The Experimental Study Of The Effect Of Packing On Direct Contact Evaporation In Bubble Column

Direct contact heat exchanger has many disadvantages which is incomparable for traditional exchanger,such as simple construction,fairly high heat transfer coefficient,fairly high heat transfer coefficient and lower heat transfer temperature difference.As an important chemical equipment,the bubble tower still can be optimized.In this paper,we choose water and pentane as the continuous phase and the dispersed phase respectively.On the one hand,we study the heat transfer performance of the direct contact heat transfer from the macroscopic perspective,the main influencing parameters include water inlet temperature and flow rate,pentane flow rate,different dumped packing as well as different contact way between water and pentane.On the other hand,we also study the drobble size distribution in the 2D column from the microscopic perspective and analyze the effect of packing on drobble size distribution.And the conclusion can be drawn as follows:(1)Compared with co-current,the counter-current can extend contact time between water and pentane,during which the pentane evaporates gradually in the bubble column,reduce the optimal column height,and improve the volumetric heat transfer coefficient more than 20%~30%.When it is counter-current,the pentane vapor and water separate in the column,so the gas-liquid separator is not necessary.The optimal column height and the volumetric heat transfer coefficient decrease with the increasing of water inlet temperature,especially when the inlet water temperature is relatively low.So we need to take in account of reducing optimal column height and improving heat transfer coefficient comprehensively when choosing appropriate inlet water temperature.In the initial stage of the evaporation process,if the flow of water is turbulent stage,the heat transfer process can be enhanced to a great extent.So a suitable water flow rate for enhancing heat transfer is important.The packing can effectively reduce optimal column height and improve heat transfer coefficient,especially when the inlet water temperature is relatively low and pentane flow rate is relatively high.Attaching Dixon rings in column can improve heat transfer coefficient more than 110%,and Raschig rings are only 64%.And the packing performs better in co-current contact.Beyond that,the packing increases the flow resistance in the column,so it causes the extra pressure drop.And the packing can also lower the foam layer thickness,so reducing the height of the evaporator And Dixon rings performs better than Raschig rings.(2)In 2D column without packing,increasing water temperature lead to pentane evaporate more quickly,and the drobble size distribution is more uniform and has a wider range.In the initial stage of evaporation,increasing pentane flow rate almost has no influence on drobble size distribution.However,when pentane has evaporated to a certain amount,the larger pentane flow rate will result in more uniform and better range of drobble size distribution.Attaching the packing into 2D column can increase the heat transfer interface and enhance heat transfer performance.After attaching the packing,the effect of water temperature and pentane flow rate on drobble size distribution weakens.