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- Further development and experimental testing of a resistive sensor for monitoring frost formation in refrigeration systemsPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro Dinho daRefrigeration systems are widely accepted as a mean to prevent food degradation. These systems usually rely on fin-and-tube heat exchangers to lower the air temperature. Due to long operation times and surface temperatures below dew point, frost may form and accumulate on the evaporators fin surface. This frost accumulation reduces and may clog the airflow, decreasing the system efficiency. Usually, most systems use a time-controlled system (stopping the compressor with or without powering a heating resistor inserted among fins to heat) to melt the ice. This method does not measure or predict the amount of frost formed, thus it is not reliable. Ice sensors that are cheap, reliable and easy to implement in commercial systems are studied. A resistive sensor is purposed, that measures the voltage between two electrodes with the water phase change (condensation and solidification -freezing-), as these states have different resistive values. Different electrode materials, morphologies and configurations are studied in order to obtain the best design.
- Standalone docking station with combined charging methods for agricultural mobile robotsPublication . Varandas, Leonor Cristina Pinheiro dos Santos; Gaspar, Pedro Dinis; Aguiar, MartimOne of the biggest concerns in the field of agriculture is around the energy efficiency of robots that will perform agriculture’s activity and their charging methods. In this paper, two different charging methods for agricultural standalone docking stations are shown that will take into account various variants as field size and its irregularities, work’s nature to which the robot will perform, deadlines that have to be respected, among others. Its features also are dependent on the orchard, season, battery type and its technical specifications and cost. First charging base method focuses on wireless charging, presenting more benefits for small field. The second charging base method relies on battery replacement being more suitable for large fields, thus avoiding the robot stop for recharge. Existing many methods to charge a battery, the CC CV was considered the most appropriate for either simplicity or effectiveness. The choice of the battery for agricultural purposes is if most importance. While the most common battery used is Li-ion battery, this study also discusses the use of graphene-based new type of batteries with 45% over capacity to the Li-ion one. A Battery Management Systems (BMS) is applied for battery balancing. All these approaches combined showed to be a promising method to improve a lot of technical agricultural work, not just in terms of plantation and harvesting but also about every technique to prevent harmful events like plagues and weeds or even to reduce crop time and cost.
- Thermal Management of Short-Range Distribution of Perishable Food Products Using Phase Change Materials in Packaging: Real-Time Field Data AcquisitionPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro Dinho daMaintaining a stable temperature is critical in ensuring the longevity of perishable foods, and frequent fluctuations due to short-range distribution conditions can negatively affect this stability. To mitigate these variations, an innovative modular packaging system utilizing phase change materials (PCMs) was employed in the transport and storage of horticultural products. This study’s real-time thermal condition data, collected using a wireless data acquisition system inserted in the packaging, demonstrated the efficacy of PCM in increasing temperature stability within the crates of horticultural products. The field tests conducted over 8 h showed that PCM-equipped packaging boxes exhibited a temperature variation of less than 1 °C, compared to non-PCM boxes, which saw variations up to 3 °C. This marked reduction in temperature fluctuation signifies the potential of PCM in improving thermal and logistics management in food conservation, thus reducing food waste. However, it is essential to implement a system for PCM alveoli reuse to avoid adverse environmental impacts. Future research should focus on the PCM alveoli autonomy and quantity requirements for specific conditions, and integrate sensors to monitor transport dynamics to enhance the understanding of temperature stability in perishable food transportation.
- Frost Measuring and Prediction Systems for Demand Defrost ControlPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro Dinho daIt is widely known that the defrosting operation of evaporators of commercial refrigeration equipment is one of the main causes of inefficiency on these systems. Several defrosting methods are used nowadays, but the most commonly used are still time-controlled defrosting systems, usually by either electric resistive heating or reverse cycle. This happens because most demand defrost methods are still considered complex, expensive, or unreliable. Demand defrost can work by either predicting frost formation by processing measured conditions (fin surface temperature, air humidity, and air velocity), operative symptoms of frost accumulation (pressure drop and refrigerant properties), or directly measuring the frost formation using sensors (photoelectric, piezoelectric, capacitive, resistive, etc.). The data measured by the sensors can be directly used by the system but can also be processed either by simple algorithms or more complex systems that use artificial intelligence and predictive methods. This chapter approaches frost sensing and prediction for command of demand defrost systems.
- Reutilização direta de termoplásticos em máquinas de Modelagem por Deposição de Material FundidoPublication . Aguiar, Martim Lima; Gaspar, Pedro Miguel de Figueiredo Dinis OliveiraCada vez mais a acumulação de plástico nas lixeiras é um problema. A sua composição não biodegradável e produção geralmente feita a partir de combustíveis fósseis fazem com que seja de extrema importância que este plástico se mantenha no ciclo da reciclagem. Políticas de incentivo á reciclagem, ou punição à má separação de resíduos têm-se provado eficazes para combater o problema, no entanto a contínua e crescente utilização de plásticos requer o desenvolvimento de novas abordagens que contribuam também a este fim. Viemos também numa era em que o crescimento da tecnologia de modelação por deposição de material fundido (comumente referida como impressão 3D) está a atingir uma escala exponencial, podendo num futuro muito próximo ser um eletrodoméstico comum de encontrar em habitações domésticas, pondo em causa o funcionamento da produção de bens tal como a conhecemos. Na presente dissertação apresenta-se o dimensionamento e etapas de construção de uma extrusora de termoplástico com dimensões reduzidas, especificamente construída para extrudir resina termoplástica politereftalato de etileno e todas as suas componentes, assente no estudo de termoplásticos, máquinas de fabricação aditiva e da extrusão. Esta proposta pretende contribuir para a redução do desperdício de termoplásticos, permitindo que a reciclagem seja feita em ambiente doméstico e o produto desta utilizado em máquinas de modelação por deposição de material fundido. Assim, é possibilitada a criação de novos bens a partir de plásticos que seriam descartados, trazendo assim os lucros da reciclagem para o utilizador, diminuindo o desperdício e custos associados ao transporte.
- Low-Cost IoT Remote Sensor Mesh for Large-Scale Orchard MonitorizationPublication . Varandas, Leonor Cristina Pinheiro dos Santos; Faria, João; Gaspar, Pedro Dinis; Aguiar, MartimPopulation growth and climate change lead agricultural cultures to face environmental degradation and rising of resistant diseases and pests. These conditions result in reduced product quality and increasing risk of harmful toxicity to human health. Thus, the prediction of the occurrence of diseases and pests and the consequent avoidance of the erroneous use of phytosanitary products will contribute to improving food quality and safety and environmental land protection. This study presents the design and construction of a low-cost IoT sensor mesh that enables the remote measurement of parameters of large-scale orchards. The developed remote monitoring system transmits all monitored data to a central node via LoRaWAN technology. To make the system nodes fully autonomous, the individual nodes were designed to be solar-powered and to require low energy consumption. To improve the user experience, a web interface and a mobile application were developed, which allow the monitored information to be viewed in real-time. Several experimental tests were performed in an olive orchard under di erent environmental conditions. The results indicate an adequate precision and reliability of the system and show that the system is fully adequate to be placed in remote orchards located at a considerable distance from networks, being able to provide real-time parameters monitoring of both tree and the surrounding environment.
- Medium materials for improving frost detection on a resistive sensorPublication . Aguiar, Martim Lima; Gaspar, Pedro Dinis; Silva, Pedro D.; Silva, A. P.; Martinez, A. M.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.
- Frost measurement methods for demand defrost control systemsPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro Dinho daIt is widely known that defrosting operation on commercial refrigerators is one of the main causes of inefficiency on these systems. Several defrosting methods are used nowadays, but the most commonly used are still time-controlled defrosting, usually by either electric resistive heating or reverse cycle, as most demand defrost methods are usually complex, expensive or unreliable. Demand defrost can work by either predicting frost formation by processing measured conditions (fin surface temperature, air humidity and air velocity) and/or frost accumulation symptoms such as pressure drop and refrigerant properties. Other way of knowing when to defrost is to directly measure the frost formation using sensors such as photoelectric, capacitive or resistive. This review gathers some of the methods that can be used for directly measuring frost accumulation on the evaporator fin surface.
- Testing of a resistive sensor with fabric medium for monitoring frost formation in refrigeration systemsPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro D.; Duarte, DianaRefrigeration is one of the key elements for food preservation. With global temperatures increasing due to global warming, the efficiency in refrigerated storage systems must be improved. One of the problems that is yet to be solved in these systems is the efficient and accurate removal of the frost formed on the heat exchanger surface. In previous works, a low-cost resistive sensor has been developed to detect frost formation for accurate removal. This paper shows the results of an experimental study carried out to increase the accuracy, by placing different configurations of a fabric medium in between the sensor electrodes.
- Modeling the heat transfer and the pressure loss in flat fin-and-tube compact heat exchangersPublication . Aguiar, Martim; Gaspar, Pedro Dinis; Silva, Pedro Dinho daFin-and-tube heat exchangers (HX) have wide application in the industry. The study of HXs with reduced tube diameter has allowed the development of more compact and equally efficient equipment. Most of the HXs of this type are composed of flat fins, not only due to the ease of construction but also to their reliability in long-term operation and reduced friction characteristics. The formulation of mathematical equations that predict the effect of the geometric characteristics on the heat transfer and friction factors of the HXs lead many researchers to try to establish correlations that approximate the experimental results. In this paper is developed a computational tool based on literature correlations is used to evaluate the Colburn and friction factors for flat fin-and-tube compact HXs. The results of predictions show the Colburn and friction factors behavior for different geometrical parameters (fin pitch, tube diameter, tube number) and typical Reynolds number.