Date of Award

5-1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Majid Keyhani

Committee Members

R. V. Arimilli, Stan Johnson, F. E. Weber

Abstract

A heat and mass transfer test stand was fabricated and used to investigate nonisothermal falling film absorption of water vapor into a solution of aqueous lithium bromide. The absorber was made of borosilicate glass for visual inspection of the falling film. Experiments were conducted on an internally cooled smooth tube of about 0.019 m outside diameter and of 1.53 m length. Laboratory testing evaluated the tube's performance at varying falling film flow rates, pressures, temperatures, and concentrations. No heat and mass transfer additive was used during testing nor had it been previously added to the stand.

The coolant temperature profile was measured along the running length of the absorber. The interface temperature of the falling film was measured with a new technique using thermographic phosphors. Information gleaned from the coolant measurements led to the development of a predictive algorithm. The algorithm was validated against the experimental data from this study and also from data published in the open literature. The algorithm predicts the absorber load and the mass absorbed within ± 10 and ± 14%, respectively.

The data, for testing of aqueous LiBr at 0.62 and 0.64 mass fraction of LiBr, were reduced to nondimensional parameters and were successfully correlated into both Nusselt and Sherwood formulations. The average absolute error in the Nusselt correlation is about ± 3.5% of Nu number reduced from the experimental data. The Sherwood correlation is about ± 5% of the reduced Sh data. The data by Grossman and Alefeld (1996) were reduced to the author's Nu and Sh formulations, and were within 5% of the correlations developed in the present study.

The hydrodynamics of the falling film, the absorber load, the mass absorbed, transport coefficients, and pertinent absorption data are presented as functions of the Re, Pr, Sc, Ja and Ka numbers. The data will prove useful in establishing design guidelines for the improvement in combined heat and mass exchangers.

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