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Article
Publication date: 17 October 2018

Stephen Loh Tangwe and Michael Simon

The purpose of this paper is fourfold: to experimentally determine the standby thermal energy losses in various hot water cylinders in both scenarios, without isotherm

Abstract

Purpose

The purpose of this paper is fourfold: to experimentally determine the standby thermal energy losses in various hot water cylinders in both scenarios, without isotherm blanket installation and with isotherm blanket installation; to analytically evaluate the performance of either the geyser, split- or integrated-type ASHP water heaters based on the number of heating up cycles and total electrical energy consumptions over a 24-h period without isotherm blankets and with isotherm blankets installed; to demonstrate the impact of the electrical energy factors of the split- and integrated-type ASHP water heaters under both the scenarios (without and with the isotherm blankets installed); and to use statistical tests (one way ANOVA and multiple comparison procedure tests) to verify whether any significant difference in the standby thermal energy losses occurred for each of the heating devices under both the scenarios.

Design/methodology/approach

The methodology was divided into monitoring of the performance of the electrical energy consumptions and ambient conditions of the hot water heating technologies without isotherm blanket installation and with isotherm blanket installation.

Findings

The results reveal that the average standby thermal energy loss of the geyser without the installation of an isotherm blanket was 2.5 kWh. And this standby loss can be reduced to over 18.5 per cent by just installing a 40-mm thick isotherm blanket on the tank. The statistical tests show a significant mean difference in the group electrical energy consumed to compensate for the standby losses under both scenarios. In contrast, the average standby thermal energy losses for the split- and integrated-type ASHP water heaters were 1.33 kWh and 0.92 kWh, respectively. There was a reduction of 15.5 per cent and 3.5 per cent in the electrical energy consumed in compensating for standby losses for both the split and integrated types, respectively, but there was no significant mean difference in the standby losses under both scenarios for the two systems. Again, without any loss of generality, the electrical energy factor of both the ASHP water heaters decreased upon installation of the isotherm blanks.

Research limitations/implications

The experiments were conducted only for a 150-L geyser and 150-L split- and integrated-type ASHP water heaters. The category of the different types of ASHP water heaters was limited to one because of the cost implication.

Practical implications

The experiments were not conducted with various hot water storage tanks installed in different positions (roof, inside or outside of a building wall, etc.) so that actual real-life observations could be obtained. The challenges of easy disassembling and deployment of systems and DAS to different positions were also a real concern.

Social implications

The findings can help homeowners and ESCO in deciding whether to install isotherm blankets on storage tanks of ASHP water heaters on the basis of the impact of standby losses and its potential viability.

Originality/value

The experimental design and methodology are the first of its kind to be conducted in South Africa. The results and interpretation were obtained from original data collected from a set of experiments conducted. The findings also show that the installation of isotherm blanket on an electric geyser can result in a significant mean reduction in the standby losses. In contrast, an installation of the isotherm blankets on the storage tanks of ASHP water heaters can reduce the standby losses, but there exists no significant mean difference.

Details

Journal of Engineering, Design and Technology, vol. 16 no. 5
Type: Research Article
ISSN: 1726-0531

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Article
Publication date: 22 February 2021

Juan Carlos Lucas Aguirre, German Antonio Giraldo Giraldo and Misael Cortés Rodríguez

In order to understand interactions aw vs equilibrium moisture content (EMC) in fortified coconut powder, moisture sorption isotherms were constructed under different…

Abstract

Purpose

In order to understand interactions aw vs equilibrium moisture content (EMC) in fortified coconut powder, moisture sorption isotherms were constructed under different storage conditions in order to predict the changes in their physical, chemical and microbiological properties that occur during storage and processing, which are unique to each food.

Design/methodology/approach

For which the moisture sorption isotherms were determined at three different temperatures (15, 25 and 35 °C), in a range of water activity from 0.1 to 0.90. Nine models, namely, the GAB, BET, Oswin, Smith, Halsey, Henderson, Chung and Pfost, Peleg and Caurie equations, were fitted to the sorption data. Various statistical tests were adopted as criteria to evaluate the fit performance of the models.

Findings

Of the models tested, the Peleg model gave the best fit to experimental data (R2 = 0.997; RMSE = 0.276), across the full range of water activities and at different temperatures. Humidity of the monolayer (mo) was found between 2.54 and 2.34%, a fundamental parameter to define the storage and control conditions, given that it is considered the value at which the product is more stable. The net sorption isosteric heat (Qst) increased to maximum and then diminished with increased moisture content (Xw); maximum values were obtained in the Xw interval between 0.48 and 2.87% (db), being between 35.72 and 99.26 kJ/mol, where the maximum value indicates coverage of the strongest bond sites and higher adsorbate-adsorbent interaction.

Originality/value

These results provide reliable experimental data on water absorption isotherms of the CP + FAC important to determine optimal processing, storing and packaging conditions.

Details

British Food Journal, vol. 123 no. 7
Type: Research Article
ISSN: 0007-070X

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Article
Publication date: 10 December 2018

Ahad Abedini, Saeed Emadoddin and Taher Armaghani

This study aims to investigate the numerical analysis of mixed convection within the horizontal annulus in the presence of water-based fluid with nanoparticles of aluminum…

Abstract

Purpose

This study aims to investigate the numerical analysis of mixed convection within the horizontal annulus in the presence of water-based fluid with nanoparticles of aluminum oxide, copper, silver and titanium oxide. Numerical solution is performed using a finite-volume method based on the SIMPLE algorithm, and the discretization of the equations is generally of the second order. Inner and outer cylinders have a constant temperature, and the inner cylinder temperature is higher than the outer one. The two cylinders can be rotated in both directions at a constant angular velocity. The effect of parameters such as Rayleigh, Richardson, Reynolds and the volume fraction of nanoparticles on heat transfer and flow pattern are investigated. The results show that the heat transfer rate increases with the increase of the Rayleigh number, as well as by increasing the volume fraction of the nanoparticles, the heat transfer rate increases, and this increase is about 8.25 per cent for 5 per cent volumetric fraction. Rotation of the cylinders reduces the overall heat transfer. Different directions of rotation have a great influence on the flow pattern and isotherms, and ultimately on heat transfer. The addition of nanoparticles does not have much effect on the flow pattern and isotherms, but it is quantitatively effective. The extracted results are in good agreement with previous works.

Design/methodology/approach

Studying mixed convection heat transfer in the horizontal annulus in the presence of a water-based fluid with aluminum oxide, copper, silver and titanium oxide nanoparticles is carried out quantitatively using a finite-volume method based on the SIMPLE algorithm.

Findings

Increasing the Rayleigh number increases the Nusselt number. Increasing the Richardson number increases heat transfer. Adding nanoparticles does not have much effect on the flow pattern but is effective quantitatively on heat transfer parameters. The addition of nanoparticles sometimes increases the heat transfer rate by about 8.25 per cent. In constant Rayleigh numbers, increasing the Reynolds number reduces heat transfer. The Rayleigh and Reynolds numbers greatly affect the isotherms and streamlines. In addition to the thermal conductivity of nanoparticles, the thermo-physical properties of nanoparticles has great effect in the formation of isotherms and streamlines and ultimately heat transfer.

Originality/value

Studying the effect of different direction of rotation on the isotherms and streamlines, as well as the comparison of different nanoparticles on mixed convection heat transfer in annulus.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 14 November 2019

Leo Lukose and Tanmay Basak

The purpose of this paper is to study thermal (natural) convection in nine different containers involving the same area (area= 1 sq. unit) and identical heat input at the…

Abstract

Purpose

The purpose of this paper is to study thermal (natural) convection in nine different containers involving the same area (area= 1 sq. unit) and identical heat input at the bottom wall (isothermal/sinusoidal heating). Containers are categorized into three classes based on geometric configurations [Class 1 (square, tilted square and parallelogram), Class 2 (trapezoidal type 1, trapezoidal type 2 and triangle) and Class 3 (convex, concave and triangle with curved hypotenuse)].

Design/methodology/approach

The governing equations are solved by using the Galerkin finite element method for various processing fluids (Pr = 0.025 and 155) and Rayleigh numbers (103 ≤ Ra ≤ 105) involving nine different containers. Finite element-based heat flow visualization via heatlines has been adopted to study heat distribution at various sections. Average Nusselt number at the bottom wall ( Nub¯) and spatially average temperature (θ^) have also been calculated based on finite element basis functions.

Findings

Based on enhanced heating criteria (higher Nub¯ and higher θ^), the containers are preferred as follows, Class 1: square and parallelogram, Class 2: trapezoidal type 1 and trapezoidal type 2 and Class 3: convex (higher θ^) and concave (higher Nub¯).

Practical implications

The comparison of heat flow distributions and isotherms in nine containers gives a clear perspective for choosing appropriate containers at various process parameters (Pr and Ra). The results for current work may be useful to obtain enhancement of the thermal processing rate in various process industries.

Originality/value

Heatlines provide a complete understanding of heat flow path and heat distribution within nine containers. Various cold zones and thermal mixing zones have been highlighted and these zones are found to be altered with various shapes of containers. The importance of containers with curved walls for enhanced thermal processing rate is clearly established.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 27 May 2014

Ahmad Mashal, Jehad Abu-Dahrieh, Ashraf A. Ahmed, Lukumon Oyedele, No’man Haimour, Ahmad Al-Haj-Ali and David Rooney

The purpose of this paper is to investigate the performance of natural Jordanian zeolite tuff to remove ammonia from aqueous solutions using a laboratory batch method and…

Abstract

Purpose

The purpose of this paper is to investigate the performance of natural Jordanian zeolite tuff to remove ammonia from aqueous solutions using a laboratory batch method and fixed-bed column apparatus. Equilibrium data were fitted to Langmuir and Freundlich models.

Design/methodology/approach

Column experiments were conducted in packed bed column. The used apparatus consisted of a bench-mounted glass column of 2.5 cm inside diameter and 100 cm height (column volume = 490 cm3). The column was packed with a certain amount of zeolite to give the desired bed height. The feeding solution was supplied from a 30 liter plastic container at the beginning of each experiment and fed to the column down-flow through a glass flow meter having a working range of 10-280ml/min.

Findings

Ammonium ion exchange by natural Jordanian zeolite data were fitted by Langmuir and Freundlich isotherms. Continuous sorption of ammonium ions by natural Jordanian zeolite tuff has proven to be effective in decreasing concentrations ranging from 15-50 mg NH4-N/L down to levels below 1 mg/l. Breakthrough time increased by increasing the bed depth as well as decreasing zeolite particle size, solution flow-rate, initial NH4+ concentration and pH. Sorption of ammonium by the zeolite under the tested conditions gave the sorption capacity of 28 mg NH4-N/L at 20°C, and 32 mg NH4-N/L at 30°C.

Originality/value

This research investigates the performance of natural Jordanian zeolite tuff to remove ammonia from aqueous solutions using a laboratory batch method and fixed-bed column apparatus. The equilibrium data of the sorption of Ammonia were plotted by using the Langmuir and Freundlich isotherms, then the experimental data were compared to the predictions of the above equilibrium isotherm models. It is clear that the NH4+ ion exchange data fitted better with Langmuir isotherm than with Freundlich model and gave an adequate correlation coefficient value.

Details

World Journal of Science, Technology and Sustainable Development, vol. 11 no. 2
Type: Research Article
ISSN: 2042-5945

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Article
Publication date: 29 July 2021

Nirmalendu Biswas, Nirmal Kumar Manna, Dipak Kumar Mandal and Rama Subba Reddy Gorla

This study aims to investigate thermo-bioconvection of oxytactic microorganisms occurring in a nanofluid-saturated porous lid-driven cavity in the presence of the magnetic…

Abstract

Purpose

This study aims to investigate thermo-bioconvection of oxytactic microorganisms occurring in a nanofluid-saturated porous lid-driven cavity in the presence of the magnetic field. The heating is provided through a bell-shaped curved bottom wall heated isothermally. The effects of the peak height of the curved bottom wall, bioconvection Rayleigh number (Rb), Darcy number (Da), Hartmann number (Ha), Peclet number (Pe), Lewis number (Le) and Grashof number (Gr) on the flow structure, temperature and the iso-concentrations of oxygen and microorganisms are examined and explained systematically. The local and global, characteristics of heat transfer and oxygen concentration, are estimated through the Nusselt number (Nu) and Sherwood number (Sh), respectively.

Design/methodology/approach

The governing equations of continuity, momentum, energy and additionally consisting of species transport equations for oxygen concentration and population density of microorganisms, are discretized by the finite volume method. The evolved linearized algebraic equations are solved iteratively through the alternate direction implicit scheme and the tri-diagonal matrix algorithm. The computation domain has meshed in non-uniform staggered grids. The entire computations are carried out through an in-house developed code written in FORTRAN following the SIMPLE algorithm. The third-order upwind and second-order central difference schemes are used for handling the advection and diffusion terms, respectively. The convergence criterion for the iterative process of achieving the final solution is set as 10–8 and 10–10, respectively, for the maximum residuals and the mass defect.

Findings

The results show that the flow and temperature distribution along with the iso-concentrations of oxygen and microorganisms are markedly affected by the curvature of the bottom wall. A secondary circulation is developed in the cavity that changes the flow physics significantly. The Nu increases with the peak height of the curved bottom wall and Da; however, it decreases with Ha and Rb. The Sh increases with Da but decreases with Ha and the peak height of the curved wall.

Research limitations/implications

A similar study of bioconvection could be extended further considering thermal radiation, chemical attraction, gravity, light, etc.

Practical implications

The outcomes of this investigation could be used in diverse fields of multi-physical applications such as in food industries, chemical processing equipment, fuel cell technology and enhanced oil recovery.

Originality/value

The insights of bioconvection of oxytactic microorganisms using a curved bottom surface along with other physical issues such as nanofluid, porous substance and magnetic field are addressed systematically and thoroughly.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0961-5539

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Content available
Book part
Publication date: 4 May 2018

Intan Lestari

Purpose – The purpose of this paper to immobilization provides biosorbent particle with density and mechanichal strength, immobilization can save the cost of separating…

Abstract

Purpose – The purpose of this paper to immobilization provides biosorbent particle with density and mechanichal strength, immobilization can save the cost of separating from biomass, can be regeneration and to increase adsorption capacity for metal ions.

Design/Methodology/Approach – The parameters affecting the adsorption, such as initial metal ion concentration, pH, contact time, and temperature, were studied. The analysis of biosorbent functional group was carried out by Fourier Transform Infrared Spectroscopy, SEM-EDX, for elemental analysis.

Findings – Optimum pH condition for biosorption Cd(II) was pH 5, contact time was 45 min, and initial concentration was 250 mg/L. Biosorbent analysis was characterized using SEM-EDX and FTIR analysis. Kinetics adsorption was studied and analyzed in terms of the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. The result showed that the biosorption for Cd(II) ion followed the pseudo-second-order kinetic model. Biosorption data of Cd(II) ion at 300°K, 308°K, and 318°K was analyzed with Temkin, Langmuir, and Freundlich isotherms. Biosorption of Cd(II) by durian seed immobilization in alginate according to the Langmuir isotherm equation provided a coefficient correlation of r2 = 0.939 and maximum capacity biosorption of 25.05 mg/g.

Details

Proceedings of MICoMS 2017
Type: Book
ISBN:

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Article
Publication date: 25 February 2021

Leo Lukose and Tanmay Basak

The purpose of this paper is to address various works on mixed convection and proposes 10 unified models (Models 1–10) based on various thermal and kinematic conditions of…

Abstract

Purpose

The purpose of this paper is to address various works on mixed convection and proposes 10 unified models (Models 1–10) based on various thermal and kinematic conditions of the boundary walls, thermal conditions and/ or kinematics of objects embedded in the cavities and kinematics of external flow field through the ventilation ports. Experimental works on mixed convection have also been addressed.

Design/methodology/approach

This review is based on 10 unified models on mixed convection within cavities. Models 1–5 involve mixed convection based on the movement of single or double walls subjected to various temperature boundary conditions. Model 6 elucidates mixed convection due to the movement of single or double walls of cavities containing discrete heaters at the stationary wall(s). Model 7A focuses mixed convection based on the movement of wall(s) for cavities containing stationary solid obstacles (hot or cold or adiabatic) whereas Model 7B elucidates mixed convection based on the rotation of solid cylinders (hot or conductive or adiabatic) within the cavities enclosed by stationary or moving wall(s). Model 8 is based on mixed convection due to the flow of air through ventilation ports of cavities (with or without adiabatic baffles) subjected to hot and adiabatic walls. Models 9 and 10 elucidate mixed convection due to flow of air through ventilation ports of cavities involving discrete heaters and/or solid obstacles (conductive or hot) at various locations within cavities.

Findings

Mixed convection plays an important role for various processes based on convection pattern and heat transfer rate. An important dimensionless number, Richardson number (Ri) identifies various convection regimes (forced, mixed and natural convection). Generalized models also depict the role of “aiding” and “opposing” flow and combination of both on mixed convection processes. Aiding flow (interaction of buoyancy and inertial forces in the same direction) may result in the augmentation of the heat transfer rate whereas opposing flow (interaction of buoyancy and inertial forces in the opposite directions) may result in decrease of the heat transfer rate. Works involving fluid media, porous media and nanofluids (with magnetohydrodynamics) have been highlighted. Various numerical and experimental works on mixed convection have been elucidated. Flow and thermal maps associated with the heat transfer rate for a few representative cases of unified models [Models 1–10] have been elucidated involving specific dimensionless numbers.

Originality/value

This review paper will provide guidelines for optimal design/operation involving mixed convection processing applications.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 10 December 2019

Akbar Eslami, Zahra Goodarzvand Chegini, Maryam Khashij, Mohammad Mehralian and Marjan Hashemi

A nanosilica adsorbent was prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET.

Abstract

Purpose

A nanosilica adsorbent was prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET.

Design/methodology/approach

The optimum conditions for the highest adsorption performance were determined by kinetic modeling. The adsorbent was used for the adsorption of acetaminophen (ACT), and the parameters affecting the adsorption were discussed like pH, initial concentration, contact time and adsorbent dosage. The adsorbent have been characterized by SEM, XRD and BET analysis. The kinetic models including pseudo-first-order and pseudo-second-order with Langmuir and Freundlich isotherm models were applied to investigate the kinetic and isotherms parameters.

Findings

The adsorption of ACT increased to around 95% with the increase of nanosilica concentration to 30 g/L. Moreover, the adsorption process of ACT follows the pseudo-second-order kinetics and the Langmuir isotherm with the maximum adsorption capacity of 609 mg/g.

Practical implications

This study provided a simple and effective way to prepare of nanoadsorbents. This way was conductive to protect environmental and subsequent application for removal of emerging pollutants from aqueous solutions.

Originality/value

The novelty of the study is synthesizing the morphological and structural properties of nanosilica-based adsorbent (specific surface area, pore volume and size, shape and capability) and improving its removal rate through optimizing the synthesis method; and studying the capability of synthesis of nanosilica-based adsorbent for removal of ACT as a main emerging pharmaceutical water contaminant.

Details

Pigment & Resin Technology, vol. 49 no. 1
Type: Research Article
ISSN: 0369-9420

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Article
Publication date: 13 November 2019

Hossam Altaher, Yehia H. Magdy and Anwar F. Al Yaqout

The disposal of wastewater containing silver is an environmental concern. Due to the toxicity of silver, treatment of such wastewater is necessary. Real wastewater…

Abstract

Purpose

The disposal of wastewater containing silver is an environmental concern. Due to the toxicity of silver, treatment of such wastewater is necessary. Real wastewater contains a complex matrix of pollutants. The purpose of this paper is to study the adsorption behavior of silver in single and binary systems (with nickel) onto granular activated carbon.

Design/methodology/approach

The effect of silver ions concentration and the mass of adsorbent on the adsorption behavior were analyzed. Five two-parameter isotherms (Langmuir, Elovich, Freundlich, Dubinin–Radushkevich and Temkin) were applied to investigate the adsorption mechanism. Both linear and nonlinear regressions were tested for the first three isotherms. The experimental data were also fitted to Redlich–Petersons, Sips and Toth models.

Findings

A direct relationship between the initial silver ion concentration and its adsorption capacity was observed, whereas an inverse relationship between the adsorbent mass and the adsorption capacity was documented. The Langmuir model was found to best-fit the data indicating monolayer adsorption behavior. The maximum uptake was 2,500 mg/g in the single adsorption system. This value decreased to 909 mg/g in the binary system. The adsorption was found to have an exothermic chemical nature.

Originality/value

The study of the silver adsorption in a single system is inaccurate. Real wastewater contains a complex matrix of pollutants. This research gives a clear insight into the adsorption behavior in binary systems.

Details

World Journal of Science, Technology and Sustainable Development, vol. 17 no. 2
Type: Research Article
ISSN: 2042-5945

Keywords

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