Performance of Horizontal Smooth Tube Absorber With and Without 2-Ethyl-Hexanol

2001 ◽  
Vol 124 (1) ◽  
pp. 177-183 ◽  
Author(s):  
Ick-Soo Kyung ◽  
Keith E. Herold
Keyword(s):  
Mass Transfer ◽  
Tube Bundle ◽  
Lithium Bromide ◽  
Mass Transfer Process ◽  
The Novel ◽  
Absorption Refrigeration ◽  
Transfer Coefficients ◽  
Significant Augmentation ◽  
Aqueous Lithium Bromide ◽  
Flow Activity

Absorption of water vapor into aqueous lithium bromide is a fundamental step in absorption refrigeration. When the liquid film is laminar, the coupled heat and mass transfer process is controlled by mass transfer, resulting in low transfer coefficients. Significant augmentation of mass transfer, and hence of the coupled process, is achieved by introducing a trace amount (on the order of 100 ppm) of 2-ethyl-hexanol. The alcohol acts as a surfactant and drives Marangoni convection that effectively mixes the liquid providing a much higher effective mass diffusivity. The film flow in the presence of the alcohol is noticeably different with a complex, apparently unstructured appearance. The flow activity, which can be easily observed, has never been satisfactorily explained until the recent introduction of the Vapor Surfactant theory. This paper presents a series of experimental results of absorption in an actual chiller facility. The novel features of the work include measurement of the effect of inlet subcooling, discussion of the effect of droplets ejected from the tube bundle and an explanation of the importance of flux in the alcohol augmentation physics.

Effects of a Nonabsorbable Gas on Interfacial Heat and Mass Transfer for the Entrance Region of a Falling Film Absorber

1996 ◽  
Vol 118 (1) ◽  
pp. 45-49 ◽  
Author(s):  
T. A. Ameel ◽  
H. M. Habib ◽  
B. D. Wood
Keyword(s):  
Mass Transfer ◽  
Water Vapor ◽  
Analytical Solution ◽  
Liquid Film ◽  
Heat And Mass Transfer ◽  
Vertical Wall ◽  
Lithium Bromide ◽  
Entrance Region ◽  
Falling Film ◽  
Aqueous Lithium Bromide

An analytical solution is presented for the effect of air (nonabsorbable gas) on the heat and mass transfer rates during the absorption of water vapor (absorbate) by a falling laminar film of aqueous lithium bromide (absorbent), an important process in a proposed open-cycle solar absorption cooling system. The analysis was restricted to the entrance region where an analytical solution is possible. The model consists of a falling film of aqueous lithium bromide flowing down a vertical wall which is kept at uniform temperature. The liquid film is in contact with a gas consisting of a mixture of water vapor and air. The gas phase is moving under the influence of the drag from the falling liquid film. The governing equations are written with a set of interfacial and boundary conditions and solved analytically for the two phases. Heat and mass transfer results are presented for a range of uniform inlet air concentrations. It was found that the concentration of the nonabsorbable gas increases sharply at the liquid gas interface. The absorption of the absorbate in the entrance region showed a continuous reduction with an increase in the amount of air.

The Correlation of Simultaneous Heat and Mass Transfer Experimental Data for Aqueous Lithium Bromide Vertical Falling Film Absorption

2000 ◽  
Vol 123 (1) ◽  
pp. 30-42 ◽  
Author(s):  
William A. Miller ◽  
Majid Keyhani
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Lithium Bromide ◽  
Falling Film ◽  
Bulk Concentration ◽  
Design Data ◽  
Flux Approximation ◽  
Aqueous Lithium Bromide ◽  
Simultaneous Heat

A study of simultaneous heat and mass transfer was conducted on a vertical falling film absorber to better understand the mechanisms driving the heat and mass transfer processes. Thermographic phosphors were successfully used to measure the temperature profile along the length of the absorber test tube. These measures of the local variations in temperature enabled calculation of the bulk concentration along the length of the absorber. The bulk concentration varied linearly, which infers that the concentration gradient in the direction of flow is approximately constant. The implication is that the mass flux and therefore the absorber load can be solved for using a constant flux approximation. Design data and correlations are sparse in the open literature. Some experimental data are available; however, all literature data to date have been derived at mass fractions of lithium bromide ranging from 0.30 to 0.60. Experiments were therefore conducted with no heat and mass transfer additive on an internally cooled smooth tube of 0.01905-m outside diameter and of 1.53-m length. The data, for testing at 0.62 and 0.64 mass fraction, were scaled and correlated into both Nu and Sh formulations. The average absolute error in the Nu correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sh correlation is about ±5% of the reduced Sh data. Data from the open literature were reduced to the authors Nu and Sh formulations, and were within 5% of the correlations developed in the present study. The study therefore provides test data with no heat and mass transfer additive and correlations for the coupled heat- and mass-transfer process that are validated against the extensive experimental data.

Analysis of Aqueous Lithium Bromide Absorption Refrigeration Systems

2021 ◽  
pp. 1-18
Author(s):  
Dongchuan You ◽  
Hameed Metghalchi
Keyword(s):  
Lithium Bromide ◽  
Double Effect ◽  
Environmental Safety ◽  
Coefficient Of Performance ◽  
Low Grade ◽  
Absorption Refrigeration ◽  
Solution Energy ◽  
Exit Temperature ◽  
Single Effect ◽  
Aqueous Lithium Bromide

Abstract Aqueous lithium bromide absorption refrigeration systems have been studied in recent years and their advantages like environmental safety and utilization of low-grade energy have been proved. Research on improving their performance has been increasing lately. In this paper, single effect and parallel flow double-effect aqueous lithium bromide absorption refrigeration systems have been studied. Mass, energy, entropy and exergy balances have been used to model the absorption refrigeration systems. Parametric studies have been done to investigate effects of cooling load, evaporator exit temperature, condenser exit temperature, generator vapor exit temperature, absorber exit temperature, solution energy exchanger effectiveness on the performance of the system. The analyses show coefficient of performance and exergetic efficiency of double-effect absorption refrigeration is higher than those of a single-effect refrigeration. The effect of other parameters on performance of both single and double-effect systems have been described in detail in the article.

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