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

61 results found

Jiao F, AL Ghafri SZ, Seneviratne KN, Akhfash M, Hughes TJ, Johns ML, May EFet al., 2022, Interfacial tension measurements of methane + propane binary and methane + propane + n-heptane ternary mixtures at low temperatures, Journal of Chemical Thermodynamics, Vol: 171, ISSN: 0021-9614

The interfacial tension (IFT) between a liquid and a gas is essential in the design of liquid-gas separators as it determines the size of liquid droplets which can become entrained in the gas phase. In liquefied natural gas (LNG) plants, the scrub column is designed to remove components heavier than propane. However, if this column is poorly designed, these heavier components can carry over in the top product and potentially cause a solids formation problem in the main cryogenic heat exchanger. Therefore, accurate measurements and predictions of IFT are required to ensure good separation of heavy components prior to the liquefaction of the natural gas. In this work, reference-quality IFT measurements of methane + propane binary mixtures and methane + propane + n-heptane ternary mixtures were conducted at low temperatures (204 to 230) K and pressures up to the mixtures’ critical points using the differential capillary rise method in a high-pressure visual sapphire cell. The combined standard absolute uncertainties of the measured IFT were between (0.04 and 0.96) mN·m−1. The absolute deviations of measured IFT from values predicted with a Parachor model were within 3 mN⋅m−1, while a Linear Gradient Theory model over predicts mixtures’ IFT by up to 5.2 mN⋅m−1. The reference-quality IFT experimental data provided by this work should facilitate improvements of prediction models and allow separators in LNG plants to be designed with more confidence.

Journal article

Li M, Lim VWS, Al Ghafri SZ, Ling N, Adebayo AR, May EF, Johns MLet al., 2022, Minimum miscibility pressure of CO<inf>2</inf> and oil evaluated using MRI and NMR measurements, Journal of Petroleum Science and Engineering, Vol: 214, ISSN: 0920-4105

The minimum miscibility pressure (MMP) between CO2 and crude oil is a critical parameter for CO2 enhanced oil recovery (EOR). Whilst different methodologies have been employed to determine MMP, these methods are either time-consuming or unable to be executed in the actual rock core samples from the relevant reservoir and as such, do not directly consider any accompanying kinetic effects. Here we consider a range of nuclear magnetic resonance (NMR) measurement techniques performed on a benchtop NMR apparatus in terms of their ability to estimate MMP; specifically 1D imaging, self-diffusion measurements and T1/T2 relaxation measurements. Such MMP measurements were performed on two model oils (decane and hexadecane), allowing for validation against comparable MMP literature data, and a local crude oil sample – in this case the results were compared against a PVT measurement performed using a high-pressure variable volume cell (VVC). Reasonably good agreement with these alternative sources of MMP data were realized via NMR measurements of self-diffusion; these provided consistent estimates of MMP for a wider range of oils when compared to 1D imaging and NMR relaxation measurements. NMR T2 measurements however performed equivalently to self-diffusion measurements for higher viscosity fluids based on the limited number of samples studied; such measurements require much simpler NMR hardware and are more readily accessible in both the laboratory and in the field.

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

High boiling-point components in mixed refrigerants can improve the performance of natural gas and hydrogen liquefaction facilities. However, such heavy compounds can freeze out from the refrigerant mixture, posing blockage and plant shutdown risks for cryogenic heat exchangers. To improve the predictions of these conditions, freezing and melting temperatures of pure iso-pentane and (methane + iso-pentane) binary systems were measured at temperatures down to 87.5 K and pressures up to 13 MPa. The iso-pentane melting data are compared with predictions of a thermodynamic model embedded in the ThermoFAST software package. Adjusting the model's fusion molar volume change parameter to force agreement with the measurements reduced the deviations of the experimental data from the model by over 90% relative to the default parameter value. The measured melting data for binary mixtures were used to confirm solubility predictions for iso-pentane in mixed refrigerants. Adding 20 mol% iso-pentane to a methane-rich refrigerant increases the available duty for cooling natural gas or hydrogen from (313–123) K by a factor of three. This improvement outweighs the risk of freeze-out in this refrigerant with the melting temperature being 98 K, which is 15 K lower than the minimum temperature needed for LNG production.

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: 029901-029901, ISSN: 0047-2689

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

Growing interest in liquefied natural gas (LNG) as a rocket fuel demands reliable prediction and an improved understanding of the changes in its composition arising from the preferential boil-off of lighter components during long duration storage. Unfortunately, current methods of predicting boil-off gas (BOG) evolution from cryogenic liquids are based on limited experimental data. This work reports a series of new experiments which measure the temporal change in BOG production, composition, and pressure at industrially relevant conditions for both ternary mixtures of methane, ethane, and nitrogen and an LNG mixture used as rocket fuel. Faster pressure build-up rates are consistently observed with decreasing initial liquid volume fraction, whilst a decline of 8% in the LNG higher heating value was observed after thirty-three days of weathering. The data is compared with a robust and efficient superheated vapor (SHV) model, implemented in the software package BoilFAST, which allows for reliable calculations of self-pressurisation and boil-off losses for different tank geometries and thermal insulation systems. The model exhibits good agreement with the experimental data across all conditions explored. Finally, the potential effect of LNG composition and heating value changes on rocket engine performance was assessed by examining changes in the adiabatic flame temperature and burnt gas volume ratio. While our data suggest that the rocket engine performance would improve as a result of weathering, the effectiveness of the weathered LNG as a coolant in a regeneratively cooled rocket engine decreases.

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, ISSN: 0047-2689

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, 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

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

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

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

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

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

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

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

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

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

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

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 (CO2), 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

Arami-Niya A, Xiao X, Al Ghafri SZS, Jiao F, Khamphasith M, Pouya ES, Sadaghiani MS, Yang X, Tsuji T, Tanaka Y, Seiki Y, May EFet al., 2020, Measurement and modelling of the thermodynamic properties of carbon dioxide mixtures with HFO-1234yf, HFC-125, HFC-134a, and HFC-32: vapour-liquid equilibrium, density, and heat capacity, INTERNATIONAL JOURNAL OF REFRIGERATION, Vol: 118, Pages: 514-528, ISSN: 0140-7007

Journal article

Yang X, Arami-Niya A, Xiao X, Kim D, Al Ghafri SZS, Tsuji T, Tanaka Y, Seiki Y, May EFet al., 2020, Viscosity Measurements of Binary and Multicomponent Refrigerant Mixtures Containing HFC-32, HFC-125, HFC-134a, HFO-1234yf, and CO2, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 65, Pages: 4252-4262, ISSN: 0021-9568

Journal article

Al Habsi SSA, Al Ghafri SZS, Bamagain R, Martin Trusler JPet al., 2020, Experimental and modelling study of the phase behavior of (methyl propanoate + carbon dioxide) at temperatures between (298.15 and 423.15) K and pressures up to 20 MPa, Fluid Phase Equilibria, Vol: 519, Pages: 1-8, ISSN: 0378-3812

In this work, we report phase equilibrium measurements on the system (methyl propanoate + carbon dioxide) carried out with a high-pressure quasi-static-analytical apparatus. The measurements were made along six isotherms at temperatures from (298.15 to 423.15) K and at pressures up to the critical pressure at each temperature. Vapor-liquid equilibrium (VLE) data obtained for the mixture have been compared with the predictions of the Statistical Associating Fluid Theory coupled with the Mie potential and a group-contribution approach for the functional group interaction parameters (SAFT-γ Mie). The group interaction parameters in SAFT-γ Mie for the COO–CO2 interaction have been revised in this work by fitting to our experimental VLE data. After tuning, the SAFT model was found to be in good agreement with the measured data for both the liquid and vapor phases. Additionally, the data were compared with the predictions of the Peng-Robinson equation of state (PR-EoS) with one-fluid mixing rules and a temperature-independent binary parameter. This model fitted the VLE data well, except in the critical region. The present work is expected to contribute to optimization of biodiesel production processes.

Journal article

Siahvashi A, Al Ghafri SZS, May EF, 2020, Solid-fluid equilibrium measurements of benzene in methane and implications for freeze-out at LNG conditions, FLUID PHASE EQUILIBRIA, Vol: 519, ISSN: 0378-3812

Journal article

Al Ghafri SZS, Hughes TJ, Perez F, Baker CJ, Siahvashi A, Karimi A, Arami-Niya A, May EFet al., 2020, Phase equilibrium studies of high-pressure natural gas mixtures with toluene for LNG applications, FLUID PHASE EQUILIBRIA, Vol: 518, ISSN: 0378-3812

Journal article

Jiao F, Al Ghafri SZS, Hughes TJ, May EFet al., 2020, Extended calibration of a vibrating tube densimeter and new reference density data for a methane-propane mixture at temperatures from (203 to 423) K and pressures to 35 MPa, JOURNAL OF MOLECULAR LIQUIDS, Vol: 310, ISSN: 0167-7322

Journal article

Xiao X, Rowland D, Al Ghafri SZS, May EFet al., 2020, Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on Ab Initio Calculations and Viscosity Ratio Measurements (vol 49, 029901, 2019), JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA, Vol: 49, ISSN: 0047-2689

Journal article

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