1,720,976 research outputs found
A streamfunction-vorticity formulation of spatially periodic flows
No full textIn this paper we implement the spatially periodic boundary conditions in finite element solutions of the Navier-Stokes equations based on the streamfunction-vorticity formulation. Periodic boundary conditions are enforced at both inflow/outflow and lower/upper boundaries. As an example of application we consider the fluid flow, at two different Reynolds numbers, through an array of pin fins. The limiting assumption of symmetry conditions at the boundaries parallel to the main flow is shown to yield unphysical-looking configurations
Climatic change mitigation: analysis of electrical fans usage impact on dwellers heat stress
Full text linkClimate change is responsible for a consistent increase in ambient temperatures, leading to social and health problems for individuals residing indoors. The effect should be seriously considered by authorities, especially regarding people's health; high temperatures can be very dangerous for elder people and in general for vulnerable categories. Mitigation approaches are important in case of heat waves that are expected to increase in frequency and intensity due to climatic change effects. One approach for avoiding such a problem is to install cooling systems, but sometimes this isn't a viable solution, for example in case of low-income families which cannot afford the expense for the installation and the bill costs for running such systems. An alternative solution is using electric ventilators and the main objective of this paper is to revise the effect of electric fans and assess if they can be useful for mitigating the heat effect on people inside buildings. The results showed that the number of hours with people exposed to heat strain, in the worst-case scenario, dropped from 168 without a fan to 13 with an active fan, confirming the positive effect of this system
Thermal Comfort and Energy Saving Optimization for HVAC Systems with Night Ventilation Cooling
No full textA significant part of the primary energy demand in industrialized countries is due to space heating and cooling in buildings. Furthermore especially in Europe, the use of HVAC systems is becoming highly popular, thus, the development of efficient cooling techniques is a very important research task to prevent an uncontrolled energy consumption increase. Night ventilation is a passive cooling technique that can significantly reduce the cooling loads and energy requirements, but a trade off must be made between energy cost savings and zone thermal comfort. The Multi-Objective Genetic Algorithms (MOGA) optimizations tools can be helpful in developing optimized cooling systems while maintaining comfort conditions constraints
Modeling of Components for the Numerical Simulation of a Perforated Plate Diffuser at Different Working Conditions
No full textThe techniques available for the simulation of the complex geometries common in air diffusers are quite different from the ones optimized for a complete room simulation. For this reason the full room simulation usually neglects the complexities of the diffusers introducing ad hoc boundary con- ditions often requiring extensive experimental setups for a correct definition. An alternative approach could be the use of numerical analysis for the diffuser characterization. In this work a detailed analysis of a perforated plate type diffuser is performed, particular effort has been devoted to the perforated plate modeling comparing different possible approaches. The simulation has been carried out using the commercial code FLUENT 6.
Analysis of the coupled effect of steel studs and surface emissivity on internal insulation systems performance
Full text linkMany kinds of insulation systems have been developed and applied over the years to all the constructive elements of the building, but the two most used strategies remain the external and internal insulation of vertical walls. However, about the latter often a significant issue is neglected: the overestimation of the thermal performance by disregarding the contribution of construction elements. Usually a uniform stratigraphy of the wall is considered and the evaluation of the performance of a non-uniform one leads to erroneous results about the overall behavior of the system. In this paper, we developed a different approach considering the presence of the steel studs used to attach this package to the existing wall and their influence on the thermal behavior of the structure. Through both experimental and numerical analysis, the possible application of low-e sheets inside the air cavity in various configurations and with different thicknesses of insulation is also taken into account. Results showed that neglecting the presence of the steel studs leads to an erroneous evaluation of the conductance of the refurbished wall with errors reaching up to 28.0% in low-e high-insulated cases. This work highlights how careful the designers have to be when using standard formulas to compute the thermal resistance of internal insulation wall systems
Analisi numerica e sperimentale del campo di moto indotto in una stanza da un diffusore a pannello forellinato
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modellazione dei componenti di un diffusore forellinato e simulazione del campo di moto indotto al variare delle condizioni di funzionamento
No full textLe tecniche necessarie per la modellazione computazionale delle
complessità geometriche
e fluidodinamiche di un diffusore sono piuttosto diverse da quelle
ottimizzate per l'analisi del moto dell'aria in una stanza. Per questa
ragione la maggior parte delle simulazioni del moto dell'aria negli ambienti
utilizzano solo diffusori semplici o schematizzati in forma semplificata
in base a considerazioni basate prevalentemente sull'esperienza e
raramente anche su sperimentazioni. Per ottenere informazioni sul comportamento
dei diffusori allo scopo di
semplificare le corrispondenti condizioni al contorno per lo studio del
moto dell'aria nell'ambiente si sta diffondendo, recentemente, l'uso
della fluidodinamica computazionale, favorita anche dalle prestazioni
crescenti degli elaboratori a basso costo. In questo lavoro ci si propone
di determinare il comportamento di un diffusore forellinato, mediante
una analisi dettagliata del terminale, discriminando tra i diversi modelli
disponibili nei codici commerciali
per tener conto dei componenti quali il filtro e la griglia forata.
In particolare, vengono confrontati i dati ottenuti utilizzando il
modello di strato poroso e di salto di pressione per diversi valori
della portata
Numerical analysis of heat and mass transfer in a passive building component cooled by water evaporation
No full textIn this paper the performance of a special passive building component is investigated. It consists of a ventilated roof where the lower surface of the channel in which flows the external air, is maintained wet. For thermal performance evaluation purposes have been carried out numerical analysis of the flow thermal and water vapour concentration fields within the duct. As results the temperature and specific heat fluxes distributions on the wet lower surface are shown, moreover, to evaluate the overall performance of the component the averaged values of thermal fluxes are presented. The effect of pressure due to different wind regimes are investigated along with the behaviour of the roofing system subject to different climatic conditions. For the evaluation of mass and thermal fluxes the influence of buoyancy term has been taken into account. In order to obtain an estimate of the thermal cooling flux on the wet surface suitable procedures were coded and linked to a commercial program for computational fluid dynamics (FluentTM6.0). A recently presented approach to solve the coupled heat and mass transfer problem has been adopted
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