The absorber represents the most critical component in absorption systems and one of the key issues. In this component complex heat and mass transfer phenomena during the absorption process takes place simultaneously. For this reason the development of mathematical models validated against experimental data always constitutes useful tools for the design and improvement of falling film absorbers. A testing device has been designed and built to reproduce absorption phenomena in vertical LiBr-H2O falling film absorbers with the primary objective to obtain experimental data. On the other hand, a mathematical model of falling film absorption of H2O vapour in LiBr aqueous solutions has been implemented. Wave regime is considered by including and solving the Free Surface Deflection Equation. The numerical results are validated using the experimental data.\ud \ud During the development of this work, the authors have paid careful attention to the verification of experimental data. Such verification consists of performing energy and mass balances in the fluid film side. Important discrepancies were found in our experimental data. Therefore, an extensive study was carried out in order to find the source of such errors. The conclusion is that there is a drag of LiBr solution in the water vapour which increases with the Re number. This mist flow cannot be measured experimentally, but can be evaluated in an indirect way. The mathematical models have been adapted in order to consider the influence of mist flow. On the other hand, in the literature there are not many experimental works related to falling film absorbers which expose enough information to verify the reliability of their experimental data.Peer ReviewedPostprint (author's final draft

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Portal del coneixement obert de la UPC http://upcommons.upc.edu/e-prints Aquesta és una còpia de la versió author's final draft d'un article publicat a la revista International Journal of Refrigeration.

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The paper studies thermal design and describes the experimental set-up of a domestic-scale prototype experimental cooling system based on a 7kW of nominal capacity single-stage small LiBr-H2O air-cooled absorption machine. The paper illustrates the characteristics based on a methodical procedure for the design and sizing of the small capacity air-cooled absorption machine. IntroductionHigh initial investment is the main factor that impedes an extended use of solar absorption cooling system. Low capacity installations have the price of the absorption chiller as the most limiting factor. The development of air-cooled systems in order to explore the possibility of avoiding the cooling tower and therefore, to decrease the price of the whole installation, results very interesting. In the present research an air-cooled absorption machine will be developed, in this case driven by hot water below 100ºC (suitable for solar cooling applications) with a single effect cycle configuration. The key aspect in the present development is the systematic application of advanced numerical tools and experimental techniques as usual methodology for an accurate design. MethodologyThe whole research is divided in three main steps .i) The first stage consists in the design, construction and test of a pre-industrial prototype.ii) New prototypes will be developed in the second stage. The main objective is to obtain a first experience in real-life application of an absorption chiller with an autonomous control and purge systems. iii) Development of a first small series of chillers with the definitive version of the control and purge systems.In stage one thermal design is done using CTTC software as well as it will be described later. Mechanical design has been done using CAD and 3D software in order to avoid errors, saving hours of mounting and in order to do an easy serie fabrication as is described at third point before.On the other hand this research is in parallel with project FERASOL which aim is obtaining new mathematical models in order to simulate falling film in vertical tubes in several regimes as well as creation of new facilities where heat and mass transfer phenomena can be observed and studied. An extended research is being carried so that results are being applied on air-cooled absorption machine design (Garcia-Rivera et al., 2008). It is expected to reduce the size of the whole chiller in the next future. Numerical modellingThe whole system has been numerically analysed as well as each individual component, using a high level numerical detailed heat and mass transfer analysis. Absorber, desorber, condenser and evaporator are dimensioned using semiempirical models that could use heat transfer and pressure drop correlations provided in the literature . Flooded evaporators are modelled taking account of heat and mass transfer coefficients as well as absorber and condenser are modelled using an own tube-fin high level numerical code; desorber is numerically modelled taking account absorption phenomena of heat and mass t...