Dynamic modelling of refrigerated truck chambers

A refrigerated truck chamber is always under variable conditions. Not only weather changes but also loading and unloading processes can make the chamber behaviour dependent on time. A prediction of relevant properties distributions (velocity, temperature and relative humidity) in refrigerated chambers requires the simultaneous solution, by an iteration process, of the three-dimensional non-linear differential equations for the momentum and heat/mass transport. Basically, these two transport phenomena are coupled by the buoyancy force due to natural convection. However, especially for non-steady state thermal conditions, the high computations times become unattractive the simultaneous integration. For the majority of refrigerated truck chambers, in which the air flow is mainly dominated by forced convection, the equations can be decoupled and the two transport phenomena can be treated separately. Therefore, in the case of dynamic (transient) simulation, this strategy makes the problem much simpler and can strongly reduce the computation time. In this study the simulation method described here was applied in a case study modelling (steady and transient) and was validated by measurements taken from an experimental reduced-scale model.info:eu-repo/semantics/publishedVersio

Performance evaluation of CFD codes in building energy and environmental analysis

Experimental studies in building energy usage and environmental analysis are very time consuming and expensive, and require sophisticated sensors and instrumentation techniques. So, there has been great interest in developing Computational Fluid Dynamics (CFD) computer codes to improve building design and HVAC systems. The majority of these CFD programs are based on the solution of Navier-Stokes equations, the energy equation, the mass and concentration equations as well as the transport equations for turbulent velocity and its scale. The aim of this study is to present the advantages, applicability and potentialities of CFD in building design. The advantages and the performance of (two) commercial CFD codes and an academic CFD code develop for this purpose are evaluated. The codes were applied to predict typical situations of the airflow in buildings and the predictions were compared with experimental results.info:eu-repo/semantics/publishedVersio

Detailed CFD modelling of open refrigerated display cabinets

A comprehensive and detailed computational fluid dynamics (CFDs) modelling of air flow and heat transfer in an open refrigerated display cabinet (ORDC) is performed in this study. The physical-mathematical model considers the flow through the internal ducts, across fans and evaporator, and includes the thermal response of food products. The air humidity effect and thermal radiation heat transfer between surfaces are taken into account. Experimental tests were performed to characterize the phenomena near physical extremities and to validate the numerical predictions of air temperature, relative humidity, and velocity. Numerical and experimental results comparison reveals the predictive capabilities of the computational model for the optimized conception and development of this type of equipments. Numerical predictions are used to propose geometrical and functional parametric studies that improve thermal performance of the ORDC and consequently food safety.info:eu-repo/semantics/publishedVersio

Simulation of air-supply systems efficiency in refrigerated vehicles to prevent food spoilage

An improper air distribution within refrigerated truck chambers is the major cause of inadequate road transport of perishable products under controlled temperature. Inadequate temperature control permits microbial and/or enzymatic deterioration. Experimental results in refrigerated long road vehicles show temperatures differences in the cargo of as much as 12ºC. This paper presents a computational model to predict, and visualize, the temperature conditions (e.g. velocity, temperature and relative humidity) in refrigerated truck chambers. The model consists of a computer procedure, in which the general equations describing the airflow pattern and the heat/mass transfer in a refrigerated room are solved using the finite volume method. The effect of turbulence is described by the k-ε turbulence model. The computer model was experimental validated by measurements taken from a reduced-scale model designed to provide similarity with a prototype. The model was applied to calculate the indoor cold conditions provided by different types of air supply systems used in compartments of long road vehicles

Estudo numérico do desempenho térmico de expositores refrigerados abertos

A crescente utilização de equipamentos expositores refrigerados em estabelecimentos comerciais de produtos alimentares, desencadeou um apreciável incremento do consumo energético neste sector. Por motivos comerciais, muitos destes equipamentos são abertos ao ar ambiente. A reduzida eficácia da barreira térmica produzida pela vedação aerodinâmica da cortina de ar traduz-se, para além dos relevantes custos energéticos, numa menor qualidade de conservação dos alimentos expostos. Este trabalho tem por objectivo apresentar um estudo numérico do desempenho térmico de expositores refrigerados abertos. O código de Dinâmica de Fluidos Computacional (CFD) – Phoenics é utilizado para prever e visualizar o escoamento turbulento do ar e a transferência de calor no espaço refrigerado. Estudos experimentais complementares permitiram validar o modelo computacional para a configuração estudada, evidenciando as potencialidades do código para este tipo de aplicação. Resultados numéricos correspondentes a um estudo preliminar de optimização são apresentados e discutidos.info:eu-repo/semantics/publishedVersio

Modelação de problemas AVAC-R com códigos de DFC

A modelação computacional constitui hoje em dia uma poderosa ferramenta de cálculo para projecto, permitindo antecipar e/ou corrigir problemas no domínio da engenharia de climatização e da refrigeração. Neste artigo descrevem-se e comparam-se, sucintamente, dois pacotes comerciais de Dinâmica de Fluidos Computacional (DFC), que os autores desta comunicação têm vindo a adaptar para descrever o escoamento tridimensional e turbulento do ar, a transferencia de calor e a distribuição da concentração de espécies em espaços climatizados ou refrigerados. Estudos experimentais complementares têm permitido validar os modelos computacionais propostos, evidenciando as suas potencialidades para aplicações de engenharia. Como exemplo, são apresentadas e discutidas previsões numéricas resultantes da aplicação dos modelos a casos de estudo concretos.info:eu-repo/semantics/publishedVersio

Influência da localização da condição de fronteira de pressão fixa e constante na simulação de aberturas ao ar ambiente

No presente trabalho faz-se um estudo comparativo da influência da localização da condição de fronteira (cf) de pressão fixa a simular uma abertura ao ar ambiente. Foram desenvolvidos vários modelos de CFD para equipamento expositor refrigerado com a cf de pressão fixa imposta para: 1/3 L; 2/3 L; L; e 3/2 L, sendo L a largura do equipamento. Os resultados numéricos são comparados com valores experimentais segundo a classe climática n.º 3 da Norma EN 441. São evidenciados os méritos e as limitações da aplicação prática destes modelos e explicitadas considerações a ter em conta durante a definição das cf de pressão fixa.info:eu-repo/semantics/publishedVersio

CFD Parametric Studies for Global Performance Improvement of Open Refrigerated Display Cabinets

A detailed CFD modelling of an open refrigerated display cabinet has been formulated in a previous study. Some modifications are introduced in order to perform parametric studies dealing with low-cost geometrical and functional characteristics for improvement of the global performance and energy efficiency. The parametric studies are devoted to the analysis of the thermal response and behaviour inside the food conservation space influenced by (1) air flow rate through the evaporator heat exchanger; (2) air curtain behaviour; (3) hole dimensions and distribution of the back panel; (4) discharge and return grilles angles; and (5) flow deflectors inside the internal duct. The analysis of the numerical predictions from the parametric studies allows the development of an optimized model for the conception of an open refrigerated display cabinet with a more adequate configuration. The numerical predictions of the optimized model show lower product temperature and reduced electrical energy consumption, allowing the improvement of the food safety and the energy rationalization of the refrigeration equipment

Psicossomática um estudo histórico e epistemológico

Artigo originado da Dissertação de Mestrado “ Uma Contribuição ao Estudo da Relação Câncer de Mama e Alexitimia”¹. Trata-se de um detalhado estudo teórico sobre o tema, abrangendo a psicossomática desde suas origens às abordagens atuais. Procura fazer um levantamento de quais doenças que se encontram sob esta denominação e qual o fator etiológico predominante se biológico ou psíquico. Analisa também a alexitimia em sua relação com a psicossomática. Sugerir ainda o termo somatopsicose como o mais indicado para referenciar as doenças designadas psicossomáticas