and at pressures up to 390 MPa with standard uncertainty of 0.06%. By means of thermodynamic integration, the measured sound-speed data were combined with initial density and isobaric heat capacity values obtained from extrapolated experimental data to derive a comprehensive set of thermodynamic properties of liquid toluene over the full measurement range. Extensive uncertainty analysis was performed by studying the response of derived properties to constant and dynamic perturbations of the sound-speed surface, as well as the initial density and heat capacity values. The relative expanded uncertainties at 95% confidence of derived density, isobaric heat capacity, isobaric expansivity, isochoric heat capacity, isothermal compressibility, isentropic compressibility, thermal pressure coefficient and internal pressure were estimated to be (0.2, 2.2, 1.0, 2.6, 0.6, 0.2, 1.0 and 2.7)%, respectively. Due to their low uncertainty, these data and derived properties should be well suited for developing a new and improved fundamental Helmholtz equation of state for toluene.

Journal article

Xiao X, Trusler JPM, Yang X, Thol M, Al Ghafri SZS, Rowland D, May EFet al., 2021, Equation of state for solid benzene valid for temperatures up to 470 K and pressures up to 1800 MPa, Journal of Physical and Chemical Reference Data, Vol: 50, Pages: 1-25, ISSN: 0047-2689

The thermodynamic property data for solid phase I of benzene are reviewed and utilized to develop a new fundamental equation of state (EOS) based on Helmholtz energy, following the methodology used for solid phase I of CO2 by Trusler [J. Phys. Chem. Ref. Data 40, 043105 (2011)]. With temperature and molar volume as independent variables, the EOS is able to calculate all thermodynamic properties of solid benzene at temperatures up to 470 K and at pressures up to 1800 MPa. The model is constructed using the quasi-harmonic approximation, incorporating a Debye oscillator distribution for the vibrons, four discrete modes for the librons, and a further 30 distinct modes for the internal vibrations of the benzene molecule. An anharmonic term is used to account for inevitable deviations from the quasi-harmonic model, which are particularly important near the triple point. The new EOS is able to describe the available experimental data to a level comparable with the likely experimental uncertainties. The estimated relative standard uncertainties of the EOS are 0.2% and 1.5% for molar volume on the sublimation curve and in the compressed solid region, respectively; 8%–1% for isobaric heat capacity on the sublimation curve between 4 K and 278 K; 4% for thermal expansivity; 1% for isentropic bulk modulus; 1% for enthalpy of sublimation and melting; and 3% and 4% for the computed sublimation and melting pressures, respectively. The EOS behaves in a physically reasonable manner at temperatures approaching absolute zero and also at very high pressures.

Journal article

Kim D, Al Ghafri SZS, Yang X, Mylona SK, Hughes TJ, McElroy L, May EFet al., 2021, High Pressure Thermal Conductivity Measurements of Ternary (Methane plus Propane plus Heptane) Mixtures with a Transient Hot-Wire Apparatus, INTERNATIONAL JOURNAL OF THERMOPHYSICS, Vol: 42, ISSN: 0195-928X

Journal article

Al Ghafri SZS, Jiao F, Hughes TJ, Arami-Niya A, Yang X, Siahvashi A, Karimi A, May EFet al., 2021, Natural gas density measurements and the impact of accuracy on process design, FUEL, Vol: 304, ISSN: 0016-2361

Journal article

Oakley J, Xiao X, Al Ghafri SZS, Graham BF, Hughes TJ, May EFet al., 2021, High-Pressure Melting Temperature Measurements in Mixtures Relevant to Liquefied Natural Gas Production and Comparisons with Model Predictions, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 66, Pages: 4103-4111, ISSN: 0021-9568

Journal article

Sadaghiani MS, Arami-Niya A, Marsh B, Al Ghafri SZS, May EFet al., 2021, Vapor-Liquid Equilibria for Carbon Dioxide+3,3,3-Trifluoropropene Binary Mixtures at Temperatures between (288 and 348) K, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 66, Pages: 4044-4055, ISSN: 0021-9568

Journal article

Xiao X, Al Ghafri SZS, Rowland D, Hughes TJ, Hnedkovsky L, Hefter G, May EFet al., 2021, Isobaric heat capacity measurements of natural gas model mixtures (methane + n-heptane) and (propane + n-heptane) by differential scanning calorimetry at temperatures from 313 K to 422 K and pressures up to 31 MPa, Fuel, Vol: 296, ISSN: 0016-2361

Heat capacities of pure methane (1), propane (2) and n-heptane (3), and binary mixtures of (methane or propane + n-heptane) at n-heptane mole fractions of (0.070 to 0.750), were measured at temperatures (313 to 42) K and pressures (6.00 to 31.10) MPa using a Tian-Calvet-type differential scanning calorimeter with a combined standard uncertainty of (2.20 to 2.68) % (k = 1). The results for pure methane, propane and n-heptane agreed within 2% of the values calculated from reference equations of state (EOS). In contrast, for the two sets of mixtures measured above their cricondenbars, averaged absolute deviations of 4.6%, 3.7% and 1.2% were observed between the measured cp values and those predicted by the GERG-2008, Peng-Robinson (PR) and SAFT-γ Mie EOS, respectively. The divergences of cp from model calculations for the binary mixtures near the critical region were also investigated. The root mean square (r.m.s.) deviations of the measured heat capacities from those calculated using the GERG-2008, PR, and SAFT-γ Mie exhibited relatively large but similar values of 7.1%, 7.4% and 7.2% for [0.850 CH4 + 0.150 n-C7H16] and 9.1%, 6.9% and 8.0% for [0.930 C3H8 + 0.070 n-C7H16]. This work reveals that the SAFT-γ Mie EOS can adequately describe most heat capacity data above the cricondenbar, while none of the models provide reliable predictions near the critical region.

Journal article

Siahvashi A, Al Ghafri SZS, Graham BF, May EFet al., 2021, Experimental study of impurity freeze-out in ternary methane plus ethane plus benzene mixtures with applications to LNG production, JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING, Vol: 90, ISSN: 1875-5100

Journal article

Al Ghafri SZS, Perez F, Park KH, Gallagher L, Warr L, Stroda A, Siahvashi A, Ryu Y, Kim S, Kim SG, Seo Y, Johns ML, May EFet al., 2021, Advanced boil-off gas studies for liquefied natural gas, APPLIED THERMAL ENGINEERING, Vol: 189, ISSN: 1359-4311

Journal article

Perez F, Al Ghafri SZS, Gallagher L, Siahvashi A, Ryu Y, Kim S, Kim SG, Johns ML, May EFet al., 2021, Measurements of boil-off gas and strati fi cation in cryogenic liquid nitrogen with implications for the storage and transport of lique fi ed natural gas, ENERGY, Vol: 222, ISSN: 0360-5442

Journal article

Xiao X, Oakley J, Al Ghafri SZS, Hughes T, Rowland D, Hnedkovsky L, Hefter G, May EFet al., 2021, Isobaric heat capacities of a methane (1) + propane (2) mixture by differential scanning calorimetry at near-critical and supercritical conditions, FUEL, Vol: 289, ISSN: 0016-2361

Journal article

Xiao X, Rowland D, Al Ghafri SZS, May EFet al., 2021, Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on <i>Ab Initio</i> Calculations and Viscosity Ratio Measurements (vol 49, 013101, 2020), JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA, Vol: 50, ISSN: 0047-2689

Journal article

Siahvashi A, Al Ghafri SZS, Yang X, Rowland D, May EFet al., 2021, Avoiding costly LNG plant freeze-out-induced shutdowns: Measurement and modelling for neopentane solubility at LNG conditions, ENERGY, Vol: 217, ISSN: 0360-5442

Journal article

Kim D, Yang X, Arami-Niya A, Rowland D, Xiao X, Al Ghafri SZS, Tsuji T, Tanaka Y, Seiki Y, May EFet al., 2020, Thermal conductivity measurements of refrigerant mixtures containing hydrofluorocarbons (HFC-32, HFC-125, HFC-134a), hydrofluoroolefins (HFO-1234yf), and carbon dioxide (CO<sub>2</sub>), JOURNAL OF CHEMICAL THERMODYNAMICS, Vol: 151, ISSN: 0021-9614

Journal article

Souza LFS, Ghafri SZSA, Fandiño O, Martin Trusler JPet al., 2020, Vapor-liquid equilibria, solid-vapor-liquid equilibria and H2S partition coefficient in (CO2 + CH4) at temperatures between (203.96 and 303.15) K at pressures up to 9 MPa, Fluid Phase Equilibria, Vol: 522, Pages: 1-13, ISSN: 0378-3812

Vapor-liquid equilibrium (VLE) measurements of the (CO2 + CH4) system are reported along seven isotherms at temperatures varying from just above the triple point to just below the critical point of CO2 at pressures from the vapor pressure of pure CO2 to approximately 9 MPa, including near-critical states. From these data, the critical locus has been determined and correlated over its entire length. The VLE data are correlated with the Peng-Robinson equation of state (PR-EoS), using a temperature-dependent binary interaction parameter, and also compared with the predictions of the GERG-2008 equation of state. The former represents the phase compositions across all isotherms with a root-mean-square mole-fraction deviation of S = 0.0075 while, for the latter, S = 0.0126. Measurements of the three-phase solid-vapor-liquid equilibrium (SVLE) line are reported at temperatures from approximately (204 to 216) K and a new correlation is developed which is valid from 145 K to the triple point of CO2. Additionally, we report the partitioning of trace levels of H2S between coexisting liquid and vapor phases of the (CO2 + CH4) system and compare the results with the predictions of the PR-EoS.

Journal article

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