Área efetiva de força e coeficiente de descarga para escoamentos em difusores radiais: um conjunto amplo de dados de soluções numéricas para aplicação em válvulas de compressores de refrigeração
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Data
2020-12-11
Autores
Ferreira, Ricardo Lopes
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
O projeto de válvulas do tipo palheta usadas em compressores de sistemas de refrigeração desempenha um papel importante no desenvolvimento de compressores mais eficientes. Entretanto, a modelagem e a solução do problema são complexas por envolverem um fenômeno de interação fluido-estrutura, o que torna o projeto de válvulas eficientes um grande desafio. Por necessitar de elevados recursos e tempos computacionais para resolver o problema real de interação fluido-estrutura, a simulação global do compressor geralmente emprega o modelo quase-estático para representar o comportamento das válvulas. Dois parâmetros globais obtidos da solução desse modelo são usados para a simulação do compressor: a área efetiva de força, para determinar a força do escoamento sobre a válvula, e o coeficiente de descarga, para determinar a vazão do escoamento pela válvula. Devido à complexidade geométrica das válvulas, a geometria simplificada do difusor radial é muito empregada. Vários trabalhos já reportaram dados para os parâmetros globais obtidos de simulações numéricas de escoamentos em difusores radiais. Entretanto, os dados são limitados, não representando a ampla faixa de operação necessária para o projeto e simulação dos compressores. O objetivo deste trabalho é preencher esta lacuna, fornecendo dados dos parâmetros globais, obtidos por simulação numérica de escoamentos em difusores radiais, para ampla faixa de operação de compressores de refrigeração. O Método de Volumes Finitos, implementado no código aberto e de licença gratuita OpenFOAM\R e validado com dados experimentais, foi empregado para resolver o problema do escoamento estacionário e incompressível em difusores radiais com razões de diâmetro iguais a 1,15, 1,3, 1,5 e 1,7. Escoamentos com números de Reynolds variando de 3.000 até 50.000 e afastamentos adimensionais entre discos variando de 0,01 até 1,0 foram simulados para as quatro geometrias de difusores radiais. Os resultados mostram que o aumento da razão de diâmetro de 1,15 a 1,7 produz redução da área efetiva de força de até 80\% para os menores afastamentos entre discos e aumento de até 40\% para o maior afastamento entre discos. Entretanto, o coeficiente de descarga não é significativamente influenciado pela razão de diâmetro. Para um aumento do número de Reynolds de 3.000 a 50.000, o aumento da área efetiva de força é menor, atingindo apenas 13\% no maior afastamento entre discos, para o caso do difusor radial com a maior razão de diâmetro. A influência do número de Reynolds sobre coeficiente de descarga é ainda menor, produzindo um aumento máximo de 8\% para o maior afastamento entre discos.
The design of reed-type valves used in refrigeration system compressors plays an important role in the development of more efficient compressors. However, the modeling and solution of the problem are complex because they involve a phenomenon of fluid-structure interaction, which makes the design of efficient valves a great challenge. Because it requires high computational resources and computational time to solve the actual problem of fluid-structure interaction, the overall compressor simulation usually employs the quasisteady model to represent valve behavior. Two global parameters obtained from the solution of this model are used for compressor simulation: the effective force area, to determine the force of the flow over the valve, and the discharge coefficient, to determine the mass flow rate through the valve. Due to the geometric complexity of the valves, the simplified geometry of the radial diffuser is widely employed. Several studies have reported data for the global parameters obtained from numerical simulations of flows in radial diffusers. However, the data are limited, not representing the wide range of operating conditions required for the design and simulation of the compressors. The objective of this work is to fill this gap by providing data of the global parameters, obtained by numerical simulation of flows in radial diffusers, for a wide range of operating conditions of refrigeration compressors. The Finite Volume Method, implemented in the free and open-source software OpenFOAM® and validated with experimental data, was used to solve the problem of stationary and incompressible flows in radial diffusers with diameter ratios equal to 1.15, 1.3, 1.5, and 1.7. Flows with Reynolds numbers ranging from 3,000 to 50,000 and dimensionless distance between disks ranging from 0.01 to 1.0 were simulated for the four radial diffuser geometries. The results show that when the diameter ratio increases from 1.15 to 1.7 the effective force area reduces 80% for small distances between discs, but increases 40% for the largest distance between discs. However, the discharge coefficient is not significantly influenced by the diameter ratio. For Reynolds number increasing from 3,000 to 50,000, the effective force area increases only 13% for the largest distance between discs, for the case of the radial diffuser with the highest diameter ratio. The influence of the Reynolds number on the discharge coefficient is even lower, producing a maximum increase of 8% for the largest distance between discs.
The design of reed-type valves used in refrigeration system compressors plays an important role in the development of more efficient compressors. However, the modeling and solution of the problem are complex because they involve a phenomenon of fluid-structure interaction, which makes the design of efficient valves a great challenge. Because it requires high computational resources and computational time to solve the actual problem of fluid-structure interaction, the overall compressor simulation usually employs the quasisteady model to represent valve behavior. Two global parameters obtained from the solution of this model are used for compressor simulation: the effective force area, to determine the force of the flow over the valve, and the discharge coefficient, to determine the mass flow rate through the valve. Due to the geometric complexity of the valves, the simplified geometry of the radial diffuser is widely employed. Several studies have reported data for the global parameters obtained from numerical simulations of flows in radial diffusers. However, the data are limited, not representing the wide range of operating conditions required for the design and simulation of the compressors. The objective of this work is to fill this gap by providing data of the global parameters, obtained by numerical simulation of flows in radial diffusers, for a wide range of operating conditions of refrigeration compressors. The Finite Volume Method, implemented in the free and open-source software OpenFOAM® and validated with experimental data, was used to solve the problem of stationary and incompressible flows in radial diffusers with diameter ratios equal to 1.15, 1.3, 1.5, and 1.7. Flows with Reynolds numbers ranging from 3,000 to 50,000 and dimensionless distance between disks ranging from 0.01 to 1.0 were simulated for the four radial diffuser geometries. The results show that when the diameter ratio increases from 1.15 to 1.7 the effective force area reduces 80% for small distances between discs, but increases 40% for the largest distance between discs. However, the discharge coefficient is not significantly influenced by the diameter ratio. For Reynolds number increasing from 3,000 to 50,000, the effective force area increases only 13% for the largest distance between discs, for the case of the radial diffuser with the highest diameter ratio. The influence of the Reynolds number on the discharge coefficient is even lower, producing a maximum increase of 8% for the largest distance between discs.
Descrição
Palavras-chave
Compressores de refrigeração, Válvula tipo palheta, Difusor radial, Área efetiva de força, Coeficiente de descarga, Simulação numérica, Volumes finitos, Refrigeration compressor, Reed type valve, Radial diffuser, Effective force area, Discharge coefficient, Numerical simulation, Finite volume, OpenFOAM