A Serve tube is a boiler fire tube with internal longitudinal ribs. The ribs increase the internal surface exposed to hot gases. Explore how selected rib dimensions change open area, internal perimeter and geometric hydraulic diameter.
Serve Tube Selected Rib-Geometry Reference
Compare an idealized ribbed bore. The results describe geometry, not heat-transfer gain or boiler performance.
Equation Used
- The smooth bore is circular.
- All selected ribs are identical, longitudinal and rectangular in section.
- Each rib base replaces an equal bore-wall width, so only two flanks add developed perimeter.
- Thermal, fluid, structural, manufacturing and safety behavior are excluded.
The selected rib profile is a normalized rectangular idealization and is not a historical dimensional reconstruction.
Documented longitudinal-rib topology
William Eaves's 1893 boiler-tube patent explicitly refers to longitudinal internal ribs used in what were then known as Serve tubes. It says internal projections present additional heat-absorbing surfaces and describes a separate spiral retarder for deflecting the gas column.
The animation therefore shows selected continuous longitudinal ribs and moving gas markers. It does not portray the ribs themselves as a helix or claim a calculated flow field.
What the calculator determines
Select a circular bore diameter, rectangular-rib height and base width, and integer rib count. The calculator reports smooth-bore flow area, selected open area after subtracting rib rectangles, ideal developed internal-surface ratio, and geometric hydraulic diameter.
Additional surface area does not give a proportional heat-transfer improvement; gas flow, temperature and fouling also matter.
Selected ideal geometry
For diameter D, N identical longitudinal rectangular ribs of height h and base width b: A0 = πD²/4, Aopen = A0 − Nbh, Pw = πD + 2Nh, surface ratio = Pw/(πD), and Dh = 4Aopen/Pw.
This approximation treats each rib base as replacing the same bore-wall width and adds two rib flanks. It neglects bore curvature across each narrow rib base and any rounded fillets.
Selected-input arithmetic
For a 50 mm bore with five 4 mm-high, 3 mm-wide ribs, smooth area is about 1,963.5 mm², selected open area about 1,903.5 mm², developed-surface ratio about 1.255, and geometric hydraulic diameter about 38.6 mm.
Rectangular-rib approximation
The selected rectangular ribs are an idealized geometry, not measured dimensions or profiles for a particular surviving Serve tube. Rib-root radii, manufacturing details, tube wall thickness, joints, fouling and separate retarders are not included.
The calculator does not predict heat-transfer coefficient, duty, gas velocity, Reynolds number, pressure loss, draft, steam output, temperature, stress, fatigue, safe operation or maintenance interval.
Questions
Were Serve-tube ribs helical?
The 1893 patent calls the established Serve-tube ribs longitudinal; its spiral component is a separate inserted retarder.
Does surface ratio equal heat-transfer gain?
No.
Can this size a boiler tube?
No.
References & Further Reading
- Wikipedia contributors. Fire-tube boiler. Wikipedia
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