316L Sanitary & Hygienic
Sanitary Heat Exchanger Selection: Tube-in-Tube, Plate and Scraped-Surface Compared
Choosing a hygienic heat exchanger is a trade between thermal performance, cleanability and pressure capability. The same duty can usually be met by two or three types; the right answer depends on what is in the product and how often you clean.
Type comparison
| Type | Typical U (W/m²K) | Approach temperature achievable | Pressure capability | Cleanability | Handles particulates |
|---|---|---|---|---|---|
| Gasketed plate-and-frame | 3 000–6 000 (liquid/liquid) | 1–2 °C | Up to ~16–25 bar, gasket-limited | Excellent if gaskets are maintained; CIP-able | Poor — narrow channels block |
| Brazed / welded plate | 3 000–5 000 | 2–3 °C | Up to ~30–40 bar | Chemical cleaning only — not for product with soil | No |
| Tube-in-tube (concentric / multi-tube) | 800–2 000 | 3–6 °C | High, up to 40+ bar on the product tube | Excellent — smooth bore, fully drainable, no gaskets in product | Good |
| Hygienic shell-and-tube (multi-tube, welded product side) | 800–1 800 | 3–8 °C | Very high | Very good; the product side can be orbitally welded | Good |
| Scraped-surface | 300–1 000 | 5–10 °C | Moderate | Good, but mechanically complex | Excellent — designed for it |
| Corrugated tube-in-tube | 1 500–3 000 | 2–4 °C | High | Good, turbulence also aids CIP | Moderate |
Reading the numbers
The overall heat transfer coefficient U and the resulting area requirement differ by a factor of three to five between a plate exchanger and a tube-in-tube unit. That does not automatically make the plate exchanger the right choice, because the comparison that matters is installed and operating cost over the life of the plant:
• Tube-in-tube: 2–4× the area for the same duty, but no gaskets in the product path, high pressure capability, tolerant of solids, and fully drainable — which matters more than area in aseptic and pharmaceutical service.
• Scraped-surface: the only sensible answer for crystallising, very viscous or heavily fouling product.
Selection by application
| Application | Recommended type | Reason |
|---|---|---|
| WFI / purified water cooling, pharmaceutical water loops | 316L tube-in-tube, electropolished, double tube sheet | No gasket crevice, fully drainable, eliminates cross-contamination risk |
| Milk and dairy product heating / cooling | Plate for pasteuriser regeneration; tube-in-tube for product-to-product on UHT | Plate gives close approach; tubular handles higher pressure and fouling |
| Beer wort cooling | Gasketed plate, or tube-in-tube where hop solids are present | Plate for thermal performance; tubular for cleanability with trub |
| Juice with pulp, fruit preparations | Corrugated tube-in-tube or scraped surface | Particulates block plate channels |
| Aseptic product cooling after UHT | Tube-in-tube with a steam barrier, or aseptic plate with a steam seal | Sterility barrier is as important as heat transfer |
| CIP solution heating | Plate or tubular, stainless | Cost-driven; clean fluid |
| Utilities (glycol, hot water, steam condensate) | Brazed plate or shell-and-tube | No product-contact cleanability requirement |
Hygienic design requirements
- No cross-contamination path. Where product and utility are separated by a single wall, use a double tube sheet or a double-wall plate with a vented gap so any leak is visible rather than mixing.
- Drainability. The product side must drain completely; specify a slope and a drainable connection at the low point.
- Surface finish. Ra ≤ 0.8 µm, or Ra ≤ 0.4 µm electropolished for pharmaceutical and aseptic duty — smoother surfaces foul more slowly and clean faster.
- Velocity. Keep the product-side velocity high enough for good heat transfer and low enough to avoid erosion: 1–3 m/s is typical for liquids in hygienic tubular units.
- Connections. Tri-Clamp or aseptic unions on product; verify that the nozzle size does not create a dead leg.
- Materials. 316L product contact; gaskets in EPDM, FKM or PTFE with the appropriate food-contact certification.
Sizing inputs we need
To size a hygienic exchanger we need: product and utility fluids, inlet and outlet temperatures for both sides, flow rates (or the heat duty), maximum allowable pressure drop on each side, physical properties (density, viscosity, specific heat, thermal conductivity) at the mean temperature, fouling factor, CIP conditions, and the required documentation. With those we return the required area, the selected model, the approach temperature and the pressure drop on both sides.
KOSA supplies 316L hygienic tube-in-tube and plate heat exchangers with full material and surface-finish certification.
Frequently Asked Questions
When should I choose a tube-in-tube exchanger over a plate exchanger?
Choose tube-in-tube when the product contains particulates or pulp, when a gasket in the product path is unacceptable, when the pressure is high, or when the exchanger must be fully drainable and sterilisable as in pharmaceutical water and aseptic service. A plate exchanger is preferred where thermal performance and footprint dominate and the fluid is clean.
What is approach temperature?
Approach temperature is the smallest temperature difference between the two streams in the exchanger, usually at the hot or cold end. A smaller approach means better heat recovery but more area. Plate exchangers typically achieve 1 to 2 degrees Celsius while tubular units achieve 3 to 6 degrees Celsius.
Why use a double tube sheet design?
A double tube sheet provides two separate barriers between the product and the utility, with a vented gap between them. If one joint leaks, the fluid escapes visibly through the vent instead of contaminating the product, which is a critical requirement in pharmaceutical and high-purity applications.
What surface finish is needed on a hygienic heat exchanger?
Ra 0.8 micrometres or better is standard for food and beverage product contact surfaces. Pharmaceutical water and aseptic duties commonly specify electropolished surfaces at Ra 0.4 micrometres or better, because smoother surfaces foul more slowly and clean more quickly.
How does fouling affect exchanger selection?
Fouling reduces the effective heat transfer coefficient over time, so the exchanger must be sized with an appropriate fouling factor and cleaned on a defined cycle. Products that foul heavily, such as milk at pasteurisation temperature or products that crystallise, favour designs that clean easily or a scraped-surface unit.
Send us the process data — fluid, inlet pressure, differential pressure, temperature, required flow and pipe size — and our engineers will return a sized selection with Cv calculation, leakage class and material recommendation, plus documentation packs for FAT / IQ-OQ.
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