Global modeling of heat and mass transfers in spiral tubular absorber of a water-lithium bromide absorption chiller

摘要

In this work, a simplified nonlinear coupled model and a simplified linear coupled model are examined in order to determine the model that better approaches the global mass and heat transfers during water vapor absorption by a falling film of LiBr solution in a spiral tubular absorber of an absorption chiller. The linear coupled model gives up analytical expressions that are used to determine overall heat and mass transfer coefficients from the experimental measurements taken at the inlet and outlet of absorber. These coupled overall transfer coefficients are used with the uncoupled ones that are deduced from the LMD method to determine the simulated absorption parameters along the absorber area. The comparison between the two models based essentially on the different parameters values at the inlet and the outlet of the absorber shows that nonlinear model approaches better experimental results. It shows also that the use of overall coupled transfer coefficients is not significant at low solution flow rates usually encountered in absorption chiller application and therefore the use of the overall transfer coefficients extracted from LMD method approaches well experimental data. The nonlinear model which is the approved model points up that the absorbed water vapor quantity and the overall effective mass transfer coefficient for the spiral tubular absorber increase with decreasing cooling water temperatures.