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Know your heat exchanger

13 February 2022

When it comes to choosing the right heat exchanger, the biggest factor that needs to be considered is the nature of the materials being processed and the requirements for the finished product, says Matt Hale. 

Different materials have different handling requirements, and while the process being undertaken –for example cooling or pasteurisation – is also an important factor, product identity is the most important consideration for both the client and our engineers: there is no ‘one size fits all’ solution.

For the simplest fluids such as milk, smoothies and juices multi-tube designed offer a good solution. As materials become more viscous in nature, such as honey, soups and creams, then a tube-in-tube or annular space design  may be more appropriate. For the most viscous materials with high fouling potential, you should consider a scraped surface heat exchanger.

More complicated
For materials containing particles or pieces things become more complicated. As a starting point you would use a tube-in-tube solution, where the inner tube provides more room for the product to flow without damage. If the product contains particles but is also viscous, then an annular space design will offer a better solution and will be less susceptible to fouling.

Nearly all HRS tubular heat exchangers feature corrugated tubes which improve heat transfer while minimising fouling. Where materials display laminar flow properties, corrugations provide little benefit, so smooth tubes are used. There also comes a point where products may be too viscous to be effectively treated in a tubular heat exchanger. When this occurs, a scraped surface unit will be required and when the product also contains particles, as outlined above, such as whole strawberries, then a reciprocating scraped surface heat exchanger should provide the necessary combination of gentle handling while preventing and removing fouling as it occurs.

Some co-products and waste streams also need gentle handling. For example, some of the by-products from meat processing need to be handled gently in order to preserve shelf life and so the reciprocating scraped surface designs are often specified in such situations.

In contrast, some products do not need to maintain the integrity of their ingredients, so a scraped surface heat exchanger may be preferable. The R Series features a scraper bar which rotates at around 300 rpm and breaks up or homogenises materials such as mechanically deboned meat (MDM) or jams and sauces.

Many systems will use a combination of two or more heat exchangers – for example a simpler exchanger to pre-cool or pre-heat the bulk of the product and then a more specialist system to perform the main process.  Ultimately the considerations about product identify and preserving product integrity are the same whether you are cooling or heating.

Matt Hale is international sales & marketing director at HRS Heat Exchangers.


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