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A highly effective multi-string humidifier with a low gas stream pressure drop for desalination


The humidification-dehumidification (HDH) process is appealing for small-scale distributed desalination of high-salinity water. We report a new design of compact light-weight humidifiers with high effectiveness and low electric energy consumption for HDH systems. The new design consists of a dense array of vertically aligned strings, along which thin films of a heated liquid feed are allowed to flow under gravity. A counterflowing gas stream makes direct contact with liquid films carrying the generated water vapor to a dehumidifier. The unique geometric configuration of our design affords high interface-to-volume ratios necessary for high heat/mass exchange effectiveness and straight contiguous gas flow paths for reduced gas-phase pressure drops. We constructed a 0.4 m-tall prototype and examined the effects of the liquid flow rate, air velocity and feed liquid salinity on the heat/mass transfer performance and the gas stream axial pressure drop. Compared with previously reported pad humidifiers and spray columns, the present multi-string humidifier achieves almost 5 times the evaporation rate per humidifier volume at comparable gas stream pressure drops or an order of magnitude reduction in the gas stream pressure drop at comparable total evaporate rates. Our work demonstrates a highly-effective but compact and light-weight multi-string humidifier with a small gas stream axial pressure drop for HDH and related applications.

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