Transient model for the development of an air-cooled LiBr-H2O absorption chiller based on heat and mass transfer empirical correlations

Abstract

• Development of a transient model based on heat and mass transfer correlations for absorption chillers (H 2 O-LiBr). • Generic expressions for heat&mass transfer used, parameter identification minimized. • A new zero order model for absorber and generator is developed. • Experimental validation with an agreement of 5% for COP and 11% for cooling capacity. • The new model is used for the development of a direct air-cooled absorption chiller. This work describes transient numerical modeling of a direct air-cooled, single-effect absorption chiller. The model is lumped parametric based on transient mass, momentum, and energy balances, applied to the internal components of the absorption machine. Thermal and mass storage in each one of the components are taken into account in the transient evaluation, and pressure losses in the SHX are evaluated using a pressure drop coefficient. This work aims to improve the available numerical modeling propositions by using embedded available heat and mass transfer empirical correlations, based on previous experiences in falling film absorption. This approach minimizes the need for experimental parameter identification and allows scalability studies. The experimental validation has been organized in three steps: (i) absorber zero-order model, steady-state conditions; (ii) the whole chiller, also in steady-state conditions; (iii) transient conditions. For the steady-state conditions, most results have an agreement within the margin of the uncertainty of the experiments, with a medium discrepancy of 5% in COP and 11% in the cooling capacity. For transient conditions, the comparison of the outlet temperatures of the secondary streams, reveals discrepancies under 0.5 K, except in some fast transient periods, where higher differences are perceived. To perform the numerical simulations is used as an in-house modular object-oriented simulation platform (NEST platform). Finally, the performance of a prototype demonstration 7 kW air-cooled LiBr-H 2 O absorption chiller is predicted through a designed test campaign. This model put gives valuable information for the definition of further regulation and control protocols.