As an alternative to simplify the simulations and facilitate the implementation of absorbers and regenerators in simulation software packages as TRNSYS[8], a simplified model was developed. In this model, the liquid-desiccant stream is represented by one single node in the у direction. The temperature of the liquid-desiccant is assumed constant, at the same temperature of the wall. The air stream is also represented by only one node in the direction across the channel. The energy and species equations for the air stream are:

The desiccant concentration is evaluated using a species balance for every step of the simulation, with the water mass transfer absorbed by the desiccant solution calculated through equation (22). The heat transfer coefficient is calculated using a correlation for Nusselt number for laminar flow in tubes with rectangular cross section [9]:

The mass transfer coefficient is then determined using the Chilton-Colburn analogy:

It should be noted that the analogy and the correlation above are valid only for constant temperature and concentration along the interface desiccant-air. Although this is not the case, for sufficiently high desiccant flow rates the change in concentration is small. The assumption of constant concentration in the desiccant film is similar to the assumption of constant thickness, i. e., it is only possible to assume a constant film thickness if the desiccant flow rate is relatively high. It is assumed, in the simplified model, that the heat generated by the absorption of the water vapour into the desiccant solution is immediately removed, what effectively decouples the mass and heat transfer phenomena.