Fluid dynamics of thin liquid films flowing down vertical flexible fibers

To recover low-temperature industrial waste heat at low temperatures (<100 °C), condensing heat transfer technology has been widely employed. However, indirect condensers are limited by liquid–solid droplet formation, which reduces efficiency. To enhance mass transfer rates while maintaining low pressure drops, the Direct-contact Liquid-on-Flexible-Fiber Condenser employs thin liquid film direct condensation for waste heat recovery. Its efficiency depends on the flow characteristics of the liquid film along flexible fibers. However, experimental data and flow studies using de-ionized water—a low-surface-tension, low-viscosity medium with superior condensing performance compared to oil—are scarce. This study applies a two-dimensional axisymmetric model and corresponding experimental setup to investigate the hydrodynamic characteristics of de-ionized water thin films along flexible fibers. We examine thin-film dynamics in multicomponent gas atmospheres (air, steam, and steam/CO2), where gas effects on flow remain unexplored, under temperature (20–60 °C) and inlet flow rates (21–29 ml/min), with a focus on interfacial mobility. Results show that the inlet flow rate and temperature significantly affect liquid film flow patterns and stability: Increasing the liquid film flow rate from 21 to 27 ml/min, the bead frequency is increased by 273.3% and spacing by 73.6% on average, but diameter is reduced by 16.5%. At a constant flow rate of 25 ml/min, increasing the temperature from 40 to 60 °C reduced the bead spacing and diameter by 16.7% and 6.9%, respectively. The variation in the gas-phase atmosphere affects the flow characteristics by less than 8%.