本文選題：糊狀區(qū)　切入點：固液相變　出處：《山東建筑大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：多孔介質(zhì)內(nèi)固液相變問題廣泛存在于自然界和眾多工業(yè)領(lǐng)域。固液相變材料作為一種被廣泛應(yīng)用的儲能材料,在實際應(yīng)用中往往不是單一組分的物質(zhì),相變發(fā)生時的溫度并非在某一恒定值,而是在一個區(qū)間范圍內(nèi),此時存在一個固相和液相共存的區(qū)域——糊狀區(qū)。糊狀區(qū)的存在及其特性對相變過程有著重要的影響。研究固液相變的流動和熱質(zhì)交換規(guī)律,探討固液相變界面(糊狀區(qū))的發(fā)展、遷移及熱質(zhì)傳遞特性規(guī)律有著重要的意義。本文基于對糊狀區(qū)的物理特性分析,提出一種描述糊狀區(qū)流動特征的“多相流-多孔介質(zhì)”兩區(qū)域模型,即將糊狀區(qū)中靠近固相表面的低液相率區(qū)域采用BrinkmannForchheimer-Darcy多孔介質(zhì)滲流模型;靠近液相的高液相率區(qū)域采用多相流模型。為獲得考慮多孔骨架條件下,骨架對固液相變的整場和局部流動換熱特性以及對糊狀區(qū)影響的規(guī)律,本文基于焓法分別建立了多孔骨架內(nèi)固液相變的表征元(REV)尺度和孔隙尺度的數(shù)學(xué)模型。在數(shù)學(xué)模型的求解方面,采用格子-Boltzmann方法(LBM),通過選擇適當(dāng)?shù)碾x散速度模型、平衡態(tài)分布函數(shù)及源項,分別建立了研究固液相變糊狀區(qū)的REV尺度和孔隙尺度下的LBM模型。并通過一系列的數(shù)值實驗驗證了模型或方法應(yīng)用的有效性及正確性。本文以方腔內(nèi)固液相變過程為研究對象,首先模擬研究了無多孔骨架的固液相變過程,重點關(guān)注糊狀區(qū)的特性,分析了無量綱參數(shù)(普朗特數(shù)Pr、瑞利數(shù)Ra,斯蒂芬數(shù)Ste)對糊狀區(qū)發(fā)展、遷移及其內(nèi)部的流動和傳熱的影響規(guī)律。研究結(jié)果表明:1)糊狀區(qū)的厚度與相變溫度半徑T_R直接相關(guān),T_R越小,糊狀區(qū)厚度越薄;2)糊狀區(qū)常數(shù)C及高、低液相率區(qū)的分界點trg的選取與相變材料的物性及糊狀區(qū)內(nèi)部構(gòu)造有著密切的關(guān)系;3)相變材料的無量綱物性參數(shù)(Prandtl數(shù)Pr、Rayleigh數(shù)Ra、Stefan數(shù)Ste)對糊狀區(qū)和相變過程有著明顯的影響;低Pr數(shù)條件下,相變前期會產(chǎn)生多渦結(jié)構(gòu),會影響糊狀區(qū)的形狀和遷移;Ra數(shù)的大小影響著液相區(qū)和糊狀區(qū)的自然對流強(qiáng)度,同時影響著糊狀區(qū)的形狀及內(nèi)部的換熱流動,Ra數(shù)的增大,融化速率隨之增大,糊狀區(qū)減薄,對應(yīng)熱壁面的換熱能力增強(qiáng);Ste影響融化速率的快慢,Ste越大,糊狀區(qū)厚度增大,其下部區(qū)域的速度隨之增大,在整個相變過程中系統(tǒng)的蓄熱量隨Ste數(shù)增大而減小。以上述為基礎(chǔ),本文進(jìn)一步模擬分析了考慮多孔骨架時骨架對固液相變過程的影響�；赗EV尺度分析了骨架對相變過程中糊狀區(qū)及整場流動換熱的影響,研究表明:1)骨架的達(dá)西數(shù)Da的增大或孔隙率e的減小,相應(yīng)液相區(qū)和糊狀區(qū)的流動效應(yīng)越明顯,糊狀區(qū)的厚度越薄,其形狀則越彎曲,孔隙率e增大一方面降低了系統(tǒng)的換熱能力,另一方面相變材料體積的增加,可以增大系統(tǒng)的蓄熱量;2)骨架的添加并不一定對相變過程起促進(jìn)作用,其他條件相同時,骨架的導(dǎo)熱能力越強(qiáng),糊狀區(qū)的邊界彎曲度越小,準(zhǔn)穩(wěn)態(tài)階段未融化的體積越大�；诳紫冻叨认卵芯苛斯羌軐ο嘧冞^程中流動換熱的局部細(xì)節(jié)的影響規(guī)律,研究顯示:1)在相變過程中,由于糊狀區(qū)邊界和骨架的影響,在局部會產(chǎn)生渦流;2)孔隙尺度下骨架孔隙率e對相變過程及糊狀區(qū)的影響與REV尺度所得結(jié)論一致,且骨架的高導(dǎo)熱性對系統(tǒng)整體的傳熱特性有一定的促進(jìn)作用,隨著骨架的導(dǎo)熱性能的增強(qiáng),但其促進(jìn)效果逐漸減弱。
[Abstract]:Solid-liquid phase change in porous media widely exist in nature and many industrial fields. The solid-liquid phase change materials has been widely used as a storage material, in the practical application is often not a single component material, the temperature is not the phase change occurs at a constant value, but in a range, at this time: the mushy zone region of a solid phase and liquid phase coexistence. The existence and characteristics of the mushy zone has an important influence on the phase transition process. Research on solid-liquid phase change flow and heat exchange rules of solid-liquid interface (mushy zone) development, plays an important role in migration and the heat and mass transfer characteristics analysis. In this paper, based on the physical characteristics of the mushy zone, presents a description of flow characteristics of the mushy zone "of multiphase flow in porous media -" two region model, the mushy zone in low liquid fraction near the solid surface by Br InkmannForchheimer-Darcy porous medium seepage model; multiphase flow model with high liquid fraction near the liquid phase. For considering the porous skeleton under the condition of the whole skeleton on solid-liquid phase change and the local flow and heat transfer characteristics and the influence on the law of the mushy zone, based on the enthalpy method were established for characterization of solid-liquid phase change element within the porous framework (REV) mathematical model of scale and at the pore scale. In the mathematical model, the lattice -Boltzmann method (LBM), by selecting the appropriate discrete velocity model, the equilibrium distribution function and the source term, we established the LBM model of the REV scale and the pore scale study of solid-liquid phase change of mushy zone under the effective. And the correctness of the application model or method is verified through a series of numerical experiments. The solid-liquid phase change process in cavity as the research object, studies the non porous solid simulation first The liquid phase change process, focus on the characteristics of the mushy zone, analysis of the dimensionless parameters (Prandtl number Pr, Rayleigh number Ra, the Stephen number Ste) on the development of mushy zone, influence of flow and heat transfer and internal. The results show that: 1) the thickness and phase transition temperature of T_R is directly related to the radius of the mushy zone T_R, the smaller the mushy zone thickness; 2) mushy zone constant C and high and low liquid fraction zone selection TRG cut-off point of phase change materials in the mushy zone and the internal structure are closely related; 3) the dimensionless physical parameters of phase change materials (Prandtl Pr number, Rayleigh number Ra, Stefan Ste) has a significant impact on the mushy zone and the phase change process; low Pr conditions, early phase will produce eddy structure, will affect the shape and migration of the mushy zone; the number of Ra affects the intensity of natural convection in liquid region and mushy zone, also affect the mushy zone the shape and the The internal flow and heat transfer, the increase of Ra number, the melting rate increases, mushy zone thickness, corresponding heat wall heat capacity enhancement; Ste effect of the melting speed of the Ste, the greater the mushy zone thickness increases, the lower area of speed increases, heat storage system in the whole process with phase transformation the Ste number increases. On the basis, this paper further analyze the influence of skeleton on solid-liquid phase change process with porous skeleton. REV scale analysis of the impact of the skeleton of the mushy zone and the transformation process of flow and heat transfer based on the research shows: 1) the skeleton of the Darcy number Da increases or porosity e the effect of the corresponding flow decreases, liquid phase region and the mushy zone is more obvious, the mushy zone thickness is thin, its shape is bent, the porosity of e increased while reducing the heat transfer capacity of the system, the phase change material volume increased on the other hand, can increase Large quantity of heat storage system; 2) framework does not necessarily add on the phase change process and play an important role in other conditions, thermal conductivity of skeleton is stronger, the mushy zone boundary curvature smaller, quasi steady stage not melt the larger volume. Based on the pore scale studied, skeleton of details heat flow during the phase change process of the research shows: 1) in the transformation process in the mushy zone due to the influence of edge and skeleton, eddy current generated in the local council; 2) under the influence of pore size porosity of e phase transformation process and mushy zone and REV scale consistent, high thermal conductivity and the skeleton are the effect on the heat transfer characteristics of the whole system, with the enhancement of thermal conductivity of the skeleton, but its effect is gradually weakened.

【學(xué)位授予單位】：山東建筑大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TB34

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