Browsing by Issue Date, starting with "2015-08"
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- Experimental analysis to optimize the performance of air curtains and heat exchangersPublication . Nascimento, Samuel Mariano do; Heidinger, Gustavo Galdi; Gaspar, Pedro Dinis; Silva, Pedro Dinho daThis chapter reports an overview about experimental studies concerning the thermal performance of air curtains and heat exchangers installed in vertical open refrigerated display cases. The air curtain analysis shows the influence on the thermal performance by varying the width of the discharge air grille and the perforation density of the back panel by a mathematical model. The variation on the perforation density of the back panel and the width of discharge air grille alter significantly the thermal entrainment factor and the energy consumption of the equipment. Focusing the influence of environmental conditions on the performance of the heat exchanger, a second mathematical model was developed to evaluate the total heat load, its partial components and the condensate water mass. This analysis provides valuable information to the design of the air curtain and heat exchanger based on in-store environmental conditions and airflow efficiency.
- Haemodialysis in Diabetic Patients Modulates Inflammatory Cytokine Profile and T Cell Activation StatusPublication . Almeida, Ana Catarina Silva; Lourenço, Olga; Fonseca, A. M.Diabetic nephropathy (DN) is a common complication in patients with diabetes, and most of them need renal replacement therapy such as haemodialysis (HD). These patients have a high tendency to develop infections and exhibit anomalies in the immune system. The objective of this study was to assess the expression of activation-related markers on T cells, as well as to quantify inflammatory cytokines, before and after a single HD session in DN patients. The study involved DN patients under HD treatment who signed an informed consent form. Blood samples before and after one HD session were collected, to analyse the expression of CD25, CD69 and CD71 in T cells. We also quantified IL-12p70, IL-8, IL-10, IL-1β, TNF-α and IL-6 in serum samples using the cytometric bead array technique. After the HD session, there was an increase in the CD4/CD8 ratio due to significant alterations in both subsets. The relative percentage of CD25+ cells and CD8+ CD25+ increased significantly after the HD session, while the relative percentage of CD69 T cells decreased. There was a significant decrease in the CD25 mean fluorescence intensity values for CD4+ T, as well as in the case of CD71 in T cells after the HD session. Regarding cytokine synthesis, we found a significant increase in IL-10 and IL-6 and a decrease in IL-8 after HD session. This study showed that a HD session in DN patients affects the T cell activation status in the two major subpopulations and differentially modulates the production of inflammatory cytokines.
- Energy analysis and heat loads calculation approach: application to agrifood industrial premisesPublication . Gonçalves, J.; Silva, Pedro Dinho da; Gaspar, Pedro DinisNowadays, the agrifood industry is increasingly concerned about energy bills. Thus, there is an increasing trend on the implementation of measures and procedures that ensure and promote energy efficiency. Computational modelling is a powerful tool for project and design of engineering systems, allowing to anticipate and/or correct problems that may lead to inefficiencies. The purpose of this paper is to assess the energy performance of refrigerated premises of a real company modelled in EnergyPlus. The data that characterize the company and the production process were collected previously through an energy audit. Results of the comparison between real case and simulation show that the cooling system represents 56.4% and 47.8% of the total electrical energy consumption, respectively. Also, it is found that heat transmission loads trough cold rooms envelope and air infiltration are those that most affect the energy performance, accounting for almost 80% of the refrigeration needs of the company.
- 3D transient CFD modeling of sliding door operation and its influence on the thermal performance of cold roomsPublication . Carneiro, Rui; Gaspar, Pedro Dinis; Silva, Pedro Dinho daThe need of rationalize energy consumption in agrifood industry has fasten the development of methodologies to improve the thermal and energy performances of cold rooms. This paper presents a 3D transient Computational Fluid Dynamics (CFD) modelling of a cold room to evaluate the air infiltration rate through sliding doors. A species transport model is used for modelling the tracer concentration decay technique. Numerical predictions indicate that air temperature difference between spaces affects the air infiltration. For this case study, the infiltration rate increases 0.012 m3 s-1 per K of air temperature difference. The knowledge about the evolution of air infiltration during door opening/closing times allows to draw some conclusions about its influence on the air conditions inside the cold room, as well as to suggest best practices and simple technical improvements that can minimize air infiltration, and consequently improve thermal performance and energy consumption rationalization.
- Optimal Hydro-Wind Power Generation for Day-Ahead Pool MarketPublication . Silva, António José Cerejo da; Mariano, S.; Calado, M. Do RosárioWind power production is uncertain. The imbalance between power committed and delivered on pool markets produces increased costs on the system, which must be paid by defaulting producers, decreasing their revenues. In order to invert this situation wind producers may submit their bids join with hydro resources, due to their availability. This paper proposes an optimization technique regarding the maximum benefit for both producers, taking into account the wind unpredictability. A cascaded hydro system is considered.
- Handbook of Research on Advances and Applications in Refrigeration Systems and TechnologiesPublication . Gaspar, Pedro Dinis; Silva, Pedro Dinho daThe Handbook of Research on Advances and Applications in Refrigeration Systems and Technologies is organized into twenty-four chapters. The chapters present the recent research concerning refrigeration systems and applications and survey the state of the art in this field. The contributors review advances in processes and equipments design, efficient heat and mass transfer processes, optimization of real operating systems, modeling and predictive computational tools, innovative technologies, among others.
- On the Modeling of a Spray Impingement Onto a Hot SurfacePublication . Silva, A. R. R.; Rodrigues, Christian; Barata, Jorge M MThe present investigation addresses the impingement of a spray onto a heated solid surface under crossflow conditions at low pressure injection - typical of port-injection engines - during cold start. The characteristics of the initial spray are established by employing an empirical procedure, which relies on a comprehensive set of free spray measurements. This computational study considers the presence of a crossflow moving perpendicularly to an interposed surface and the formation of a dynamic liquid film over the impingement wall. Both previous conditions are often neglected in numerical simulations, despite their importance on the final outcome. Distinct wall and crossflow temperatures are analyzed systematically to evaluate the influence of droplets evaporation on the final outcome of spray impingement, and, particularly, on the distribution of the thin liquid film over the surface. The present computational model already proved to deliver accurate predictions of the spray/wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which reproduce more adequately what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and perform within the range of conditions for which it is now formulated. The analysis shows that higher temperatures lead to smaller impinging droplets, an increase in the number of depositing droplets but a decrease in the fraction of mass of particles contributing to the liquid film; and a more uniform distribution of the liquid layer over the surface.
- Advanced statistical analysis of the collision of wall jet with a boundary layerPublication . Silva, André; Panão, Miguel; Barata, Jorge M MLaser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are analyzed using advanced statistical tools. Namely, finite mixtures of probability density functions, which determine the best fitting using a Bayesian approach based on a Markov Chain Monte Carlo (MCMC) algorithm. This approach takes into account eventual multimodality and heterogeneities in velocity field distributions. Therefore, it provides more complete information about the probability density function of multimodal velocity distributions and allows the identification of characteristic velocities in the heterogeneous data. The experiments are performed for a wall jet-to-boundary layer velocity ratio of 2, and include mean and turbulent velocity characteristics along the two normal directions contained in planes parallel to the nozzle axis. The results, which have relevance to flows encountered by VSTOL aircraft, quantify the structure of the complex ground vortex flow. The results revealed that in the collision zone the rms velocity fluctuation appears to be overestimated for the horizontal component, probably due to the measured velocity range, oscillating between positive and negative values. The results revealed that finite mixture was able to accurately reconstruct a mathematical function describing the probability distribution obtained experimentally. The results shows that U and u'rms rms provide an idea of the flow dynamics, their use is limited and an important amount of information associated with the highly curved flow complexity is lost, preventing a more accurate description of turbulent structures emerging from the collision of wall jet with a boundary layer.