离心风机设计、选型与技术分析离心风机概述:离心风机是各个工厂、企业普遍使用的设备之一,特别是离心风机的应用更为广泛。锅炉鼓风、消烟除尘、通风冷却都离不开离心风机,在电站、矿井、化工以及环保工程,离心风机更是不可缺少的重要设备,正确掌握离心风机的设计,对保证离心风机的正常经济运行是很重要的。 离心风机设计方案的选择 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。
Centrifugal fan design, selection and technical analysis of centrifugal fan overview: centrifugal fan is one of the equipment used in various factories and enterprises, especially the application of centrifugal fan is more extensive. The centrifugal fan is inseparable from the boiler blast, the smoke elimination and the ventilation and cooling. In the power station, the mine, the chemical industry and the environmental protection engineering, the centrifugal fan is an indispensable and important equipment. It is very important to master the design of the centrifugal fan correctly and to ensure the normal economic operation of the centrifugal fan. The selection of centrifugal fan design scheme is usually given when the centrifugal fan is designed: volume flow, full pressure, working medium and its density (or working medium temperature), sometimes there are structural requirements and special requirements.
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;离心风机结构简单,工艺性好;材料及附件选择方便;有足够的强度、刚度,工作安全可靠;运转稳定,噪声低;调节性能好,工作适应性强;离心风机尺寸尽可能小,重量轻;操作和维护方便,拆装运输简单易行。
Most of the requirements for centrifugal blower design are that the working point of satisfying 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 centrifugal fan is simple in structure and good in technology; the selection of material and accessories is convenient; it is strong enough to be strong enough. Degree and stiffness, safe and reliable work, stable operation, low noise, good adjustment performance, strong adaptability, small size of the centrifugal fan, light weight, convenient operation and maintenance, simple and easy transportation.
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: 随着离心风机的用途不同,要求也不一样,如公共建筑所用的离心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。离心风机设计时几个重要方案的选择:
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, with the different uses of centrifugal fans, the requirements are different, for example, the centrifugal fan used in public buildings is generally used for ventilation and ventilation. The most important requirement is low noise, and the multi wing centrifugal fan has this characteristic, and the centrifugal fan with large flow is often used as a double suction type; and some high pressure is used. Centrifugal fan has a lower specific speed, and its relative leakage rate is generally larger. Several important options for centrifugal fan design are:
(1)叶片型式的合理选择:常见离心风机在一定转速下,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 blade type: the common centrifugal fan is smaller in the pressure coefficient of the rear impeller at a certain speed at a certain speed, and the diameter of the impeller is larger and its efficiency is higher; the forward impeller is opposite to the T impeller.
(2)离心风机传动方式的选择:如传动方式为A、D、F三种,则离心风机转速与电动机转速相同;而B、C、E三种均为变速,设计时可灵活选择离心风机转速。一般对小型离心风机广泛采用与电动机直联的传动A,,对大型离心风机,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 selection of the transmission mode of centrifugal fan: if the transmission mode is A, D and F, the speed of the centrifugal fan is the same as the motor speed; while the three kinds of B, C and E are all variable speeds, and the speed of the centrifugal fan can be flexibly chosen in the design. Generally, the transmission A is widely used for the small centrifugal fan, which is directly connected with the motor. For the large centrifugal fan, sometimes the belt drive is discomfort, and the transmission mode is D and F drive. 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。对高比转数离心风机,可采用缩短的蜗形,对低比转数离心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离心风机进口速度方案,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 centrifugal fan with high specific speed, the shortened worm shape can be adopted, and the standard worm shape is generally adopted for the centrifugal fan with low specific speed. Sometimes, in order to reduce the size of volute, the outlet speed of volute is larger than that of centrifugal fan inlet speed. The outlet diffuser is used to improve the static pressure value.
(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,这种损失将降低离心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 centrifugal fan and increase 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:叶轮是离心风机传递给气体能量的唯一元件,故其设计对离心风机影响甚大;能否正确确定叶轮的主要结构,对离心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。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。
(7) the determination of the main geometric dimensions of the inlet and outlet of the centrifugal impeller: the impeller is the only component of the centrifugal fan transmitted to the gas energy, so its design has a great influence on the centrifugal fan, and whether the main structure of the impeller can be correctly determined can play a key role in the performance parameters of the centrifugal 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. In the design and analysis of the key technology, the key to designing the centrifugal fan is to grasp the determination of the impeller outlet outlet angle 2A.
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℃)。
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).
三种叶片型式的叶轮,目前均在离心风机设计中应用。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,故在现代生产的离心风机中,特别是功率大的大型离心风机多数用后弯叶片。
The three blade type impeller is currently used in the design of centrifugal fans. The front curved blade impeller is characterized by small size weight and low price. The backward blade impeller can improve efficiency and save energy. In the modern centrifugal fan, the large centrifugal fan, especially the large power, uses the back bend blade.
现代前弯叶片离心风机效率,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。
The efficiency of the modern forward bending blade centrifugal fan has been greatly improved than the old type, so it is still widely used in the occasion of small flow and high pressure or in the situation of low pressure and large flow.
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离心风机中,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,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。
Radial outlet blades are not commonly used in China. In some centrifugal fans that require wear resistance and corrosion resistance, radial blades are usually used. When the centrifugal fan impeller is designed, there is a certain relationship between the specific speed and the type of blade. Therefore, at the same time, the influence of the three type of blade on the pressure, the radial size and the efficiency must be considered.
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。
The correct determination of the outlet angle beta 2A of the impeller blade of the centrifugal fan will lay a solid foundation for the determination of the other main geometric dimensions of the impeller, and thus plays a key role in the performance of the whole centrifugal fan.
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