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Indexed by:期刊论文

Date of Publication:2017-03-01

Journal:EDS Conference on Desalination for the Environment - Clean Water and Energy

Included Journals:SCIE、CPCI-S、Scopus

Volume:69

Page Number:344-351

ISSN No.:1944-3994

Key Words:CO2 chemical reaction; Non-condensable gas; Horizontal-tube falling film evaporation; Volume element size

Abstract:A reliable prediction of non-condensable gases (NCG) desorption is of great significance for enhancing heat transfer efficiency and optimizing the geometrical parameters in a horizontal-tube falling film evaporator. As chemical desorption of NCG in horizontal-tube falling film evaporation is a complex transfer process involving the coupling effects of fluid hydrodynamics, phase change and chemical reaction, little attention has been given to a predictive estimation of NCG desorption. A simulation model, which integrates the chemical reaction in seawater film with heat transfer of falling film evaporation, is developed to predict the carbon dioxide (CO2) chemical desorption rate in horizontal-tube bundles. The size of differential volume elements in this model is determined by the controlling chemical reaction time rather than an assumption. The concentration of the carbonate system in the seawater film is calculated by the falling film evaporation rate which was predicted through modelling both external film evaporation and internal condensation. A good agreement between the predictions and the practical operating data of a multi-effect distillation (MED) desalination plant proves that the present model is reliable and accurate. The results show that the varying volume element sizes in tube bundles determined by chemical reaction time depend more on brine temperature than pH and salinity. The profiles of the concentration and pH in the brine film well explain the characteristics of the CO2 chemical desorption rates in preheating and evaporation sections of tube bundles in a reference MED.