Heat Transfer Coefficient in Downward Flow Vertical Liquid Film Type Evaporator

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  • 下降式垂直円管型液膜蒸発装置の熱伝達係数
  • カコウシキ スイチョクエンカンガタ エキマク ジョウハツ ソウチ ノ ネツ デ

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Abstract

Experiments were made on a vertical long tube evaporator (Cu-pipe : 13.47 mmI.D., 1.2 mint and 1.2 m height) using H2O and H2O-CH3OH systems. Heat transfer coefficients were evaluated by measuring the pipe wall's temperature with metal-sheathed insulated C-C thermocouples (dia. of flexible protector : 1.0 mm) buried in the heating wall.<BR>The correlation of the over-all coefficient was proved to be similar to that of the upward-type evaporator. Condensing heat transfer coefficient of saturated steam in the heating jacket was about 46% larger than the calculated values by Kirkbride's equation. Regarding the heat transfer coefficient of annular liquid flow with evaporation, it was found that the correlation between Nu/ (Pr) 1/3 and Reynolds number of evaporating vapor Rev was not influenced by feed mass flow rate F. The correlation was as follows : <BR>Nu=0.82 (Rev) 0.46 (Pr) 1/3<BR>The heat transfer coefficients depended not only on the mean thickness of liquid film but also on the turbulence of interior and surface of liquid film. The results of this experiment, arranged by using Lockhart and Martinelli's parameter 1/Xtt, were analogous to the results obtained by Dengler et al. using upward water-air two-phase flow.

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