A simple model for falling film absorption on vertical tubes in the presence of non-absorbables |
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Authors: | Marc Medrano Mahmoud Bourouis Horacio Perez-Blanco Alberto Coronas |
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Affiliation: | a Centre of Technological Innovation in Energy Upgrading and Refrigeration (CREVER), Universitat Rovira i Virgili, Autovia de Salou, s/n, 43006,, Tarragona, Spain;b Department of Mechanical Engineering, The Pennsylvania State University, University Park, 338 A Reber Building, University Park, PA 16802, USA |
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Abstract: | Most water–lithium bromide (LiBr) absorption chillers have a purge system to remove non-absorbable gases that cause a reduction in cooling capacity. Generally, the non-absorbables are originated in corrosion/passivation processes inside the machine, but leaks can also be a source of concern. However, since leaks must be corrected immediately to avoid machine deterioration, this study is mostly aimed at the non-absorbables evolved during operation. This paper analyses the effect of inlet non-absorbable air concentration, outlet purge velocity, absorber pressure and cooling water temperature on the falling film absorption process inside a vertical tube absorber, based on a simple transport coefficient model. This model consists of three ordinary differential equations solved with as method for initial-value problem, and a set of auxiliary equations. The study shows that the effect of non-absorbables can be significant, and furthermore provides a quantitative framework to aid in purge design. The nominal working conditions in this study were a solution Reynolds number of 100, an absorber pressure of 1.3 kPa, a cooling water temperature of 35 °C and an inlet solution concentration of 62% LiBr by weight. The results indicate that a minimum vapour velocity is required to sweep the non-absorbables along the absorber towards the purge, thus preventing reduced absorption fluxes. At a cooling water temperature of 35 °C, an inlet air concentration of 20% (by mole) resulted in a 61% reduction in mass absorption flux. |
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Keywords: | Absorption system Absorber Falling film Verticle tube Non-absorbable gas Absorption ModellingAuthor Keywords: Systè me à absorption Absorbeur Film tombant Tube vertical Gaz non condensable Absorption Modé lisation |
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