Direct numerical simulation of heat transport in dispersed gas-liquid two-phase flow using a front tracking approach

In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of heat transport in dispersed gas-liquid two-phase flow using the Front Tracking (FT) approach. Our model extends the FT model developed by van Sint Annaland et al. (2006) to non-isothermal conditions. In FT an unstructured dynamic mesh is used to represent and track the interface explicitly by a number of interconnected marker points. The Lagrangian representation of the interface avoids the necessity to reconstruct the interface from the local distribution of the fractions of the phases and, moreover, allows a direct and accurate calculation of the surface tension force circumventing the (problematic) computation of the interface curvature. The extended model is applied to predict the heat exchange rate between the liquid and a hot wall kept at a fixed temperature. It is found that the wall-to-liquid heat transfer coefficient exhibits a maximum in the vicinity of the bubble that can be attributed to the locally decreased thickness of the thermal boundary layer

Direct numerical simulation of complex multi-fluid flows using a combined immersed boundary (IB) and volume of fluid (VOF) approach

In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of complex multi-fluid flows in which simultaneously (moving) deformable (drops or bubbles) and non-deformable (moving) elements (particles) are present, possibly with the additional presence of free surfaces. Our model combines the VOF model developed by van Sint Annaland et al. (2005) and the Immersed Boundary (IB) model The Volume of Fluid (VOF) part features i) an interface reconstruction technique based on piecewise linear interface representation ii) a three-dimensional version of the CSF model of Brackbill et al. (1992). The Immersed Boundary (IB) part incorporates both particle-fluid and particle-particle interaction via a Direct Forcing Method (DFM) and a hard sphere Discrete Particle (DP) approach. In our model a fixed (Eulerian) grid is utilized to solve the Navier-Stokes equations for the entire computational domain. The no-slip condition at the surface of the moving particles is enforced via a momentum source term which only acts in the vicinity of the particle surface. Specifically Lagrangian force points are used which are distributed evenly over the surface of the particle. Dissipative particle-particle and/or particle-wall collisions are accounted via a hard sphere DP approach using a three-parameter particle-particle interaction model accounting for normal and tangential restitution and tangential friction. The capabilities of the hybrid VOF-IB model are demonstrated with a number of examples in which complex topological changes in the interface are encountered

Direct Numerical Simulation of Particle Mixing in Dispersed Gas-Liquid-Solid Flows using a Combined Volume Of Fluid and Discrete Particle Approach

In this paper a hybrid model is presented for the numerical simulation of gas-liquid-solid flows using a combined Volume Of Fluid (VOF) and Discrete Particle (DP) approach applied for respectively dispersed gas bubbles and solid particles present in the continuous liquid phase. The hard sphere DP model, originally developed by Hoomans et al. (1996) for dense gas-solid systems, has been extended to account for all additional forces acting on particles suspended in a viscous liquid and has been combined with the VOF model presented recently by van Sint Annaland et al. (2005) for complex free surface flows. In this paper the physical foundation of the combined VOF-DP model will be presented together with illustrative computational results highlighting the capabilities of this hybrid model. The effect of bubble-induced particle mixing has been studied focusing on the effect of the volumetric particle concentration. In addition particle mixing was studied in systems with coalescing bubbles

Managing Achilles Pain (the MAP study) – A process evaluation of data collection methods

Background Process evaluations explore the way in which a study was conducted. The Managing Achilles Pain study (MAP study) had the primary aim of assessing the feasibility of the protocol for a future large longitudinal cohort study that would investigate the association and predictive relationship of self-efficacy, working alliance and expectations with outcome in the management of Achilles tendinopathy. Objectives This study aimed to evaluate the processes conducted in the MAP study by exploring the acceptability of the study procedures from the participants' and physiotherapists' perspectives. Design A qualitative evaluation using semi-structured telephone interviews. Method All physiotherapists and participants who participated in the MAP study were invited. Data from physiotherapists (n = 6) and participants (n = 7) were transcribed and analysed using the Framework Approach. Findings From the physiotherapists' perspective 4 themes were identified relating to obstacles; (1) access to participants; (2) recall; (3) visibility; (4) time, and 4 themes were identified relating to facilitating success; (1) training; (2) motivation; (3) incentives; (4) simplicity. From the participants' perspective 2 themes were identified relating to obstacles; (1) information from the physiotherapist; (2) follow up, 3 themes were identified relating to facilitating success; (1) motivation; (2) website; (3) questionnaire, and 1 theme relating to unintended consequences of participating in the study; positive experience. Conclusions Although clinicians are enthused to be involved in research, organisational factors impact levels of engagement. Key influences to optimising the potential success of a study include the publicising of the study; optimising verbal recruitment strategies; and clarity in communication

Chemische Proces Intensificatie

Introductie nieuwe leerstoel Chemische Proces Intensificati

Wiskunde onmisbaar onderdeel van proceschemie

Duurzame energie is in opmars. Toch zijn we nog voor een groot deel afhankelijk van fossiele brandstoffen. Hoe benut je die brandstoffen zo efficiënt mogelijk met zo min mogelijk schade voor het milieu? De NLT-module ‘Oude energie in nieuwe vaten’ gaat hier uitgebreid op in. Naast de nodige scheikunde bevat de module een flinke portie wiskunde. Martin van Sint Annaland, hoogleraar Chemical Process Intensification aan de Technische Universiteit in Eindhoven, was betrokken bij de ontwikkeling van de NLT-module en vertelt ons iets over de achtergronden. In de proceschemie ontstaat er steeds meer belangstelling voor het efficiënter benutten van grondstoffen en energie , legt Van Sint Annaland uit. Daarnaast wil je schadelijke bijproducten zoveel mogelijk voorkomen. Het komt dus neer op meer en veiligere producten maken met minder grondstoffen en minder energie