Numerical and experimental investigation of a thermosiphon solar water heater system thermal performance used in domestic applications

The thermosiphon is a passive heat exchange method, which circulates a fluid within a system without the need for any electrical or mechanical pumps. The thermosiphon is based on natural convection where the thermal expansion occurs when the temperature difference has a corresponding difference in density across the loop. Thermosiphons are used in different applications such as solar energy collection, automotive systems, and electronics. The current study aims to investigate thermosiphon thermal performance used in domestic applications. The thermal performance of a thermosiphon has been studied by many researchers; however, according to the knowledge of the authors, the influence of the amount of the working fluid on the thermal output has not yet been investigated. Therefore, the influence of the amount of working fluid within the riser pipe has been investigated on the thermal performance of the thermosiphon. In the current study, a computational fluid dynamics model is involved. This model has been validated by comparison with experimental findings. The maximum variation between numerical and experimental results is 14.2% and 11.2% for the working fluid at the inlet and outlet of the absorber pipe, respectively. Furthermore, the results show that the amount of working fluid inside the closed thermosiphon has a great influence on the thermal performance of the system. Additionally, it is found that Case-B, when the amount of working fluid is less than by 10% compared to the traditional model, is the best case among all cases under study. Furthermore, a correlation equation to predict water temperature at the exit of the absorber pipe has been established with an accuracy of 95.05%.     

Mixed Reversible Covalent Crosslink Kinetics Enable Precise,Hierarchical Mechanical Tuning of Hydrogel Networks

Hydrogels play a central role in a number of medical applications and new research aims to engineer their mechanical properties to improve their capacity to mimic the functional dynamics of native tissues. This study shows hierarchical mechanical tuning of hydrogel networks by utilizing mixtures of kinetically distinct reversible covalent crosslinks. A methodology is described to precisely tune stress relaxation in PEG networks formed from mixtures of two different phenylboronic acid derivatives with unique diol complexation rates, 4‐carboxyphenylboronic acid, and o‐aminomethylphenylboronic acid. Gel relaxation time and the mechanical response to dynamic shear are exquisitely controlled by the relative concentrations of the phenylboronic acid derivatives. The differences observed in the crossover frequencies corresponding to pK_a differences in the phenylboronic acid derivatives directly connect the molecular kinetics of the reversible crosslinks to the macroscopic dynamic mechanical behavior. Mechanical tuning by mixing reversible covalent crosslinking kinetics is found to be independent of other attributes of network architecture, such as molecular weight between crosslinks.     

Linking Hydro-Physical Variables and Landscape Metrics using Advanced Data Mining for Stream-Flow Prediction

Water Resources Management - In Streamflow prediction the most important triggering/controlling variables are related to climate, physiography, and landscape patterns. This study investigated the...     

Insights into isotherm making in the sorptive removal of fluoride from drinking water

The defluoridation research has thrown up many technologies, with adsorption as a popular alternative, especially among fluoride endemic habitations of the developing world. In the endeavor to develop novel adsorbents for defluoridation, the adsorption potential of hardened alumina cement granules (ALC) were examined through isotherm fitting. Though the adsorbent showed enhanced adsorption capacity at higher fluoride concentration ranges, the errors associated with linearization in isotherm fitting were also found to be increasing. The propagation of these errors was more prominent in Dubinin-Radushkevich and Langmuir models but negligible in Freundlich. The chi2 analysis, used to correlate the equilibrium experimental data and the isotherm models, also suggested poor correlations at higher fluoride concentration ranges for all the models. The procedure of linear and nonlinear regression through optimization of error functions rendered the 'best-fit' model and optimum model parameters, through sum of normalized error (SNE) values. Though ALC exhibited maximum monolayer adsorption capacity of 34.36 mgg(-1) in concentration variation studies of fluoride in the range of 2.5-100 mg l(-1) in synthetic water, it got reduced to 10.215 mgg(-1) in dose variation studies and further to 0.9358 mgg(-1) in natural ground water. Though Langmuir appeared as the best-fit model in terms of R2 in synthetic studies of different fluoride concentrations, the procedure of linear and nonlinear regression demonstrated that Freundlich was the best-fit. The nonlinear chi2 analysis together with minimum SNE values convincingly demonstrated that the equilibrium studies with dose variations of ALC offers more reliable isotherm parameters than those with high fluoride concentrations. The sorption of fluoride by ALC appeared endothermic with Freundlich adsorption capacity parameter increased from 0.5589 to 0.9939 lg(-1) in natural water and 3.980-7.5198 lg(-1) in synthetic water systems for a rise in temperature from 290 to 310 K. The study deviates from conventional methodologies of relying solely on R2 values in selecting 'best-fit' isotherm model, and basically demonstrates how the optimum model parameters like 'adsorption capacity' evolves through linear and nonlinear regression using error functions.     

An efficient,clean synthesis of 3,3′-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) derivatives

A clean, simple and efficient method for the synthesis of 3,3′-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) derivatives has been developed which uses the reaction of 2-hydroxynaphthalene-1,4-dione and aromatic aldehydes in the presence of a catalytic amount of LiCl in aqueous media. To the best of our knowledge, this is the first report on such a synthesis of 3,3′-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione).     

Numerical and experimental study of a thermosyphon closed‐loop system for domestic applications

A numerical and experimental study has been conducted to enhance the thermal performance of the thermosyphon system. The enhancement response focused on the temperature of both the working fluid within the system loop and water inside the tank. To achieve this, three models were investigated to increase the surface area of the riser pipe without changing the amount of the working fluid. The first one (model A) involved increasing the diameter of the riser pipe and inserting a closed tube inside it to maintain the same amount of working fluid. The second method (model B) involved adding toroidal fins around the riser pipe. However, the third model (model C) combined both models (A and B). The thermal performance of the thermosyphon system for the conventional model has been compared experimentally. Furthermore, numerical simulations for all cases have been done using commercial computational fluid dynamics, ANSYS R 19.3 software. The results show that there is good agreement between the experimental and numerical results. Furthermore, it is found that the thermal responses of models A and B are approximately equal and both are higher than that of the traditional model. Moreover, the thermal performance of model C is found to be higher than those of all the other models under study.     

Biodegradation of aromatic hydrocarbons in a compost biofilter

Two laboratory‐scale biofilters filled with the same type of packing material were operated at different gas flow rates and influent concentrations of toluene and xylene in order to investigate their performance in treating waste gas streams. The columns contained a mixture of municipal compost as a base material and wood chips as a bulking agent in an 80:20 ratio; the porosity was 54%. Microbial acclimation was achieved by addition of nutrient‐enriched solution along with pollutants for a week by daily mixing and natural aeration. During the start‐up of the systems with inlet concentrations of 20 and 70 ppm for toluene and xylene, respectively, high biomass growth resulted in pressure drops in excess of 2000 Pam^?1. Under steady state conditions, the response of each biofilter to variations in contaminant mass loading was studied by either changing the influent concentration or flow rate of the inlet waste stream. The results show that organic loading rates of up to 110 and 150 gm^?3h^?1 can be handled without any indication of the elimination capacity being saturated. However, maintaining the pressure drop below 1000 Pam^?1 to avoid operational problems, optimal organic loading rates for toluene and xylene of 78 ± 8 and 80 ± 14 gm^?3h^?1 respectively are suggested for an HRT value of 60 s. Under these conditions, elimination capacities of 73 ± 4 and 73 ± 14 gm^?3h^?1 and removal efficiencies of 94 ± 6% and 91 ± 8% were achieved for toluene and xylene, respectively. Copyright © 2003 Society of Chemical Industry     

Feasibility analysis of As(III) removal in a continuous flow fixed bed system by modified calcined bauxite (MCB)

This study examine the feasibility of As(III) removal from aqueous environment by an adsorbent, modified calcined bauxite (MCB) in a continuous flow fixed bed system. MCB exhibited excellent adsorption capacity of 520.2 mg/L (0.39 mg/g) with an adsorption rate constant 0.7658 L/mgh for an influent As(III) concentration of 1mg/L. In a 2 cm diameter continuous flow fixed MCB bed, a depth of only 1.765 cm was found necessary to produce effluent As(III) concentration of 0.01 mg/L, from an influent of 1 mg/L at a flow rate of 8 mL/min. Also, bed heights of 10, 20, and 30 cm could treat 427.85, 473.88 and 489.17 bed volumes of water, respectively, to breakthrough. A reduction in adsorption capacity of MCB was observed with increase in flow rates. The theoretical service times evaluated from bed depth service time (BDST) approach for different flow rates and influent As(III) concentrations had shown good correlation with the corresponding experimental values. The theoretical breakthrough curve developed from constantly mixed batch reactor (CMBR) isotherm data also correlated well with experimental breakthrough curve.     

Analytical Solution of Classic Coupled Thermoelasticity Problem in a Rotating Disk

A fully analytical solution of the classic coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads is presented. Axisymmetric thermal and mechanical boundary conditions are considered in general forms of arbitrary heat transfer and traction, respectively, at the inner and outer radii of the disk. To solve the governing system of equations, an analytical procedure based on the Fourier-Bessel transform is employed. Closed form formulations are presented for temperature and displacement fields. The results of the present formulations are in good agreement with the numerical results available in the literature. The radial distribution and time history of temperature, displacement and stresses are shown and discussed. The propagation of elastic waves and their reflection from the boundary of the disk are clearly shown. In addition, effects of coupling parameter and angular velocity on temperature, displacement and stress fields are investigated.     

Investigations on the kinetics and mechanisms of sorptive removal of fluoride from water using alumina cement granules

This paper examines the kinetics of fluoride removal from water by the adsorbent alumina cement granules (ALC), exploring the mechanisms involved. ALC exhibited a biphasic kinetic profile of sorption with an initial rapid uptake phase followed by a slow and gradual phase. The kinetic profile has been modeled using pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model and Elovich model. The kinetic sorption profiles offered excellent fit with pseudo-second-order model with a high R² value of 0.9987. The value of activation energy of the system (17.67 kJ mol⁻¹) indicates the significance of diffusion in the sorption process. The rate-limiting step of sorption was evaluated by analyzing the response of the system to pH, inert electrolyte concentration, and desorption pattern of the adsorbent, instead of assigning it to a single kinetic model. Accordingly, the surface reactions involving the heterogeneity of the surface site bonding energy or other reactions occurring on the surface of ALC were found predominant in defining the rate-limiting step. The dominant mechanism of fluoride removal appeared to be a chemisorptive ligand exchange reaction involving the formation of inner-sphere complexation of fluoride with ALC.