本文關(guān)鍵詞：場(chǎng)協(xié)同分析外部流動(dòng)及板翅管換熱器周期性熱流體優(yōu)化

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【摘要】：世界范圍內(nèi)能源利用面臨著嚴(yán)重的問(wèn)題,存在能源利用效率低和換熱器笨重的缺點(diǎn),使該系統(tǒng)的經(jīng)濟(jì)可行性有所降低。在板翅管換熱器中,為了得到高效率的能源轉(zhuǎn)化技術(shù),建立數(shù)學(xué)模型對(duì)換熱器進(jìn)行優(yōu)化分析,使用場(chǎng)協(xié)同理論(FSP)作為強(qiáng)化傳熱的方法和理論依據(jù)。拋物型能量方程使用格林函數(shù)結(jié)合加權(quán)殘差方法求解得到溫度分布。然后,通過(guò)對(duì)管壁面幾何參數(shù)和等溫邊界的對(duì)流換熱系數(shù)進(jìn)行分析建立協(xié)同場(chǎng)。為了方便求解和自定義,使用FLUENT軟件,一個(gè)離散的通用的傳遞方程被使用,該方程基于湍流對(duì)流傳熱,用于求解協(xié)同作用。數(shù)值模擬被認(rèn)為在圓形和橢圓形管束的平移周期邊界條件下有有限的壓力梯度。從得出Nu數(shù)的結(jié)果表明,對(duì)流換熱不僅取決于溫差、流體速度和流體性質(zhì),而且取決于流場(chǎng)和溫度場(chǎng)之間的場(chǎng)協(xié)同角和場(chǎng)協(xié)同數(shù)。當(dāng)增加進(jìn)口流速時(shí),橢圓形管束中傳熱效果顯著增強(qiáng),場(chǎng)協(xié)同數(shù)增加,場(chǎng)協(xié)同角減少。在相同的操作工況下,圓形管束設(shè)計(jì)和橢圓形管束設(shè)計(jì)所得平均場(chǎng)協(xié)同角分別為78.97°和66.31°使用場(chǎng)協(xié)同優(yōu)化后板翅管換熱器的橢圓形管束,與圓形管束相比,場(chǎng)協(xié)同角和場(chǎng)協(xié)同數(shù)分別增加22.68%和35.98%。由于沒(méi)有實(shí)驗(yàn)驗(yàn)證第一演繹的場(chǎng)協(xié)同原理,本文通過(guò)實(shí)驗(yàn)分析加熱平板表面的協(xié)同情況,實(shí)驗(yàn)使用熱成像系統(tǒng)和快速照相機(jī)得到溫度場(chǎng)和流場(chǎng)。通過(guò)設(shè)置四種不同射流高度和射流速度,在Re數(shù)為2,602～6,505之間時(shí),使用場(chǎng)協(xié)同原理對(duì)所得流場(chǎng)和溫度場(chǎng)進(jìn)行優(yōu)化分析�；谄桨迳淞鞯玫降膱�(chǎng)協(xié)同分析方程被用來(lái)研究由實(shí)驗(yàn)得耢向加熱平板的溫度場(chǎng)和流場(chǎng)之間的協(xié)同作用,尤其是中心積分區(qū)域得到的有清晰速度流線的流場(chǎng)和溫度場(chǎng)之間的協(xié)同作用。傳熱過(guò)程的不可逆性可表示為火積(Entransy)耗散極值原理EED,熵產(chǎn)最小化原理MEG,外部泵功耗原理EPWC,和火用(Exergy)損最小化原理EDM。板翅管換熱器的對(duì)流層流和湍流傳熱的場(chǎng)協(xié)同方程是基于耗散極值原理進(jìn)行的,而其他的傳熱過(guò)程只進(jìn)行層流對(duì)流換熱場(chǎng)協(xié)同方程以減小計(jì)算成本。將傳熱過(guò)程粘性耗散及其產(chǎn)熱過(guò)程的不可逆性設(shè)為單一目標(biāo)優(yōu)化約束條件,通過(guò)泛函變分?jǐn)?shù)值模擬,構(gòu)建附加體積力的動(dòng)量方程與能量方程進(jìn)行耦合,然后得到穩(wěn)定的層流對(duì)流換熱最優(yōu)場(chǎng)協(xié)同方程。場(chǎng)協(xié)同方程的解給出了優(yōu)化后的流場(chǎng),從管表面到兩管之間區(qū)域的旋渦尺寸不斷減小,在管束中隨著流體流動(dòng)Nu數(shù)不斷增加。根據(jù)以上不同的原理進(jìn)行優(yōu)化分別得到的最優(yōu)協(xié)同場(chǎng)有不同的粘性耗散效應(yīng)。通過(guò)這種新的優(yōu)化方法獲得最優(yōu)速度場(chǎng)方程,進(jìn)而得到穩(wěn)定的層流對(duì)流換熱最優(yōu)速度場(chǎng)。除此此外,數(shù)值研究得到顯式二維不可壓縮流解析解,這些解是完全或非協(xié)同的。這些解是在邊界上協(xié)同的,使協(xié)同作用僅發(fā)生在流體和管表面之間的邊界。這些解除了具有驗(yàn)證完全或非協(xié)同存在的可能性的理論意義,還可以用于進(jìn)一步檢查某區(qū)域的協(xié)同效果的準(zhǔn)確性和有效性,為選擇和設(shè)計(jì)合適的強(qiáng)化換熱設(shè)備提供參考。最后,使用以速度優(yōu)化模式作為方向,設(shè)計(jì)出傾斜渦發(fā)生器,在實(shí)際的設(shè)備可以引入使用。傾斜的渦發(fā)生器能產(chǎn)生渦旋流動(dòng),以提高整體流場(chǎng)層流與湍流之間的熱交換。作為說(shuō)明性的例子,對(duì)在板翅管換熱器中有無(wú)渦發(fā)生器換熱和流動(dòng)進(jìn)行場(chǎng)協(xié)同角分析,結(jié)果表明,在管壁上下表面附近安裝渦發(fā)生器后得到最優(yōu)的場(chǎng)協(xié)同角為86.53。,效能因子為PEC=2.33。
【關(guān)鍵詞】：板翅管換熱器 場(chǎng)協(xié)同角 優(yōu)化 粘性耗散 傳熱效率
【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TK172
【目錄】：

• Abstract5-7
• 摘要7-20
• 1 Introduction20-36
• 1.1 Motivation of the study20-22
• 1.1.1 Flow a cross bank of tubes20-21
• 1.1.2 Heat transfer enhancement techniques21-22
• 1.2 Background to the study22-33
• 1.2.1 Plate finned tube heat exchanger22-28
• 1.2.2 Fluid flow and heat transfer modeling for current plate finned tube heat exchanger28-33
• 1.3 Study objectives33
• 1.4 Layout of thesis33-36
• 2 Review on FSP as convective heat transfer mechanism36-51
• 2.1 Synergy based momentum and energy equations36-39
• 2.2 Synergy based on the conservation equation for mechanical energy39-40
• 2.3 Examples of convection with different field synergy techniques40-45
• 2.3.1 Two parallel porous plates40-41
• 2.3.2 Single finned tube41-42
• 2.3.3 Micro channels with different ribs42-43
• 2.3.4 Circular tube fitted with helical screw-tape inserts43-44
• 2.3.5 Effects of the fouling in round tube44-45
• 2.4 Optimization method of convective heat transfer using extremum entransy dissipation EED45-47
• 2.5 Computational fluid dynamics CFD47-50
• 2.5.1 Preprocessing and solver47-48
• 2.5.2 Governing equations of thermo-fluid field48
• 2.5.3 Turbulence models48-49
• 2.5.4 Numerical methods49-50
• 2.6 Closure50-51
• 3 Numerical investigations of convective heat-flow over round and elliptic tube bundle basedon field synergy principle51-74
• 3.1 Physical model51-54
• 3.2 Boundary conditions and CFD simulation54-56
• 3.3 Mesh verification56-57
• 3.4 Effect of fluid flow and heat transfer57-61
• 3.5 Tube row number effect61-62
• 3.6 Tube pitch effect62-64
• 3.7 Analysis of temperature difference64-65
• 3.8 Analysis of pressure drop65-67
• 3.9 Analysis of heat transfer enhancement and effectiveness67-70
• 3.10 Concept of field synergy factor70-73
• 3.11 Closure73-74
• 4 Experimental study of field synergy principle on a heated plate74-88
• 4.1 Variation of the total heat transfer rate74
• 4.2 Visualization fluid flow and temperature distributions74
• 4.3 Experiment set-up74-76
• 4.4 Measurement system76-78
• 4.5 Uncertainty of the experiment and accuracy78-79
• 4.6 Velocity field79-81
• 4.7 Temperature field81-83
• 4.8 Effect of operating and configuration of parameters83-84
• 4.9 Synergy number84-87
• 4.10 Closure87-88
• 5 Field synergy equations based on the approaches of minimum heat consumption in heatconvection88-118
• 5.1 Laminar field synergy equation based Euler's equation and EED88-92
• 5.2 Field synergy equation for turbulent convection92-97
• 5.3 Water-flow heated by symmetrical rows of tube using RNG k-ε model97-98
• 5.4 Fully developed turbulent flow in elliptical tube bundle by RNG k-ε model98-100
• 5.5 Water now through a heated tube bundle with uniform heat flux condition100-102
• 5.6 Predictive optimization method based on the minimum heat transfer entropy generation MEG102-107
• 5.6.1 Basic assumptions102
• 5.6.2 Basic equations102-103
• 5.6.3 Integal constraint and objective functional103
• 5.6.4 Solution of the variational problem103-107
• 5.7 Derivation of optimization equations for external pump work consumption EPWC107-111
• 5.7.1 Heat transfer enhancement107-108
• 5.7.2 Optimization equations108-111
• 5.8 Optimization of the heat transfer process using application of exergy destruction minimization EDM111-116
• 5.9 Closure116-118
• 6 Numerical solutions of analytical convective synergy field and novel designs118-138
• 6.1 Numerical solution method for analytical convective synergy field119-120
• 6.2 Synergy solution with heat source(Ⅰ)using method of separating all variables with addition120-122
• 6.2.1 Full synergy field120
• 6.2.2 Non-synergy field120-122
• 6.3 Synergy solutions with heat source(Ⅱ)concise solution family using method of separating variables with addition122-126
• 6.3.1 Solution with linear temperature distribution122-124
• 6.3.2 Solution with-out heat sources124-126
• 6.4 Synergy solution with heat source(Ⅲ)using hybrid method of separating variables126-127
• 6.5 Novel designs of plate finned tube heat exchanger127-129
• 6.6 Grid independence for novel designs129-130
• 6.7 Evaluation of novel enhanced heat transfer in plate finned tube heat exchanger130-133
• 6.8 Performance evaluation criteria PEC133-137
• 6.9 Closure137-138
• 7 Conclusion138-142
• 7.1 Principal conclusions138-140
• 7.2 Innovation points140-141
• 7.3 Future work141-142
• References142-149
• Achievements as a PhD student149-150
• Acknowledgement150-151
• About the Author151-153

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