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 Improved utilization of desiccant material in packed bed dehumidifier using composite particles(2011) Ramzy K, A.; Kadoli, R.; Ashok Babu, T.P.Solid desiccant dehumidifiers are widely used in drying processes. In most of these dehumidifiers, the desiccant material is used as packed bed of granule or spherical particles. Investigations of intra-particle heat and mass transfer processes has shown that the entire portion of the particle is not participating effectively during adsorption as well as desorption processes [Pesaran AA, Mills F. Moisture transport in silica gel packed beds-I. Theoretical study. International Journal of Heat and Mass Transfer 1987; 30: 1037-49]. This is because the diffusion rate is very small compared to that of convection. In the present work, a new desiccant composite particle, in which the unutilized portion of the spherical desiccant particle is replaced with an inert particle, is proposed. By replacing the conventional particles with composite particles for the same mass of desiccant material, the available area for heat and mass transfer increases and more amount of desiccant material is effectively utilized. Further, in order to ascertain the improvement in the performance of the desiccant bed using the composite particles, various factors like thermo-physical properties of the inert material, composite particle thickness ratio, bed configuration, bed volume, the pressure drop and the increase in total adsorbed or desorbed mass have to be considered. In view of this, a theoretical investigation of the operation of vertical solid desiccant packed bed dehumidifier, using both conventional silica gel particles as well as the new proposed composite silica gel particles has been reported. A modified solid side resistance (MSSR) model is developed for the prediction of intra-particle temperature and water content profiles. Results of the present theoretical models, when applied to packed bed of conventional silica gel particles, agree well with the experimental results from the literature for both desorption and adsorption processes. From the theoretical results, more utilization for the desiccant material is obtained when ordinary silica gel particles are replaced by composite silica gel particles. For the same amount of desiccant material and same mass flow rate of air, using particles of 0.2 thickness ratio the pressure drop decreases by about 60% for the case investigated. In addition, an increase of about 11.07% and 20.46% in total mass adsorbed and desorbed respectively are obtained. At the time when adsorption process ends, an increase of 15.5% in the bed effectiveness has been obtained. In addition, the expected improvement in total mass adsorbed and desorbed is observed to be dependent on the inert material thermo-physical properties for thickness ratio less than 0.5. An optimization technique relating the composite particle design, resulting savings in pressure drop and bed volume increase is proposed. © 2010 Elsevier Ltd.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 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.Item Experimental study on sorption–desorption characteristics of natural composite desiccant with metal embedment(Elsevier Ltd, 2023) Dasar, S.R.; Anish, S.; Kadoli, R.; Yadav, A.K.The present study investigates the effect on total moisture sorption, moisture sorption rate, moisture desorption rate, and reduction in the temperature of dehumidified air of metal-embedded natural composite desiccants (MENCDs), which can be used in dehumidification systems. A natural composite desiccant, in which the unutilized portion of the spherical desiccant material is replaced with a metallic ball, is proposed. Stainless steel balls with a diameter of 4.75 and 6.35 mm are used to make different thickness ratios (TR = 1, 0.525, and 0.365) of MENCDs. The natural composite desiccant is prepared from dried cow dung and polyvinyl pyrrolidone with a ratio of 3:1. Experiments are conducted to find the optimum thickness ratio of MENCDs. The total moisture sorption, moisture sorption rate, total heat load reduction, and exergy efficiency of these dehumidification systems are investigated under different relative humidities (RH = 65% to 85%), and at a constant temperature and velocity. Desorption characteristics are tested under 328 K and 5% RH. The total moisture sorption of MENCDs with a TR of 0.365 is found to be 11.84 g/100 g, which is 17% higher compared to natural composite desiccants (i.e., TR = 1) at 85% RH, whereas, the total moisture sorption rate is 0.4 g/100 g⋅min, which is 20.57% higher for TR of 0.365 compared to TR = 1. Moisture desorption rate for TR = 0.365 is 16.66% higher compared to TR = 1. The average exergy efficiency of these systems is 60%. The average exergy efficiency of these composite desiccants with a TR = 0.365 is 9.6% higher compared to TR = 1. The average total heat load reduction for composite desiccants with a TR = 0.365 is 24% higher compared to TR = 1. The experimental study shows that the MENCDs will help to increase total heat load reduction, sorption and desorption rate, and total moisture sorption of dehumidified air with optimum thickness ratio for enhanced utilization of a composite desiccant for dehumidification systems. © 2023 Elsevier Ltd