Abstract
The previously developed model of natural draft wet-cooling tower flow, heat and mass transfer is extended to be able to take into account the flow of supersaturated moist air. The two phase flow model is based on void fraction of gas phase which is included in the governing equations. Homogeneous equilibrium model, where the two phases are well mixed and have the same velocity, is used. The effect of flue gas injection is included into the developed mathematical model by using source terms in governing equations and by using momentum flux coefficient and kinetic energy flux coefficient. Heat and mass transfer in the fill zone is described by the system of ordinary differential equations, where the mass transfer is represented by measured fill Merkel number and heat transfer is calculated using prescribed Lewis factor.
Highlights
Various models of natural draft cooling tower flow, heat and mass transfer exist
The previously developed model of natural draft wet-cooling tower flow, heat and mass transfer is extended to be able to take into account the flow of supersaturated moist air
The effect of flue gas injection is included into the developed mathematical model by using source terms in governing equations and by using momentum flux coefficient and kinetic energy flux coefficient
Summary
Various models of natural draft cooling tower flow, heat and mass transfer exist. Classical approach is described in reference [1], where simple algebraic draft equation is used to calculate moist air mass flow rate. This work is leading to relatively complex CFD model of natural draft cooling tower flow, heat and mass transfer. The present model provides data to estimate plume. Another benefit of present model is the inclusion of flue gas injection. Flue gas injection has contradictory effect on natural draft wet-cooling tower mass flow rate and thereby on water cooling. From one point of view is flue gas injection reducing cross sectional area of cooling tower and reduces mass flow rate, but from the other point of view it creates ejector effect which increases mass flow rate. The inclusion of momentum and energy flux coefficients into the governing equation generalizes the model and allows to include multidimensional effect in quasi one-dimensional model
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