Falling film flow pattern transition of ionic liquid aqueous solution on horizontal tube bundles

The 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) ionic liquid aqueous solution is a promising absorbent used in absorption refrigeration technology. In this paper, the falling film flow pattern transition of the [EMIm]Ac ionic liquid aqueous solution was experimentally studied. The findings reveal that the critical Reynolds number for flow pattern transitions rises with increases in tube spacing, inlet liquid temperature, and circulating liquid temperature. In comparison to deionized water, the ionic liquid aqueous solution exhibits much smaller critical Reynolds numbers, and provides a more stable liquid film, and produces much smoother and clearer interfaces between liquid and gas. Additionally, hysteresis in flow pattern transitions is observed, and it generally increases with increasing tube spacing, inlet liquid temperature, and circulating liquid temperature. Criteria for flow pattern transitions are developed, and flow pattern maps are constructed for conditions with increasing and decreasing film flow rates, respectively.