【Q&A Question 173】October 10, 2016
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This post was last edited by liuquan1100 on 2017-8-25 22:29. [Q&A Question 173] October 10, 2016: What principle governs whether the medium flows through the tube side or the shell side of a heat exchanger? The answer key will be available after responding; scoring is based on answering the key points. Answer: Tube side: 1. Media that are prone to scaling and contamination flow on the tube side, making cleaning easier. 2. The high-pressure medium flows through the tube side, preventing the shell from being under pressure and reducing the amount of metal required for the shell. 3. The corrosive medium flows in the tube side to prevent simultaneous corrosion of the tube and shell. 4. Toxic media should flow in the tube side to minimize the risk of leaks. Shell side: 1. Saturated steam flows through the shell side, which facilitates condensate drainage and keeps it cleaner. 2. The cooled fluid flows through the shell side, allowing the shell to enhance the cooling effect. 3. Fluids with high viscosity or low flow rates flow through the shell side; baffles are used to induce turbulence at low Reynolds numbers, thereby increasing the convective heat transfer coefficient. 4. When the temperature difference between the hot and cold streams is large, the shell side has a higher convective coefficient, as the wall temperature is closer to the side with the higher heat transfer coefficient.
①Unclean and scale-prone fluids should be used in the tube side, as cleaning inside the tubes is more convenient； ②Corrosive fluids should be routed in the tube side to prevent simultaneous corrosion of the tube bundle and the shell ； ③Fluids with high pressure should flow in the tube side to prevent the shell from being subjected to pressure ； ④Saturated steam should flow in the shell side, as the heat transfer coefficient for steam condensation is independent of flow velocity, and the condensed liquid can be easily removed ； ⑤If the temperature difference between the two fluids is large, when using a fixed-tube-sheet heat exchanger, it is advisable to arrange the fluid with a higher heat transfer coefficient in the shell side in order to reduce thermal stress.
It depends on the specific circumstances to decide whether the two media will be in the tube side or the shell side; the choice is made by comparing the two media. However, the following principles must be followed: (1) Corrosive media should be placed in the tube side, to prevent corrosion of both the tube side and shell side materials. (2) Toxic media flow in the tube side, which reduces the chances of leakage. (3) Fluids with low flow rates should flow through the tube side to allow for an optimal flow velocity, while fluids with high flow rates are better suited to flow through the shell side. (4) High-temperature, high-pressure fluids flow through the tube side, as the smaller diameter of the tubes allows them to withstand higher pressures. (5) Fluids that tend to form scale flow through the tube side in fixed-tube-sheet and floating-head heat exchangers, and through the shell side in U-tube heat exchangers, which facilitates cleaning and scale removal ； In a cooler, generally, the cooling water flows through the tube side, while the fluid to be cooled flows through the shell side. (6) Fluids with high viscosity flow in the shell side, as the flow cross-section and direction in the shell side are constantly changing, which facilitates heat transfer. (7) The flow direction of the fluid also has a significant impact on heat transfer. To make full use of the principle of convection due to temperature differences in the same medium, thereby improving heat transfer efficiency and reducing energy consumption, whether in the tube side or the shell side, when the fluid is heated or evaporated, its flow direction should be from bottom to top ； When the fluid is cooled or condensed, the flow direction should be from top to bottom.
Media that are corrosive, toxic, have high temperatures or pressures, as well as those prone to scaling, should all be handled in the tube side
Higher viscosity or lower flow rate: shell side
Media that are prone to scaling and contamination, high-pressure media, corrosive media, and toxic media flow in the tube side. Clean, high-viscosity, forms shell layers
Hot shell, cold tube; high-pressure tube, low-pressure shell; the tube is prone to corrosion while the shell is not