Study of Drying Nanoceramic Colloid by A LiBr Absorption/Exhaust System

• Main Authors: Tzu-ChingHsu, 徐梓青
• Other Authors: Jenq-Shing Chiou
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/86422869784617149337

博士 === 國立成功大學 === 機械工程學系碩博士班 === 99 === It is well known that drying of liquid-borne powders will create agglomerates and the problem of agglomeration is particularly acute in the range of nano-scale size. There are many kinds of drying process for nano-particles, each one has its advantage and limitation but none of them can be free from particle agglomeration. Since the liquid water will instantaneously flush into steam under the condition where the pressure is below its saturated state, and the outward expansion force during flashing is able to counteract the attracting force among particles, it is thus reasonable to use vacuum dry technique to prevent/mitigate agglomeration. In the tests of drying θ-Al2O3 colloid (solution of nano-particles and water), we used other drying methods to compare with our proposed vacuum drying. The degree of re-dispersibility obtained from each dried powder was taken as the level of product quality. The results indicated that the quality of powders from vacuum drying were better than that from others. Especially when the vacuum drying added microwave energy heating, the re-dispersed powders can almost return to the state of original colloid. Although the vacuum dry technology had been used in the fields of drying solid food, timber and medicine powder, this technology has not been used in the situation when the water-content percentage is high. The behind reason may be due to the fact that the flashing process of water will be terminated once the environment pressure rise above saturation state due to the tremendous volume expansion when liquid water converts to vapor. This study proposed the concept of LiBr-H2O absorption cooling system, which can continuously absorb the expanded steam in the vacuum chamber and keep the chamber pressure below the saturated value. To promote the absorption rate of steam, we changed different kinds of cooling-tube-bundle. The results show that the bundle made by low-fin-tube has a slightly better efficiency than that the one made by smooth-tube, and the enhanced effect of using flat plate connected between the upper and lower tubes was found to be insignificant. By adding a small amount of 2-ethyl-hexanol into LiBr solution was found very effective to improve the ability of absorption. However, the exhausted steam containing 2-ethyl-hexanol would have a strong bad order and may contaminate the nearby environment. The most important contribution of this study is to demonstrate that our designed device can continuously absorb and expel steam from the vacuum chamber, which indeed is the most important step to achieve applying the vacuum drying device for mass production.