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Cooling and heating media

Certain liquids have to be held at a constant temperature, heated or cooled. This is achieved by using appropriate heating or cooling agents. Two different processes are used here:

  • Endless spirals with a defined laminar or turbulent flow.
  • Double jackets or templates. A double jacket is welded at certain points distributed over the entire surface. Under high pressure, cushions form at the non-welded points, into which the liquid coolant is poured.

Cooling media

For cooling the contents of a tank, a variety of different media can be used :

1. Ice water:
Where previously ice water used to be trickled over the tank, nowadays the cooling water is provided in an endless spiral.
2. Glycol:
When fast cooling is desired, glycol is often used: in comparison to water it offers a major advantage: the freezing point can be extremely low without the liquid actually freezing.

3. Ammonia:
This agent is sprayed into the cooling zone in liquefied form, which causes the coolant to be depressurised and attempt to become gaseous again . The result : ammonia absorbs a large volume of coldness.

Disadvantages of ammonia :

  • The agent is hazardous
  • The increased pressure necessitates thicker sheathing
  • Expensive process
  • The cooling circuit cannot be regulated with precision

 

Heating media

For heating the contents of a tank, a variety of different media can be used:

1. Hot water:
Hot water is transported in a spiral surrounding the tank. Heat can be fed in up to temperatures shortly before the evaporation point (80 - 90 degrees)

2. Steam:
Steam provides a stronger effect than hot water. Here, water is heated up until it evaporates. It is then passed through a spiral or a template. Though steam provides a stronger effect than water, there are limits here as well. The temperature involved is 120 - 150 degrees.

3. Heating oil:
In order to achieve a stronger effect than steam, heating oil can be used. The heating temperature achievable can reach 250 - 300 degrees here. However, these high temperatures have to be taken into due account when selecting the materials involved, otherwise material deformation may occur during exposure to severe heat .

4. Electric heating:
A electric heating strip - similar to an underfloor heating system - is used here to warm up the liquid in the tank.  As with hot-water heating,  temperatures of around 80 - 90 degrees can be achieved here.

 

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Calculating the cooling surface area

On the subject of temperatures, you will find here a report by Peter Gross on how how to calculate cooling surface areas.