離心風機設計、選型與技術分析離心風機概述:離心風機是各個工廠、企業普遍使用的設備之一,特別是離心風機的應用更為廣泛。鍋爐鼓風、消煙除塵、通風冷卻都離不開離心風機,在電站、礦井、化工以及環保工程,離心風機更是不可缺少的重要設備,正確掌握離心風機的設計,對保證離心風機的正常經濟運行是很重要的。 離心風機設計方案的選擇 離心風機設計時通常給定的條件有:容積流量、全壓、工作介質及其密度(或工作介質溫度),有時還有結構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.
對離心風機設計的要求大都是:滿足所需流量和壓力的工況點應在最高效率點附近;最高效率值要盡量大一些,效率曲線平坦;壓力曲線的穩定工作區間要寬;離心風機結構簡單,工藝性好;材料及附件選擇方便;有足夠的強度、剛度,工作安全可靠;運轉穩定,噪聲低;調節性能好,工作適應性強;離心風機尺寸盡可能小,重量輕;操作和維護方便,拆裝運輸簡單易行。
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,同時滿足上述全部要求,一般是不可能的。在氣動性能與結構(強度、工藝)之間往往也有矛盾,通常要抓住主要矛盾協調解決。這就需要設計者選擇合理的設計方案,以解決主要矛盾。例如: 隨著離心風機的用途不同,要求也不一樣,如公共建筑所用的離心風機一般用來作通風換氣用,一般最重要的要求就是低噪聲,多翼式離心風機具有這一特點;而要求大流量的離心風機通常為雙吸氣型式;對一些高壓離心風機,比轉速低,其泄漏損失的相對比例一般較大。離心風機設計時幾個重要方案的選擇:
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)葉片型式的合理選擇:常見離心風機在一定轉速下,后向葉輪的壓力系數中Ψt較小,則葉輪直徑較大,而其效率較高;對前向葉輪則相反。
(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)離心風機傳動方式的選擇:如傳動方式為A、D、F三種,則離心風機轉速與電動機轉速相同;而B、C、E三種均為變速,設計時可靈活選擇離心風機轉速。一般對小型離心風機廣泛采用與電動機直聯的傳動A,,對大型離心風機,有時皮帶傳動不適,多以傳動方式D、F傳動。對高溫、多塵條件下,傳動方式還要考慮電動機、軸承的防護和冷卻問題。
(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)蝸殼外形尺寸的選擇:蝸殼外形尺寸應盡可能小。對高比轉數離心風機,可采用縮短的蝸形,對低比轉數離心風機一般選用標準蝸形。有時為了縮小蝸殼尺寸,可選用蝸殼出口速度大于離心風機進口速度方案,此時采用出口擴壓器以提高其靜壓值。
(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)葉片出口角的選定:葉片出口角是設計時首先要選定的主要幾何參數之一。為了便于應用,我們把葉片分類為:強后彎葉片(水泵型)、后彎圓弧葉片、后彎直葉片、后彎機翼形葉片;徑向出口葉片、徑向直葉片;前彎葉片、強前彎葉片(多翼葉)。表1列出了離心風機中這些葉片型式的葉片的出口角的大致范圍。
(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)葉片數的選擇:在離心風機中,增加葉輪的葉片數則可提高葉輪的理論壓力,因為它可以減少相對渦流的影響(即增加K值)。但是,葉片數目的增加,將增加葉輪通道的摩擦損失,這種損失將降低離心風機的實際壓力而且增加能耗。因此,對每一種葉輪,存在著一個最佳葉片數目。具體確定多少葉片數,有時需根據設計者的經驗而定。根據我國目前應用情況,在表2推薦了葉片數的選擇范圍。
(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)全壓系數Ψt的選定:設計離心風機時,實際壓力總是預先給定的。這時需要選擇全壓系數Ψt,全壓系數的大致選擇范圍可參考表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)離心葉輪進出口的主要幾何尺寸的確定:葉輪是離心風機傳遞給氣體能量的唯一元件,故其設計對離心風機影響甚大;能否正確確定葉輪的主要結構,對離心風機的性能參數起著關鍵作用。它包含了離心風機設計的關鍵技術--葉片的設計。而葉片的設計最關鍵的環節就是如何確定葉片出口角β2A。關鍵技術的設計分析在設計離心風機時,關鍵就是掌握好葉輪葉片出口角β2A的確定。
(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.
根據葉片出口角β2A的不同,可將葉片分成三種型式即后彎葉片(β2A<90℃),徑向出口葉片(β2A=90℃)和前彎葉片(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).
三種葉片型式的葉輪,目前均在離心風機設計中應用。前彎葉片葉輪的特點是尺寸重量小,價格便宜,而后彎葉片葉輪可提高效率,節約能源,故在現代生產的離心風機中,特別是功率大的大型離心風機多數用后彎葉片。
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.
現代前彎葉片離心風機效率,比老式產品已有顯著提高,故在小流量高壓力的場合或低壓大流量場合中仍廣為采用。
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.
徑向出口葉片在我國已不常用,在某些要求耐磨和耐腐蝕的離心風機中,常用徑向出口直葉片。 離心風機葉輪設計時還必須考慮到比轉速與葉片型式存在一定的關系,故在確定葉片出口角的同時,必須綜合考慮三種葉片型式對壓力、徑向尺寸和效率的影響。
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.
正確確定了離心風機葉輪葉片出口角β2A將為葉輪其它主要幾何尺寸的確定奠定了堅實的基礎,從而對整臺離心風機的性能起著關鍵的作用。
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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