Constant Moisture Content Research Articles

Separation of drying strains and the calculation of drying stresses considering the viscoelasticity of red pine wood during drying

ABSTRACTThe objective of this study was to separate drying strains into elastic, viscoelastic, and viscous strains using free shrinkage and recovery from the deformation of slices at stress relief. The apparent shrinkage deformation was obtained by measuring the change in width of drying specimens during drying. Using the slice method, elastic and viscoelastic deformation were defined as the instantaneous change in width of a slice right after cutting and the change in the width of a slice with constant moisture content during 48 h, respectively. Viscous deformation, permanent and nonrecoverable deformation of wood, was defined as the difference in deformation between free shrinkage and the sum of the apparent, elastic, and viscoelastic deformations. These elastic, viscoelastic, and viscous strains were applied to a viscoelastic model, and coefficients of viscoelasticity and viscosity were derived. The drying stress and deformation of red pine wood at specific times during the drying process can be predicted using each coefficients and modulus of elasticity obtained by experiment.

Use of Time Domain Reflectometry to Estimate Moisture and Density of Unbound Road Materials: Laboratory Calibration and Field Investigation

Soil moisture content and dry density of unbound granular pavement materials are important properties for compaction control that influence pavement performance under cyclic loading. Under these loading conditions, increasing moisture content can accelerate significant changes in density. Time domain reflectometry (TDR) is a method for measuring the moisture content and density of soils with rod probe sensors. This paper introduces new calibration functions for TDR measurements using these rod probe sensors embedded in the soil. TDR measurements were taken in the laboratory for a typical road base material at two basically different conditions: at constant moisture content with different dry densities and at constant dry density with different moisture contents. In this study, a relationship was developed between the voltage drop occurring for the passage of an electromagnetic wave through the soil and the bulk density. The permittivity of the soil sample obtained from the travel time of TDR signals was used to calculate the volumetric moisture content. Finally, the gravimetric moisture content was obtained from the volumetric moisture content and bulk density relationship. For the validation of the calibration functions, rod probe sensors were installed in a road to obtain in situ moisture content and density under field conditions. Laboratory results indicate that the calibration functions are independent of moisture and density, and the field test shows the applicability of the method. The newly developed calibration functions allow for the monitoring of the long-term pavement performance, leading to a better understanding of the time-dependent evolution of, for example, rutting of roads.

Stoichiometric Equilibrium Modeling of Corn Cob Gasification and Validation Using Experimental Analysis

Prediction of gasifier performance is generally carried out using two techniques, namely, kinetic modeling and chemical equilibrium modeling. The later model was adopted in the current study because it is not governed by any of the gasifier design parameters. Chemical equilibrium modeling was deployed to compute and ascertain the influence of the equivalence ratio (ER), moisture content (MC), and reaction temperature (RT) on corn cob gasification. The simulation studies reveal that, for a gasification system, with an increase in the ER (for a constant MC and RT), the higher heating value (HHV) of producer gas drops, with an increase in the MC (for a constant ER and RT), the H2 content increases but CO decreases, and with an increase in the RT (for a constant ER and MC), both the H2 and CO contents increase. An attempt was made toward validating the simulated results by subjecting corn cob to gasification in a 25 kWth downdraft gasifier. A comparative analysis on the simulation results and experimental out...

Perpendicular Mechano-Sorptive Strains during Moisture Desorption from Eucalyptus nitens Specimens

The purpose of this paper was to determine the mechano-sorptive strains produced during desorption of moisture from Eucalyptus nitens specimens, from a perspective of modeling wood drying stresses. Eucalyptus nitens samples were tested in the radial and tangential directions. The mechano-sorptive strain was measured by cantilever bending during desorption. The runs were performed in a conditioning chamber at constant low temperature and variable equilibrium moisture content. Four load levels were considered for testing. The results showed that the mechano-sorptive strain during desorption of moisture was proportional to applied stress and reached the maximum value in the tangential direction. Also, the mechano-sorption coefficient depended on wood orientation and reached the maximum value of 5.46 × 10-2 in the tangential direction.

Shear strength features of unsaturated clayey sand by lab test

Abstract To study the shear feature of the clayey sand subgrade, the equations of soil–water characteristic curve with different net mean stresses were established based on laboratory test and non-linear elastic theory. The laboratory result shows that the net mean stress has significantly affected on the soil–water characteristic curve shape. The greater the net mean stress, the smaller moisture content of soil. The shear features of clayey sand were also figured out using triaxial equipment with mini air and water pressure sensors in non-drained and non-exhaust state. The results of research indicate that the net confining pressure and moisture content have significant effect on the strength, deformation, and yield feature of unsaturated clayey sand. The shear strength increases with the growth of net confining pressure in case of constant moisture content. The cohesion and friction angle of soil become larger with the increase of moisture content less than optimum content; while the water content is greater than the optimum water content, they show the opposite trend. The unsaturated clayey sand shows obvious dilatancy deformation in shearing. In the phase of shear contraction, the shear stress increases with the growth of suction and net confining pressure, which declines after it reach the peak point. Results of this research will be a benefit for the engineer.

Quantification based on dimensionless dendrometry and drying of residual biomass from the pruning of orange trees in Bolivar province (Ecuador)

AbstractIn this work, a new approach to evaluating the amount of residual biomass obtained from orange trees based on normalization of variables is proposed for Bolivar province, Ecuador. So far, several models to quantify the amount of residues obtained from pruning have been proposed from dendrometric and cultivation variables, such as height, crown diameter, stem diameter, area per plant, yield, and age. However, the high dispersion of their values, caused by uncontrolled conditions, gave models with a low‐medium coefficient of determination. The aim of this work has been to develop several models in order to predict wet available biomass using dimensionless dendrometric parameters from height, diameter and height of the crown, and the stem height. They improved the coefficients of determination to 0.94 for the global mathematical model. The drying process of pruned materials has also been analyzed. Residual biomass with 50% initial moisture content was dried outdoors on cement and agricultural soil until it reached constant moisture content. Models used to describe the drying process of agricultural products were employed to fit the observed data of the drying process of orange tree chips. Among the tested models, the Midili and Page models were those that best fitted the observed data in the drying process. The information offered by these equations is of vital importance because they help estimate the amount of biomass that is generated in a given area, and the implementation geographic information system (GIS) maps. In addition, logistic algorithms can be applied. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Effect of Fly Ash and Rice Husk Ash on Permanent Deformation Behaviour of Subgrade Soil under Cyclic Triaxial Loading

This work presents the laboratory study conducted on fly ash and rice husk ash as soil stabilizers. Using these stabilizers, the deformation behaviors of subgrade soil-mixtures under repeated triaxial loading was conducted. Resilient strain, permanent strain and resilient modulus were ascertained at different deviator stress level and confining pressures at constant moisture content. Admixing of fly ash and rice husk ash reduces the maximum dry density but increase the water demands. The variations of elastic deformation and resilient modulus were significantly influenced by fly ash and rice husk ash contents. Better performances were observed for admixed soil irrespective of number of load applications. The results obtained from the laboratory confirm the potential use of subgrade soil admixed with fly ash and rice husk ash with respect to the permanent deformation.

Wood quality assessment of Pinus radiata (radiata pine) saplings by dynamic mechanical analysis

The use of dynamic mechanical analysis was explored as a possible method of screening for wood quality in breeding programmes. Viscoelastic properties along the grain of wood from 18-month-old Pinus radiata saplings were measured using a humidity-controlled dynamic mechanical analyser. Storage modulus and tanδ were determined independently for opposite wood (OW) and compression wood (CW) in 25 trees in the temperature range from 10 to 45 °C at 5 °C intervals at three frequencies (0.1, 1 and 10 Hz) at constant moisture content of 9 %. Storage modulus and tanδ were frequency and temperature dependent. The two wood types did not differ significantly in their storage modulus. But OW exhibited significantly higher tanδ values than CW. The relationship of viscoelastic properties with physical (acoustic velocity, basic density and longitudinal shrinkage) and chemical wood properties was explored. There was a strong correlation (R = 0.76) between storage modulus and dynamic MOE (measured by acoustics). In addition, tanδ was positively correlated with longitudinal shrinkage. Monosaccharide compositions of the cell wall polysaccharides and lignin contents were determined and showed significant differences in the relative proportion of major cell wall components in OW and CW. Correlations between tanδ and xylose, originating from heteroxylans, and lignin content were found for CW, suggesting that the damping behaviour of cell walls is controlled by the matrix between cellulose fibril aggregates.

Dendrometric characterization of corn cane residues and drying models in natural conditions in Bolivar Province (Ecuador)

The use of biomass raw material from agricultural areas is a challenge for Ecuatorian government. However there is lack information about surveying systems and processing in its height and weather conditions. The objective of this work was to develop methods to quantify straw residues, easily applicable in corn areas of Guaranda (Ecuador), and model the drying process at different air conditions. Two dendrometric equations were obtained for predicting dry available biomass by stem and cultivated area respectively, from corn mean height and radius of the stem. High coefficients of determination were obtained (0.94 and 0.97 respectively). Straw chips with initial moisture content ranging from 70 to 80% with an average moisture content of 76.7% wet basis were dried until they reached constant moisture content. Traditional models used to describe the drying process of agricultural products were employed to fit the observed data of the drying process of straw corn chips. Among the tested models, the Midili, Page, and sigmoid model were those that best fit the observed data representing the drying process. The effective diffusion (Def) was determined by means of an analytical solution of Fick's second law. Effective moisture diffusivity values obtained at natural outdoor drying conditions were 2.443E-11 and 2.035E-10 m2/s, for the first and second falling periods, respectively.

Hygro-mechanically coupled modelling of creep in wooden structures, Part I: Mechanics

In the paper at hand, a modelling approach for the simulation of the anisotropic long-term behaviour of wooden structures subjected to mechanical loading at constant moisture content for the use within the framework of the Finite Element Method is presented. Using a standard-solid body-model in serial combination with a Bingham-element allows for the differentiation between linear viscoelastic and non-linear viscoelastic–viscoplastic behaviour with respect to the applied stress level. Creep failure is considered by means of the concept of strain-energy density. Due to the cylindrical anisotropy of wood, the four material properties required for the description of the creep behaviour are determined depending on material direction and loading type (tension, compression, shear) by means of the re-calculation of experimental results. Finally the approach is applied to the re-calculation of two test-series in bending and to the analysis of a face staggered joint. The paper at hand is the first part of a more complex model and deals with the mechanical long-term behaviour of wood. In the second part, the hygro-mechanical coupling is covered with respect to the consideration of the influence of moisture content on mechanically induced creep and mechano-sorptive effects caused by simultaneous mechanical loading and moisture changes.

Flow and foam properties of extruded maize flour and its biopolymer blends expanded by microwave

Maize flour and blends from starch and zein biopolymers were processed as dense materials by extrusion (120°C, 300J·g−1) and press-molding (140°C, 10min) at a constant moisture content (26%wb), and then foamed by microwave heating. The mechanical properties of foams, determined by a 3-point bending test, were governed by density, in agreement with an open solid foam model. The density and 3D cellular structure of the foams were determined by X-ray tomography. In the same interval of density [0.15, 0.3g·cm−3], foams from microwaved materials had a finer cellular structure than directly expanded materials at extruder outlet. The study of melt rheological behavior with Rheoplast® (100–160°C, SME≤200J·g−1) showed that protein content (0–15%) did not affect shear viscosity but increased elongational viscosity. This trend, similar to the one reported for the storage modulus in a rubbery state, could be attributed to dissipative effects in a starch/protein interphase, explaining the difference of expansion between starch, blends and flour.

Green apple baked snacks functionalized with edible coatings of methylcellulose containing Lactobacillus plantarum

The aim of the present work was to develop a healthy snack as a vehicle of probiotic bacteria. Apple snacks were coated with methylcellulose films containing fructooligosaccharides and Lactobacillus plantarum CIDCA 83114. Dehydration of the snacks at 60 °C for 50 min allowed obtaining a product with water content, crispness and visual aspect similar to those before applying the film-forming solution, without major detrimental effects for microorganisms. Sensory attributes of coated snacks were evaluated by an experienced sensory panel, receiving good scores in taste (6.5 ± 0.6), color (7.7 ± 0.4), texture (7.2 ± 0.4) and overall acceptability (7.2 ± 0.3). Storage of the snacks at 20 °C and 60% RH caused only a mild decrease in the bacterial cultivability after 90 days (1.4 log CFU/g), and a significant number of bacteria were still alive after the simulated gastric (5.5 × 106 ± 0.7 × 106 CFU/g) and intestinal (1.0 × 106 ± 0.4 × 106 CFU/g) digestions of the stored samples. The force–deformation curves showed a typical pattern of brittle materials up to 90 days of storage. The Tg followed a similar trend, in accordance with the constant moisture content. An organoleptically attractive food product was obtained which after 90 days of storage presented a high load of cultivable lactobacilli (2.0 × 108 ± 0.7 × 108 CFU/g). This concentration is well above the minimum considered necessary (106–107 CFU/g) to obtain the benefits of probiotic consumption.

Analysis of Grinding Kinetics and Flow Behavior of Adzuki Bean (Phaseolus Angularis) Flour for Hopper Design

AbstractThe grinding characteristics of Adzuki beans (Phaseolus angularis, AB), also known as red beans, at constant moisture content (14.32% ± 0.23) and the flow properties of the AB flour were analyzed. A sigmoid model suitably described the grinding kinetics of the AB flour (R2 > 0.98). Flow properties of the AB flour having different particle sizes were measured, and the powder flow properties were applied for designing a hopper design. At the smallest particle size (d[3,2] = 267.09 μm), the ratio of change in the bulk density increased from 2.52 to 13.51% as the particle size decreased from d[3,2] = 1,560.43 to 267.09 μm. After image analysis, particles with more circular shapes showed a lower internal friction angle. Because of the lower flow ability, the smallest particle required larger values of the hopper angle and a larger minimum size of the hopper opening.Practical ApplicationsAdzuki bean flour is widely applied in the food processing industry, and many mixing and packing processes require a suitable dimension of hopper. Because powder flow characteristics determine the efficiency of transportation through a hopper in the silo, it is very important to identify the powder flow behavior of a hopper design while avoiding arching, which is a stable obstruction that forms over the point of the narrowest cross section of the storage vessel. Therefore, the hopper angle and the opening size should be enough to avoid arching. This study estimated the energy consumption required to obtain particles of a certain size for designing the grinding process and determined a suitable dimension for hoppers that process different particle sizes.

Cavity expansion in unsaturated soils exhibiting hydraulic hysteresis considering three drainage conditions

Cavity expansion theory assists in the interpretation of in situ tests including the cone penetration test and pressuremeter test. In this paper, a cavity expansion analysis is presented for unsaturated silty sand exhibiting hydraulic hysteresis. The similarity technique is used in the analysis. The soil stress–strain behaviour is described by a bounding surface plasticity model. Results of oedometric compression tests, isotropic compression tests and triaxial shear tests for both saturated and unsaturated states are used to calibrate the model. The void ratio, suction, degree of saturation and effective stress are fully coupled in the analysis. The influence of where the initial hydraulic state is located on the soil–water characteristic curve on the cavity wall pressure is investigated and found to be significant. Also, the effects of three different drainage conditions (constant suction, constant moisture content and constant contribution of suction to the effective stress) on cavity wall pressure are studied. It is found that the drainage condition in which the contribution of suction to the effective stress is constant offers a good approximation to the other two. This may simplify interpretation of in situ tests. When testing occurs quickly, meaning a constant moisture content condition prevails, a constant contribution of suction condition can be assumed without loss of significant accuracy. The contribution of suction assumed in the interpretation can be taken as being equal to the in situ value, although this discovery may not be applicable to all soil types, constitutive models and soil–water characteristic curves. Copyright © 2015 John Wiley & Sons, Ltd.

Engineering and functional properties of four varieties of pulses and their correlative study

Physical and functional properties of Rajma (Phaseolus vulgaris), Mung Beans (Vagna radiate), Black gram (Vigna mungo) and Masoor dal (Lens culnaris) were determined at constant moisture content of 8.0 %. The average principle diameters was found to be 7.97, 3.62, 6.17 and 3.02 mm and average sphericity 57.22, 80.10, 66.04 and 98.69 % for Rajma, Mung beans, Black gram and Masoor dal respectively. Porosity of Rajma grains (19.0 %) was found to be lower compared to Mung beans (28.33 %), Black gram (35.53 %) and Masoor grains (39.25 %). The coefficient of friction was found to be maximum on cardboard followed by sunmaica and it was least on glass. The flours had poor flowability having a compressibility index of 24.90, 52.60, 58.40 and 39.69 and Hausner’s ratio 1.238, 1.385, 1.503 and 1.630 for Rajma, Mung beans, Black gram and Masoor dal respectively. Solubility was found to be highest at pH 8 and minimum at pH 4. Water absorption capacity of Black gram was highest. Foam capacity, foam stability and oil absorption of Mung beans was highest. Pearson’s correlation between engineering properties of grains and functional properties of flour was also calculated to predict functional properties of the sample.

Substrate Moisture Content Effects on Growth and Shelf Life of Angelonia angustifolia

Wilting during shelf life is a major cause of postharvest shrink for bedding plants shipped long distances from production greenhouses to retail outlets. The objective of this research was to determine if irrigation at lower, constant substrate moisture content (SMC) during greenhouse production would be a feasible way to acclimate plants for reduced shrinkage during shelf life while potentially conserving irrigation water. In two separate experiments conducted in the fall and spring seasons, rooted plugs of Angelonia angustifolia ‘Angelface Blue’ (angelonia) were grown in greenhouse production until a marketable stage in substrates irrigated at SMC levels of 10%, 20%, 30%, and 40% using a controlled irrigation system. At the end of the greenhouse production stage, plants were irrigated to container capacity and subjected to a simulated shipping environment in shipping boxes in the dark for 2 days. After shipping, plants were placed back in the greenhouse and watered minimally to simulate a retail environment. Data were taken at the end of each stage, i.e., greenhouse production, simulated shipping, and simulated retail. Results indicated that as SMC decreased from 40% to 10%, plants were shorter in height but had proportional and more compact flowering sections. The volume of water received by the 40% SMC plants was three times greater (fall) and 12 times greater (spring) than the 20% SMC plants during greenhouse production and two times greater (fall) and nine time greater (spring) during simulated retail. During production, midday water potentials decreased as the SMC levels decreased, but at the end of the simulated retail, the midday water potentials were the same, suggesting that plants that were drought-stressed during production were acclimated to lower water levels experienced in retail settings. Overall, the 20% SMC treatment produced the best postharvest quality plant resulting from reduced plant height without detrimental effects on flowering. The results demonstrate that while conserving water, controlled irrigation at a lower SMC can produce high-quality plants that have equal shelf life to those that are irrigated at high levels.

Effect of barley β-glucan concentrate on oscillatory and creep behavior of composite wheat flour dough

Soluble dietary fibers can be used as valuable functional ingredients in food products because of their ability to influence the structural properties of the matrix in which they are embedded. The influence of barley β-glucan concentrate (BGC) addition (up to 10%) into standard wheat flour dough was evaluated through small and large deformation rheological measurements at selected temperatures (25–85°C). Upon addition of BGC (⩽5%), significant increase in mixing time, dough stability and water absorption, and decrease in extensibility were recorded. The mechanical strength of the composite doughs lowered with increasing water content but it improved with BGC incorporation at constant moisture content within the studied frequency range (0.1–10Hz). Both the elastic modulus (G′) and the complex viscosity (η∗) of doughs showed the temperature dependency within the frequency range tested. Time–temperature superposition of η∗–ω curves fitted well for up to 5% BGC incorporation when G′–ω failed at similar condition. Creep–recovery tests for BGC incorporated doughs recorded greater resistance to deformation. Differential scanning calorimetric measurement showed the protein denaturation temperature was influenced by both levels of wheat flour substitution by BGC and moisture content in the dough. Scanning electron microscopy used to study microstructure of doughs.

Creep behaviour of single hemp fibres. Part II: Influence of loading level, moisture content and moisture variation

This work investigates the tensile creep behaviour of single hemp fibres under constant and cyclic loading coupled to constant or variable moisture content environment. Results show that the primary creep strain rate of such fibres decreases with the increasing stress, while the secondary creep strain rate increases. Load cycling at an average load higher than constant creep load produces a large additional extra creep strain and an increase of the creep rate. Both primary and secondary creep strain rates increase with the increasing moisture content. More creep is also observed in cyclic humidity conditions than in a constant environment at the high-humidity. In agreement with some observations on synthetic fibres, we showed that this accelerated creep is only observed for high moisture cycling rates. This mechanosorptive effect is consistent with sorption-induced stress-gradient explanations proposed in literature.

Differential response of nonadapted ammonia-oxidising archaea and bacteria to drying-rewetting stress.

Climate change is expected to increase the frequency of severe drought events followed by heavy rainfall, which will influence growth and activity of soil microorganisms, through osmotic stress and changes in nutrient concentration. There is evidence of rapid recovery of processes and adaptation of communities in soils regularly experiencing drying/rewetting and lower resistance and resilience in nonadapted soils. A microcosm-based study of ammonia-oxidising archaea (AOA) and bacteria (AOB), employing a grassland soil that rarely experiences drought, was used to test this hypothesis and also whether AOB were more resistant and resilient, through greater tolerance of high ammonia concentrations produced during drought and rewetting. Treated soils were dried, incubated for 3 weeks, rewetted, incubated for a further 3 weeks and compared to untreated soils, maintained at a constant moisture content. Nitrate accumulation and AOA and AOB abundance (abundance of respective amoA genes) and community composition (DGGE analysis of AOA amoA and AOB 16S rRNA genes) were poorly adapted to drying-rewetting. AOA abundance and community composition were less resistant than AOB during drought and less resilient after rewetting, at times when ammonium concentration was higher. Data provide evidence for poor adaptation of microbial communities and processes to drying-rewetting in soils with no history of drought and indicate niche differentiation of AOA and AOB associated with high ammonia concentration.

Calorimetric and heat transfer studies of the spontaneous combustion of two low carbon fuels

The self-heating and heat transfer characteristics of creosote-treated wooden railway tie dust and roofing asphalt shingle particles, which are considered as low carbon fuels, are investigated. Self-heating was measured with isothermal calorimetry and thermal conductivity was measured using a guarded hot plate. The self-heating of petroleum coke and poplar wood pellets were also measured as reference materials. Self-heating models and heat transfer parameters were then defined assuming constant moisture content. The self-heating of petroleum coke was found to be similar to coal, while both poplar pellets and railway tie dust were found to be more reactive compared to oven test results of similar materials. As both poplar pellets and railway ties both had significant water content, the higher reactivity was attributed to the effect of moisture. Furthermore, critical conditions for spontaneous combustion were evaluated with the Frank–Kamenetskii parameter, assuming an ambient temperature of 40 °C. It was found that cubic volumes of railway tie dust and asphalt particles, 1.6 m and 58 m to a side, respectively, would spontaneously combust; however, compaction effects associated with asphalt softening may invalidate the assumptions of the Frank–Kamenetskii spontaneous combustion theory.