7 practical heat exchanger technical questions

7 practical heat exchanger technical questions

1. How does the heat exchanger transfer heat?

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

　　 2. What is the influence of the medium flow rate on the heat transfer effect?

　　Answer: The greater the velocity of the medium in the heat exchanger, the greater the heat transfer coefficient. Therefore, increasing the flow rate of the medium in the heat exchanger can greatly improve the heat exchange effect, but the negative effect of increasing the flow rate is to increase the pressure drop through the heat exchanger and increase the energy consumption of the pump, so it must be suitable range.

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

Answer: Adopting specially designed heat exchange tube surface structure, such as finned tube, nail-head tube, threaded tube, etc., on the one hand, increases the heat transfer area, on the other hand, the turbulence of the special surface greatly increases the flow of the fluid outside the tube. The degree of turbulence can improve the overall heat exchange effect of the heat exchanger in both aspects, so these surface structures have better performance than the surface of the light pipe.

　　 4. What are the commonly used methods for descaling the surface of heat exchange tubes?

　　Answer: Commonly used methods for descaling on the surface of heat exchange tubes include: manual descaling with steel brazing, mechanical descaling, pressure water descaling, and chemical descaling.

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

　　Answer: One is to use a structure that increases the heat transfer surface, such as:

　　(1) Use finned tubes, nail-head tubes, threaded tubes, bellows, etc.;

　　(2) Machining the pipe surface, spiral groove pipe, threaded pipe, etc.;

　　 (3) The use of small diameter pipes can increase the number of pipes on the same tube sheet area and increase the heat transfer area.

　　 The second is to increase the flow rate of the fluid in the heat exchanger, which can greatly improve its heat transfer coefficient, such as:

　　 (1) Adding spoilers, such as inserting a spiral belt in the tube, and setting up baffles and dummy tubes outside the tube;

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

　　 In addition, the use of materials with good thermal conductivity to make heat exchangers, good anti-corrosion and anti-fouling measures for heat exchangers, and timely cleaning of fouling are all means to improve the heat transfer effect.

　　 6. Why does the cooling water heat exchanger produce scale?

　　Answer: Scale is formed by crystallization of dissolved salts in water and attached to the tube wall of the heat exchanger. It is characterized by compactness and rigidity, firm adhesion, and difficult removal. A large number of suspended particles in water can become seeds. Other impurity ions, bacteria, rough metal surfaces, etc. have a strong catalytic effect on the crystallization process, greatly reducing the supersaturation required for crystallization, so the cooling water heat exchanger It is easy to produce scale.

　　 7. Why does the heat exchanger tube foul? How to descale?

　　Answer: Heat exchangers are mostly heat exchange systems with water as the heat carrier. As some salts crystallize out of water when the temperature rises, they adhere to the surface of the heat exchange tube and form scale. Adding a polyphosphate buffer to the cooling water can also cause scale precipitation when the pH of the water is high. The scale formed in the initial stage is relatively soft, but with the formation of the scale layer, the heat transfer conditions deteriorate, the crystal water in the scale gradually loses, and the scale layer becomes hard and firmly adheres to the surface of the heat exchange tube.

In addition, like scale, when the working conditions of the heat exchanger are suitable for the solution to precipitate crystals, a scale layer formed by the crystallization of materials can accumulate on the surface of the heat exchange tube; when the fluid contains more mechanical impurities and organic matter, the fluid When the flow rate is small, some mechanical impurities or organic matter will also be deposited in the heat exchanger, forming loose, porous or colloidal dirt.