Comparison of Commercial and Open-Source CFD Solvers on Surface Tension Dominated Flows

Problems involving multiphase flows require a physical understanding of how the phenomenadevelop and the specific interactions they manifest. For surface tension relevant flows, suchas bubbles and droplets, the importance of modelling and predicting small-scale behaviouris crucial in accurately defining the liquid-gas interface and complex interactions that may takeplace. Axisymmetric numerical simulations of single droplets impacting onto thin liquid films areperformed using commercial and open-source CFD codes. ANSYS Fluent®is the commercialsoftware employed, whereas Basilisk is the open-source CFD solver adopted. The incompress-ible Navier-Stokes equations are coupled and handled differently throughout each software.A solution-adaptive mesh refinement tool is adopted to reduce computational cost. Softwarecomparison is based on quantitative and qualitative analysis, namely crown height and outerdiameter measurements, and the crown curvature and occurrence of splashing, respectively.Results show that Basilisk simulations are in good agreement with the experimental data. Fluent follows the tendency for the crown outer diameter however, in terms of height, the modelunder-predicts its growth and collapses at later stages of the impact for lower thicknessesFundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Effect of Vapour Bubble Initial Displacement on Droplet Impact onto Liquid Films

Heat and mass transfer mechanisms regarding droplet impact have been extensively studied for dry surfaces, and in terms of droplet evaporation/combustion during free-fall. On the contrary, the droplet impact phenomena onto heated liquid films is a topic overlooked in the literature and requires further understanding in terms of hydrodynamics and phase change. Therefore, this work focuses on numerically simulating droplet impact onto liquid films in the presence of vapour bubbles. The crown height, diameter and overall development are analysed as a function of the position of the bubble related to the axis of symmetry. Results show that the crown overall growth is affected if the vapour bubbles detach and contact the crown wall. The size of the vapour bubbles also influences the detachment from the surface.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Influence of Dimensionless Temperature on Droplet Impact onto Heated Liquid Films for Subcooled Boiling Regimes

Heat and mass transfer mechanisms related to multiphase flows occur in several applications such as spray cooling, quenching, internal combustion engines and plasma spraying. These mechanisms have become increasingly important due to the need of achieving higher heat rate coefficients associated with phase-change processes, such as evaporation and condensation. Specifically, the phenomenon of droplet impact onto non-heated liquid films has been extensively researched, both experimentally and numerically. However, the influence of temperature on droplet impact and liquid film stability has been overlooked in the literature, which is a focal point in understanding interfacial phenomena. The main objective of this work is to experimentally study droplet impact onto heated liquid films. Therefore, an experimental facility was designed for this purpose. A borosilicate glass surface is used to contain the liquid film. This surface is placed above an aluminium block with four embedded cartridge heaters of 250W each, heating the liquid film by conduction. Immersion type-k thermocouples are employed for liquid film temperature measurements. Liquid film evaporation rates are calculated in order to ensure the liquid film thickness prior to the droplet impact. Water and n-decane are the fluids adopted due to their differences in thermophysical properties and saturation temperature. The impact conditions are 100 < W e < 300, 0.5 < h* < 1.5, and a dimensionless temperature of θ < 0.6. Qualitative analysis is performed regarding crater and central jet evolution, and quantitative data regarding evaporation rate and central jet height are measured. The dimensionless temperature affects the droplet impact phenomena, creating recirculation zones near the crater and the impact surface, and affecting the crater formation. The central jet height increases with increasing values of θ for h* = 1.0 and h* = 1.5, whereas for h* = 0.5, the measurements do not follow a similar tendency. The emerging time of the central jet is delayed for higher values of θ, meaning that future studies regarding crater evolution should be considered. The dimensionless temperature also promotes central jet breakup, as well increasing the number of secondary droplets originated from the breakup.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Influence of Vapour Bubbles Size and Spacing on Droplet Impact Outcomes under Subcooled Boiling Regimes

Multiphase flows are characterised as heterogeneous mixtures of two or more phases, such as gas-liquid or solid-liquid. These are extremely complex due to the underlying dynamics that may occur, which include interfacial phenomena, such as boiling and evaporation, and interactions between phases. Specifically, droplet impact onto heated wetted surfaces has been overlooked in the literature, which involves heat and mass transfer mechanisms related to sensible heating, condensation and evaporation. The droplet impact phenomenon occurs in several industrial applications, such as internal combustion engines, electronics cooling devices, heat exchangers, among others. In numerical terms, improving efficiency and reliability of simulations is of interest to understand the behaviour of mathematical models for complex physical systems. The main objective of this work is to numerically simulate droplet impact onto a heated liquid film in the presence of vapour bubbles in a 2D-axisymmetric assumption. The numerical model solves the incompressible mass, momentum and energy equations coupled with the VOF method and height functions for accurately capturing the interface. Phase-change processes such as evaporation and condensation are neglected for the current simulations. Water and n-decane are the fluids adopted for the simulation. The impact conditions are D0 = 3.0 mm, h* = 0.5, and U0 = 3.0 m/s. Different vapour bubble sizes, (Dv), and spacings, (xv), are studied to evaluate the vapour bubble phenomena and crown geometrical parameters. An initial vapour bubble is positioned on the axis of symmetry, xs = 0, and, therefore, in the droplet trajectory. Results indicate that vapour bubbles have a lower influence on crown diameter, and a higher influence on crown height. Increasing the size of vapour bubbles leads to a decrease in both crown diameter and height, whereas an increase in the vapour bubbles spacing causes an increase in the crown height and diameter. The initial vapour bubble positioning in relation to the axis of symmetry is a factor that should also be considered in future studies.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

The impact of temperature on heated liquid films: Crater and jetting impact dynamics

The droplet impact phenomena onto liquid films are a field extensively researched for over a century, which are driven by many practical applications such as heat exchangers, internal combustion engines and spray cooling. Despite the extensive work on wetted surfaces, the influence of temperature on droplet outcome, local evaporation/boiling effects, and liquid film stability has been overlooked in the literature. Therefore, the main objective of this work is to evaluate the influence of the liquid film temperature on the crater and jet dynamics. The experimental setup was designed for this purpose, in which a borosilicate glass surface that contains the liquid film is placed over an aluminium block with embedded cartridge heaters, heating it by conduction. Water, n-decane and n-heptane are the fluids adopted for the experiments due to their differences in thermophysical properties and saturation temperature. Different conditions are considered, which include two dimensionless thicknesses, h*= 1.0 and h*=1.5, and a range of dimensionless temperatures, theta = 0, theta = 0.2, theta = 0.4 and theta = 0.6. Qualitative and quantitative analyses are performed regarding crater evolution, and central jet height and breakup measurements, respectively. Evaporation rate measurements are required due to the influence on the liquid film thickness variation. Qualitative results show that temperature differences promote the formation of recirculation zones near the impact surface and the crater boundaries, as well as the influence on the crater shape and curvature. In terms of the quantitative analysis, the central jet height measurements for the n-heptane and n-decane reveal that higher values of the dimensionless temperature lead to an increase in the jet height, as well as promoting and increasing the occurrence and number of secondary droplets, respectively. Water follows a similar trend with the exception of theta = 0.2, which can be explained by a time scale analysis.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

A study of droplet deformation: The effect of crossflow velocity on jet fuel and biofuel droplets impinging onto a dry smooth surface

The aeronautical sector has been, in the last decade, one of those that most invested in more efficient and ecological solutions in order to reduce significantly greenhouse gas and pollutant emissions. The introduction of biofuels in fuel mixtures for aircraft engines is a promising alternative in this sector. The main objective of this experimental study is understanding the influence of crossflow variation on droplet deformation and consequent impact outcomes. An experimental facility was developed and validated to study the impact of single droplets onto a dry, smooth aluminium impact surface under the influence of several crossflow velocities. Different crossflow velocities of 4,5,6,7 and 8m/s were tested. A combination of conventional jet fuel and a biofuel was considered to understand the behavior of jet fuel and biofuel mixtures, and three fluids were used: 100% jet fuel, 75% jet fuel/25% biofuel and 50% jet fuel/50% biofuel. Several parameters, including velocity components, impact angle and eccentricity, were analysed for the different crossflow velocities, and the spread and splash regimes were also defined for the different fluids. The results display that, for each crossflow velocity, an increase in the droplet impact velocity causes a shift from the spread to the splash regime. The presence of a crossflow induces deformation on the droplet, altering its outcome. Ellipsoidal droplets promote the occurrence of spreading, whereas splashing tends to occur for spherical forms, corresponding to higher and lower eccentricity values, respectively. A substantial increase in the crossflow velocity leads to aerodynamic breakup of the droplet.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

BioWorkbench: A High-Performance Framework for Managing and Analyzing Bioinformatics Experiments

Advances in sequencing techniques have led to exponential growth in biological data, demanding the development of large-scale bioinformatics experiments. Because these experiments are computation- and data-intensive, they require high-performance computing (HPC) techniques and can benefit from specialized technologies such as Scientific Workflow Management Systems (SWfMS) and databases. In this work, we present BioWorkbench, a framework for managing and analyzing bioinformatics experiments. This framework automatically collects provenance data, including both performance data from workflow execution and data from the scientific domain of the workflow application. Provenance data can be analyzed through a web application that abstracts a set of queries to the provenance database, simplifying access to provenance information. We evaluate BioWorkbench using three case studies: SwiftPhylo, a phylogenetic tree assembly workflow; SwiftGECKO, a comparative genomics workflow; and RASflow, a RASopathy analysis workflow. We analyze each workflow from both computational and scientific domain perspectives, by using queries to a provenance and annotation database. Some of these queries are available as a pre-built feature of the BioWorkbench web application. Through the provenance data, we show that the framework is scalable and achieves high-performance, reducing up to 98% of the case studies execution time. We also show how the application of machine learning techniques can enrich the analysis process

Nutritional evaluation of flour obtained from Tacca leontopetaloides used as an alternative food in Muanza-Mozambique

Tubers from wild Tacca leontopetaloides plants are frequently used as a food commodity, but when consumed raw it has a bitter taste and can be toxic, thus threatening food security. This study aimed to evaluate the nutritional composition of flour from T. leontopetaloides subjected to distinct washing treatments, hoping to improve its suitability as a pivot food commodity in regions affected by poverty and food insecurity, such as Muanza (Sofala, Mozambique). To remove the bitter taste and potentially toxic compounds, flour from T. leontopetaloides was subjected to a single washing (SW) and to 13 sequential deep washing cycles (DW). Samples were analysed for several nutritional and mineral parameters, including carbohydrates, proteins, lipids, fibre, energy, phosphorous, potassium, calcium, magnesium, and sodium. Flours prepared with SW had (per 100 g): 5.25 mg proteins, 0.73 mg fats, 0.43 mg fibres, 935 mg phosphorous, 833.7 mg potassium, 120 mg calcium, 275.3 mg magnesium, and 333.6 mg sum. Deep washing significantly decreased protein (80%) and mineral contents (by at least 27%) and eliminated the presence of glycosides and quinones, but a rich nutritional profile was still preserved after this procedure. Overall, T. leontopetaloides flour has a balanced nutritional profile when adequately washed, thus serving as a promising food commodity.info:eu-repo/semantics/publishedVersio