Plugging a leaking tube removes its flow and heat-transfer surface, but the remaining bundle does not always retain the same operating conditions. Tube position, pass arrangement and pump response influence the revised capacity. A simple percentage derating can miss these effects. [1]
Make a tube map with pass ID, location and repair history. Distinguish a plug at each end from a verified isolated tube under the approved repair procedure. Preserve the interspace and leakage-monitoring requirements of a double-wall construction.
Recalculate the changed quantities
| Change | First calculation | Additional check |
|---|---|---|
| Heat-transfer area | Active tube length and surfaces | Position-dependent thermal contribution |
| Flow area | Active tubes per pass | New velocity and maldistribution |
| Hydraulic resistance | Revised pressure-drop curve | Installed pump operating point |
| Mechanical response | Changed flow and support exposure | Vibration or local wear conditions |
Compare fixed-flow and actual-pump cases
If the same total flow passes through fewer equal tubes, mean velocity increases as Q/(nA). Here Q is volume flow in m³/s, n is the active parallel-tube count and A is one tube’s internal flow area in m², giving velocity in m/s. In the real circuit, higher resistance can lower total flow. Calculate the pump/system intersection rather than assuming either fixed flow or fixed velocity.
Plugging concentrated in one pass can restrict that pass more than an evenly distributed count. A thermal model should use the actual map. The remaining surface may receive different temperatures and flow, changing more than its area.
Closing tubes shifts both the bundle resistance and the pump operating point. Solve their intersection rather than holding total flow constant unless the controller actually maintains it. [2]
Recalculate velocity after tube plugging
Assume 100 equal parallel tubes each have 100 mm² flow area and total flow is fixed at 0.010 m³/s. Velocity is 1.00 m/s. Plugging 10 tubes raises it to 1.111 m/s if total flow truly stays fixed. Recalculate the actual pump/system intersection and heat-transfer area before assigning capacity; fixed-flow arithmetic alone does not establish installed duty.
For a second, independent assumption, let Q be in L/s, pump pressure 50 − 0.25Q² kPa and clean bundle pressure 0.25Q² kPa. Their intersection is 10 L/s. After plugging, assume bundle resistance scales as 1/n²: its coefficient becomes 0.25/0.9². The new intersection is 9.46 L/s, giving 1.051 m/s through 90 tubes. This hydraulic screen still needs a thermal-duty check at the resulting flow.
References
- U.S. Department of Energy, DOE-HDBK-1012/2-92, Thermodynamics, Heat Transfer, and Fluid Flow, Volume 2, 1992.
- U.S. Department of Energy, DOE-HDBK-1012/3-92, Thermodynamics, Heat Transfer, and Fluid Flow, Volume 3, 1992.