Ways to enhance heat transfer in heat exchangers

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Heat exchangers are heat exchange devices that are widely used in the field of industrial production. According to relevant statistics, the cost of heat exchange equipment in chemical plants accounts for approximately 10% to 20% of the total cost of such equipment; in oil refineries, heat exchange equipment makes up around 35% to 40% of all process equipment. It is also widely used in other industrial sectors such as power generation, nuclear energy, metallurgy, food processing, transportation, and home appliances. Therefore, it is very important to study heat transfer enhancement techniques for heat exchangers in order to reduce the heat transfer area. Enhancing heat transfer in a heat exchanger means taking certain technical measures, through the analysis and calculation of various factors that affect heat transfer, in order to increase the amount of heat transferred by the heat exchange equipment, or to reduce its volume while maintaining the existing level of heat transfer. The methods commonly used to enhance heat transfer in heat exchangers fall into three categories: increasing the heat transfer area (F) ； Increase the heat transfer temperature difference (Δt) ； Increase the heat transfer coefficient (K). 1. Increasing the heat transfer area: Expanding the heat transfer area is the most common and simplest method used to enhance heat transfer efficiency. In the process of increasing the heat transfer area of exchangers, simply enlarging the size of the equipment to boost the heat transfer area or adding more units to increase the heat transfer capacity not only requires higher investment in equipment, but also results in larger floor space requirements; moreover, the improvement in heat transfer efficiency is not significant. This approach has now been abandoned. Currently, the most common approach is to enhance heat transfer by appropriately increasing the heat transfer area per unit volume of the equipment. For example, in heat exchangers, materials such as finned tubes, corrugated tubes, and plate-fin heat transfer surfaces, which offer a large heat transfer area per unit volume, are widely used. By employing these materials, the heat transfer area per unit volume of each individual piece of equipment can be significantly increased, thereby achieving efficient and compact heat exchange systems. 2. Increase the heat transfer temperature difference: Δt. The heat transfer temperature difference is one of the common methods used to enhance the heat exchange efficiency of heat exchangers. During the operation of the heat exchanger, increasing the pressure of the steam inside the radiant heating tubes, raising the temperature of the hot water used for heating, replacing tap water with cooler deep well water for the condenser cooling water, and lowering the temperature of the cooling water in the air cooler – all these measures can directly increase the heat transfer temperature difference (Δt) of the heat exchanger. However, there is a limit to increasing the heat transfer temperature difference (Δt) of the heat exchanger; we cannot use it as the primary method to enhance its heat transfer efficiency. Relying on increasing the heat transfer temperature difference (Δt) in the heat exchanger can only improve its heat transfer efficiency to a limited extent ； At the same time, an increase in the heat transfer temperature difference will increase the irreversibility of the entire thermal system, reducing its availability. 3. Enhancing the heat transfer coefficient: The value of the heat transfer coefficient (K) of a heat exchanger is actually determined by the total thermal resistance in the heat transfer process. The greater the total thermal resistance, the lower the value of the heat transfer coefficient (K) ； The lower the heat transfer coefficient (K) of a heat exchanger, the worse its heat transfer performance. During operation, the total thermal resistance of a heat exchanger is the sum of its individual thermal resistances; therefore, to change the heat transfer coefficient, it is necessary to analyze each of these individual thermal resistances in the heat transfer process. How to control each individual thermal resistance in the heat transfer process of a heat exchanger is crucial for determining its heat transfer coefficient. The three methods mentioned above for enhancing heat transfer efficiency are more or less utilized in heat exchangers. However, since expanding the heat transfer area and increasing the temperature difference for heat transfer are often limited by factors such as space, equipment, funding, and practical constraints, it is not possible to continuously improve these aspects. Therefore, the main focus of current research on improving heat transfer efficiency in heat exchangers is on finding ways to enhance this efficiency by controlling the heat transfer coefficient of the heat exchangers. The most commonly used technique to improve the heat transfer coefficient of heat exchangers today is the addition of flow perturbators inside the heat exchange tubes. Through the action of these perturbators, the thermal resistance in the heat transfer process is reduced, thereby achieving an improvement in the heat transfer coefficient of the heat exchanger.