离心风机设计时通常给定的条件有:容积流量、全压、工作介质及其密度(或工作介质温度),有时还有结构上的要求和特殊要求等。 对离心风机设计的要求大都是:满足所需流量和压力的工况点应在最高效率点附近;最高效率值要尽量大一些,效率曲线平坦;压力曲线的稳定工作区间要宽;风机结构简单,工艺性好;材料及附件选择方便;有足够的强度、刚度,工作安全可*;运转稳定,噪声低;调节性能好,工作适应性强;风机尺寸尽可能小,重量轻;操作和维护方便,拆装运输简单易行。
When the centrifugal fan is designed, the conditions are the volume flow, the full pressure, the working medium and its density (or the temperature of the working medium), and sometimes the requirements and special requirements of the structure.The requirements for the design of the centrifugal fan are mostly that the working point to meet the required flow and pressure should be near the highest efficiency point; the maximum efficiency value should be as large as possible, the efficiency curve is flat; the stable working interval of the pressure curve should be wide; the fan structure is simple and the craft is good; the material and accessories are convenient to choose; sufficient strength, enough strength, Stiffness, work safety *; stable operation, low noise; good adjustment performance, work adaptability; fan size as small as possible, light weight; easy operation and maintenance, easy and easy to disassemble and transport.
然而,同时满足上述全部要求,一般是不可能的。在气动性能与结构(强度、工艺)之间往往也有矛盾,通常要抓住主要矛盾协调解决。这就需要设计者选择合理的设计方案,以解决主要矛盾。例如:随着风机的用途不同,要求也不一样,如公共建筑所用的风机一般用来作通风换气用,一般最重要的要求就是低噪声,多翼式离心风机具有这一特点;而要求大流量的离心风机通常为双吸气型式;对一些高压离心风机,比转速低,其泄漏损失的相对比例一般较大。
However, it is not possible to meet all of the above requirements. There are always contradictions between aerodynamic performance and structure (intensity, process). Usually, we must seize the main contradiction and solve it in a coordinated way. This requires the designer to choose a reasonable design plan to solve the main contradiction. For example, as the use of the fan is different, the requirement is different, for example, the fan used in the public building is generally used for ventilation and ventilation. The most important requirement is the low noise, the multi wing centrifugal fan has this characteristic, and the centrifugal fan with large flow is usually a double suction type, and some high pressure centrifugal fans are used. The relative loss of leakage rate is relatively large.
离心风机设计时几个重要方案的选择: Several important options for centrifugal fan design are:
(1)叶片型式的合理选择:常见风机在一定转速下,后向叶轮的压力系数中Ψt较小,则叶轮直径较大,而其效率较高;对前向叶轮则相反。
(1) the rational selection of the type of blade: the common fan at a certain speed, the pressure coefficient of the rear impeller is less t, then the diameter of the impeller is larger, and its efficiency is higher; the forward impeller is the opposite.
(2)风机传动方式的选择:如传动方式为A、D、F三种,则风机转速与电动机转速相同;而B、C、E三种均为变速,设计时可灵活选择风机转速。一般对小型风机广泛采用与电动机直联的传动A,,对大型风机,有时皮带传动不适,多以传动方式D、F传动。
对高温、多尘条件下,传动方式还要考虑电动机、轴承的防护和冷却问题。
(2) the choice of fan transmission mode: if the transmission mode is A, D, F three kinds, the fan speed is the same as the motor speed; while the three kinds of B, C, E are all variable speed, and the fan speed can be flexibly chosen when the design is designed. Generally, the transmission A is directly connected with the motor for small fans. For large fans, sometimes the belt drives are uncomfortable, mostly driven by D and F.
For high temperature and dusty conditions, the protection and cooling of motors and bearings should also be considered.
(3)蜗壳外形尺寸的选择:蜗壳外形尺寸应尽可能小。对高比转数风机,可采用缩短的蜗形, 对低比转数风机一般选用标准蜗形。有时为了缩小蜗壳尺寸,可选用蜗壳出口速度大于风机进口速度方案,此时采用出口扩压器以提高其静压值。
(3) size selection of volute: the size of the volute should be as small as possible. For the high specific speed fan, the shortened worm shape can be adopted, and the standard worm shape is generally adopted for the low specific speed fan. Sometimes, in order to reduce the size of volute, the outlet speed of volute is larger than that of the fan inlet speed. The outlet diffuser is used to increase the static pressure value of the volute.
(4)叶片出口角的选定:叶片出口角是设计时首先要选定的主要几何参数之一。为了便于应用,我们把叶片分类为:强后弯叶片(水泵型)、后弯圆弧叶片、后弯直叶片、后弯机翼形叶片;径向出口叶片、径向直叶片;前弯叶片、强前弯叶片(多翼叶)。表1列出了离心风机中这些叶片型式的叶片的出口角的大致范围。
(4) the selection of blade outlet angle: blade outlet angle is one of the main geometric parameters to be selected when designing. In order to facilitate the application, we classify the blades as: strong back curved blade (pump type), back curved circular arc blade, back bend blade, rear curved wing shaped blade, radial outlet blade, radial straight blade, front bend blade, and strong front curved blade (multi wing blade). Table 1 lists the approximate ranges of the blade outlet angles in the centrifugal fans.
(5)叶片数的选择:在离心风机中,增加叶轮的叶片数则可提高叶轮的理论压力,因为它可以减少相对涡流的影响(即增加K值)。但是,叶片数目的增加,将增加叶轮通道的摩擦损失,这种损失将降低风机的实际压力而且增加能耗。因此,对每一种叶轮,存在着一个最佳叶片数目。具体确定多少叶片数,有时需根据设计者的经验而定。根据我国目前应用情况,在表2推荐了叶片数的选择范围。
(5) the selection of the number of blades: in a centrifugal fan, increasing the number of blades of the impeller can increase the theoretical pressure of the impeller, because it can reduce the influence of relative eddy current (that is, increase the K value). However, the increase of blade number will increase the friction loss of impeller passage, which will reduce the actual pressure of the fan and increase the energy consumption. Therefore, there is an optimum number of blades for each impeller. The number of blades determined specifically depends on the designer's experience. According to the current application situation in China, the choice of blade number is recommended in Table 2.
(6)全压系数Ψt的选定:设计离心风机时,实际压力总是预先给定的。这时需要选择全压系数Ψt,全压系数的大致选择范围可参考表3。
(6) the selection of full pressure coefficient T: when designing centrifugal fans, the actual pressure is always given in advance. At this time, the total pressure factor t should be chosen, and the general selection range of the total pressure coefficient can be referred to table 3.
(7)离心叶轮进出口的主要几何尺寸的确定:叶轮主要尺寸示于图1。叶轮是风机传递给气体能量的唯一元件,故其设计对风机影响甚大;能否正确确定叶轮的主要结构,对风机的性能参数起着关键作用。它包含了离心风机设计的关键技术--叶片的设计。而叶片的设计最关键的环节就是如何确定叶片出口角β2A。
(7) determination of the main geometric dimensions of the inlet and outlet of the centrifugal impeller: the main dimensions of the impeller are shown in Figure 1. The impeller is the only element that the fan sends to the gas energy, so its design has a great influence on the fan, and whether the main structure of the impeller can be correctly determined can play a key role in the performance parameters of the fan. It contains the key technology of centrifugal fan design - blade design. The most important part of blade design is how to determine the outlet angle of blade 2A.
关键技术的设计分析
在设计离心风机时,关键就是掌握好叶轮叶片出口角β2A的确定。
根据叶片出口角β2A的不同,可将叶片分成三种型式即后弯叶片(β2A<90℃),径向出口叶片(β2A=90℃)和前弯叶片(β2A>90℃)。
三种叶片型式的叶轮,目前均在风机设计中应用。前弯叶片叶轮的特点是尺寸重量小,价格便宜,而后弯叶片叶轮可提高效率,节约能源,故在现代生产的风机中,特别是功率大的大型风机多数用后弯叶片。
现代前弯叶片风机效率,比老式产品已有显著提高,故在小流量高压力的场合或低压大流量场合中仍广为采用。
径向出口叶片在我国已不常用,在某些要求耐磨和耐腐蚀的风机中,常用径向出口直叶片。
离心风机叶轮设计时还必须考虑到比转速与叶片型式存在一定的关系(例表4),故在确定叶片出口角的同时,必须综合考虑三种叶片型式对压力、径向尺寸和效率的影响,再综合表1和表4之后确定。
正确确定了离心风机叶轮叶片出口角β2A将为叶轮其它主要几何尺寸的确定奠定了坚实的基础,从而对整台离心风机的性能起着关键的作用。
Design and analysis of key technology
When designing centrifugal fans, the key is to grasp the determination of impeller outlet outlet angle 2A.
According to the difference of the exit angle beta 2A of the blade, the leaves can be divided into three types, namely, the back bend blade (beta 2A<90 C), the radial exit blade (beta 2A=90 C) and the front curved blade (beta 2A > 90).
The three blade type impeller is currently used in fan design. The front - bend blade impeller is characterized by small size weight and low price. The backward blade impeller can improve efficiency and save energy. So, most of the large fan in modern production, especially large power fan, uses back bend blade.
The efficiency of modern front vane blower is much higher than that of old products, so it is still widely used in small flow, high pressure or low pressure and large flow situations.
Radial outlet blades are not commonly used in China. In some fans which require wear resistance and corrosion resistance, they are usually used for radial outlet straight blades.
When the centrifugal fan impeller is designed, there is a certain relationship between the specific speed and the type of blade (Table 4). Therefore, when the blade exit angle is determined, the influence of the three type of blade type on the pressure, radial size and efficiency must be considered, and then the comprehensive table 1 and the table 4 must be determined.
The impeller outlet angle of centrifugal fan impeller 2A will be determined correctly.
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