Uniform Moisture Distribution Research Articles

Influence of wind and bed slope on water and soil moisture distribution in solid‐set sprinkler systems

AbstractThe present study was carried out to investigate the effects of wind and bed slope on uniformity of water and soil moisture distribution in solid‐set sprinkler systems. For that, six plots of 25 × 30 m with bed slopes varying from 1.3 to 13.4% were selected in the Bileh‐Savar Sprinkler Irrigation Network in Iran. For each plot, uniformity of water distribution and soil moisture monitoring tests were performed with three replications under different climates and operating pressures. In each of the tests, water application depth and soil moisture were measured at 164 and 143 spots in each plot, respectively. Based on computations and with regard to the ranges of environmental and systemic variations, uniformity coefficients of water application varied from 45 to 84%. In order to investigate the variations among different parameters, a number of relations were obtained to hold among different assessment indices. The results showed that proper management of the operating pressure during irrigation could largely cancel out the negative effects of high wind speed and also its variations on water application uniformity. The sensitivity analysis of the relations obtained also revealed that the uniformity coefficient of soil moisture is more sensitive to the uniformity coefficient of water application than to plot bed slope. Also, the fields with milder bed slopes are more suitable for improving uniformity of soil moisture distribution. The findings indicate a more uniform distribution of soil moisture compared to that of water depth across the plots. Hence, it seems that in arid and semi‐arid areas where water resources are scarce, there will be no need for higher water consumption to increase uniformity of water application beyond 75%. Copyright © 2008 John Wiley & Sons, Ltd.

Caractérisation géostatistique de la variabilité spatiale de l’humidité du sol à l’aide des cartes dérivées des données radar à synthèse d’ouverture de RADARSAT-1

This paper examines the potential of RADARSAT-1 C-band synthetic aperture radar (SAR) data for quantifying the spatial variability of soil moisture in the Roseau River basin, in Manitoba, Canada. To compensate for the lack of accuracy in the measurement of roughness, we applied a semi-empirical calibration technique. The procedure improved the performance of the integral equation model (IEM). An inversion of the calibrated version of IEM was implemented to extract soil moisture maps. Adjustments to the semivariograms using an exponential model showed the existence of an effect of spatial organization. The correlation lengths obtained are in good agreement with those reported in the literature using in situ measurements (~100 m). However, we highlighted the influence of semivariogram spatial extents on such estimations. Yet, it has been shown that this effect can be modeled using exponential type functions (R2 > 0.90). During the analysis of the apparent variances, we confirmed the predominance of microstructure errors over the effect of radar speckle. We also outlined an increasing pattern in the apparent variances in relation to the scale of the geostatistical analyses. This pattern was less pronounced during relatively dry periods. This derives from the predominance of evaporation mechanisms, which create a uniform spatial distribution of moisture in the soil superficial layers.

Eigensensitivity analysis of moisture-related buckling of marine composite panels

In this paper, an approximate closed-form solution is presented to compute the moisture-related buckling of symmetric angle-ply laminates. The environment corresponds to a steady state condition, which provides a uniform moisture distribution for the laminate. The laminate consists of four layers [ θ/− θ] s constructed of low, moderate and high stiffness ratio materials. Comparative results using the Rayleigh–Ritz method provides a means of assessing the accuracy of the expression. For certain laminate architectures, several modes must be computed to ascertain the lowest buckling mode, and once identified, provides an excellent approximation for the mode computed using the Rayleigh–Ritz method.

Influence of root resistivity on plant water uptake mechanism, Part II: analytical solutions for low/moderate soil-root conductivity ratio

A one-dimensional approximate analytical model, which preserves the main features of soil-crop-atmospheric hydrodynamics, has been suggested for plant roots of low soil-root conductivity ratio (SRCR). The proposed approach involves physically based concepts, such as mass balance equation, Darcy’s law, and related water uptake and plant transpiration functions. Two main assumptions have been made to derive the analytical solution: (1) gravitational flow is adopted and (2) the uniform soil moisture distribution within the root water activity zone is supposed. The mass balance equation in its integral form is solved by the method of characteristics. This leads to the two functional equations for soil pressure head and root potential, which can be solved simultaneously by using common software. The model has been further verified against the numerical one. The model represents a reasonable compromise between the complicated mechanism of unsaturated water flow with root water uptake (RWU) and still insufficient knowledge of the soil-plant-atmospheric continuum. It is able to account for temporal fluctuations in root activity zone and provides a relatively simple algorithm for investigation of RWU-mechanism. Besides the theoretical and applicative importance, this flow model yields water and velocity distributions within soil profile, and, thereby, constitutes a preliminary step toward solution of contaminant transport problems in vadose zone.

Performance evaluation of an automated surge irrigation in paired row furrows

An automatic surge irrigation system was fabricated and field tested to establish its efficacy under on-farm irrigation water management. The system was based on sequential operation. A time switch and an electromagnetic valve were the main components of the system. Field evaluation of this automatic surge irrigation system was carried out at Tamil Nadu Agricultural University, Coimbatore. Efficacy of automatic surge irrigation system over continuous flow system was experimentally evaluated in paired row furrows of 120 cm width in terms of waterfront advance times, infiltration patterns and soil moisture distribution efficiencies. Automatic surge flow was found to make the soil reach its basic infiltration rate much quicker, 35 to 50 percent of the time elapsed in continuous flow. This facilitates quicker waterfront advance resulting in more uniform storage and distribution of soil moisture from head to tail end of the field with minimum losses. Surge flow in 160 m long furrow was found to cause 48 percent reduction in the advance time as taken by the continuous flow and it took 59 percent of the net duration of irrigation to advance to the tail end. Though it is better than continuous flow in saving advance time the greater proportion for its advance time (59%) over the net irrigation time limits its application up to 120 m long furrows only. The longitudinal distribution of soil moisture after irrigation was found to be more uniform in furrows under automatic surge flow compared to continuous flow.

A theoretical expression for drying time of thin lumber

An analytical expression for the drying time of thin lumber is derived, based on a method presented in this study. The laws of moisture content change in wood as function of mass transfer are used for the theoretical approach. The diffusion equation for moisture content is set up for a three-dimensional block of lumber based on the assumption of uniform initial distribution of moisture throughout the specimen. The boundary condition stipulates that the moisture gradient at the boundary is proportional to the deviation of the moisture content of the slab from the equilibrium value at that temperature. These conditions are used to derive an analytical expression for the time required to get from an initial moisture distribution to a desired final moisture content of thin lumber. For a sample calculation, the result of drying time agrees within 10% with the prediction of previously published analytical formulas for the drying curve.

A Model for Microwave-Assisted Drying of Leather: Development and Validation

In this work microwave energy is employed in the drying process of leather sheets to achieve an uniform moisture distribution along their entire surface and to obtain an enhanced final quality for this material. In order to obtain a deeper understanding of the process, a new three-stage drying model has been derived based on the knowledge of the dielectric properties versus moisture content and the specific energy use during each of the drying periods. The model validation shows a close behavior between experimental and simulated results. The fast convergence of experimental drying curves indicates that a very uniform moisture distribution along the hides can be obtained provided that microwave energy is properly used.

Response of C 3 and C 4 Grasses to Supplemental Summer Precipitation

Rangeland plant productivity and species composition are affected by moisture availability and grazing intensity. We examined warm- and cool-season grass productivity and relative distribution on grazed and ungrazed sites, receiving either natural precipitation or precipitation plus limited supplemental irrigation. The amount of additional water varied depending on rainfall during the previous week and was intended to shorten the interval between precipitation events and provide a more uniform seasonal moisture distribution. Irrigation treatments were superimposed in 1997 and 1998 on paddocks that had not been grazed for about 55 years or continuously stocked during the growing season for 15 years. Cool-season grasses dominated the ungrazed plots, comprising about 90% of the total biomass. In the grazed plots, the proportion of C3 grasses ranged from 30 to 81%. The proportion of C3 grasses in the grazed treatment decreased from spring to fall and decreased with supplemental irrigation. Root biomass was greater and more concentrated near the soil surface in the grazed compared with the ungrazed plots. Irrigation had no effect on root biomass in the grazed plots while irrigation reduced total root biomass and root biomass in the top 5 cm of the soil profile in the ungrazed plots. Irrigation increased total aboveground biomass only at the August 1997 harvest. Aboveground biomass of warm-season grasses, however, increased under irrigation in the grazed plots in August and November 1997 and August 1998. These increases, however, were offset by a reduction in cool-season grasses in November 1997 and August 1998. Warm-season grasses were particularly responsive to the supplemental irrigation treatments and tended to increase under irrigation at the expense of cool-season grasses. Because of the increased proportion of warm-season grasses, grazed plots were more responsive to irrigation than ungrazed plots. DOI:10.2458/azu_jrm_v55i5_skinner

Response of C3 and C4 grasses to supplemental summer precipitation

Rangeland plant productivity and species composition are affected by moisture availability and grazing intensity. We examined warm- and cool-season grass productivity and relative distribution on grazed and ungrazed sites, receiving either natural precipitation or precipitation plus limited supplemental irrigation. The amount of additional water varied depending on rainfall during the previous week and was intended to shorten the interval between precipitation events and provide a more uniform seasonal moisture distribution. Irrigation treatments were superimposed in 1997 and 1998 on paddocks that had not been grazed for about 55 years or continuously stocked during the growing season for 15 years. Cool-season grasses dominated the ungrazed plots, comprising about 90% of the total biomass. In the grazed plots, the proportion of C3 grasses ranged from 30 to 81%. The proportion of C3 grasses in the grazed treatment decreased from spring to fall and decreased with supplemental irrigation. Root biomass was greater and more concentrated near the soil surface in the grazed compared with the ungrazed plots. Irrigation had no effect on root biomass in the grazed plots while irrigation reduced total root biomass and root biomass in the top 5 cm of the soil profile in the ungrazed plots. Irrigation increased total aboveground biomass only at the August 1997 harvest. Aboveground biomass of warm-season grasses, however, increased under irrigation in the grazed plots in August and November 1997 and August 1998. These increases, however, were offset by a reduction in cool-season grasses in November 1997 and August 1998. Warm-season grasses were particularly responsive to the supplemental irrigation treatments and tended to increase under irrigation at the expense of cool-season grasses. Because of the increased proportion of warm-season grasses, grazed plots were more responsive to irrigation than ungrazed plots.

Effects of microwave on the drying, checking and mechanical strength of baked biscuits

The influence of high-frequency radiation on quality in terms of checking and mechanical strength of low-moisture baked products was investigated. Biscuits baked in a convection, reel oven were compared to biscuits of very similar moisture content and appearance that were baked in the same oven until the falling-rate drying period but then immediately microwaved for 30 s in a 700 W microwave oven. Microwave baking was found to significantly reduce checking to 5% compared to 61% in conventional biscuits. The average breaking stress required for intact microwaved biscuits two weeks after baking was 997 kPa, while that for conventional samples was 610 kPa. The structure of conventional biscuits was generally found to weaken at a faster rate than microwaved biscuits. Microwaved biscuits were also found to be less susceptible to checking upon exposure to high ambient humidity. In addition, the finite element software, FIDAP, was used to predict heat and mass transfer with respect to time and position during microwaving under various conditions. A biscuit was modeled as an axisymmetric short cylinder. Simulations confirmed greater drying rates and more uniform internal moisture profiles for microwaved biscuits. A minimum microwaving time of approximately 28 s was predicted to be necessary to produce a uniform moisture profile for a power absorption of 1.7 W/g. An elevation in the biscuit temperature during baking as well as a more uniform moisture distribution found in microwaved biscuits were thought to be critical factors in determining checking behavior and mechanical strength.

DYNAMIC EVALUATION OF THE DEHYDRATION RESPONSE CURVES OF FOODS CHARACTERIZED BY A POULTICE-UP PROCESS USING A FISH-PASTE SAUSAGE. I. DETERMINATION OF THE MECHANISMS FOR MOISTURE TRANSFER

In order to discern the mechanism for the transfer of moisture in foods as they are drying, the pore structure of food and the distribution of moisture in food matrices were studied in detail by using a fish-paste sausage that was prepared with various contents ofmo isture (W 0). A uniform distribution ofmois ture was achieved with a poultice-up process. The void fractions (Vf ) that occurred as a result ofchanges in the pore structure of the food were evaluated from a graphical analysis of SEM photographs on a cross-sectional observation ofthe sausage. The Vf -values obtained changed drastically depending on the W0 and were classified into two regions: I (W 0 > 100%-d.b.), which gave Vf = 0.10 ± 0.08, and II (W 0 < 100%-d.b.), which gave Vf = 0.24 ± 0.05 at a drying temperature of 35°C. For the analysis ofmois ture state, the temperature-programmed desorption (TPD) profiles and the correlation time ofwater protons evaluated from nuclear magnetic resonance (NMR) were effectively used. The results produced three states ofmois ture: weakly and strongly restricted water at Region I and gaseous water at Region II.

Influence of Temper Duration and Weight Distance on System Output in the Corn Dry‐Milling Process

ABSTRACTInitial uniform distribution of moisture in the corn kernel is transformed into nonuniform distribution through tempering to facilitate easy fractionation of corn components. Proper temper duration is essential for effectiveness of the tempering process: a short temper time is insufficient to cause necessary nonuniformity; a long temper duration may allow moisture to redistribute uniformly. Untempered corn suffers from lack of beneficial swelling stress and therefore produces lower yields of flaking grits, coarse grits, and germ. For tempered corn, the system throughput exponentially decreases with temper duration and then stabilizes; the period of stabilization is dependent on weight distance. Throughput values are lower at longer weight distances. At a temper duration of 0.066 m, throughput was ≈33–50% at 0.053 m weight distance. Tail stock fraction rapidly and nonlinearly decreases with increase in temper duration; the rate of decrease is higher at longer weight distance. The peak values of flaking grits can exceed 50% at some combinations of weight distance and temper duration. Coarse grit yields were 9–19% and 16–24% for the shorter and longer weight distances, respectively. Germ recovery improved due to tempering, and differed only by ≈0.5% at the two weight distances. Tempering lowered the oil content of flaking grit, but the temper duration did not have much influence on moisture content of various fractions.

Moisture conditions in coated exterior wood Part 4: Theoretical basis for observed behaviour. A computer modelling study

A theoretical investigation of moisture movement in pine sapwood was undertaken using two different models of behaviour. Firstly a model was developed using a single diffusion process; this model predicted levels of water absorption and moisture content which were in broad agreement with experimental results. However, this approach proved to be over-simplistic, and predicted a more rapid penetration of moisture than was observed in practice. The model also failed to predict the deceleration in absorption which was recorded in laboratory tests. Consequently, the predictions of the model were of a more uniform moisture distribution than was consistent with experience. A development of the model, to include flow mechanisms appropriate for the level of moisture content, gave more realistic predictions. The improved model is based on different flow mechanisms in three distinct regions of moisture content. Below fibre saturation point (FSP), a diffusion mechanism is assumed for the calculation of moisture flow. Between FSP and a threshold, termed the irreducible saturation point (ISP), flow takes place through the cell wall material. Above the ISP, a continuous path is established for moisture movement from cell to cell through the bordered pits. The improved model proved capable of predicting levels of moisture uptake and moisture content, and of predicting the moisture gradients observed in practice. It also provided an explanation of some of the observed patterns of wood moisture movement reported in earlier parts of this series of papers. In particular it explained why, when water is absorbed by coated timber, the rise in surface moisture content appears not to exceed FSP. Additionally it provided an understanding of the continuing penetration of moisture in depth during the early stages of drying. This is a significant conclusion, because it imposes a limitation, in principle, on the performance of high permeability wood coatings.

Solutions of Luikov equations of heat and mass transfer in capillary porous bodies through matrix calculus: a new approach

In this paper an eigen value analysis approach is employed to obtain the solutions of the Luikov system of linear partial differential equations addressed to the most general type of boundary conditions. The Luikov equations provide a well established model for the analysis of various simultaneous heat and mass diffusion problems in capillary porous bodies. However,analytical methods to achieve a complete and satisfactory solution of these equations is still lacking in the literature because of non inclusion of the existence of a countable number of complex roots in almost all the solutions. A specific example on contact drying of a moist porous sheet with uniform initial temperature and moisture distribution is considered. The influence of the complex roots on the dimensionless temperature, moisture content, and the local rate of drying is demonstrated. A set of benchmark results is obtained for reference purposes.

SIMULTANEOUS HEAT AND MOISTURE TRANSFER IN CHEDDAR CHEESE DURING COOLING I. NUMERICAL SIMULATION

ABSTRACT Numerical simulation method was developed and used to predict temperature and moisture distribution in large Cheddar cheese block during cooling based on a simultaneous heat and mass transfer model. The predicted results agreed well with the experimental results. The results suggest that cooling for 3 to 4 days would be sufficient to achieve fairly uniform distribution of temperature and moisture in a 640 lb Cheddar cheese block.

Moisture conditioning and transport properties of concrete test specimens

An experimental investigation is reported of drying and conditioning concrete at 50°C to obtain a uniform moisture distribution, prior to testing for air permeability and water absorption rate. The use of 100 mm cubes of concrete with a cast-in cylindrical cavity facilitated assessment of moisture distribution and measurement of air permeation through the surface layers of concrete: the moisture distribution was assessed by comparing the relative humidities measured within the cavity and at the surface of the test specimen. Partial drying followed by sealed storage at 50°C for a few days provided a rapid and convenient method of obtaining a uniform moisture distribution. The test results for a range of concretes indicated that air permeability and water absorption rate were very sensitive to the moisture content of the concrete, particularly at relative humidities above 60% and which were common for field exposure. The transport properties of the empty capillary pore system could be assessed using test specimens preconditioned at 60% relative humidity, but preconditioning at 85% relative humidity might be more appropriate for assessing field performance if there is a risk of carbonation induced corrosion.

EFFECTS OF IRRIGATION ONPROSOPIS JULIFLORAAND SOIL PROPERTIES OF AN ALKALI SOIL

SUMMARY Field studies on an alkali soil (Aquic Natrustalf, pH 10.4 and ESP 90) examined the performance of Prosopis juliflora (SW) DC under irrigated and rainfed conditions. After 2 years, plant mortality was respectively 36 and 9 per cent in the rainfed and irrigated treatments; and mean plant height and diameter at 5 cm above ground level were respectively 137.0 cm and 2.1 cm in the rainfed treatment and 214.0 cm and 2.8 cm in the irrigated treatment. Biomass productivity in the irrigated treatment was three times that in the rainfed treatment. Water use efficiency was also higher in the irrigated treatment due to the higher biomass yield. There was little difference between the chemical composition of the parts of plants grown under rainfed and irrigated conditions. Irrigation resulted in an appreciable decrease in pH and electrical conductivity, a significant increase in water infiltration characteristics, and a more uniform distribution of moisture throughout the soil.

紙のカール ＩＩＩ 履歴に依存するカールの数値シミュレーション

Numerical simulation of history-dependent curl has been made on the basis of the viscoelastic laminate model [5]. Curl behavior of paper under varying humidity conditions depends not only on the present value of moisture content but also on the moisture history that paper has experienced in the past, such as typically seen in Figs. 1 to 3. In order to predict such complex curl behavior, a computer simulation model was developed by using the classical lamination theory and the general linear theory of viscoelasticity which was proposed by Coleman [4]. Drying stress effects were incorporated by assuming presence of stresses in the reference state, which was taken in the final drying stage [5].Simulation results for curvature response to repeated humidity cycling showed that the paper curl can be separated into two components, i. e., reversible and irreversible componets. The reversible component is essentially determined by difference in hygroexpansion coefficients between top and bottom sides of the sheet, whereas the irreversible curl is governed mainly by mechanical causes, i. e., asymmetric distribution of drying stresses and two-sidedness in relaxation moduli. When the top and bottom sides of the sheet are subjected to different moisture histories and returned to the original uniform moisture distribution, such as often seen in printing and xerography processes, paper shows residual curl after the process in the absence of non-uniformity in paper properties in the thickness direction. This phenomenon is caused by viscoelastic relaxation of hygro-stress gradient which is produced during the process. In this case it is, therefore, important to control the “average” values of hygroexpansion coefficients and relaxation moduli through the thickness, as well as the two-sidedness of these properties.Since paper curl is a complex manifestation of different effects of non-uniformity, a measure for curl control varies with practical situations. The computer simulation model developed in this study provides a rational design tool for various paper products by clarifying each contribution of the different curl mechanisms.

Unsaturated flow in a centrifugal field: Measurement of hydraulic conductivity and testing of Darcy's Law

A method has been developed to establish steady state flow of water in an unsaturated soil sample spinning in a centrifuge. Theoretical analysis predicts moisture conditions in the sample that depend strongly on soil type and certain operating parameters. For Oakley sand, measurements of flux, water content, and matric potential during and after centrifugation verify that steady state flow can be achieved. Experiments have confirmed the theoretical prediction of a nearly uniform moisture distribution for this medium and have demonstrated that the flow can be effectively one‐dimensional. The method was used for steady state measurements of hydraulic conductivity K for relatively dry soil, giving values as low as 7.6 × 10−11 m/s with data obtained in a few hours. Darcy's law was tested by measuring K for different centrifugal driving forces but with the same water content. For the sand at a bulk density of 1.82 Mg/m3 and 27% saturation, results were consistent with Darcy's law for K equal to 5.22 × 10−10 m/s and forces ranging from 216 to 1650 times normal gravity.

The expansion of wafer and its relation to the cracking of chocolate and ‘bakers’ chocolate’coatings*

SummaryThe linear expansion of a wafer was found to be directly proportional to any increase in moisture content over most of the range from 0.5% to the moisture content in equilibrium with the atmosphere to which the wafer was exposed. the average gain in linear dimension of the wafer per 1% increase in moisture content was 0.4%, which was sufficient to cause cracking of the chocolate coating. the time taken for the coating to crack, as a result of adsorption of water vapour from the atmosphere through holes in the coating, was measured as a function of type and thickness of coating, initial moisture content of the wafer and the relative humidity of the atmosphere. the results were examined in relation to commercial attempts to minimize cracking of the coating by prior conditioning of the wafer sheet. It was concluded that cracking will only be inhibited if (i) there is uniform distribution of moisture within the wafer and (ii) there are no holes or flaws in the coating.