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

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.

Department of Mechanical Engineering

Fulltext

Journal of Applied Sciences

Evaluation of heat and mass transfer coefficients 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

The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 Î1/4m that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate. © 2010 Author(s).

Department Of Civil Engineering

World University root node

Atmospheric Chemistry and Physics

An overview of the Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08)

The Amazon is one of the few continental regions where atmospheric aerosol particles and their effects on climate are not dominated by anthropogenic sources. During the wet season, the ambient conditions approach those of the pristine pre-industrial era. We show that the fine submicrometer particles accounting for most cloud condensation nuclei are predominantly composed of secondary organic material formed by oxidation of gaseous biogenic precursors. Supermicrometer particles, which are relevant as ice nuclei, consist mostly of primary biological material directly released from rainforest biota. The Amazon Basin appears to be a biogeochemical reactor, in which the biosphere and atmospheric photochemistry produce nuclei for clouds and precipitation sustaining the hydrological cycle. The prevailing regime of aerosol-cloud interactions in this natural environment is distinctly different from polluted regions.

Department of Humanities and Social Sciences

Science

Rainforest aerosols as biogenic nuclei of clouds and precipitation in the Amazon

A vapor ejector refrigeration system has been designed and developed to operate with ammonia. In this paper, performance of ejector refrigeration system has been experimentally studied with three different area ratio ejectors by varying operational parameters namely generator, condenser and evaporator temperatures. Effect of non-dimensional parameters like compression ratio, expansion ratio and area ratio on the system performance is studied. Entrainment ratio and coefficient of performance of the system increase with increase in ejector area ratio and expansion ratio and they increase with decrease in compression ratio. © 2006 Elsevier Ltd. All rights reserved.

GENERAL

Renewable Energy

Experimental investigations on ejector refrigeration system with ammonia

Treatment of effluents is a serious issue for present process industries. Several new techniques are being developed which require the knowledge of effluent physical and transport properties for design and development of treatment plants. In this work density, kinematic viscosity, thermal conductivity and specific heat capacity of the tannery effluent (soak liquor) were measured for various salt concentrations of soak liquor ranging from 3% to 20%. A non-linear regression analysis has been carried out using these experimental data and the empirical correlations are presented. © 2007 Elsevier Ltd. All rights reserved.

International Communications in Heat and Mass Transfer

Measurement of physical and transport properties of tannery effluent (soak liquor)

Presently, tanneries in Tamilnadu, India are required to segregate the effluent of soaking and pickling sections from other wastewater streams and send it to shallow solar pans for evaporation to avoid land pollution. A large area of solar pans is required for evaporating the water in the effluent at salt concentration in the range of 4-5%. An experimental study has been made by using fibre reinforced plastic flat plate collector (FRP-FPC) and spray system in a pilot plant with a capacity to handle 5000 l per day, which increases the evaporation rate. After increasing the salt concentration level to near saturation limit, the concentrated liquid was sent to conventional solar pans for its continued evaporation and recovery of salt. In this improved system, the rate of evaporation was found to be 30-40% more than that in the conventional solar pans. The performance is compared with the theoretically simulated performance. © 2007 Elsevier Ltd. All rights reserved.

Solar Energy

Open fibre reinforced plastic (FRP) flat plate collector (FPC) and spray network systems for augmenting the evaporation rate of tannery effluent (soak liquor)

With an ever-increasing population and rapid growth of industrialization, there is a great demand for fresh water, especially for drinking. In view of this, different desalination technologies have evolved with a thrust for utilization of renewable energy sources such as solar energy, ocean thermal energy, geothermal energy, and waste heat. Flash desalination is a technology in which fresh water is produced from seawater by evaporation and subsequent condensation. One such desalination technique involves different processes like pressurization of seawater using a pump, creation and maintenance of vacuum using jet pump in a flash chamber, evaporation of seawater at reduced pressure using warm water from the sea surface and condensation of water vapour using cold water from the deep sea. A two-phase variable geometry jet pump was designed, developed and tested for the flash desalination system to create a vacuum inside the flash chamber. The area ratio of the jet pump used for the investigation was 0.25. Experimental results are reported from tests on the jet pump with a view to assessing the optimum distance between orifice exit and mixing tube entrance. Overall performance of the jet pump was assessed by plotting its characteristics. Performance of the jet pump was analyzed by plotting iso-efficiency curves on characteristics curves drawn for various primary water flow rates. The optimum orifice to mixing tube distance of the jet pump was found and corresponding maximum efficiency was reported. Maximum vacuum created by the jet pump at an optimum condition, i.e., at maximum jet pump efficiency, with respect to time was determined. © 2006 Elsevier B.V. All rights reserved.

Desalination

Experimental investigations on a two-phase jet pump used in desalination systems

A desalination system has been designed for converting brackish water into potable water utilizing ocean thermal gradient. The desalination plant evaporates the water by flash and surface evaporation and subsequently the vapour is condensed to get potable water. An experimental plant with a capacity of 20 lph was designed for a typical ocean thermal gradient. The designed operating conditions of the plant are evaporator temperature, 30°C and condenser temperature, 10°C. Experimental performance of the system was evaluated by varying the condenser and evaporator temperatures and chamber vacuum pressure. © 2007.

Experimental studies on desalination system for ocean thermal energy utilisation

An experimental study has been made to augment evaporation of tannery effluent (soak liquor) and compare the performance of the conventional fibre reinforced plastic (FRP) flat plate collector with an open FRP flat plate collector. As the tannery effluent flows over FRP flat plate collectors in the form of thin film, the effluent is heated by gaining heat from the absorber due to exposure to solar radiation. Hence, the partial pressure at the interface of the effluent increases, resulting to increase in pressure difference between the interface and air. Thus, leading to increase in mass transfer rate. In this paper, performance comparison is made between the FRP open flat plate collector and the conventional FRP flat plate collector, to understand the effect of climatic conditions, concentration and mass flow rate of the effluent. This study shows that the conventional FRP flat plate collector gives better performance than the open FRP flat plate collector.

International Energy Journal

Comparison of conventional and open flat plate collectors for evaporation of tannery effluent (december 2006)

Heat and mass transfer analysis of an incompressible, laminar boundary layer over solar flat plate collector evaporation systems for tannery effluent (soak liquor) is investigated. The governing equations are solved for various liquid to air velocity ratios. Profiles of velocity, temperature and concentration as well as their gradients are presented. The heat transfer and mass transfer coefficients thus obtained are used to evaluate mass of water evaporated for an inclined fibre-reinforced plastic (FRP) solar flat plate collector (FPC) with and without cover. Comparison of these results with the experimental performance shows encouraging trend of good agreement between them.

Journal of Zhejiang University: Science

Studies on solar flat plate collector evaporation systems for tannery effluent (soak liquor)

A desalination system using a spray tower and Vapour Compression Refrigeration (VCR) system is proposed for obtaining fresh water from brackish water. In the spray tower, simultaneous heat and mass transfer take place between the brackish water and air, which results in the evaporation of the brackish water and humidification of the air. Fresh water is obtained from the humidified air by condensing the water vapour using a VCR system. Parametric studies were carried out to study the effect of various operational parameters on the fresh water production rate. Copyright © 2006 Inderscience Enterprises Ltd.

International Journal of Nuclear Desalination

Desalination using spray tower and vapour compression refrigeration system

The experimental investigation of the performance of a vapour ejector refrigeration system is described. The system uses R134a as working fluid and has a rated cooling capacity of 0.5 kW. The influence of generator, evaporator and condenser temperatures on the system performance is studied. This kind of system can be operated with low grade thermal energy such as solar energy, waste heat, etc. The operating conditions are chosen accordingly as, generator temperature between 338 K and 363 K, condenser temperature between 299 K and 310.5 K, and evaporator temperature between 275 K and 285.5 K. Six configurations of ejectors of different geometrical dimensions are selected for the parametric study. The performance of the refrigeration system at different operating temperatures is presented. © 2006 Elsevier Ltd and IIR.

International Journal of Refrigeration

Experimental investigation on R134a vapour ejector refrigeration system

An ejector refrigeration system has been designed and developed to operate with a simulated (electric) heat source, which can be realized in practical applications by renewable energy sources like solar energy, geothermal energy, etc., or waste heat. In this paper, an experimental study on an ejector refrigeration system working with ammonia is presented. The influence of the generator, condenser, and evaporator temperatures on the ejector refrigeration system performance is presented. The entrainment ratio and COP of the system increase with increasing generator and evaporator temperatures and decrease with increasing condenser temperature. © 2005 Elsevier ltd. All rights reserved.

Experimental studies on an ammonia ejector refrigeration system

Experiments were carried out on a R134a vapour ejector refrigeration system to study the influence of ejector configurations and operating conditions on its performance at critical mode. The influence of boiler temperature, which represent the solar energy collection temperature and that of evaporating temperature, which denotes the cooling load temperature, have been studied. Coefficient of performance was obtained for evaporating temperatures in the range of 275 K to 285.5 K and boiler temperatures between 338 K and 363 K. It has been observed that ejector configuration has significant influence in deciding the operating range and overall system performance.

Proceedings of the Solar World Congress 2005: Bringing Water to the World, Including Proceedings of 34th ASES Annual Conference and Proceedings of 30th National Passive Solar Conference

Influence of ejector geometry on performance of R134a vapour ejector refrigeration system suitable for solar energy applications

With ever-increasing population and rapid growth of industrialization, there is a great demand for fresh water, especially for drinking, as natural resources are becoming limited. In view of the above, different desalination technologies are evolving with a thrust for utilization of renewable energy sources like solar energy, ocean thermal energy, geothermal energy and waste heat. Vacuum desalination is one such technology in which fresh water is produced from brackish water by evaporation and subsequent condensation. This desalination technique involves different processes like pressurization of brackish water by a pump, creation and maintenance of a vacuum using jet pumps, and evaporation of brackish water at reduced pressure using waste heat from a power plant such as water from condenser. In this paper an analysis of a vacuum desalination system is presented. By applying the mass, momentum and energy balances across the various components, the governing equations are obtained for the analysis. These equations are solved using simulation. Validation of the simulated performance is made with the experimental data available in the literature. The study was carried out by varying operational parameters such as evaporator temperature, condenser temperature, evaporator flow rate, condenser flow rate and chamber pressure. Yield of fresh water obtained from the system increased as condenser temperature decreased and the evaporator temperature increased. Further, the yield increased as chamber pressure decreased. © 2005 Elsevier B.V. All rights reserved.

Analysis of a jet-pump-assisted vacuum desalination system using power plant waste heat

A new method has been proposed for evaporating the tannery effluent (soak liquor). The system suggested works on the principle of forced convective evaporation. Soak liquor is sprayed and air is made to flow against the falling liquor in an enclosed tower to facilitate the direct contact heat and mass transfer between them. Effect of various parameters like mass flow rate, relative humidity, temperature range, approach, etc. on the performance of the system is studied experimentally. Rate of evaporation increases with increase in mass flow rate and temperature range of liquor. Evaporation rate decreases with increase in relative humidity. The air pressure-drop increases with both air and liquor mass flow rates. It is observed that the tower characteristic increases with increase in ratio of mass flow rates (L/G) and with decrease in approach. It is shown that the forced convective evaporation system is better than the existing methods of evaporation.

Experimental studies on solar forced convective evaporation system for tannery effluent (soak liquor)

When an ejector is operated at choking-mode, it gives a better performance with higher entrainment ratio. To obtain this better performance at different operating conditions, area ratio of the ejector is varied. A computer code based on existing one-dimensional ejector theory is written to analyze performance of the ejector. The code includes effects of friction at the constant-area mixing chamber and change in specific heat of the working fluid besides internal irreversibility of the ejector. The simulated performance is compared with the available experimental data from the literature for validation. The effects of operating parameters on critical ejector area ratio and critical entrainment ratio are studied. Comparison of performance of ejector with environment friendly refrigerants, R134a, R152a, R290, R600a and R717 is made. © 2003 Elsevier Ltd. All rights reserved.

Applied Thermal Engineering

Analysis of an ejector with environment friendly refrigerants

A numerical technique for evaluating the performance of forced convective evaporation system for tannery effluent is presented. The paper describes a mathematical model, which treats the airflow to be two dimensional and liquid flow to be one-dimensional. The turbulence in airflow is modeled with low Reynolds number k-ε model. The interface heat and mass transfer are represented by Reynolds flux model. The governing equations are solved using a modified MAC (Marker and Cell) method. The model is embodied into a computer code, which is applicable to forced convective evaporation system as well as mechanical draft cooling towers of both counter flow and cross flow types. Predicted results compare well with the available data in the literature and with that of experimental data and give closer results than the existing models. Distributions of air velocities, pressure, moisture fraction and air and water temperatures have been presented. The model can be used as design as well as optimization tool. © 2003 Elsevier Ltd. All rights reserved.

Numerical simulation of forced convective evaporation system for tannery effluent

Vapour ejector refrigeration system yields better performance when the ejector operates at choking-mode. A computer code based on existing one dimensional ejector theory has been developed to carry out a study on performance of the system. When operating conditions are changed, the critical performance parameters of the system get shifted to different critical values. The code includes effects of change in specific heat of the working fluid and friction at the constant-area mixing chamber besides internal irreversibility of the ejector. The simulated performance results are compared with the available experimental data from the literature for validation. The effects of operational parameters and ejector configurations of the system on critical performance are studied. Also, comparison of performance of the system with environment friendly refrigerants, R134a, R152a, R290, R600a and R717 is made. © 2004 Elsevier SAS. All rights reserved.