Temperature dependent thermal conductivity of magnetocaloric materials: impact assessment on the performance of active magnetic regenerative refrigerators

Due to the dynamic nature of the active magnetic regenerative mechanism in magnetocaloric refrigeration, the thermal conductivity of the refrigerant is a critical parameter. Experimental studies have shown how the thermal conductivity of high-performance magnetic refrigerants can drastically change around their Curie temperatures (TC). However, this fact has been largely ignored in the numerical simulation of devices, raising the need to assess the impact of this approximation, particularly when the simulations are aimed at optimizing or dimensioning a particular device geometry. In this paper we show how, by employing a unidimensional numerical model of a magnetic refrigerator with parallel plates, two different temperature dependent thermal conductivity scenarios of the refrigerant affect the resulting temperature span and cooling power. By considering a gadolinium-like material as the refrigerant with thermal conductivities varying 50% near its TC, a change of the resulting device temperature span of  ∼15% is reached. The cooling power is also affected, changing also  ∼15% when the considered systems are at half their respective maximum temperature span. Our results are also discussed in terms of other geometries where the impact of these effects can be even larger, namely in cases where the axial thermal conduction in the AMR element is not negligible, or the time-scale of longitudinal thermal processes has a larger impact on the optimum operating frequency.publishe

Development of structural layers PVC incorporating phase change materials for thermal energy storage

The use of poly(vinyl chloride) (PVC) structural layers incorporating phase change materials (PCM) for latent heat thermal energy storage (LHTES) has become more attractive in the recent years compared to other supporting materials. In this study, PVC layers with different types of PCM were prepared using blending and compression moulding methods. Two types of synthesized PCM, one based on paraffin and calcium carbonate (PCM@CaCO3) and the other on paraffin, silica and graphene oxide (PCM@SiGO) have been developed to enhance the thermal conductivity of the PVC matrix and thus achieve a more effective charging and discharging process. PVC layers prepared using a commercial PCM (PCM@BASF) were also prepared for comparison. SEM images and DSC results reveal homogeneous distribution of the PCM in PVC layers and that most PCM particles are undamaged. The shell material (in the case of PCM@BASF) and the shape stability (in the case of synthesized PCM@CaCO3 and PCM@SiGO) prevent leakage of molten paraffin during the PVC layer production. The thermal conductivity profile of the PVC layer without PCM have a decreasing tendency with the temperature increase when determined using different measurement approaches, the transient plane heat source method (HotDisk Analyser, TPS 2500 S) and thermal flux meter method (steady-state method). However, for PVC layers with PCM the thermal conductivity profile shows a different behaviour when the mean surface temperature of the specimen is below the phase change transition temperature range (increasing tendency). During phase change transition (18–26 °C), the thermal conductivity presents two distinct tendencies. Firstly, the thermal conductivity reveals a decreasing tendency as the mean temperature of the specimen rises and afterwards an increasing tendency. Secondly, when the mean surface temperature is above the phase change transition temperature range, the thermal conductivity profile shows a decreasing tendency, independent of the PCM. The mechanical properties of PVC layers were also assessed and the results obtained revealed that the incorporation of PCM into the PVC matrix reduces the mechanical performance of the composites, however for LHETS applications not subjected to high tensile stress levels (over 1 kPa), this is not a significant drawback.publishe

Detection of adulterations in tradictional portuguese game meat products by polymerase chain reaction technique

Authenticity assessment and fraud detection in processed meat products have becn attracting an increased attention driven by public health, economic and legal cancems, and also for religiolls reasons. Currcntly, ooe af the major issues conceming adulterations in the meat indust:ry regards the fraudulent substitution af higher commercial valued meat species by less expensive oDes [1]. The manufacture af traditional meat products is a long-established practice in the Northeast of Portugal. One of the most appreciated products is called "Alheiras", which are traditional smoked fermented sausages, mainly produced with pork and poultry meat. In addition to the two Portuguese Alheiras with Protected Geographical Indication (pGI), other types of "Alheiras" are now available in the market, including the ones produced with game meat. Due to the game meat particular taste, intense Oavour and seasonality, it generally eommands higher prices compared to other meats [1]. Sinee game meat "Alheiras" should, totally or partially, include different types of game meat, they are particularly prone to fraudulent meat substitutions

Species identification and authentication of hare (Lepus) meat by the use of the mitochondrial cytb gene

Nowadays, consumers are increasingly concerned with issues of food safety and authenticity. In particular, game meat has been much appreciated by consumers for their exotic flavour and texture, low in fat and cholesterol as well as by the absence of steroids or other drugs. Food authenticity assessment is important in that it avoids unfair competition among producers and allows consumers to have accurate information about the products they purchase. Therefore, it is important to ensure that species of high commercial value declared are not replaced by other species of lesser value [I]

Authentication of a traditional game meat sausage (Alheira) by species-specific PCR assays to detect hare, rabbit, red deer, pork and cow meats

Alheira is a traditional meat product that is typical from the Northeast region of Portugal and much appreciated. It is a sort of sausage produced industrially or by small artisanal producers, having wheat bread and meats as main ingredients. Game meat Alheira (Alheira de caça) is considered one of the most attractive products since it should include different game meats. The aim of the present work was to identify the species of origin of meats added to game meat Alheira samples to verify their compliance with labelling. Species-specific PCR assays targeting mitochondrial genes of rabbit, hare, red deer, cow and pork were optimised and applied to industrial and artisanal samples. The assays revealed adequate specificity for each of the targeted species, with sensitivities of 0.01-0.1%. Results of the evaluation of 18 commercial samples identified several inconsistencies with labelling, namely the absence of declared game species (red deer, hare and rabbit) in ten samples and the presence of undeclared cow species in nine of the analysed samples. These findings indicate the occurrence of misleading labelling, suggesting the adulteration by substitution of game meats by cow meat to reduce production costs and the need to protect and valorise this kind of traditional food product.The authors acknowledge the financial support of the University of Porto/Santander Totta “Projectos pluridisciplinares 2010” and the Fundação para a Ciência e a Tecnologia (FCT) through grant no. PEst-C/EQB/LA0006/2013.info:eu-repo/semantics/publishedVersio

Identification of duck, partridge, pheasant, quail, chicken and turkey meats by species-specific PCR assays to assess the authenticity of traditional game meat Alheira sausages

Game meat Alheira (Alheira de caça) sausage is a traditional fermented product typical from the Northeast region of Portugal, having bread and meats (including game) as main ingredients. It is a particularly appreciated product by consumers that commands higher prices, especially in comparison with the common Alheira produced with pork and poultry meats. Following our previous work in which several mammalian game meat species were successfully identified in game meat Alheira sausages for authentication purposes, the present work aimed at identifying game bird's species for the overall assessment of labelling compliance. For that purpose, several species-specific PCR assays targeting mitochondrial DNA for the detection of game and domestic bird's meat, namely duck, partridge, pheasant, quail, chicken and turkey were developed, optimised and applied to commercial samples of game meat Alheira for their authentication. The assays revealed a high specificity and sensitivity to detect the addition of all evaluated species down to a level of 0.01% (w/w). PCR results indicated the existence of several inconsistencies with the labelled information, namely the absence of declared game species (duck, partridge and pheasant) and the presence of undeclared poultry meat, pointing out to adulterations owing to substitution of game by domestic meat species. Since this is considered a high-valued traditional product that should be valorised and protected, this work puts in evidence the need for inspection programs to enforce regulation. © 2014 Elsevier Ltd.The authors acknowledge the financial support of the University of Porto/Santander Totta “Projectos pluridisciplinares 2010” and the Fundação para a Ciência e a Tecnologia (FCT) through grant no. PEst-C/EQB/LA0006/2013.info:eu-repo/semantics/publishedVersio

Detecção de adulterações em alheiras de caça: identificação de carne de aves com base em marcadores moleculares

A avaliação da autenticidade de produtos cárneos inclui diferentes aspectos, como a substituição de carnes com valor económico elevado, por outras de menor valor, e a presença de espécies não declaradas no rótulo [I]. Actualmente, para além da Alheira tradicional, produzida à base de carne de porco e/ou de aves (galinha e peru) são comercializadas Alheiras de caça, geralmente com preço mais elevado. Neste tipo de produtos processados, torna-se difícil a diferenciação das carnes utilizadas, pelo que são propícios a adulterações. Várias técnicas analíticas com base na detecção de proteínas (cromatográficas, electroforéticas e imunológicas) têm sido aplicadas na identificação de espécies em produtos cárneos. Devido à maior estabilidade do DNA, comparativamente com as proteínas, a sua utilização como molécula alvo através da técnica de reacção em cadeia da polimerase (PCR) apresenta-se como uma alternativa específica, rápida e sensível, mais adequada para a identificação de espécies em alimentos processados. Neste trabalho, propõe-se a identificação de espécies de aves (galinha, peru, faisão, perdiz e pato) em Alheiras de caça pela técnica de PCR. Prepararam-se misturas padrão contendo quantidades conhecidas de cada carne em estudo e procedeu-se à extracção de DNA pelo método Wizard [2]. O rendimento de extracção e a pureza dos extractos foram avaliados por espectrofotometria. Para a detecção de carne de perdiz e fa isão, utilizaram-se primers específicos para o gene mitocondrial 12S rRNA [1]. Para a detecção de peru, galinha e pato, foram desenhados primers específicos tendo como alvo o gene cytb. Os resultados demonstraram a especificidade e sensibilidade das reacções, permitindo detectar a adição de todas as espécies em carne de porco até ao nível de 0,01 %, à excepção do peru (0,1%). As metodologias propostas foram aplicadas com sucesso a 15 amostras comerciais de alheiras de caça, tendo-se detectado várias inconsistências na rotulagem, como a ausência de espécies de caça declaradas (faisão, perdiz e pato) e a presença de carnes (galinha e peru) não rotuladas

Direct and Inverse Magnetocaloric effects in A-site ordered PrBaMn2O6 manganite in low magnetic fields

The magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite has been studied by direct methods and by the specific heat measurements. Direct measurements of the MCE in low magnetic fields were performed using recently proposed modulation technique and by classic direct method in high fields. Direct and inverse MCE are observed at Curie and Neel points correspondingly. A value of the inverse MCE in the heating run is less than in the cooling regime. This effect can be attributing to competition between ferromagnetic and antiferromagnetic interactions. Indirectly estimated and direct MCE values considerably differ in around first order AF transition.Comment: 8 pages, 5 figure

Enhancement of physical and reaction to fire properties of crude glycerol polyurethane foams filled with expanded graphite

The reation to fire of polyurethane foams (PUFs) has been a subject of increasing relevance, so in this study the reaction to fire performance of PUFs derived from crude glycerol (CG) has been improved using expanded graphite (EG). The influence of different loadings of EG on the physical–mechanical properties of composite foams has been assessed and the results obtained show that it has significant positive impact. Moreover, the reaction to fire of the PUF and EG/PUF composites has been investigated and the results obtained showed that the fire behavior of composite foams containing as little as 5 wt% of EG are significantly improved. Indeed a dramatic reduction of the rate of heat release, mass loss rate, effective heat of combustion and specific extinction area, has been observed even for a relative low amount of EG. Likewise, the use of Infrared Thermography as a function of time has proven that, when EG is used, the combustion stops suddenly and the temperature drops sharply compared with the behavior of the unfilled PUF sample, which suggests that EG acts like a flame extinguisher. The results obtained have proven the suitability of CG for the production of PUFs and that the addition of EG considerably improves the reaction to fire of composite foams.publishe

Enhancement of resistivity and magnetization of Bi1-xLaxFe1-yMnyO3 ceramics by composition optimization

This work aims at studying the effect of La and Mn substituents on the structural, electrical and magnetic properties of Bi1-xLaxFe1-yMnyO3 (0≤x≤0.30; 0≤y≤0.20) at room temperature, in order to find out the optimal compositions that provide both high resistivity and remnant magnetization. The analysis of the XRD patterns and Raman spectra suggest a progressive transition from a rhombohedral for x0.20. Moreover, we observe satellite peaks associated with an incommensurate modulated (IM) orthorhombic structure for x≥0.15 with y = 0, and x = 0.20 with y = 0.10. We were able to achieve a decrease by several orders of magnitude of the leakage current density and the emergence of a weak ferromagnetic response in the range of compositions 0.10<x≤0.3 and 0<y<0.1. These improved physical properties are a consequence of the absence of secondary phases and the breaking of the spiral cycloid spin structure. In particular, the compositions within 0.18≤x≤0.30 and 0.01<y<0.05 with IM orthorhombic structure exhibit the lowest conductivity and highest remnant magnetization. The outcome of this work suggests an alternative route to enhance multiferroic properties of BiFeO3, with simultaneous La (0.10≤x≤0.30) and moderate Mn (0.01<y<0.1) substitution.publishe