本文選題：超聲波 + 換能器　； 參考：《長沙理工大學(xué)》2014年碩士論文

【摘要】：換熱器是暖通空調(diào)、熱能工程、化工等領(lǐng)域的主要換熱設(shè)備,這些設(shè)備在運行中普遍存在結(jié)垢現(xiàn)象,從而導(dǎo)致其傳熱效果下降,并影響設(shè)備安全。目前,常規(guī)除垢方法存在維護(hù)成本高、產(chǎn)生化學(xué)廢液等問題,難以滿足生產(chǎn)工藝需求,超聲波除垢技術(shù)以其綠色環(huán)保、成本低廉、效果明顯等優(yōu)點得到推廣。但是在工程應(yīng)用中,由于超聲波參數(shù)匹配及換能器布置不合理會造成除垢效率下降,以及換熱器部分區(qū)域無除垢效果。因此,深入研究超聲波除垢效率和范圍是非常必要的。據(jù)有關(guān)學(xué)者研究,超聲波的指向性決定了除垢范圍,而聲強則對除垢效率有一定影響。本文在點聲源指向性函數(shù)基礎(chǔ)上,建立了非點聲源的指向性函數(shù)和聲強的數(shù)學(xué)模型,并利用MATLAB軟件模擬計算了在不同頻率、換能器半徑參數(shù)下超聲波指向性函數(shù)分布情況,以及超聲波聲強與換能器半徑、超聲波頻率、輻射角度之間的關(guān)系。根據(jù)模擬計算,得出以下結(jié)論：(1)超聲波頻率為28kHz時,換能器半徑越大,指向性函數(shù)分布范圍越小,聲場逐漸向換能器垂直方向聚集,當(dāng)換能器半徑為50mm時,超聲波指向性范圍集中在換能器中心區(qū)域。(2)換能器半徑為30mm時,頻率越大,指向性函數(shù)范圍越小,頻率為60kHz時,超聲波指向性范圍達(dá)到最小。(3)超聲波聲強與功率的平方根成正比,與傳播距離的二次方成反比,功率越大,聲強越大；傳播距離越遠(yuǎn),聲強越小。(4)超聲波頻率為40kHz時,隨著換能器半徑增大,換能器垂直方向處的聲強值逐漸增大,其它輻射角度處的聲強值較小,當(dāng)半徑為50mm時,聲強在換能器垂直方向處達(dá)到最大。本文在理論研究的基礎(chǔ)上,還進(jìn)行了超聲波除垢實驗,根據(jù)實驗研究,得出以下結(jié)論：(1)頻率為20 kHz時,除垢范圍最大,隨著頻率的增大,除垢范圍逐漸縮小,集中在換能器圓心的垂直方向附近,換能器半徑對除垢范圍的影響規(guī)律與頻率類似。除垢范圍受頻率和換能器半徑的影響規(guī)律與指向性函數(shù)模擬圖形吻合。(2)換能器中心處,除垢效率最大,隨著角度向兩邊擴散,除垢效率逐漸減��；當(dāng)頻率為20kHz、換能器半徑為15mm時,各輻射角度處除垢效率相差不大,在50%～60%之間,隨著頻率或換能器半徑的增大,換能器兩邊的除垢效率低,中心處的除垢效率高,最大達(dá)到了95.5%。實驗結(jié)論與聲強模擬圖形基本吻合。
[Abstract]:Heat exchanger is the main heat exchanger in the fields of HVAC, thermal engineering, chemical engineering and so on. The scaling phenomenon exists in the operation of these equipments, which results in the decrease of heat transfer effect and affects the safety of the equipment. At present, the conventional scale removal methods have the problems of high maintenance cost, chemical waste liquid and so on, so it is difficult to meet the requirements of production process. Ultrasonic scale removal technology has been popularized because of its advantages of green environment protection, low cost and obvious effect. However, in engineering application, the efficiency of scale removal will decrease due to ultrasonic parameter matching and unreasonable arrangement of transducer, and there is no scaling removal effect in some parts of heat exchanger. Therefore, it is necessary to study the efficiency and scope of ultrasonic scale removal. According to relevant scholars, the directivity of ultrasonic wave determines the scale of scale removal, and the intensity of sound has a certain effect on the efficiency of scale removal. Based on the directivity function of point sound source, a mathematical model of directivity function and sound intensity of non-point sound source is established, and the distribution of ultrasonic directivity function under different frequency and transducer radius parameters is simulated by MATLAB software. And the relationship between ultrasonic intensity and transducer radius, ultrasonic frequency, radiation angle. According to the simulation calculation, the following conclusion is drawn: when the ultrasonic frequency is 28kHz, the larger the transducer radius is, the smaller the distribution range of directivity function is, and the sound field gradually accumulates to the vertical direction of transducer. When the transducer radius is 50mm, When the radius of the transducer is 30mm, the larger the frequency, the smaller the range of directivity function, and when the frequency is 60kHz, The directivity range of ultrasonic wave is the smallest, the ultrasonic intensity is directly proportional to the square root of the power, and inversely proportional to the second power of the propagation distance. The greater the power, the greater the sound intensity, and the farther the propagation distance, the smaller the sound intensity. 4) when the ultrasonic frequency is 40kHz, With the increase of the radius of the transducer, the sound intensity in the vertical direction of the transducer increases gradually, and the sound intensity at the other radiation angles is smaller. When the radius is 50mm, the sound intensity reaches the maximum in the vertical direction of the transducer. On the basis of theoretical research, the ultrasonic scale removal experiment is carried out in this paper. According to the experimental study, the following conclusions are drawn: when the frequency is 20 kHz, the scale removal range is the largest, and with the increase of the frequency, the scale removal range is gradually reduced. The effect of the transducer radius on the scale removal range is similar to that of the frequency. The effect of frequency and transducer radius on the scale removal range coincides with the simulation pattern of directivity function. At the center of the transducer, the scale removal efficiency is the greatest, and the scale removal efficiency decreases gradually with the angle diffusing to both sides. When the frequency is 20 kHz and the transducer radius is 15mm, the efficiency of scale removal at each radiation angle is not different. Between 50% and 60%, with the increase of frequency or the radius of the transducer, the efficiency of scale removal on both sides of the transducer is low, and the scale removal efficiency at the center of the transducer is high, with the maximum of 95.5%. The experimental results are in good agreement with the sound intensity simulation pattern.
【學(xué)位授予單位】：長沙理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TU83
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本文編號：1904998