Abstract
In this study, ammonia vapor absorption with NH3/LiNO3 was assessed using correlations derived from a semi-empirical model, and artificial neural networks (ANNs). The absorption process was studied in an H-type corrugated plate absorber working in bubble mode under the conditions of an absorption chiller machine driven by low-temperature heat sources. The semi-empirical model is based on discretized heat and mass balances, and heat and mass transfer correlations, proposed and developed from experimental data. The ANN model consists of five trained artificial neurons, six inputs (inlet flows and temperatures, solution pressure, and concentration), and three outputs (absorption mass flux, and solution heat and mass transfer coefficients). The semi-empirical model allows estimation of temperatures and concentration along the absorber, in addition to overall heat and mass transfer. Furthermore, the ANN design estimates overall heat and mass transfer without the need for internal details of the absorption phenomenon and thermophysical properties. Results show that the semi-empirical model predicts the absorption mass flux and heat flow with maximum errors of 15.8% and 12.5%, respectively. Maximum errors of the ANN model are 10.8% and 11.3% for the mass flux and thermal load, respectively.
Highlights
Absorption cooling systems appear to be promising energy-saving technologies if they use residual/available heat or solar energy for their operation [1]
Systems with a NH3 /LiNO3 mixture do not require rectification of the refrigerant vapor emitted from the generator because the absorbent is a salt, and these systems can operate at lower activation temperatures compared to ammonia/water (NH3 /H2 O) systems
This sub-section presents the heat and mass transfer correlations developed and proposed considering the data collected by Amaris [41] from an experimental study of the H-type plate heat exchanger (PHE) absorber
Summary
Absorption cooling systems appear to be promising energy-saving technologies if they use residual/available heat or solar energy for their operation [1]. Former experimental investigations have shown that the major limiting aspect of the NH3 /LiNO3 mixture is its elevated viscosity, which restricts heat and mass transfer, primarily in the absorber, in comparison to the NH3 /H2 O mixture [4,5,6,7]. This limitation has motivated studies aimed at enhancing the absorption process with NH3 /LiNO3 by employing passive techniques [8,9,10].
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