How to improve the heat transfer coefficient of the tube bundle dryer?

1. Optimize the tube bundle structure
Choose the appropriate tube bundle material: It is preferred to use materials with good thermal conductivity to make the tube bundle, such as copper alloy or stainless steel with high thermal conductivity. Copper alloy has a high thermal conductivity. For example, the thermal conductivity of copper is about 380-400W/(m・K), which can transfer heat more effectively than ordinary stainless steel (thermal conductivity is about 16-20W/(m・K)). However, in practical applications, it is also necessary to consider the cost, corrosion resistance and other factors of the material for comprehensive selection.
Adjust the size and arrangement of the tube bundle: Appropriately reducing the diameter of the tube bundle can increase the heat transfer area per unit volume. For example, reducing the tube diameter from 50mm to 30mm will significantly increase the heat transfer area under the same tube bundle volume. At the same time, the arrangement of the tube bundle will also affect the heat transfer effect. The use of regular triangle arrangement can arrange more tube bundles in the same space than the square arrangement, which increases the heat transfer area, but attention should be paid to the reasonable design of the material flow channel to ensure that the material can flow smoothly between the tube bundles and fully contact the tube bundles.
Tube bundle surface treatment: Special treatment of the tube bundle surface can enhance the heat transfer effect. For example, the use of micro-nano structure coating increases the roughness of the tube bundle surface, prolongs the residence time of the material on the tube bundle surface, and strengthens the heat conduction process. Or chemical plating, electroplating and other methods are used to form a film with better thermal conductivity on the surface of the tube bundle to improve the thermal conductivity of the tube bundle.
2. Improve material properties and flow state
Pretreatment of materials: Pretreatment of materials, such as crushing, screening and other operations, to make the material particle size uniform and moderate. For large particle materials, appropriate crushing can be carried out to increase the contact area between the material and the tube bundle; for powdery materials, granulation and other methods are used to form particles of appropriate size to avoid agglomeration of powdery materials and affect heat transfer. For example, when drying certain chemical raw materials, making the raw material powder into particles with a diameter of 3-5mm can significantly improve the contact effect between the material and the tube bundle.
Enhance the turning and mixing of the material: Rationally design the lifting plate or stirring device inside the dryer so that the material can be fully turned during the drying process. The shape, angle and number of the lifting plate should be optimized according to the characteristics of the material. For example, the use of spiral lifting plates can guide the material to form a spiral flow path inside the cylinder, so that the residence time of the material in the dryer is prolonged, and it can ensure that the material can fully contact all parts of the tube bundle, thereby improving the heat transfer coefficient. In addition, appropriately increasing the rotation speed of the tube bundle can also enhance the turning effect of the material, but be careful to avoid excessive speed that causes material breakage or increased equipment wear.
3. Optimize operating conditions
Control the parameters of the heat medium: Increasing the temperature and flow rate of the heat medium can enhance the heat transfer effect. Within the range allowed by the equipment, appropriately increase the temperature of the heat medium (such as steam or heat transfer oil) to increase the temperature difference between the heat medium and the material, thereby increasing the power of heat transfer. At the same time, reasonably adjusting the flow rate of the heat medium and determining the optimal flow rate through experiments or simulation calculations can not only ensure sufficient heat transfer, but also avoid energy waste and equipment damage. For example, for steam heat medium, when the pressure increases from 0.8MPa to 1.2MPa (corresponding to temperature increase), the heat transfer coefficient will increase when other conditions remain unchanged; and controlling the steam flow rate at around 10-15m/s may achieve better heat transfer effects.
Maintaining the vacuum degree of the equipment (if applicable): Operating the tube bundle dryer under negative pressure conditions can reduce the boiling point of water, making it easier for the water in the material to evaporate, and is also conducive to heat transfer. Maintaining a certain vacuum degree inside the dryer through equipment such as a vacuum pump, such as controlling the vacuum degree between -0.08MPa and -0.09MPa, can speed up the drying speed and improve the heat transfer coefficient. However, attention should be paid to the sealing and stability of the vacuum system to prevent air leakage from affecting the vacuum effect.