納米流體強化傳熱機理及數(shù)學(xué)模型的研究
發(fā)布時間：2018-07-17 07:58
【摘要】：納米流體是將納米顆粒添加到基礎(chǔ)液體中形成穩(wěn)定懸浮的多相系統(tǒng)。由于納米流體在粘度、比熱容、導(dǎo)熱率、換熱能力等性能方面都顯著區(qū)別于傳統(tǒng)傳熱工質(zhì),可以作為更高效的傳熱和冷卻介質(zhì)。對于提高汽車發(fā)動機發(fā)動機傳熱效率、改善排放及降低油耗,促進冷卻系統(tǒng)向緊湊化、輕型化、高效化發(fā)展。本文圍繞納米MgO粉體的制備實驗、納米流體的制備與分散劑的選擇實驗、納米MgO在丙二醇中分散于穩(wěn)定性的研究、納米流體運輸參數(shù)的研究、納米流體傳熱性能及納米流體數(shù)學(xué)模型的研究幾方面內(nèi)容,研究MgO/丙二醇納米流體懸浮液的穩(wěn)定性,探討流體強化傳熱機理。主要工作如下:1、納米MgO粉體制備實驗用不同的液相化學(xué)法制備MgO納米粉體,熟悉制備流程,掌握制備技術(shù)。2、納米流體的制備及分散劑選擇實驗通過直接將MgO納米粉體與丙二醇直接混合的“兩步法”制備MgO/丙二醇納米流體;采用超聲振動、機械攪拌等方法及沉降試驗優(yōu)化選擇出能使MgO/丙二醇納米流體穩(wěn)定懸浮的分散劑。3、納米MgO在丙二醇中穩(wěn)定性研究通過球磨改性的方法,用偶聯(lián)劑改性納米MgO,增加懸浮液分散穩(wěn)定性;并且實驗分析了超聲振動、機械攪拌、分散劑等因素對納米流體的影響,納米MgO在丙二醇中的最佳分散工藝。從顆粒沉降與擴散運動的角度對納米流體穩(wěn)定性機理進行理論分析,得出結(jié)論,要想使納米顆粒在基液中長期穩(wěn)定,就必須使納米顆粒具有較小的表面能和較大的擴散速率并且納米顆粒間位能的高低對納米流體的穩(wěn)定有重要影響,總位能越低,納米流體越穩(wěn)定。4、納米流體運輸參數(shù)研究研制了用電流量法測定流體比熱容的裝置,測量了不同溫度下不同濃度的MgO/丙二醇納米流體的比熱容,發(fā)現(xiàn)流體比熱容隨溫度變化的增益特性。采用NDJ-8S型數(shù)顯粘度計測量了MgO/丙二醇納米流體的粘度,實驗結(jié)果表明,顆粒的份額、基液屬性、溫度和懸浮液的穩(wěn)定性對納米流體的粘度有重要影響。5、納米流體傳熱特性研究測定不同丙二醇基納米流體的自然對流換熱系數(shù),并設(shè)計組裝可用于測量納米流體導(dǎo)熱系數(shù)的瞬態(tài)熱絲法測量裝置,測量不同納米流體的導(dǎo)熱系數(shù),并結(jié)合實驗結(jié)果探討納米流體強化傳熱的特異性及規(guī)律。6、納米流體數(shù)學(xué)模型研究通過對納米顆粒引入分形維數(shù)的概念,并分析納米顆粒微觀結(jié)構(gòu),對傳統(tǒng)的H-C模型進行修正,推導(dǎo)出一種預(yù)測低濃度納米流體導(dǎo)熱系數(shù)的導(dǎo)熱模型。通過研究溫度和濃度對粘度的影響,推導(dǎo)出了關(guān)于溫度和濃度因素的粘度計算模型。
[Abstract]:Nano-fluid is a multi-phase system in which nanoparticles are added to the base liquid to form a stable suspension. Because the properties of nano-fluid in viscosity, specific heat capacity, thermal conductivity and heat transfer ability are obviously different from the traditional heat transfer working medium, it can be used as a more efficient heat transfer and cooling medium. It can improve the heat transfer efficiency of automobile engine, improve the emission and reduce the fuel consumption, and promote the development of the cooling system towards compact, light and high efficiency. This paper focuses on the preparation of nano-MgO powders, the preparation of nano-fluids and the selection of dispersant, the stability of nano-MgO dispersion in propylene glycol, the transport parameters of nano-fluids. The heat transfer performance of nano-fluid and the mathematical model of nano-fluid are studied in this paper. The stability of MgO / propylene glycol nano-fluid suspension is studied and the mechanism of fluid heat transfer enhancement is discussed. The main work is as follows: 1. The preparation of nano-MgO powders was conducted by different liquid-phase chemical methods. They were familiar with the preparation process. Master preparation technology .2.The preparation and dispersant selection experiment of nano-fluids prepared by "two-step method" directly mixing MgO nano-powder with propylene glycol; Ultrasonic vibration, The dispersant. 3, which can make MgO / propylene glycol nano-fluid suspension stably, was optimized by mechanical agitation and sedimentation test. The stability of nano-MgO in propylene glycol was studied by ball milling method. The effects of ultrasonic vibration, mechanical stirring, dispersant and other factors on nano-MgO were analyzed, and the optimum dispersion process of nano-MgO in propylene glycol was analyzed. From the angle of particle sedimentation and diffusion movement, the stability mechanism of nano-fluid is theoretically analyzed, and the conclusion is drawn that in order to make the nanoparticles stable in the base solution for a long time, The surface energy and diffusion rate of nanoparticles must be small, and the potential energy between nanoparticles has an important effect on the stability of nano-fluids, and the total potential energy is lower. The more stable the nanoscale fluid is, the more stable the nanometer fluid transport parameter is. The specific heat capacity of the MgO / propylene glycol nanoscale fluid at different temperature is measured by electric flow method, and the specific heat capacity of MgO / propylene glycol nanoscale fluid at different temperature is measured. The gain characteristics of the specific heat capacity of the fluid with the change of temperature are found. The viscosity of MgO / propylene glycol nanofluids was measured by NDJ-8S digital display viscometer. The temperature and the stability of suspensions have an important influence on the viscosity of nano-fluids. The heat transfer characteristics of nano-fluids are studied and the natural convection heat transfer coefficients of different propylene glycol groups are measured. A transient hot-wire measuring device was designed and assembled to measure the thermal conductivity of nanoscale fluids, which can be used to measure the thermal conductivity of different nanoscale fluids. Combining with the experimental results, the specificity and regularity of heat transfer enhancement of nano-fluid are discussed. The mathematical model of nano-fluid is studied by introducing the concept of fractal dimension to nanoparticles, and analyzing the microstructure of nano-particles, and modifying the traditional H-C model. A thermal conductivity model for predicting the thermal conductivity of low concentration nanoscale fluids is derived. By studying the influence of temperature and concentration on viscosity, the viscosity calculation model of temperature and concentration factors is derived.
【學(xué)位授予單位】：青海大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB383.1
本文編號：2129697
[Abstract]:Nano-fluid is a multi-phase system in which nanoparticles are added to the base liquid to form a stable suspension. Because the properties of nano-fluid in viscosity, specific heat capacity, thermal conductivity and heat transfer ability are obviously different from the traditional heat transfer working medium, it can be used as a more efficient heat transfer and cooling medium. It can improve the heat transfer efficiency of automobile engine, improve the emission and reduce the fuel consumption, and promote the development of the cooling system towards compact, light and high efficiency. This paper focuses on the preparation of nano-MgO powders, the preparation of nano-fluids and the selection of dispersant, the stability of nano-MgO dispersion in propylene glycol, the transport parameters of nano-fluids. The heat transfer performance of nano-fluid and the mathematical model of nano-fluid are studied in this paper. The stability of MgO / propylene glycol nano-fluid suspension is studied and the mechanism of fluid heat transfer enhancement is discussed. The main work is as follows: 1. The preparation of nano-MgO powders was conducted by different liquid-phase chemical methods. They were familiar with the preparation process. Master preparation technology .2.The preparation and dispersant selection experiment of nano-fluids prepared by "two-step method" directly mixing MgO nano-powder with propylene glycol; Ultrasonic vibration, The dispersant. 3, which can make MgO / propylene glycol nano-fluid suspension stably, was optimized by mechanical agitation and sedimentation test. The stability of nano-MgO in propylene glycol was studied by ball milling method. The effects of ultrasonic vibration, mechanical stirring, dispersant and other factors on nano-MgO were analyzed, and the optimum dispersion process of nano-MgO in propylene glycol was analyzed. From the angle of particle sedimentation and diffusion movement, the stability mechanism of nano-fluid is theoretically analyzed, and the conclusion is drawn that in order to make the nanoparticles stable in the base solution for a long time, The surface energy and diffusion rate of nanoparticles must be small, and the potential energy between nanoparticles has an important effect on the stability of nano-fluids, and the total potential energy is lower. The more stable the nanoscale fluid is, the more stable the nanometer fluid transport parameter is. The specific heat capacity of the MgO / propylene glycol nanoscale fluid at different temperature is measured by electric flow method, and the specific heat capacity of MgO / propylene glycol nanoscale fluid at different temperature is measured. The gain characteristics of the specific heat capacity of the fluid with the change of temperature are found. The viscosity of MgO / propylene glycol nanofluids was measured by NDJ-8S digital display viscometer. The temperature and the stability of suspensions have an important influence on the viscosity of nano-fluids. The heat transfer characteristics of nano-fluids are studied and the natural convection heat transfer coefficients of different propylene glycol groups are measured. A transient hot-wire measuring device was designed and assembled to measure the thermal conductivity of nanoscale fluids, which can be used to measure the thermal conductivity of different nanoscale fluids. Combining with the experimental results, the specificity and regularity of heat transfer enhancement of nano-fluid are discussed. The mathematical model of nano-fluid is studied by introducing the concept of fractal dimension to nanoparticles, and analyzing the microstructure of nano-particles, and modifying the traditional H-C model. A thermal conductivity model for predicting the thermal conductivity of low concentration nanoscale fluids is derived. By studying the influence of temperature and concentration on viscosity, the viscosity calculation model of temperature and concentration factors is derived.
【學(xué)位授予單位】：青海大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB383.1
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