碳氫燃料熱裂解與引發(fā)裂解換熱對比實(shí)驗

第65卷第S1期化工學(xué)報Vol. 65 No S12014年5月CIESC JournalMay 2014研究論文碳氳燃料熱裂解與引發(fā)裂解換熱對比實(shí)驗賈貞健1,周偉星2,黃洪雁',于文力(哈爾濱工業(yè)大學(xué)能源科學(xué)與工程學(xué)院,黑龍江哈爾濱150001;哈爾濱工業(yè)大學(xué)基礎與交叉科學(xué)研究院,黑龍江哈爾濱150001)摘要:通過(guò)流動(dòng)管反應器對碳氫燃料RP3在超臨界條件下的熱裂解及引發(fā)裂解進(jìn)行了實(shí)驗,對兩種條件下的燃料吸熱能力及傳熱特性進(jìn)行了對比分析,并對裂解產(chǎn)物進(jìn)行了采樣分析。結果表明,引發(fā)裂解降低了燃料的裂解起始溫度,在一定溫度區間內提高了燃料的裂解率,從而有效提高了燃料熱沉,在相同熱通量條件下,降低了燃料溫度,并降低了加熱段壁面溫度。對流換熱受化學(xué)反應及物性變化的影響,燃料裂解吸熱可增強換熱而大量氣態(tài)產(chǎn)物的生成會(huì )降低換熱,因此,裂解反應的增強不一定增強換熱。關(guān)鍵詞:熱裂解;引發(fā)裂解;RP3;換熱;熱沉;超臨界DOI:10.3969/ 1. Issn.0438-1157.2014.z1.022中圖分類(lèi)號:TQ028.8文獻標志碼:A文章編號:0438-1157(2014)S1-138—06Heat transfer of thermal cracking and initiated cracking of aviation keroseneJIA Zhenjian, ZHOU Weixing, HUANG Hongyan, YU WenliSchool of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China:2 Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of TechnologyHarbin 150001, Heilong jiang, China)Abstract: Nitro-propane(NP) was employed as the initiator to investigate the effect of initiated crackingon heat transfer of aviation fuel RP-3 with a one-stage and cracking system operating under supercriticalpressure. The pyrolysis products are analyzed using a chromatograph/ mass spectrometry (GC-MS). Theheat sink, conversion rate and heat transfer coefficient were calculated based on the experimental results.Experimental results indicate that the heat transfer characteristics are influenced by the pyrolysis rate andphysical property change caused by products distribution. NP accelerates the pyrolysis and increases theheat sink of fuel in temperature range of 800 K to 900 K. Under the same heat flux conditions, the effectsof NP are reflected in the reduction of fuel and wall temperature. The reductions of fuel and walltemperature increase first and decrease along the flow direction, and the maximum decrease is more than 10K. However, the Reynolds numbers decrease because of large amount gaseous products generated bypyrolysis reaction, which has negative effect on the convective heat transfer. So the influence of initiatedcracking on the heat transfer of RP-3 is not a simple effect of promotion or inhibition, the regularity isdifferent in different temperature ranges.Key words: thermal cracking; initiated cracking; RP-3; heat transfer; heat sink; supercritica2014—01-23收到初稿,2014-01-31收到修改稿Received date: 2014-01-23聯(lián)系人:周偉星。第一作者:賈貞健(1987-),男,博土研Corresponding author: Prof. ZHOU Weixing, zhouweixing@究生基金項目:國家自然科學(xué)基金項目(11079017)Foundation item: supported by the National Natural ScieFoundation of China(11079017)第Sl期賈貞健等:碳氫燃料熱裂解與引發(fā)裂解換熱對比實(shí)驗13獻[10-12]亦有同樣結論。但在發(fā)動(dòng)機冷卻通道引言?xún)?燃料的冷卻效果不僅與其熱沉有關(guān),其傳熱特以吸熱型碳氫燃料為冷卻劑的再生冷卻技術(shù)是性也對冷卻通道的設計十分重要131,因此有必高超聲速飛行熱防護的主要方式之一13。在再生要對引發(fā)裂解對換熱的影響進(jìn)行研究冷卻過(guò)程中,燃料吸收燃燒室釋放的熱量,當加熱本文選用硝基丙烷為引發(fā)劑,對航空燃料RP到一定溫度后發(fā)生熱解反應。熱解反應通常為吸熱3的熱裂解及引發(fā)裂解進(jìn)行了對比實(shí)驗,通過(guò)GC反應,可提供額外的冷卻能力,提高燃料的化學(xué)吸MS分析了反應產(chǎn)物分布,分析了引發(fā)劑對化學(xué)反熱是提高燃料吸熱能力的有效方式之應速率的影響,通過(guò)對壁面溫度及燃料溫度的測在燃料中添加引發(fā)劑是提高熱沉的有效手段之量,計算了燃料吸熱能力和對流傳熱系數,分析了俄羅斯航空發(fā)動(dòng)機中央研究所(CIAM)已研引發(fā)裂解對燃料吸熱能力及傳熱特性的影響,對引制出一種液體引發(fā)劑,在500~630℃溫度范圍發(fā)劑的添加及冷卻通道設計具有指導意義。內,引發(fā)劑濃度小于0.18%時(shí),能使燃料裂解速1實(shí)驗系統及流程度提高2~7倍,裂解起始溫度降低約100K。Wickham等67在引發(fā)劑對燃料裂解和化學(xué)熱沉的實(shí)驗系統如圖1所示,系統主要包括油箱、平影響方面做了大量的研究工作,他們選擇了正庚烷流泵、流量計、加熱段、直流電加熱系統、冷凝器和2,2,4-三甲基戊烷為研究對象,考察了引發(fā)及采樣系統。加熱段為內徑1mm、壁厚1mm、劑對不同烴類(lèi)分子結構裂解和熱沉的影響。最近,長(cháng)度1000mm的高溫合金管,水平放置,并通過(guò)篩選高性能的引發(fā)劑成為熱點(diǎn),Wang等。研究了直流電源進(jìn)行加熱,加熱能力最高可達IMW三乙胺的引發(fā)作用,發(fā)現其作用的溫度范圍為823m-2。20個(gè)直徑0.1mm的K型熱電偶均勻焊接~923K,乙基自由基起引發(fā)作用。Liu等對比在管外壁上(圖2),通過(guò)測量沿程管壁溫度分布了硝基丙烷、三乙胺、3,6,9-三甲基-1,4,7-過(guò)來(lái)計算散熱損失及燃料吸熱量,流體溫度及壁面溫氧化丙酮的引發(fā)作用,發(fā)現硝基丙烷效果最好,文度測量誤差分別為士2K和士3Kreactorfilter syringe pumpflow meter:Othermocouplespump====二〓二二圖1一段加熱裂解系統Fig 1 On壓力由被壓閥調節,為保證在一致實(shí)驗條件下烷(NP)為引發(fā)劑,引發(fā)劑含量為體積分數比較引發(fā)裂解與熱裂解的換熱,燃料分別由兩個(gè)平0.6%,實(shí)驗壓力為3MPa流泵供給。加熱后的燃料冷卻后經(jīng)采樣系統收集,將氣相和液相產(chǎn)物分離,產(chǎn)物由GCMs( Agilent2傳熱及產(chǎn)物分析7890A-5975C)進(jìn)行分析。實(shí)驗以航空燃料RP32.1傳熱分析為介質(zhì),流量0.73g·s-1,由 Micro motion elite本實(shí)驗通過(guò)測量沿管長(cháng)的外壁面一維溫度分CMF010測量流量(測量誤差為士0.1%),硝基丙布,經(jīng)過(guò)計算獲得不同加熱條件下流體溫度和管內化工學(xué)報第65卷1050mmo exper1000mmo theor50mm2蘭z蘭圖2實(shí)驗段參數及控制體Fig 2 Flow reactor schematic and control volume for tube300400500600700800對流傳熱系數沿管長(cháng)的一維分布temperature/K2.1.1熱通量計算實(shí)驗中采用圓管電加熱方式,圖4氮氣熱沉實(shí)驗值與理論值的比較可認為是全周均勻加熱。工質(zhì)加熱功率為電功率與Fig 4 Heat sink of N2 with fuel temperature at散熱功率之差。散熱功率與管外壁的溫度有關(guān),可atmospheric pressure通過(guò)空加熱實(shí)驗標定,見(jiàn)圖3。假定管壁均布n個(gè)熱電偶,每個(gè)熱電偶實(shí)測溫度代表其所處的一小段式中,k為管壁的熱導率,q為2.1.1節中算得到管壁的平均溫度,則穩態(tài)時(shí)該段管壁對應的流體加的加熱熱通量,A為管內壁換熱面積,S為管壁橫截面面積,L為管長(cháng)。方程的定解條件為:r=r,熱熱通量可表示為t=t,d/d,=0。根據測量的外壁溫和加熱功率,采用 Matlab ode45算法求解,即可獲得與每個(gè)熱式中U和Ⅰ對應實(shí)驗段兩端的電壓和電流,L為電偶測點(diǎn)對應的內壁溫實(shí)驗段長(cháng)度,d和d對應管外徑和內徑,q為管2.1.3,沿管長(cháng)流體溫度計算碳氫燃料在裂解前,外壁的散熱熱通量。認為其熱沉與壓力和溫度有關(guān),實(shí)驗中系統壓力保持不變,因此燃料熱沉只與流體溫度有關(guān)。通過(guò)實(shí)驗獲得流體溫度與熱沉的關(guān)系,即可計算流體溫度沿管長(cháng)分布。采用 Jiang等的實(shí)驗方法對管內流體溫度進(jìn)行測量,計算得到的流體溫度與測量值最大誤差為士4K。2.1.4對流傳熱系數測量計算本文通過(guò)實(shí)驗測量參數來(lái)計算管內對流傳熱的傳熱系數。通過(guò)已獲20得的內壁溫分布和流體溫度分布,在已知熱通量的8001000條件下即可通過(guò)式(3)計算傳熱系數的沿程分布temperature/K由誤差分析可知,傳熱系數最大誤差為6.52%。圖3散熱熱通量隨壁面溫度的變化q(3)Fig 3 Heat loss with surface temperature of tube2.2產(chǎn)物分析為確定實(shí)驗精度,實(shí)驗前加熱流量1g·s-的燃料裂解后,經(jīng)冷凝器冷卻后,完成氣液分純凈氮氣(9.99%),結果如圖4所示,實(shí)驗值離,液態(tài)成分進(jìn)入集液器收集;氣態(tài)組分經(jīng)氣體轉與理論值誤差小于3%。子流量計測量氣體體積流量,同時(shí)利用氣袋對其進(jìn)2.1.2內壁面溫度計算采用全周電加熱,假設行收集,后經(jīng)氣相色譜儀進(jìn)行分析;由于燃料成分沿管長(cháng)加熱功率分布均勻,忽略軸向導熱,管壁可復雜,裂解后的液態(tài)收集后只進(jìn)行質(zhì)量測量,用以以按照具有均勻內熱源的一維穩態(tài)導熱問(wèn)題進(jìn)行處計算燃料產(chǎn)氣率來(lái)評價(jià)燃料的裂解程度理,控制方程為在經(jīng)以上分析后可得:氣體體積流量V,氣體+}+是(出)+數=0(2)成分(g、B、g等)及對應摩爾(體積)分數(f、f、f。等);液體質(zhì)量流量m,燃料產(chǎn)氣率第S1期賈貞健等:碳氫燃料熱裂解與引發(fā)裂解換熱對比實(shí)驗41的計算式為1401833.5WZ=-m×100%(4)a1978.W=(Mf。+Mf+Mfe+…)V/2.24(5)式中m為氣態(tài)組分質(zhì)量;m為液態(tài)組分質(zhì)量;M為氣體g。的分子量。3結果與討論00·0母8如圖5所示,有引發(fā)劑的燃料與不含引發(fā)劑的燃料相比,在40cm以后降低了壁面溫度,降低效position/cm果可達10K以上,沿管程,其降低壁面溫度的能力呈現先上升后下降的趨勢。在不同熱通量條件圖6不同加熱功率下熱裂解與引發(fā)裂解流體溫度之差下,降低壁面溫度的趨勢是一致的,但由于熱通量Fig 6 Fuel temperature difference between thermalcracking and initiated cracking不同時(shí),會(huì )導致裂解及引發(fā)裂解反應強度,致使吸熱能力有所不同,因而降低壁面溫度的程度方面會(huì )有區別?？赏茰y在這兩種加熱功率時(shí),引發(fā)裂解大O RP-3RP-3+NP約發(fā)生在40cm位置處。o1833.5Wa1979.IW圖7加熱功率1833.5W傳熱系數比較0Fig 7 Comparison of heat transfer coefficients of twoposition/cmtypes of cracking at heating power of 1833. 5 W圖5不同加熱功率下熱裂解與引發(fā)裂解外壁面溫度之差熱系數。由于裂解的增強,生成的氫氣、C~cracking and initiated cracking的烴類(lèi)一般處于亞臨界狀態(tài),此類(lèi)氣體的存在對換熱不利,因此引發(fā)裂解對換熱影響是受裂解增強程圖6為沿管程流體溫度的差值,引發(fā)劑存在度與物性影響的。時(shí),在40~100cm范圍內,流體溫度明顯降低,由于裂解反應為吸熱反應,引發(fā)劑增強裂解后最高可達14K。引發(fā)劑的存在使燃料在較低溫度會(huì )提高燃料的化學(xué)吸熱能力,圖8為燃料的總熱沉具有與不存在引發(fā)劑時(shí)相同的熱沉能力。同樣,隨流體溫度變化比較。由圖中可看出,引發(fā)裂解在在流動(dòng)反應器中,其提高熱沉的能力存在極值,800~900K溫度范圍內提高了燃料的熱沉,約在當反應達到一定程度后,引發(fā)劑的作用效果不再850K時(shí)引發(fā)劑的影響最為明顯?？芍?在文中實(shí)明顯。驗條件下,引發(fā)劑NP在800K后開(kāi)始促進(jìn)RP3在發(fā)動(dòng)機冷卻通道中,提高對流傳熱系數是降的裂解,其作用效果會(huì )隨流體溫度的提高呈先上升低壁面溫度的有效手段之一17。引發(fā)劑可在一定后下降的趨勢,最終趨于0范圍內提高燃料的熱沉能力,圖7顯示了引發(fā)裂解為測定引發(fā)劑對熱裂解的影響,對燃料裂解程對傳熱的影響。比較40~100cm范圍內的傳熱系度進(jìn)行了分析。由圖9可知,引發(fā)劑NP將RP3數可知,引發(fā)裂解不能顯著(zhù)提高燃料的對流傳熱系裂解起始溫度大約提高了50K。而在800K前,數,相反,在一定范圍內,引發(fā)裂解反而降低了傳由于裂解緩慢,裂解度較低,燃料熱沉能力并不能·142·化工學(xué)報第65卷o RP-3O RP-32.6RP-3+NPa RP-3+NI65070075080085090095060圖8燃料熱沉比較圖10 Reynolds數比較Fig 8 Total heat sink with fuel temperatureFig. 10 Reynolds number along tube atheating power of 1833. 5 wO RP-3e RP-3+NP4結論通過(guò)流動(dòng)反應器對熱裂解及引發(fā)裂解進(jìn)行了對比實(shí)驗研究,通過(guò)測量壁面溫度分布、燃料熱沉及裂解產(chǎn)物,分析了引發(fā)裂解對燃料吸熱能力及換熱性能的影響。結果表明:(1)硝基丙烷(NP)裂解生成的丙基自由基850促進(jìn)了航空燃料RP-3裂解,同時(shí)降低了RP3裂temperature/K解起始溫度約50K;(2)燃料吸熱能力及裂解率測量結果顯示,在圖9產(chǎn)氣率比較Fig 9 Yield of gas with fuel temperature800~900K溫度范圍內,引發(fā)劑促進(jìn)作用明顯,提高了燃料熱沉及裂解速率;顯著(zhù)提高。850K左右時(shí),NP裂解加快,自由基(3)同熱通量條件下,吸熱能力的增強可降低的增加顯著(zhù)提高了燃料的裂解速率,隨著(zhù)溫度升流體溫度及壁面溫度,降低程度呈先上升后下降的高,熱裂解程度提高,引發(fā)效果會(huì )隨溫度提高而降趨勢,降低程度最高可達10K以上;低,在出口溫度達到910K后,引發(fā)效果幾乎(4)裂解生成大量氣體,降低了燃料流動(dòng)消失。Reynolds數,對對流換熱不利,綜合裂解吸熱對RP3組分十分復雜,為便于燃料物性的計算,換熱的促進(jìn)作用,裂解的增強對對流換熱不是一直釆用 Zhong等3發(fā)展的10組分替代燃料,裂解后起提高作用組分則假設液相無(wú)變化,采用 Chung等的方法References計算燃料黏度,基于SRK方法計算燃料密度[9201由于裂解后生成大量氣體,氣體黏度隨溫度升高而1] Wagner W R, Shoji J M. 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