The Boiling of Thin Liquid Film in a Spray Evaporator

• Main Authors: Ching Fu Yang, 楊景福
• Other Authors: Jenq-Shing Chiou
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/24947337397639171793

碩士 === 國立成功大學 === 機械工程學系 === 89 === Abstract The heat transfer performance of the shell-tube evaporator is investigated under both pool boiling and spray boiling conditions. The pool boiling usually has a low heat transfer coefficient at lower heat flux and the spray boiling suffers a serious dry out at higher heat flux. The test results indicated both the problems mentioned above could be resolved by installing a liquid collector underneath to each heater tube. The thin liquid film existing between the bubble and heater surface can be evaporated easier and is believed to contribute a high heat transfer. This area of this thin liquid film will increase after the installation of liquid collector, since the swelling bubble tends to be squeezed due to the narrow gap between the heater and collector surfaces. When the heat flux is not too high, the heat transfer coefficient of pool boiling will be enhanced by the installation of liquid collector. On the case of spray evaporator, liquid collector can keep heater wet and thus prevent or delay the possible early dry-out. The experimental data also showed that heat transfer performance became better as the gap getting smaller, however, the performance will turn worse when the gap is too small such that the make-up coolant has difficulty to flow into the gap. Under our test conditions, the optimum gap size of this experiment is 0.6mm where the Bond number is 0.49.