A Mani

Department of Mechanical Engineering

Absorption

Ammonia

Correlation methods

MASS TRANSFER

Parameter estimation

Water

Bubbles (in fluids)

Diffusion

enthalpy

finite element method

Friction

Galerkin methods

Gas absorption

Heat flux

Heat transfer coefficients

Pressure effects

Refrigeration

Reynolds number

SPECIFIC HEAT OF LIQUIDS

Viscosity of liquids

BUBBLE ABSORBER

GALERKIN APPROACH

BUBBLE ABSORBERS

HEAT FLUX DENSITY

Mass flow rates

VOID FRACTIONS

Heat transfer

Bubble

finite element analysis

mathematical modeling

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Finite element analysis of a bubble absorber

International Journal of Numerical Methods for Heat and Fluid Flow

Experimental investigations have been carried out to study heat and mass transfer characteristics of Tetrafluoro ethane (R134a) in Dimethyl formamide (DMF) solution in a compact bubble absorber of vapour absorption refrigeration system of 1 TR capacity. Plate heat exchangers have been used as system components. Bubble absorption principle is employed in the absorber and hot water supplies heat to the generator. Effect of operating parameters such as circulation ratio, absorber and generator temperatures on heat and mass transfer effectiveness, overall heat transfer coefficient and volumetric mass transfer coefficient are investigated. It is found that heat and mass transfer effectiveness of absorber are better at lower circulation ratios and higher generator temperatures. Experimental results are compared with those obtained from numerical model developed earlier by the authors and the agreement is generally fair. From the experimental data, a correlation has been obtained for volumetric mass transfer coefficient, using multi-linear regression analysis. © 2012 Elsevier Ltd and IIR. All rights reserved.

International Journal of Refrigeration

Heat and mass transfer studies on a compact bubble absorber in R134a-DMF solution based vapour absorption refrigeration system

Experimental investigations have been carried out to visualize bubble behavior and effect of gas flow rate and liquid concentration on bubble characteristics of Tetrafluoro ethane (R134a) in liquid R134a-Dimethyl Formamide (DMF) solution in a glass absorber. Bubble behavior was studied in still as well as flowing solution. At lower gas flow rates, bubbles tend to be spherical due to the dominance of surface tension. At higher gas flow rates, bubbles tend to be hemispherical due to the dominance of inertia force. Bubble diameter during detachment increases with increase in gas flow rates. Also, the bubble diameter initially increases as the solution concentration increases up to 0.075kgkg -1 and then starts decreasing as the solution concentration increases further. At lower solution concentrations, effect of absorption driving potential (x eq-x l) is dominant than that of surface tension, due to this bubble diameter increases. When the solution concentration is increased further, effect of surface tension is dominant resulting in decrease in bubble diameter. Bubble diameter measured from the experiments is compared with that of the numerical model developed by the authors and other literature experimental correlations and it is found that the agreement is good. A correlation for bubble diameter during detachment is presented from the experimental studies, which can be useful for the design of R134a-DMF bubble absorber. © 2012 Elsevier Inc.

Experimental Thermal and Fluid Science

Experimental studies on bubble characteristics for R134a-DMF bubble absorber

Experimental investigations have been carried out to study heat and mass transfer characteristics of Tetrafluoro ethane (R134a) in Dimethyl formamide (DMF) in a glass absorber. Effects of operational parameters viz.; gas flow rate, solution flow rate, solution initial concentration, solution pressure, solution temperature and cooling water flow rate on absorber performance are analyzed. Absorption rate and heat transfer rate increase as the gas flow rate, solution flow rate, cooling water flow rate and solution pressure increase whereas they decrease as the solution initial concentration and solution temperature increase. Heat and mass transfer rates determined from the experiments are compared with numerical model and it is found that agreement is good. A correlation for mass transfer coefficient is presented from the experimental studies within ±20% error band. © 2012 Elsevier Ltd and IIR. All rights reserved.

Experimental studies on heat and mass transfer characteristics for R134a-DMF bubble absorber

A phenomenological theory of heat and mass transfer is applied to model the absorption of the R134a gas bubble in liquid R134a-dimethyl formamide (DMF) solution. Required properties of R134a-DMF liquid solution namely liquid density, surface tension, diffusion coefficient, thermal conductivity, specific heat, etc., have been calculated using experimental correlations. Results have been obtained by modeling on a computer using MATLAB. The bubble dynamics during bubble growth are studied using this model. Liquid concentration, temperature, heat and mass transfer rates, local heat and mass transfer coefficients are estimated at the bubble interface. Absorption rate, coupled heat transfer rate, average heat and mass transfer coefficients over the entire bubble life span are also calculated. This model results are validated using experimental results of ammonia-water solution. The maximum bubble radius determined from this study is compared with available experimental correlations and it is found that agreement is good. Heat and mass transfer rates obtained from this model are compared with the literature experimental results. The results are in good agreement with the predictions of the model. © 2010 Elsevier Ltd. All rights reserved.

International Journal of Heat and Mass Transfer

Heat and mass transfer studies on R134a bubble absorber in R134a/DMF solution based on phenomenological theory

Experiments are carried out on a bubble absorber, operating as part of a vapour absorption refrigeration system working with HCFC22-DMF to obtain heat and mass transfer and pressure drop data. The results are evaluated to obtain the dependence of absorption process on different parameters. Experimental data are compared with the numerical correlation relating Sherwood number, Reynolds number, Schmidt number and length to diameter ratio developed earlier by the authors. Also the experimental pressure drop is compared with the pressure drop obtained from other well known classical correlations and the numerical model.Experiments are carried out on a bubble absorber, operating as part of a vapour absorption refrigeration system working with HCFC22-DMF to obtain heat and mass transfer and pressure drop data. The results are evaluated to obtain the dependence of absorption process on different parameters. Experimental data are compared with the numerical correlation relating Sherwood number, Reynolds number, Schmidt number and length to diameter ratio developed earlier by the authors. Also the experimental pressure drop is compared with the pressure drop obtained from other well known classical correlations and the numerical model.

International Communications in Heat and Mass Transfer

Experiments on a bubble absorber

The Vapour Absorption Refrigeration System (VARS) has generated renewed interest and is being viewed as one of the alternatives for vapour compression refrigeration due to its potential for waste heat utilization. To improve the efficiency of these systems, it is necessary to study heat and mass transfer processes in absorption system components. The absorber, one of the crucial components in VARS is considered for study. Experimental investigation is carried out to study heat and mass transfer characteristics in a glass absorber. A new combination of Rl 34a/DMF is used as the working fluid to overcome the limitations of well known working pairs, ammonia-water and lithium bromide-water. The effects of parameters viz., gas flow rate, solution initial concentration, solution pressure and solution temperature on absorber performance are analyzed. Heat and mass transfer coefficients evaluated from the experiments are compared with the numerical model and it is found that agreement is good. Heat and mass transfer coefficients increase as the gas flow rate, solution initial concentration and solution temperature increase whereas they decrease as the solution pressure increases. Sherwood number andNusselt number evaluated from the experimental data are compared with those obtained from the numerical correlations developed earlier by the authors ©2011 Asian Network for Scientific Information.

Fulltext

Journal of Applied Sciences

Evaluation of heat and mass transfer coefficients for r134a/dmf bubble absorber

Journal	International Journal of Numerical Methods for Heat and Fluid Flow
Publisher	Emerald Group Publishing Ltd.
ISSN	09615539
Open Access	No