本文關(guān)鍵詞：蒸汽在高分壓不凝氣體中擴(kuò)散流動(dòng)的傳質(zhì)研究　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 擴(kuò)散栓塞區(qū) 壓力峰 凝結(jié)換熱 紅外光譜 不凝氣體

【摘要】：本研究基于973項(xiàng)目"鋼鐵生產(chǎn)過(guò)程高效節(jié)能基礎(chǔ)研究"子課題"生產(chǎn)過(guò)程的能量轉(zhuǎn)化與優(yōu)化配置方法"。主要針對(duì)中低溫余熱回收設(shè)備中的熱管換熱器進(jìn)行蒸汽凝結(jié)換熱的研究。文獻(xiàn)研究表明,熱管中混入少量不凝氣體就會(huì)對(duì)裝置換熱效果造成巨大抑制。在使用前需要進(jìn)行抽真空操作,而抽真空耗能耗時(shí),特別是大型熱管換熱裝置,且抽真空后管內(nèi)仍會(huì)殘留少量不凝氣體影響換熱。本文設(shè)計(jì)開(kāi)發(fā)一種不抽真空的重力回路熱虹吸管,有效解決不凝氣體對(duì)換熱設(shè)備帶來(lái)凝結(jié)換熱的抑制。相比傳統(tǒng)回路熱管,不抽真空的重力回路熱虹吸管無(wú)需管芯材料,工作液依靠重力在系統(tǒng)內(nèi)自循環(huán),僅在冷凝管末端增加氣液分離器,將不凝氣體引入氣液分離器,可大幅降低不凝氣體在冷凝管中對(duì)蒸汽凝結(jié)傳熱的抑制。同時(shí),氣液分離器限制了不凝氣體在回路系統(tǒng)內(nèi)循環(huán)流動(dòng),避免不凝氣體對(duì)蒸發(fā)器和冷凝器換熱造成循環(huán)影響。研究發(fā)現(xiàn),不抽真空重力回路熱虹吸管內(nèi)存在大量不凝氣體時(shí),蒸汽在高分壓不凝氣體中形成混合傳熱傳質(zhì)區(qū)域,我們將此區(qū)域定義為擴(kuò)散栓塞區(qū)。在擴(kuò)散栓塞區(qū)不凝氣體阻礙蒸汽流動(dòng),蒸汽通過(guò)流動(dòng)+擴(kuò)散的方式到達(dá)液膜表面凝結(jié)換熱,同時(shí)不凝氣體逆蒸汽流動(dòng)方向發(fā)生逆向擴(kuò)散并達(dá)到局部區(qū)域的動(dòng)態(tài)平衡。實(shí)驗(yàn)研究了重力回路熱虹吸管內(nèi)不凝氣體對(duì)系統(tǒng)啟動(dòng)過(guò)程的影響發(fā)現(xiàn),不凝氣體含量、系統(tǒng)充液率、蒸發(fā)器熱負(fù)荷以及氣液分離器安裝位置均會(huì)對(duì)系統(tǒng)啟動(dòng)時(shí)間、運(yùn)行壓力及蒸發(fā)器和冷凝器溫度造成影響。研究表明:1)重力回路熱虹吸管啟動(dòng)過(guò)程蒸汽與不凝氣體在蒸汽管中形成擴(kuò)散栓塞區(qū),蒸汽推動(dòng)擴(kuò)散栓塞區(qū),并壓縮不凝氣體進(jìn)入冷凝管及末端的氣液分離器,當(dāng)擴(kuò)散栓塞區(qū)進(jìn)入冷凝管后,系統(tǒng)壓力迅速降低,形成啟動(dòng)過(guò)程"壓力峰"現(xiàn)象;2)系統(tǒng)充液率越高,啟動(dòng)過(guò)程壓力越大,啟動(dòng)時(shí)間越長(zhǎng);蒸發(fā)器熱負(fù)荷越大啟動(dòng)時(shí)間越短;不凝氣體含量越高,啟動(dòng)時(shí)間越長(zhǎng);3)氣液分離器內(nèi)有效初始?xì)庀嗳莘e越大,回路熱虹吸管啟動(dòng)越容易。不抽真空重力回路熱虹吸管進(jìn)入動(dòng)態(tài)平衡工作階段后,大量不凝氣體聚集在氣液分離器內(nèi)并逆蒸汽流動(dòng)方向,向冷凝管逆向擴(kuò)散,與蒸汽形成擴(kuò)散栓塞區(qū),影響冷凝管內(nèi)的凝結(jié)換熱。實(shí)驗(yàn)表明:1)不凝氣體提升系統(tǒng)運(yùn)行壓力及蒸發(fā)器的蒸發(fā)溫度,有利于提高局部凝結(jié)換熱量,但會(huì)影響整個(gè)換熱系統(tǒng)的換熱能力;2)擴(kuò)散栓塞區(qū)放大了由于蒸汽蒸發(fā)凝結(jié)自平衡引起的系統(tǒng)壓力震蕩,使冷凝管管壁溫度振幅增大,而擴(kuò)散栓塞區(qū)的震蕩可以提升局部的凝結(jié)換熱效率;3)擴(kuò)散栓塞區(qū)的存在大幅改變了冷凝管內(nèi)蒸汽的凝結(jié)分布,不凝氣體含量越大,蒸汽凝結(jié)越集中在冷凝管前段,70%充液率蒸發(fā)器熱負(fù)荷為3.0kW時(shí),不抽真空工況在冷凝管前段的平均熱流密度是抽真空工況的1.67倍,有效冷凝管長(zhǎng)度比抽真空工況短;4)系統(tǒng)內(nèi)添加含量為0.5-1wt%乙醇后,會(huì)促進(jìn)蒸汽的局部凝結(jié)換熱,降低不凝氣體對(duì)凝結(jié)換熱的影響,提升換熱器的換熱效率。為了檢測(cè)擴(kuò)散栓塞區(qū)內(nèi)不凝氣體的分布,我們?cè)O(shè)計(jì)了一套非接觸式紅外檢測(cè)平臺(tái),利用水蒸氣和不凝氣體(空氣)對(duì)紅外光譜中特定光譜吸收率的不同,測(cè)量水蒸氣在石英玻璃冷凝管中的分布,得到了冷凝管內(nèi)擴(kuò)散栓塞區(qū)的分布位置及擴(kuò)散栓塞區(qū)內(nèi)組分濃度分布。最后基于組分輸運(yùn)方程建立了擴(kuò)散栓塞區(qū)內(nèi)蒸汽與不凝氣體的流動(dòng)擴(kuò)散模型,使用Maxwell-Stefan組分?jǐn)U散代替組分輸運(yùn)方程中的Fick定律擴(kuò)散項(xiàng),并數(shù)值計(jì)算得到模型在某些工況下的近似解。將擴(kuò)散栓塞區(qū)模型計(jì)算得到的數(shù)值解與實(shí)驗(yàn)數(shù)據(jù)相比較,發(fā)現(xiàn)模型能準(zhǔn)確描述出冷凝管內(nèi)蒸汽及NCG的擴(kuò)散流動(dòng)規(guī)律。
[Abstract]:This study is based on the 973 project "steel production of" energy efficient process based sub project "of the production process of energy conversion and optimal allocation method. Mainly for low temperature waste heat recovery equipment in heat pipe steam condensation heat transfer heat exchanger. Literature research shows that heat pipe mixed with a small amount of non condensable gas will change the effect of heat on the device caused great inhibition. Before use to operate the vacuum, vacuum pumping and energy consumption and time-consuming especially for large heat pipe heat exchanger, and the vacuum tube will remain a small amount of non condensable gases affect heat transfer. This paper designs a vacuum gravity loop thermosyphon Straw and effectively solve the non condensable gas on heat exchangers bring condensation heat transfer is inhibited by. Compared with the traditional gravity loop heat pipe, loop thermosyphon Straw without vacuum without tube core material, working fluid by gravity self circulation within the system, only in the cold The condensate tube end to increase gas-liquid separator, the non condensable gas into a gas-liquid separator, which can greatly reduce the non condensable gas in the pipe to inhibit condensation of steam condensation heat transfer. At the same time, the gas-liquid separator limits the gas circulation in the loop system, avoid non condensable gas on the evaporator and condenser heat transfer caused by circulation influence. Found that without vacuum gravity loop thermosyphon Straw in the existence of a large number of non condensable gas, steam to form mixed heat and mass transfer area in the high pressure gas in this area, we will define the diffusion zone. The steam flow in the embolism hinder the diffusion of non condensable gas embolism zone, steam flow through the way to the film surface diffusion + condensation heat transfer, dynamic balance and non condensable gas steam flow direction inverse reverse diffusion and reach the local area. Experimental study of the gravity loop thermosyphon Straw in non condensable gas on system startup That process, gas content, system filling rate, the evaporator heat load and a gas-liquid separator installation position will affect the system startup time, operating pressure and temperature of the evaporator and the condenser. The results show that: 1) gravity loop thermosyphon Straw starting process steam and non condensable gas in the steam pipe in the form of diffusion embolism steam diffusion zone, the embolization area, a gas-liquid separator and compressed non condensable gases into condensing tube and at the end, when the spread of embolism area into the condenser tube, quickly reduce the system pressure, the formation of starting process of "pressure peak" phenomenon; 2) system liquid filling rate is high, start-up pressure is, the longer the start the greater the heat load of evaporator; start time is short; the non condensable gas content is high, the start time is longer; 3) in the gas-liquid separator effective initial gas phase volume bigger, loop thermosyphon Straw start more easily without vacuum gravity. The loop thermosyphon Straw into dynamic equilibrium stage, a large number of non condensable gas accumulation in the gas-liquid separator and inverse steam flow direction, the reverse diffusion to the condenser tube, forming the diffusion area and the effect of embolization steam condensing tube condensation heat transfer. The experimental results show that: 1) the non condensable gas extraction temperature and evaporator operating pressure evaporation system, is conducive to the improvement of local condensing heat transfer, but will influence the heat transfer capacity of heat exchanger system; 2) diffusion area enlarged embolism due to steam condensate system since the pressure balance caused by the shock, the condensing tube wall temperature amplitude increases and the diffusion area of the shock can enhance the embolization of the condensation heat transfer efficiency of the local 3); diffusion embolism zone exists significantly changed the condensing tube steam condensate distribution, gas content is bigger, more concentrated in front of steam condensation condensation tube, filling rate 70% evaporator heat load of 3.0kW, The average heat flux without vacuum conditions in front of the condenser pipe is 1.67 times of the vacuum conditions, effective condensation tube length than the vacuum condition is short; 4) within the system to add content of 0.5-1wt% ethanol, will promote the local heat transfer of steam condensation, reduce the impact of non condensible gas, improve thermal efficiency heat exchanger. In order to detect distribution of diffusion gas embolism in the District, we designed a non-contact infrared detection platform, the use of water vapor and non condensable gas (air) to specific infrared spectra, absorption rate, water vapor distribution measurement in quartz glass condensing tube, get the distribution and diffusion zone in condensation pipe embolism embolism diffusion area within the component concentration distribution. Finally based on component transport equations of the diffusion zone embolism steam and incondensable gas flow diffusion model, using the Maxwell-Stefan component expansion Instead of scattered component lose Fick transport equation in law of diffusion, and the numerical calculation of the approximate solution is obtained under some conditions. The model solutions are compared with experimental data of numerical diffusion model to calculate the embolization area, found that the model can accurately describe the diffusion of steam and NCG tube condensation flow patterns.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TK124

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本文編號(hào)：1382433