Hi everyone,

I am designing a total condenser operating under full vacuum conditions. The process involves steam entering the shell side at 165°C and leaving as condensate. The tube side uses a process gas as a coolant (80,000 kg/h) in a U-tube bundle (2 passes). The exchanger is relatively "short and fat" (approx. 1000 mm length x 740 mm diameter), in BXU configuration.
The main challenge is the very low steam flow (5,000 kg/h) relative to the s&t size, which creates significant hydraulic distribution and duty control issues.
I have tested these configurations
1. BXU: Pressure drop is concentrated 100% in the inlet nozzle. The bundle is hydraulically "transparent" (approx 0.3 kPa in the cross). This clearly violates the rule of thumb of bundle pressure drop > 66.7%of the total to ensure flow uniformity. Without this resistance, I am concerned about a localized "rain effect" directly under the nozzle, leaving the rest of the 1-meter bundle ineffective
2. BJ21U: Similar results. Despite the divided flow, the longitudinal velocity is too low to "activate" the bundle hydraulically.
3. TEMA BGU :This configuration performs better regarding distribution because the longitudinal baffle and the required path force a higher internal resistance.

The system uses Flooded Surface Control (varying the condensate level to adjust active surface area).
For a BGU design, the longitudinal baffle must be continuously welded to the shell. Does this create excessive thermal stress risks in vacuum service, or is it a non-issue for a 1-meter shell?
If I still use a Type X , is the combination of an Annular Distributor (Vapor Belt) and a perforated Distribution Plate (min. 20% open area) considered reliable enough to satisfy the 2/3 Rule and distribute vapor over such a short bundle?
Given that the BGU uses segmental baffles (even with 12 mm drainage notches), is the condensate level control as linear and stable as in a Type X, which provides a perfectly flat free surface?
In the worst-case clean turndown, what measures would you recommend to mitigate water hammer risks in the presence of low-pressure vapor?

I would appreciate insights from anyone who has dealt with this type.of vacuum condensers and the trade-offs between cross-flow and split-flow hydraulics. Is type G suitable for this case? I have to evaluate the submerged area during the turndown? Would you still make a Type X or Type J with a vapor belt and perforated plate instead of a Type G? Although with vapor belts the situation in terms of DP would not improve much?

Thanks a lot.

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