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O presente trabalho aborda o estudo de um sistema de armazenamento de hidrogénio no estado líquido com sistema de refrigeração integrado. O principal objetivo será estudar a viabilidade da utilização do hidrogénio líquido, recorrendo a um modelo matemático para cálculo dos ganhos térmicos do tanque contemplando diferentes geometrias, dimensões e materiais construtivos. Para isso será então dimensionado um sistema de refrigeração. A revisão bibliográfica apresenta as propriedades e características de maior relevância do hidrogénio, algumas questões de segurança no que toca à utilização de hidrogénio como combustível, métodos de armazenamento, método de cálculo para definir o ganho térmico do tanque, materiais ideais para a construção do tanque, fluidos frigorigéneos adequados para uso criogénico e método de cálculo para dimensionamento do sistema de refrigeração. Após a obtenção dos resultados foi possível concluir que o tanque cilíndrico disposto na horizontal apresenta o valor de ganho térmico mais reduzido, 3,32 W, 1 a 400% inferior quando comparado com o tanque cilíndrico disposto na vertical e esférico, nomeadamente. O material de isolamento com melhor comportamento são as microesferas apresentando valores de ganho térmico 17 a 32 vezes inferiores aos valores da poliimida no caso do tanque cilíndrico e esférico, nomeadamente. O aumento da espessura em 500% é traduzido na redução do ganho térmico entre 400 a 450%. A amplitude térmica diária poderá implicar uma variação do ganho térmico de 3,5 a 7% entre as temperaturas mínima e máxima. O sistema de refrigeração apresenta um COP de 7,04 e o termo Wcomp/Qevap apresenta um valor de 0,14. Por forma a obter a melhor eficiência de compressão deverá ser considerado o sobreaquecimento ou sobreaquecimento e subarrefecimento do R-702p. O aumento da temperatura de condensação em 35oC é traduzido na diminuição do COP em 19% e o aumento do fluxo mássico em 8%. Quando utilizado o R-134a no último subciclo são obtidos COP até 11% superiores, razões de compressão 7% inferiores e temperaturas de sobreaquecimento 22% inferiores. Quanto ao consumo energético mensal por unidade de massa de hidrogénio, o tanque cilíndrico apresenta o seguinte valor 2984,3 kJ/kgLH2 e o tanque esférico 11114,3 kJ/kgLH2. Estes valores representam 2,51 e 9,36% da energia armazenada no tanque cilíndrico e esférico, nomeadamente.
The present work addresses the study of a liquid hydrogen storage system with an integrated refrigeration system. The main objective will be to study the feasibility of using liquid hydrogen, using a mathematical model to calculate the thermal gains of the tank considering different geometries, dimensions, and construction materials. For this, a cooling system will be dimensioned. The literature review presents the most relevant properties and characteristics of hydrogen, some safety issues regarding the use of hydrogen as a fuel, storage methods, calculation method to define the thermal gain of the tank, ideal materials for the construction of the tank, refrigerants suitable for cryogenic use and calculation method for dimensioning the refrigeration system. After obtaining the results, it was possible to conclude that the cylindrical tank arranged horizontally has the lowest thermal gain value, 3,32 W, 1 to 400% lower when compared to the cylindrical tank arranged vertically and spherical, namely. The insulation material with the best performance are microspheres, presenting values of thermal gain 17 to 32 times lower than the values of polyimide in the case of cylindrical and spherical tanks, namely. Increasing the thickness by 500% translates into a reduction in thermal gain between 400 and 450%. The daily thermal amplitude may imply a variation of the thermal gain of 3,5% to 7% between the minimum and maximum temperatures. The refrigeration system has a COP of 7,04 and the Wcomp/Qevap term has a value of 0,14. To obtain the best compression efficiency, overheating or overheating and subcooling of R702p should be considered. The increase in condensing temperature by 35oC translates into a decrease in COP by 19% and an increase in mass flow by 8%. When using R-134a in the last sub cycle, up to 11% higher COP, 7% lower compression ratios and 22% lower superheat temperatures are obtained. As for the monthly energy consumption per unit of mass of hydrogen stored, the cylindrical tank has the following value 2984,3 kJ/kgLH2 and the spherical tank 11114,3 kJ/kgLH2. These values represent 2,51 and 9,36% of the energy stored in the cylindrical and spherical tank, namely.
The present work addresses the study of a liquid hydrogen storage system with an integrated refrigeration system. The main objective will be to study the feasibility of using liquid hydrogen, using a mathematical model to calculate the thermal gains of the tank considering different geometries, dimensions, and construction materials. For this, a cooling system will be dimensioned. The literature review presents the most relevant properties and characteristics of hydrogen, some safety issues regarding the use of hydrogen as a fuel, storage methods, calculation method to define the thermal gain of the tank, ideal materials for the construction of the tank, refrigerants suitable for cryogenic use and calculation method for dimensioning the refrigeration system. After obtaining the results, it was possible to conclude that the cylindrical tank arranged horizontally has the lowest thermal gain value, 3,32 W, 1 to 400% lower when compared to the cylindrical tank arranged vertically and spherical, namely. The insulation material with the best performance are microspheres, presenting values of thermal gain 17 to 32 times lower than the values of polyimide in the case of cylindrical and spherical tanks, namely. Increasing the thickness by 500% translates into a reduction in thermal gain between 400 and 450%. The daily thermal amplitude may imply a variation of the thermal gain of 3,5% to 7% between the minimum and maximum temperatures. The refrigeration system has a COP of 7,04 and the Wcomp/Qevap term has a value of 0,14. To obtain the best compression efficiency, overheating or overheating and subcooling of R702p should be considered. The increase in condensing temperature by 35oC translates into a decrease in COP by 19% and an increase in mass flow by 8%. When using R-134a in the last sub cycle, up to 11% higher COP, 7% lower compression ratios and 22% lower superheat temperatures are obtained. As for the monthly energy consumption per unit of mass of hydrogen stored, the cylindrical tank has the following value 2984,3 kJ/kgLH2 and the spherical tank 11114,3 kJ/kgLH2. These values represent 2,51 and 9,36% of the energy stored in the cylindrical and spherical tank, namely.
Description
Keywords
Armazenamento de hidrogénio Estado líquido Ganho térmico Sistema de refrigeração integrado Hydrogen storage Liquid state Thermal gain Integrated cooling system