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.

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.

scholarly journals The Correlation of Coupled Heat and Mass Transfer Experimental Data for Vertical Falling Film Absorption

1999 ◽  
Author(s):  
William A. Miller ◽  
Majid Keyhani
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Water Vapor ◽  
Heat And Mass Transfer ◽  
Mass Fraction ◽  
Operating Conditions ◽  
Falling Film ◽  
Design Data ◽  
Vertical Column ◽  
Absorption Chillers

Abstract Absorption chillers are gaining global acceptance as quality comfort cooling systems. These machines are the central chilling plants and the supply for comfort cooling for many large commercial buildings. Virtually all absorption chillers use lithium bromide (LiBr) and water as the absorption fluids. Water is the refrigerant. Research has shown LiBr to be one of the best absorption working fluids because it has a high affinity for water, releases water vapor at relatively low temperatures, and has a boiling point much higher than that of water. The heart of the chiller is the absorber, where a process of simultaneous heat and mass transfer occurs as the refrigerant water vapor is absorbed into a falling film of aqueous LiBr. The more water vapor absorbed into the falling film, the larger the chiller’s capacity for supporting comfort cooling. Improving the performance of the absorber leads directly to efficiency gains for the chiller. The design of an absorber is very empirical and requires experimental data. Yet design data and correlations are sparse in the open literature. The experimental data available to date have been derived at LiBr concentrations ranging from 0.30 to 0.60 mass fraction. No literature data are readily available for the design operating conditions of 0.62 and 0.64 mass fraction of LiBr and absorber pressures of 0.7 and 1.0 kPa. Experiments were conducted on an internally cooled smooth tube 0.01905 m in outside diameter and 1.53 m in length. Tests were conducted with no heat and mass transfer additive. The data, for testing at 0.62 and 0.64 mass fraction of LiBr, were scaled and correlated into both Nusselt (Nu) and Sherwood (Sh) formulations. The average absolute error in the Nusselt correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sherwood 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. Hence, this study provides correlations for the complex heat and mass transfer process that is validated against extensive experimental data. The study therefore contains useful information for the design of a vertical column absorber operating with no heat and mass transfer additive.

Simultaneous heat and mass transfer during evaporation from a film of liquid into the turbulent gas

1982 ◽  
Vol 47 (3) ◽  
pp. 766-775 ◽  
Author(s):  
Václav Kolář ◽  
Jan Červenka
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Liquid Film ◽  
Heat And Mass Transfer ◽  
Driving Forces ◽  
Proper Definition ◽  
Definition Of ◽  
Simultaneous Heat ◽  
Theory And Experiment

The paper presents results obtained by processing a series of published experimental data on heat and mass transfer during evaporation of pure liquids from the free board of a liquid film into the turbulent gas phone. The data has been processed on the basis of the earlier theory of mechanism of heat and mass transfer. In spite of the fact that this process exhibits a strong Stefan's flow, the results indicate that with a proper definition of the driving forces the agreement between theory and experiment is very good.

scholarly journals Modeling of conjugated heat and mass transfer in the entrance region of falling liquid film at various values of the Froude number

2018 ◽  
Vol 194 ◽  
pp. 01007
Author(s):  
Maria V. Bartashevich
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Liquid Film ◽  
Froude Number ◽  
Heat And Mass Transfer ◽  
Water Solution ◽  
Lithium Bromide ◽  
Entrance Region ◽  
Falling Film ◽  
Falling Liquid Film

Mathematical model of conjugated heat and mass transfer in absorption on the entrance region of the semi-infinite liquid film of lithium bromide water solution is investigated for different values of Froude number. The calculations shown that larger values of Froude number corresponds to a smaller thickness of the falling film. It was demonstrated that for large values of the Froude number the heat transfer from the surface is greater than for smaller values.

scholarly journals Experimental heat and mass transfer studies on horizontal falling film absorber using water-lithium bromide

2020 ◽  
Vol 24 (3 Part B) ◽  
pp. 1923-1934 ◽  
Author(s):  
Banu Arshi ◽  
N.M. Sudharsan
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Water Flow Rate ◽  
Lithium Bromide ◽  
Cooling Water ◽  
Horizontal Tube ◽  
Working Fluid ◽  
Falling Film ◽  
Cooling Water Flow Rate

Vapour absorption systems are more viable technology option in energy and environmental perspective in cooling and heating applications. Among the four major components of vapour absorption system, the absorber plays a vital role in deciding the performance, size and cost. Horizontal falling film absorbers comparatively contain good heat and mass transfer characteristics than other type of absorbers for working fluids such as water-lithium bromide. Literature shows that experimental approach of performance evaluation of absorber is more realistic and accurate than the theoretical approach. Hence in the present work, a detail experimental study has been done on horizontal tube falling film absorber using water-lithium bromide as a working fluid. The set-up consists of two major components viz. absorber and generator. Absorber contains three columns of tubes, with eight rows in each column. Detailed parametric study has been done by considering influence of spray density, cooling water-flow rate, cooling water temperature and concentration on solution temperatures, cooling water temperatures, inlet and outlet concentrations, heat flux, mass flux, heat transfer coefficient, and mass transfer coefficient with the help of plots. Results have been validated and literature gaps have been discussed.

scholarly journals The Experimental Analysis of Local Heat and Mass Transfer Data for Vertical Falling Film Absorption

1999 ◽  
Author(s):  
William A. Miller ◽  
Majid Keyhani
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Film Flow ◽  
Local Heat ◽  
Falling Film ◽  
Transfer Processes ◽  
Mass Transfer Processes ◽  
Falling Film Absorption ◽  
Film Absorption ◽  
Simultaneous Heat

Abstract In pure heat transfer, specifications of effectiveness, fluid properties, and flows enable calculation of the heat exchanger area. In the case of falling film absorption, a simultaneous heat and mass transfer governs the performance of the absorber. The exchange of mass across the liquid-vapor interface involves the generation of heat. The heat effects associated with the mass exchange increase the temperature, which affects the equilibrium state of the pressure and composition and in turn affects the mass. The falling film flow rate coupled to the physical properties of kinematic viscosity and surface tension govern the flow regime of a vertical falling film. Wavy-laminar, roll-wave laminar, and turbulent flows will develop convective contributions that can enhance the transfer of mass into the film. The combined interaction of all these factors makes the absorption process very difficult to analyze and predict. A study of simultaneous heat and mass transfer was therefore conducted on a vertical falling film absorber to better understand the mechanisms driving the heat and mass transfer processes. Falling films are characteristically unstable, and a wavy-laminar flow was observed during the experimental study. The wavy flow further complicates the problem; therefore, only limited information is known about the temperature and concentration profiles along the length of the absorber that describe the local heat and mass transfer rates. Hence, this study presents much-needed experimental data on the heat and mass transfer processes in the absence of heat and mass transfer additive. Absorption experiments were conducted in a mini-absorber test stand at various falling film flow rates, at various absorber pressures, and with various compositions of the binary salt solution. 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, from which one may infer 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 by using a constant flux approximation.

Sign in / Sign up

Export Citation Format

Share Document