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

The inter-tube flow mode transitions of three working fluids under the conditions of two distribution heights, eight different orifice configurations were measured with the visualization method, and the effect of liquid distribution on falling-film flow transitions was discussed. Five flow modes and four flow transitions were obtained by a high-speed camera. The measurement results agree well with literature data from reduced film Reynolds number and non-dimensional Galileo number, and the maximum relative deviation of transition Reynolds number is less than 15%. The experiment results show that the orifice configuration has a significant influence on inter-tube flow mode transition. The transition Reynolds number decreases with an increase in the hole diameter at a fixed adjacent hole distance while it increases with an increase in adjacent hole distance at a fixed hole diameter. The direct distribution causes larger transition boundary than the indirect one, and the difference between the transition boundaries under direct distribution and indirect distribution decreases with the increase in the non-dimensional characteristic parameter. The influence of the distribution height on flow mode transitions may be ignored when the non-dimensional characteristic parameter is greater than 40.