Predicting Sorption Isotherms and Net Isosteric Heats of Sorption of Maize Grains at Different Temperatures

2014 ◽  
Vol 10 (3) ◽  
pp. 393-401 ◽  
Author(s):  
André Talla
Keyword(s):  
Moisture Content ◽  
Sorption Isotherms ◽  
Isosteric Heat ◽  
Sub Saharan Africa ◽  
Maximum Deviation ◽  
Different Temperatures ◽  
Sub Saharan ◽  
C 50 ◽  
The Stability ◽  
Monolayer Moisture

Abstract In Sub-Saharan Africa, drying maize on their stem was the traditional technique frequently used; this technique must be improved to avoid contaminations and to increase the quality of drying. However, the method of storage is accountable for the most significant losses after harvest, because mildew develops when the conditions of storage (too high temperature and moisture of the air) do not tally with the final content of the dried product. Sorption isotherms of products are most important to model moisture uptake during storage and distribution. Sorption isotherms of intermediate moisture content maize grains were determined using the gravimetric static method of saturated salt solutions at 30°C, 40°C, 50°C, and 60°C, and GAB equation was applied to discuss the results. This model correctly describes the evolutions of maize sorption isotherms, with maximum deviation of 0.0080 kg water/kg db. The net isosteric heat of sorption was determined also, using the Clausius–Clapeyron equation, and it was varied from 463 kJ/kg to 1,264 kJ/kg, decreasing with increasing moisture content. This effect was well described by an exponential function with a regression coefficient R2 > 97%. The monolayer moisture content was found to decrease with increasing temperature. These results can be used to predict the potential changes in the stability of maize grains and later for the development of a system of suitable drying.

Analysis of Moisture Desorption Isotherms of Eggplant (Solanum melongena)

2010 ◽  
Vol 16 (5) ◽  
pp. 417-425 ◽  
Author(s):  
R. Moreira ◽  
F. Chenlo ◽  
M.D. Torres ◽  
N. Vallejo
Keyword(s):  
Moisture Content ◽  
Solanum Melongena ◽  
Gravimetric Method ◽  
Sorption Isotherms ◽  
Isosteric Heat ◽  
Integral Enthalpy ◽  
Differential Enthalpy ◽  
Different Temperatures ◽  
Enthalpy And Entropy ◽  
Monolayer Moisture

Sorption isotherms of eggplant were determined employing, as experimental technique, a static gravimetric method, using saturated salt solutions to achieve the equilibrium. The experiments were carried out at different temperatures (20, 35, 50 and 65 °C). The sorption isotherms can be classified, according to Brunauer’s classification, as type II or III depending on temperature. Equilibrium moisture content data were correlated by two models usually applied to foodstuffs (Brunauer-Emmet-Teller (BET) and Halsey). BET model was employed to determine monolayer moisture content (0.121 kg/kg d.b.). Halsey model was selected by the goodness of fitting. Experimental data were analyzed by a thermodynamic approach to obtain some properties as net isosteric heat, equilibrium heat and differential and net integral entropy. The differential enthalpy and entropy decreased with increasing moisture content and satisfied the compensation theory. The net integral enthalpy and entropy showed maximum values (~31 kJ/mol and ~88 J/mol.K) at 0.093 (kg/kg d.b.) of moisture content.

scholarly journals Moisture sorption isotherms of castor beans. Part 1: Mathematical modeling and hysteresis

2016 ◽  
Vol 20 (8) ◽  
pp. 751-756 ◽  
Author(s):  
André L. D. Goneli ◽  
Paulo C. Corrêa ◽  
Gabriel H. H. de Oliveira ◽  
Osvaldo Resende ◽  
Munir Mauad
Keyword(s):  
Moisture Content ◽  
Sorption Isotherms ◽  
Moisture Sorption ◽  
Environmental Condition ◽  
Adsorption And Desorption ◽  
Moisture Sorption Isotherms ◽  
Different Temperatures ◽  
The Difference ◽  
The Stability ◽  
And Storage

ABSTRACT Sorption isotherms are of great importance in post-harvest procedures, especially for predicting drying and storage, which help to establish the final moisture content of the product under certain environmental condition. Hysteresis is a phenomenon that occurs due to the difference between adsorption and desorption curves, which aids the evaluation of chemical and microbiological deteriorations, indicating the stability of stored products. Moisture sorption isotherms of castor beans were determined and hysteresis was analyzed. Static gravimetric technique at different temperatures (25, 35, 45 and 55 ± 1 °C) was used. Saturated salt solutions in the range of 37-87% ± 2% were utilized to create the required controlled relative humidity environment. Equilibrium moisture content data were correlated by different mathematical models and the Modified Halsey model presented good adjustment for the data, according to statistical procedures. Hysteresis between adsorption and desorption isotherms is present over the range of 0.2-0.9 of water activity, regardless of the temperature. This phenomenon decreases with temperature increase.

Moisture Sorption Isotherms and Thermodynamic Properties of Carrot

2011 ◽  
Vol 7 (3) ◽  
Author(s):  
Valeria S. Eim ◽  
Carmen Rosselló ◽  
Antoni Femenia ◽  
Susana Simal
Keyword(s):  
Moisture Content ◽  
Dry Matter ◽  
Sorption Isotherms ◽  
Moisture Sorption ◽  
Isosteric Heat ◽  
Nonlinear Regression Analysis ◽  
Mean Relative Error ◽  
Moisture Sorption Isotherms ◽  
Different Temperatures ◽  
Water Sorption Isotherms

The water sorption isotherms of carrot were determined at five different temperatures (at 10, 20, 30, 40 and 50ºC) within wide ranges of moisture content (1.3-78.4 kg water /100 kg dry matter) and water activities (0.165-0.907) by using a standardized conductivity thermohygrometer. The sorption isotherms exhibited the type III behaviour, thus, an increase in temperature promoted a decrease in water activity. The GAB, Halsey, Henderson, Iglesias & Chirife and Oswin models were tested to fit the experimental data by using nonlinear regression analysis. The GAB and Henderson models satisfactorily described the sorption isotherms (mean relative error < 5.6%). The net isosteric heat of sorption (Qstn) and the differential entropy (Sd), estimated as functions of the moisture content, decreased as the carrot moisture content increased.

Modeling of moisture sorption isotherm and evaluation of net isosteric heat for spray-dried fortified coconut (Cocos nucifera L.) powder

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Juan Carlos Lucas Aguirre ◽  
German Antonio Giraldo Giraldo ◽  
Misael Cortés Rodríguez
Keyword(s):  
Experimental Data ◽  
Moisture Content ◽  
Sorption Isotherms ◽  
Moisture Sorption ◽  
Isosteric Heat ◽  
Fundamental Parameter ◽  
Sorption Data ◽  
Content Type ◽  
Moisture Sorption Isotherms ◽  
Different Temperatures

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

Moisture Sorption Isotherms of Osmotically Dehydrated Sweet Pepper

2007 ◽  
Vol 3 (5) ◽  
Author(s):  
Jatindra Kumar Sahu ◽  
Ajita Tiwari
Keyword(s):  
Moisture Content ◽  
Sorption Isotherms ◽  
Moisture Sorption ◽  
Isosteric Heat ◽  
Sweet Pepper ◽  
Coefficient Of Determination ◽  
Clapeyron Equation ◽  
Moisture Sorption Isotherm ◽  
Moisture Sorption Isotherms ◽  
Monolayer Moisture

Moisture sorption isotherms of osmotically dehydrated sweet peppers were determined at 15oC, 30oC and 40oC using static desiccator techniques. In the study, seven levels of water activity in range of 0.08 to 0.91 were used by the use of saturated salt solutions. The isotherms were found to be sigmoid type and of BET classification II. Out of seven sorption models i.e. BET, modified BET, Hasley, Caurie, GAB, Oswin and Smith, fitted to the experimental data, Oswin model was found to be the best for accurate prediction of moisture sorption isotherm with highest value of coefficient of determination (R2) and lowest values of standard error (SE) and relative deviation parentage (Rd). The value of monolayer moisture content of the osmotically dehydrated sweet pepper was found to be 3.037%, 3.934% and 4.432% (db) at 15oC, 30oC and 40oC respectively. The values of net isosteric heat of sorption as calculated by Clausius–Clapeyron equation showed a regular fall with increase in moisture content.

Sorption Properties of Cape Gooseberry (Physalis peruviana L.)

2012 ◽  
Vol 8 (1) ◽  
Author(s):  
Farid B. Cortés ◽  
Veronica López ◽  
Benjamin A. Rojano
Keyword(s):  
Free Energy ◽  
Moisture Content ◽  
Gibbs Free Energy ◽  
Isosteric Heat ◽  
Sorption Equilibrium ◽  
Physalis Peruviana ◽  
Different Temperatures ◽  
Gab Model ◽  
Monolayer Moisture ◽  
Cape Gooseberry

The sorption equilibrium of water for cape gooseberry at different temperatures (25, 35, 50 and 60°C) over a range of relative humidity levels, from 0.10 to 0.90, were determined using a gravimetric static method. The isosteric heat and Gibbs free energy were calculated from the sorption equilibrium. GAB, BET, SMITH, modified de Halsey, modified de Chung-Pfost, modified Oswin and modified Henderson models were tested to fit the experimental data. The GAB model was found to be the most suitable for describing the sorption curves. The monolayer moisture content values for the sorption at different temperatures were calculated using the BET model. The sorption curves show a Type III behavior. The isosteric heat decreased with increases in moisture content, while the Gibbs free energy increased.

Economic freedom, competition and bank stability in Sub-Saharan Africa

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Emmanuel Sarpong-Kumankoma ◽  
Joshua Yindenaba Abor ◽  
Anthony Q. Q. Aboagye ◽  
Mohammed Amidu
Keyword(s):  
Economic Freedom ◽  
Banking Sector ◽  
Generalized Method Of Moments ◽  
Sub Saharan Africa ◽  
Bank Stability ◽  
Content Type ◽  
Show Evidence ◽  
Negative Effect ◽  
Sub Saharan ◽  
The Stability

PurposeThis study aims to analyze the potential implications of economic freedom and competition for bank stability.Design/methodology/approachUsing system generalized method of moments and data from 139 banks across 11 Sub-Saharan African (SSA) countries during the period 2006–2012, this study considers whether the degree of economic freedom affects the relationship between competition and bank stability.FindingsThe results show evidence of the competition-fragility hypothesis in SSA banking, but suggests that beyond a setting threshold, increases in market power may also be damaging to bank stability. Financial freedom has a negative effect on bank stability, suggesting that banks operating in environments with greater financial freedom generally tend to be less stable or more risky. The authors also find evidence of a conditional effect of economic freedom on the competition–stability relationship, implying that bank failure is more likely to occur in countries with greater economic freedom, but with low competition in the banking sector.Practical implicationsThe results suggests to policy makers that a moderate level of competition and economic freedom may be the appropriate policy to ensure the stability of banks.Originality/valueThe study provides insight on the competition–bank stability relationship, by providing new empirical evidence on the effect of economic freedom, which has not been previously considered.

Sorption Isotherms and Isosteric Heat of Peanut Pods, Kernels and Hulls

2007 ◽  
Vol 13 (3) ◽  
pp. 231-238 ◽  
Author(s):  
P.C. Corrêa ◽  
A.L.D. Goneli ◽  
C. Jaren ◽  
D.M. Ribeiro ◽  
O. Resende
Keyword(s):  
Experimental Data ◽  
Relative Humidity ◽  
Moisture Content ◽  
Mathematical Models ◽  
Equilibrium Moisture Content ◽  
Sorption Isotherms ◽  
Isosteric Heat ◽  
Statistical Parameters ◽  
Peanut Hulls ◽  
Pass Through

This study was carried out to evaluate the sorption isotherms of peanut pods, kernels and hulls for several temperature and humidity conditions and to fit different mathematical models to the experimental data, selecting the one best fitting the phenomenon. The dynamic method was applied to obtain the hygroscopic equilibrium moisture content. The environmental conditions were provided by means of an atmospheric conditioning unit, in which removable perforated trays were placed to allow air to pass through peanut mass, each one containing 50 g of the product. The mathematical models frequently used for the representation of hygroscopicity of agricultural products were fit to the experimental data. Based on those results, it was concluded that peanut pods, kernels and hulls presented differentiated hygroscopicity. The equilibrium moisture content for peanut pods, kernels and hulls increased with an increase in the relative humidity at any particular temperature and decreased with increase in temperature at constant relative humidity. At a constant water activity, peanut hulls samples had higher equilibrium moisture content than the pods and kernels samples. Based on statistical parameters, the modified Henderson and Chung-Pfost models were found to adequately describe the sorption characteristics of peanut pods, kernels and hulls. Isosteric heat of desorption were evaluated by applying the Clausius—Clapeyron equation to experimental isotherms and decreased with increasing moisture content. The peanut hulls had higher isosteric heat of sorption than that peanut pods and kernels.

Adsorption Isotherms for Red Onion Slices Using Empirical and Neural Network Models

2011 ◽  
Vol 7 (6) ◽  
Author(s):  
Hamid Reza Gazor ◽  
Afshin Eyvani
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Moisture Content ◽  
Equilibrium Moisture Content ◽  
Multilayer Perceptron ◽  
Sorption Isotherms ◽  
Network Models ◽  
Isosteric Heat ◽  
Neural Network Models ◽  
Isosteric Heat Of Adsorption

Moisture sorption isotherms of red onion slices were determined at 30, 40, 50, and 60°C using the standard gravimetric static method over a range of relative humidity from 0.11 to 0.83. The experimental sorption curves were fitted by seven empirical equations: modified Henderson, modified Chung–Pfost, modified Halsey, modified Oswin, modified Smith, modified BET, and GAB. Also three types of Artificial neural network models: linear, multilayer perceptron, and radial basis function were tested and developed to predict the equilibrium moisture content of onion slices and the selected models were trained by using related algorithms. The modified Oswin model was found acceptable for predicting adsorption moisture isotherms and fitting to the experimental data, based on the coefficient of determination (R2= 0.991), mean relative percent error (MRE=15.019), and standard error of estimation (SEE=1.371). Besides, multilayer perceptron model with four layers (2: 17: 14: 1) was selected as the best artificial neural network for estimation of onion slices’ equilibrium moisture content by considering R2= 0.993 and good performance. The net isosteric heat of adsorption of moisture was determined by applying the Clausius–Clapeyron equation to the sorption isotherms at different temperatures. The net isosteric heat of adsorption of red onion slices varied between 1.46 and 4.96 kJ/mol at moisture content varying between 2% and 52% (d.b.).

A hysteresis model suitable for numerical simulation of moisture content in wood

Holzforschung ◽  
2007 ◽  
Vol 61 (2) ◽  
pp. 175-181 ◽  
Author(s):  
Henrik Lund Frandsen ◽  
Staffan Svensson ◽  
Lars Damkilde
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Sorption Isotherms ◽  
Ambient Air ◽  
Domain Model ◽  
Hysteresis Phenomenon ◽  
Hysteresis Model ◽  
Worst Case ◽  
Different Temperatures ◽  
History Of

Abstract The equilibrium moisture content in wood depends not only on the current relative humidity in ambient air, but also on the history of relative humidity variations. This hysteresis dependence of sorption in wood implies that in the worst case the moisture content for a given relative humidity may deviate by 30–35%. While researchers seem to have reached a general agreement on the hypothesis for the sorption hysteresis phenomenon, only a few models describing the phenomenon are available. Current models such as the independent domain model have numerical deficiencies and drawbacks. This paper presents a new hysteresis model, which mathematically resolves in closed-form expressions, with the current relative humidity and moisture content as the only input parameters. Furthermore, the model has the advantage of being applicable to different sorption isotherms, i.e., different species and different temperatures. These features make the model relatively easy to implement into a numerical method such as the finite element method.

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