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Authors
Abstract(s)
Para que se obtenham temperaturas inferiores às disponíveis no meio ambiente, quer seja para fins de conservação de alimentos ou para obtenção de conforto térmico, as serpentinas do evaporador, geralmente, operam a temperaturas inferiores às do ponto de congelação da água. O gelo formado na superfície das mesmas é prejudicial tanto a nível energético como térmico do sistema. Desta forma, a sua remoção é crucial para restabelecer as condições de funcionamento desejadas.
Os dispositivos utilizados atualmente na indústria da refrigeração para monitorizar a formação de gelo à superfície dos evaporadores possuem resultados que permanecem ainda aquém do desejado, pelo que estes continuam a ser um objeto de estudo com enorme potencial de exploração.
Na presente dissertação foi estudada a viabilidade de utilização de um dispositivo simples e de baixo custo para a monitorização da formação de gelo na superfície dos evaporadores. Tendo em conta os requisitos a que este está desde logo sujeito, optou-se pela utilização de um sensor resistivo. O conceito do dispositivo testado baseia-se na variação que a formação de gelo impõe à resistência mensurada entre elétrodos. Uma vez que se verificam efetivamente diferentes resistividades elétricas entre os materiais em estudo, seguiram-se os estudos experimentais de forma a apurar se o dipositivo e respetivos circuitos eletrónicos possuem sensibilidade suficiente para atingir o objetivo proposto.
Verificada a sensibilidade do dispositivo em condições mais favoráveis, seguiu-se a calibração da distância entre elétrodos em condições reais. Reunidas as condições necessárias, procedeu-se à realização do estudo experimental e correspondente análise. Através de minuciosa análise de resultados, o circuito eletrónico capaz de automatizar todo o processo foi dimensionado e projetado numa placa de circuito impresso.
Os resultados obtidos permitiram concluir que, tanto a configuração do circuito utilizado como o conceito associado ao dispositivo em utilização possuem potencial para serem utilizados como dispositivos de monitorização da formação de gelo. No entanto, existem alguns ajustes a efetuar até que este possa atingir um patamar de aplicação generalizada.
In order to obtain temperatures lower than those available in the environment, whether for purposes of preserving food or for obtaining thermal comfort, the evaporator coils typically operate at temperatures below the water freezing point. The ice formed on the surface thereof is detrimental to both thermal and energy level of the system. Thereby, its removal is critical to restore the desired operating conditions. Currently the devices used in the refrigeration industry to monitor the ice formation on the surface of the evaporators have results that are still below the desirable, so these remain an object of study with great potential exploration. In the present work, the feasibility of using a simple and low cost device for monitoring the ice formation on the evaporator surface was studied. Taking knowledge of the requirements to which it is immediately subject, it was decided to use a resistive sensor. The device concept under examination is based on the influence that ice formation has in the resistance variation measured between the electrodes. Since it was effectively verified the different electrical resistivity between the materials under study, they were followed by experimental studies in order to determinate whether the respective dispositive and electronic circuits have enough sensitivity to achieve the proposed objective. Once checked the device sensitivity in more favorable conditions, then it was followed by the calibration of the distance between electrodes in real conditions. Fulfilled the necessary conditions, we proceeded to carry out the experimental study and corresponding analysis. Through detailed analysis of results, the electronic circuit capable of automating the entire process was scaled and designed in a printed circuit board. The results allow to conclude that both the circuit configuration used as the concept associated with the device in use, have potential to be used as icing monitoring devices. However, it needs some adjustments to make until being able to reach a generalized application level.
In order to obtain temperatures lower than those available in the environment, whether for purposes of preserving food or for obtaining thermal comfort, the evaporator coils typically operate at temperatures below the water freezing point. The ice formed on the surface thereof is detrimental to both thermal and energy level of the system. Thereby, its removal is critical to restore the desired operating conditions. Currently the devices used in the refrigeration industry to monitor the ice formation on the surface of the evaporators have results that are still below the desirable, so these remain an object of study with great potential exploration. In the present work, the feasibility of using a simple and low cost device for monitoring the ice formation on the evaporator surface was studied. Taking knowledge of the requirements to which it is immediately subject, it was decided to use a resistive sensor. The device concept under examination is based on the influence that ice formation has in the resistance variation measured between the electrodes. Since it was effectively verified the different electrical resistivity between the materials under study, they were followed by experimental studies in order to determinate whether the respective dispositive and electronic circuits have enough sensitivity to achieve the proposed objective. Once checked the device sensitivity in more favorable conditions, then it was followed by the calibration of the distance between electrodes in real conditions. Fulfilled the necessary conditions, we proceeded to carry out the experimental study and corresponding analysis. Through detailed analysis of results, the electronic circuit capable of automating the entire process was scaled and designed in a printed circuit board. The results allow to conclude that both the circuit configuration used as the concept associated with the device in use, have potential to be used as icing monitoring devices. However, it needs some adjustments to make until being able to reach a generalized application level.
Description
Keywords
Evaporador Gelo Segurança Alimentar e Eficiência Energética. Sensor Resistivo Sistemas de Refrigeração