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1.
《Journal of Agricultural Engineering Research》1995,60(1):15-24
The effect on compressibility of incorporating peat into four remoulded Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa using a compression machine. Air-dry peat was applied at four levels (0, 4, 8 and 12% by mass) to the soils (two sandy loams, clay loam and clay) and tested at three moisture contents close to the Proctor optimum moisture content of the soils. Compression curves (bulk density versus log applied stress) for each soil at the moisture levels tested were almost linear and parallel over the range of stresses from about 100 to 1000 kPa.Mean values of dry bulk density declined significantly at 0.001 level with increasing peat content from 1·23 to 0·87 Mg m-3. Mean bulk density values increased significantly at 0·001 level with increasing applied stress and moisture content and declined with increasing clay content. Significant interaction effects were observed between soil type and peat content and between peat content and moisture content. Peat incorporation resulted in greater soil compression, but the increases were less evident in clay than in sandy loam soils. Soil compression refers to the decrease in soil volume with the application of external load. The compression index, C (slope of the dry bulk density versus log applied stress relationship), increased significantly at 0·05 level from 0·21 Mg/m3 in one sandy loam soil to 0·38 Mg/m3 in the clay soil. While the C value did not differ significantly with increasing peat content in the sandy loams and the clay loam, it decreased significantly at 0·01 level in the clay soil. An equation expressing C as a function of initial soil bulk density before compression and a strain parameter was developed in order to explain the variation of C in the soils tested. A method is described that can be adopted to quantify the effect of peat on soil compressibility. 相似文献
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《Journal of Agricultural Engineering Research》1999,72(1):27-35
Moisture content of shelled maize,Zea maysL., was correlated with the attenuation and phase shift of electromagnetic waves travelling through a layer of grain. Several calibration equations are presented in the paper that are based on measurements taken at 15·2 GHz for various grain densities, moisture contents and temperatures. Validation of the calibration equations indicated that moisture content can be predicted with an uncertainty less than ±0·72% moisture content w.b. at the 95% confidence level. Moisture predictions are largely independent of bulk density variations at temperatures from 4 to 45°C and moisture contents from 9 to 19% w.b. By following one approach described, the grain bulk density can be determined from the same measurements with an uncertainty of less than 25 kg/m3. With another approach, the grain bulk density cannot be determined, but moisture content is determined independent of the material bulk density and compensated for temperature. No differences among three maize hybrids were observed in the measured data. 相似文献
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《Journal of Agricultural Engineering Research》1996,63(2):87-92
Several physical properties of lentil seed were evaluated as a function of moisture content. The average diameter, thickness, unit mass and volume of seed were 6·64 mm, 2·65 mm, 0·070 g and 49·08 mm3respectively at 6·5% m.c.d.b. Studies on rewetted seed showed that as moisture content increased from 6·5 to 32·6% d.b., bulk density decreased from 1190 to 935 kg/m3, porosity increased from 27·4 to 32·0%, projected area increased from 56 to 82 mm2and terminal velocity increased from 10·95 to 12·06 m/s. The static and dynamic coefficients of friction of lentil seed against galvanized sheet metal, plywood and rubber surfaces increased with moisture content in the range from 6·5 to 32·6% d.b. The largest coefficient of friction was against a rubber surface, ranging from 0·374 to 0·532. The effect of moisture content was as great as or greater than the difference between the surfaces. 相似文献
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《Journal of Agricultural Engineering Research》1988,39(4):259-268
The dependence of physical properties of gram on moisture content was determined. The best approximate shape was found to be a prolate spheroid. At 10·9% moisture content d.b., the measurements yielded an average 1000 grain weight of 0·173 kg, a mean surface area of 133·4 mm2, and sphericity and roundness of 74% and 70% respectively. In the moisture range from 9·64 to 31·0% d.b., studies on rewetted gram showed that the bulk density changed from 780 to 708 kg/m3, kernel density from 1311 to 1257 kg/m3; porosity from 40·5 to 43·7% and static coefficient of friction from 0·384 to 0·651 over surfaces of different materials. The angle of repose was observed to change from 25·5° to 30·4° in the moisture range from 8·62 to 17·6% d.b. 相似文献
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《Journal of Agricultural Engineering Research》1999,72(2):145-150
Makhana is the popped expanded kernel of the gorgon nut (Euryale ferox) and is used as a delicious food in India. Presently, it is sorted, graded and used as an ingredient of various ready-to-eat products. High volumetric expansion of makhana increases transport cost and makes it too expensive in distant places. Makhana thus requires further processing to get some value-added products of minimum volume. To develop any kind of product and mechanized system for their production, physical properties are required. Furthermore, since makhana is a seasonal and regional crop its storage conditions are also needed for keeping it appropriately at processing centres. Physical properties of makhana at moisture contents ranging from 5 to 20% (dry basis) and equilibrium moisture content at relative humidities ranging from 11·2 to 88% at temperature 30°C were determined using standard techniques. Physical properties were found to be: test weight (weight of 1000 makhana) 286 to 384 g; bulk density 56·5–84·6 kg/m3; particle density 105–240·6 kg/m3; porosity 29·4–48·9%; angle of repose 33–35·6°; and static coefficient of friction 0·596–0·82 and 0·493–0·684 on galvanized iron and stainless steel, respectively. The equilibrium moisture content of makhana was found to be between 11·5 and 58·9% (dry basis) within the ranges of variables studied. 相似文献
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《Journal of Agricultural Engineering Research》1993,54(3):219-229
Several physical properties of pumpkin seeds and kernels were evaluated as functions of moisture content. The average length, width, thickness and unit mass of the seed were 16·91 mm, 8·67 mm, 3·00 mm and 0·203 g respectively. Corresponding values for the kernel were 14·62 mm, 6·89 mm, 2·50 mm and 0·160 g respectively. In the moisture range from 4 to 40% d.b., studies on re-wetted seed showed that the bulk density increased from 404 to 472 kg/m3, true density decreased from 1179 to 1070 kg/m3, porosity decreased from 65·73 to 55·46% and terminal velocity increased from 4·7 to 6·5 m/s. For the kernel, the corresponding values changed from 481 to 554 kg/m3, 1080 to 1143 kg/m3, 55·46 to 51·53% and from 4·27 to 5·25 m/s respectively. In the moisture range of 4 to 27% d.b. the static coefficient of friction varied from 0·41 to 0·76 for seed and from 0·34 to 0·65 for kernel over different material surfaces, while angle of repose varied from 30 to 52° for seed and 34 to 42° for kernel. 相似文献
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《Journal of Agricultural Engineering Research》1994,57(2):129-136
The effect on compactibility of incorporating peat into four Trinidadian agricultural soils before compaction was investigated in a laboratory experiment. A factorial experiment was used to study the effect of peat applied at four levels (0, 4, 8 and 12% by mass) on the maximum dry bulk density (MDBD) and optimum moisture content (OMC) of the four soils (two sandy loams, clay loam and clay) compacted using 5, 15 and 25 Proctor hammer blows. The compaction tests were carried out at different moisture contents which varied according to the values of the plastic limits of the soils.Results showed that while the mean values of MDBD of the soils declined significantly (p = 0.001) from 1·51 to 0·92 Mg m-3 with increasing peat content, the mean values of OMC increased from 24·2 to 42·6%. While MDBD increased, OMC decreased with increasing compaction levels. This applied to all the soils tested. The clay soils had significantly lower values of MDBD and greater values of OMC than the sandy loam soils. There were significant interaction effects between soil type and level of added peat and between compaction level and level of added peat. These interactions were used to describe the effect of peat on soil compactibility. Multiple linear regression equations based on compactive effort, sand content, clay content and percentage peat content, were generated for predicting values of MDBD and those of OMC of compaction of the soils used in this study. There was reasonable agreement between the equation for predicting MDBD and a similar equation derived for Nigerian soils in previous work. A good negative relationship obtained between MDBD and OMC is also similar to the one derived from previous research. 相似文献
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《Journal of Agricultural Engineering Research》1996,63(1):73-85
Pressure drops were measured in clean wheat beds for superficial air velocities up to 0·42 m/s at grain moisture contents in the range of 12·8–22·3% w.b. At 12·8% moisture content, pressure drops were determined in wheat for fines contents up to 10·60% (w/w). It was found that pressure drops decreased by up to 30% with moisture content and increased with fines by up to 75%. The selection of a model was made using the results of clean grain. A Shedd-type equation (model 1), the Hukill & Ives’ equation (model 2), and an Ergun-type equation (model 3), all of two parameters, were examined. Model 3 behaved better than model 2 and both gave lower errors than model 1. Model 3 was simplified by considering the parameter of the quadratic term as a multiplier of that of the linear term. The resultant expression (model 4) behaved better than model 2 and was called the approximate, Ergun-type equation. With this model, the non-linear influence of grain moisture content was better predicted than with a linear model proposed previously. With regard to the effect of fines, the use of model 4 permitted a linear relationship between pressure drop ratio and fines content that was independent of air velocity, a feature that was substantially adequate to describe the experimental results. Model 4 is suggested for further work on the resistance to airflow of grain beds. 相似文献
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退化草地复合体力学特性与影响因素研究 总被引:2,自引:0,他引:2
为采用机械手段有效打破高坚实度退化草地板结性土层形成的土壤-根系复合体结构,对退化草地形成的复合体结构基本力学特性进行了研究。通过测定退化草地复合体的紧实程度、容重、含水率、孔隙度和含根量分布,对退化草地形成的复合体的物理性状进行了分析;通过对复合体原状试样进行剪切、无侧限压缩和回弹模量试验,对复合体的抗剪、无侧限抗压和回弹等基本力学特性进行了研究,并在此基础上通过正交试验探讨了容重、含水率和含根量对上述力学特性的影响。研究发现,退化草地形成的复合体具有加剧土壤紧实程度、聚集根系向浅层分布等特征;复合体的抗剪强度、无侧限抗压强度和回弹模量因根系的存在与无根系分布的土层相比有很大变化;复合体容重、含水率和含根量均对其力学特性产生了影响,且各因素的影响存在交互作用,根系的存在可增强复合体结构的抗剪强度和无侧限抗压强度,但对于回弹模量的影响却表现出一定的差异性。 相似文献
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《Journal of Agricultural Engineering Research》1988,39(4):269-275
Values of specific heat, thermal conductivity and thermal diffusivity of rewetted whole grain were found. The specific heat of the grain shows a nonlinear relationship both with temperature and moisture content in the range of 292 to 308 K and 12·4 to 32·4% d.b. respectively, resulting in a second-order multiple regression equation. Bulk thermal conductivity increases both with increase in temperature and moisture content in the ranges 283 to 312 K and 11·5 to 27·2% respectively and was found to vary from 0·114 to 0·247 W/m K. Thermal diffusivity increases with increase in moisture content and decreases with increase in temperature in the temperature and moisture ranges of 293 to 307 K and 12·5 to 26·5% respectively, and its value lies between 9·46 × 10−8 to 16·35 × 10−8 m2/s. 相似文献
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N. Madankumar 《Agricultural Water Management》1985,10(4):305-312
Soil moisture characteristics can be established directly from the physical properties of soils such as mechanical analysis and bulk densities. Multiple regression equations were worked out by taking first fractions of sand (E1), silt + clay (E' = E2 + E3) and bulk density (P), and second fractions of sand (E1), silt (E2), clay (E3) and bulk density (P) as independent variables to predict the parameter b, the air-entry potential ψe and the saturation moisture content s of the soil-moisture characteristics equation. Regression equations were tested for soils of different textural and structural compositions and showed good agreement between estimated and experimentally determined values. 相似文献
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《Journal of Agricultural Engineering Research》1996,63(4):333-343
Heat and mass transfer characteristics of alfalfa pellets are needed in the optimization of coolers for freshly-made pellets and in managing storage schedules of the pellets in silos and bins. Moisture diffusivity and thermal properties are important parameters used to characterize the heat and mass transfer ability of a material. In this study, experimental thin-layer data on (a) moisture desorption, (b) moisture absorption and (c) rate of heating of alfalfa pellets were collected. By applying the inverse theory and using second order mass transfer and heat transfer equations in cylindrical coordinates, the moisture absorption and desorption data were used to estimate the moisture diffusivity as a function of moisture content of the pellets while the heating rate data were used to estimate the thermal properties (thermal conductivity and specific heat) as a function of pellet temperature.Better estimates were obtained when moisture diffusivity of the pellets was exponentially related to moisture content in comparison with a linear relation between moisture diffusivity and moisture content. Moisture diffusivity during desorption (2·40×10-9to 4·12×10-9 m2/s) was about three times that of the values of diffusivity during moisture absorption (7·50×10-10to 1·26×10-9 m2/s). A good fit to the experimental heating rate data was obtained when thermal conductivity and specific heat of the pellets were linearly related to temperature. Over a temperature range of 2 to 110°C, estimated particle thermal conductivities and specific heats of the pellets were in the range of 0·04 to 0·19 W/m K and from 962 to 2114 J/kg K respectively. 相似文献
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《Journal of Agricultural Engineering Research》1996,63(2):129-136
Information don the shrinkage of grain both in bulk and as individual kernels is important in postharvest processing of these materials. The mass and volume of samples of wheat and canola seeds exposed either to humid or dry air were measured during adsorption or desorption cycles. When the grains were exposed to 90% r.h. at 40°C, the bulk density of wheat decreased almost linearly from 790 to 686 kg/m3as the kernel moisture content increased from 8% to 22% w.b. The bulk density of canola descreased by 11 kg/m3, from 672 to 661 kg/m3as the kernel moisture content increased from 5% to 19% w.b. The laws of mixtures were used to develop the following equations to predict grain kernel (vk)and grain bulk volume (vb)respectively as functions of moisture adsorption or desorption:vk/vk0=[1-M0/1+(γ-1)M0] [1+(γ-1)M/1-M]andvb/vb0={[1-(M0-M)][1+(γ-1)M]/[1+(γ-1)M0]} (1-ϵ0)/(1-ϵ)wherevkandvk0are the kernel volumes,vbandvb0are the bulk porosities at the kernel moisture contents ofMandM0respectively;γis the dry kernel density and is assumed to be a constant for each grain. Compared with experimental data, the kernel volumes of both wheat and canola, adequately predicted by the first equation. The second equation gave an adequate prediction of the bulk volume of canola by assumingϵ= ϵ0,but not for wheat unlessϵwas expressed as a polynomial function of kernel moisture content. 相似文献
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末端开路同轴探头法测量土壤复介电值用于表征土壤含水率具有准确、快捷的优点。针对目前土壤介电同轴探头集总测量模型没有充分考虑探头的参数以及土壤体积对测量结果影响等问题,基于电磁场理论,对末端开路同轴探头建立了准静态数学模型,适用于土壤的复介电常数准确测量。通过全波软件仿真和模型计算结果对比,以无水乙醇介电实测值和理论值对比,验证模型的准确性。采用本文介电测量模型对不同含水率的黄绵土进行测量计算,复介电常数实部与实测土壤含水率二阶多项式拟合决定系数大于0.965,表明本文所提土壤介电测量方法适用于土壤复介电常数和含水率的测量。 相似文献