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A comprehensive understanding of the hydrothermal properties of soil is required to model heat distribution in unsaturated soils. In this study, we aim to model heat distribution throughout the profile of unfrozen soil while its thermal diffusivity varies with time and depth. The proposed model is based on the fundamental solution of the one‐dimensional transient heat conduction equation using the decomposition method. We calibrate our model using experimental data from soils of different textures in the literature. The new model can estimate soil thermal diffusivity at different depths and times and uses easily accessible characteristics such as the degree of saturation and the texture of the soil. In this study, the performance of the new model is compared to the performance of the simplified model in which constant thermal diffusivity is considered throughout the profile. Moreover, the model is validated by comparing it with in‐situ temperature measurements within depth of soil profiles with different textures. The results show a very good agreement between the predicted and the measured temperature throughout the soil profiles. Such a validation shows that with increasing degree of soil saturation, depletions in temperature for fine‐textured soils are more significant than those for coarse‐textured soils. Finally, the new model is applied to a double‐layer soil in the Alsace region to define temperature variation in the profile of soil with different characteristics in each layer. For a double‐layer profile, the continuity of the temperature as well as the heat flux is verified at the interface between the two layers. 相似文献
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相变材料回填地埋管换热器蓄能传热特性 总被引：2，自引：1，他引：1
为了探讨相变回填材料固液相变对地埋管换热器蓄能传热性能的影响,建立了带有相变的垂直U型埋管换热器传热数学模型,并利用显热容法对相变材料的相变问题进行了处理。基于模型的数值求解,分析了夏冬季运行工况下相变材料固液相变对U型埋管换热器蓄能性能及其周围土壤温度热响应特性的影响规律,结果表明：同样条件下,相变材料固液相变会减缓埋管周围土壤温度变化趋势,缩小埋管热影响区域;夏季工况采用较低相变温度、冬季采用较高相变温度的相变材料均可以明显改善其换热效果,同时相变潜热大的相变材料可以明显增加地埋管的蓄能效果。研究结论对于缓解土壤热影响区域、改善地埋管换热器的蓄能传热性能具有重要意义。 相似文献
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随着能源压力的日益增大,世界各国都十分重视可再生能源的利用与开发,地源热泵技术作为一种清洁、高效的可再生能源,近年得到了较快的发展。该文利用无限长线热源传热计算模型,讨论了介质内过余温度场的分布特性。结果表明：介质内温度响应在孔壁处最大,随离孔壁距离的增加呈指数衰减,随时间的增加而增大;热传播区域随时间的增加而增大,随介质的热扩散系数的增加而增大。针对工程中群埋管换热器情况,利用叠加原理计算群埋管的孔壁温度,定义换热器的热响应半径为其他钻孔引起的过余温度影响系数≤5％时相邻钻孔中心线之间的垂直距离。在大量计算分析基础上,提出了竖直埋管换热器热响应半径计算方法。计算结果表明该文方法具有较好的计算精度,竖直埋管换热器的热响应半径随岩土热扩散系数增大而增大,随持续运行时间增加而增大,随钻孔排数增加而增大,随着钻孔孔径增大而增大;钻孔布置方式不同对钻孔热响应半径的影响较明显,相同布置方式下钻孔直径对其热响应半径的影响较小。针对工程中常见的115和135 mm 2种孔径,绘制了不同岩土介质下钻孔单排、双排和三排以上布置时热响应半径-运行时间的关系曲线。工程算例表明该文方法简单方便,为工程设计提供了便利。 相似文献
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青海湖芨芨草干草原浅层土壤温度和导温率的基本特征 总被引：2，自引：0，他引：2
通过解析芨芨草(Achnatherum splendens)干草原原生植被生长季中期5、10、20、40、60和80cm 6个土层连续监测的土壤温度资料,探讨其生长季土壤温度和土壤导温率的基本特征。结果表明:芨芨草干草原表层(<20cm)土壤温度日变化明显,遵循正弦波动规律;20-40cm为正弦波动和线性振荡的过渡层,40cm以下无显著日变化。土壤温度日变化振幅(A)和相位(φ)随土壤深度(z)增加分别呈现几何级数衰减(A=4.60e-6.74z,R2=0.93)和线性延迟(φ=6.14z+7.67,R2=0.95)模式;表层土壤温度对脉冲式降水表现为渐变式响应并出现同温层;典型晴天下土壤导温率(κ)随土壤深度增加而指数升高(κ=2×10-7e4.21z,R2=0.92),34.7cm土层的土壤温度日变化与5.0cm反相,而土壤温度日变化恒温层为86.0-102.0cm土层。 相似文献
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基于覆盖层能量平衡法的园艺设施覆盖材料传热系数理论解析与验证 总被引：2，自引：1，他引：2
该文提出了一种园艺设施覆盖材料传热分析以及传热系数的理论计算方法，即覆盖层能量平衡法。该方法通过覆盖层辐射传热和对流换热的能量平衡，建立全面反映覆盖材料传热各主要影响因素的传热模型，得出了传热系数的理论解析计算方法，可根据覆盖材料的红外辐射发射率、反射率和透过率等热物理特性和保温比、角系数等与覆盖层构造相关的参数以及设施内外气温、天空辐射温度、植物与室内地面温度、室外风速等工作环境条件，定量分析覆盖层的传热，得出传热系数的理论计算值。 相似文献
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The primary objective of this study was to investigate the impact of observation scale on the estimation of soil thermal properties. Transients are usually filtered out and ignored when classical Fourier approaches are used to deconstruct and model temperature time series. It was hypothesized that examination of such transients may be more important in identifying and quantifying short-term perturbations in internal soil heat transfer induced by agronomic disturbances. Data-logged temperatures were collected at 10-minute intervals from thermistor probes installed at 10 and 25 cm depths in isolated areas of two grassed plots. One plot （6T） had been treated twice with 6 Mg ha^-1 composted turkey litter as received. The other plot （NPK） was fertilized at the same time with NPK fertilizer. Various methods were used to analyze the series to obtain apparent soil thermal diffusivity （D-value） at various time scales. Results supported the hypothesis that short-term differences in internal soil heat transfer between the 6T and NPK plots were more manifest and effectively captured by estimated D-values calculated from the monthly and daily partial series. The 6T plot had higher soil organic matter content than the NPK plot and had lower apparent soil thermal diffusivity. Diurnal soil temperature amplitudes, required to calculate the mean D-values from partial series, were more effectively obtained using a temperature change rate method. The more commonly used Fourier analysis tended to be effective for this purpose when the partial series reasonably presented well-defined diurnal patterns of increasing and decreasing temperatures. 相似文献
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农田土壤热特性受地表能量平衡、土壤特性和作物生长的影响,存在显著的时空变异性,而目前缺乏关于作物行尺度土壤热特性变异特征的研究。本研究采用定位试验,利用热脉冲技术监测了玉米农田行尺度四个位置处（1/2行间、1/4行间、棵下和棵间）两个深度（2 cm和4.5 cm）土壤热特性的时空变异规律,并分析了土壤温度和含水量对土壤热特性的影响。结果表明,在试验期间,热导率、热容量和热扩散率的变化范围分别为0.66—2.22 W/(m?K),1.46—4.49 MJ/(m3?K)和4.07×10-7—6.88×10-7 m2/s。降雨之后,热导率和热容量增加,且随着时间推移逐渐降低。2 cm深度的土壤热特性的波动较大,棵下位置土壤热导率和热容量值最大,波动最为明显;土壤热扩散率在1/2行间位置最大。在4.5 cm深度,各位置土壤热特性变化趋势基本一致,土壤热导率和热容量值在1/2行间位置最大,土壤热扩散率在棵间位置最大。综合两个土层数据得出1/4行间位置的热导率和热容量更具代表性。本研究中土壤热特性对土壤含水量的响应规律较为明显,随着土壤含水量增加,热导率和热容量线性增加,热扩散率则表现出先增加后降低的规律。在测定的土壤温度范围内,热扩散率随土壤温度增加呈上升趋势。该研究可以为农田水热管理提供理论依据。 相似文献
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《Land Degradation \u0026amp; Development》2017,28(7):2290-2297
Reclamation following mining activities often aims to restore stable soils that support productive and diverse native plant communities. The soil re‐spread process increases soil compaction, which may alter soil water, plant composition, rooting depths, and soil organic matter. This may have a direct impact on vegetation establishment and species recruitment. Seasonal wet/dry and freeze/thaw patterns are thought to alleviate soil compaction over time. However, this has not been formally evaluated on reclaimed landscapes at large scales. Our objectives were to (1) determine soil compaction alleviation, (2) rooting depth, and (3) spatial patterns of soil water content over a time‐since‐reclamation gradient. Soil resistance to penetration varied by depth, with shallow compaction remaining unchanged, but deeper compaction increased over time rather than being alleviated. Root biomass and depth did not increase with time and was consistently less than the values in the reference location. Plant communities initially had a strong native component, but quickly became dominated by invasive species following reclamation, and soil water content became increasingly homogeneous over the 40‐year chronosequence. Seasonal weather patterns and soil organic matter additions can reduce soil compaction if water infiltration is not limited. Shallow and strongly fibrous‐rooted grasses present in reclaimed sites added organic matter to shallow soil layers, but did not penetrate the compacted layers and allow water infiltration. Strong linkages between land management strategies, soil properties, and vegetation composition can advance reclamation efforts and promote heterogeneous landscapes. However, current post‐reclamation management strategies are incompletely utilizing natural seasonal weather patterns to reduce soil compaction. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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探针有限特性对热脉冲技术测定土壤热特性的影响 总被引：1，自引：1，他引：0
在利用热脉冲方法测定热特性时,通常对探针形状做理想化处理,即假设探针为线性热源,热导率无限大而热容量为零。在实际应用中,探针本身的有限特性(有限半径以及有限热容量)会导致热特性测定误差。为了研究探针有限特性对热脉冲技术测定土壤热特性的影响,该研究采用改进的热脉冲探针(直径2 mm、长度40 mm、间距8 mm)测定土壤热特性,并分别使用PILS(pulsed infinite line source,无限长线性脉冲热源)和ICPC(identical cylindrical perfect conductors,近似圆柱形完美导体)2种理论估计土壤热特性,比较分析了探针有限特性对热脉冲技术测定热特性结果的影响。结果表明:1)与PILS理论相比,利用ICPC理论拟合得到的温度升高曲线,可以有效减少探针有限半径和热容量对土壤热特性测定结果的影响。与ICPC理论相比,在0.03~0.25 m3/m3的含水率范围内,用PILS理论得到的砂土热扩散率和热导率分别偏低11.8%和5.2%;与模拟热容量相比,PILS和ICPC理论分别将热容量高估16.1%和7.9%;2)探针有限特性对土壤热特性的影响与含水率有关:在干土上最大;随着土壤含水率的增加,其影响逐渐降低。该研究对提高热脉冲技术测定土壤热特性的准确性具有指导意义。 相似文献
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The coupled heat and mass transfer in soil can be analysed by examining the temperature dependence of thermal conductivity. We have measured the thermal conductivity of two kinds of soil (Ando soil and Red Yellow soil) as a function of both temperature (5–75°C) and water content by the twin heat probe method. From our results we concluded that the thermal conductivity resulting from the latent heat transfer can be separated from the apparent thermal conductivity by subtracting the thermal conductivity at a temperature near 0°C from that at a higher temperature. The relation between the phenomenological enhancement factor (β) and the volumetric air‐filled porosity was divided into two parts: β increases linearly as the volumetric air‐filled porosity increases from zero (that is, water saturation), to the point at which soil water potential corresponds to ?320 J kg?1; from that point to oven‐dry condition, β decreased logistically with the volumetric air‐filled porosity. From these results, we could generalize the behaviour of β. 相似文献
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Alteration of soil thermal properties by structure formation 总被引：2，自引：0，他引：2
Temperatures were measured in a disturbed and a structured loess soil to study the influence of aggregation on thermal properties. The disturbance was done by mechanically destroying soil aggregates, and the structured soil was obtained by subjecting the disturbed soil to several irrigation and drying cycles. In all soils, five harmonics of a Fourier-series representation accounted for ≥99% of the variance of daily soil surface temperatures, and two to three harmonics did so below the soil surface. For soil water contents between 0.04 and 0.23 m3 m-3, the apparent thermal diffusivity, computed by the harmonic method, was higher in the structured soil than in the disturbed soil. The same was true for the apparent thermal conductivity, since the volumetric heat capacities of both the disturbed and structured soil were similar. The differences in the apparent thermal diffusivity and conductivity were attributed to increased heat conduction and water vapour transport in the structured soil. 相似文献
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Arctic terrestrial ecosystems are characterized by large deposits of near‐surface soil organic carbon in poorly drained areas. Recent changes in Arctic regions such as warming and changes in water balance have adverse effects on the dynamics of near‐surface oxygen, leading to a potential increase in oxidation of near‐surface carbon and emission of CO2. This study investigated oxygen diffusivity characteristics, in both gaseous and liquid phases, in the upper 10 cm of an organic soil profile from a peatland in Disko, West Greenland (69°N). Two commonly used methods for calculating diffusivity of gaseous‐phase oxygen were applied and discussed to select the most appropriate method for highly porous media, for example peat soil. We measured diffusivity of gaseous‐phase oxygen with a one‐chamber diffusion set‐up in soil at different air contents (mimicking draining), and described it numerically with a previously developed parametric diffusivity model. We obtained precise measurements of liquid‐phase oxygen diffusivity along a depth profile (0–2 cm) in water‐saturated peat soil with a diffusivity microsensor coupled to a micromanipulator. The results show that the choice of an appropriate diffusivity model is critical for predicting oxygen diffusivity in organic soil and that diffusivity in mineral soil is not representative for organic soil. Furthermore, the importance of the non‐linear functionality between water saturation and diffusivity is demonstrated. This highlights the importance of measuring and modelling oxygen diffusivity rather than relying on measurements of observed water content in future studies of CO2 and CH4 dynamics in Arctic soil systems subject to climate changes. 相似文献
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为了探讨不同因素对桩基螺旋型地埋管换热性能的影响,建立了桩基螺旋型地埋管换热器的传热数学模型,分析了桩基直径、桩基深度、螺旋管组数、土壤类型对桩基螺旋型地埋管换热量及土壤温度分布的影响,结果表明:增加桩基直径有利于改善桩基的蓄热能力、提高螺旋型埋管的换热性能,但是单位管长换热量会减小,因此,桩基直径不可无限制增加;桩基深度的增加有利于提高桩基螺旋型埋管换热器的换热量,而且对单位长度桩基的换热量影响很小,因此,可以通过增加桩基深度来提高换热量;同样条件下,黏土、砂土、砂岩中砂岩最有利于桩基换热器换热,土壤温度上升速率和幅度最低,而黏土换热效果最差,土壤温度上升速率最快;此外,螺旋管组数越多,换热器换热量越大,但是单位管长换热量会大幅下降。试验验证表明:所建桩基螺旋埋管模型预测出的换热量与土壤温度值与对应试验值吻合较好,其最大相对误差分别在9.7%与9.2%以内。 相似文献
15.
R.L. Raper D.W. Reeves J.N. Shaw E. van Santen P.L. Mask 《Soil & Tillage Research》2007,96(1-2):174-181
The negative impacts of soil compaction on crop yields can often be alleviated by subsoiling. However, this subsoiling operation is often conducted at unnecessarily deep depths wasting energy and excessively disturbing surface residue necessary for erosion control and improved soil quality. A corn (Zea mays L.)–cotton (Gossypium hirsutum L.) rotation experiment was conducted over 4 years on a Coastal Plain soil with a hardpan in east-central Alabama to evaluate the potential for site-specific subsoiling (tilling just deep enough to eliminate the hardpan layer) to improve crop yields while conserving energy. Seed cotton yield showed benefits of subsoiling (2342 kg/ha) compared to the no-subsoiling treatment (2059 kg/ha). Averaging over all years of the study, site-specific subsoiling produced cotton yields (2274 kg/ha) statistically equivalent to uniform deep subsoiling at a 45 cm depth (2410 kg/ha) while not excessively disturbing surface soil and residues. Significant reductions in draft force were found for site-specific subsoiling (59% and 35%) as compared to uniform deep subsoiling at a 45 cm depth in shallow depth hardpan plots (25 cm) and medium depth hardpan plots (35 cm), respectively. Calculated fuel use for site-specific subsoiling was found to be reduced by 43% and 27% in the shallow and medium depth hardpan plots, respectively, as compared to uniform deep subsoiling in these same plots. Producers in the Coastal Plains who can determine (or who know) the depth of their root-impeding layer and perform site-specific subsoiling can have comparable cotton yields to traditional uniform depth subsoiling with reduced energy requirements. 相似文献
16.
Drainage is often claimed to increase soil temperatures in early spring by decreasing the soil's heat capacity. Measurements of water table depth, soil water content and soil temperature were made during winter and spring on mole-pipe drained and undrained plots of a silt loam soil under pasture. Despite differences in water table depth and soil water content, drainage had no observable effect on soil temperature. Laboratory measurements of the thermal properties of soil cores at a matric potential of ?4kPa and then at saturation showed the volumetric heat capacity increased from 3.1 to 3.3 MJ m?3 K?1, with a proportional increase in the thermal conductivity from 1.1 to 1.2 W m?1 K?1. The thermal diffusivity remained unchanged. These values were used in a numerical simulation of the effects of drainage on the seasonal and diurnal oscillations in soil temperature. It is argued that the soil heat flux under pasture in spring is unaffected by drainage. The predicted temperature differences due to drainage are of the order of 0.2°C. As differences of this magnitude were observed between replicate thermometers in the field, it follows from the calculations above that any differences in soil temperature due to drainage would be too small to detect. 相似文献
17.
不同温度下的土壤热导率模拟 总被引：13，自引：7，他引：6
土壤热导率是研究陆地表层水热盐耦合运动的基本物理参数。由于水汽潜热传热在高温下的显著作用,高温下的土壤热导率显著高于常温值。该研究的目的是建立能够有效预测高温下土壤热导率的模型。在气体扩散定律的基础上,该文结合常温土壤热导率模型,提出了一个计算高温土壤热导率的新方法。并利用热脉冲技术实际测定了不同温度、不同含水率下的土壤热导率,对新模型进行了测试验证。结果表明,Cass等的水汽运移促进因子参数依赖于土壤质地,且存在较大的不确定性。经过对该参数修正后,建立的热导率模型均能够较好地模拟出高温下的土壤热导率。 相似文献
18.
温室土壤含水率与导热率空间分布及相关性 总被引：4，自引：4，他引：0
为探究土壤含水率与导热率的空间分布特征和相关性,选取温室中8 m×8 m供试地块,以1 m×1 m网格间距布设采样点,测定0～40 cm土壤含水率,并同步获取0～20 cm土层的导热率。基于经典统计学、地统计学、回归分析和谱分析等理论,对土壤含水率与导热率的空间分布特征和相关性进行研究。结果表明,土壤含水率在0～40 cm土层呈现先升高后降低的趋势,且在20～30 cm土层均值最大。10～20 cm土层土壤导热率比0～10 cm土层高15.60%。各深度土层中土壤含水率及导热率存在着较强的空间相关性（块金系数<0.192）,而试验中随机因素引起的空间变异程度较低（块金值<0.540）,最小变程大于采样间距,说明网格布设满足空间分析要求。在供水均匀条件下,不同深度土层的蒸发强度与邻域地块的土壤水分含量亦会影响含水率空间分布。在含水率范围为17%～28%时,0～20 cm土层土壤含水率与导热率呈线性正相关（R2=0.837）,谱分析结果显示导热率在含水率序列上呈现长程负相关。 相似文献
19.
《Communications in Soil Science and Plant Analysis》2012,43(13-14):2385-2394
Abstract In Western Australia soil samples to measure soil‐test phosphorus (P) are collected November to March when soils are usually dry. Most of the soils are hard‐setting when dry and it is difficult to penetrate and collect soil samples to 10 cm using the traditional sampler, which is a 2.5 cm diameter tube that is pushed into the soil by foot. Farmers collect too few soil samples at shallow depths to measure soil‐test P. In Part 1 of this paper, it was shown that soil‐test P can vary markedly for individual soil samples collected from uniform areas in paddocks. Consequently, an adequate number of soil samples needs to be collected and bulked from defined areas to measure soil‐test P. Phopshorus accumulates near the top of the soil of (i) pastures since P fertilisers are applied to the surface of pastures, and (ii) crops sown by minimum (conservation) tillage. Crops are increasingly being sown using conservation tillage methods. Collecting too few soil samples to a shallow depth can result in large errors when estimating the current P status of soils and determining optimum fertiliser application levels. A new rotating blade method of collecting soil samples to the standard 10 cm depth for measuring soil‐test P was compared with the traditional sampler. The new sampler successfully penetrated hard‐setting soils to the standard depth and the soil samples it collected produced similar soil‐test P as the traditional sampler. Consequently, the same soil‐test P calibrations determined using the traditional sampler can also be used for the new sampler. The new sampler is, therefore, recommended for collecting soil samples to measure soil‐test P. It should have application wherever hard‐setting soils pose a problem for soil P testing. 相似文献
20.
Evidence of anisotropy is reported for advective air and water permeabilities in soils. Thus, anisotropy is likely to exist also for diffusive gas fluxes. Information about direction‐dependent soil gas diffusivity is scarce and most modeling approaches assume isotropy. At hundreds of closely lying positions in a compacted and adjacent undisturbed forest soil, gas diffusivity (Ds/D0) was measured either in vertical or horizontal direction. The volume‐independent diffusion efficiency (i.e., diffusivity divided by air‐filled porosity) was fitted by a generalized additive model (GAM). Significant regressors were air‐filled porosity (?), soil depth, and the discrete diffusion direction. The model yields in all cases higher vertical diffusion efficiencies. The compaction factor did not yield a significant regressor of its own, i.e., the reduction of diffusivity in the compacted soil was the same as in low‐porosity samples of the undisturbed profile. To elucidate the role of sharing vertically and horizontally orientated pore space and a potential competition between diffusivity in different spatial directions, simple geometric models consisting of 3‐dimensionally crossed pores have been parameterized. These models provided a good explanation of the typical nonlinear Ds/D0(?) relationship. By simple one‐parameter correction (linear or power function), this mechanistic model could be fitted to the data. The one‐parameter correction of the geometric model could be a straightforward approach to consider direction dependence of measured diffusivities. However, by applying this approach to the observations the anisotropy effect was not clearly evident, which could be attributed to a changing Ds/D0(?) relationship with depth. As a reason for the preference of the vertical gas diffusion the dominance of vertical stresses and the activity of anecic earthworms are discussed. Direction dependency of gas diffusivity seems to be a basic feature of natural pore systems and has to be considered for modeling gas fluxes in soils. Generally, a preferential vertical diffusion direction reduces horizontal balancing and increases the heterogeneity of gas concentrations in the soil air. 相似文献