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Abstract(s)
O objetivo desta dissertação é estudar o método de armazenamento de hidrogénio no estado
líquido, procurando a melhor solução para o seu armazenamento, e posterior dimensionamento
do sistema de refrigeração correspondente, a partir do cálculo dos ganhos térmicos do tanque de
armazenamento. Para estudar a possibilidade de utilização deste método, é usado um modelo
matemático que possibilita calcular os ganhos térmicos do tanque e que permite o
dimensionamento do sistema de refrigeração a integrar.
Com esse intuito, é feita uma pesquisa bibliográfica para efeito de enquadramento do tema em
estudo e uma descrição dos modelos matemáticos utlizados. Nesta pesquisa são abordados os
temas que se consideram fundamentais, designadamente: características e aspetos de segurança
do hidrogénio, armazenamento e produção de hidrogénio, armazenamento e produção de
hidrogénio líquido, reservatórios utilizados para este armazenamento – onde se consideram
várias geometrias utilizadas bem como vários materiais adequados para a construção dos
reservatórios. Para terminar realiza-se um estudo sobre os fluidos frigorigéneos adequados para
uso criogénico.
Após a obtenção de resultados é possível concluir que a geometria esférica apresenta o menor
valor de ganho térmico – aproximadamente 6,53W. Esse valor é cerca de 1,7 vezes inferior
quando comparado com as geometrias cilíndricas. O material do isolamento considerado para a
obtenção destes valores foi a espuma de poliuretano 10-2.
O sistema de refrigeração selecionado apresenta um COP de 2,9 e uma razão de compressão de 3.
A partir dos diferentes estudos realizados concluiu-se que: a realização do sobreaquecimento e
subarrefecimento do R-702p permite obter uma melhor eficiência de compressão. O aumento da
temperatura de condensação é traduzido numa diminuição do COP e num aumento do caudal
mássico. Concluiu-se ainda que a melhor alternativa à utilização do R-134a será o R-1234yf e
relativamente ao valor obtido para o consumo energético mensal, por unidade de massa de
hidrogénio, este valor corresponde a menos de 1% da energia armazenada nos tanques.
The aim of this dissertation is to study the method of storing hydrogen in a liquid state, looking for the best solution for storing it and then sizing the corresponding cooling system, based on the calculation of the thermal gains of the storage tank. In order to study the possibility of using this method, a mathematical model is used to estimate the thermal gains of the tank and allows the sizing of the cooling system which is to be used. To this end, a bibliographical survey was carried out to provide a framework for the subject under study and a description of the mathematical models used. This research covers the topics that are considered fundamental, namely: the characteristics and safety aspects of hydrogen, the storage and production of hydrogen, the storage and production of liquid hydrogen, the tanks used for this storage – where various geometries are considered, as well as various materials suitable for the construction of the tanks. Finally, a study is carried out on the refrigerants suitable for cryogenic use. After obtaining the results, it can be concluded that the spherical geometry has the lowest thermal gain value – around 6,53W. This value is 1,7 times lower when compared with the cylindrical geometries. The insulation material used to obtain these values was 10-2 polyurethane foam. The selected refrigeration system has a COP of 2,9 and a compression ratio of 3. From the various studies carried out, it was concluded that: superheating and subcooling the R-702p enables better compression efficiency to be obtained. The increase in condensation temperature results in a decrease in COP and an increase in mass flow. It is also considered that the best alternative to using R-134a is R-1234yf and as for the value obtained for monthly energy consumption per unit mass of hydrogen, this corresponds to less than 1% of the energy stored in the tanks.
The aim of this dissertation is to study the method of storing hydrogen in a liquid state, looking for the best solution for storing it and then sizing the corresponding cooling system, based on the calculation of the thermal gains of the storage tank. In order to study the possibility of using this method, a mathematical model is used to estimate the thermal gains of the tank and allows the sizing of the cooling system which is to be used. To this end, a bibliographical survey was carried out to provide a framework for the subject under study and a description of the mathematical models used. This research covers the topics that are considered fundamental, namely: the characteristics and safety aspects of hydrogen, the storage and production of hydrogen, the storage and production of liquid hydrogen, the tanks used for this storage – where various geometries are considered, as well as various materials suitable for the construction of the tanks. Finally, a study is carried out on the refrigerants suitable for cryogenic use. After obtaining the results, it can be concluded that the spherical geometry has the lowest thermal gain value – around 6,53W. This value is 1,7 times lower when compared with the cylindrical geometries. The insulation material used to obtain these values was 10-2 polyurethane foam. The selected refrigeration system has a COP of 2,9 and a compression ratio of 3. From the various studies carried out, it was concluded that: superheating and subcooling the R-702p enables better compression efficiency to be obtained. The increase in condensation temperature results in a decrease in COP and an increase in mass flow. It is also considered that the best alternative to using R-134a is R-1234yf and as for the value obtained for monthly energy consumption per unit mass of hydrogen, this corresponds to less than 1% of the energy stored in the tanks.
Description
Keywords
Hydrogen storage liquid thermal gain