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  本文關(guān)鍵詞：導線絕緣層在弱浮力環(huán)境下著火早期演變特性的研究　出處：《中國科學院研究生院(工程熱物理研究所)》2016年博士論文　論文類型：學位論文

  更多相關(guān)文章： 微重力 弱浮力 導線絕緣層 著火早期演變特性 火災(zāi)監(jiān)測

【摘要】：為保障載人航天器的防火安全,應(yīng)探索微重力下火災(zāi)發(fā)生的早期演變機理。但地面微重力實驗時間短,同時空間搭載實驗費用昂貴,所以非常需要在地面開展微重力實驗?zāi)M研究�；谌醺×Νh(huán)境模擬微重力效應(yīng)的思路,本文開展了弱浮力下載人航天器中典型非金屬材料導線絕緣層著火早期演變特性的研究�；诟鞣N微重力燃燒的地面實驗?zāi)M方法,系統(tǒng)研究了弱浮力下過載電流時導線絕緣層的著火早期演變特性,具體包括溫升特性、煙氣輸運特性以及產(chǎn)物煙黑的分布特性,并相應(yīng)地預測了微重力下導線絕緣層著火早期的演變機理。全文主要研究內(nèi)容如下：首先,在第2章系統(tǒng)總結(jié)了微重力燃燒的地面實驗?zāi)M方法,詳細介紹了低壓法和窄通道法的模擬原理、有效性及其不足；并提出改進,尤其在窄通道法基礎(chǔ)上提出了低壓窄通道法,給出其具體原理,并指出了該方法在研究熱厚材料著火早期演變特性方面的優(yōu)勢。此后,分三章逐步介紹過載電流下絕緣層的著火早期演變特性。第3章,首先建立了絕緣層著火早期溫升特性的簡化物理模型,并基于模型得到絕緣層溫升曲線的理論解,進而分析了弱浮力對其影響機理。此后,利用低壓法研究了壓力、氧氣濃度、環(huán)境組分、電流大小、絕緣層種類和厚度等因素對絕緣層著火早期溫升特性的影響。結(jié)果表明,隨著壓力的降低,絕緣層的溫升率、平衡溫度逐步增大,達到平衡溫度的時間逐步減小,從而證明低壓法有效地抑制了浮力對流,使得自然對流散熱被明顯削弱。接著利用窄通道法研究了通道高度、壁面種類等因素對絕緣層著火早期溫升特性的影響。結(jié)果表明,隨著通道高度的降低,絕緣層的溫升率、平衡溫度逐步增大,達到平衡溫度的時間逐步減小,從而證明窄通道法也可有效地抑制浮力對流,使得自然對流散熱被明顯削弱。另外,結(jié)果表明,應(yīng)選擇壁面蓄熱能力弱、壁面導熱系數(shù)小的材料來減少窄通道的壁面熱損失；并且水平放置的窄通道抑制浮力對流的效果要優(yōu)于垂直放置的。最后,驗證了低壓窄通道法模擬微重力下絕緣層著火早期溫升特性的有效性,并指出其適用范圍。第4章,首先建立了絕緣層煙氣微團析出的簡化物理模型,并基于模型揭示了煙氣微團運動軌跡和煙氣噴射角的變化規(guī)律,指出壓力對煙氣微團輸運特性的影響機理,并預測了微重力下的結(jié)果。然后,利用低壓法研究了壓力、環(huán)境組分、氧氣濃度、電流大小、絕緣層種類和厚度等因素對絕緣層著火早期煙氣輸運特性的影響。結(jié)果表明,在純氮氣環(huán)境下,壓力越低,絕緣層破損模式依次為熱膨脹模式、煙氣噴射模式、鼓泡模式,其熱降解程度越來越劇烈,絕緣層相應(yīng)的析出煙氣時間或起泡時間減小,煙氣噴射角增大,表明壓力有效削弱了浮力對流作用。而在空氣組分和純氧氣環(huán)境下,隨著壓力的降低,由于氧氣含量的減少,絕緣層氧化分解程度降低,絕緣層析出煙氣的時間增大,此外煙氣噴射角隨著壓力降低逐步增大,這再次表明壓力有效削弱了浮力對流作用。此外,降低氮氣稀釋劑含量可以增加絕緣層的氧化分解速度,表明只降低氮氣含量的低壓環(huán)境可以克服低壓法抑制化學反應(yīng)速率的不足。隨著過載電流的增加,絕緣層析出煙氣的時間縮短,煙氣量明顯增加,所以為了預防火災(zāi)需要有效監(jiān)視用電設(shè)備的工作電流大小。最后,研究表明絕緣層種類對于絕緣層的煙氣輸運特性影響大,應(yīng)優(yōu)先選用熱穩(wěn)定性良好的材料作為絕緣層。接著利用窄通道法研究了通道高度、通道放置方式對絕緣層著火早期煙氣輸運特性的影響。結(jié)果表明,隨著窄通道高度的降低,通道內(nèi)部絕緣層煙氣的輸運特性明顯不同,依次呈現(xiàn)：發(fā)散型、聚散型和聚附型；且當窄通道通道高度在10mm-15mm時,煙氣的自然對流流動過程被有效地抑制,與微重力下絕緣層煙氣輸運過程相似。進一步,相比垂直放置方式,水平放置的窄通道可更有效地抑制浮力對流,得到類似微重力下的煙氣輸運特性。最后,采用低壓窄通道法研究了絕緣層的煙氣輸運特性。結(jié)果表明,低壓窄通道法在10mm-21.4mm通道高度內(nèi),能夠獲得近似微重力下的煙氣輸運特性。第5章,首先闡述激光衰減法測量煙黑濃度的原理,并闡述了煙黑濃度數(shù)據(jù)反演算法和降噪原理,并基于此編寫了一套煙黑濃度Matlab計算程序。此后,搭建了全場煙黑濃度測量的實驗系統(tǒng),并驗證了該實驗系統(tǒng)和數(shù)據(jù)處理方法的有效性。接著,研究了環(huán)境組分、壓力、氮氣稀釋劑對絕緣層著火早期煙黑分布特性的影響。結(jié)果表明,在空氣組分下,隨著壓力降低,絕緣層著火早期的煙黑濃度先降低,此后又逐漸增大。而在相同壓力時,純氧環(huán)境工況,絕緣層著火早期生成的煙黑最多,說明氧氣含量增加會促進絕緣層的分解,釋放出更多煙黑,這表明可用低壓富氧環(huán)境來預測微重力下的結(jié)果。另外,若在氧氣含量一定時,隨著氮氣稀釋劑含量的降低,絕緣層析出的煙黑濃度逐步增加,因此只降低稀釋劑含量建立的弱浮力環(huán)境,可更好地預測微重力下的結(jié)果。此外,無論何種環(huán)境組分,隨著壓力降低,由于浮力對流被逐步抑制,使得水平方向上絕緣層的煙黑擴散更遠,而垂直方向上絕緣層的煙黑分布更加均勻,逐步接近微重力下的煙黑分布狀況。最后,利用場發(fā)射掃描電鏡分析了典型工況下絕緣層生成的煙黑顆粒形態(tài)和粒徑。結(jié)果表明,隨著壓力的降低,絕緣層的煙黑顆粒等效直徑逐漸增大,該趨勢與微重力下的結(jié)果一致�？傊�,通過本文的研究,獲得了弱浮力環(huán)境下過載電流時導線絕緣層著火早期的演變特性,預測了微重力下的變化趨勢,并基于著火早期演變特性的結(jié)果對微重力模擬方法提出了有效改進。本文工作將為今后微重力下材料防火性能的檢驗和著火早期的監(jiān)測,提供了堅實的理論依據(jù)和大量的基礎(chǔ)數(shù)據(jù)。
[Abstract]:In order to protect the fire safety of manned spacecraft, the early evolution mechanism of the fire in microgravity should be explored. However, the experiment time of ground microgravity is short and the space loading experiment is expensive, so it is very necessary to carry out the research of microgravity experiment on the ground. Based on the idea of simulating the microgravity effect in the weak buoyancy environment, the early evolution characteristics of the insulation layer of typical non-metallic conductor insulation in the buoyancy force download spacecraft are studied in this paper. The ground simulation method based on various experimental microgravity combustion, weak buoyancy under overload current when the ignition wire insulation layer of the early evolution characteristics of system were studied, including the temperature rise characteristics of flue gas, transport properties and distribution characteristics of the products and the corresponding soot, predicted under microgravity insulation fire early evolution mechanism. The main research contents are as follows: firstly, the second chapter summarizes the simulation method of ground microgravity combustion experiment, introduces the simulation principle, low voltage method and narrow channel approach is effective and its shortcomings; and put forward the improvement, particularly in the narrow channel law put forward low pressure narrow channel method, gives the specific principle. And pointed out that the method of fire early evolution characteristics of the advantages in the study of thick material. Since then, the characteristics of the early ignition evolution of the insulation layer under overload current are introduced in three chapters. The third chapter first establishes a simplified physical model of the temperature rise characteristics of the insulation layer at the early stage, and obtains the theoretical solution of the temperature rise curve of the insulation layer based on the model, and further analyzes the influence mechanism of the weak buoyancy on it. Since then, the influence of pressure, oxygen concentration, environmental components, current size, insulation layer type and thickness on the temperature rise characteristics of insulation layer has been studied by low pressure method. The results show that with the decrease of pressure, the temperature rise rate and equilibrium temperature of insulation layer gradually increase, and the time to reach equilibrium temperature decreases. This proves that the low pressure method effectively suppresses buoyancy convection and makes the natural convection heat dissipation obviously weakened. Then the narrow channel method was used to study the influence of the height of the channel and the type of the wall on the temperature rise of the insulating layer at the early stage of ignition. The results show that with the decrease of the height of the channel, the temperature rise rate and the equilibrium temperature of the insulation layer gradually increase, and the time to reach the equilibrium temperature decreases. This proves that the narrow channel method can also effectively restrain buoyancy convection, and the natural convection heat dissipation is obviously weakened. In addition, the results show that the wall heat loss of narrow channel should be chosen to reduce the wall heat loss of narrow channel, and the effect of buoyant convection is better than that of vertical placement. Finally, the validity of the low pressure narrow channel method to simulate the early temperature rise characteristics of the insulating layer under the microgravity is verified, and the scope of its application is pointed out. In the fourth chapter, first, a simplified physical model for the separation of flue gas microcluster in insulation layer is established. Based on the model, the variation rule of flue gas microcluster trajectory and flue gas injection angle is revealed, and the influence mechanism of pressure on the characteristics of flue gas microtransport is pointed out, and the results under microgravity are predicted. Then, the influence of pressure, environmental components, oxygen concentration, current size, type and thickness of insulation layer on the transport characteristics of flue gas at the early stage of ignition were studied by low pressure method. The results show that in pure nitrogen environment, the lower the pressure, damage to the insulation layer pattern followed by thermal expansion mode, gas injection mode, the bubble model, the thermal degradation degree is increasing, the insulating layer corresponding precipitation time of flue gas or foaming time decreases, flue gas injection angle increases, that pressure can reduce the buoyancy convection. In the composition of air and pure oxygen environment, as the pressure decreased due to the decrease of oxygen, reduce the degree of oxidative decomposition of insulating layer, the insulating layer of the flue gas precipitation time increases, in addition to flue gas injection angle as the pressure decreases gradually increased, it shows once again that the pressure effectively weakened the buoyancy convection. In addition, reducing the content of nitrogen diluent can increase the decomposition rate of insulating layer, indicating that the low pressure environment that only reduces nitrogen content can overcome the shortage of low pressure method to inhibit the chemical reaction rate. With the increase of overload current, the time of flue gas emission from insulation layer is shortened, and the amount of smoke is increased. Therefore, in order to prevent fire, it is necessary to effectively monitor the working current of electrical equipment. Finally, the study shows that the type of insulating layer has great influence on the gas transport characteristics of the insulating layer, and the material with good thermal stability should be chosen as the insulating layer. Then the narrow channel method was used to study the effect of channel height and channel placement on the gas transport characteristics at the early stage of ignition. The results show that with the decrease of the height of the narrow channel, the channel transport properties of internal insulation layer of flue gas is obviously different, which appears divergent, and type of type and poly; and when the narrow channel height in 10mm-15mm, natural convection flow process of flue gas is effectively suppressed, and the insulating layer of flue gas transport under microgravity a similar process. Further, the narrow channel placed horizontally can more effectively suppress the buoyancy convection and obtain the gas transport characteristics under microgravity compared with the vertical placement. Finally, the gas transport characteristics of the insulating layer are studied by the low pressure narrow channel method. The results show that the low pressure narrow channel method can obtain the gas transport characteristics under the approximate microgravity at the height of the 10mm-21.4mm channel. The fifth chapter first describes the principle of laser attenuation measurement of soot concentration, and expounds the soot concentration data inversion algorithm and the denoising principle, and based on this to prepare a set of soot concentration calculation program Matlab. Since then, the experimental system was built to measure the soot concentration field, and verifies the validity of the experimental system and data processing method. Then, the research of environmental components, pressure, nitrogen diluent on the insulation effect of ignition soot distribution characteristics of early
【學位授予單位】：中國科學院研究生院(工程熱物理研究所)
【學位級別】：博士
【學位授予年份】：2016
【分類號】：V445;V416.5
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本文編號：1339911