S. F. C. F. Teixeira

Testing thermal comfort of trekking boots: An objective and subjective evaluation

The study of the thermal comfort of the feet when using a specific type of shoe is of paramount importance, in particular if the main goal of the study is to attend to the needs of users. The main aim of this study was to propose a test battery for thermal comfort analysis and to apply it to the analysis of trekking boots. Methodologically, the project involves both objective and subjective evaluations. An objective evaluation of the thermal properties of the fabrics used in the boots was developed and applied. In addition, the thermal comfort provided when using the boots was also assessed both subjective and objectively. The evaluation of the thermal comfort during use, which was simulated in a laboratory environment, included the measurement of the temperature and moisture of the feet. The subjective assessment was performed using a questionnaire. From the results obtained, it was possible to define an optimal combination of fabrics to apply to trekking boots by considering the provided thermal insulation, air permeability and wicking. The results also revealed that the subjective perception of thermal comfort appears to be more related to the increase in temperature of the feet than to the moisture retention inside the boot. Although the evaluation of knits used in the boots indicated that a particular combination of fibres was optimal for use in the inner layer, the subjective and objective evaluation of thermal comfort revealed that the evaluation provided by users did not necessarily match the technical assessment data. No correlation was observed between the general comfort and specific thermal comfort assessments. Finally, the identification of thermal discomfort by specific foot areas would be useful in the process of designing and developing boots.

A quasi-one-dimensional model for gas/solids flow in venturis

There is considerable interest in the use of venturis to meter gas/solids flows. However, as there are two unknowns, the gas and solids flow rates, two pieces of information are required to calculate these values. It has been suggested that the pressure drop to the throat of the venturi and the recovery of pressure across the diffuser can be used for this purpose. A quasi-one-dimensional model for gas/solids flows in venturis has been developed. This model allows for the acceleration and deceleration of the gas and the solid particles as well as for changes in the thickness of the boundary layer. The last term is particularly important in the prediction of the pressure recovery in the diffuser. Predictions of the model have been validated against (previously published) experimental data. These show excellent agreement between the model and the experiments. In places the predictions are better than those from Computational Fluid Dynamics.

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.

Teaching differential equations in different environments: A first approach

The use of specific softwares was the basis for a new approach for teaching ordinary and partial differential equations, in the field of heat transfer and fluid mechanics. The main objective was to enhance learning effectiveness of Numerical Methods in the post‐graduate course of Polymers Engineering at the University of Minho. This degree takes place into two different environments: at the university campus and at the industrial field. Different commercial codes were used, namely EXCEL, MATLAB, and FLUENT, as well as two tools developed in house at University of Minho: CoNum and a graphics application PDE v.1. Lectures were based on videoconferencing and other web utilities. The teaching methodology presented and discussed in this article was well received and accepted by the post‐graduate students, motivating teachers to improve their teaching/learning strategies.

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.

On solving the profit maximization of small cogeneration systems

Cogeneration is a high-efficiency technology that has been adapted to small and micro scale applications. In this work, the development and test of a numerical optimization model is carried out in order to implement an analysis that will lead to the optimal design of a small cogeneration system. The main idea is the integration of technical and economic aspects in the design of decentralized energy production considering the requirements for energy consumption for the building sector. The nonlinear optimization model was solved in MatLab®environment using two local optimization methods: the Box and the SQP method. The optimal solution provided a positive annual worth and disclosed reasonable values for the decision variables of the thermo-economic model. Both methods converged for the same solution, demonstrating the validity of the implemented approach. This study confirmed that the use of numerical optimization models is of utmost importance in the assessment of energy systems sustainability.

A lining for the Thermal Comfort of Trekking Boots – Experimental and Numerical Studies

In this paper, a study on the design and development of functional shoe linings that are thermally comfortable is presented. The comfort of foot wear, in this case, trekking boots, that is perceived by the user greatly depends on the ability of the boot to maintain the foot surface in an equilibrium state in terms of thermo-physiological comfort (Schols et al., 2004). This is related to the capacity of removing the moisture that results from transpiration away from the foot surface. With these premises in mind, a study on the development of new lining constructions using different raw materials has been conducted. As far as methodology is concerned, this study involves two different stages. The first stage includes an objective evaluation of the thermal comfort of the boots. This stage involves several tasks, including the conception and development of the fabrics to be used in the inner layer of the boots and the development of a thermo-physiological model of the human foot, in order to simulate the temp...

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