In the design of the centrifugal fan, the need to consider the body structure, volume flow, working medium temperature and density, and sometimes need to take into account some special requirements and so on. Therefore, we should first understand the centrifugal fan of the general design requirements, in order to carry out a reasonable design, to avoid mistakes.
The requirements for centrifugal fan design are generally: meet the required flow and pressure conditions should be in the vicinity of the highest efficiency point; the highest efficiency value should be as large as the efficiency curve flat; pressure curve stable working range to wide; fan structure is simple Easy to operate and easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate, easy to operate , Easy disassembly and transportation.
In fact, it is generally impossible to meet all of the above requirements, for example, there is often a contradiction between aerodynamic performance and structure (strength, process). The solution to the contradiction is to seize the main contradictions to coordinate the solution, which requires designers to choose a reasonable design. Centrifugal fans use different requirements are not the same, such as public buildings used in centrifugal fans are generally used for ventilation, the most important requirement is the low noise, multi-wing centrifugal fan with this feature; and require large flow Of the centrifugal fan is usually double suction type; for some high-pressure centrifugal fan, than the low speed, the relative proportion of its leakage loss is generally larger.
Centrifugal fan in the design should pay attention to the following:
(1) leaf exit angle selection: leaf exit angle is the design of the first to be selected one of the main geometric parameters. In order to facilitate the application, the leaves are usually classified as: strong after bending the blade, after bending the circular blade, after bending straight blade, after bending machine wing blade; radial exit leaves, radial straight blade.
(2) reasonable choice of blade type: common fan at a certain speed, the impeller to the smaller pressure coefficient, the impeller diameter is larger, and its high efficiency; the opposite is the opposite of the impeller.
(3) the choice of volute size: volute size should be as small as possible. For the high than the number of wind turbines, can be used to shorten the scroll, the lower than the number of wind turbines generally use the standard scroll. Sometimes in order to narrow the volute size, optional volute export speed is greater than the fan inlet speed program, this time using the export diffuser to improve its static pressure value.
(4) the choice of the number of leaves: In the centrifugal fan, increasing the number of leaves of the impeller can increase the theoretical pressure of the impeller, because it can reduce the impact of relative vortex. However, the increase in the number of blades will increase the friction loss of the impeller channel, which will reduce the actual pressure of the fan and increase the energy consumption. Thus, for each impeller, there is an optimal number of blades. Determine the number of leaves, sometimes based on the experience of the designer.
(5) the choice of full pressure coefficient: the design of centrifugal fan, the actual pressure is always given in advance. At this time need to select the full pressure coefficient.
(6) the determination of the main geometric dimensions of the impeller inlet and outlet: the impeller is the only component of the fan's energy delivered to the gas, so its design has a great influence on the fan; can the correct structure of the impeller be determined correctly and the performance parameters of the centrifugal fan Key role. It contains the key technology of centrifugal fan design - the design of the blade. The key part of the design of the blade is how to determine the blade exit angle.