Although some of the heat exchangers discussed earlier in this issue can be disassembled for cleaning, that process is difficult, time consuming and expensive. The heat exchanger must be isolated, disconnected from piping, disassembled, cleaned, reassembled and put back in service. In large systems, this could take several days and will prevent heating or cooling operation in any portion of the system involving the heat exchanger during that time.
Severely fouled brazed plate heat exchangers, or sealed shell and coil heat exchangers, may need to be replaced. Again, a costly and time-consuming process.
The best way to avoid these situations is to minimize the possibility of debris entering heat exchangers. This can be done by installing high-performance separators that capture dirt and magnetic particles upstream of the heat exchanger.
Some designers, by default, specify wye strainers as a means of capturing dirt particles in the system. While this approach is partially effective, it does have limitations. One is that the pressure drop through a wye strainer increases significantly as debris collects on the internal strainer basket, as shown in Figure 5-3. The increased pressure drop decreases flow in the circuit, which negatively impacts the heat transfer performance of any heat exchanger.
Another limitation of wye strainers is that they must be isolated and disassembled for cleaning. This requires temporary shutdown of the circuit and some minor drainage of system fluid.
Finally, wye strainers do not capture magnetic particles such as magnetite that form when dissolved oxygen in the water fluid reacts with steel or cast iron components in the system. Magnetite will be attracted to magnetic fields generated by circulator motors, especially the strong fields generated by permanent magnets in wet rotor circulators with electronically commutated motors.