Papers by Keyword: Liquid Fraction

Abstract: The depletion of fossil fuels and the environmental burden of biomass residues have driven interest in hydrothermal carbonization as a sustainable pathway for energy and material production. This study investigates the valorization of coffee parchment, an underutilized by-product of coffee processing, through microwave-assisted hydrothermal carbonization with liquid fraction recirculation. The primary aim was to evaluate how operating conditions and liquid reuse affect hydrochar properties and process efficiency. Experiments were conducted at temperatures between 70 and 110 °C and residence times from 60 to 180 minutes, using a modified microwave reactor. Hydrochar samples were characterized for surface acidity, functional groups, iodine number, and morphology, while the recirculated liquid fraction was monitored for its influence on subsequent reactions. Results show that total acid density increased with temperature and time, peaking at 3.39 mmol g⁻¹ at 110 °C and 180 minutes, while sulfonic and weak acid densities remained unchanged. Liquid fraction recirculation enhanced surface acidity but reduced iodine number and porosity due to pore blockage from soluble organics. FTIR analysis confirmed enrichment of oxygenated groups, and SEM images revealed cavity formation and pore collapse across recirculation cycles. These findings highlight the potential of liquid fraction recirculation to tailor hydrochar properties for catalytic rather than adsorptive applications, advancing sustainable strategies for coffee waste utilization.

Abstract: This work investigated liquid fraction in ZA27 zinc alloy interlayered with SSC-ADC12 aluminum alloy workpieces for Transient Liquid Phase (TLP) diffusion bonding. The results clearly indicated that liquid fraction had a necessary influence on TLP diffusion bonding. In other words, the high liquid fraction and bonding time tends to produce excellent bond strength. The maximum bond strength at 27.21 MPa was from 100% liquid fraction and 90 min from bonding time. The hardness increased by approximately 23.36% comparing to SSC-ADC12 aluminum alloy and by 11.18% comparing to the ZA27 zinc alloy. The microstructure was homogeneous in the bond line and formed to MgZn₂ and CuZn₄ intermetallic compound under Scanning Electron Microscope. According to Energy Dispersive X-Ray Spectrometer analysis, Zn atoms had the ability to move about 4.381 mm from the bond line and the elements' uniform distribution.

Abstract: The foundry casting process is complex and takes various stages to produce the desired component; as a result, simulation is necessary before manufacturing. Hot spots are areas that become thermally isolated and take the longest to cool, resulting in cavities during the solidification of the casting. So it is important to know about the hot spot location and size so that any casting designer can identify the hot spot behaviours before the casting. To predict the initiation of the hot spot, a 3D aluminium permanent mould casting model has been developed by Ansys Fluent. The suitable boundary and initial conditions such as temperature, pressure, convectional heat transfer coefficient, etc. are reasonably established in the simulation of Ansys Fluent. The simulation has been performed for varied pouring parameters i.e. pouring velocity and pouring temperature, to examine the beginning of hot spots. This study can predict the position and approximate size of the hot spots for various pouring conditions and it is found that a hot spot is commonly located below the riser.

Abstract: A numerical modeling of diffusion-controlled heat and specie transfer using a source base method to determine evolution of liquid/solid fraction from energy equation both for constant densities in the phases and variable densities as a function of temperature and concentration was developed to predict macro-solute redistribution in binary alloy system. From the results, it is observed that there was a solute depleted zone near the chill surface and that, the source base method can be effectively implemented without the need for setting a large arbitrary value in determining the derivative of liquid fraction-temperature function . The cooling curve and the liquid volume fraction versus temperature profile shows a smooth transition from fully liquid to mushy zone and then to fully solid state, hence, adequate handling of the jump discontinuity was ensured. The liquid fraction-temperature relation outlined in this work is suitable for tracking the liquid/solid interface.

Abstract: The fraction liquid present during semi-solid processing has a critical effect. Conventionally the process window has been defined by inspecting the liquid fraction versus temperature curve (derived from thermodynamic prediction using a thermodynamic prediction software package for example, or derived from differential scanning calorimetry results). It has been assumed that a freezing range with temperature is required for semi-solid processing to be possible. However, recently a South African group (Curle, Moller and Wilkins) has shown that it is possible to rheo-process both high-purity aluminium and a binary Al-Si eutectic alloy i.e. materials with no freezing range. This behaviour highlights the fact that it takes time for liquid to form i.e. the kinetics of melting are important. Here the liquid fraction vs time for high purity aluminium is derived from experimental results to identify the process window in terms of time rather than temperature. The time sensitivity in thixoforming or rheocasting depends on the sample mass, the heat flux and the phase transformation temperature. It is also important in determining the vulnerability to defects such as hot tears, which tend to occur particularly with the alloys which are conventionally wrought rather than cast such as the 2000 series aluminium alloys.

Abstract: In case of metal sheet forming of alloys in semisolid state, modelling of the process is very essential to predict flow behaviour, temperature distribution of the alloy etc. towards improvement of the product quality and to reduce manufacturing costs. Accordingly, the present work develops a model to predict the behaviour during metal sheet forming of an Al-alloy (A356) in semisolid state. The semisolid alloy passes through a rectangular channel having small depth and larger width. The alloy in semisolid state is cooled from the top at a controlled rate. In the model, the respective flow field is represented by the momentum conservation equation. The non-Newtonian behaviour of the semisolid slurry is incorporated considering the Herschel–Bulkley model. The agglomeration and de-agglomeration phenomena of the suspended particles under shear are represented using a time dependent structural parameter. The temperature field is predicted considering the transient energy conservation equation, and hence the fraction of solid is continuously updated. The solution considers an apparent viscosity of the semisolid alloy as a function of structural parameter, shear stress and shear rate. The governing equations are finally solved by finite difference method. The work predicts velocity, temperature and liquid fraction distribution of the semisolid slurry.

Abstract: This work brings out the numerical simulation of the stir casting technique for aluminium silicon carbide Metal Matrix Composite (MMC) in a closed crucible and the effect of the blade geometry and rotational velocity on solidification of the metal matrix composite has been predictedusing Computational Fluid Dynamics (CFD) approach. The material used in the crucible is silicon carbide in aluminiummetal matrix. Geometric modelling and meshing have been carried out using ANSYS ICEM CFD. Computer simulations have been carried using the commercial CFD package, ANSYS FLUENT. The calculations used 2-D discrete phase, solidification and melting model and enthalpy method. Mushy state mixing, indicative of the solidification patterns have been studied to predict the most suitable ratio of crucible to blade dimensions and speed of stirring to obtain the most uniform type of solidification which in turn induces some enhanced mechanical properties to the casting.

Abstract: We have previously investigated foams with monodispersed bubbles using a polarised light scattering technique. The liquid fraction and the bubble size distribution were found to influence scattering properties of polarised light and correlate with the Mueller matrix elements. This paper focused on an investigation of the Mueller matrix of a bidispersed foam. Comparisons were made between the results of bidispersed foam and monodispersed foam.

Abstract: The processing window is important for the semisolid processability of alloys. This study focusses on the kinetics of diffusion. It compares prediction of fraction liquid versus temperature taking into account both thermodynamic and kinetics, with experimental results from Differential Scanning Calorimetry (DSC) and Single Pan Scanning Calorimetry (SPSC). SPSC is a novel technique with an order of magnitude higher accuracy than DSC. A range of Al-Si binary alloys has been investigated. The studies reveal that the simulation results predicted by DICTRA (DIffusion-Controlled TRAnsformations) show the same pattern with experimental results in the relationship of fraction liquid-temperature. However, the SPSC results are closer to the prediction results than DSC curves even with the relatively large sample size associated with SPSC. This is potentially a significant result as conventionally one of the difficulties is predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing. DSC results are known to be unrepresentative because the heating rates which can be achieved in DSC are much lower than those in induction heating. In addition, the DSC results are dependent on sample size and heating rate. The long term aim is to gain confidence in prediction with software packages which will reduce trial and error.