Development and application of new high efficiency cooler technology
Due to the limitations of the manufacturing process and technical level, the early coolers can only adopt a simple structure, a small heat transfer area, a large volume, and a bulky, such as a coiled-
Due to the limitations of the manufacturing process and technical level, the early coolers can only adopt a simple structure, a small heat transfer area, a large volume, and a bulky, such as a coiled-tube cooler. However, with the development of the manufacturing process, the shell-and-tube cooler has emerged slowly. The unit volume of this cooler has a large heat transfer area, and the heat transfer effect is good. It has been a long-term industrial production. A typical cooler, in the 20s of the 1920s, appeared a plate cooler, a cooler made of plate, compact structure, good heat transfer effect. There are many kinds of traditional coolers, and there is no unified division method. At present, the main division methods are:
New high efficiency cooler
According to the flow direction of the hot fluid and the cold fluid: downstream, counterflow, crossflow, mixed flow.
According to the method of transferring heat, it is divided into three categories: partition type, hybrid type, and regenerative type. The coolers in which the cold and hot fluids of the partition wall cooler are separated by solid partitions and exchange heat through the partition walls are also called surface coolers, and such coolers are the most widely used.
The wall-mounted cooler can be divided into a tube type and a plate type according to the structure of the heat transfer surface. The tube cooler uses the surface of the tube as a heat transfer surface, including a casing cooler and a shell-and-tube cooler; the plate-type cooler uses a plate surface as a heat transfer surface, including a plate cooler, a spiral plate cooler, and a plate Wing coolers, plate coolers and umbrella coolers. It is currently the most widely used tube cooler and plate cooler.
Technical progress of new high efficiency cooler
The so-called new high-efficiency cooler means that the heat transfer efficiency of the cooler is improved by the enhanced heat transfer technology on the basis of the conventional cooler, and the energy loss in the heat exchange process is reduced. In terms of enhanced heat transfer technology, the main purpose is to increase the heat transfer per unit time and unit heat transfer area of the heat exchange equipment as much as possible. From a large aspect, the reinforcement method is no more than three: increase the heat transfer coefficient, Increase the unit heat transfer area and increase the heat transfer temperature difference.
Heat transfer enhancement of tubular cooler
The heat transfer enhancement of the tube cooler mainly includes the strengthening of the tube process and the strengthening of the shell side.
Tube heat transfer enhancement
The enhanced heat transfer of the tube is usually a tube that is processed to obtain various structures, such as a spiral groove tube, a transverse groove tube, a bellows, a low-threaded fin tube (threaded tube), a spiral flat tube, and a porous tube. Surface tubes, pin fin tubes, and the like are heat-strengthened by these shaped tubes. E.g:
The spiral corrugated pipe wall is extruded by a light pipe. As shown in Figure 1, there are single head and long head. The heat transfer enhancement in the pipe is mainly determined by two flow modes: one is the flow near the spiral groove. The limiting effect is to make the internal fluid flow in the tube as a whole secondary flow caused by the spiral motion; the second is the shape resistance caused by the spiral groove, and the reverse pressure gradient is generated to separate the boundary layer. The spiral grooved tube has the function of enhancing heat transfer on both sides, and is suitable for working conditions such as convection, boiling and condensation. The anti-fouling performance is higher than that of the light pipe, and the heat transfer performance is 2 to 4 times higher than that of the light pipe.
The bellows is analyzed from the viewpoint of fluid mechanics: at the peak, the fluid velocity decreases, the static pressure increases, the flow velocity increases at the trough, and the static pressure decreases. The flow of the fluid is repeated under varying axial pressure gradients, creating a sharp vortex that flushes the boundary layer of the fluid and thins the boundary layer. Therefore, the use of bellows as the heat exchange tube theoretically: due to the existence of the node, the disturbance of the fluid flow in the tube is increased, so that the bellows has a better heat transfer effect, but the flow characteristics are not as good as the light pipe. At low Reynolds number, the heat transfer and resistance performance ratio of the bellows is significantly better than that of the light pipe; at high Reynolds number, the heat transfer and resistance performance ratios of the bellows and the light pipe are very close.