本文選題：吸收式制冷 + 數(shù)值模擬��； 參考：《長(zhǎng)安大學(xué)》2017年碩士論文

【摘要】：溴化鋰吸收式制冷機(jī)組具有節(jié)電、環(huán)境友好且可以利用生產(chǎn)余熱等優(yōu)勢(shì),近年來對(duì)溴化鋰吸收式制冷機(jī)組的性能研究十分廣泛。蒸發(fā)器作為溴化鋰吸收式制冷的制冷裝置,蒸發(fā)器的傳熱傳質(zhì)效率是影響溴化鋰吸收式制冷機(jī)組性能的重要因素之一。溴化鋰吸收式制冷機(jī)組內(nèi)的蒸發(fā)器形式為降膜式,在真空環(huán)境下,水溶液在水平管外降膜流動(dòng),包含氣液兩相流,流動(dòng)過程同時(shí)伴隨著復(fù)雜的傳熱傳質(zhì)現(xiàn)象。本文從研究水平管管外降膜蒸發(fā)流動(dòng)的傳熱傳質(zhì)角度出發(fā),主要對(duì)管外降膜蒸發(fā)換熱模型及換熱機(jī)理以及管外降膜蒸發(fā)換熱影響因素進(jìn)行了研究。本文分析了橫向?qū)α鲗?duì)水平管降膜蒸發(fā)的影響,建立了數(shù)學(xué)模型,并通過對(duì)基本控制方程的求解,得到在橫向?qū)α饔绊懴碌囊耗ず穸圈摹⒀毓鼙谝耗ち魉賣、垂直管壁液膜流速v及總速度U隨圓周角θ、噴淋密度Г以及y方向的距離的無量綱量η的變化規(guī)律,并重點(diǎn)分析了橫向?qū)α魉俣葀對(duì)總速度的影響,結(jié)果表明:液膜厚度δ隨圓周角增加先減小后增加,在圓周角為90°時(shí)達(dá)到最小值,其平均值隨噴淋密度的增加而增加;沿管壁液膜流速u,隨圓周角的增加先增加后減小,在圓周角為90°時(shí)達(dá)到最大值,其平均值隨噴淋密度及y方向無量綱長(zhǎng)度的增加而增加;垂直管壁液流速流速v隨圓周角的增加先減小后增加,在圓周角為90°時(shí)達(dá)到最小值,其平均值隨噴淋密度及y方向無量綱長(zhǎng)度的增加而增加;液膜總速度U的變化規(guī)律與沿管壁液膜流速u相同,U的數(shù)值大小受到垂直管壁液膜流速v的一定影響。同時(shí),本文提出了借用無量綱量對(duì)基本控制方程進(jìn)行化簡(jiǎn)求解的方法,從而得到傳熱傳質(zhì)過程的無量綱溫度及無量綱質(zhì)量分?jǐn)?shù)的求解方法。本文使用數(shù)值模擬軟件Fluent對(duì)本文建立的基礎(chǔ)物理模型(噴淋密度Г為0.1kg/(m·s),管徑φ為10mm,布液高度h為10mm,管間距d為10mm,時(shí)間t為0.32s時(shí)的水平管降膜蒸發(fā)流動(dòng)模型)的流動(dòng)、傳質(zhì)、傳熱進(jìn)行模擬與分析,并分對(duì)不同噴淋密度、不同管徑、不同布液高度及不同管間距對(duì)流動(dòng)、傳質(zhì)、傳熱的影響進(jìn)行模擬與分析。借助前處理軟件Gambit對(duì)物理模型進(jìn)行網(wǎng)格劃分,采用后處理軟件CFD-Post對(duì)模擬結(jié)果進(jìn)行處理與繪圖,使用origin軟件進(jìn)行數(shù)據(jù)處理。在模擬前,針對(duì)本文研究的多相流問題,選定VOF多相流模型及編譯自定義函數(shù)(User Defined Function,以后簡(jiǎn)寫為UDF),采用分離式求解器求解控制方程,設(shè)定溶液的物性參數(shù),設(shè)置工作壓力為870Pa,將基于蒸發(fā)原理的兩相傳熱傳質(zhì)的UDF文件嵌入模型,選用PISO算法對(duì)迭代進(jìn)行求解。模擬后得到的分析結(jié)果為:(1)基礎(chǔ)模型取不同的噴淋密度,隨噴淋密度的增加,液膜厚度增加,液膜速度增加,液膜傳熱及傳質(zhì)效果下降,本文模擬在噴淋密度為0.1kg/(m·s)時(shí)達(dá)到最佳傳熱傳質(zhì)效果;(2)對(duì)基礎(chǔ)模型取不同的管徑,隨管徑的增加,液膜厚度減小,液膜速度增加,但液膜穩(wěn)定性降低,導(dǎo)致液膜傳熱及傳質(zhì)效果先增強(qiáng)后下降,本文模擬在管徑為16mm時(shí)達(dá)到最佳傳熱傳質(zhì)效果;(3)對(duì)基礎(chǔ)模型取不同的布液高度,隨布液高度的增加,液膜厚度減小,液膜速度增加,液膜的傳熱及傳質(zhì)效果先增強(qiáng)后下降,本文模擬在布液高度為10mm時(shí)達(dá)到最佳傳熱傳質(zhì)效果;(4)對(duì)基礎(chǔ)模型取不同的管間距,隨管間距的增加,液膜厚度減小,液膜速度增加,液膜的傳熱及傳質(zhì)效果先增強(qiáng)后下降,本文模擬在管間距為10mm時(shí)達(dá)到最佳傳熱傳質(zhì)效果;(5)由以上幾點(diǎn)可以得出,液膜的傳熱及傳質(zhì)是耦合的,其變化趨勢(shì)相同。在液膜穩(wěn)定鋪展的條件下,液膜的厚度越薄、速度越低,其傳熱、傳質(zhì)效果越好。所得到的分析結(jié)果與之前的理論分析及前人的實(shí)驗(yàn)結(jié)果相似。
[Abstract]:With power saving LiBr absorption chiller, environmental friendly and can make use of waste heat production and other advantages, in recent years, research on performance of lithium bromide absorption chiller evaporator widely. As the lithium bromide absorption refrigeration device of refrigeration, heat and mass transfer efficiency of the evaporator is one of the important factors affecting the performance of LiBr absorption chiller. The lithium bromide absorption evaporator form refrigeration unit in the falling film, in a vacuum environment, water solution of falling film flow outside the horizontal tube, including gas-liquid two-phase flow, flow process accompanied by the phenomenon of heat and mass transfer complex. This paper from the research level tube falling film evaporation heat transfer of flow of the main tube falling film evaporation the heat transfer model and heat transfer mechanism and tube falling film evaporation heat transfer influence factors were studied. This paper analyzes the transverse convection of horizontal tube falling film evaporation The influence of the mathematical model was established, and by solving the basic equations, obtained the film thickness in the delta transverse convection under the influence of the liquid velocity along the tube wall u, vertical wall liquid velocity V and the total rate of U with the circular angle theta, no variation of nondimensional ETA gamma spray density and the Y direction in the distance, and analyzes the influence of V on the total speed, transverse convection velocity results show that the film thickness decreased with the increase of the delta angle increased in the circumferential angle of 90 degrees reached the minimum value, the average value increases with the spray density along the tube wall; liquid velocity increased with the increase of u the circular angle increases first and then decreases in the circumferential angle is 90 degrees maximum, the average value with the increase of spray density and Y direction of dimensionless length increases; vertical wall flow rate of V increased with the circular angle decrease after increase in the circumferential angle of 90 degrees to minimum The average value, with the increase of spray density and Y direction of dimensionless length increases; variation of total film speed of U with the same liquid velocity along the tube wall u, numerical size U affected vertical wall liquid velocity of v. At the same time, is presented in this paper based method to simplify and solve for the control equations nondimensional, resulting in dimensionless temperature and heat transfer process and the solving method of dimensionless mass fraction. Based on the physical model established in this paper using the numerical simulation software Fluent (f 0.1kg/ spray density (M - s), pipe diameter is 10mm, height h 10mm liquid distribution, tube spacing D 10mm, t 0.32s for the horizontal tube falling film evaporation flow model) flow, mass transfer, heat transfer is simulated and analyzed, and the different spray density, different diameter, different height and different liquid distribution tube spacing on the flow, mass transfer, heat transfer effect For simulation and analysis. By pre-processing software Gambit to mesh the physical model, the postprocessing software CFD-Post processing and drawing on the simulation results, Origin software was used for data processing. In the simulation, according to the research of multiphase flow, multiphase flow model and selected VOF (User Defined Function compile custom function later, abbreviated as UDF), the separated solver control equation, the physical parameters of the solution set, set the working pressure of 870Pa, UDF file embedded in the heat and mass transfer model based on the principle of evaporation, using PISO algorithm to solve the iterative analysis. Simulation results are obtained: (1) based model of different spray density, with the increase of spray density, the film thickness increases, the film speed increase, decrease heat transfer and mass transfer in the liquid membrane, the simulation of spray density was 0.1kg/ (M - s) to The best heat transfer effect; (2) on the basis of the model with different diameter, with the increase of the diameter of the film thickness decreases, the film speed increases, but the stability of liquid membrane is reduced, resulting the heat transfer and mass transfer effects first increased and then decreased, this paper simulated the best heat transfer effect is 16mm in diameter; (3) on the basis of the model take the cloth liquid height is different, with the height of liquid film thickness increases, decreases, the film speed increases, heat transfer and mass transfer effect of the film first increased and then decreased, this paper simulated the best heat transfer and the height of 10mm in liquid distribution; (4) on the basis of model with different distance between tubes, with increasing tube the spacing of film thickness decreases, the film speed increases, heat transfer and mass transfer effect of the film first increased and then decreased, the simulation in tube spacing is 10mm to achieve the best heat transfer effect; (5) the above points can be concluded that the heat transfer and transfer film The mass is coupled, and the change trend is the same. Under the condition of stable spreading of liquid film, the thinner the liquid film and the lower the speed, the better the heat and mass transfer effect is. The obtained results are similar to previous theoretical analysis and previous experimental results.

【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB657

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