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Heat exchanger selection tips

20 February 2017

Heat exchangers are a well-established tool for the thermal processing of materials – cooking, pasteurisation and sterilisation – as well as for heating or cooling food products. Matt Hale offers advice on choosing the right solution for your application. 

Choosing the right heat exchanger for an application first requires an understanding of the factors that need to be considered. These can be broadly divided into commercial considerations and technical considerations. The questions below should provide a good starting point with which to begin a tender process or will provide a basis on which to compare different proposals.

Do I need a heat exchanger? While they are eminently preferable in many situations, particularly where a cooling or heating source is already available or is required for more than one process, heat exchangers may be over-kill for simple situations, where a straightforward heating element or simpler refrigeration system may be more suitable.

What type of heat exchanger do I need? The simplest forms of heat exchangers are plate heat exchangers, which consist of combinations of plates and gaskets through which the product and the heating or cooling medium move. They can do a very good job with simple Newtonian fluids like milk and thin oils. However, for more viscous substances, non-Newtonian fluids and processes requiring high levels of heat transfer, tube-in-tube heat exchangers may be a better option.

These come in different forms – including those with corrugated tubes to increase product turbulence, which prevents fouling and improves operating efficiency. For high fouling and viscous fluids, scraped surface heat exchangers are available. Reciprocating and rotary versions allow different products to be handled carefully, so that key quality characteristics can be maintained or mixing increased, while providing maximum operating efficiency. 

Will the system cope with my products? The heat exchanger must be capable of providing the right amount of heat transfer. Different materials have different thermal properties and this should be considered when designing a heat exchanger. Factors such as viscosity, solids content and texture need to be assessed alongside product flow rates to ensure that the product receives the correct treatment. 

The heat exchanger set-up should be capable of handling the maximum amount of product required at any time. While there will be physical constraints on the size of individual heat exchanger elements, in most cases it is possible to combine multiple units into suitable arrays in order to increase treatment capacity.

What other benefits could the system deliver? A benefit of many HRS heat exchangers is their ability to recover heat from the end of the process and re-use it. In many cases this allows the system to be more efficient, reducing the amount of heat needed in the first place. However, in some situations – for example, where the heat source is plentiful – then the recaptured heat can be used for another process or for something else altogether. These additional cost savings need to be offset against the capital and running costs of the heat exchanger.

What are the maintenance requirements? These will vary according to the type of heat exchanger chosen, its design, and the environment in which it is used. However, more important than the maintenance requirements is how easy maintenance is and the cost of routine space parts such as seals and gaskets. 

How much will the system cost? Cost is often the most important factor when making an investment decision. However, it is important to compare both the capital cost of different units and the anticipated operating costs and service life. For example, a 25% higher purchase price may easily be recouped by greater product efficiency and reduced serving costs over the same, or even longer, operating life. Only by considering all the associated costs will you be able to make an accurate investment decision.

What back-up and support is there?  It is important to have back-up in the event of a problem. Ask whether your supplier offer features such as extended maintenance and servicing and whether you would you be able to take advantage of any future upgrades, such as improvement in tube design. 

It is impossible to cover every potential situation in an article such as this, but I have highlighted a few of the most common issues which apply to nearly every heat exchanger purchase or installation. Your individual circumstances will be unique and another key consideration when making your final decision should be how well your chosen supplier appreciates this.

Matt Hale is international sales manager at HRS Heat Exchangers.

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