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題名 | 以實驗方法研究速溶茶之質傳性質= |
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作者 | 陳世銘; 洪偉智; |
期刊 | 農業工程學報 |
出版日期 | 19880900 |
卷期 | 34:3 1988.09[民77.09] |
頁次 | 頁117-123 |
分類號 | 473.4 |
語文 | chi |
關鍵詞 | 性質; 速溶茶; 實驗; 質傳; |
中文摘要 | 本研究係依據雙面加熱雙面脫水模式,以實驗迴歸的方式來探討速溶茶在冷凍乾燥時質傳性質,以作為進一步控制速溶茶乾燥條件的基礎。 加熱板溫度設定為30℃或50℃,乾燥室壓力控制在40~45Pa之間,由速溶茶質量與時間的關係,以迴歸方法求得30﹪固形物之速溶茶的擴散係數平均值為0.0029m²/s。實驗同時顯示30℃或50℃ 的加熱板溫度對實驗結果之擴散係數值影響不大。本實驗分析除了可以求得速溶茶的擴散係數外,尚可算出冷凍乾燥機的質傳係數,因此可藉以判斷乾燥時水蒸氣移動之阻力主要來自乾燥機性能或是速溶茶本身之物理結構特性。以本研究為例,主要阻力在於速溶茶,若要縮短乾燥時間,應由改善速溶茶孔隙結構著手。 為確保乾燥過程中凍結的速溶茶不會溶化,當乾燥室壓力為45Pa時,凍結溫度至少要在零下25℃以下,且加熱板溫度最好不要超過30℃。 |
英文摘要 | In this study, the two-side heating and two-side dehydration model was used, and the experiments were conducted to evaluate the mass transfer diffusivity of instant tea during freeze drying processes, in order to provide a basis for better controls of drying conditions. The temperature of heating plates were set at 30℃ or 50℃ while the pressure of drying chamber was regulated to 40~45Pa. The regression results of experiments indicate that the average value of diffusivity for instant tea (30﹪solid) is 0.0029 [m²/s]. It is also found that the heating-plate temperatures (30℃ or 50℃) contribute very little effects to the diffusivity. This analysis not only can be used to estimate the diffusivity of instant tea, but also can be employed to calculate the mass transfer coefficient of the freeze dryer. The values of diffusivity and mass transfer coefficient can be used to determine either the physical structure of instant tea or the performance of the freeze dryer is the dominant in the resistance to the vapor transport during drying. In this study, the major resistance is due to the nature of instant tea. In order to reduce the drying time, the porous structure of instant tea needs to be modified. When the pressure of the chamber is 45[Pa], in order to assure that the frozen instant tea would not melt during the drying process, it is suggested that the freezing temperature be below -25℃ and the heating-plate temperature be better not exceed 30℃. |
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