Hydrocooling heat transfer

Refrigeration AG provides equipment and complete engineering in order to cool any fruits and vegetables. Customer requirements like product output, existing inlet and desired outlet temperatures as well as refrigerant have to be selected. Refrigaration AG will provide out of this data a customized offer, which varies from main technical specifications (like residence time, conveyor velocities, main dimensions and water demand) to single components or even complete turn-key projects.

Hydrocooling definition

From the moment the product is harvested its aging begins, particularly in hot climates. Whatever the post harvest cooling system is, the most important step is to get the harvest to the pre-cooler as quickly as possible, in order to speed up the production process or to keep quality requested standards. If warm produce is cooled directly by chilled water or brine, the process is known as hydrocooling.

Processing vegetables hydrocooling serves different purposes: Removal of field heat from the produce cooling it down to 4,0°C or lower as well as cleaning of produce at the same time and reducing fruit rotting organism through the use of chlorine. All of these effects improve the shelf-life of fruit. Most fresh fruit and vegetables require total cooling immediately after harvest to deliver the highest quality product to the consumer. Conventional refrigeration systems are slow to cool and the longer time spent in reducing the produce to its required temperature the greater the weight loss.

Nothing is quicker than vacuum cooling but the evaporation principle on which it works means high weight loss and greatly reduced shelf life. Hydrocooling is an especially fast and effective way to cool produce items which are slow to cool according to their large volume to cover surface area relationship. These items include sweet corn, melons and many large tree fruit.

Hydrocooling advantages

Hydrocooling 

  • cools produce rapidly (about 15 time faster than air)
  • allows greater harvesting and marketing flexibility
  • easily handles large amounts of produce
  • is a very effective method and lends itself particularly to root crop and stone fruits. Cooling is quick, weight loss is negligible and not like weight loss of 3% with air or vacuum cooling.
Complete hydrocooling stainless steel unit including conveyer belt
Complete hydrocooling stainless steel unit including conveyer belt
Acid citric mixture tank aside
Acid citric mixture tank aside
Ice water supply onto the conveyer belt without product
Ice water supply onto the conveyer belt without product
Ice water supply onto the conveyer belt with product
Ice water supply onto the conveyer belt with product

Direct product chilling with heat transfer temperatures of 0.5°C till -0.5°C

Ice water with temperatures of 0.5°C can perform very well for direct product chill down of large quantities of product in a very short time. As a result it has been used for many years in food cooling and process cooling wordwide. Ice water slightly over 0°C has no risk of freezer burn and is ideal for direct product cooling as such in most of the applications. Many customers are critical about the use of ice water due to too moisture, but they forget, that fruits and vegetables are resistant to rain by nature. Fish and seafood are naturally under water.

Furthermore, the overall product is a combination of the heat transfer calculation of the final product and the calculation of the economics of these heat exchangers. Both are therefore prior components of the overall system, which are not negligible. In addition, we calculate the necessary quantities of water or ice in the case of direct product cool down. However, the components of ice water (0.5 ° C) and / or chip ice (-0.5 ° C) are of primary importance to us in this heat transfer calculation. In cases where ice water (0.5 ° C) is insufficient for the cooling process, mainly in the meat industry and the fish processing, ice (-0.5 ° C) must be used.

Hydrocooling principle

Inside the hydrocooler the produce remains continuous in contact with large quantities of ice water or brine until the desired final produce’s temperature is reached. The time the produce remains in contact with water is called residence time and its length depends on the properties of produce (kind, shape, size, inlet and outlet temperatures), type of hydrocooler, type of packaging and mean ice water temperature.

During cooling the heat of produce is transferred to the water increasing the return water temperature (usually a low temperature change). This water is collected, filtered if necessary, recooled and recycled. It is ideal to change the hydrocooler water daily. However, many operations base the timing of such cleanings on the amount of produce run through the hydrocooler.

Types of Hydrocoolers and products suitable for Hydrocoolers

There are different types of Hydrocoolers which differentiate themselves 

1. in the way that ice water or brine comes in contact with the produce:

  • Shower Hydrocoolers (produce is exposed to a shower of ice water or brine)
  • Immersion Hydrocoolers (produce is immersed in ice water or brine inside an insulated vat)

2. in the method of moving or placing the produce:

  • Continuous (warm produce is placed on one end of conveyor belt , and cooled produce is removed at the opposite end) 
  • Batch (warm produce is placed into the  hydrocooler and remains stationary on site until the needed residence time is over, afterwards it is removed)

3. in the way that produce is packed:

  • loose product
  • boxed product (in cartons or bulk bins)
  • palletized product (in cartons or bulk bins)

Every hydrocooler uses a determined combination of these three factors.

Hydrocooling is high suitable for processing following vegetables:

Asparagus, Artichoke, Corn, Broccoli, Cabbage, Carrots, Cherries, Kiwi, Leek, Melon, Nectarines, Peaches, Pears, Radish, Salad, etc.

Hydrocooling is also suitable for cooling other kind of produce like bottled products (food, medicine or chemistry), or food packed in foil.

We have always assimilated engineering science and thermodynamics optimally in the various manufacturing processes.

Thermodynamicists,mechanical engineers and welding engineers define the dimensioning, design and construction of customised heat exchanger panels and systems in materials ranging from mild and austenitic steels through to titanium, and ensure successful distribution of their work worldwide.

In doing so they fall back on production engineering expertise and calculations developed in the course of the past hundred years that are still being continuously optimised in an ongoing process.

In the perception of our customers, the Buco product stands for:

Technical and process-oriented consulting
Thermodynamic efficiency
Quality and longevity