Equilibrium Moisture Content Values Research Articles

Impact of sugar reduction on the glass transition temperature and sorption isotherm of freeze-dried tomato powder

The objective of this work was to improve the drying of tomato juices after identifying the main parameters that are responsible for sticking during drying. Glass transition temperature (Tg) which is one of the key parameter, depends on the juice composition, mainly sugar. In order to reduce sugar, centrifugation was applied to the juices. Tg was determined by differential scanning calorimetry (DSC) for freeze-dried tomato juice and tomato pellet conditioned at various water activity (aw) (0.1–0.5). The glass transition curve showed that Tg decreased with increasing of the moisture. Comparison of powders obtained by juice and pellet from centrifugation shows that the Tg of freeze-dried pellets is higher than that of juice at equal aw values. Adsorption isotherms of freeze-dried tomato juice and pellet were determined at 25 °C and a relative humidity (RH) of 0–98% using a dynamic technique. The data obtained were fitted to GAB model that best fitted the experimental data. The equilibrium moisture content (X) value of the freeze-dried pellets are lower and had the same value of 8% dry mass. X is lower because the pellet powders are less hygroscopic than tomato juice powders because of the reduction of soluble compounds by centrifugation, notably sugars. Reducing the product sugar content by centrifugation enables to raise Tg without using carriers and obtain less hygroscopic powders, which is advantageous for product storage.

Hygroscopicity of nitrocellulose with different nitrogen content

AbstractResearch on the hygroscopic behavior of NC is essential because it affects the mechanical properties, combustion properties, and safe storage of NC‐based products. In this study, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) are used to characterize the chemical structure, crystal structure, and microscopic morphology of NC, respectively. The moisture adsorption isotherms of NC fibers with different nitrogen content are determined by dynamic vapor sorption (DVS) and fitted with Hailwood‐Horrobin (H−H) and Guggenheim‐Anderson‐de Boer (GAB) models. The specific surface area and surface energy of NC are also measured by inverse gas chromatography (IGC). The results show that as the nitrogen content of NC increases, the intensity of the −OH characteristic absorption peak is weakened, the crystallinity does not change much, the number of cracks and pores on the NC fiber surface increases, and the equilibrium moisture content (EMC) of the NC decreases in general. In addition, the fitting results based on the H−H and GAB models show that, under low humidity conditions, the EMC value of NC is determined by the adsorbed water content of the monolayer, which is mainly related to the −OH content in NC. However, with the increase of humidity, the EMC value of NC is gradually determined by the multilayer adsorbed water content, which is influenced by both the nitrogen content and the fiber cleavage structure. Meanwhile, the IGC results show that the surface energy of the NC consists mainly of the dispersive surface energy (values >46 mJ m−2), with the specific surface energy contributing approximately 25 mJ m−2. The total surface energy of NC and the bonding strength between NC molecules and water molecules decrease with increasing nitrogen content.

Carboxyl-modified nanocellulose (cNC) enhances the stability of cNC/pullulan bio-nanocomposite hard capsule against moisture variation

The quality of polysaccharide-based films and hard capsules is often affected by changes in relative humidity, manifesting as unstable water content, and changes in mechanical strength that make them brittle or soft. Herein, carboxyl-modified nanocellulose (cNC) was prepared and used as a new component to successfully improve the moisture resistance of cNC/pullulan/high-acyl gellan bio-nanocomposite hard capsules (NCPGs). Homogenously dispersed cNC in the pullulan/high-acyl gellan matrix could render the formation of more hydrogen bonds that provided additional water-binding sites and limited the free movement of pullulan and high-acyl gellan molecular chains within NCPGs. This contributed to a decreased amount of pooling adsorption water and an increased amount of Langmuir adsorption water in NCPGs, as compared to pullulan/high-acyl gellan hard capsules (PGs) without cNC. Therefore, the equilibrium moisture content (EMC) values of NCPGs decreased at 83 % relative humidity and increased at 23 % relative humidity compared to those of PGs. Together with enhanced mechanical and barrier properties, NCPGs effectively protected encapsulated amoxicillin and probiotic powder from changes in the outside humidity. Additionally, NCPGs exhibited faster drug release. This study presents a new mechanism and strategy for fabricating films and hard capsules with enhanced stability against moisture variation.

Influence of thermal pretreatments on dimensional change and humidity sensitivity of densified spruce and poplar wood

The effect of thermal pretreatments on the dimensional change and humidity sensitivity of densified spruce (Picea orientalis) and poplar (Populus nigra) wood were investigated. A thermal pretreatment was applied on the wood specimens at 140 °C, 160 °C, 180 °C, and 200 °C for 7 h and 9 h. Wood specimens were then compressed at ratios of 20 % and 40 % at a temperature of 150 °C. The results showed that spring-back and thickness swelling increased in all specimens (thermally pre-treated and untreated) depending on the increase in compression ratio. However, set-recovery was determined higher at 20 % compression ratio. The equilibrium moisture content values ​​of untreated specimens and thermally pre-treated specimens at low temperatures (140 ºC and 160 ºC) were found lower than uncompressed specimens. The impact of compression ratio on equilibrium moisture content was not clear. Thermal pretreatments significantly affected the dimensional stability and hygroscopicity of densified specimens (especially poplar wood). Depending on the increase in thermal pretreatment temperature and duration, spring-back, set-recovery and thickness swelling in wood specimens decreased up to 31 %, 67 % and 62 %, respectively. In addition, equilibrium moisture content and water absorption decreased with the increase in thermal pretreatment temperature and duration. Moreover, the thermal treatment temperature was more important than duration on the investigated properties.

Sorption properties of paper treated with silane-modified starch

Sorption properties of paper products are important when applying paper as the packaging material. Hydrophobicity, i.e. reduced affinity of paper surface to liquid water, is of particular importance from the point of view of the direct impact on packed goods. However, hygroscopicity of the material is significant during storage of goods. The analysis of changes in the hygroscopic properties of paper products induced by the treatment with silane modified starch was presented. The results on the hygroscopicity of treated paper were related to the previously published results on the hydrophobicity. The discrete values of equilibrium moisture content allowed constructing adsorption and desorption isotherms. The three-parameter Guggenheim, Anderson, and De Boer (GAB) model, the four-parameter Generalized D’Arcy and Watt (GDW), and Yanniotis and Blahovec (Y-B) sorption isotherm models were used to quantify the hygroscopic properties for all options of untreated and modified paper samples. The effectiveness of silanes for improving hygroscopic properties was determined and compared to their impact on hydrophobicity of the studied materials. It was found that 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane was the only silane improving hydrophobic and hygroscopic properties. The analysis of the applied models of sorption isotherms depicted that the GAB model was not valid for describing water sorption isotherms in the case of the tested materials, while the GDW and Y-B models provided a much more realistic description of water sorption mechanisms. The evaluation of the results of fitting the GDW model indicated that water molecules bonding to the primary sites was the dominating mechanism of sorption.

Study of mass transfer and hygroscopic properties of Australian mass-timber panels and species in hot and humid conditions- moisture sorption and desorption

ABSTRACT Wood is a commonly used building material with numerous advantages over other construction products. However, in engineered wood products such as cross-laminated-timber and laminated veneer lumber moisture absorption can lead to decay, swelling, deformation, and glue line failures, diminishing their properties. Understanding moisture intrusion processes in these materials can aid manufacturers, engineers, and architects in developing effective moisture management strategies during and after construction. The porosity of CLT 3P sections was 56.5%, higher than CLT 2P sections at 36.8%. True density varied among species, with radiata pine, southern pine, and shining gum measuring 1358, 1411, and 1031 kg/m3, respectively. True density values for CLT 3P, CLT 2P, and LVL were 1202, 837, and 1406 kg/m3, respectively. The species and sample type significantly influenced porosity and density values, crucial for future moisture modelling and predicting moisture gain/loss during wetting and drying processes. Moisture sorption and desorption properties were examined for Australian timber species, CLT, and LVL at different temperatures. LVL samples exhibited higher moisture content and dimensional changes, possibly due to improved moisture transfer facilitated by lathe checks. CLT samples demonstrated greater anisotropic behaviours than those of LVL samples. The product type and sample type had significant effects on equilibrium moisture content values.

Size Effect on Hygroscopicity of Waterlogged Archaeological Wood by Simultaneous Dynamic Vapour Sorption

Hygroscopicity is one of the most important properties of wood and plays a decisive role in its dimensional stability. In this context, conservation plans for waterlogged archaeological wood (WAW) and relevant waterlogged artefacts must be created. The size of the sample required for a moisture sorption assessment may affect the results for (and thus the perception of) the hygroscopicity of a testing artefact. Herein, to investigate the effects of the sample size on the hygroscopicity of WAW as measured via dynamic vapour sorption (DVS), typical WAW and recent (i.e., sound) wood are processed into four differently sized samples, ranging in thickness from 200 mesh to millimetre. The equilibrium moisture contents (EMCs) of the wood samples are simultaneously measured using simultaneous DVS. The sorption isotherms show that the EMC values of the recent wood at each relative humidity increase as the sample size decreases, with the superfine powder sample achieving the highest EMC of all of the recent samples. Although the WAW has a higher EMC than that of recent wood, the effect of the size of the WAW sample on its hygroscopic properties is surprisingly not as pronounced as that for the recent wood. In addition, the hysteresis between the samples of different sizes of the archaeological wood is significantly smaller than that for the reference samples. Furthermore, regarding the standard deviations of the parameters obtained from the Guggenheim Anderson de Boer and Hailwood–Horrobin models, the values for WAW are all much smaller than those for the reference wood. This further verifies the disappearance of the size effect of the hygroscopicity for WAW.

Modelling sorption processes of 10-h dead Pinus pinaster branches

Background Forest fuel moisture content (FMC) is an important parameter that determines wildfire risk; therefore, its accurate prediction is of great importance. In the absence of rainfall, dead FMC changes mainly by water vapour sorption processes.Aims In the present work, sorption processes of 10-h dead Pinus pinaster branches (PPBs) were studied in order to develop a moisture content prediction model for this fuel type.Methods Laboratory tests were used to determine sorption curves, timelag and equilibrium moisture content (EMC) for different environmental conditions. Sorption curves and EMC were modelled with existing sorption models. Dead PPBs moisture content was determined in field tests carried out in central Portugal to validate the sorption models.Key results Sorption curves were not pure exponential functions, but had different timelag values until equilibrium was reached. EMC values allowed us to obtain a sigmoid curve and hysteresis effect.Conclusions Comparing predicted and observed FMCs of PPB, the Modified Henderson and Pabis models for sorption curves and the Van Wagner model for EMC show high prediction ability.Implications The model can be applied in early fire risk assessment, in particular in the methods that use other fuels besides fine forest fuels.

Physicochemical, Rheological and Moisture Adsorption Characteristics of Two Basmati Rice (<em>Oryza sativa</em> L.) Varieties Differing in Amylose Content

Purpose: The purpose of this study was to determine the physicochemical, viscosity and moisture sorption properties of high-amylose (At-306) and low-amylose (At-405) basmati varieties. Research Method: The viscometer method was used to measure the apparent viscosity of the flour samples at 65 and 75°C. Moisture adsorption isotherms were determined by the gravimetric method at 28, 35 and 45°C. Findings: The bulk-density, grain-hardness, gelatinization temperature, protein and amylose contents of the At-306 and At-405 varieties were in the range of 794-780 kg m-3, 55.5-49.7 N, 70.34-66.14°C and 8.80-8.00% and 26.70-15.37%, respectively. At-405 samples showed significantly higher viscosity (8-13.5 Pa s) at 65°C and lower viscosity (1.4-5.3 Pa s) at 75°C but the opposite trend was observed for the At- 306. The flow behavior index, varied with temperature between 0.55-0.54 and 0.75-45, respectively, for At-306 and At-405. At-306 showed a higher equilibrium moisture content (EMC) value compared to At- 405 when aw>0.70. The GAB isothermal model best described the experimental EMC data (R2adj>0.98 and MRD<3.8). At-306 has a higher specific surface area (≈115.5 m2 g-1 d.b) and higher monolayer moisture content (≈3.3 g/100 g) than At-405. The effective pore size of At-306 and At-405 varied between 1.04-12.82 and 0.73-9.18 nm, respectively. The isosteric-heat of adsorption was significantly higher for At-405 than At-306. Research Limitations: Further studies with medium amylose basmati are needed to confirm the applicability of these findings. Originality/ Value: This result provides some information of the physicochemical, rheological and storability characteristics of low and high basmati flours for the food industry application.

Effect of low molecular weight melamine-urea-formaldehyde resin impregnation on poplar wood pore size distribution and water sorption

This study aimed to investigate the relationship between the properties of pore size distribution and water sorption in melamine-urea-formaldehyde (MUF) resin-impregnated wood by scanning electron microscopy (SEM), nitrogen adsorption (NAD) measurement, mercury intrusion porosimetry (MIP), water-soaking, and moisture adsorption over saturated salt solutions. The results showed that MUF resin not only filled the macropores and mesopores of the wood, such as those of vessels and wood fibers, but also penetrated the cell walls and replaced some hygroscopic groups of cell wall polymers, thus significantly reducing the water sorption. The porosity and cumulative pore volume of the RI140 and RII140 samples (impregnated with 10% and 20% MUF resin solution, respectively, with each dried at 140 ℃) were 19.25% and 1.20 mL·g−1, and 9.85% and 0.89 mL·g−1, respectively, which were lower than those obtained for the control group (CK). The specific surface area of RII140 was lower than that of CK. The pore size range of the CK and RII140 samples was 3.1–22.9 nm and 2.5–5.1 nm, respectively. The water absorption rate and equilibrium moisture content values for MUF resin-impregnated wood were inversely proportional to the drying temperatures and weight percent gain (WPG). The MUF resin leaching efficiency was inversely proportional to the drying temperature but proportional to the WPG.

Moisture sorption isotherms and hysteresis of soybean grains

Knowledge of the relationship between the equilibrium moisture content of the product and the air that involves it is essential to guarantee product quality and preserve its characteristics during storage. This trend can be studied by sorption isotherms. Thus, this study aimed to obtain desorption and adsorption isotherms of soybean grains to determine the mathematical model that best fits the experimental data and analyze the hysteresis phenomenon. Soybean grains with a moisture content of 21.95% (db) were used to verify the desorption process. The grains were dried until 3.50% (db) for the adsorption process. The static-gravimetric method was employed to determine the equilibrium moisture content of the grain at different temperatures (10, 20, 30, 40, and 50°C) and relative humidity levels (0.10 to 0.92%). Eight mathematical models were fitted to the experimental data. The modified Halsey model satisfactorily represented the desorption and adsorption phenomena of soybean grains. The equilibrium moisture content of soybean grains increased along with an increment in water activity. The increase in temperature led to a reduction in the equilibrium moisture content of soybean grains at a constant water activity. The equilibrium moisture content values obtained by desorption are higher than those obtained by adsorption, indicating the hysteresis phenomenon at the studied temperature range. The isotherms obtained for the desorption and adsorption process were classified as type III because of the high oil content in soybean grains.

Material Properties of Traditional Handmade Paper Samples Fabricated from Cellulosic Fiber of Lokta Bushes.

Handmade papers (HPs) are fabricated from fibrous biomass of Lokta bushes and other plant species following traditional eco-friendly method in Nepal. Although HP fabricated from Lokta bushes is believed to be durable and resistant to bugs and molds, material properties of this paper are not reported in literature. In this study, we measured several material properties of 10 handmade Lokta paper samples collected from local enterprises and paper industries. The mean caliper, grammage, apparent density, equilibrium moisture content, Cobb 60, brightness, opacity, tensile strength, and tensile index values in the paper samples ranged from ∼90 to 700 μm, 50 to 150 g/m2, 0.2 to 0.4 g/cm3, 4 to 7%, 50 to 400 g/m2, 56 to 67%, 83 to 98%, 30 to 2900 N/m, and 1 to 27 Nm/g, respectively. These properties suggested that the HPs are lightweight papers with intermediate to high strength. The tensile strength was found to be significantly higher along the length direction (p < 0.05). Characteristic features of cellulose, hemicellulose, and lignin were observed in FTIR spectra. The crystalline and amorphous phases were also identified in X-ray diffraction (XRD) data. Electron microscopy images revealed a nicely cross-linked network of intact fibers having almost parallel arrangement of microfibrils. These features could provide strength and durability to the paper samples. Understanding the material properties of HPs down to the sub-microscopic level may help improve the paper quality and find novel applications in the future.

Study on equilibrium moisture sorption characteristics and modeling of Karaya (Sterculia urens Roxb.) gum

BackgroundKaraya gum is heavily acetylated polysaccharide and used for medicinal purposes as a bulk-forming laxative. It is also used in the paper and textile industries as well as food stabilizer. So its moisture sorption behavior study is important. The moisture sorption isotherms of karaya gum were investigated at four experimental temperatures (30, 40, 50 and 60 °C) under the water activities range from 0.10 to 0.95 using static gravimetric method.ResultsMaximum value of equilibrium moisture content (EMC) of karaya gum (39.7%, db) was noted with the set of highest water activity (0.92) at lowest temperature (30 °C) and minimum value of EMC (2.5%, db) with lowest water activity (0.11) at highest temperature (60 °C). The sorption data were fitted with GAB, Iglesias and Chirife, Caurie, Halsey and BET models. The adequacy of the sorption isotherm models were observed statistically using goodness of fit parameters. The well-known GAB model best interpreted the equilibrium data in a satisfactory manner in the test gum. The monolayer moisture content, estimated using GAB model, was found to be 12.66 g/100 g and 7.4 g/100 g gum at 30 °C and 60 °C, respectively. The isosteric heat of sorption was found to be maximum (36.24 kJ/mol) at 5% moisture content (db) of karaya gum.ConclusionMoisture sorption behavior of karaya gum was found to be temperature dependent. EMC decreases with the increase in temperature at particular water activity. The sorption behavior of the test gum expressed the typical type-II sigmoid-shaped curve. Isosteric heat of sorption of karaya gum was decreased with the increase in moisture content.

Initial Desorption of Reaction Beech Wood

The research aimed to obtain empirical data for modeling the initial desorption in reaction wood from the cross-section of the green beech (Fagus sylvatica L.) log. Firstly, we analyzed the chemical composition, macro and microscopic structure of tension and opposite wood tissue. Then, the Equilibrium Moisture Content (EMC) was measured by the Dynamic Vapor Sorption method during the initial desorption. The used air parameters were specific for the mild drying schedule of green beech timber (t = 20, 35, and 50 °C, Relative Humidity (RH) ranging from 95 to 0 %). Relationships between the EMC of reaction wood and drying parameters were modeled using the Response Surface Method (RSM). The tests revealed: different hygroscopic properties of tension and opposite wood, the dependence of EMC value on temperature, and differences between EMC values for initial (first) and second desorption. Moreover, it was confirmed that, during initial desorption, the EMCs of reaction wood are significantly higher than reference EMC data. The differences in the EMC value are up to 0.14 kg/kg (for air with RH above 90 %). The presented polynomial model of the initial desorption of reaction beech wood can improve drying schedules for beech sawn timber with a high amount of reaction tissue.

Effects of heat treatment on surface roughness and bonding strength of wood material

The purpose of this paper is to determine the effects of heat treatment on some properties of black pine (Pinus nigra A.) and larex (Larix decidua), woods. For this purpose, test samples were heat treated at 140, 160, 180 and 200°C for 2 and 5 hours. The air-dried density, equilibrium moisture content (EMC), surface roughness and bonding strengths of the test samples were analyzed. The average surface roughness parameter (Ra) was analyzed parallel to the grains. The results indicated significant differences depending on the wood species, heat treatment temperatures and treatment times. Based on the findings in this study, all parameters decreased depending on the heat treatment conditions. The density and EMC values of the control specimens were higher than the heat-treated samples. Also the surface roughness values obtained in black pine samples were higher than larex samples. On the other hand, bonding strength values obtained in larex samples were significantly higher than that of black pine samples. These parameters should be taken into account in the application areas of heat-treated wood material, the usage amount of which is constantly evolving in the woodworking industry.

Equilibrium Moisture Content Modeling and Study of Circulating-Bed Drying Kinetics of Non-Fragrant and Fragrant Paddy Varieties

Due to maintaining good quality of rice grain kernel varieties during post-harvesting and in-store period, the thermos-physical properties which relate to surrounding conditions (temperature and relative humidity) of each rice variety are essential, especially on its moisture content and diffusion mechanism. Therefore, the main objectives of this research are to determination of the thermo-physical properties (in terms of equilibrium moisture content (EMC) and effective diffusivity (Deff)) of local non-glutinous GorKhor55 (RD55) and Hom Thammasat (HT) paddy varieties and to field experiment study of the small-scale circulating-bed dryer with capacity of 1 - 1.5 ton. The EMC experiment using gravitational method is carried on and the experimental results are simulated by non-linear regression analysis. The results show that the predicted data using Modified Oswin model is the most suitable fitting to the exact EMC data for both paddy varieties. The effective diffusivity of both paddy varieties is the function of inlet drying temperature. For the last purpose of this work, the drying kinetics of RD55 and HT paddy varieties with initial moisture content (MC) of 20.1 and 24.6 % dry-basis, respectively are studied using the circulating-bed technique. The inlet drying temperature is set as 45 and 55 °C including operation conditions of 1 stage and 2 stages circulating-bed drying. The inlet air velocity is fixed at 0.41 m/s and the grain mass flow rate of circulation is 0.23 kg/s. The desired final MC after drying of each experiment is in ranges of 16.5 - 16.8 % dry-basis. All of experimental data are non-linear regression analyzed by conventional drying equation models and the simulation results stated that the most suitable model for the circulating-bed drying of RD55 variety with inlet drying temperature of 45 and 55 °C is the Logarithmic and Approximation of diffusion model, respectively.&#x0D; HIGHLIGHTS&#x0D; &#x0D; The special parameter of equilibrium moisture content value of these two rice varieties have been firstly determined&#x0D; The compact circulating-bed dryer with LPG fuel source for farmer community has been tested and run. The drying kinetics models for both rice varieties were evaluated among drying temperature of 45 - 50 deg. Celsius&#x0D; From the Fick’s law of diffusion, the effective diffusion coefficient of the rice varieties were determined and formulated the relationship between this coefficient and drying temperature&#x0D;

Equilibrium moisture content map for Laos

Providing the equilibrium moisture content values for territories is important for avoiding major problems due to dimensional changes in wooden products. This study evaluated the average equilibrium moisture content values for twelve months (from 1981 to 2020) for Laos and produced an equilibrium moisture content map. A model was used to generate the equilibrium moisture content values based on temperature and relative humidity data obtained from the POWER Data Access Viewer v2.0.0. for 18 provinces (148 districts) based on the geographic coordinates of each district in Laos. The lowest equilibrium moisture content (12% to 13%) values were found in Vientiane Capital City, Vientiane province, Louangprabang, Bokeo, Attapeu, Louang Namtha, Oudomxay, Houaphan, Sayaburi, Savannakhet, Salavan, and Champasak province. The rest of the districts, which had an equilibrium moisture content ranging from 13% to 16%, were mostly found on the eastern part of Laos and a small part of Northern Laos. The monthly swinging average value of the equilibrium moisture content ranged from 10% to 18% across the country. The equilibrium moisture content values for each district in Laos were also defined.

Wood-water interactions of thermally modified, acetylated and melamine formaldehyde resin impregnated beech wood

Abstract The wood-water interactions of modified beech wood (Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM1), 200 (TM2) and 220 °C (TM3), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.

Predicting the fine fuel moisture content in Dalmatian black pine needle litter

During the last three decades, there has been an increase in the incidence of severe crown fires affecting black pine forests in the sub-Mediterranean area. The objective of this study was to develop and test a model to predict fine fuel moisture content for Dalmatian black pine (Pinus nigra J.F. Arnold subsp. dalmatica (Vis.) Franco) needle litter. We performed laboratory measurements of equilibrium moisture content and response time of dead black pine needles to modify the hourly fine fuel moisture code (FFMC) model, and we compared the predictive ability of the hourly FFMC model with that of modified model (PnFFMC). Field tests showed that although the hourly FFMC model reproduced trends in moisture content of black pine needles quite well, it consistently overestimated moisture content (mean absolute error 3.9%). The PnFFMC model performed better than the hourly FFMC model and was closer to the line of equivalence (mean absolute error 0.9%). This study indicates that the hourly FFMC can easily be modified by incorporating appropriate species-specific equilibrium moisture content and response time values, leading to more accurate predictions of fine fuel moisture content. The need to use recently fallen needles in fuel moisture modelling for Mediterranean pine species is highlighted.

Modeling Heat and Mass Transfer of Long-Grain Hybrid Rice in a Chilled Environment

HighlightsThis study determined adsorption and desorption isotherms of long-grain hybrid rough rice in chilled environments.Parameters of the sorption models were evaluated by fitting experimental data in a thin layer drying equation.The moisture diffusivity and activation energy values of rough rice subjected to chilled environments were determined.The finite element method was used to simulate the heat and mass transfer of long-grain hybrid rice at low temperatures. Abstract. While chilling aeration technology for grains has found use in other countries, application in the U.S. for rice has not yet been widely adapted by the industry. The aim of this study was to determine the moisture sorption behavior of rough rice in chilled environments. Such data is vital for automated grain conditioning monitoring and control of aeration systems at cool ambient conditions. Adsorption and desorption isotherms of hybrid long-grain rough rice (XL745) subjected to temperature environments which are typical in U.S. storage conditions (5°C to 15°C) were measured. A dynamic vapor sorption analyzer, the IGAsorp, which consists of an ultrasensitive microbalance within a controlled environment was used to accurately measure water sorption in rice. Changes in sample weight were continuously monitored across a range of equilibrium relative humidity (10% to 70%) until a steady-state mass was attained. Nonlinear regression analysis was used to estimate empirical constants of five models used for describing grain sorption isotherms. The appropriateness of each model in describing the equilibrium data was evaluated to minimize the root mean square error (RMSE). The modified Chung-Pfost equation best described the experimental data with RMSEs of 0.557 and 0.912 for adsorption and desorption data, respectively. The equilibrium moisture content (EMC) of rice measured at 5°C with 10% relative humidity (RH) was 12.5% (dry basis), which was higher than the EMC value predicted from other studies by extrapolation at 30°C (9.1% d.b.). All five prediction models (modified Chung-Pfost, modified Henderson, modified Oswin, modified Halsey, and GAB) were in good agreement for experimental data at moderate temperature conditions (e.g., at 30°C). The results indicated that it is more accurate to use newly developed constants for EMC models of rice in chilled environments. A three-dimensional ellipsoid shape was used to describe rough rice geometry. Mathematical models were developed to predict the moisture and temperature distribution during the drying processes at 5°C and 15°C. Models were solved by the finite element method using Comsol Multiphysics® simulation program. Increasing the drying temperature from 5°C to 15°C increased the effective moisture diffusivity from 9.0×10-13 to 1.1×10-12 m2/s. The drying activation energy value was 25.1 kJ/mol in the chilled environments investigated. Keywords: Activation energy, Chilled environment, Equilibrium moisture content, Mathematical modeling, Moisture diffusivity, Rough rice.