Study on Membrane Contactors: Performance Analysis, System Simulation and Fields of Application

University of Genoa – DIPTEM Chapter 1 9 1. Introduction Dehumidification and air quality control are some of the fields in which significant efforts are being made to reduce power consumption of the systems and to limit their emissions of pollutants in ambient. The Montreal and Kyoto protocol have established common paths of research and technological evolution for all the withdrawing countries in order to find solutions and new technology for the above mentioned aims with particular regard to reduction of power consumption, pollutants emission containment and new refrigerants with low environmental impact (GWP, LCCP). Up to now the researches have been performed in every field of application, from the civil one for the air conditioning of public places to the dehumidification and air quality control for industrial purposes; for instance, an important field is the automotive one: in this contest, the withdrawal of the European countries to the Kyoto protocol has brought to the ban of the automotive refrigerant R134a in favour of the carbon dioxide as alternative refrigerant at low environmental impact. In air conditioning one possibility to reduce the power consumption is the adoption of liquid or solid desiccants, solution that allows to remove the latent load independently of the sensible one, i.e. it is possible to control the relative humidity independently of the temperature of the process air. When high latent loads have to be removed, or when heat otherwise unused is available to regenerate the salt solution, significant power savings can be obtained. But nowadays the systems working with liquid or solid desiccants uses the direct contact technology with some disadvantages: great dimensions to obtain sufficient exchange surfaces, carry over of solution droplets in the stream of the process air, in case of liquid solutions, and scarce versatility of usage. This research have been performed to study the exchangers with semi- permeable membranes, called membrane contactors, that allow to use liquid salt solutions for the air dehumidification in direct contact. By means of a calculation code developed in FORTRAN by the DIPTEM the behaviour of the contactor has been simulated to find the better working conditions both in dehumidification and humidification mode. The indications obtained in such a way have been used for the study of some air conditioning system solutions: by means of Matlab-Simulink the model of each system has been built in order to compare their performances. On the basis of the previous results, the best system configuration for air conditioning of civil application and the best one for automotive application have been chosen. The performances of the systems with membrane contactors have been compared with those of the traditional systems for each application. Finally, taking into account the power saving calculated by means of the Simulink models, some economical considerations have been drawn comparing the innovative system and a traditional air conditioning system.