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FOOD & BEVERAGE
IMPROVING HEAT TRANSFER EFFICIENCY
Matt Hale, International Sales & Marketing Director, HRS Heat Exchangers, looks at the numerous benefits corrugated tubes provide over the use of smooth tubes in tubular heat exchangers
O
ver the last forty-plus years, HRS Heat Exchangers have gained a reputation for producing highly efficient tubular heat exchangers which provide unrivalled heat exchange capacity combined with consistent performance with a relatively small operational footprint. The key to this is our use of corrugated tube technology. The three most common types of heat exchanger are plate heat exchangers, tubular heat exchangers and scraped surface heat exchangers, although a number of other specialist designs exist. Plate heat exchangers are suitable for use with simple viscous fluids such as water, milk and some thin oils, while highly viscous materials or those which require thorough mixing (for example to keep complex emulsions together) often require scraped surface heat exchangers. For most materials between these two extremes, tubular heat exchangers are the preferred choice.
Design configurations A number of design configurations of tubular heat exchanger are available (such as annular space, double tube and multitube), but the biggest influence on the efficiency of tubular heat exchangers is the type of tube used, and simply put, corrugated tubes are more efficient at transferring heat than smooth ones. They also provide a number of other benefits. When a fluid moves through a tube, the dynamics are affected by factors such as pressure, viscosity, and the design of the tube wall. In a smooth tube, fluids usually follow a smooth path in which the particles that make up the fluid do not interfere with each other – known as laminar flow. However, where the smooth flow is disrupted, for example by disrupting the surface of the tube, tiny whirlpools form in the fluid creating turbulence
– unsurprisingly known as turbulent flow. This turbulence makes tubular heat exchangers more efficient by preventing viscous or suspended materials sticking to the wall of the tube, where they can form a boundary layer, which acts as insulation and prevents efficient heat transfer. The creation of this turbulent flow, and the resulting improvement over efficiency (compared to a smooth tube) is the key benefit of corrugated tube heat exchangers.
Smaller footprint
Because a corrugated tube provides greater levels of heat transfer rate compared to a smooth tube of the same length, a heat exchanger with the same thermal performance can be smaller. For example, if corrugations increase the heat transfer by 10 per cent compared to a smooth tube, then the unit can be made 10 per cent shorter than an equivalent smooth-tube while delivering the same performance. This increased thermal efficiency – which can be up to three- times that of a smooth tube heat exchanger – also means that less space is required to achieve the same level of heat transfer. Depending on the
final application, a corrugated tube heat exchanger can therefore be up to half the size of its smooth tube equivalent. This is why HRS heat exchangers are popular for installations where space is restricted.
Increasing operational time A corrugated tube reduces or prevents the formation of a boundary layer, so it also greatly reduces the time and effort which is required to remove it. Therefore, operational time between cleaning cycles is much greater for corrugated tubes than smooth ones, further increasing the overall efficiency of the process.
In many situations, a corrugated tube provides sufficient turbulence to prevent the need for mechanical agitation of viscous materials (such as scraped- surface or screw-driven heat exchangers). With no moving parts, in such situations a corrugated tube is easier to clean and maintain and may be more reliable. However, it is important to remember that for many materials or applications, a scraped surface heat exchanger is still the best choice.
Significant benefits When taken together, the benefits of corrugated tubes are so significant that at HRS Heat Exchangers, we don’t use smooth tubes in our non-scraped tubular heat exchangers. The increased heat transfer efficiency, particularly at higher flow rates, means that less heat transfer area is required, so we can produce shorter, more compact designs which are also cheaper to manufacture.
HRS Heat Exchangers
www.hrs-heatexchangers.com
MAY 2024 | PROCESS & CONTROL 25
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