UCLA

The flow of liquid films down thin vertical fibers is of significant interest in various applications, such as fiber coating and string-based heat and mass exchangers. This unique configuration can provide an enhanced high rate of exchange in heat and mass. However, the fluid dynamics and interfacial heat and mass transfer mechanisms of these films are convoluted and depend on several parameters, including wettability, size of the nozzle and the fiber, and stream-wise liquid temperature/concentration change. This dissertation aims to develop a high-efficiency heat and mass exchanger utilizing a unique string-based configuration and presents a comprehensive investigation of the wetting interaction of liquids with nozzles and vertical fibers using experimental, numerical, and theoretical approaches. We conducted a systematic study on the capillary-driven rise of liquids on small cylindrical nozzles and the alteration of flow regimes of liquids flowing on a fiber as a result of stream-wise property change. Our proposed flow regime diagrams incorporate the effects of flow parameters to predict flow behavior under various conditions. We further developed simplified analytical and numerical models to simulate the transient liquid flow on the nozzle and the fiber at significantly lower computational costs. We considered liquids with a wide range of viscosity values in our studies and validated our solutions using extensive experimental and high-fidelity simulation data. Finally, we designed, constructed, and operated a complete multi-string humidification-dehumidification (HDH) desalination setup, which produced ~60 L of fresh water per day while working at an RR and GOR of 7.5% and 2.9, respectively. Our exchanger's unique configuration enables high mass exchange rates per device volume, resulting in enhanced exchanger effectiveness, and allows for air circulation at low electrical consumption rates. Additionally, an intermediate bypass air-line reduced the stream-to-stream enthalpy difference, resulting in higher thermal efficiency. During our reliability study, we demonstrated that our system is capable of efficiently processing hypersaline brine streams with concentrations as high as 250 g/L. Given the relatively high thermal efficiency, low maintenance requirements, and low electrical consumption of the multi-string desalination device, these novel devices have demonstrated their potential to reduce the cost of producing fresh water.