For the development of successful long term space flights, and the establishment of permanent bases in space, a well controlled self sustained closed environment is required. In order to optimize a closed-loop bio-regenerative life support system, it is necessary to control the hydrodynamics and the coupled heat and mass transfer, which develop in a space habitat concerned with humans and plants. We have designed a ground based experimental setup and protocol to measure the air flow velocities and concomitant mass transfer by condensation of water vapour from humid air on a horizontal flat plate of small size (area 25 cm2), in a controlled air flow conditions (flow regime, hygrometry, temperature). An active isothermal surface was kept below the dew point, by using thermoelectricity, and precise weighing of the condensate in order to evaluate the rate of mass flux. An air-conditioned closed circuit wind tunnel has been used to produce laminar to weakly turbulent flows. Almost 70 condensation experiments have been performed at an ambient temperature (19-23 °C) for a relative humidity between 35-65 %, and for the velocity range 1.0-3.0 m/s. The condensing unit behaves as a blunt-faced body and mass transfer coefficients were deduced. When increasing the flow intensity it was found that the Sherwood number had a dependence on Re2/3. An empirical relation was proposed to estimate the surface temperature. The flow behaviour within the boundary layer and the analysis of the drop growth on the flat plate surface under weakly turbulent flows has been discussed. This experimental work will be helpful to develop theoretical models for further studies with other geometries.
