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A simple model for falling film absorption on vertical tubes in the presence of non-absorbables.

Author(s) : MEDRANO M., BOUROUIS M., PEREZ-BLANCO H., et al.

Type of article: Article, IJR article

Summary

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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Pages: 108-116

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Details

  • Original title: A simple model for falling film absorption on vertical tubes in the presence of non-absorbables.
  • Record ID : 2003-1803
  • Languages: English
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 26 - n. 1
  • Publication date: 2003/01

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