Hydraulics & Pneumatics November/December 2022

www.hpmag.co.uk HYDRAULICS & PNEUMATICS November/December 2022 31 will claim that their designs will operate for years without the need maintenance but will also admit that cleaning (which often involves similar levels of disassembly to servicing) depends on the viscosity, fouling and scaling potential of the product. In other words, admitting that real world performance is much less impressive than the theory. In contrast, corrugated shell and tube heat exchangers are specifically designed to reduce fouling, meaning that their performance parameters are based on real-world operational situations. The total cost of ownership factor Obviously, the total cost of ownership (a combination of the capital cost and operational costs over the working life of the unit) is a major factor when considering which type of heat exchanger to invest in. Proponents of PHEs will claim that they provide the lowest cost of ownership, but they rarely mention one of the biggest maintenance costs involved in running plant heat exchangers – gasket replacement. The gaskets between each plate are an inherent design feature of PHEs but are prone to failure, particularly when operating at high temperatures. This is particularly true where operation involves many repeated heating and cooling cycles, which stress both the gasket material, but also the metal plates which are often just 0.5-0.6 mm thick. Even when they do not fail, regular gasket replacement is often part of the standard service requirement. This means that the price of gaskets needs to be considered in the overall cost of ownership, along with the down time and direct servicing costs. Because the majority of shell and tube designs are of welded construction, there are no internal gaskets to fail or replace. Where removable tubes are used, O-ring gaskets are the norm, making them much easier and cheaper to replace than the bespoke gasket designs required for plate heat exchangers. Once the cost of gasket replacement is factored in over the life of a plate heat exchanger, then the total cost of ownership assessment swings back towards shell and tuber heat exchangers. With much simpler routine maintenance and cleaning, and no need for the regular replacement of expensive, bespoke gaskets, more and more users are appreciating the benefits of shell and tube heat exchangers. www.hrs-heatexchangers.com In a shell and tube heat exchanger, the product flows through the tube/s, while the service fluid flows through the gap between the tube and the shell. BELOW: One element of plate heat exchanges which is often not considered is the cost of gasket replacement. Shell and Tube heat exchangers contain fewer gaskets, and these are normally simple O-rings.