Seven practical technical questions of heat exchanger

1 How does the heat exchanger conduct heat? Answer: in the common wall type heat exchanger, there are mainly two heat transfer modes: conduction and convection The heat flow body first transfers heat to one side of the tube wall by convection, then transfers heat from one side of the tube wall to the other side by conduction, and then transfers heat to the cold fluid by convection on the other side of the tube wall, thus completing the heat transfer process of the heat exchanger 2 What is the effect of medium velocity on heat transfer? Answer: the larger the flow 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 there should be a certain suitable range 3 How does the surface structure of the heat exchange tube affect the heat exchange effect? Answer: the special designed surface structure of heat exchange tube, such as fin tube, pin head tube, threaded tube, etc., on the one hand, increases the heat transfer area, on the other hand, the turbulence effect of the special surface greatly increases the turbulence degree of the fluid outside the tube, on the other hand, both can improve the overall heat exchange effect of the heat exchanger, so these surface structures are superior to the performance of the smooth tube surface 4 What methods are commonly used for descaling the surface of heat exchange tube? Answer: the common methods of descaling on the surface of heat exchange tube are: manual descaling with steel chisel, 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 the structure of increasing the heat transfer surface, such as: (1) using finned tube, pin head tube, threaded tube, corrugated tube, etc.; (2) machining the tube surface, spiral groove tube, threaded tube, etc.; (3) using small diameter tube can increase the number of tubes on the same tube plate area and increase the heat transfer area The second is to increase the flow rate of fluid in the heat exchanger, which can greatly improve the heat transfer coefficient, such as: (1) adding a spoiler, such as inserting a spiral belt in the tube, setting baffles, false tubes outside the tube; (2) increasing the number of tube side or shell side In addition, the use of materials with good thermal conductivity to manufacture heat exchanger, anti-corrosion and scale prevention measures for heat exchanger, and timely cleaning of scale are all means to improve the heat transfer effect 6 Why does the cooling water heat exchanger produce scale? Answer: the scale is formed by the crystallization of dissolved salts in water and attached to the tube wall of heat exchanger It is characterized by compactness, hardness, firm adhesion and difficult removal A large number of suspended particles in water can be crystal seeds Other impurity ions, bacteria, rough metal surfaces, etc have strong catalytic effect on the crystallization process, greatly reducing the supersaturation required for crystallization, so the cooling water heat exchanger is easy to produce scale 7 Why does the heat exchanger tube scale? How to remove scale? Answer: most heat exchangers are heat exchange systems with water as heat carrier As some salts crystallize out of water when the temperature rises, they attach to the surface of heat exchange tube and form scale When adding polyphosphate buffer to cooling water, when the pH value of water is high, the scale can also be precipitated The scale formed in the initial stage is relatively soft, but with the formation of the scale layer, the heat transfer condition deteriorates, the crystalline water in the scale gradually loses, the scale layer becomes hard and firmly adheres to the surface of the heat exchange tube In addition, just like scale, when the working conditions of the heat exchanger are suitable for the solution to precipitate crystal, the scale layer formed by material crystallization can be accumulated on the surface of the heat exchanger tube; when the fluid contains more mechanical impurities and organic matters, and the flow rate of the fluid is small, some mechanical impurities or organic matters will also deposit in the heat exchanger, forming loose, porous or colloidal dirt.