太阳辐照下湿份分层土壤中热湿传输的数值模拟

考虑温度对土壤湿分迁移的影响，建立描述存在干饱和层时的土壤热湿传递的数学模型，并就自然环境和恒定太阳辐照下两种情况进行数值模拟，获得不同环境条件下土壤中温度和湿分分布以及水分蒸发的动态特性，分析干饱和土壤层对土壤热湿迁移与水分蒸发以及温度对土壤湿分传输的影响。     

一维土柱非饱和蒸发试验与数值分析

为揭示在蒸发条件下非饱和土中水分的运动规律,进行了一维土柱非饱和蒸发室内试验,并采用湿/热耦合的非等温渗流方程对蒸发条件下土壤水分的运动规律进行了数值模拟,通过将数值计算结果与试验结果进行对比,验证了湿/热耦合的非等温渗流方程的可靠性,同时发现干土层的形成是引起土壤水分运动形式发生转变的根本原因,即在干土层形成前,土壤内水分的运动以液态流动形式为主;在干土层形成后,干土层以下土壤的水分仍以液态流动形式向上运移,在干土层内则是以水蒸气扩散的形式向大气运动。     

大气对流对土壤内热湿迁移影响的实验研究

对土壤内热湿迁移过程进行了研究,通过对土壤内热湿迁移机理分析,根据质量守恒和能量守恒原理,建立了土壤非饱和区热湿迁移的理论模型,对大气对流环境条件下砂土内热湿迁移过程进行了实验研究,实验测量和数值计算,获得了不同大对流速度作用下土壤中温度,含水率分布以及水分蒸发强度的变化。     

湿帘空调原理及应用探讨

一、湿帘降温原理湿帘空调系统是利用水蒸发时吸收空气中的显热转化成水蒸汽的汽化潜热而降低空气温度的。水分蒸发的多少与空气中的水蒸汽分压及空气温度有关。当空气中的水蒸汽含量达到一定值后,将达到饱和而不能再进一步增大。这个饱和水蒸汽含量的大小与空气的温度有关。空气的温度越高,相应的饱和水蒸汽含量也越大。因此,空气越干燥、温度越高,采用湿帘空调系统可获得的温降幅度也越大。     

建筑屋面太阳能被动蒸发冷却研究

提出利用多孔含湿材料太阳能被动蒸发冷却建筑屋面的新方法，建立了多孔含湿材料利用太阳能被动蒸发的热质耦合传递数学模型，通过理论分析，数值计算和实验测试，揭示了热过程规律，结果表明，利用太阳能被动蒸发多孔含湿材料水分降温方法是可行的。     

水分迁移对地下土壤温湿度场分布的影响

建立了考虑水分迁移影响下的一维土壤热湿传递数学模型;计算分析了土壤高温蓄热过程中土壤温湿度场随时间和空间的动态变化规律;揭示了土壤热湿传递中含水率峰值现象及成因;探讨了地下土壤热湿传递特性及水分迁移规律。搭建了一维土壤高温蓄热热湿传递测试实验台,通过实验测试对数学模型进行了验证,实验结果与模拟值吻合得较好。     

太阳能辅助热泵干燥粮食的数值模拟研究

粮食的干燥过程实质上是多孔介质热湿耦合传递的过程。基于多孔介质热质传递理论,通过数值模拟的方法,针对利用太阳能辅助热泵干燥粮食时热风随时间变化的情况,采用综合温度和空气绝对湿度作为瞬态边界条件来对干燥过程中粮食内部温度和水分的变化进行模拟研究。模拟结果显示小麦水分在干燥150h后达到安全水分13.6%(干基),而实验结果显示小麦水分在干燥135h后达到安全水分13.6%(干基),二者对比相差不大,并且模拟温度与试验温度吻合较好。     

太阳辐照条件下土壤内温湿度场的动态模拟

根据质量守恒和能量守恒定律，同时对土壤非饱和区热湿迁移机理进行分析，建立了土壤非饱和区热湿迁移的理论模型。通过数值分析，模拟了太阳辐照条件下土壤内温度和含水率分布曲线。     

土壤高温蓄热过程中热湿传递特性的数值研究

建立了一维土壤高温蓄热热湿传递模型,采用控制容积法对模型进行离散处理,利用Matlab软件编程求解,计算分析了热源温度和土壤初始含水率对土壤温湿度场分布的影响,探讨了地下土壤热湿传递特性及水分迁移规律。     

土壤高温储热热湿迁移过程的初步研究

初步建立了土壤高温储热热湿迁移过程的数学模型,并进行了数值求解.结果表明,土壤热湿迁移过程中的湿度场稳定时间明显滞后于温度场,且与土壤类型和水力传导特性等有关.对于水力传导性较差的土壤,在高温储热初期,靠近热源的地方容易产生湿份聚集,使得湿度曲线出现一个短期峰值.与低温储热相比,土壤高温储热时湿度迁移对温度场的影响较大,温度场呈整体降低趋势,降低幅度顺序为:砂土>壤土>粘土.在该文模拟条件下,粘土的热湿迁移过程对于初始湿度的变化不敏感,而砂土的热湿迁移过程则依赖于初始湿度,且影响程度随着初始湿度的增加而增大.     

Study of heat and moisture transfer in soil with a dry surface layer

Mathematical model for describing simultaneous heat and moisture transfer in the porous soil with a dry surface layer was developed by using the volume-averaging method. Numerical simulation was conducted to investigate water evaporation, transient distributions of temperature and moisture in the porous soil at environmental conditions, which might be useful for agricultural application. In order to validate the mathematical model and numerical method, an experiment was conducted under natural environmental conditions. An additional experiment was conducted in a closed-loop wind tunnel to investigate the temperature effect on soil moisture transport. Theoretical and experimental results indicate that the dry surface layer has an important effect on heat and moisture migration in soil and the influence of temperature on moisture transport in unsaturated soil is significant.     

Experimental investigation of thermal and moisture behaviors of wet and dry soils with buried capillary heating system

An experimental study of thermal and moisture behaviors of dry and wet soils heated by buried capillary plaits was done. This study was carried out on a prototype similar to an agricultural tunnel greenhouse. The experimental procedure consisted on three different measuring phases distinguished by three different operational conditions of the capillary plaits: heating at 70 °C, heating at 40 °C and without heating in summer. During an experimental run, quantities measured are soil temperature, soil water content at various depths, soil surface heat flux, solar radiation under the plastic cover, internal relative humidity, internal and external air temperature. In unsaturated moist soils, the transport of heat is complicated by the fact that heat and mass transfer is a coupled process. During the daily soil temperature variation, it was found that the surface temperature amplitude was higher in wet soil than in dry soil. The water content increased during daytime and decreased during nighttime. The diurnal variation amplitude of water content was higher without underground heating and decreased with the buried heat source temperature.     

垂直埋管热湿传递线源模型的建立及其计算条件

现有的土壤传热模型忽略了水分迁移对传热的影响,根据质量与能量守恒原理,在原有的垂直埋管土壤源热泵一维线源模型上发展了传热传湿数学模型,并对模型中土壤的各参数进行了分析,为下一步的数值模拟计算以及进一步研究土壤含水率对传热影响奠定基础。     

估测裸地土壤含水量的土壤反射光谱信息分解模型

分析了土壤光谱响应机制,将土壤的反射光谱信息分解为干土反射、水分反射和水膜镜面反射三部分。提出了一种新的估测裸地土壤含水量的方法,并给出了具体的实现流程。该方法利用波谱数据库得到干土的波谱特性数据,从遥感影像中提取地物反射率信息,建立像元光谱分解模型,从而计算土壤含水量。实例分析表明,计算结果和实际监测数据相吻合,含水量灰度图中不同含水量区域之间的界线明显,便于统计分析,适于进行大范围土壤水分监测。     

不同环境条件下土壤温度日变化的计算模拟

应用多孔介质中传热传质的数学模型，对夏天和冬天，环境风速分别为4m／s和1m／s以及环境相对湿度分别为35％和85％这3种情况下高为500mm，半径为250mm的圆柱土壤床中温度的日变化进行了比较。根据数值模拟的结果绘出土壤中不同深度处温度的日变化曲线表明：(1)土壤中各点的温度随气温和土壤表面获得的辐射能的周期性变化而呈周期性变化；(2)随着深度的增加，土壤温度受气温和太阳辐射的影内变小，温度变化的滞后效应越来越明显；(3)在夏天，一天的大部分时间土壤表层的温度高于深层的温度，冬天则恰恰相反；(4)风速对土壤表层的温度影内较大。风速越大，土壤温度降低得越多；(5)干燥气候下，由于土壤水分的蒸发制冷作用，一天中土壤各点的温度低于湿润气候下相应各点的温度，土壤表层尤为明显。     

Investigation of heat and moisture migration in unsaturated soil under natural boundary conditions

Theoretical and experimental investigations were conducted to determine the heat and moisture migration in unsaturated soil under natural surface boundary conditions. Theoretically, a new model of heat and moisture migration in unsaturated porous media was developed, in which the gradients of volume water content, temperature, and partial vapor pressure were considered as the main driving forces which influence the process of heat and moisture migration in unsaturated soil. A set of coupled, nonlinear, partial differential equations were developed, which are related dynamically to the surface boundary conditions. Heat and moisture migration in sandy soil under solar radiation and air convection were studied experimentally. Temperature, volume water content, and water table evaporation were measured under unsteady conditions. The predictions are in good agreement with experimental data from a fairly sandy soil. © 1999 Scripta Technica, Heat Trans Asian Res, 28(1): 3–17, 1999