TechTip: Self-venting Nozzles in Condensers
Self-venting nozzles are often desired in partial or complete condensers. HTRI recommends sizing these nozzles for gravity condensate flow to produce weir-type flow.
Xist can help users size self-venting nozzles properly with warning or informative messages; however, certain criteria must be met for the software to complete the necessary calculations.
Xist uses the Froude number to determine whether or not a nozzle is self-venting, but this Froude number is only calculated when a separate liquid outlet nozzle is specified or complete condensation has occurred. Xist assumes that if there is only one nozzle through which two-phase flow exits that the liquid will not flow by gravity but is carried out by vapor velocity. Xist criteria for self-venting nozzles will require users to assess whether or not reported pressure drops for outlet nozzles are real.
Depending on specified process conditions and geometry, a warning message is issued if the Froude number is greater than 0.3 and the flooded tube area is greater than 5% of the total tube area. An informative message is issued if the Froude number is greater than 0.3 and the flooded tube are is less than 5% of the total tube area.