The moment material emerges from the freezing liquid, the mesh belt, baskets, and product surfaces all carry a layer of medium. This medium leaves the tank with the discharge, while water condensing on the tunnel inner walls returns to the tank with the product—one out, one in—and the liquid volume and concentration in the tank begin to drift. In continuous production on an immersion chiller line, managing these two losses is more practical than increasing refrigeration capacity after the fact.
Problem
Carryover and dilution are two different things—don’t treat them as one
Liquid carryover is physical entrainment: medium adheres to product, baskets, and mesh belt, leaving with the discharge. Condensate dilution is a separate path: moisture from humid workshop air and from the product itself condenses on cold inner walls, then flows back into the tank along the mesh belt and tank body. The former shows as slowly dropping liquid level and rising medium consumption; the latter shows as level rising rather than falling while concentration drops. The corrective actions for these two phenomena are completely different—distinguish them first before defining measures.
What happens after concentration drifts
The freezing point of food-grade freezing liquid changes with concentration. Once diluted by water, the freezing point rises, and at the same evaporation temperature the liquid temperature can no longer hold steady. In the published parameters of DKN-RHV-2000L, the quick-freeze liquid temperature uniformity is stated as ±3℃; this figure presumes stable medium conditions in the tank. When concentration is out of balance, liquid temperature differences appear across different positions in the tank first—heat exchange conditions on both sides versus the middle of the mesh belt, and upper versus lower layers, become inconsistent—and the core temperature of discharged product begins to scatter.
Three common approaches on site
Top up without measuring. Add medium when the level drops, never measure concentration for years, and the added medium is not the same ratio as the original—the tank condition becomes increasingly unclear.
Air knives installed and left fixed. Different products and different loading heights require different nozzle angles and air volumes. Once the nozzles are welded in place, changing products carries away a batch of medium.
Condensate drained directly to the floor. Condensate in the tunnel mixed with medium lands on the floor, increasing medium consumption and making the discharge area floor slippery.
Principles and Key Parameters
What determines carryover volume
- Product surface condition: products with grooves and many cuts carry more liquid than smooth products; baskets with large mesh openings and low walls also lose more medium.
- Loading density and stack height: the denser the product stack, the more the pieces shield each other during discharge, and the air knife cannot reach the middle layers.
- Mesh belt and lift section: a segmented lift belt quickly raises the product at the tail, first shaking adhering medium back into the tank, then entering the air knife section.
- Viscosity and surface tension of the medium itself: viscosity rises at low temperatures, making wall adherence more pronounced—this is also why the liquid temperature should not be pushed lower than the process requires.
- Discharge speed: the faster the mesh belt speed, the shorter the air knife dwell time.
Where condensate comes from
The dew point of workshop air, the temperature difference between the tunnel cover and inner walls, and the frequency of opening the cover are the three main sources. GB 14881-2025, the National Food Safety Standard—General Hygienic Regulation for Food Production, explicitly requires in its building structure provisions that ceilings prevent condensate dripping or be fitted with diversion grooves, drip trays, and similar devices, and that piping and conduits avoid being placed above exposed food (Foodmate implementation comparison interpretation, effective 2026-09-02: http://www.foodmate.net/zhiliang/guanli/174430.html). On the equipment side, the corresponding approach is to reduce moisture aggregation on inner walls and route condensed water to drain paths outside product exposure.
DKN-RHV-2000L published parameters excerpt
| Item | Parameter |
|---|---|
| Tunnel inner chamber dimensions | 23260 mm (L) × 2360 mm (W) × 570 mm (H) |
| Mesh belt effective width | 2000 mm |
| Equipment tunnel external dimensions (approx.) | 28000 mm (L) × 3500 mm (W) × 2280 mm (H) |
| Quick-freeze capacity | 0～2000 kg/h (capacity varies by product) |
| Working temperature | ≤ -35℃ |
| Temperature control accuracy | ±2℃ |
| Quick-freeze liquid temperature uniformity | ±3℃ |
| Tunnel cycle time | 20～100 min adjustable |
| Power supply specification | 380V / 50Hz |
| Total unit power | 320 kW (compressor + evaporative condenser + circulation pump + air knife + lift opening) |
| Running power | approx. 270 kW |
| Freezing liquid | Food-grade, suitable for direct food contact, liquid temperature up to -50℃ |
| Mesh belt mechanical lift height | 700 mm |
| Working space height between mesh belt and hold-down belt | approx. 350 mm |
| Cabinet insulation thickness | 120 mm high-density foam |
For export regions requiring 60Hz or other voltage levels, reselect the model; the table above is for 380V/50Hz configuration.
Selection and Configuration Points
Configure the discharge end with two air knife stages plus high-pressure air flow for water removal, with adjustable nozzle angles. The front stage blows medium on the product surface back to the recovery section; the rear stage handles residual water removal. When changing products or adjusting loading height, it must be possible to reset nozzle angles and air volume—this is the key to managing carryover over the long term.
The recovery path must return to the tank. A confluence structure is provided below the tail air knife zone and recovery device, returning both heat and medium to the tank; the discharge-end recovery section must have an independent return line and floor drainage to keep recovered medium off the workshop floor.
The lower part of the tank is sloped for confluence, fitted with a drain pipe and shut-off valve. Draining old medium before cleaning, liquid change, or extended shutdown relies on this structure. Do not substitute temporary pumps and hoses.
Configure concentration and level with online detection plus automatic replenishment. An online quick-freeze liquid concentration detection system works with the level signal to automatically replenish within a set range (automatic replenishment unit is optional). For models without automatic replenishment, concentration detection should still be retained; otherwise replenishment volume can only rely on experience.
Reduce condensate flowing back into the tank. Inner surface coating to reduce moisture aggregation, condensate diversion and drainage devices inside the tunnel, and controlling cover opening frequency are used together—doing only one has limited effect.
Provide adequate hygiene and service access. Medium piping uses sanitary quick-connects, the cover can automatically flip open to both sides, the mesh belt and supports can be mechanically lifted, and the freezing tank lower part is fitted with a drain pipe. Whether daily cleaning and liquid change time can be reduced depends on whether space has been left at these points.
Records follow replenishment volume. Record level, concentration, replenishment volume, and cleaning time each shift; after one week of continuous production, it becomes clear whether carryover is stable. If replenishment volume suddenly rises, first check air knife angle, recovery device return, and mesh belt adherence, then consider other causes.
Application Scenarios
In central kitchens, braised foods, steamed meats, and soup products need to drop from above 60℃ to the chilled range after coming out of the pot; production lines where product form suits immersion heat exchange can organize the discharge section with this configuration. For continuous quick-freezing of prepared dish conditioning packs and aquatic slices, the medium-side focus is packaging compatibility: packaging must withstand medium temperature, seals must not fail, and leakage must not occur. Small items such as pastries and balls have high loading density; the air knife and recovery sections must be recalibrated to the actual loading height.
If the product cannot contact liquid medium, or the product form is not suitable for immersion, a food blast chiller using forced-air circulation is more appropriate. The difference in heat exchange method between the two routes was compared in the cooked food cooling window article; refer to it alongside actual site conditions.
FAQ
How much freezing liquid carryover is normal
There is no universal figure. Product form, loading method, and air knife configuration vary widely, and carryover differs greatly. In engineering practice, back-calculate from replenishment volume and concentration records: record replenishment volume each shift during continuous production; under stable production this figure should fluctuate within a certain range. A continuous rise indicates a problem in some link.
Why is there water in the tunnel
Moisture carried in by food and water vapor in humid workshop air condense when they meet cold inner walls. GB 14881-2025 has explicit clauses on ceilings preventing condensate dripping and piping not being placed above exposed food; on the equipment side, the corresponding measures are inner surface treatment, condensate diversion and drainage devices, and management of cover opening frequency (Yibin market regulation: https://m.sohu.com/a/1082186702_121106884/).
How often should concentration be measured
Continuous online detection is recommended, with manual re-testing and records. Re-testing is mandatory at these points: batch changeover, after cleaning, and restart after extended shutdown, because replenishment water and cleaning residual water both change concentration.
Can tap water be added directly
No. Dilution raises the freezing point, disrupts the medium formulation, and introduces calcium, magnesium, and chloride ions, accelerating corrosion and scaling in piping and heat exchangers. Use the same model medium for replenishment; when dilution is truly needed, use pure water or deionized water per the medium supplier’s ratio.
Will the air knife blow medium into the workshop
The air knife and water removal devices are arranged above the tank and recovery section; the air flow direction blows adhering medium back to the recovery section, not toward the workshop floor. During installation and commissioning, confirm the recovery section return path, air knife coverage, and discharge area floor drainage. Once these three points are confirmed, recovered medium overflow will not occur during operation.
Specific tank dimensions, medium type and temperature, and air knife and recovery section configuration vary with product form, batch weight, infeed and target core temperature, and are determined according to working conditions when preparing the equipment technical proposal. If there are uncertainties in the process, you can describe the working conditions on the contact page for discussion.