In the working condition of steam heating air, the outlet temperature on the tube side failing to reach the set value is often related to insufficient consideration of heat transfer area, medium flow velocity, and material matching during the selection stage. When design and selection personnel face such problems, they need to confirm one by one from the aspects of design boundaries, material selection, structural compensation, and operation and maintenance interfaces. The following takes the GCH-380 shell-and-tube heat exchanger as an example to sort out the key points of selection in a question-and-answer format.
The design pressure of the GCH-380 shell-and-tube heat exchanger is 1.6 MPa, and the design temperature covers -20°C to 150°C. During selection, it is necessary to check whether the maximum working pressure and maximum working temperature on the process side fall within this range. If the medium temperature approaches the upper limit of 150°C, the reduction of the allowable stress of the material with increasing temperature should be reviewed; if the ambient temperature may be lower than -20°C, the material toughness requirements under low-temperature conditions should be communicated with the manufacturer. Design boundaries are not isolated parameters; the combination of pressure and temperature determines the wall thickness calculation basis for the shell and tube bundle, and also directly affects the selection grade of connecting parts such as flanges and gaskets.
The corrosiveness of the medium determines the material of the shell and tube bundle. Selection personnel should provide key information such as the name, concentration, temperature of the media on both sides, and whether chloride ions are contained. For neutral or weakly corrosive media, a carbon steel shell with a stainless steel tube bundle is a common combination; for highly corrosive media, both the shell and tube bundle need to be made of stainless steel or, as required, materials such as duplex stainless steel. Material selection also needs to take into account thermal conductivity and cost, and the scheme cannot be determined solely by a single indicator of corrosion resistance. If the medium contains particulate matter, the risk of fouling and wear of the tube bundle should also be evaluated, and the flow velocity adjusted or anti-impact structures added if necessary.
Flow velocity is related to pressure drop and heat transfer efficiency. Increasing the flow velocity can enhance heat transfer, but the pressure drop rises accordingly, increasing the energy consumption of pumps or fans. During selection, the allowable pressure drop range needs to be clarified, and a reasonable flow velocity calculated back accordingly. For the gas side, excessively high flow velocity may also cause vibration, and the natural frequency of the tube bundle needs to be checked. The liquid-side flow velocity is usually controlled within a reasonable range to avoid erosion corrosion. The flow cross-sections of the tube side and shell side of the GCH-380 shell-and-tube heat exchanger can be adjusted according to process requirements. Selection personnel should provide the flow rates on both sides and the allowable pressure drop so as to determine the baffle spacing and the number of tube passes.
Temperature changes cause a thermal expansion difference between the shell and the tube bundle, which needs to be compensated through structural design. The fixed tubesheet structure is simple and suitable for occasions with small temperature differences and where the shell-side medium is not prone to fouling; a structure with an expansion joint can absorb part of the thermal elongation; the floating head or U-tube type allows the tube bundle to expand and contract freely and is easy to clean. During selection, the compensation method should be chosen according to the temperature difference, medium cleanliness, and maintenance conditions. When the temperature difference is large and the shell side is prone to fouling, priority should be given to a structure that facilitates tube bundle removal for cleaning.
During the selection stage, the orientation of nozzles, flange standards, anchor bolt positions, and reserved maintenance space should also be confirmed. For the working condition of steam heating air, the selection of the steam trap and the position of the air-side vent will affect the stability of the outlet temperature, and it is recommended to consider them together during system design. The GCH-380 shell-and-tube heat exchanger can be configured with nozzle specifications and material certification documents according to project requirements, facilitating the designer to complete piping layout and acceptance.
