CFD Codes efficiency case study: Ability to perform numerical simulations in the refrigerated compartment of a foodstuff transportation vehicle

The purpose of the present work is to describe the ability of the advanced computer packages (CFD codes) to perform numerical simulations of general refrigeration engineering problems. The case study concerns the modelling of three-dimensional turbulent airflow with thermal buoyant effects and air temperature distribution in the refrigerated compartment of a perishable foodstuff transportation vehicle. The numerical predictions obtained with three commercial codes (PHOENICS, FLUENT and CFX) and an academic one are evaluated and compared with experimental data. The validation of the numerical results is analysed and the modelling capabilities, usage simplicity and user interface of each code are discussed.info:eu-repo/semantics/publishedVersio

Diferenças na intensidade de alteração química de sedimentos Pliocénicos a norte e sul do Mondego

Procede-se a uma análise comparativa de características mineralógicas e geoquímicas (elementos maiores), usadas na definição de intensidade de altyeração química, de sedimentos pliocénicos colhidos na margem Atlântica a norte e sul do rio Mondego. Ainda que se note alguma influência da granulometria dos sedimentos nas características composicionais, as unidades a norte do Mondego revelam sempre alteração química menos intensa que as unidades a sul do Mondego. Estas diferenças justificam-se por proveniência distinta e não devem ter qualquer significado climático

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

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

Patterns of alpha and beta diversity of epigean arthropods at contrasting land-uses of an oceanic island (Terceira, Azores)

"[…]. To study the effect of land-use change in biological communities it is necessary to understand how are the different components of diversity distributed in space. Diversity has long been separated into different components according to the phenomena that interest ecologists (Whittaker, 1960, 1972): i) local species richness, i.e., alpha (community) diversity that measures the species richness of a local assemblage; ii) beta diversity, the degree of difference between communities (Whittaker et al., 2001), that measures turnover of species between communities and; iii) gamma (regional) diversity, which can be considered an equivalent to alpha diversity on a larger scale, but reflects the allopatric distribution of related taxa. Alpha diversity, of which species richness is just the most visible measure, is perhaps the most studied aspect of diversity. However, probably more important than knowing how many species live in a site at a given time, it is to know what species are these. In islands, where the introduction of non-indigenous species is one of the major threats to indigenous species (Borges et al., 2006; Martín et al., 2008), especially endemics, this question is even more significant. Even if man-made habitats are species rich, they may be empty of species considered as conservation priority and abundant in exotic species (Cardoso et al. 2009a). […]" (da Introdução)Fundação para a Ciência e a Tecnologia, Portugal

Medium materials for improving frost detection on a resistive sensor

Reducing food waste demands improvements in refrigeration systems. Furthermore, the rise of temperatures worldwide demands more capable and efficient refrigeration equipment. One of the problems that affects refrigeration equipment is the accumulation of frost in the heat exchanger that reduces efficiency, and in extreme cases, blocks the air flow. Usually, defrosting is timed for the worst-case scenario, which results in many unnecessary defrosting operations that compromise the efficiency, and temperature stability in the refrigerated environment. This paper presents a low-cost resistive sensor’s reliability case studies, using several materials and configurations.This study is within the activities of project “Pack2Life – High performance packaging”, project IDT in consortium n.o 33792, call n.o 03/SI/2017, Ref. POCI-01-0247-FEDER-033792, promoted by COMPETE 2020 and co-funded by FEDER within Portugal 2020. This work has was supported by the project Centro-01-0145-FEDER000017 - EMaDeS - Energy, Materials and Sustainable Development, co-funded by the Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the EU through the European Regional Development Fund (ERDF). The authors thank the opportunity and financial support to carry on this project to Fundação para a Ciência e Tecnologia (FCT) and R&D Unit “Centre for Mechanical and Aerospace Science and Technologies” (C-MAST), under project UIDB/00151/2020. The authors also thank Cláudia Monteiro for her assistance in the production of the ceramic samples.info:eu-repo/semantics/publishedVersio

Three-Dimensional CFD modelling and analysis of the thermal entrainment in open refrigerated display cabinets

This study presents a three-dimensional Computational Fluid Dynamics (CFD) simulation of the air flow pattern and the temperature distribution in a refrigerated display cabinet. The thermal entrainment is evaluated by the variations of the mass flow rate and thermal power along and across the air curtain considering the numerical predictions of abovementioned properties. The evaluation on the ambient air velocity for the three-dimensional (3D) effects in the pattern of this type of turbulent air flow is obtained. Additionally, it is verified that the longitudinal air flow oscillations and the length extremity effects have a considerable influence in the overall thermal performance of the equipment. The non uniform distribution of the air temperature and velocity throughout the re-circulated air curtain determine the temperature differences in the linear display space and inside the food products, affecting the refrigeration power of display cabinets. The numerical predictions have been validated by comparison with experimental tests performed in accordance with the climatic class n.º 3 of EN 441 Standard (Tamb = 25 ºC,φamb = 60%; vamb = 0,2 m s-1). These tests were conducted using the point measuring technique for the air temperature, air relative humidity and air velocity throughout the air curtain, the display area of conservation of food products and nearby the inlets/outlets of the air mass flow.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

Experimental analysis of the thermal entrainment three dimensional effects in re-circulated air curtains

The application of air curtains devices to HVAC&R systems have been developed in order to improve the thermal and mass separation between two contiguous spaces with differentiated air behaviours. The refrigeration equipments installed inside commercial spaces and open to the surroundings suffer alterations of their thermal behaviours and energy efficiency due to variations in magnitude and orientation of the air velocity. The location of the air conditioning system discharge grilles, the mass flows rates originated by pressure differences due to openings to the external environment and the air flow perturbation due to the circulation of the consumers nearby the opening of the display cases, among others, affect the re-circulated air curtain behaviour and the overall performance of the equipment.This study presents the experimental results obtained from tests carried out for the climatic class n.º 3 of EN 441 (Tamb = 25 ºC, φamb = 60%; vamb = 0,2 m/s) and the analysis of the threedimensional effects observed in the thermal interaction through the air curtains installed in open vertical refrigerated display cases. The obtained results are related to the air temperature, air relative humidity and air velocity measurements fields throughout the air curtain. From the analysis of the obtained results some comparable effects in the fields of the same properties for the display space of the exposition and conservation of food products and nearby the inlets/outlets of the air mass flow, can be sorted out. The evaluation of the ambient air velocity three-dimensional effects in the pattern of this type of turbulent air flow is obtained. Additionally, it is verified that the longitudinal airflow fluctuations and the length extremity effects of the display case have a considerable influence in the overall thermal performance of the equipment. The non-uniform distribution of the air temperature, relative humidity and velocity throughout the air curtain determines temperature differences in the linear dimension display space and inside the food products, affecting the correct behaviour of the display cases. Besides that, this study helps to show some of the fragilities of the numerical models bi-dimensional formulation.info:eu-repo/semantics/publishedVersio

Terras raras nos sedimentos Pliocénicos entre os rios Vouga e Mondego (Portugal) = Rare earth elements in the Pliocene sediments between rivers Vouga and Mondego (Portugal)

A geoquímica de sedimentos argilosos do Pliocénico é usada para determinar as principais fases transportadoras de terras raras. Foram consideradas 3 fácies, associadas a sedimentação em planície de inundação e em pântano-lago, e dois sectores. A concentração de terras raras pesadas é substancialmente maior nos sedimentos de pântano-lago que nos de planície de inundação. Ainda que os minerais de argila integrem parte das terras raras, o xenótimo e a monazite são os principais minerais a transportar aqueles elementos. Outras fases (p. ex. matéria orgânica) em sedimentos de pântano-lago devem reter uma parte significativa das terras raras, em particular das terras raras pesadas. As concentrações de terras raras nos dois sectores não são muito diferentes, sugerindo que a proveniência era similar