Simulated Moisture Content Research Articles

Evaluation of water movement and nitrate dynamics in a lysimeter planted with an orange tree

Adoption of high input irrigation management systems for South Australian horticultural crops seeks to provide greater control over timing of irrigation and fertilizer applications. The HYDRUS 2D/3D model was used to simulate water movement in the soil under an orange tree planted in a field lysimeter supplied with 68.6mm of irrigation water over 29 days. Simulated volumetric water contents statistically matched those measured using a capacitance soil water probe. Statistical measures (MAE, RMSE, tcal) indicating the correspondence between measured and simulated moisture content were within the acceptable range. The modelling efficiency (E) and the relative efficiency (RE) were in the satisfactory range, except RE at day 19. Simulated daily and cumulative drainage fluxes also matched measured values well. Cumulative drainage flux was 48.9% of applied water, indicating large water losses even under controlled water applications. High drainage losses were due to light texture of the soil and high rainfall (70mm) during the experimental period. Simulated root water uptake was 40% of applied water.The calibrated HYDRUS model was also used to evaluate several scenarios involving nitrate fertigation. The numerical analysis of NO3-N dynamics showed that 25.5% of applied fertilizer was taken up by the orange tree within 15 days of fertigation commencement. The rest of the applied NO3-N (74.5%) remained in the soil, available for uptake, but was also vulnerable to leaching later in the growing season. The seasonal simulation revealed that NO3-N leaching accounted for 50.2% of nitrogen applied as fertilizer, and plant N recovery amounted to 42.1%. The scenario analysis further revealed that timing of a nitrogen application in an irrigation event had little impact on its uptake by citrus in the lysimeter. However, slightly higher NO3-N uptake efficiency occurred when fertigation was applied late in the daily irrigation schedule, or was spread out across all irrigation pulses, rather than being applied early or in the middle. Modelling also revealed that pulsing of irrigation had little impact on nitrate leaching and plant uptake. Applying less irrigation (50% or 75% of ETC) resulted in higher nitrate uptake efficiency. This study showed that timing of water and fertilizer applications to an orange crop can be better regulated to enhance the efficiency of applied inputs under lysimeter conditions.

Evaluation of soil plant system response to pulsed drip irrigation of an almond tree under sustained stress conditions

The quantification of components of the water balance is essential for designing strategies for improving water productivity of almond under different irrigation management. It is also needed for minimising the offsite movement of nutrients out of the rhizosphere. The present investigation involves the use of HYDRUS-2D simulations conducted on field data recorded for a full grown surface drip irrigated almond orchard over a season (July 20, 2009 to May 31, 2010). The model evaluated the daily fluctuations in water under full pulsed (FIp), sustained deficit pulsed (SDIp) and full continuous (FIc) irrigation. The impact of pulsing on the dynamics of the water flux was also assessed. In the SDIp treatment, water was applied to replace 65% of calculated crop evapotranspiration (ETc), compared to 100% ETC replacement in the other two treatments. The data showed that the RMSE between weekly measured and simulated moisture content in the whole domain clustered within 0.022–0.04cm3cm−3, with their magnitude equal to the standard error of the water content measurements. The variation was further reduced (0.013–0.026cm3cm−3) when considering only the 30cm soil depth, the site of maximum root density in almonds, indicating a good prediction of seasonal soil moisture distribution and plant water uptake. However, sap flow measurements underestimated water uptake by 31% as compared to the simulated root water uptake. Water uptake efficiency under SDIp (68%) was higher compared to full water application conditions under FIp and FIc (54–55%). The higher irrigation amounts (565–583mm) under 100% ETC treatments (FIp and FIc) largely contributed to non-productive water fluxes (deep drainage losses and evaporation). The leaching fraction was estimated to be 0.14 under SDIp, in spite of the fact that negligible drainage was predicted during the mid season of almond growth (November to January). The average modelled soil solution salinity (ECsw) of the profile also remained below the threshold for yield reduction during the growing season in all treatments. The seasonal water uptake by almonds under pulsed (FIp) and slow discharge continuous irrigation (FIc) remained almost on par, indicating that pulsing did not provide any added advantage, although it is a viable alternative to slow discharge continuous irrigation. The irrigation water productivity (WPI) increased substantially (37%), yield was reduced by 8% and about 35% of irrigation water was saved under sustained deficit irrigation (SDIp) compared to full irrigation (FIp). We conclude that in regions with severe water scarcity, SDIp appears to be a promising deficit irrigation strategy for almond cultivation, and irrigating almonds above the SDIp level may enhance unproductive water usage in the form of accelerated drainage, which eventually may lead to potential danger of migration of nutrients and solutes to the groundwater, thereby posing a threat to the quality of groundwater and receiving surface water bodies.

Three-dimensional simulation of humid-air dryer using computational fluid dynamics

A three-dimensional (3-D), mathematical model for the analysis of the flow distribution in a humid-air dryer was developed employing a computational fluid dynamics package, FLUENT®. A thin-layer drying approach for a sphere-shaped object was coupled with 3-D modeling framework. The model was validated by comparing the simulated moisture content (MC) of red pepper with experimentally measured MC with drying time. The present model was employed to obtain optimized dryer design with the most homogeneous flow distribution inside the drying trays. Consequently, two parametric studies are presented and discussed: (i) varying inner structure, and (ii) varying drying objects in the dryer.

Wildfire Potential Mapping over the State of Mississippi: A Land Surface Modeling Approach

A relationship between the likelihood of wildfires and various drought metrics (soil moisture-based fire potential indices) were examined over the southern part of Mississippi. The following three indices were tested and used to simulate spatial and temporal wildfire probability changes: (1) the accumulated difference between daily precipitation and potential evapotranspiration (P - E); (2) simulated moisture content of the top 10 cm of soil; and (3) the Keetch-Byram Drought Index (KBDI). These indices were estimated from gridded meterological data and Mosaic-simulated soil moisture data available from the North American Land Data Assimilation System (NLDAS-2). The relationships between normalized fire potential index deviations and the probability of at least one fire occurring during the following five consecutive days were evaluated using a 23-year (1986-2008) forest fire record for an evenly spaced grid (0.25° x 0.25°) across the state of Mississippi's coastal plain. Two periods were selected and examined (January-mid June and mid September-December). There was good agreement between the observed and logistic model-fitted fire probabilities over the study area during both seasons. The fire potential indices based on the top 10 cm soil moisture and KBDI had the largest impact on wildfire odds, increasing it by almost 2 times in response to each unit change of the corresponding fire potential index during January-mid-June period and by nearly 1.5 times during mid-September-December. These results suggest that soil moisture-based fire potential indices are good indicators of fire occurrence probability across this region.

Modeling of mass transfer and initiation of hygroscopically induced cracks in rice grains in a thermally controlled soaking condition: With dependency of diffusion coefficient to moisture content and temperature – A 3D finite element approach

Rice grains develop cracks and eventually break during soaking. Since published simulation studies on hygroscopic swelling induced cracking were scarce, the present study attempts to model the mass transfer of moisture and hygroscopic swelling of rice grains using principles of finite element analysis performed in three dimensions (3D). Ultimately, to understand the crack formation in response to the existence of tensile and compressive stresses caused by moisture gradient in the grain during soaking. An empirical equation was developed to establish dependency of the diffusion coefficient of rice to both moisture content and temperature. Using a 3D replica of short grain japonica rice, the modeling was carried out using existing laws of diffusion and was validated using experimental data. Results showed that the rate of moisture diffusion and hygroscopic swelling were found to increase with increase in soaking temperature. The internal stress, however, was found to decrease with increase in soaking temperature. The simulated moisture content and increase in volume of rice grain were favorably in agreement with experimental results. Highly stressed sites that are prone to breakage have been clearly identified.

Simulation of Trough Withering of Tea using One Dimensional Heat and Mass Transfer Finite Difference Model

One-dimensional heat and mass transfer mathematical model was developed to simulate moisture content of tea leaves during trough withering. Model solutions were approached using finite difference method with appropriate boundary conditions. A computer program written in QBASIC was used to calculate the real time moisture content of tea leaves and other psychometric parameters of conditioned air during withering. Four experiments were performed using commercial type of withering trough to validate the developed model. Leaf samples were drawn from top, middle and bottom layers of the leaf bed in the trough for one-hour time interval for 12 h of the test period. Simulated moisture data calculated by the program was compared with the experimental data. Time and space increments of the model were chosen minimizing the estimation error of moisture content. Results showed that the experimental and simulated moisture data were in close agreement for top, middle and bottom layers of the withering trough with standard errors in the range of 0.2940&ndash;1.2872, 0.7148&ndash;1.1025 and 0.7106&ndash;4.5478, respectively on percent wet basis. <strong>Keywords</strong>: Fresh tea leaves; one dimensional heat and mass transfer model; withering trough DOI: <a href="http://dx.doi.org/10.4038/tar.v22i3.3701">http://dx.doi.org/10.4038/tar.v22i3.3701</a> <em>Tropical Agricultural Research </em>22(3) (2011) 282-295

Experimental and Simulated Performances of a Batch-Type Longan Dryer with Air Flow Reversal Using Biomass Burner as a Heat Source

This article presents experimental performance of a batch-type longan dryer using a biomass burner with air flow reversal and also presents modeling of the longan dryer for drying of whole longan. The dryer essentially consists of a biomass burner and a drying bin with an arrangement for periodic air flow reversal. Three drying runs with loading capacity of 2,000, 1,500, and 1,000 kg of whole longan were carried out. There was no significant difference in temperatures in different positions (except inlet and outlet) inside the dryer (p < 0.05) or moisture content inside the dryer (p < 0.05). Whole longan was dried from an initial moisture content of 74% (wb) to a final moisture content of 14% (wb). The drying time of whole longan in the longan dryer was 60, 54, and 48 h for 2,000, 1,500, and 1,000 kg loading, respectively. The quality of dried product was also good in comparison to the high-quality product in markets. To simulate the performance of the longan dryer for drying of whole longan, a set of partial differential equations was developed and the equations were solved using the finite difference technique. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5 (Compaq Computer Corp., TX). The simulated moisture contents agreed well with the experimental data. This model can be used to provide the design data and it is also essential for optimal dryer design.

Solute‐Dependent Capillarity‐Induced Focused Flow during Infiltration into Alcohol‐Contaminated Soil

Most organic compounds, when dissolved in water, decrease the surface tension of the water and many change the wettability of porous media. This directly affects capillary pressures and can induce water flow and solute transport in the vadose zone. This study investigated a coupled unsaturated flow and transport phenomenon, solute‐dependent capillarity‐induced focused flow (SCIFF), that has significant implications for infiltration into contaminated unsaturated zones. A two‐dimensional laboratory flow cell and the two‐dimensional hysteretic saturated–unsaturated flow and transport numerical model HYDRUS‐2D, which was modified to include solute concentration‐dependent hydraulic functions, were used to demonstrate and quantify the effect of SCIFF on point‐source infiltration of clean water into contaminated sand. The difference between the SCIFF infiltration event and traditional water infiltration into uncontaminated sand is striking. Highly focused vertical flow with very little horizontal migration was characteristic of the SCIFF infiltration event from a constant‐flux point source. The SCIFF resembles a single finger as in classic flow instability fingering; however, the SCIFF system has the added complexities of aqueous solute concentration‐dependent hydraulic functions. The SCIFF mechanism may well be active at many sites where the vadose zone has significant contamination with organic compounds. Another significant finding was that the magnitude and trend in moisture content changes measured by time domain reflectometry (TDR) did not match point values from the simulations because the TDR sample area extended beyond the width of the SCIFF zone. A good match between TDR and simulated values was obtained by determining the average simulated moisture content within the same region sampled by the TDR.

Development of mathematical model for simulating moisture content during the re-wetting of brown rice stored in film packaging

In order to develop a re-wetting method for brown rice by using film packaging technique, a mathematical model suitable for designing the packaging was established. The re-wetting of brown rice was achieved by selecting a film permeability that controls the rate of water adsorption in the rice. In the model, changes in relative humidity (RH) inside the package were determined by incorporating the permeation rate of water vapour through the film and the rate of water vapour adsorption on the rice. The change in rice moisture content was determined from the mass of water vapour adsorbed onto the rice. For validation of the model, a 50 g of sample brown rice at a moisture content of 10% wet basis (w.b.) was packaged with a polybutylene terephthalate film pouch. The package was exposed to a humid environment of 25 °C and 89.5% RH for 10 weeks. The moisture content of brown rice in the package increased to 19% w.b. without cracking. Comparing measurements to values calculated from the proposed model, the model adequately described the changes in RH and the rice moisture content in the package with a root mean square error (RMSE) of 3.0% and a 0.2% dry basis (d.b.), respectively.

Modeling Soil Water Uptake by Plants Using Nonlinear Dynamic Root Density Distribution Function

Water uptake by plants is one of the major components of water balance of the vadose zone that greatly influences the contaminant and moisture movement in variably saturated soils. In this study, a nonlinear macroscopic root water uptake model that includes the impact of soil moisture stress is developed. The model incorporates the spatial and temporal variation of root density in addition to the dynamic root depth considerations. The governing moisture flow equation coupled with the water extraction by plants term is solved numerically by an implicit finite-difference method. The simulation is performed for various physical scenarios subjected to different boundary conditions. The model is tested first without considering the water uptake and results are compared with observed data available in the literature for two cases. A nonlinear water uptake term is subsequently incorporated in the model which is then simulated for corn crop for constant root depth under various characteristic moisture availability environments. Results show that the water extraction rate is closely related to the soil moisture availability in addition to the root density. The plants are observed to extract moisture mainly from the upper root dense soil profile when water content is in an optimal range, otherwise, the peak of the uptake moves to other soil layers where the moisture is easily available. Finally, the model is applied to a corn field and simulated results are validated with field data. The simulated moisture content for 2 months of crop growing season shows a reasonably good agreement with the observed data.

Experimental and modelling performances of a roof-integrated solar drying system for drying herbs and spices

This paper presents experimental performance of solar drying of rosella flower and chili using roof-integrated solar dryer and also presents modelling of the roof-integrated solar dryer for drying of chili. Field-level tests for deep bed drying of rosella flower and chili demonstrated that drying in the roof-integrated solar dryer results in significant reduction in drying time compared to the traditional sun drying method and the dry product is a quality dry product compared to the quality products in the markets. The payback period of the roof-integrated solar dryer is about 5 years. To simulate the performance of the roof-integrated solar dryer for drying herbs and spices using hot air from roof-integrated solar collectors, two sets of equations were developed. The first set of equations was solved implicitly and the second set of equations was solved explicitly using finite difference technique. The simulated air temperatures at the collector outlet agreed well with the observed air temperatures. Good agreement was also found between experimental and simulated moisture contents.

Aggregation of vertical flow in the vadose zone with auto- and cross-correlated hydraulic properties

Summary Quantifying water flow across larger areas of the vadose zone has applications in water resources management and climate modeling. The nonlinearity of unsaturated flow and the variability of vadose zone parameters make it difficult, if not impossible, to accurately simulate near-surface water content and flux with large-scale models. Monte Carlo simulations of one-dimensional infiltration and evaporation were conducted with the Richards equation to simulate moisture content and flux in a heterogeneous field according to the streamtube concept. A set of 126 retention curves and saturated hydraulic conductivities from the UNSODA database was used to generate random fields of hydraulic parameters with pre-defined auto- and cross-correlation. Two stochastic parameters were used: the retention shape factor, ln mn , and either the retention scale parameter θ s or ln h G or the saturated hydraulic conductivity, ln K s . Infiltration is mostly governed by ln K s . The evaporative flux is strongly determined by the “structural” parameter ln h G and also by the “textural” parameter ln mn . The water content in the upper part of the soil depends mostly on ln mn and somewhat on θ s . Cross-correlations all resulted in clusters with consistently low or high water contents and moisture fluxes. Aggregation to obtain results at larger scales was done by a posteriori averaging of local results. This procedure is a convenient benchmark for large-scale modeling approaches. In an example of a priori aggregation, effective retention parameters were optimized to synthetic retention curves for the larger pixel scale and subsequently used in the Richards equation. The amount of infiltrated water was overestimated by up to 40%, large parts of the upper profile were erroneously predicted to be saturated. Although effective hydraulic properties have been used successfully in evaporation studies, considerable errors, which increased with pixel size, also occurred for evaporation. The stream tube modeling offers a convenient and accurate, albeit mundane, approach to elucidate the role of hydraulic properties and to obtain large-scale hydrological data.

Simulation of solar drying of chilli in solar tunnel drier

This article presents modelling of a solar tunnel drier by taking into account heat transfer in the collector and coupled heat and mass transfer within the drying unit. One set of equations was developed to predict cover temperature, absorber temperature and air temperature in the collector and another set of partial differential equations was developed to predict the air and chilli temperatures and moisture content for drying of green chilli in the solar tunnel drier. The first set of equations was solved iteratively and the second set of equations was solved numerically on the basis of an exponential solution over the finite difference grid element using the outlet air conditions of the collector as inlet conditions of the drying unit. The simulated air temperatures in the collector and the drier agreed well with the observed air temperatures. Good agreement was also found between experimental and simulated moisture contents for drying green chilli.

Estimation of green moisture content distribution in hemfir timber by stochastic simulation

AbstractThis paper describes an improved stochastic model designed to simulate systems, such as green timbers, that cannot be analyzed as a unit but as a collection of a large number of similar components. The stochastic model provides a piecewise green moisture content frequency distribution curve by using nondestructive measurements such as of timber weight. A new, relatively simple two-parameter function was designed to describe the log-normal moisture concentration distribution above the fiber saturation point, and the parameters of this function were determined by fitting the experimental timber weights with the results of the stochastic model. The simulated green moisture content distributions showed good agreement with the experimental data for Pacific coast hemlock (hemfir) timbers, thus providing a piece of information that is indispensable for applying stochastic simulation to industrial drying of timbers.

Application of PESTFADE to Simulate Nitrate Leaching in a Fertigated Corn Field in Thailand

In this paper, we describe the modification and application of a pesticide transport model to simulate nitrate leaching in irrigated soils. The model PESTFADE consists of Runoff/Erosion, Water Flow, Heat Flow and Convection–Adsorption–Diffusion–Degradation submodels. The Soil Conservation Service (SCS) equation for estimating runoff and the Universal Soil Loss Equation (USLE) for calculating soil erosion were modified so the model can evaluate chemical partitioning in runoff and sediments, as well as to take into account multiple chemical applications. The model was validated using measured data from a fertigated corn field at the AIT Experimental Farm, Thailand. Specifically, in 1999 and 2000 observed values of moisture content and nitrate concentrations in the unsaturated zone were used as a basis for verifying the validity of the simulated values. Also some error statistics were used to assess the accuracy and performance of the model in comparison with measured data. Validation results indicate that the model simulated moisture content quite well as reflected by the close fit between measured and predicted values in the upper 60 cm of the soil profile. Specifically, the measured moisture content at this depth ranged from 28–36% during the growing period in 1999 while model results gave values ranging from 29–40%. In 2000, measured values ranged from 30–34.5% and the corresponding simulated values ranged from 33–37%. Despite the slight overprediction by the model, the average relative error (RE) of 0.05 indicates that model results are within acceptable range. Simulated nitrate concentrations also provided good correspondence, with observed data for the 100 kg N ha−1 treatments in 1999 ranging from 0.7–1.1 mg L−1 and model results ranging from 0.5–0.98 mg L−1. The model generally underpredicted nitrate concentrations for both years and for other application rates, which perhaps attributed to the higher simulated values of moisture content allowing more leaching, and thus less nitrate remaining in the crop root zone. Nevertheless, model results are within acceptable range as reflected in the small values of RE and other statistical variables (RE ranged from 0.07–0.4 and SE from 0.12–0.7). Thus it can be inferred that the model can be adopted for simulating soil moisture distribution and nitrate leaching in a fertigated corn field under Thailand soil and climatic conditions.

Surfactant effects on unsaturated flow in porous media with hysteresis: horizontal column experiments and numerical modeling

Many organic compounds depress the surface tension of water relative to their aqueous concentration. These surface-active organic solutes have been shown to cause water flow in unsaturated porous media. Flow in these systems typically occurs from contaminated (high concentration) regions toward cleaner (lower concentration) regions. That flow is characterized by significant drainage and rewetting associated with the advance of the solute front. In the literature, modeling of unsaturated flow and transport in systems with solute concentration-dependent surface tensions has been limited to simulations without hysteresis in the hydraulic functions. However, experimental evidence is also presented which shows that hysteresis is a factor. We modified the hysteretic unsaturated flow and transport numerical model HYDRUS 5.0 to include concentration-dependent effects of a mobile organic solute. The moisture content-pressure head and unsaturated hydraulic conductivity functions were scaled for concentration-dependent surface tension and viscosity, respectively. The modified model successfully simulated data from surfactant-induced flow in 1-D horizontal column experiments. The effects of hysteresis were shown to be important to accurately simulate flow in these systems. For example, at final steady state, hysteretic simulations predicted uniform concentration and pressure profiles, but moisture contents that varied with distance. The final simulated moisture contents ranged from 0.12 to 0.25 along the column. In contrast, a non-hysteretic simulation would predict uniform distributions of concentration, pressure and moisture content. Dispersivity also had an effect on flow simulations. Lower dispersivity values caused sharper surfactant concentration gradients, which resulted in larger capillary pressure gradients and higher fluxes near the solute front. The modeling approach used here is expected to be applicable to many organic compounds of environmental interest that depress surface tension and thereby are capable of inducing unsaturated flow in porous media.

Simulation of Recirculating Circular Grain Dryer with Tempering Stage

ABSTRACT The diiffusion model describing internal diiffusion of moisture within a grain kernel during drying and tempering stages was incorporated in the cross-flow drying model to simulate the recirculating circular grain dryer with drying and tempering stages. Experiments were conducted on an experimental prototype recirculating circular grain dryer for wheat and rough rice drying. The simulated grain temperature and moisture content were compared with the experimental data of drying wheat and rough rice, the maximum deviation of the outlet grain temperature was 5°C and the maximum deviation ofthe final grain moisture content was 0.3% w.b. The simulating program for recirculating circular grain dryer was used for analyzing the effects of structure parameters and hot air parameters on the dryer performance. Recommendations for design of the recirculating circular grain dryers are drawn from the experiments and simulation.

Estimating forage yield and quality changes during field drying for hay. 2. Model of forage drying

A forage drying submodel (HayDry) has been developed for use in an operational model of weather-induced forage quality losses during field drying for hay. HayDry simulates changes in bulk swath forage moisture content during field drying periods that may or may not be prolonged by rain. Model inputs are hourly solar irradiance (or net radiation), air temperature and humidity, wind speed and rainfall. Forage drying is estimated by the Penman-Monteith combination equation, with canopy resistance estimated as an empirical function of surface water, forage moisture content and forage dry-matter yield. Forage wetting and rehydration are estimated by a distributed rewetting submodel. HayDry was developed and validated in three steps: (1) a sensitivity analysis identified key model parameters; (2) established values for key parameters were evaluated by comparing the simulated forage moisture contents with field measurements during two rain-free and two prolonged drying periods; (3) the model was independently validated during a third prolonged drying period and at a second site. The simulated changes in forage moisture matched closely the measured sequence of drying, rewetting by dew and rewetting by rain, for forage mixtures that were predominantly alfalfa. The mean forage moisture content during drying was simulated to within 20% during rain-free and prolonged drying periods at both sites.

DYNAMIC SHRINKAGE AND VARIABLE PARAMETERS IN BAKKER-ARKEMA'S MATHEMATICAL SIMULATION OF WHEAT AND CANOLA DRYING

Abstract The bulk volume shrinkage was linearly related to instantaneous grain moisture reduction. The shrinkage coefficient was found to be primarily a function of air relative humidity. The Bakker-Arkema's bulk grain drying model was modified to incorporate the shrinkage equation. A correction factor for thin layer drying equation was also introduced to reduce deviation between the experimental and simulated moisture content. The Bakker-Arkema model showed significant improvement due to these modifications.

Simulation of Low Temperature Rough Rice Drying and Rewetting in Shallow Beds

Equilibrium simulation model was used for estimating the drying and rewetting of long-grain rough rice in shallow beds due to forced aeration. Limitations of the simulation model were examined for the relative influences of grain layer thickness, time step, and airflow rate on predicted moisture content profiles in grain beds. A value of grain dry matter-to-air ratio equal to or greater than 0.27 based on 1-h time step was determined to yield close agreement between experimental and simulated moisture content profiles. Under such conditions, the simulated moisture content profiles were insensitive to the changes either in layer thickness or time step for a fixed value of grain dry matter-to-air ratio based on 1-h time step. Results showed that equilibrium model predicted rough rice drying and rewetting in shallow-beds reasonably well when the developed criterion for grain dry matter-to-air ratio was applied in the simulation scheme.