Effects of liquid supply method on falling-film mode transitions on horizontal tubes

The effects of liquid supply method on falling-film transitions between horizontal tubes are experimentally studied. Several different liquid supply designs are considered, including variations in orifice size and arrangement, and experiments are conducted with ethylene glycol, water, and a mixture of ethylene glycol and water at 30°C and 40°C. It is found that the mode transitions can be sensitive to the details of the liquid-feeding scheme. In some cases, the transitional Reynolds numbers differ by more than 50% for different feeding arrangements. The experimental results demonstrate that the transitional Reynolds numbers increase with an increase in the orifice spacing at a fixed orifice diameter; transitional Reynolds numbers also increase with an increase in the orifice diameter at a fixed orifice spacing-to-diameter ratio. The effect of feeding height depends on the orifice spacing. From images analysis, it is also found that the jet shapes are different with different feeding methods. A new correlation for transition that includes the effects of liquid feeding method is developed using the experimental data. These results are important to those conducting experiments on falling film mode transitions and may have implications on the design and operation of falling-film heat exchangers.