The tube side and shell side of the heat exchanger

Additional notes for the second floor: 1) Saturated steam should be used in the shell side, as it is relatively clean; the surface heat transfer coefficient is independent of flow velocity, and the condensate can be easily removed. 2) Fluids with low flow rate and high viscosity are generally better suited for the shell side, as turbulence can be achieved there when Re>100. However, this is not absolute; if the flow resistance loss permits, feeding such fluids into the tube and using a multi-pass structure can also yield a high surface heat transfer coefficient. 3) If there is a large temperature difference between the two fluids, in heat exchangers with rigid structures, it is advisable to pass the fluid with a higher surface heat transfer coefficient through the shell side in order to reduce thermal stress. 4) The material that needs to be cooled is generally placed in the shell side to facilitate heat dissipation. It is often impossible to meet all of the above conditions simultaneously; it is necessary to focus on the key aspects. For example, considerations should first be given to factors such as fluid pressure, corrosion prevention, and cleaning requirements, and only thereafter should adjustments be made to meet requirements related to reduced resistance or other factors.

On the 2nd floor, (5) fluids with high viscosity or low flow rate are routed through the tube layer to increase the flow velocity. For 3rd floor, 2) fluids with low flow rate and high viscosity are generally better suited for the shell side, as turbulence can be achieved there when Re>100. However, this is not absolute; if the flow resistance loss permits, feeding such fluids into the tube and using a multi-pass structure can also yield a high surface heat transfer coefficient. It seems like you two have opposite opinions; the fluid with higher viscosity should flow through the shell side, right?

In a reboiler, steam generally flows through the tube side. If it is a heat exchanger, it is determined based on the medium being heated.

Thank you all. During the study process… could we outline a general approach? I mean, which one should be given priority? If several conditions are met, which one should be chosen first?

There are many factors to consider when deciding whether hot or cold fluids should flow through the tube side or the shell side; there is no universal rule for this. The overall requirements are, first, to facilitate heat transfer and corrosion prevention, and second, to reduce fluid flow resistance and scaling while making cleaning easier. Generally, the following principles can be referred to, along with specific manufacturing processes, to make a determination. 1. Corrosive media should flow in the tube side to prevent corrosion of both the tube side and shell side materials. 2. Toxic media are routed through the tube side, which reduces the chances of leakage. 3. Fluids with low flow rates should flow through the tube side, so as to achieve 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; due to the small diameter of the tubes, they can 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; this 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 keep changing, which facilitates heat transfer at low Reynolds numbers.

The selection principles for determining whether the medium flows in the shell side or the tube side are: improving the heat transfer coefficient, achieving a reasonable pressure drop, and facilitating maintenance. 1. The cooling water should flow in the tube side. The cooling water used in coolers and condensers is generally river water, well water, or seawater. In all cases, the cooling water flows through the tube side. Japan often uses brass tubes as heat transfer tubes. When seawater is used, it is also useful to use aluminum-brass for the lining of heat transfer tubes or floating heads, as well as composite steel plates. II. Fluids that evaporate or vaporize, as well as those that condense and liquefy, generally flow through the shell side, as this improves heat transfer efficiency and reduces pressure losses. III. Water vapor and heat carriers generally flow in the tube side. When water vapor is used as a heat carrier, it generally flows through the tube side; sometimes it also flows through the shell side. However, for refrigerants such as ammonia and Freon, it is similar – they all flow through the tube side. IV. In oil refining pipelines, it is common practice for crude oil to flow through the tube side, while the residue at the bottom of the tower flows through the shell side; the side streams from distillation generally also flow through the shell side. 1. Fluids under high pressure are suitable for use in the tube side, eliminating the need to thicken the shell and flanges; U-tubes are the most appropriate choice for high-pressure media. 2. Fluids prone to scaling are suitable for use in the tube side; cleaning can be done without removing the tube bundle, but the use of U-tubes should be avoided. 3. Media with precipitates or inclusions should flow in the shell side. For media with low flow rates, if they flow through the tube side, the sediment or impurities present in the medium can block the heat transfer tubes; however, increasing the flow rate will inevitably lead to wear and corrosion of these heat transfer tubes. Therefore, in this case, the medium should flow through the tube side; if sediment settles at the bottom of the shell, it is possible to easily implement appropriate measures to remove the sediment. 4. Gases with high flow rates should flow through the shell side. Due to the presence of baffle plates and their arrangement, the shell side has a larger flow area than the tube side; as a result, the flow velocity is lower, and the corresponding pressure drop is also lower. 5. High-temperature media should be passed through the tube side, which can reduce heat loss, require a smaller insulation thickness, and is more economical. 6. Fluids requiring a low pressure drop should flow through the shell side. Since the fluid in the tube side must have a higher flow rate to increase the heat transfer rate, the pressure drop in a typical heat exchanger is generally greater on the tube side than on the shell side. Therefore, if the device requires a very low pressure drop for operation, the selected fluid should be used in the shell side. The relationship between the flow rate of a fluid, its heat transfer coefficient, and pressure drop is as follows: increasing the flow rate can raise the heat transfer coefficient, but it also increases the pressure drop; moreover, corrosion or wear accelerates as a result of the higher flow rate. 7. Corrosive fluids should be routed in the tube side. If a corrosive fluid flows in the shell side, the shell side must be made of corrosion-resistant materials ； If a corrosive fluid flows in the tube side, the tube side must be made of corrosion-resistant material. This is more economical. As for the tubes, as long as there are spare tubes, carbon steel materials can be used; therefore, it is appropriate to use tubes for the flow of corrosive fluids. 8. Fluids with a high film heat transfer coefficient should flow in the tube side. Generally, the fluid with a high heat transfer coefficient is used in the pipe side, which is beneficial for improving the overall heat transfer coefficient. Especially when finned tubes are used, the increased heat transfer area can compensate for the low heat transfer coefficient in the shell side, while also allowing the diameter and length of the heat exchanger to be reduced. 9. Fluids with high viscosity should flow in the shell side. For fluids with high viscosity, increasing the flow rate will lead to a greater pressure drop. In line with the 8th selection principle, it is appropriate to route the fluid with a low heat transfer coefficient through the shell side. 10. Gases containing condensed gas or liquid should flow in the tube side. Fluids containing these substances, as they flow in the shell side, cause the condensed gas or liquid to separate from the gas during the heat exchange process; this fluid then flows within the heat exchanger, thereby affecting the heat transfer efficiency. Placing it in the pipe stage can prevent the aforementioned phenomenon from occurring. 11. Pulsating fluids should flow in the shell side. If a pulsed fluid flows through the tube side, the vibrations generated by these pulses can affect the tightness of the expansion joints, posing a risk of leaks and resulting in accidents. In the shell side, due to its larger volume, measures such as installing anti-impact plates at the inlet of the shell side can be taken to reduce the impact of pulses. To eliminate the effect of pulses, it is adjusted through a regulating device before entering the heat exchanger. None of the above principles are absolute; specific issues need to be analyzed on a case-by-case basis. For example, in the case of special process conditions (high temperature, high pressure, severe scaling, or high corrosivity), these particularities must be given priority, requiring necessary trade-offs between improving the heat transfer coefficient and reducing pressure drop.

Generally, the fluid to be used in the pipe side can be selected in the following order. a) Cooling water ； b) Fluids that are corrosive or prone to deposit accumulation ； c) the one with lower viscosity among the two fluids ； d) Fluids under high pressure ； e) Fluids with higher temperatures ； f) Fluids with low flow rates. The few exceptions mentioned above are: a) Condensed steam or water vapor generally flows through the shell side ； b) If the temperature of a fluid changes significantly, it is common to use the shell side in such cases, in order to reduce problems related to the structural integrity of the equipment caused by thermal expansion.

For fixed-tube-sheet heat exchangers, the criteria for selecting the flow paths for the fluids in the tube side and shell side are roughly as follows: 1) Fluids that are dirty or prone to scaling should flow in the tube side, as cleaning inside the tubes is easier; 2) Corrosive fluids should also flow in the tube side, to prevent both the tube bundle and the shell from being corroded, and to facilitate cleaning and maintenance; 3) Fluids with high pressure should flow in the tube side, to avoid putting stress on the shell; 4) Toxic fluids should flow in the tube side, to reduce the risk of leaks; 5) The fluid to be cooled should flow in the shell side, as this facilitates heat dissipation and improves the cooling effect; 6) Saturated steam should flow in the shell side, as this makes it easier to remove condensate and non-condensable gases, and keeps the steam clean and free from contamination; 7) Fluids with low flow rates or high viscosity should flow in the shell side, as baffle plates can help achieve turbulence even at low Reynolds numbers (Re>100), although multiple tube passes can also be used inside the tubes; 8) If there is a large temperature difference between the two fluids, the fluid with a higher thermal expansion coefficient should flow in the shell side, to reduce the temperature difference between the tube walls and the shell walls. In practice, it is often not possible to take all of these principles into account simultaneously, as they may conflict with each other. In such cases, it is necessary to focus on the most important factors based on the actual situation. Moreover, different heat exchangers require different considerations; for example, in U-tube heat exchangers, dirty or scaling-prone fluids cannot flow in the tube side.

This issue is specifically discussed in the section on heat transfer in textbooks on principles of chemical engineering. . . Please, the original poster, go and read the university textbooks or review old courses. . . Haha. . Generally, unclean media flow through the tube side. . . Here, only this one point will be emphasized. . . Based on my many years of design experience as well as experiments conducted in actual oil refining operations regarding the reversal of fluid flow, it’s not a major issue whichever path the fluid takes through the pipes. . . Using pipes to convey dirty materials is so that high-pressure water guns can be used to clean the inside of the pipes. . . :lol

Principles for arranging fluid flows in shell-and-tube heat exchangers: I. Temperature – High-temperature fluids generally flow through the tube side； Additionally, sometimes to save insulation material and reduce the shell thickness, the high-temperature stream can also be routed through the shell side. II. Pressure: Logistics involving higher pressures should be handled in the tube side, while the shell side does not need to withstand high pressures. III. Viscosity: Fluids with higher viscosity should flow through the shell side. Under the influence of baffles, both the cross-sectional area of the flow channel and its direction of flow continuously change, allowing turbulence to be achieved at low Reynolds numbers Re, thereby yielding a higher heat transfer coefficient. IV. Corrosion: Fluids with high corrosivity should be routed through the tube side, allowing the shell to be made of ordinary materials, while only the tubes, tube sheets, and end caps are constructed from corrosion-resistant materials. V. Pressure Drop: Process streams with specific requirements regarding pressure drop should be located in the tube side, as the heat transfer coefficient and pressure drop calculations for the tube side have smaller errors. VI. Scaling: Streams that are dirty and prone to scaling should be routed through the tube side, to facilitate cleaning and control of scaling. If it is necessary to use the shell side, square tube arrangements should be employed, and detachable heat exchangers (floating head type, stuffing box type, U-tube type) should be used. VII. Flow velocity: Fluids with a low flow rate should flow through the shell side, as it is easier for the fluid to become turbulent there, thereby increasing the heat transfer coefficient. Fluids that require an increased flow rate to raise the convective heat transfer coefficient should flow in the tube side, as the cross-sectional area inside the tubes is smaller than that on the shell side, and it is easier to use multiple passes to increase the flow rate. VIII. Heat transfer coefficient: Streams with a low heat transfer coefficient, such as gases, should flow in the shell side, as this facilitates an increase in the heat transfer coefficient. IX. Materials: To remove steam condensate, and because they are relatively clean with a weak relationship between the convective heat transfer coefficient and flow velocity, steam generally flows in the shell side. Table 1 below presents the general selection criteria for heat exchangers based on different process conditions. From the perspective of economic design of heat exchangers, for shell-and-tube heat exchangers, priority should be given to the arrangement of the fluid flows. If the temperatures of the two fluids cross each other (that is, the exit temperature of the high-temperature fluid is lower than that of the cold fluid), a heat exchanger with counterflow flow pattern should be considered. Although an F-type shell can be used for shell-and-tube heat exchangers, this type of shell is not recommended in most cases due to heat and fluid leakage between the longitudinal partitions. Table 1 Process Conditions and Arrangements of Fluid Flow
Process Conditions
Shell-and-tube heat exchangers
Special types of heat exchangers recommended for use
High pressure on the shell side and tube side √ U-tube type; High temperature √ U-tube type, coiled tube type
High fouling coefficient √ Plate-type and spiral plate-type heat exchangers
High-viscosity fluids √ Plate-type and spiral plate-type heat exchangers, devices to enhance turbulence (such as twisted tubes), and static mixers, etc.
Low pressure drop √ √ X-type shell, baffle rod-type heat exchangers, and spiral plate-type heat exchangers
Low flow rate √ Plate-type, spiral plate-type, shell-and-tube type, and multi-tube heat exchangers
Corrosive fluids √ Heat exchangers made of corrosion-resistant materials or special materials (graphite, glass, polytetrafluoroethylene, etc.)
Low temperature difference √ √ Counter-current type heat exchangers. Such as single-tube, multi-tube, spiral-plate, and plate heat exchangers, etc., and heat transfer enhancement tubes can be used. Temperature cross √ √ Heat exchangers of counterflow type, such as: single-pass, multi-tube, spiral plate, and plate heat exchangers. Frozen fluid √ Bayonet type, and heat exchangers with boxorboot

Corrosive, toxic, low flow rate, high temperature and pressure, prone to scaling; in fixed-plate and floating-head heat exchangers, the fluid flows through the tube side while it flows through the shell side in U-tube heat exchangers. In coolers, usually the cooling water flows through the tube side and the fluid to be cooled flows through the shell side; fluids with high viscosity also flow through the shell side.

I see that the steam in the factory also flows through pipes; how is this contradictory?

In simple terms: clean tasks go to the tube side, and dirty tasks go to the shell side!

It should be a clean shell-type design; the dirty version has tubes, which are easier to clean