Preliminary characterization of carbon dioxide transfer in a hollow fiber membrane module as a possible solution for gas–liquid transfer in microgravity conditions Be ´range `re Farges a,⇑ , David Duchez a , Claude-Gilles Dussap a , Jean-Franc ßois Cornet b a Clermont Universite ´, Universite ´ Blaise Pascal – Laboratoire de Ge ´nie Chimique et Biochimique, BP 10448, F-63000 Clermont-Ferrand, France b Clermont Universite ´, ENSCCF – Laboratoire de Ge ´nie Chimique et Biochimique, BP 10448, F-63000 Clermont-Ferrand, France Received 27 June 2011; received in revised form 28 September 2011; accepted 3 October 2011 Available online 10 October 2011 Abstract In microgravity, one of the major challenge encountered in biological life support systems (BLSS) is the gas–liquid transfer with, for instance, the necessity to provide CO 2 (carbon source, pH control) and to recover the evolved O 2 in photobioreactors used as atmosphere bioregenerative systems. This paper describes first the development of a system enabling the accurate characterization of the mass transfer limiting step for a PTFE membrane module used as a possible efficient solution to the microgravity gas–liquid transfer. This original technical apparatus, together with a technical assessment of membrane permeability to different gases, is associated with a balance model, determining thus completely the CO 2 mass transfer problem between phases. First results are given and discussed for the CO 2 mass transfer coefficient k CO 2 L obtained in case of absorption experiments at pH 8 using the hollow fiber membrane module. The consistency of the proposed method, based on a gas and liquid phase balances verifying carbon conservation enables a very accurate determination of the k CO 2 L value as a main limiting step of the whole process. Nevertheless, further experiments are still needed to demonstrate that the proposed method could serve in the future as reference method for mass transfer coefficient determination if using membrane modules for BLSS in reduced or microgravity conditions. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Hollow fiber membrane; Gas–liquid mass transfer; CO 2 mass transfer coefficient; Gas and liquid data reconciliation; Microgravity; Photo- bioreactor 1. Introduction and objectives Life support systems are very complex systems even if they use a reduced number of elementary steps. Indeed, in particular, they require numerous operation of gas–liquid mass transfer. Whereas these operations are standard processes found in industrial based society, they are one of the major difficulties encountered in micrograv- ity or reduced gravity conditions because they require gravitational forces to drive and to separate the fluid phases. However, gas–liquid mass transfer in closed photo- synthetic photobioreactors (PBR) is very important in reduced gravity environment found for example on Moon and Mars because it permits to provide efficiently carbon dioxide (CO 2 ) to microalgae in the PBR as carbon source and pH control and to recover the produced oxygen (O 2 ) by microalgae to regenerate the crew atmosphere. Fortunately, nowadays, several possibilities exist in order to obtain efficient mass transfer conditions and mixing phases in microgravity or reduced gravity. Among them, membrane technologies present a lot of advantages, especially for space applications. 0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.10.004 ⇑ Corresponding author. Tel.: +33 (0)4 73 40 55 21; fax: +33 (0)4 73 40 78 29. E-mail address: berangere.farges@univ-bpclermont.fr (B. Farges). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 49 (2012) 254–261