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Quotes - Engineering - SalesTwo processes, one kind of exchanger
Ultra-high-temperature processing takes milk, cream, plant-based drinks and liquid nutrition to 275 to 285 F (135 to 140 C) and holds for 2 to 5 seconds. The product is commercially sterile and, filled aseptically, keeps for months at room temperature. Extended shelf life processing stops short: 250 to 260 F for a few seconds, or a lower temperature with microfiltration, and the product keeps 30 to 90 days refrigerated with a fresher flavor than UHT.
In both cases the heat exchanger is doing something HTST never asks of it: holding a wall hot enough to denature whey protein and precipitate calcium phosphate for hours at a time. Deposits build from the moment the run starts. The exchanger design is therefore about wall temperature, velocity and area margin, not just heat transfer, and the run length between cleanings is a number the design has to deliver.
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Run length at 285°F is bought with area margin and velocity
A heater sized for the clean duty hits its pressure drop limit in two to three hours. Give it 25 percent extra surface, a 7 degree hot water approach and 5 to 7 ft/s product velocity, and the same product runs 8 to 14 hours before CIP.
Heating section
- Final heater on pressurized hot water, 5 to 10 degrees above product setpoint
- Product velocity 5 to 7 ft/s to thin the deposit layer
- Multi-tube or corrugated tube-in-tube, 316L, 20 Ra or better
- Back pressure valve holds product above its boiling point
- Area margin of 20 to 30 percent for fouling over the run
Cooling section
- Regeneration against incoming raw product first
- Tower or chilled water stage next, glycol stage last
- Sterile product side kept above raw side pressure throughout
- Sterile barrier on the utility side of the cooler if the utility is not sterile
- Outlet at 40 F for ESL, 70 to 80 F to an aseptic tank for UHT
Recommended construction by UHT and ESL duty
At sterilization temperatures the tubular constructions dominate on run length; plates come back in where the product is thin and the plant accepts a shorter cycle.
| DUTY / CONDITION | RECOMMENDED CONSTRUCTION | WHY |
| UHT final heater, milk or plant-based drinks, 275 to 285 F | Multi-Tube | Bundle of small sanitary tubes gives high velocity and wall shear; no gaskets at 285 F; withstands 150 psig product pressure |
| ESL heater, 250 to 260 F, thin products | Corrugated Tube | Corrugation raises the product coefficient so wall temperature stays close to bulk; single product path is easy to CIP |
| Cream, creamers, liquid nutrition at UHT temperature | Single Tube-in-Tube | Large product bore, no crossflow channel to plug; handles the viscosity climb as protein sets up |
| Regeneration section, sterile against raw | Double Tubesheet | Sterile and raw product separated by a vented gap in the tubesheet; a leak shows outside the product path |
| ESL line on thin milk where the plant cleans every 8 hours | Gasketed Plate | Lowest cost per square foot and highest regeneration; run length is shorter, so it fits plants that already stop each shift |
| Pressurized hot water set feeding the heater | U-Tube | Plant steam on the tube side, water at 290 to 300 F on the shell side; free expansion over the daily heat-up |
Designing for fouling at 285 F
Type A fouling, the soft white whey-protein deposit, forms fastest between 165 and 230 F; Type B, the hard mineral scale, dominates above 230 F. A UHT heater sees both, in that order, along its length. The practical design response is to keep the wall temperature as close to the product temperature as the area allows, which means a small hot water approach, a high product velocity and more tube length than the clean duty needs. A heater sized with no fouling margin will hit its pressure drop limit in two to three hours; one sized with 25 percent area margin and a 7 degree approach runs 8 to 14 hours on the same product.
Preheating and holding are part of the fouling answer. Preheating to 195 to 205 F and holding for 30 to 60 seconds before the final heater lets the whey protein denature and complex with casein in the bulk rather than on the wall, and it is why many UHT lines run three to four times longer between cleanings than the same heater fed cold. The preheat hold coil is a sanitary holding tube, sloped and instrumented like an HTST tube.
The cooling side sets the shelf life more than people expect. Product leaving the sterile hold at 285 F is regenerated against incoming raw product, then cooled on water, then on glycol. The regenerator is where a leak would put raw product into sterile product, so the sterile side runs at higher pressure and the section is commonly double tubesheet or double-wall plate. For ESL, the outlet has to be at 40 F or below before the filler; for UHT into an aseptic tank, 70 to 80 F is fine and the glycol stage drops out.
Run length is a design number, not luck
Pressure and the back pressure valve
Water boils at 285 F at about 52 psia, so the product has to be held above roughly 40 psig in the heater and holding tube or it flashes and the hold time goes to zero. A back pressure valve downstream of the cooler sets the whole line 15 to 20 psi above saturation. The exchanger design pressure follows from the valve setting plus pump shutoff, which is why UHT product sides are typically rated 150 psig rather than the 100 psig common on HTST.
Sterile barriers
Every place where a non-sterile fluid meets the sterile product across a single wall is a risk: the regenerator, the coolers, the gland of every valve downstream of the hold. Coolers on the sterile side are usually fed with sterile condensate or run with a steam barrier on the utility connections, and the regenerator uses a double tubesheet or double-wall plate so a failure has somewhere to show up.
ESL heating and cooling on one skid
An ESL line for flavored milk, creamers or plant-based drinks often runs 250 to 260 F for 2 to 4 seconds with a preheat hold, then regenerates and cools to 38 F. The whole thing fits on one frame: a U-tube hot water set, a corrugated tube heater, a sloped hold coil, a double-tubesheet regenerator and a straight-tube glycol cooler. Cream and pudding bases take a single tube-in-tube heater instead of the corrugated multi-tube.
What settles the quote
Product and total solids, flow, raw inlet temperature, sterilization temperature and hold, preheat hold if any, required run length between CIP, outlet temperature and destination, and the hot water or steam pressure available. Those ten items are the whole specification. Call and talk it through with an engineer: 1-805-484-2992
Common FAQs
UHT reaches 275 to 285 F for 2 to 5 seconds and the product is commercially sterile for ambient storage. ESL runs 250 to 260 F for a few seconds, or lower with filtration, and keeps 30 to 90 days refrigerated with less cooked flavor. The exchangers are the same families; ESL runs cooler and fouls slower.
Gasket life at 285 F and the deposit rate on a narrow plate channel both cut the run short. Plates still work on the regeneration and cooling sections and on ESL lines that clean every shift. The final heater is tubular in nearly every line HeatX quotes.
Eight to fourteen hours is a reasonable design target for milk with preheat holding and a 25 percent area margin. Without preheat holding, or with a large hot water approach, expect two to four hours.
Pressurized hot water at 290 to 300 F from a U-tube steam-to-water set, chilled water for the intermediate cooler, and propylene glycol at 25 to 28 F for the final ESL cooler. Direct steam on the product exchanger is not used on indirect lines.
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