Loading...
9 results
Search Results
Now showing 1 - 9 of 9
- Experimental study of a photovoltaic solar dryerPublication . Grilo, Tiago Santos; Pires, Luís; Silva, Pedro Dinho da; Nunes, JoséThis experimental work focuses specifically on the development and construction of a prototype and the study of different strategies to optimize food drying from solar energy. The main study variable is the efficiency of the solar dryer. In order to optimize the system and increase the drying rate it was decided to use a photovoltaic panel which will power a resistive load - thus obtaining higher air temperature which enters the drying chamber. First, are shown some considerations about the range of applications and methods of harnessing solar energy, emphasizing how important it is to conserve food products through solar drying. To elucidate this concept existing models of solar dryers are reviewed, highlighting the most efficient and representative of each category, in order to understand the work already developed in this area. All experimental results were obtained in drying trials during the summer of 2016. These results demonstrate the advantages and disadvantages of each strategy adopted. Calculations were made and performance parameters discussed, allowing to take conclusions about the modus operandi and design of this type of units. In order to benefit the most of the energy generated, and thus reduce waste, certain measures have been identified that promote the correct use of PV panels for drying agricultural products. All of this work is for the purpose of being adopted by local farmers.
- Efficient cooling at post-harvest phase: a comparative study between air-cooling and hydro-cooling processesPublication . Ferreira, João; Silva, Pedro Dinho da; Pires, Luís C.; Gaspar, Pedro Dinis; Nunes, JoséThe pre-cooling of peaches is a very demanding process regarding energy conservation and management. Inappropriate cooling techniques and cooling times lead to post-harvest phase losses, resulting in wasted energy and produce. This work studies the difference in cooling time between air and hydro-cooling and the influence of peach size in their cooling time in the post-harvest phase. A numerical model was developed to evaluate the peach temperature during the pre-cooling stage. The results from the model were compared with experimental data and a set of correlations of the half-cooling time and the seven eighth cooling time as a function of the peach size were developed. Globally, the information provided in this work in terms of cooling times in both air and hydro cooling equipments could be used to improve the efficiency of the pre-cooling process by keeping the quality of the produce but reducing the energy consumption by peach.
- Development of an experimental unit for studying the solar drying processPublication . Parente, Daniel; Pires, Luís Carlos Carvalho; Silva, Pedro Dinho da; Nunes, JoséThe removal of moisture by drying, prevents the growth and reproduction of these microorganisms, which cause rotting, and minimizes many of the reactions of deterioration from moisture, revealing itself a crucial preservation method. Portugal is a country with great potential for exploitation of solar energy, the implementation of a drying system based on this renewable source, facing devices with high energy consumption and hence more expensive, is attractive. With this, the present work emerges, in order to, by building a sustainable drying model, evaluate their performance, so that can be a good solution. First, were done characterization tests with the dryer unload, studying the temperatures and the relative humidity (RH) inside the drying chamber. The influence of various air gap heights and of operation modes, under natural and forced convection were studied. The developed unit was subsequently used in cherry drying. The first drying test, allowed dry 15 kg cherry in 124 hours. The second with 25 kg was carried out under adverse conditions, therefore presented an additional drying time of 25 hours from the first. The results of the studies realized indicate great potential of the drying mechanism proposed, capable of reaching temperatures of 55 °C inside the drying chamber, for an ambient temperature and humidity of 31,7 ºC and 28%, respectively, and an intensity of solar radiation of 918 W/m2.
- The cherry drying as a complementary conservation process to conservation in coldPublication . Nunes, José; Silva, Pedro Dinho da; Pires, Luís; Gaspar, Pedro Dinis; Andrade, Luís P.Cherry is greatly enjoyed by consumers because of its excellent organoleptic and nutritional characteristics. This fruit is of the non-climacteric type, which forces its immediate commercialization after harvesting or else it should be properly conserved in cold. Every year there is a big waste of fresh cherry because he could not be marketed before deteriorating both in cooling chambers, or even in their own cherry trees due to a rapid ripening. In this project, the process of making cherry raisins is studied so as to provide increased use of fresh cherry. For that purpose, three different processes of dehydration of fresh cherry have been used, such as freeze drying, hot-air drying and solar drying. Three types of samples of pitted cherries were also used - natural cherry, blanching cherry and bleaching cherry with osmotic solution of fructose. In order to assess the performance of the dryers the curves of drying rate were determined and to assess the quality of the cherry raisins, fundamental parameters were determined, namely moisture content, water activity (aw), texture, total soluble solids and total acidity. The results show that the drying rate of cherry samples is similar in the lyophilizer and hot air dryer, and yet faster in the latter. The dryer with lower rate drying and hence with higher drying time was the solar dryer. The characteristics of the cherry raisins depend on the type of dryer used and the pre-treatment used. The blanching pretreatment proved to be the most suitable. Regarding dryers, the solar dryer provided good quality cherry raisins, showing great potential at industrial level with the advantage of not consuming energy.
- Experimental tests using deactivation of coolant fluid circulation to mitigate frost formation on the heat exchanger surfacePublication . Panoias, Pedro; Silva, Pedro Dinho da; Gaspar, Pedro Dinis; Pires, Luís Carlos Carvalho; Nunes, JoséThe use of cold for conservation of food products requires large consumption of electricity. In order to obtain lower temperatures than those available in the same space, the evaporator coils, generally operate at temperatures lower than the freezing point of the water. The ice formed on the surface is detrimental both to the thermal and the energetic level of the refrigeration system. Thus, ice removal is critical to reestablish the desired operating conditions. This paper presents a refrigeration apparatus setup composed by two heat exchangers connected in parallel. The coolant fluid circulation is deactivated during short periods of operation, and the ice formation on the coil surface is analyzed. The results show that this strategic deactivation of coolant fluid circulation proved to be a viable operating condition since allowed an extension of the refrigeration system operation with a stable cooling power and so better thermal efficiency.
- Quantification of the thermal resistance variation in evaporators surface due to ice formationPublication . Carrilho, Diogo G.; Silva, Pedro Dinho da; Pires, Luís Carlos Carvalho; Gaspar, Pedro Dinis; Nunes, JoséRefrigeration takes a very important role in society. Nowadays, a big portion of the refrigeration processes are taken into account in the food and drinks storage, and also in the cooling of closed spaces. The method of heat removal from the surrounding air through the evaporation of a fluid, being a process of continuous improving, has suffered many enhancements in order to obtain better energetic consumption levels. One of the main restrictions of the usual refrigeration mechanisms is the icing verified in the external surface of the evaporators, as a part of the refrigeration cycle. The present work discusses the mitigation process of ice formation through a proposed heat exchangers configuration. The experimental unit built for this purpose allows the ice layer formation over the heat exchangers surface for several values of air flow rate, temperature and relative humidity. The evaluation of the thermal resistance of the heat exchangers surface together with the condensates collected provides an insight of the consequences of the different air conditions and of the proposed configurations on the ice formation process.
- Characterization of refrigeration systems in the Portuguese food processing industryPublication . Morais, Diogo Cerqueira; Silva, Pedro Dinho da; Gaspar, Pedro Dinis; Pires, Luís C.; Andrade, Luís P.; Nunes, JoséThis paper presents the results of audits performed in 60 companies of the food processing industry, specifically of meat, dairy, horticultural and bread products. The refrigeration volume, type of refrigeration system, refrigerant, building and insulation materials of infrastructure and refrigeration chambers, average air temperature and humidity, and the energy consumption are presented, compared and discussed per sector. The analysis allows to provide several measures and best practices aimed for the improvement of the thermal performance and energy efficiency of the food processing industry. The implementation of simple and very cost-effective transversal electricity savings measures such as awareness and/or training of operators, proper maintenance and monitoring tasks can benefit the sector. Tailored energy efficiency measures by sector, which may offer savings on several levels, are discussed. These best practices may increase productivity and competitiveness and reduce the environmental impact, and thus improve the global sustainability of the Portuguese food sector.
- Análise das condições de conforto em ambientes refrigeradosPublication . Fernandes, Eduardo; Silva, Pedro Dinho da; Gaspar, Pedro Dinis; Pires, Luís Carlos Carvalho; Nunes, JoséO presente estudo avalia as condições de frio a que os trabalhadores estão sujeitos no sector agroindustrial avaliando dois casos, uma empresa de distribuição alimentar e uma empresa de lacticínios. De forma a avaliar as condições de conforto térmico dos trabalhadores foram seguidos os procedimentos indicados em normas internacionais. Foram realizados inquéritos e efectuadas medições experimentais de forma a caraterizar as zonas e as condições em que os trabalhadores operam, bem como para avaliar os níveis de atividade de cada trabalhador. O trabalho desenvolvido permitiu identificar o tipo de exposição a que cada trabalhador está sujeito assim como determinar os índices característicos de conforto térmico, nomeadamente o índice IREQ. Os resultados mostram que ocorrem situações em que os trabalhadores possuem isolamento térmico adequado às condições onde estão inseridos mas que ainda assim manifestam sensações relacionadas com o desconforto térmico. Por outro lado, verificou-se também que alguns dos trabalhadores que possuem níveis de isolamento térmico supostamente insuficientes manifestam sensações térmicas neutras. Conclui-se assim que os trabalhadores apresentam uma tendência para uma aclimatação efectiva a ambientes frios que não aparece referida nas normas correspondentes.
- Estudo comparativo de processos de secagem da cerejaPublication . Nunes, José; Silva, Pedro Dinho da; Andrade, Luís P.; Pires, Luís Carlos Carvalho; Tomé, Rute; Gaspar, Pedro DinisA cereja fresca é um produto muito apreciado pelos consumidores devido às suas ótimas características organoléticas e nutricionais. Este produto é muito perecível e tem um período produtivo sazonal muito curto. Alguma quantidade de fruta perde o seu valor comercial quando ultrapassa o seu estado de maturação. Uma forma de valorizar este produto e o rendimento dos produtores é realizar a sua desidratação para obtenção de passas de cereja, com vantagens de estabilidade, valor nutricional e de comercialização. De entre os vários métodos atualmente possíveis para a realização da secagem é desejável a utilização daqueles que obtenham ótimos produtos desidratados e com baixos custos de funcionamento, nomeadamente com a energia. No presente estudo efetuámos a avaliação comparativa dos processos de secagem de cereja da Beira Interior por intermédio dos métodos da liofilização, secagem por ar quente e secagem solar. Apesar de algumas limitações o secador solar apresentou um bom desempenho para obtenção de passas de cereja com ótimas características de aw, cor, sabor, aspeto visual, para a secagem de cerejas com pré-tratamentos e não envolve custos com a energia, podendo ser preferido em relação aos outros dois métodos. Os restantes processos apresentaram como grande desvantagem o elevado consumo de energia.