José Carlos Teixeira

Development of new spacer device geometry: a CFD study (Part I)

Asthma is a widespread disease, affecting more than 300 million individuals. The treatment in children is based upon an administration of a pressurised metered-dose inhaler added with a spacer. The efficiency of drug delivery to the patient is strongly affected by the transient airflow pattern inside the spacer device. This paper presents a computational fluid dynamics (CFD) analysis of airflow inside a commercially available spacer device with wide application. This study, carried out in Fluent™, was the basis of an optimisation procedure developed to improve the geometry of the spacer and develop a more efficient product. The results show that an appropriate control of the boundary layer development, by changing the spacer shape, reduces the length of the recirculation zones and improves the flow. It can be concluded that CFD is a powerful technique that can be successfully applied to optimise the geometry of such medical devices.

Contact angle measurement of SAC 305 solder: numerical and experimental approach

The solder process comprises the ability of a melted alloy to flow or spread on a substrate for the formation of a metallic bond driven by the physical–chemical properties of the system. Thus, the study of wetting behaviour is an important step in the characterisation of solder alloys and requires the discussion of different parameters that affect the solder junctions. The main objective of this work is to use a CFD study to determine the influence of several parameters in the melting shape obtained with a solder, of the SAC 305 type and compare the numerical results with experimental data. The computational model was implemented in ANSYS Fluent® and the simulations were carried out involving the melting of a material using the volume of fluid method to capture the solidification/melting interfaces based on an enthalpy-porosity approach. The results show that shape of the melted solder is greatly influenced by the contact angle and, to a smaller extent, by the surface tension. It was also concluded that it is possible to accurately predict the shape of the melted solder using computational fluid dynamic tools in complement to the experimental validation.

Influence of Copper Layer Content in the Elastic and Damping Behavior of Glass-Fiber/Epoxy-Resin Composites

The impact in the elastic behavior and internal friction, caused by the introduction of Copper layers in Glass-Fiber/Epoxy Resin composites and temperature effects, were studied and evaluated recurring to Dynamic Mechanical Analysis. It is shown that the introduction of Copper layers increases the storage modulus of the composites and delays their glass transition temperature, however, it allows a faster transformation. Additionally, it is concluded that the introduction of Copper layers elevates the internal friction during the glass transition phase by the inversion of the deformation mechanism due to thermal expansion and increase in the Poisson’s ratio of the epoxy resin to a value near 0.5 where its deformation is approximately isochoric. This increase in damping capacity is relevant in application with cyclic fatigue and mechanical vibration.

Thermal comfort assessment of a surgical room through computational fluid dynamics using local PMV index.

BACKGROUND Studies concerning indoor thermal conditions are very important in defining the satisfactory comfort range in health care facilities. OBJECTIVE This study focuses on the evaluation of the thermal comfort sensation felt by surgeons and nurses, in an orthopaedic surgical room of a Portuguese hospital. METHODS Two cases are assessed, with and without the presence of a person. Computational fluid dynamic (CFD) tools were applied for evaluating the predicted mean vote (PMV) index locally. RESULTS Using average ventilation values to calculate the PMV index does not provide a correct and enough descriptive evaluation of the surgical room thermal environment. As studied for both cases, surgeons feel the environment slightly hotter than nurses. The nurses feel a slightly cold sensation under the air supply diffuser and their neutral comfort zone is located in the air stagnation zones close to the walls, while the surgeons feel the opposite. It was observed that the presence of a person in the room leads to an increase of the PMV index for surgeons and nurses. That goes in line with the empirical knowledge that more persons in a room lead to an increased heat sensation. CONCLUSIONS The clothing used by both classes, as well as the ventilation conditions, should be revised accordingly to the amount of persons in the room and the type of activity performed.

Modeling a stirling engine for cogeneration applications

The interest on decentralized power generation technology has been drastically increasing over the last few years. This great interest is due to the necessity of achieving new ways for improving energy efficiency, the national security of energy supply and the reduction of carbon dioxide emissions. Combined heat and power generation (CHP) systems can be a good option to achieve those goals. In Europe and for the building sector, this fact can be translated in the development of low power systems (micro-CHP), designed to fulfill building equivalent loads. These systems will replace the usual boilers that satisfy the dwelling’s heat requirements and, additionally, generate electricity for own consumption or export back to the electricity grid. The most cited technologies in small and micro-scale are Fuel Cells, Internal Combustion Engines, and Stirling Engines. Stirling Engines are gaining some attention due to their advantages: high total efficiency, fuel flexibility, low emissions, low noise/vibration levels and good performance at partial load. Due to these characteristics, Stirling engines seem to be a good alternative for residential energy conversion, and thus, a pathway for more energy-efficient systems that rise to the challenges of increasing market competition. Many studies have been conducted in order to assess Stirling Engines performance, but the integration of technical and economic evaluation for micro-CHP systems applications is an issue that is not focused in literature, and is the final objective of this project.Copyright

Optimal design of micro-turbine cogeneration systems for the portuguese buildings sector

The use of combined heat and power (CHP) systems to produce both electric and thermal energies for medium-size buildings is on the increase, due to their high overall efficiency, high energy prices and political and social awareness. In this paper, an energy-economic study is presented. The main objective is to implement an analysis that will lead to the optimal design of a small cogeneration system, given the thermal power duration curve of a multi-family residential building. A methodology was developed to obtain this curve for a reference B-class building located in the North of Portugal. The CHP unit is based on a micro gas-turbine and includes an Internal Pre-Heater (IPH), typical of these types of small-scale units, and an external Water Heater (WH). A numerical optimization method was applied to solve the thermo-economic model. The mathematical model yields an objective function defined as the maximization of the annual worth of the cogeneration system. A purchase cost equation was used for each major plant component that takes into account size and performance variables. Seven decision variables were selected for the optimization algorithm, including performance of internal gas-turbine components and electrical and thermal powers. The results show that, the revenue from selling electricity to the grid and fuel costs have the greatest impact on the annual worth of the system. The optimal solution for the small CHP is sensitive to fuel price, electricity feed-in-tariff, capital cost and to the thermal load profile of the building. High European energy prices point towards future micro gas-turbines with better electrical efficiencies, achieved via a higher pressure-ratio compressor and turbine inlet temperature.Copyright

Modeling the Reflow Soldering Process in PCB’s

In the present work two different types of case studies are modelled, carried out involving the fusing of a material using the CFD (Computational Fluid Dynamics) software Ansys Fluent, using the VOF method (Volume of Fluid) to capture the position of the existing interfaces and the Solidification/melting method which uses an enthalpy-porosity approach to simulate the fusion of the material.The first case focus itself in the analysis of fusing process and dropping behavior of the melted plate in the presence of a thermal source. The validation is made using a study found in the bibliography and then using water as the melting material given that its behavior is well known. Then tin is used as the melting material followed by the use of SAC 405 as the melting plate. This study compares various materials properties and verifies the influence of some of these particular properties by changing them (surface tension and heat of fusion).The second case focus on the simulation of a geometry obtained at balance at a constant temperature by the SAC 405 soldering alloy in the presence of a component and the copper substrate on top of a PCB.Copyright

An Experimental Setup for API Assessment of a Valved Holding Chamber Device

Typically for young children and elders, the asthma treatment procedure using pMDI devices bring some usage coordination difficulties. Therefore, and accordingly to several asthma treatment guidelines, the prescription of a VHC, as an add-on device for the pMDI, is advisable. These devices consist of an expansion chamber where the air slows down, as well as, the pMDI spray plume. Allowing the patient to breathe whenever he wants, independently from the moment of the pMDI actuation, also reduces the “cold-freon” effect and allows a more effective evaporation of the propellant. The effectiveness evaluation of VHC and pMDI devices is made through the quantification of drug delivered to the patient lungs. A simple collection filter is not enough for an accurate assessment of the device. Since the size of the particles delivered matter the most, the use of an impaction apparatus is essential. Accordingly to the Canadian normative for VHC assessment (CAN/CSA/Z264.1-02:2008), the experimental testing shall be done by using a breath simulator instead of a constant flow pump. The evolution of these tests shall move towards more realistic testing conditions. This work reports the project and construction an experimental setup for a correct assessment of the VHC devices effectiveness. The experimental setup is based in the work of Foss & Keppel (1999) and the contribution of Finlay (1998) and Miller (2002). The project and optimization of the major components, such as, breath cycle simulator by means of a cam-follower mechanism, a mixing cone and the vacuum pump used, are herein described and discussed.Copyright

Application of CFD tools to optimize natural building ventilation design

The use of natural ventilation systems may contribute considerably to the reduction of the energy consumption, while providing adequate comfort levels and hygiene standards for the occupants. Computational Fluid Dynamics (CFD) techniques are becoming increasingly attractive in the design of ventilation systems. In this work, tests on a validated CFD model, which simulates the air flow inside a standard building, were carried out in order to obtain a suitable tool to predict ventilation performance and therefore optimize the building ventilation design. The model solves the mass, momentum and energy for the air flow, coupled with the k-e turbulence model. The equations are solved by a FV discretization technique in a structured grid. Appropriated boundary conditions and the dimension of the domain were studied for more accuracy in numeric simulation. The influence of the free stream velocity profile and wind direction upon the efficiency of a natural ventilation system under isothermal conditions has been tested. The results obtained so far confirm the validity of the implemented model and its possible use for the optimal design of natural ventilation systems.

pMDI sprays: theory, experiment and numerical simulation

The inhalation therapy is a cornerstone in asthma treatment. A disease characterized by episodes of wheezing, breathing difficulties, chest tightness and coughing. Essentially it is a chronic inflammatory disorder associated with airway hyper responsiveness [1]. This disease already affects over 300 million people worldwide, growing at a rate of 50% per decade, and causes the death of 220 thousand per year [1].