What are the technical prerequisites for the selection and design of high-temperature centrifugal fans?
High temperature resistant centrifugal fanDesign scheme, motor selection and technical index analysis Centrifugal fan Brief description: High temperature resistant centrifugal fan is the fourth machine equipment widely used in every processing plant and company, and the use of centrifugal fans is more common. Centrifugal fans are indispensable for heating furnace blowers, soot and ash removal, and natural ventilation water cooling. In power plants, coal mines, chemical plants and their environmental protection equipment projects, centrifugal fans are also indispensable key machinery and equipment. Proper control of centrifugal fans The design scheme is critical to ensure the normal economic situation of the centrifugal fan. Centrifugal fan design selection The standards generally given when selecting a centrifugal fan design plan are: total capacity, total pressure, working medium and relative density (or working medium temperature), and sometimes there are structural regulations and requirements Wait.
rightHigh temperature resistant centrifugal fanMost of the design plan stipulates that the load point considering the total flow and working pressure should be around the maximum high efficiency point; the maximum high efficiency value should be as large as possible, the high efficiency curve graph is flat; the working pressure curve graph works smoothly The middle section should be wide; the centrifugal fan has simple structure and good process performance; the selection of raw materials and notes is convenient; it has any compressive strength and bending rigidity, which can be trusted during work; stable operation and low noise; good adjustment characteristics and adaptability during work Strong; the centrifugal fan size is as small as possible and very light; the actual operation and maintenance are convenient, and the disassembly and transportation are effective.
Obviously, considering all the regulations mentioned together, it is usually not. There are also differences between the aerodynamic characteristics and the structure (compressive strength, processing technology), and it is generally necessary to grasp the basic contradictions and solve them in a coordinated manner. This requires designers to choose effective scheme designs to deal with basic contradictions. For example, the main purpose of centrifugal fans is different, and the regulations are also different. For example, centrifugal fans commonly used in commercial buildings are usually used for natural ventilation. Usually the most critical regulation is low noise. Multi-wing centrifugal fans have this One characteristic; and the centrifugal fan with a large total flow is generally double breathing; for some high-pressure centrifugal fans, the specific speed ratio is low, and the relative proportion of leakage damage is usually large.
High temperature resistant centrifugal fanWhen designing a plan, a number of key plan options are selected:
(1) Effective selection of leaf form: Commonly used centrifugal fans under the necessary speed ratio, the working pressure index of the backward centrifugal impeller is smaller, the diameter of the centrifugal impeller is large, and its high efficiency is higher; compared with the forward centrifugal impeller Relatively.
(2) Selection of centrifugal fan drive system method: if the drive system method is A, D, F, the speed ratio of the centrifugal fan is the same as the motor speed ratio; while B, C, E are all speed regulation, design schemes The speed ratio of the centrifugal fan can be selected flexibly at the time. Generally, the transmission system A, which is directly connected to the motor, is commonly used for small and medium-sized centrifugal fans. For large and medium-sized centrifugal fans, sometimes the timing belt transmission is uncomfortable, and the transmission system methods D and F are mostly used. Under the high temperature and dusty standard, the transmission system method should also consider the safety protection of the motor and rolling bearing and the water cooling problem.
(3) Selection of volute size: The volute size should be as small as possible. For high specific speed centrifugal fans, a reduced worm shape can be used, and for low specific speed centrifugal fans, a standard worm shape is usually used. Sometimes in order to reduce the size of the volute, the volute outlet value rate can be used to exceed the centrifugal fan inlet rate plan plan. At this time, the outlet value diffuser is selected to increase the wind pressure value.
(4) The selection of leaf exit value angle: The leaf exit value angle is the fourth of the main parameters of the key geometric figure to be selected first in the design plan. In order to facilitate the application, people classify the leaves as: strong backward curved leaves (centrifugal water pump type), backward curved curved leaves, backward curved straight leaves, backward curved wing-shaped leaves; axial outlet value leaves, axial straight leaves ; Forward curved leaves, strong forward curved leaves (multi-wing leaves). Table 1 lists the approximate range of the outlet value angle of this leaf-shaped leaf in the centrifugal fan.
(5) Selection of the number of leaves: In the centrifugal fan, increasing the number of leaves of the centrifugal impeller can increase the basic theoretical working pressure of the centrifugal impeller, because it can reduce the harm of relative vortex (that is, increase the K value). However, the increase in the number of leaves will increase the frictional damage of the safety passage of the centrifugal impeller, and this type of damage will reduce the actual working pressure of the centrifugal fan and increase the energy consumption. Therefore, for each centrifugal impeller, there is one best number of leaves. The main confirmation is the number of leaves, and sometimes it depends on the designer's work experience. According to the current state of application in my country, table 2 strongly recommends the selection category of leaf number.
(6) Selection of the total pressure index Ψt: When designing the centrifugal fan, the actual working pressure is always given in advance. At this time, the total pressure index Ψt must be selected. Refer to Table 3 for the approximate selection category of the total pressure index.
(7) Confirmation of the key geometrical specifications of the import and export trade of centrifugal impellers: the centrifugal impeller is the only component that the centrifugal fan transmits to the kinetic energy of the steam, so its design is very harmful to the centrifugal fan; can the key structure of the centrifugal impeller be properly confirmed? It plays a leading role in the technical parameters of the centrifugal fan. It includes the core technology of the centrifugal fan design-the design of the leaves. The most important stage of the leaf design is how to confirm the leaf outlet angle β2A. Analysis of the design plan of the core technology When designing the centrifugal fan, it is important to grasp the confirmation of the outlet value angle β2A of the centrifugal impeller leaf
. According to the difference of the leaf exit angle β2A, the leaves can be divided into several forms, namely, backward curved leaves (β2A< 95℃),="" axial="" exit="" leaves="" (β2a="95℃)" and="" forward="" curved="" leaves="" (β2a="">95). ℃).
Several leaf-shaped centrifugal impellers are currently used in the design of centrifugal fans. The characteristic of the forward curved leaf centrifugal impeller is its small size and low price. The curved leaf centrifugal impeller can improve work efficiency and save resources. Therefore, among the centrifugal fans manufactured in contemporary production, it is very large and medium-sized centrifugal fan with large output power. Partially use back bend leaves.
The high efficiency of contemporary forward curved leaf centrifugal fans is significantly higher than that of old products, so it is still widely used in places with small total flow and high working pressure or places with large total flow under bottom pressure.
Axial export value leaves are no longer common in China. In some centrifugal fans with specified wear and corrosion resistance, axial export value straight leaves are common.
The design of the suction filter centrifugal impeller must also fully consider the necessary correlation between the specific speed ratio and the leaf form. Therefore, when confirming the leaf outlet angle, it is necessary to fully consider the working pressure, axial specifications and high efficiency of several leaf forms. The harm.
Proper confirmation of the outlet value angle β2A of the suction filter centrifugal impeller leaf will establish a solid basis for the confirmation of other key geometrical specifications of the centrifugal impeller, and then play an important role in the characteristics of the entire centrifugal fan.