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In recent years, rigorous research has been carried out on the use of membrane contactors to design compact absorbers for absorption cooling systems and to extend their use in small scale applications. Moreover, the use of new working fluid mixtures has been suggested for the absorption cooling systems to cope with the limitations and problems associated with the conventional working fluid mixtures. In this study, water/(LiBr + LiI + LiNO 3 + LiCl) with mass compositions in salts of 60.16%, 9.55%, 18.54% and 11.75%, respectively, and water/(LiNO 3 + KNO 3 + NaNO 3 ) with mass compositions in salts of 53%, 28% and 19%, respectively, were investigated for air-cooled and multi-stage high temperature absorption cooling systems, respectively. Results show that a 25% increase in the absorption rate can be achieved by using water/(LiBr + Li + LiNO 3 + LiCl) when compared to water/LiBr at air-cooling thermal conditions. Furthermore, an absorption rate as high as 0.00523 kg/m 2 s is achieved when the water/(LiNO 3 + KNO 3 + NaNO 3 ) working fluid mixture is used in the membrane-based absorber of the third stage of a triple effect absorption cooling cycle. In addition, the pressure drop percentage in the case of water/(LiNO 3 + KNO 3 + NaNO 3 ) working fluid mixture is significantly lower than the water/LiBr and water/(LiBr + LiI + LiNO 3 + LiCl) working fluid mixtures because of the higher operating pressure. [ABSTRACT FROM AUTHOR]

Absorption cooling systems employing membrane based components provide an interesting opportunity to use the technology for small scale applications. Steady-state heat and mass transfer analyses of a water-lithium bromide membrane based absorber are performed. CFD (computational fluid dynamics) tool ANSYS/FLUENT 14.0 is used to perform the simulation and investigate the behaviour of the heat and mass transfer mechanisms at local levels in the channels. Results show that the solution film thickness is an important parameter which significantly affects the mass transfer mechanism. It was observed that the absorption rate increased by a factor of 3 when the solution channel thickness was reduced from 2 mm to 0.5 mm. In addition, the absorption rate was increased by a factor of 2.5 when the solution inlet flow velocity was increased from 0.00118 m/s to 0.00472 m/s. The solution film thickness and velocity can be independently controlled in plate-and-frame membrane based absorbers. Therefore to design a compact and efficient plate-and-frame membrane absorber with water as a refrigerant, an optimum value of 0.5 mm for the solution channel thickness is suggested and a solution inlet velocity of about 0.005 m/s is recommended to achieve high absorption rates with acceptable pressure drop along the solution channel. [ABSTRACT FROM AUTHOR]

The use of membrane contactor technology is well-known in the process industry and can be employed in many important fields; such as separation and absorption processes, membrane distillation, pervaporation, biotechnology, food industries etc. In recent years, research has been carried out regarding the use of membrane contactors in the components of absorption refrigeration systems. The use of membrane contactors makes it realizable to design compact components with improved heat and mass transfer. Heat and mass transfer performance of the components is significantly enhanced due to the higher area to volume ratio available. Membrane based absorber and desorber allow the reduction in size of the absorption refrigeration systems to a great extent and thus absorption refrigeration technology can be used in transport and small scale applications. In this paper, the applications of membrane contactors in absorption refrigeration systems are reviewed. The application of membrane contactors in the components of absorption refrigeration systems, the configurations of refrigeration cycles that employ membrane contactors and the characteristics of the membrane contactors used in absorption refrigeration systems are all reviewed in detail. Information is collected on the choice of working fluid mixture to be used in absorption refrigeration systems that use membrane based components and the compatibility of working fluid mixtures with the membrane contactor material is discussed. The significance and limitations of using membrane contactors in absorption refrigeration systems is included in this paper. [ABSTRACT FROM AUTHOR]