One Question per Day: Methanol Technology Exchange Edition 20180523

Ways to improve heat transfer efficiency include: 1) increasing the heat transfer area, 2) increasing the average temperature difference between the hot and cold fluids, 3) improving the heat transfer coefficient – a. by increasing the fluid flow rate, b. by changing the flow conditions, c. in heat exchangers where fluid phase change occurs, taking measures to minimize the thickness of the condensate film, d. using liquids with higher thermal conductivity as heating or cooling agents.

Ways to improve heat transfer efficiency include: 1) increasing the heat transfer area, 2) increasing the temperature difference between the hot and cold fluids, 3) improving the heat transfer coefficient – a. by increasing the fluid flow velocity, b. by changing the flow conditions, c. in heat exchangers where fluid phase change occurs, taking measures to minimize the thickness of the condensate film, d. using liquids with higher thermal conductivity as heating or cooling agents.

Currently, the following measures are primarily adopted: 1. Researching and applying enhanced heat transfer technologies to increase the heat transfer area and improve the heat transfer performance of the heat transfer surfaces; 2. Modifying the structure of the heat exchanger’s baffle plates (such as using baffle rod technologies) to enhance the heat transfer coefficient in the shell side, increase the turbulence of the fluid, and prevent short-circuit flow of the fluid; 3. Technologies for preventing fouling on the inner and outer surfaces of the heat exchange tubes (fouling-resistant coating technologies). 　　4. Research on the application of numerical heat transfer techniques. Currently, the application of enhanced heat transfer techniques is an effective method to improve heat transfer efficiency. This paper mainly discusses the use of such techniques to upgrade heat exchangers. The so-called enhancement of heat transfer in heat exchangers refers to the adoption of certain technical measures, through the analysis and calculation of various factors affecting heat transfer, to increase the heat transfer capacity of heat exchange equipment or, while maintaining the existing heat transfer capacity, to reduce its volume. 　　The methods commonly used to enhance heat transfer in heat exchangers fall into three categories: increasing the heat transfer area (F); increasing the temperature difference for heat transfer; and raising the heat transfer coefficient (K). 　　1. Increase the heat transfer area F. Increasing the heat transfer area is the most common and simplest method for enhancing heat transfer efficiency. This method has been phased out now. Currently, the most common approach is to enhance heat transfer by reasonably increasing the heat transfer area per unit volume of the equipment; for example, finned tubes, corrugated tubes, and plate-fin heat exchanger surfaces with a large heat transfer area per unit volume are widely used in heat exchangers. 　　2. Increase the heat transfer temperature difference Δt. Increasing the heat transfer temperature difference Δt in the heat exchanger is one of the common methods to enhance its heat transfer efficiency. However, there is a limit to increasing the heat transfer temperature difference Δt of the heat exchanger; we cannot rely on it as the primary method to enhance heat transfer efficiency. During use, we should consider whether the actual process or equipment conditions permit it. 　　3. Increase the heat transfer coefficient (K). The most effective measure to improve the heat transfer performance of a heat exchanger is to strive to increase its heat transfer coefficient (K). The lower the heat transfer coefficient (K) of a heat exchanger, the worse its heat transfer performance. The higher the heat transfer coefficient (K) of the heat exchanger, the better its heat transfer performance.