7 Practical Heat Exchanger Technical Q&A

　　 1. How does a heat exchanger transfer heat?

　　Answer: In the most common wall-type heat exchanger, the main heat transfer methods are conduction and convection. The hot fluid first transfers heat to one side of the tube wall by convection, then the heat is conducted through the tube wall to the other side, and finally, the heat is transferred from the other side of the tube wall to the cold fluid by convection, completing the heat transfer process of the heat exchanger.

　　 2. How does the flow velocity of the medium affect the heat transfer effect?

　　Answer: The greater the flow velocity of the medium inside the heat exchanger, the higher the heat transfer coefficient. Therefore, increasing the flow velocity of the medium inside the heat exchanger can greatly improve the heat transfer effect. However, the negative impact of increasing the flow velocity is an increase in the pressure drop across the heat exchanger, which increases the energy consumption of the pump, so there is an appropriate range.

　　 3. How does the surface structure of the heat transfer tube affect the heat transfer effect?

　　Answer: Using specially designed heat transfer tube surface structures, such as finned tubes, studded tubes, and threaded tubes, on one hand increases the heat transfer area, and on the other hand, the special surface's flow disturbance greatly increases the turbulence of the fluid outside the tube. Both aspects improve the overall heat transfer effect of the heat exchanger, so these surface structures perform better than smooth tube surfaces.

　　 4. What are the common methods for descaling the surface of heat transfer tubes?

　　Answer: Common methods for descaling the surface of heat transfer tubes include: manual descaling with steel rods, mechanical descaling, pressure water descaling, and chemical descaling.

　　 5. What are the common methods to enhance heat transfer in heat exchange equipment?

　　Answer: First, use structures that increase the heat transfer surface area, such as:

　　(1) Using finned tubes, studded tubes, threaded tubes, corrugated tubes, etc.;

　　(2) Mechanically processing the tube surface, such as spiral groove tubes, threaded tubes, etc.;

　　(3) Using small diameter tubes to increase the number of tubes on the same tube sheet area, thereby increasing the heat transfer area.

　　Second, increasing the fluid flow velocity inside the heat exchanger can greatly improve its heat transfer coefficient, such as:

　　(1) Adding flow disruptors, such as inserting spiral strips inside the tube, setting baffles or dummy tubes outside the tube;

　　(2) Increasing the number of tube passes or shell passes.

　　Additionally, using materials with good thermal conductivity to manufacture heat exchangers, implementing corrosion and scaling prevention measures, and timely descaling are all means to improve heat transfer efficiency.

　　 6. Why does scaling occur in cooling water heat exchangers?

　　Answer: Scale is formed by the crystallization and deposition of dissolved salts in water onto the heat exchanger tube walls. It is dense, hard, firmly attached, and difficult to remove. Suspended particles in the water can act as crystal nuclei, and other impurities, ions, bacteria, and rough metal surfaces strongly catalyze the crystallization process, greatly reducing the supersaturation required for crystallization. Therefore, cooling water heat exchangers are prone to scaling.

　　 7. Why do heat exchanger tubes scale? How to descale?

　　Answer: Most heat exchangers use water as the heat transfer medium. Some salts crystallize and deposit on the heat transfer tube surface as the temperature rises, forming scale. Adding polyphosphate buffers to cooling water, especially when the water pH is high, can also cause scale deposition. Initially, the scale is relatively soft, but as the scale layer forms, heat transfer conditions deteriorate, the crystallization water in the scale gradually disappears, and the scale hardens and firmly adheres to the heat transfer tube surface.

　　Additionally, similar to scale, when the operating conditions of the heat exchanger favor solution crystallization, scale layers formed by material crystallization can accumulate on the tube surface; when the fluid contains many mechanical impurities and organics and the flow velocity is low, some mechanical impurities or organics may also deposit inside the heat exchanger, forming loose, porous, or gelatinous fouling.