## 1 Introduction  
Absorption cooling chillers can be fed by any heat source, including renewable or waste heat, for example, from solar thermal collectors. Any solar thermal facility, used to obtain domestic hot water and/or heating, can be used to provide air-conditioning in the summer season, obtaining the best use for the solar facility. In this way, the electricity consumed during summer can be reduced, decreasing possible peaks in the electrical grid. In a single effect absorption chiller, there are four key components: absorber, desorber, evaporator, and condenser, as shown in Figure 1. In the desorber, an amount qd of heat is supplied to the solution flowing inside the device to separate a portion of the more volatile component (the refrigerant). In the case of the H\({}_{2}\)O-LiBr pair, the solution concentrated as a fraction of water in the superheated vapour state is separated. This vapour flows to the following component, the condenser, where the amount qc of heat is released to a recooling fluid (typically water coming from a cooling tower or ambient air). The superheated vapor is then cooled and condensed, ideally obtaining water in a saturated liquid state. These two components, desorber and condenser, work at the highest pressure inside the absorption chiller. For this reason, expansion devices are located at their outlets to reduce the pressure down to the values in the following devices (absorber and evaporator). In the condenser, liquid water expands in the throttling device to obtain a saturated two-phase flow that enters the evaporator. There, the remaining liquid water evaporates, thanks to the heat \(\mathrm{q_{e}}\) extracted from the external cold fluid, producing the desired cooling effect. Vapour generated enters into the absorber, where it comes into contact with the concentrated solution flowing from the desorber. Here, the solution absorbs the vapour and the absorption and dilution heats produced \(\mathrm{q_{a}}\) are transferred to an external recooling fluid. The diluted solution is then pumped again to the desorber to close the cycle. An additional component, a recovery heat exchanger, is added in real absorption chillers to improve the cycle efficiency. It is located between the desorber and the absorber and allows heat transfer from the hot concentrated mixture to the cold diluted one. Figure 1 shows the typical configuration used for desorber and absorber in conventional absorption chillers, corresponding to shell and tubes exchangers. In the case of the desorber, the heating fluid circulates through the tubes, while solution boils inside the shell. In the absorber, the concentrated solution is dispersed in drops at the top of the tube bank, entering into contact with the vapour flowing from the evaporator. The heat released during absorption is extracted by the recooling fluid circulating through the tubes. Both components are very large, heavy, and very sensitive to vibrations. For this reason, absorption systems are not competitive with mechanical compression chillers, and many studies are being performed to improve their design. In the last years, the use of microporous membranes located at the boundary between solution and vapour in desorbers of absorption chillers has been evaluated. In the case of components using microporous flat membranes, one possible configuration is that represented in Figure 2. There, the solution is confined in very small channels and the contact area between vapour and solution is increased because the channel thickness is tiny. In addition to this, higher mass and heat transfer coefficients are obtained owing to the flow type generated inside these small channels. Up to now, reduced, but increased number of investigations, are being developed because this technology is an alternative to reduce the size of these components. Most of the research developed on this subject has been developed in the last decade, including a review performed by [1].