Liquid flow rate effects during partial evaporation in a falling film micro contactor

• Evaporation of isopropyl-alcohol is performed in a falling film micro contactor.
• Lower liquid temperatures and evaporation rates are observed for low liquid flows.
• Channel drying occurs at low liquid flow rates due to flow or heat maldistribution.
• A heat transfer model is developed based on theoretical heat transfer coefficients.
• Measured temperatures are explained by the model for different wetting conditions.

The focus of this study is the investigation of the effect of liquid flow rate on partial evaporation, enhanced by convective nitrogen flow, in a falling film micro contactor. Experiments are performed at different flow rates and for a certain heating liquid temperature. The temperatures of the gas and liquid phases are measured at their exit points, and the evaporation rate is determined while the channels are monitored with a microscope.The channels do not appear fully wetted at low liquid flow rates, and the liquid temperature is relatively low. The bad wetting is attributed to liquid flow maldistribution that can cause temperature gradients and subsequently enhances the maldistribution by uneven evaporation. A heat transfer model is developed and solved for different numbers of wetted channels. According to the modelling results the low liquid temperatures, can be fully explained by liquid flow maldistribution and channel drying.These wetting effects are minimized by restricting the liquid flow at its exit point and increasing the amount of liquid maintained at the bottom of the contactor. This improves the temperature profile and prevents drying, as it is possible that capillary forces tend to drive liquid upwards when dry spots occur.