Measurements of particle and fluid velocities are reported for a turbulent, liquid-solid, sudden expansion flow flowing in the direction of gravity and laden with solid particles, at loadings equal to 1, 2, 3, 4, and 5 percent per volume. The measured two-phase flow velocities are compared to the characteristics of the corresponding single phase flow. Forces and flow mechanisms affecting particle dispersion in the various flow regimes are identified and it is indicated that there exist regions where the transverse Saffman lift force attains high values and controls particle dispersion. A consistent correlation between the mean reattachment point and the volumetric particle loading is indicated. All the two phase flows examined reattached upstream the corresponding mean reattachment location measured for the single phase flow. Increasing particle concentration affected locally the flow behaviour, with most obvious consequences within the recirculation zone and the near wall region.
This paper addresses the thermal bridges issues of a two storey lightweight steel framed envelope in which the VIPs are placed in an inner "protected" layer of the external walls. This configuration provides "protection" for the VIPs, allows flexibility in installation of facade elements and at the same time permits interventions and modifications (e.g. drilling, installation of appliances) on the internal side of the wall. The envelope is extensively analysed in terms of all the different types of thermal bridges utilizing commercial computational tools and standardized methodologies, and their effect on the overall thermal performance is evaluated. A total improvement of 33% on the heat transfer coefficient of the building is calculated. Results indicate the junctions between the external and internal walls, the external walls and the ceiling, the internal walls and the roof and the internal walls and the floor, respectively, as the most crucial thermal bridges. Different design modifications and solutions are assumed in order to further reduce the impact of the most crucial thermal bridges. The implementation of the modifications resulted in a further reduction of the overall thermal losses by 27.5%, leading to an overall thermal loss reduction by 60.5% as compared to the reference building.
Abstract. Solar walls can be used to increase the overall energy efficiency of a building. Phase Change Materials (PCM) are capable of increasing the effective thermal mass of building elements, thus decreasing the overall energy consumption. Recently, the incorporation of PCM in a solar wall has been proposed, aiming to increase the total energy efficiency of the system. The main scope of this work is to investigate the thermal behaviour of a PCM-enhanced solar wall (PCMESW), using experimental and numerical simulation techniques. A prototype PCMESW is installed in a large-scale test facility and is exposed to dynamically changing climate conditions. A broad range of sensors, used to monitor the time-evolution of several important physical parameters, is employed to assess the dynamic response of the PCMESW. In addition, a Computational Fluid Dynamics tool is used to numerically investigate the thermal behaviour of the PCMESW prototype. Predictions of the developing flow-and thermal-field in the PCMESW's air cavity are validated by means of comparison with the obtained measurements; in general, good levels of agreement are observed. Results of the numerical simulations may support the design optimization process of innovative PCMESW systems.
Summary During a fire event, ventilated facade systems may contribute to external fire spreading to the upper floors of a building via the facade, thus representing a significant risk. In this frame, the performance of a typical ventilated façade system under fire conditions is experimentally investigated, using a full‐scale compartment‐facade test rig. Two alternative façade configurations are examined and comparatively assessed, namely a plain façade (PF) and a ventilated façade (VF) system. Emphasis is given on the estimation of the thermal characteristics of the developed Externally Venting Flames (EVF) and the thermal boundary conditions developing on the façade's exposed surface. An extensive set of sensors was installed at the interior of the fire compartment, the façade systems and the exterior of the test configurations. Analysis of the experimental data suggests that even though gaseous combustion products managed to penetrate the air cavity of the VF system, no consistent flaming conditions were established. On the unexposed face of both PF and VF systems, temperatures remained constantly below 180°C throughout the duration of both fire tests. The Eurocode correlations are assessed against the obtained experimental data; certain parameters, such as EVF length, width and centreline temperature, are found to be under‐estimated by the Eurocode methodology.
urbulent jets impinging on plane surfaces are used extensively in the process industries to achieve intense heating, cooling or T drying rates. Examples can be drawn from the drying and blasting processes, from glass melting, from metal cutting and forming, from fire testing of building materials, from oxy-flame and bonding applications, etc.The isothermal velocity field and the overall heat and mass transfer performance of jet impingement flows have been experimentally and computationally examined by several researchers (e.g., Jambunathan et al., 1992; Baugh and Shimizu, 1989; Cooper et a1.,1993;Craft et al., 1993). The flame impingement heat transfer effects, thermal conduction, non-luminous gaseous radiation, forced convection and thermochemical heat release have been studied by Hoogendoorm e t al. (1 978), Baukal et al. (1996), and Cebhart (1997) Mathematical FormulationA finite volume approach for the solution of the elliptic momentum, energy and turbulent transport equations has been adopted. The resulting system of partial differential equations has been solved, along with the boundary and inlet conditions, in their two-dimensional form using Cartesian coordinates and an iterative procedure is employed, based on a staggered grid arrangement, using the SIMPLEST algorithm, the second order upwind differencing discretization scheme and the Tri-Diagonal Matrix Algorithm.'Author to whom correspondence niay be addressed. E-mail address: N.Markatos@ tihra.gr 834This work investigates the effects of varying the pressure of the mixture reactants and the angle of impingement on the performance characteristics of a turbulent premixed jet flame impinging on a solid surface. These effects are important for the design of torches and flaming machines used for material and metal cutting and forming. The combustion and flow characteristics are modelled using a finite volume computational approach. Based on the simulation results, it is shown that, by increasing the pressure of the mixture reactants, the flame-surface interaction mechanisms are modified. Changing the impingement angle increases the role of chemical kinetics and reduces maximum temperature values due to increased local flame extinction. The heat released and temperature predictions are compared to experimental data and the agreement is satisfactory.
The sections in this article are Introduction Theory Phenomenology Negative Temperature Coefficient ( NTC ) Stabilized Cool Flames Chemical Kinetics Applications Liquid Fuel Evaporation for Premixed Combustion Liquid Fuel Reforming for Fuel Cell Applications Internal Combustion Engines Knocking Low‐Temperature Combustion and HCCI Engines Lean Premixed Prevaporized Combustion in Gas Turbines Industrial Safety Numerical Modeling of Stabilized Cool Flame Reactors One‐Dimensional Chemical Kinetics Simulation of a Linear Flow SCF Reactor Two‐Dimensional Two‐Phase CFD Simulation of a Linear Flow SCF Reactor Three‐Dimensional Two‐Phase CFD Simulation of a Recirculating Flow SCF Reactor Outlook Summary
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