Change the shape of the heat transfer surface and set various shapes of inserts on the heat transfer surface or within the heat transfer flow path. There are many ways to change the shape of the heat transfer surface, among which those used to enhance heat transfer in the tube side include: spiral groove tubes, corrugated tubes, threaded tubes, scaled tubes, swirling tubes, and spiral flat tubes, etc. Additionally, flow disturbance elements can be used, such as filling the tube with twisted iron, spiral rings, or metal sheets, which can also enhance turbulence and disrupt the laminar boundary layer.

　　The research on heat transfer enhancement of shell-and-tube heat exchangers includes the study of heat transfer enhancement on both the tube side and the shell side. This is achieved through the use of enhanced heat transfer tube elements and optimized shell side structures.

　　Changing the shape of the heat transfer surface and placing various shaped inserts on the heat transfer surface or within the heat transfer flow path. There are many ways to change the shape of the heat transfer surface, including: spiral groove tubes, corrugated tubes, threaded tubes, scaled tubes, swirling tubes, and spiral flat tubes, among others. Additionally, disturbance elements can be used, such as filling the tube with twisted iron, spiral rings, or metal sheets, which can also enhance turbulence and disrupt the laminar boundary layer.

　　The wall of the spiral groove tube is formed by extruding a smooth tube. The main enhancement of heat transfer inside the tube is: first, the restriction effect of the spiral groove near the wall causes the fluid inside the tube to perform a global spiral motion, generating local secondary flow; second, the shape resistance caused by the spiral groove creates a reverse pressure gradient that leads to boundary layer separation. The spiral groove tube has a dual enhancement effect on heat transfer, suitable for conditions such as convection, boiling, and condensation, with anti-fouling performance superior to that of smooth tubes, and heat transfer performance improved by 2 to 4 times compared to smooth tubes.

　　The enhancement mechanism of corrugated tubes is:

　　When the fluid inside the tube flows through the transverse ribs, axial eddies are formed near the tube wall, increasing the disturbance of the boundary layer, leading to boundary layer separation, which is beneficial for heat transfer. When the eddies are about to disappear, the fluid flows through the next transverse rib, thus continuously generating eddies and maintaining a stable enhancement effect.

　　The bamboo joint structure on the surface of the heat exchange tube causes the medium flowing inside the tube to produce contraction and expansion effects, increasing the turbulence level of the medium and enhancing the heat exchange capability of the medium inside the tube. Additionally, when the medium near the tube wall flows axially along the tube, its direction and speed undergo abrupt changes at the wave nodes, forming local turbulence, which reduces the thickness of the stagnant boundary layer at the tube wall, decreases thermal resistance, and also enhances the heat transfer capability of the medium outside the tube.

　　4. Low-threaded finned tube

　　A type of high-efficiency heat exchange tube formed by rolling ordinary heat exchange tubes to create threaded fins on their outer surface. Its enhancement effect is on the outside of the tube. The enhancement effect on the medium is reflected in two aspects: on one hand, the threaded fins increase the heat exchange area; on the other hand, as the shell-side medium flows over the surface of the threaded tube, the surface threaded fins create a splitting effect on the laminar boundary layer, reducing the thickness of the boundary layer.

　　When used for evaporation, it can increase the number of bubbles formed per unit surface area, enhancing boiling heat transfer capability.

　　When used for condensation, the threaded fins are very beneficial for the dripping of condensate at the lower end of the tube, reducing the thickness of the liquid film, decreasing thermal resistance, and improving condensation heat transfer efficiency.

　　5. Spiral flat tube

　　The spiral flat tube (Twisted tube) heat exchanger was introduced by Brown Company in the United States. The structural feature of the spiral flat tube is that any cross-section of the tube is an elongated ellipse.

　　The enhancement mechanism of the spiral flat tube: due to the unique structure of the tube, both the tube side and the shell side are in a spiral flow, promoting turbulence. This heat exchanger has a total heat transfer coefficient 40% higher than that of conventional heat exchangers, while the pressure drop is almost equal. This heat exchanger can be used in gas-gas, liquid-liquid, and gas-liquid heat exchange processes.

　　6. Diamond finned tube

　　The diamond finned tube is a high-efficiency heat transfer tube with circumferentially discontinuous three-dimensional fins, and its heat transfer enhancement performance is superior to that of threaded finned tubes with circumferentially continuous fins. When used for condensation heat transfer enhancement, the special structure of the three-dimensional fins causes uneven surface tension distribution of the liquid film on the fin surface (larger at the base, smaller at the top), pulling the liquid film towards the base, significantly reducing the thickness of the liquid film on the three-dimensional fin surface, decreasing thermal resistance, and enhancing the heat transfer capability between the vapor medium and the outer wall of the tube, thereby improving heat transfer efficiency.

　　7. Corrugated tube

　　The corrugated tube is based on ordinary smooth heat exchange tubes, using a non-cutting rolling process to plastically deform the metal on the inner and outer surfaces, resulting in a tube shape with corrugations on both sides.

　　8. Surface porous tube (sintering, thermal spraying, electroplating, etc.)

　　A porous coating is prepared on the surface of ordinary smooth tubes using metal powder containing pore-forming agents. During boiling heat transfer, a large number of micropores in the coating become the nuclei for bubble formation. Since the bubbles inside the micropores are heated from all sides, the bubble nuclei rapidly expand to fill the cavity, and continuous heating causes the pressure inside the bubbles to increase rapidly, prompting the bubbles to burst out from the fine gaps on the tube surface. When the bubbles burst out, they carry significant scouring force and create a certain local negative pressure, causing surrounding lower temperature liquid to rush into the micropores, forming continuous boiling.

　　The T-shaped finned tube is a high-efficiency heat exchange tube formed by rolling a smooth tube. Its structural feature is the formation of a series of spiral ring-shaped T-shaped tunnels on the outer surface of the tube. When the outer medium is heated, a series of bubble nuclei are formed in the tunnels. Since the bubble nuclei are heated from all sides within the tunnel cavity, they rapidly expand to fill the cavity, and continuous heating causes the pressure inside the bubbles to increase rapidly, prompting the bubbles to burst out from the fine gaps on the tube surface. When the bubbles burst out, they carry significant scouring force and create a certain local negative pressure, causing surrounding lower temperature liquid to rush into the T-shaped tunnels, forming continuous boiling.