Faculty Publications
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Item Semi-analytical method for heat and moisture transfer in packed bed of silica gel(2011) Ramzy K, A.; Ashok Babu, T.P.; Kadoli, R.A semi-analytical model for the heat and mass transfer of adsorption and desorption processes of the vertical solid desiccant packed bed dehumidifier is presented on the basis of quasi-steady state assumption, and is solved using close form integration with the limits equivalent to bed and time increments, and numerically by Runge-Kutta Fehlberg and forward scheme finite difference techniques. The most important parameters during the dehumidifier operation, namely, (i) exit air temperature and humidity, (ii) axial temperature distribution in the bed and (iii) water content are evaluated. Stability of the semi-analytical method is investigated and found that the main parameters affecting the model stability are the bed and time increments size. A dimensionless parameter combining time and bed increments size and air velocity named velocity ratio is defined and investigated. It is found that when the velocity ratio equals the ratio of particle diameter to bed length, the method is stable, and as the velocity ratio is made smaller beyond the stable velocity ratio, the results remain unchanged. The results of semi-analytical and numerical models agree well with the experimental results for both desorption and adsorption processes. Using the proposed semi-analytical model, the minimum and maximum relative errors for exit air temperature are 2.24% and 11.78%, respectively and for exit air humidity the minimum and maximum errors are 3.79% and 27.17% respectively. © 2010 Published by Elsevier Ltd. All rights reserved.Item Performance studies on the desiccant packed bed with varying particle size distribution along the bed(2012) Ramzy K, A.; Kadoli, R.; Ashok Babu, T.P.The transient heat and mass transfer in a desiccant packed bed containing varying particle diameter distribution along the axial direction has been investigated using the pseudo gas controlled approach that considers the heat conduction in the bed. The numerical results of the present model and the experimental data from literature show good agreement with a maximum root of mean square of errors of 3% and 2% for exit air temperature and humidity ratio, respectively. The improvement in the total mass adsorbed and/or reduction in pressure drop has been investigated for various cases of packed bed namely, uniform particle diameter, linear, parabolic and cubic ascending and descending distributions. It has been found that there is a 25.7% reduction in pressure drop with negligible reduction in the total mass adsorbed for a desiccant bed with cubic type particle size distribution when compared to the bed with uniform particle diameter of 1.0 mm. A threshold flow velocity exists below which the total mass adsorbed is independent of particle diameter distribution type. © 2012 Elsevier Ltd and IIR. All rights reserved.Item Experimental studies on heat and mass transfer in a packed bed of burnt clay impregnated with CaCl2 liquid desiccant and exploring the use of gas side resistance model(Elsevier Ltd, 2013) Hiremath, C.R.; Kadoli, R.An experimental and theoretical study on the transient adsorption characteristics of porous clay-CaCl2 bed is presented. In the experimental work, the spherical particles of burnt clay of 10 mm average diameter impregnated with liquid CaCl2 desiccant of 0.50 (wt.%) concentration are used as working desiccant in a vertical adsorption column. The bed properties are experimentally estimated. Measurements are made for transient values of exit air relative humidity and temperature. The influence of superficial velocity, inlet humidity ratio and bed height on the adsorption performance is investigated. In the theoretical study, governing equations for heat and mass transfer based on gas side resistance model is used. The numerical results obtained are compared with the results available in literature and the present experimental study. © 2012 Elsevier Ltd. All rights reserved.Item Experimental and theoretical investigations on the cyclic operation of TSA cycle for air dehumidification using packed beds of silica gel particles(Elsevier Ltd, 2013) Ramzy K, A.K.; Kadoli, R.; Ashok Babu, T.P.Dehumidification using desiccant beds provide a good alternative for the conventional vapor compression cooling system. Desiccant material in the desiccant dehumidification system should undergo both adsorption and desorption processes. In the present work, experimental tests have been carried out for thermal swing adsorption (TSA) cycle utilizing two packed beds of silica gel spherical particles. The pseudo gas side controlled (PGC) mathematical model has been presented for predicting the cycle performance. The mathematical model has been validated using the experimental results. The root mean square of errors ranges from 1.15% to 9.03% for the exit air humidity ratio and from 1.08% to 9.68% for exit air temperature. The dynamics of desiccant bed during the cyclic operation has been investigated numerically. In addition, it has been found from the parametric study that the cycle efficiency is maximum for a regeneration temperature of 90-95°C when the bed length varies from 50 to 300mm and for desiccant particle diameter ranging from 2 to 5mm. A sensible cooling for the process air before undergoing the dehumidification period is recommended for increasing the cycle efficiency and the dehumidification time which is an added advantage. © 2013 Elsevier Ltd.Item Significance of axial heat conduction in non-isothermal adsorption process in a desiccant packed bed(2014) Ramzy, K.A.; Kadoli, R.; Ashok Babu, T.P.Numerical simulation of heat and moisture interactions between air stream and the particles in a desiccant bed provide useful insight on the dynamics of the bed and performance characteristics. Current study introduces a mathematical model for the heat and moisture transfer in desiccant packed bed based on solid side resistance (SSR) model that will now consider heat conduction along the bed. Adsorption and desorption experimental tests have been carried out for validating both solid side resistance (SSR) and solid side resistance with axial heat conduction (SSR-AC) models. The models have been used to investigate the influence of various design parameters like air velocity, particle diameter, bed length and the number of units of mass transfer, on the significance of axial heat conduction. It has been found that increasing the particle diameter or increasing air flow velocity or decreasing the bed length will reduce the influence of axial heat conduction in the bed. Moreover, it has been found that the difference in the bed performance evaluated due to the absence of axial heat conduction in the bed is notably decreasing with the decrease in the number of transfer units of heat or mass. From this study, it is recommended to consider the axial heat conduction term when number of transfer units of mass and heat are greater than unity. © 2013 Elsevier Masson SAS. All rights reserved.Item Modified PGC model and its validation by experiments for heat and moisture transfer analysis in a vertical fluidized desiccant bed(Elsevier Ltd, 2015) Ramzy K, A.; Kadoli, R.Air dehumidification in fluidized beds utilizing desiccants is an alternative for the refrigeration methods. A variety of pseudo gas controlled (PGC) model are proposed by assuming constant and varying temperature as well as water content for the solid phase to evaluate the conditions of exit air during adsorption processes. Experimental tests for moisture adsorption in silica gel fluidized bed are carried out. The modified PGC model that assumes uniform water content, varying temperature and linear porosity distributions along the bed estimates the temporal average bed water content to agree very well with the experimental data. The RMSE of the numerical results of the present model ranges from 0.2 to 6% and that obtained from the isothermal model are in the range of 6%-68%. © 2015 Elsevier Ltd. All rights reserved.Item Experimental and theoretical study on dehumidification potential of clay-additives based CaCl2 composite desiccants(Elsevier Ltd, 2018) Hiremath, C.R.; Kadoli, R.; Katti, V.V.Transported clay suitable for pot making is used as desiccant carrier. Additives like saw dust and horse dung are considered in particle preparation. Particles nearly spherical in shape are prepared manually and are dried under shadow and subsequently the particles are dried at different temperatures. These burnt particles are characterized for pore volume and surface area. The BET test reveals that clay particles subjected to 500 °C possess higher pore volume but clay-horse dung particles exhibit higher surface area. Heat treated particles of clay with additives are impregnated with CaCl2 solution of 50% concentration. The ratio of desiccant water content to surrounding layer water content varies from 14.09 to 75.34 for CaCl2 based composite desiccants. One dimensional PGC mass transfer model for process air through burnt clay – additives - CaCl2 desiccant bed is adopted. The RMSE of measured and predicted results for reduction of moisture content from the process air by composite desiccant beds are in the range of 3.26–13.2%. © 2017 Elsevier LtdItem Performance assessment of waste heat/solar driven membrane-based simultaneous desalination and liquid desiccant regeneration system using a thermal model and KNN machine learning tool(Elsevier B.V., 2021) Kiran Naik, B.; Chinthala, M.; Patel, S.; Ramesh, P.In this work, the waste heat/solar heat-driven membrane-based liquid desiccant regenerator performance, as well as desalinated water extraction rate, are predicted and analyzed by developing a thermal model and KNN–ML tool. In the membrane-based liquid desiccant regenerator, water is used as a working fluid instead of scavenging air for desalinated water extraction purpose. The proposed thermal model and KNN-ML tool are validated with the literature data and found in good agreement. Optimal inlet conditions were determined for the given operating range using the thermal model and KNN–ML tool. With vapor flux and energy exchange as the performance indicators, the water extraction rate and thermal performance of the membrane-based liquid desiccant regenerator are predicted for the optimal inlet condition using the KNN-ML tool. Also, the heat and mass transfer characteristics such as Lewis number and NTUm across the membrane in the liquid desiccant regenerator are assessed using the developed thermal model. Further, for the optimal inlet conditions, utilizing waste heat from thermal power plants (Method–I) and solar energy from solar heater (Method–II), the thermal performance and water extraction rate across the membrane in the liquid desiccant regenerator are assessed based on the developed thermal model. © 2021 Elsevier B.V.Item Experimental analysis of low-temperature grain drying performance of vertical packed clay and clay-additives composite desiccant beds(Springer, 2021) Hiremath, C.R.; Kadoli, K.A laboratory model of a forced circulation desiccant based green pea drying system operating in an open-loop is constructed and tested. The green pea drying process is divided into two stages involving dehumidification by the desiccant bed and green peas drying by dehumidified process air. Removal of moisture from the process air has been achieved by vertical packed composite desiccant beds. The composite desiccant used are heat treated clay with CaCl2 being impregnated and clay with additives like horse dung and sawdust, again being heated, treated and later impregnated with CaCl2. The green peas were dried for a process time of one hour. The drying was quite sharp during the initial process time of 500 s and from then onwards proceeded at a constant rate. For the identical bed masses, The performance of heat treated clay-additives based beds in moisture reduction and enhancement in enthalpy of process air is higher. The experimental study reveals the average heat content of air entering the dryer is 1.46, 2.46 and 2.38 kJ for heat-treated clay-CaCl2, clay-horse dung-CaCl2 and clay-sawdust-CaCl2 composite desiccant beds of 700 g mass. © 2021, Indian Academy of Sciences.Item Adsorption and desorption through packed and fluidized clay-based composite desiccant beds: a comparison study(Springer Science and Business Media Deutschland GmbH, 2022) Hiremath, C.R.; Kadoli, R.The present study considers the composite desiccant employing horse dung, sawdust with clay and later impregnating CaCl2 into the host material. The microscopic and spectroscopic experimental methods such as scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to characterize the composite desiccants. The specific heat (Cp) quantification reveals higher values for clay-additives composite desiccants with lower pore volume and larger grain sizes, whereas lower values for clay composite desiccants with higher pore volume and smaller grain sizes. Adsorption–desorption experiments for moisture removal and addition are conducted in a vertical column in static and fluidized states. The desiccant beds are subjected to an initially set value of process air velocity, relative humidity, temperature and mass of bed. Moisture removal capacity, moisture addition capacity and mass transfer coefficient are the parameter indices adopted to measure the heat and mass transfer characteristics of vertical packed and fluidized bed comprising clay-additives-CaCl2 composite desiccants. Comparing packed and fluidized beds, a higher surface area of bed in fluidization improves dehumidification performance and results in higher desorption rates. Experimental results confirmed that clay and clay-additives-based desiccants have desired adsorption–desorption characteristics of a suitable desiccant. The interesting advantage of fabricated clay and clay-additives-based composite adsorbents is that the air exits the desiccant bed at a lower temperature, saving cooling energy requirements of sorption-based systems. © 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.