During on-site commissioning, the outlet medium temperature of the heating and cooling heat exchanger often fluctuates significantly, or the heating and cooling rate fails to reach the process setpoint. Such problems are mostly related to the degree of matching with the working conditions during the selection stage. Design and selection personnel can check actual requirements item by item against the following key points.
The heat exchange area of the heating and cooling heat exchanger must be determined by calculation based on the medium inlet and outlet temperatures, flow rate, and specific heat capacity. If estimated only by experience, the heat exchange area is likely to be too small, resulting in outlet temperature failing to meet the standard; if the area is too large, it increases equipment investment and occupied space. It is recommended to use the maximum heat load required by the process as the basis and retain a reasonable margin.
The requirements of different processes for heating and cooling rates differ significantly. Under rapid heating or cooling conditions, the heat exchanger needs to consider thermal expansion compensation structures to avoid tube sheet cracking or seal failure caused by thermal stress. If the rate requirement is moderate, a relatively simple fixed tube sheet type can be selected. During selection, the maximum allowable rate should be confirmed with the process discipline.
On-site installation space is often limited, and the overall dimensions and nozzle orientation of the heat exchanger must be coordinated with the piping layout. Horizontal and vertical installation have different requirements for support structures and vent and drain locations. During selection, it is necessary to combine the equipment layout drawing to confirm maintenance space and nozzle direction, reducing on-site modification work.
The medium contacted by the heat exchanger may be corrosive, and material selection must be based on medium composition, concentration, and operating temperature. Commonly used materials include carbon steel, stainless steel, and duplex steel, etc. During selection, initial cost should not be the only consideration; maintenance and replacement costs over the service life cycle should also be evaluated.
