Theoretical and Experimental Study on the Falling-Film Evaporator Applied to Mechanical Vapor Compression

Abstract:

Based on a heat pump system of mechanical vapor recompression (MVR) designed and manufactured independently, the heat transfer performance of falling-film evaporator was measured by a combination way of theory analysis and experiment proving as the heat pump operated in practice. After the result of theoretical calculation is worked out, the start thickness and entrance velocity of the liquid film are established by adjusting the flux of raw solution. The result shows there is an optimization that the film thickness at the bottom of the tubes amounts to that of boundary layer of velocity. Additionally, it is a process of falling-film flow with heat and mass transfer between the start and end of falling-film. The last thickness of the falling film is about 0.21~0.44mm. The thickness of falling film when the falling-film flowed and heat exchange was over is compared with each other, and the effect of heat resistance on heat transfer is discussed also. It is showed that an optimal thickness is formed during the process of falling-film flow and evaporation, and disadvantages come up when it is not formed. The falling-film evaporator propelled by the MVR heat pump with low compression ratio carries through a process of strong and high-efficiency heat transfer with phase transition. It is because the states of produced vapor both before compressed and after compressed are saturated. Its heat-transfer coefficient may be as high as 1990 W/ (m²·K). The start and end thickness of falling film become great while the evaporation pressure goes up. It leads to the drop of the heat-transfer efficiency, so there is an optimization to the system in all probability.

• Periodical: Advanced Materials Research (Volumes 753-755)
• Pages: 2667-2673
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.753-755.2667
• Online since: August 2013
• Authors: Wei Ke Pang, Lu Wei Yang, Zhen Tao Zhang
• Keywords: Falling-Film Evaporator, Film Thickness, Heat Resistance, Heat-Transfer Coefficient

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