09-02-24 Topic — Selection of Preheater (Prizes for Participants)

It might be related to the medium; generally, clean substances flow through the tube side, but this isn’t a strict rule. Discussions on the tube side and shell side have taken place on Haichuan – you can search for them to take a look.

The chief engineer made the right change! As can be understood from the principle of heat exchangers.

I think it’s unreasonable: steam should flow through the shell side, and air should flow through the tube side. There is a phase change from steam to condensate, during which heat is released; having the steam flow in the shell side facilitates the discharge of condensate, while having air flow in the tube side helps to control the flow rate and ensure effective heat exchange.

The cold flow is directed through the tube side, while the hot flow goes through the shell side, taking into account the issue of steam condensation and drainage! The cold flow is directed through the shell side, while the hot flow goes through the tube side, taking into account the risk of tube blockage when the air quality is poor! It is necessary to weigh the advantages and disadvantages of both options before making a choice. If the temperature remains above 100 degrees Celsius after steam cooling, and if the local climate is harsh with strong winds and sandstorms, then the choice made by the chief engineer is the correct one! If the temperature drops below 100 degrees Celsius after cooling with steam, only the first option can be chosen!

The chief engineer is right; after all, it’s meant for heating. It is necessary to ensure the heat exchange efficiency between the hot fluid and air in order to reduce heat loss. Thereby saving energy consumption. Whether it is a condenser or a heat exchanger, its function is the same; it is still a heat exchanger. The designers’ design is also correct; it’s just that energy consumption has increased. But after the modifications, it becomes more reasonable, reducing heat energy loss.

I think the chief engineer is right. Comparing the two fluids, air is a fluid with a high volumetric flow rate at normal pressure and should therefore flow in the shell side; whereas steam is a fluid with a higher pressure but lower volumetric flow rate, and should thus flow in the tube side. When designing heat exchangers, the selection of the fluid flow space must take into account the following principles: (1) It is necessary to maximize the heat transfer coefficient on the side where it is limited, in order to make the heat transfer conditions on both sides of the heat transfer surface as similar as possible ； (2) Save metal materials as much as possible, especially valuable ones, to reduce manufacturing costs ； (3) It should be easy to clean off deposits in order to ensure reliable operation ； (4) Heat loss should be reduced in heat exchangers with higher temperatures, while cold loss should be reduced in refrigeration equipment ； (5) It is necessary to reduce the thermal stress generated due to differences in heating between the shell and the tubes, in order to simplify the structure ； (6) For heat exchangers operating under high pressure, the sealing should be as simple and reliable as possible ； (7) It should facilitate the inflow, distribution, and outflow of fluids. Based on these principles, it can be considered reasonable for fluids with a low volumetric flow rate to flow through the tube side under the following conditions ； Unclean, scale-prone fluids ； High-pressure fluid ； Corrosive fluids ； High-temperature fluids or low-temperature fluids in low-temperature devices. It is reasonable for fluids in the following situations to flow in the shell side: fluids with a high volumetric flow rate, especially gases at atmospheric pressure ； Fluid with high heat transfer coefficient in a rigid fouled heat exchanger ； High-viscosity fluids and fluids flowing in the laminar flow region ； Saturated steam.

I can’t explain the principle clearly; I’m not an expert in this field. But in all air heat exchangers I’ve seen, steam flows through the tube side, while air or other media flow through the shell side.

Simply install an empty diffuser in the air duct, with the steam flowing through the tube side.

I think the choice of the chief engineer was correct; reducing the pressure in the shell side helps to lower the cost of the equipment.

It seems that the chief engineer’s modification is correct; generally, in air heat exchangers, steam flows through the tube side, while air or other media flow through the shell side. This results in high heat exchange efficiency, which can reduce energy consumption!

This involves the selection of fluids for shell-and-tube heat exchangers, with the main considerations being the operating pressure and temperature of the two fluids, the available pressure drop, structural and corrosive factors, as well as equipment-related aspects. For fixed-tube-sheet heat exchangers, the criteria for selecting the fluid flow path in the tubes or the shell are as follows: Fluids that are dirty or prone to scaling should flow through the tubes, as cleaning inside the tubes is easier; corrosive fluids should also flow through the tubes, to prevent both the tube bundle and the shell from being corroded, and to facilitate cleaning and maintenance; fluids under high pressure should flow through the tubes, to avoid putting stress on the shell; toxic fluids should flow through the tubes, thereby reducing the risk of leaks; fluids that need to be cooled should flow through the shell, as this facilitates heat dissipation and improves the cooling effect; saturated steam should flow through the shell, as it makes it easier to remove condensate and non-condensable gases, and the steam remains clean and does not cause contamination ； Fluids with low flow rates or high viscosity should flow in the shell side, as the baffles allow turbulence to be achieved at low Reynolds numbers; however, multiple tube passes can also be used inside the tubes. If there is a large temperature difference between the two fluids, it is advisable to let the fluid with the higher flow rate flow in the shell side, thereby reducing the temperature difference between the tube walls and the shell wall. Taking all these factors into account, I believe the chief engineer made the right decision. ?

I think the chief engineer is right regarding the principle of choosing between the tube side and the shell side: when selecting the medium for the shell side, it is necessary to identify the main issue at hand in order to determine which medium is best suited for the tube side or the shell side. It should be considered comprehensively based on factors such as medium properties, temperature or pressure, allowable pressure drop, scaling, and the improvement of heat transfer coefficients. ①Media that are corrosive, toxic, subject to high temperatures or pressures, as well as those prone to scaling, should all be handled in the tube side. This is mainly because if corrosive media are used in the shell side, the materials of both the tube side and the shell side will be corroded; therefore, corrosive media are generally handled in the tube side, which helps to reduce the requirements for the materials used in the shell side ； Leakage of toxic media through the tube side is less likely ； Higher temperatures and pressures allow using the tube side, which reduces the requirements for the shell side material, and fouling on the tube side is easier to clean. ②It helps to increase the overall heat transfer coefficient and make the most of the pressure drop. In the shell side, the flow pattern and cross-section of the fluid continuously change, and baffle plates can be used to promote turbulence; turbulence is achieved when Re > 100, whereas in the tube side turbulence occurs only when Re > 1000. Therefore, fluids with higher viscosity or lower flow rates, resulting in a lower Re value, are suitable for the shell side. Conversely, if turbulence can be achieved in the tube side, it is more appropriate to use that side for such fluids. From the perspective of pressure drop, it is also advantageous to have fluids with a lower Re value in the shell side. ③It is determined based on the values of the heat transfer coefficients of the two sides of the membrane; if there is a large difference, the side with the lower membrane heat transfer coefficient can be placed in the shell side, allowing for the use of external heat transfer enhancement devices such as threaded tubes or finned tubes.

The chief engineer is right. The gas exchangers recently designed by our factory have steam flowing in the tube side, while air or other media flow in the shell side. A large amount of gas may need to be heated; on the other hand, steam flows through the tube side, resulting in a high flow velocity and thus a high heat transfer coefficient

The chief engineer is right. The chief engineer’s modifications took into account both costs and the production process

I also think the chief engineer was right in making those changes, because allowing steam to flow on the shell side doesn’t provide any insulation in terms of heat. A thermal insulation layer needs to be added on the outside for better results. Secondly, if steam is allowed to flow along the side of the shell, the thickness of the components in the structural design must also be increased, which makes the cost of the heat exchanger higher. In a third conventional heat exchanger, using the air flow on the shell side yields a better heat transfer effect.

I think it depends on the flow rate of each medium to determine it

It’s better for air to flow through the shell side; for fluids, it generally flows through the tube side； Also, with steam flowing in the tube side, it is possible to absorb heat fully and achieve excellent heat exchange

The chief engineer made the right decisions. 1. With high steam pressure, it is appropriate to use the tube side; this reduces the design pressure required for the tower. 2. When the steam temperature is high, using the shell side would increase heat loss to the surroundings (under the same insulation conditions), and since a condensation temperature is not reached, there is no need to consider the issue of condensate water. 3. With a large air flow rate, it is suitable to use the shell side, which has a larger surface area. 4. Using the tube side for steam helps to increase the flow velocity and reduce the flow rate, thereby increasing the heat transfer coefficient.

The steam should flow through the tube side. The main reasons are: high steam temperature, resulting in low heat loss in the tube side. When the flow rate of the medium to be heated is high, it flows through the shell side, resulting in lower equipment manufacturing costs.

I think the chief engineer is right. Comparing the two fluids, air is a fluid with a high volumetric flow rate at normal pressure and should therefore flow in the shell side; whereas steam is a fluid with a higher pressure but lower volumetric flow rate, and should thus flow in the tube side. When designing heat exchangers, the selection of the fluid flow space must take into account the following principles: (1) It is necessary to maximize the heat transfer coefficient on the side where it is limited, in order to make the heat transfer conditions on both sides of the heat transfer surface as similar as possible ； (2) Save metal materials as much as possible, especially valuable ones, to reduce manufacturing costs ； (3) It should be easy to clean off deposits in order to ensure reliable operation ； (4) Heat loss should be reduced in heat exchangers with higher temperatures, while cold loss should be reduced in refrigeration equipment ； (5) It is necessary to reduce the thermal stress generated due to differences in heating between the shell and the tubes, in order to simplify the structure ； (6) For heat exchangers operating under high pressure, the sealing should be as simple and reliable as possible ； (7) It should facilitate the inflow, distribution, and outflow of fluids. Based on these principles, it can be considered reasonable for fluids with a low volumetric flow rate to flow through the tube side under the following conditions ； Unclean, scale-prone fluids ； High-pressure fluid ； Corrosive fluids ； High-temperature fluids or low-temperature fluids in low-temperature devices. It is reasonable for fluids in the following situations to flow in the shell side: fluids with a high volumetric flow rate, especially gases at atmospheric pressure ； Fluid with high heat transfer coefficient in a rigid fouled heat exchanger ； High-viscosity fluids and fluids flowing in the laminar flow region ； Saturated steam. The air preheater in our company also has steam flowing through the tube side and air flowing through the shell side!!