第30卷第7期計算機(jī)與應(yīng)用化學(xué)2013年7月28日Computers and applied ChemistryJuly28,2013粉煤灰傳熱的影響研究楊偉',薛思瀚",張樹光1.遼寧工程技術(shù)大學(xué)建筑工程學(xué)院,遼寧,阜新,1230002.遼寧工程技術(shù)大學(xué)土木與交通學(xué)院,遼寧,阜新,123000摘要:近年來國內(nèi)外競相開展利用粉煤灰等制備保溫材料的硏發(fā)工作,以粉煤灰傳熱為硏究對象,對粉煤灰內(nèi)的流場、溫度玚高溫壁面平均努謝爾數(shù)M進(jìn)行硏究:采用整場求解法方法進(jìn)行數(shù)值求解,對網(wǎng)格的獨立性和計算過程進(jìn)行了驗證:得到了粉煤灰傳熱一些基本數(shù)據(jù),分析了粉煤灰溫度場和流場隨瑞利數(shù)Rα的變化規(guī)律。硏究結(jié)果表明:隨著Rα增加,開始流線均勻分布為一個順時針大窩,逐漸變化為流線集中分布在流場外側(cè),而在中央基本上保持靜止?fàn)顟B(tài):當(dāng)Ra很小時,無量綱等值線近似于平行高低溫壁面的垂直線,隨著Ra數(shù)逐漸增大,對應(yīng)的溫度等值線近似呈高溫至低溫的線性變化趨勢;Ra小于105時,高溫壁面Mat基本為2.37~3.31的定值;高溫壁面底部努謝爾數(shù)№!數(shù)大,最大值為30.8,上部Na數(shù)小,最小值為1.19。關(guān)鍵詞:粉煤灰:空氣;傳熱:數(shù)值模擬中圖分類號:TD985,O414獻(xiàn)標(biāo)識碼:A文章編號:1001-4160(2013)07-721-724DOl: 10. 11719/com. app. chem201307041引言左表面溫度為高溫壁面T、右表面溫度為低溫壁面T’上下壁面為絕熱邊界條件,粉煤灰骨架與內(nèi)部空氣近年來國內(nèi)外競相開展利用無機(jī)非金屬礦物和工業(yè)溫度相等,即采用局部熱平衡假設(shè):空氣密度隨溫度變廢棄物等制備保溫材料的研發(fā)工作。粉煤灰作為一種二化,其他熱物性為常量,采用 Brinkman擴(kuò)展達(dá)西模型描次資源進(jìn)行開發(fā)利用具有廣闊的應(yīng)用前景。由于粉煤灰述流動,在模型壁面上速度均采用無滑移邊界條件。假具有孔洞結(jié)構(gòu)、密度低、有較高的表面活性和較大的比設(shè)粉煤灰?guī)r體為各向同性、均質(zhì)的多孔介質(zhì),內(nèi)部充滿表面積等特點,非常適合用于保溫材料。徐子芳對空氣。粉煤灰、煤矸石低溫焙燒優(yōu)等保溫磚及性能分析,馮武對充滿空氣的二維不可壓縮層流的穩(wěn)態(tài)自然對流換威對礦物聚合法制備膨脹珍珠巖保溫材料的實驗研究。熱,其控制方程的無量綱形式如下他們對粉煤灰研究都是采用混合物的形式,單獨粉煤灰連續(xù)方程為的基礎(chǔ)物理研究較少。粉煤灰獨立存在時是一種多孔介△·v=0質(zhì)結(jié)構(gòu),內(nèi)部充滿飽和空氣或水等流體介質(zhì),采用數(shù)值動量方程為:計算的方法對他的基礎(chǔ)研究有重要的科學(xué)意義和實踐價P物理問題及數(shù)值方法研究對象可選為二維模型。研究區(qū)域選定為長寬為(VVv可p,PrVPrHXH的二維平面。物理模型見圖1。traPreoTan=0流體相能量方程為:Vv=V2+H(O2-0)T固體相能量方程為ar/an=0上述方程無量綱量定義為:無量綱坐標(biāo)X=xHFig. I The physical modelYyH,無量綱速度U=uh,V=wHa,無量綱壓力圖1物理模型收稿日期:2013-03-15;修回日期:2013-05-23基金項目:國家自然科學(xué)基金項目資助(50804021)作者簡介:楊偉(1965-),男,遼寧省阜新人,副教授,研究方向為流固耦合傳熱機(jī)理,E-mai:Igdyw@163.com聯(lián)系人:薛思瀚,E-mail:14704183608xueshanI63a163.com計算機(jī)與應(yīng)用化學(xué)2013,30(7)P-pH'p'oa2,無量綱準(zhǔn)則普朗特數(shù)Pr=w、達(dá)西數(shù)05021.0.505,從計算結(jié)果可以看出,都精確到小數(shù)點Da=KH2,瑞利數(shù)Ra=gB( T-THV a,無量綱溫度后2位,后3種網(wǎng)格對計算結(jié)果基本沒有影響,網(wǎng)格已具0=(7-T)(T-T)。其中:C為慣性常數(shù);an為多孔介質(zhì)有獨立性。采用100×100網(wǎng)格進(jìn)行計算。在計算之前首的有效熱擴(kuò)散系數(shù),a.k()}:k,有效導(dǎo)熱系數(shù)先進(jìn)行計算方法和程序的考核。利用 SIMPLER算法進(jìn)行求解,對流項采用QUCK格式12進(jìn)行離散,使計算具有kn(-9+,其中φ為孔隙率,k和k,分別是多孔介較高的精度?？己顺跏贾祵τ嬎憬Y(jié)果影響,選擇無量綱質(zhì)內(nèi)固體相和流體相的導(dǎo)熱系數(shù)。溫度初始值分別為0、0.5和1進(jìn)行計算,計算過程如圖2(圖無量綱邊界條件為2僅顯示計算100步)。從如圖2可知方程在收斂很快,說Y=0,Y=1,U=V=0,OT/an=0;明本文計算方法和程序的計算結(jié)果是可靠的。X=1,U=V=0,=01.0局部努謝爾數(shù)及平均努謝爾數(shù)定義為initial value is 0.5initial value is Iwarl!0.2平均努謝爾數(shù)Mu過局部努謝爾數(shù)沿壁面積分獲得,H沿壁面總長度。選代次數(shù)3網(wǎng)格劃分、數(shù)值求解Fig 2 Computation process of dimensionless temperature 0,圖2無量綱溫度θ計算過程采用非均勻網(wǎng)格明,網(wǎng)格的單元分別采用60×60、80×80、100×100、120×120共4種網(wǎng)格進(jìn)行計算。為取得4計算結(jié)果和討論穩(wěn)態(tài)解1,假定變量迭代求解滿足在計算中取粉煤灰孔隙率為0.6,比熱比為1,∑叫:g.∑q≤10Pr=0.701,Da數(shù)為102。分別針對Ra數(shù)為1、10、102、為收斂(為變量,n為迭代次數(shù))?？疾辄c(0.5,0.5)103、104、105、105、107、103、10、101°、10和導(dǎo)熱工無量綱溫度值,計算結(jié)果分別為:0.5006、0.5013,況進(jìn)行計算,部分計算結(jié)果見圖3~圖6。0.045-130.005(d)()a=10,(b)Ra10,()R10,(d)Ra=10Fig 3 Stream lines curve of Ra圖3流線數(shù)隨Ra變化關(guān)系從圖3流線數(shù)隨Ra變化關(guān)系可以看出:隨著Ra增靜止?fàn)顟B(tài)加,粉煤灰內(nèi)對流增強(qiáng),由Ra=103時流函數(shù)最大值圖4為無量綱溫度θ隨Ra變化關(guān)系。從圖中可以看Wmax≈0.045,發(fā)展至Ra=10時wmax≈13;對流強(qiáng)出:當(dāng)Ra很小時,當(dāng)粉煤灰內(nèi)內(nèi)對流作用較弱時,熱的度分布愈來愈不均勻,由開始流線均勻分布狀態(tài)Ra=103傳輸主要依靠傳導(dǎo)作用,因此無量綱等值線近似于平行一個順時針大窩,逐漸變化為流線集中分布在流場外側(cè)高低溫壁面的垂直線,隨著Ra數(shù)逐漸增大,對應(yīng)的溫度(Ra=103),即在流場外圍劇烈流動而在中央基本上保持等值線近似呈高溫至低溫的線性變化趨勢;而當(dāng)對流作2013,3楊偉,等:粉煤灰傳熱的影響研究用較強(qiáng)時,它成為熱傳輸?shù)闹饕獎恿Α?.9(a)Ra=103,(b)Ra=105,(e)Ra=10°,(d)Ra=10Fig 4 The variation relationship of 0 with the Ra圖4θ隨Ra變化關(guān)系值為237~3.31:超過該值后,Nu沿豎向壁面由高向低變小,最大值為30.8,最小值為1.19。分析其物理機(jī)理為底部溫差大,Mu數(shù)大,上部溫差小,Mt數(shù)小結(jié)語通過對粉煤灰傳熱研究,可得到以下結(jié)論:(1)隨著Ra增加,粉煤灰內(nèi)對流增強(qiáng)并且對流強(qiáng)度分布愈來愈不均勻,由開始流線均勻分布為一個順時針大窩,逐漸變化為流線集中分布在流場外側(cè),而在中央基本上保持靜止?fàn)顟B(tài)。ig. 5 Nu curve of Ra on high temperature wall.(2)當(dāng)Ra很小時,熱的傳輸主要依靠傳導(dǎo)作用,無圖5高溫壁面Nu與Ra變化關(guān)系量綱等值線近似于平行高低溫壁面的垂直線,隨著Ra數(shù)圖5為高溫壁面Na與Ra變化關(guān)系。從圖5可明顯看逐漸增大,對應(yīng)的溫度等值線近似呈高溫至低溫的線性出:瑞利數(shù)對腔內(nèi)對流換熱過程的影響是顯著的,當(dāng)瑞變化趨勢;而當(dāng)對流作用較強(qiáng)時,它成為熱傳輸?shù)闹饕麛?shù)小于103時,粉煤灰內(nèi)自然對流作用非常微弱,此時動力腔內(nèi)換熱機(jī)理主要依靠導(dǎo)熱進(jìn)行;隨著瑞利數(shù)逐漸增加,(3)當(dāng)瑞利數(shù)小于10時,腔內(nèi)換熱主要依靠導(dǎo)熱進(jìn)№u迅速增加,粉煤灰內(nèi)換熱機(jī)理主要依靠對流換熱進(jìn)行;隨著瑞利數(shù)逐漸增加,№迅速增加,換熱杋理主要依靠對流換熱進(jìn)行。(4)當(dāng)瑞利數(shù)小于103時,高溫壁面M基本為Heat conduction2.37~3.31的定值;超過該值后,底部Ma數(shù)大,最大值為30.8,上部M數(shù)小,最小值為1.19。Refer20Ra-105I Luo Daocheng. Yi Pinggui and Liu Junfeng. Development status0°and suggestion for comprehensive utilization of fine coal ash in2002,126):8-10perlite heat-insulating products, Non-metallic Mines, 2000,(9)3 Han Fuxing. Research on utilizing ceramic waste for porousceramics. Ceramic Studies Journal, 2002, 17(1): 24-26Fig 6 Nu curve of Ra on high temperature wallInvestigation of preparation and sintering of Sic porous ceramics圖6高溫壁面M與Ra變化關(guān)系A(chǔ)cta Chimica Sinica, 2003, 61(12): 2002-2007.5 Xu Zifang, Zhang Mingxu, Min Fan. Performance analysis of圖6為高溫壁面M與Ra變化關(guān)系。從圖5可明顯看preparing high-class insulation brick using fly ash, coal gangue via出:當(dāng)瑞利數(shù)小于10°時,高溫壁面Mt基本為一直線其oasting at low temperature conditions. Non-metallic Mines, 2010,33(4):13-166 Feng Wuwei, Ma Hongwen, Wang Gang, et al. Experiment724計算機(jī)與應(yīng)用化學(xué)2013,30(7)research on preparation of expended perlite heat insulatingmaterial by mineral polymerization. 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School of Civil Engineering and Transportation, Liaoning Technical University, Fuxin 123000, Liaoning Province, China)Abstract: In recent years, researches and development works on making thermal insulation material with fly ash and others are competitivelaunched at home and abroad. Heat transfer of fly ash is the object of study. The flow field, temperature field and average Nusselt numbers nieof the high temperature wall surface in the fly ash are studied. Numerical solution is carried out using whole field solving method. The gridindependence and computation process are verified. Some basic data is obtained and the change of temperature field and flow field of fly ashwith Rayleigh number Ra is analyzed. The results of the study show that: with the increase of Ra, at first the flow lines are uniformlydistributed as a clockwise big nest, gradually the flow lines are concentrated in the outer side of the flow field, while in the centre they remainmainly stationary state: When Ra is very small, non-dimensional contours approximately parallel the vertical line of wall surface of the highand low temperature, with the gradually increase of Ra, the corresponding temperature contours approximately forms as the linear trend ofthe high temperature to the low temperature: When Ra is less than 105, Nu of the high temperature wall surface is a constant value of 2. 37to 3.31: Nu of the bottom of high temperature wall surface is large, the maximum value is 30.8, Nu of the upper part is small, theminimum value is 1.1Keywords: fly ash; air; heat transfer; numerical simulation( Received:2013-03-15; Revised:2013-05-23)