INTRODUCTION The absorber is one of the major components in absorption chillers and has a direct effect on the chiller size. Introducing polymeric hydrophobic microporous membranes into the absorber design could provide one of the alternatives for achieving highly compact absorbers. For lithium bromidewater (LiBr-H2O) absorption chillers@ the hydrophobic membranes can be used to form confined solution channels. In this case@ the water vapor pressure difference across the membrane is the driving force for water vapor transfer (refrigerant). As the absorber is working under vacuum pressure@ the membrane pores are filled with water vapor@ while the hydrophobic nature of the membrane prevents penetration of the aqueous solution into the pores. Therefore@ only water vapor is transported through the membrane into the solution. Consequently@ using a narrowly confined solution flow channel formed with membrane sheets will significantly increase the mass transfer area per unit volume. The above technique as well as mass transfer enhanced at liquid/vapor interface by forced convection in the narrow confined flow channels lead to the reduced absorber unit size and weight. Drost et al. (2005) cited that the development of compact absorbers enables the deployment of small heat-actuated absorption heat pumps for distributed space heating and cooling applications@ heat-actuated automotive air conditioning@ and man-portable cooling devices. The present study is concerned with the factors that affect the water vapor transfer flux when using a membrane contactor at LiBr-H2O solution/water vapor interface in such an absorber design. Therefore@ the literature review focuses on studies which utilized membranes in absorption chiller systems. Schaal et al. (2005) experimentally investigated and simulated an absorber with a single microporous hollow fibre membrane in which ammonia/water is used. Chen et al. (2006) performed a simulation study of a proposed hybrid absorber-heat exchanger using microporous hollow fibre membrane modules for the ammonia-water absorption cycle. In their model@ they considered the ammonia-water concentration across this microporous membrane as the refrigerant driving force. In contrast@ Baker (2004) indicates that in the case of microporous membranes without a static pressure difference across the membrane the vapor partial pressure difference at the membrane sides is the driving force for mass transfer. For LiBr-H2O absorption chillers@ Ali and Schwerdt (2008) specified the characteristics of the appropriate membrane for use in this absorber design. They indicated that this membrane should have a high permeability to water vapor and must be hydrophobic to the aqueous solution with a high liquid entry pressure to avoid penetration of the membrane pores. No capillary condensation of water vapor should occur to avoid blocking of the pores. They concluded that for practical use the membrane should have a thin hydrophobic microporous active layer with a thickness up to 60 ?? on a support layer@ with a mean pore size around 0.45 ?? and porosity of up to 80 %. Throughout the literature@ more research work have been performed on using membranes for vapor desorption inside the desorber/generator of absorption heat pumps considered than the absorber case. Drost et al. (2005) experimentally studied and also simulated the ultra-thin film channel in a LiBr- H2O desorption process using microporous membrane separation. Thorud et al. (2006) experimentally investigated the performance of vapor extraction from an aqueous lithium bromide solution as a function of the film thickness@ the pressure difference across the microporous membrane and the inlet concentration to the microchannel. As the desorption process is close to a distillation process@ Sudoh et al. (1997) investigated experimentally the permeation flux of water vapor in membrane distillation of an aqueous lithium bromide solution. Riffat et al. (2004) presented and investigated experimentally a novel vapor absorption refrigeration system in which a pervaporation membrane replaces the conventional generator for concentration of the working fluids. To the authors' knowledge@ few investigations are available in literature regarding the use of the membrane contactors in absorption heat pump applications. Despite the important need for compact and low cooling capacity absorption chillers with the potential use of microporous membranes for solution/ vapor contacting purposes in the absorber@ there has been relatively little research so far concerning this topic. In addition@ there is no literature available on water vapor transfer flux through membrane contactors into lithium bromide-water solution with both the vapor and the solution under equal vacuum static pressure@ which is the case in the absorber of LiBr-H2O absorption chillers. However@ since the membrane acts as a barrier to the mass transfer process@ its properties affect the water vapor mass transfer flux. Therefore@ investigations on the water vapor (refrigerant) mass transfer flux into the aqueous solution for commercially available microporous hydrophobic membranes@ under realistic operating conditions inside the absorber@ need to be performed. The common commercially available hydrophobic microporous membranes in capillary or flat sheet shape are made of polypropylene (PP)@ polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE@ Teflon). The objective of designing a compact absorber for absorption chillers is investigated with experimental and analytical studies of hydrophobic microporous membranes. This study focuses on the influence of membrane properties on the water vapor transfer flux into a LiBr-water solution through membrane contactor at the liquid/vapor interface forming a confined narrow channel. In addition@ the effect of the flow channel dimensions on the water vapor flux is also studied.