Tube C12200 Inner Groove without External Fin
Why C12200?
C12200 (Chinese TP2) is a standard deoxidized copper. It offers good corrosion resistance, especially against hydrogen embrittlement. Its thermal conductivity runs about 380 W/(m·K), and it brazes cleanly. Compared to pure C11000, C12200 keeps a thinner, more stable oxide layer after high‑temperature brazing – a real plus for long‑life systems.
What does the inner groove do?
The groove – a spiral ridge formed by spinning or rolling – does three things. First, it makes the fluid swirl, breaking up the boundary layer. That alone can double the inside heat transfer coefficient compared to a smooth tube, especially with slow or sticky fluids. Second, it adds 15–30% more internal surface area without taking up external space. Third, the swirling action scours the wall, so fouling takes longer to build up.
Why no external fin?
You might wonder: why skip the fins? In many tubes, fins go on the outside too. But here’s why an engineer would leave them off:
- The shell‑side fluid might be dirty or viscous – fins would just trap gunk.
- Cleaning is easier with a smooth outside surface.
- It saves manufacturing cost and can use a smaller shell.
- In condensers, a smooth outer surface actually helps the liquid film drain away faster.
So “no external fin” is not a cost‑cut – it’s a deliberate choice for the right job.
Inner Groove vs. Smooth Tube
| Parameter | Inner groove | Smooth |
|---|---|---|
| Inside heat transfer | +50–100% | baseline |
| Inside area | +15–30% | 100% |
| Pressure drop (same velocity) | +20–50% | low |
| Fouling resistance | good | poor |
| Cost per meter | +10–30% | low |
| Typical velocity range | 0.5–2.5 m/s | 1–3 m/s |
If the inside thermal resistance dominates and you can’t raise velocity, go with grooves. If pressure drop is critical and the fluid is clean, smooth tube wins.
Common Dimensions of Tube C12200 Inner Groove without External Fin
Outer diameters (OD) and wall thicknesses follow industry practice (ASTM B280, GB/T 20928):
| OD (mm) | Wall (mm) | Typical use |
|---|---|---|
| 7 | 0.25–0.35 | small refrigeration, car AC |
| 9.52 | 0.30–0.45 | home AC, dehumidifiers |
| 12.7 | 0.35–0.55 | commercial AC, heat pumps |
| 15.88 | 0.40–0.70 | large chillers, industrial exchangers |
| 19.05 | 0.45–0.80 | shellandtube condensers/evaporators |
| 25.4 | 0.60–1.00 | chemical exchangers, waste heat boilers |
Coils (15–50 m) for small diameters; straight sticks (2–6 m) for larger ones.
What parameters need to specify when ordering or designing?
When ordering or designing an inner‑groove tubes, don’t just give OD and wall.
- Outer diameter, bottom wall (from groove root to outside), total wall.
- Groove height (e): 0.15–0.50 mm – more area, more turbulence.
- Helix angle (β): 15°–35° – steeper means stronger swirl but higher pressure drop.
- Apex angle (α): 30°–60° – affects formability and crush resistance.
- Number of grooves per circumference (n): 40–100.
- Minimum burst pressure (ASTM B359).
- Internal surface area per meter (m²/m).
- Residual oil content (≤5 mg/m² for refrigeration).
- Temper: soft (O60) for bending, half‑hard (H55) for straight tubes.
Among these, helix angle, groove height, and number of grooves have the biggest impact on heat transfer.
Groove profiles – what shape works best?
The cross‑section of the thread matters. Common profiles:
Trapezoidal
flat crest, sloping sides. Strong, resists crushing. Good for high‑pressure refrigerants like R410A. Most popular.
Triangular
sharp crest. Maximum turbulence and heat transfer, but wears easily. Use only in clean, low‑pressure systems.
Sawtooth
crest leans to one side. Creates directional vortices. Great for condensers where flow is one‑way.
Round‑crest
radiused top. Lowers stress concentration. Ideal for frequent thermal cycling.
For inner groove tubes (no external fins), trapezoidal or round‑crest profiles give the best balance between heat transfer and fouling resistance.
Different applications ask for different groove designs
You cannot just grab any inner‑groove tube. Here’s how real applications differ:
Air conditioner evaporator
refrigerant inside
Needs: high groove (0.30–0.45 mm), many grooves (≥70), medium helix (18°–25°).
Why: boiling needs nucleation sites – taller grooves give more sites. Too steep a helix kills pressure drop.
Chiller evaporator
water inside, refrigerant outside
Needs: low groove (0.20–0.30 mm), fewer grooves (40–60), shallow helix (15°–20°).
Why: water velocity is low (1–2 m/s). Over‑enhancement just wastes pump power. Low height also avoids trapping scale.
Condenser
cooling water inside
Needs: medium‑high groove (0.35–0.50 mm), steep helix (25°–35°), trapezoidal.
Why: condensing vapour film needs strong turbulence. Steep helix creates spiral flow that helps drain condensate. Trapezoidal profile handles water hammer.
Oil cooler
lubricating oil inside
Needs: very steep helix (30°–40°), medium height (~0.30 mm), moderate groove count (40–50).
Why: oil is viscous. You need strong rotational shear to break the boundary layer. But too many grooves will choke flow and risk cavitation.
Chemical heat exchanger
corrosive or fouling fluids
Needs: low groove (0.15–0.20 mm), round‑crest, extra wall thickness (+0.2 mm).
Why: keeps foulants from embedding in grooves. Round crest reduces stress corrosion cracking. Extra thickness gives corrosion allowance.
So yes – same inner groove concept, but the numbers change completely depending on the job.
Manufacturing and standards
C12200 inner‑groove tubes are made to ASTM B280, EN 12735, or GB/T 20928. The process:
continuous casting → extrusion → rolling → drawing → groove forming (spinning) → annealing → eddy current test.
- Key tolerances: groove height ±0.02 mm, helix angle ±1°, number of grooves ±5.
- Residual oil is checked by gas chromatography.