矽膠被覆金屬熱交換器之固結式吸附床製備與其熱質傳特性研究

Preparation of the Consolidated Adsorption Bed Employing a Silica Gel Coated Heat Exchanger and the Investigation of Its Heat and Mass Transfer Characteristics

張癸森(Kuei-Sen Chang)

指導教授 ： 鍾財王

中原大學/工學院/化學工程研究所/博士(2004年)

https://doi.org/10.6840/cycu200400319

摘要

吸附/脫附器為吸附式製冷系統中關鍵技術所在，具有熱傳與質傳雙重作用。為使系統達到高效率與高製冷量，必須縮短製冷循環週期時間，即提昇吸附/脫附器之熱傳與質傳速率。本篇研究係採用吸附劑被覆金屬表面技術，使矽膠吸附劑緊密附著於金屬基材表面，降低吸附劑與金屬熱交換器之間的接觸熱阻，達到提昇吸附/脫附器熱傳性能之目的。
為使矽膠與金屬基材之間有良好的接著性並提昇熱傳性能，本篇研究使用聚乙烯醇(PVA)作為黏結劑。經由表面性質分析與動態吸附實驗結果得知，添加少量的聚乙烯醇並不會影響矽膠的孔洞結構與質傳性能，並且在等溫吸附平衡的研究結果發現，Freundlich吸附平衡模式對於預測添加聚乙烯醇之矽膠與水氣之間的吸附平衡關係效果良好，其R2值達0.998。
對於矽膠被覆床的質傳特性可經由貫流曲線的趨勢得到了解，從實驗結果發現矽膠被覆床的製備參數對於質傳速率具有顯著的影響，並發現較薄的矽膠被覆床厚度與較小的矽膠粒子具有較陡峭的質傳區，可得到較佳的吸附質傳性能。研究中亦使用回應曲面法(RSM)來探討製備參數與再生條件對矽膠被覆床脫附性能之影響，並且藉由回應曲面演進模型之建立來描述矽膠被覆床之脫附率與脫附速率。由變異數分析與檢定係數之分析得知，極小的P-value與接近1的R2值皆說明所建立的回應曲面演進模型非常適切地表示實驗數據的變化情形。

關鍵字

矽膠被覆床 ； 回應曲面法 ； 熱傳 ； 質傳 ； 吸附式製冷

並列摘要

Adsorber/desorber is the key component of the adsorption-cooling system, and it provides a place for both the heat and mass transfer. In order to achieve high efficiency of the system, it must to be shorten a cycle of adsorption-cooling to increase the heat and mass transfer rate of the adsorber/desorber. In this study, the technology of the adsorbent coated on metal substrates is used to provide good adhesion between the silica gel and the metal substrate. The objective of this study is to decrease the contact resistance between the adsorbent and the heat exchanger, and then to promote heat transfer performance of system.
In order to enhance the adhesion between silica gels and metal substrates and to improve its heat transfer performance, the polyvinyl alcohol (PVA) is used as a binder in this study. From the results of surface properties and the dynamic adsorption experiments, the addition of PVA doesn’t affect the pore structure and the mass transfer performance of silica gels. From the results of the adsorption equilibrium experiments, the Freundlich isotherm model well predicted the adsorption equilibrium data for water vapor adsorption by the silica gel with PVA and its R2 value is 0.998.
From the shape of breakthrough curves of the silica gel-coated bed, the mass transfer characteristics are known. The mass transfer rate was affected by manufacturing variables significantly. The thinner mass transfer zone was found in the thinner silica gel layers or the smaller particle size of silica gels, and the thinner mass transfer zone resulted in the better performance of adsorption. The influence of preparation parameters and regeneration conditions on the performance of desorption in a silica gel-coated bed was studied by using a response surface methodology (RSM). Then an evolutive response surface model was proposed to describe desorption ratio and desorption rate in a silica gel-coated bed. From the results of analysis of variances and the determination coefficient, the extremely small P-value and the R2 value closed to 1, they both demonstrated that experimental data were fitted well by the evolutive model.

並列關鍵字

mass transfer ； RSM ； silica gel-coated bed ； heat transfer ； adsorption-cooling

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