Advancing Steam-Plant Heat Transfer with Corrugated Tubes and Helical Baffles

The shell-and-tube heat exchanger (STHE) remains the workhorse of every steam and power plant. It condenses exhaust and vent vapours, heats boiler feed-water, recovers heat from blow-down and condensate, and pre-heats fuel oil. For the better part of a century that workhorse has been built the same way: plain, smooth tubes guided by segmental baffles. It is robust and well understood — but it also leaves thermal performance untapped on both the tube side and the shell side. Several established techniques address that gap on one or both sides: corrugated tubes, helical baffles, and combinations of the two. This article reviews how each works, the trade-offs involved, and where it fits in steam and power service. Two combined arrangements developed and tested by Kinam Engineering Industries — HeliKorr and HeliTurbo, both the subject of design-patent applications — are used as examples.

Where the plain tube runs out of room

In a plain tube the fluid forms a slow-moving boundary layer at the wall that insulates the bulk flow from the surface — the dominant resistance to heat transfer. On the shell side, conventional segmental baffles push fluid in a zig-zag path that creates stagnant dead zones, bypass and leakage streams, high pressure drop and, at higher velocities, damaging flow-induced vibration. Wherever the controlling resistance sits, the plain-tube/segmental-baffle combination tends to oversize the unit. The enhancements discussed below address that resistance directly — at the tube wall, in the shell, or both.

1. The Shell and Tube with corrugated tube

The Shell and Tube Heat Exchanger with corrugated tube is a game changer. It results in a higher film coefficient — in many duties the tube-side coefficient is close to doubled. Hence the required heat-transfer area falls by roughly 30–50% (up to 50% in condensing service, 25–30% in single-phase duty), and less material means the finished unit is typically 15–20% cheaper for the same duty — a gap that widens with exotic alloys. The continuous turbulence also resists deposition, giving a self-cleaning effect, lower fouling and longer run-lengths. Corrugation adds about 10% tube-side pressure drop for an equal size, but because fewer or shorter tubes are needed for the same duty, the installed penalty is usually offset. Construction follows ASME Section VIII Div-1 and TEMA. An existing plain-tube exchanger can often be up-rated simply by re-tubing it with corrugated tubes.

The heat transfer enhancement experimental results were published in ASME IMECE-India 2025 conference. The results are presented in Figure 2

Where it fits in Steam Power Plants :

Corrugated tubes are well suited to condensers and vent condensers, feed-water heaters, condensate coolers, solvent and heat-recovery condensers, and process pre-heaters. They can substitute for a plain-tube STHE, and in clean duties for a gasketed plate exchanger (PHE) — the latter limited to clean fluids below about 20 bar and 200 °C and subject to gasket maintenance. They are less suitable where the shell-side fluid is sticky or prone to polymerising, and for air- or gas-only service, where the enhancement is smaller.

Table 1 — STHE vs PHE vs Corrugated tube 

2. Helical Baffle Heat Exchanger

Where the controlling resistance sits on the shell side, the answer is to change the baffle, not the tube. Helical baffles are angled plates that guide the shell-side fluid along a smooth, near plug-flow spiral around the bundle. That single change removes the segmental dead zones and bypass streams, cuts shell-side pressure drops and pumping power, lowers fouling, and largely eliminates flow-induced vibration.

Helical baffles – Selection guidelines (Rule of thumb)

• shell-side thermal resistance above ~40% of the fouled overall U;
• shell-side fouling resistance above ~30% of the fouled U;
• shell-side viscosity above 3 cP with a large unit (UA > 10,000 W/K);
• any large unit, UA > 30,000 W/K; or where segmental leakage (E-stream) exceeds 15%.

In steam plants this points to viscous-fluid heaters and coolers, large condensers, and any bundle where vibration or shell-side ΔP has been a recurring headache. The helical baffle replaces the segmental-baffle STHE directly, and is the platform for the two hybrids below.

3. HeliKorr – addressing both shell and tube sides together

HeliKorr combines the two ideas in a single exchanger: corrugated tubes inside a helical-baffle shell. The corrugation lifts the tube-side coefficient while the helical baffle lifts the shell-side coefficient, so both thermal resistances drop together rather than one becoming the new bottleneck. For duties where neither side dominated before, this is the most powerful single step available.

Typical gains versus a conventional plain-tube, segmental-baffle exchanger: heat-transfer area down 35–50%, capital cost down up to 30%, combined shell- and tube-side coefficient up 35–50%, shell-side dead zones eliminated and fouling cut by up to ~40%, flow-induced vibration suppressed, and lower pumping and life-cycle cost. 

HeliKorr is ideally suited to steam and process condensers and feed-water heaters, and is well placed to replace oversized or vibration-limited STHEs. The design is the subject of a Kinam design-patent application currently under process.

4. HeliTurbo

HeliTurbo pairs the helical-baffle shell with engineered tube-side inserts (turbulators) in otherwise plain tubes. When the tube-side fluid is viscous or slow-moving — heavy fuel oil, glycol, lube and thermal oils — the laminar film is the limiting resistance, and an insert that forces mixing transforms performance. Kinam offers three insert families to match the duty:

• Wire turbulators — for oil and glycol coolers and even water coolers on steam; they also raise wall shear to mitigate fouling, and improve bubble-cutting in vaporising service.
• Rigid soldered turbulators — soldered to the tube wall for extremely viscous oils and for air; the bond adds a conductive/convective path and lifts vaporiser performance by up to ~4×.
• Twisted-tape turbulators — swirl inserts for oil and glycol coolers, fouling mitigation by increased shear, and improved boiling in vaporisers.

Because the inserts go into plain tubes, HeliTurbo is an excellent retrofit for an existing bundle whose tube side has become the bottleneck. In a boiler house its natural homes are fuel-oil pre-heaters, viscous-oil coolers, air inter-coolers and vaporisers — duties where a plain-tube STHE would otherwise be heavily oversized. 

In steam power plant, relevant applications are :

• Boiler fuel-oil (HFO / LDO) pre-heaters and atomising-steam heaters.
• Lube-, seal- and control-oil coolers for turbines and boiler feed pumps.
• Generator hydrogen coolers and combustion-air inter-coolers.
• Glycol, thermal-oil and other viscous-fluid heaters and vaporisers, where a plain-tube STHE would otherwise be large.

Choosing the Right Enhancement

The selection logic is simply: follow the controlling resistance. If the tube side limits the duty — condensing vapours, clean liquids — start with the corrugated tube. If the shell side limits it, change to a helical baffle. If both sides limit it, HeliKorr addresses them together. And if the tube side is viscous or low-Reynolds, HeliTurbo’s inserts do the work. Table 2 summarises these options against typical steam and power duties.

Corrugated tubes and helical baffles are well-established routes to higher heat-transfer coefficients and to smaller, lower-fouling exchangers; combined in arrangements such as HeliKorr and HeliTurbo, they allow both shell- and tube-side resistances to be reduced in a single unit. In steam and power plants — where exchanger size, fouling and reliability each carry a cost — matching the enhancement to the controlling resistance, and accepting the associated pressure-drop trade-off, can meaningfully reduce surface area and life-cycle cost.

Table 2 — Matching the enhancement to the controlling resistance

Notes

* Trademark applications for HeliKorr and HeliTurbo are under process.
* Design Patents applications of HeliKorr and HeliTurbo are under process.

Authors:

Dr Rambir Bhadouriya
Vice President, New Product Development
Kinam Engineering Industries Pvt. Ltd, Mumbai

Mehul Mehta
Managing Director
Kinam Engineering Industries Pvt. Ltd, Mumbai

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