發(fā)布時間：2018-05-18 11:03

  本文選題：太陽能 + 真空管　； 參考：《東南大學(xué)》2015年碩士論文

【摘要】：太陽能是取之不盡,用之不竭的清潔能源,在當(dāng)今能源供給緊張,環(huán)境問題日益突出的形勢下太陽能的利用備受重視。太陽能與建筑一體化是現(xiàn)在太陽能集熱器發(fā)展的主流方向之一。本文提出一種新型的相變儲能型太陽能真空集熱管,該真空集熱管組成的熱水系統(tǒng)與傳統(tǒng)太陽能熱水系統(tǒng)相比不需要儲熱水箱,利用相變蓄熱原理將太陽輻射能儲存在相變材料內(nèi)并在需要時釋放出來。結(jié)合數(shù)值模擬計算與試驗研究,對集熱管內(nèi)的相變傳熱過程進(jìn)行了分析與探討,并對翅片的結(jié)構(gòu)參數(shù)進(jìn)行優(yōu)化。在太陽輻射基本原理的基礎(chǔ)上,以南京地區(qū)為例,計算各時間段內(nèi)太陽輻射強度,為下文真空管內(nèi)的傳熱研究提供基礎(chǔ)數(shù)據(jù)。選擇管長為1800mm,內(nèi)徑105mm的玻璃管作為新型相變儲能型集熱管的真空管,選擇石蠟為蓄熱材料,徑向分布有金屬翅片的U型銅管作為流體換熱通道。對太陽能真空集熱管進(jìn)行傳熱分析,計算單位時間內(nèi)集熱管吸收的太陽能輻射以及對周圍環(huán)境的熱損失,得出集熱管獲得的有用能。對比相變儲能傳熱過程的求解方法,確定焓——孔隙率法作為相變過程的計算模型并給出控制方程。運用CFD軟件對帶金屬翅片的相變儲能型真空集熱管建立三維模型,采用用戶自定義函數(shù)UDF對真空管8：00-17：00獲得的有效輻射熱流編程,并導(dǎo)入模擬軟件作為邊界條件。模擬結(jié)果表明,上午10：00左右,集熱管頂部石蠟開始熔化,石蠟整體溫度較為平均,10：00-14：20為石蠟相變蓄熱時間段,此過程石蠟體平均溫度上升緩慢,但內(nèi)部石蠟溫差不斷變大,13：00時頂部石蠟與底部石蠟的溫差達(dá)到了90K。石蠟完全熔化后,溫度上升加快,自然對流加速了石蠟的換熱過程,進(jìn)一步縮小內(nèi)部溫差。優(yōu)化金屬翅片的結(jié)構(gòu)參數(shù),對翅片厚度lmm,2mm,4mm,8mm,翅片間距為10mm,20mm, 40mm,80mm的蓄熱單元進(jìn)行模擬,分析不同翅片結(jié)構(gòu)對石蠟熔化過程及熔化時間的影響。結(jié)果表明,石蠟的熔化時間隨著翅片厚度的增加與間距的減小而減小,翅片間距對相變傳熱的影響要大于翅片的厚度,當(dāng)翅片間距達(dá)到80mm時翅片厚度對傳熱過程的影響甚微。當(dāng)翅片間距小于10mm時,翅片間距對熔化時間的影響也逐漸減小。研制并搭建新型相變儲能型真空集熱管的試驗平臺,測試所設(shè)計新型相變真空集熱管的集熱傳熱性能。分析對比試驗數(shù)據(jù)與模擬結(jié)果,驗證數(shù)值模擬的準(zhǔn)確性。對集熱管夜間實際運行工況進(jìn)行研究,當(dāng)石蠟處于凝固釋熱狀態(tài),入口水溫17℃,流速為0.071m/s,0.144m/s,0.248m/s時,出水溫度分別為41.5℃-55.96℃,32.89℃-42.4℃,29.5℃-33.7℃。
[Abstract]:Solar energy is an inexhaustible clean energy, the utilization of solar energy is paid more and more attention under the situation that energy supply is tight and environmental problems become more and more serious. The integration of solar energy and architecture is one of the main trend of solar collector development. In this paper, a new type of phase change solar energy storage vacuum collector is proposed. Compared with the traditional solar water heating system, the hot water system composed of the vacuum collector does not need a hot water tank. Solar radiation energy is stored in phase change materials and released when needed. Based on the numerical simulation and experimental study, the phase change heat transfer process in the collector tube is analyzed and discussed, and the structural parameters of the fin are optimized. Based on the basic principle of solar radiation, the solar radiation intensity in Nanjing area is calculated in different time periods, which provides the basic data for the study of heat transfer in vacuum tubes below. The glass tube with a length of 1800mm and an inner diameter of 105mm is selected as the vacuum tube of a new type of phase change energy storage collector, and a U-shaped copper tube with metal fins distributed in the radial direction is chosen as the fluid heat transfer channel, and the paraffin is used as the heat storage material. The heat transfer analysis of solar vacuum collector tube is carried out, the solar radiation absorbed by the collector tube and the heat loss to the surrounding environment are calculated in unit time, and the useful energy obtained by the collector tube is obtained. The enthalpy-porosity method is used as the calculation model of the phase change process and the governing equation is given by comparing the solution method of the phase change energy storage heat transfer process. The three-dimensional model of the phase change energy storage vacuum collector with metal fin was established by using CFD software. The effective radiation heat flux obtained from the vacuum tube 8: 00-17: 00 was programmed by the user defined function UDF, and the simulation software was introduced as the boundary condition. The simulation results show that at about 10:00 in the morning, the paraffin at the top of the collector pipe begins to melt, and the overall temperature of paraffin wax is 10: 00-14: 20, which is the average temperature of paraffin phase change, and the average temperature of paraffin increases slowly. However, the temperature difference between the top paraffin and the bottom paraffin reached 90 K. when the temperature difference between the internal paraffin wax and the bottom paraffin increased to 13: 00. After the paraffin is completely melted, the temperature rises faster, the natural convection accelerates the heat transfer process of the paraffin, and further reduces the internal temperature difference. The structural parameters of the metal fin were optimized, and the heat storage units with a thickness of lmm2 mm ~ 4 mm ~ 8 mm, a fin spacing of 10 mm ~ 20 mm, and a fin distance of 40 mm ~ 80 mm were simulated. The effects of different fin structures on the melting process and melting time of the paraffin were analyzed. The results show that the melting time of paraffin decreases with the increase of fin thickness and the decrease of fin spacing. The effect of fin spacing on phase change heat transfer is greater than that of fin thickness. When the fin spacing reaches 80mm, the fin thickness has little effect on the heat transfer process. When the fin spacing is smaller than 10mm, the influence of fin spacing on melting time decreases gradually. The experimental platform of a new type of phase change energy storage vacuum collector tube was developed and built to test the heat transfer performance of the designed new type of phase change vacuum collector tube. The accuracy of numerical simulation is verified by analyzing and comparing experimental data and simulation results. The actual operation condition of the collector pipe at night was studied. When the temperature of inlet water was 17 鈩，

本文編號：1905587