Soil Moisture Transfer Research Articles

Influence of vertical seasonal cooling device on soil heat and moisture transfer.

Influence of vertical seasonal cooling device on soil heat and moisture transfer.

Coupled heat and moisture transfer and evaporation in mulched soils

Improving water efficiency in arid and semi-arid regions is an ongoing goal in agricultural production. Straw mulching is one cultural practice which can be used to this point. Mulch layers associated with the atmospheric condition can create a variety of water and heat flux conditions at the soil surface. This study was conducted to (a) analyses the effect of a straw mulch layer on coupled heat and moisture transfer in shallow depths compared to bare soil, and (b) to develop and evaluate a method to estimate soil evaporation. Experiments were conducted in a field with grass clipping mulch and sandy soil that was moistened with natural shower and included a weighing lysimeter to measure actual evaporation. Average albedo over the mulching plot was defined as 0.49 by using lysimeter data during experiment. Near 93% and 97% of vapour flux in mulching plot and bare soil plot was under effect of temperature gradient, respectively. On average, the contribution of water vapour flux to the total moisture flux was 2% for mulching plot and 7% for bare soil plot. The heat transported by latent heat flux was 15% for mulching plot and up to 22% for bare soil plot. Observed differences between cumulative evaporation estimations and lysimeter data was about 8%. The simplicity of proposed method reduced required incoming solar radiation information, Rs, to estimate evaporation. Mulch layer could reduce significantly evaporation amount 40%.

Experimental study of dynamic effects in moisture transfer in building materials

In relation to moisture storage in porous materials, it is often assumed that the process dynamics do not affect the moisture retention. There is mounting evidence though that this notion is incorrect: various studies demonstrate that the moisture retention is influenced by the (de)saturation rates of the moisture transfer processes involved. The available evidence primarily stems from imbibition and drainage experiments on soils however, and compared to many other porous media, these tests consider rather permeable materials with relatively dominant liquid transport at comparatively large (de)saturation rates. The current knowledge may thus not be directly transferable to moisture transfer in porous media on the whole, and dedicated further research is required.This paper responds to that need, by reporting on an experimental investigation of the occurrence of dynamic effects on moisture transfer in building materials. Drying and ad-/desorption tests are executed on two building materials, in which moisture contents and moisture potentials are measured simultaneously. These are translated into dynamic retention relations and dynamic storage coefficients, which both distinctly demonstrate that moisture transfer in building materials, similar to moisture transfer in soils, is not free of dynamic effects. The findings imply that the widely accepted static theory for moisture storage in porous media is not generally valid and should be corrected for the occurrences of dynamic effects. Considering that such drying and ad-/desorption processes are dominant features in very many instances of moisture transfer in porous media, the repercussions of these findings may be large.

Impacts of dynamic interactions on the predicted thermal performance of earth–air heat exchangers for preheating, cooling and ventilation of buildings

Earth–air tunnel ventilation is an energy efficient ventilation technique that makes use of relatively stable soil temperature in shallow ground for preheating and cooling of supply air to a building. During operation, an earth–air heat exchanger interacts with the soil and atmosphere and the performance varies with the soil and atmospheric conditions. A computer program has been developed for modelling of coupled heat and moisture transfer in soil and for simulation of the dynamic thermal performance of an earth–air heat exchanger for preheating and cooling of a building. The impacts of dynamic interactions between the heat exchanger, soil and atmosphere are illustrated from the comparison of the heat transfer rate, heat exchanger temperature and supply air temperature through the heat exchanger for both preheating and cooling. It is shown that neglecting the interactions between the heat exchanger, soil and supply air would over predict the thermal performance of an earth–air heat exchanger. Neglecting the interactions between the soil surface and atmosphere while assuming axi-symmetric distributions of heat and moisture transfer as well as soil properties around the heat exchanger is not only unrealistic but also would fail to produce reliable data for long-term operational performance of the earth–air heat exchanger installed in shallow ground. The performance of an earth–air tunnel ventilation system can be enhanced when operated for both winter preheating and summer cooling of a building.

Simulation of dynamic interactions of the earth–air heat exchanger with soil and atmosphere for preheating of ventilation air

Earth–air tunnel ventilation is an energy efficient means of preheating and cooling of supply air to a building. Due to changing soil and atmospheric conditions and the consequent changes in heating and cooling loads of a building during operation, an earth–air heat exchanger interacts with the environments and the performance varies with the conditions. A computer program has been developed for modelling of coupled heat and moisture transfer in soil and for simulation of the thermal performance of an earth–air heat exchanger for building ventilation, taking account of dynamic variations of climatic, load and soil conditions. The importance of dynamic interactions between the three media – heat exchanger, soil and atmosphere – is illustrated from the comparison of the heat transfer rates and supply air temperature through the heat exchanger under continuous and intermittent operation in heating seasons. It is shown that neglecting the interactions between any two or all three media would significantly over or under predict the heat transfer rate and air temperature. Neglecting the interactions between the heat exchanger, soil and ventilating air would over predict the thermal performance of an earth–air heat exchanger whereas neglecting the interactions between the soil surface and atmosphere would fail to produce reliable data for long term operational performance of the earth–air heat exchanger installed in shallow ground. The level of over-prediction could be larger for intermittent operation than for continuous operation.

Estimation of key surface parameters in semi-arid region and their impacts on improvement of surface fluxes simulation

Uncertainties in some key parameters in land surface models severely restrict the improvement of model capacity for successful simulation of surface-atmosphere interaction. These key parameters are related to soil moisture and heat transfer and physical processes in the vegetation canopy as well as other important aerodynamic processes. In the present study, measurements of surface-atmosphere interaction at two observation stations that are located in the typical semi-arid region of China, Tongyu Station in Jilin Province and Yuzhong Station in Gansu Province, are combined with the planetary boundary layer theory to estimate the value of two key aerodynamic parameters, i.e., surface roughness length z0m and excess resistance κB-1. Multiple parameterization schemes have been used in the study to obtain values for surface roughness length and excess resistance κB-1 at the two stations. Results indicate that z0m has distinct seasonal and inter-annual variability. For the type of surface with low-height vegetation, there is a large difference between the default value of z0m in the land surface model and that obtained from this study. κB-1 demonstrates a significant diurnal variation and seasonal variability. Using the modified scheme for the estimation of z0m and κB-1 in the land surface model, it is found that simulations of sensible heat flux over the semi-arid region have been greatly improved. These results suggest that it is necessary to further evaluate the default values of various parameters used in land surface models based on field measurements. The approach to combine field measurements with atmospheric boundary layer theory to retrieve realistic values for key parameters in land surface models presents a great potential in the improvement of modeling studies of surface-atmosphere interaction.

Stochastic soil water balance under seasonal climates.

The analysis of soil water partitioning in seasonally dry climates necessarily requires careful consideration of the periodic climatic forcing at the intra-annual timescale in addition to daily scale variabilities. Here, we introduce three new extensions to a stochastic soil moisture model which yields seasonal evolution of soil moisture and relevant hydrological fluxes. These approximations allow seasonal climatic forcings (e.g. rainfall and potential evapotranspiration) to be fully resolved, extending the analysis of soil water partitioning to account explicitly for the seasonal amplitude and the phase difference between the climatic forcings. The results provide accurate descriptions of probabilistic soil moisture dynamics under seasonal climates without requiring extensive numerical simulations. We also find that the transfer of soil moisture between the wet to the dry season is responsible for hysteresis in the hydrological response, showing asymmetrical trajectories in the mean soil moisture and in the transient Budyko's curves during the 'dry-down' versus the 'rewetting' phases of the year. Furthermore, in some dry climates where rainfall and potential evapotranspiration are in-phase, annual evapotranspiration can be shown to increase because of inter-seasonal soil moisture transfer, highlighting the importance of soil water storage in the seasonal context.

Dynamic interactions between the ground heat exchanger and environments in earth–air tunnel ventilation of buildings

Earth–air tunnel ventilation is an energy efficient method of preheating or cooling of supply air to a building. The purposes of this study are to investigate the performance of earth–air heat exchangers under varying soil and atmosphere conditions and the interactions between the heat exchanger and environments. A computer program has been developed for simulation of the thermal performance of an earth–air heat exchanger for preheating and cooling of supply air, taking account of dynamic variations of climatic, load and soil conditions. The program solves equations for coupled heat and moisture transfer in soil with boundary conditions for convection, radiation and evaporation/condensation that vary with the climate both at the soil top surface and inside the heat exchanger. The importance of dynamic interactions between the heat exchanger, soil and atmosphere is illustrated from the comparison of the heat transfer rates through the heat exchanger. The predicted heat transfer rate varies with operating time and decreases along the passage of air in the heat exchanger. Neglecting the interactions would significantly over-predict the heat transfer rate and the amount of over-prediction increases with operating time.

THE SUBSTANTIATION FOR THE REGULARITIES OF PHASE TRANSFORMATION OF LIQUID AND VAPOROUS MOISTUREIN “SOIL–AIR–WATER BODY” SYSTEM

Since the regularities of phase transformation, in particular, liquid and vaporous moisture in the “soil–air–water body” system are poorly elucidated, we tried to solve this challenge taking into account the given initial prerequisites and assumptions. The patterns of evaporation (condensation) from the surface of homogenous fresh and saline water bodies and heterogeneous porousfissured soils saturated-unsaturated by underground liquid solution as well as the features of equiphase moisture transfer in unsaturated soils and phase transition in air are considered.

Simulation of anomalous-diffusion effects for drainage systems

In this paper, a drainage-system filtration model that takes into account the anomalous diffusion moisture-transfer in soil caused by the fractal properties of a medium is considered. It is shown that use of the fractal filtration model for soil leads to better agreement between the results of computations of groundwater profiles and the experimental data.

Mathematical models of soil moisture transfer: Importance of experimental assurance and upper boundary conditions

Soil moisture movement strongly depends on the upper boundary conditions (presence or absence of hydraulic pressure). The field experiments on the agrogrey medium loamy soil have shown that in the presence of pressure the movement follows preferential ways of migration. The accuracy of simulating this process depends on the initial experimental reliability of the mathematical model. This paper proposes an approach for the comparative evaluation of different methods of obtaining hydrophysical data for precise predictable modeling at the pedon scale. It should be noted that all the results are given for only one soil type, so one cannot confidently assert the relevance of similar data for other soil types.

Experimental study on heat and moisture transfer in soil during soil heat charging for solar-soil source heat pump compound system

Due to the imbalance of heating and cooling demand, the soil temperature decreases after several years' operation for soil source heat pump system, and consequently the coefficient of performance (COP) decreases. Soil heat charging with solar energy was proposed for solar-soil source heat pump compound system. Many studies have been carried out to investigate the heat and moisture transfer in soil for soil heat charging, but they failed to provide a clear description and explanation of the coupled and mutual effect between heat and moisture transfer. This paper presents an experimental study on the heat and moisture transfer in soil heat charging. The simplified testing rig was constructed to investigate the coupled and mutual effect of one-dimension horizontal heat and moisture transfer in soil heat charging. The results show that, peak volumetric water content (VWC) occurs firstly at the position near heat source and moves towards the other cold end of the tested soil pillar, but it is limited in an area near heat source. The time consumption and value for peak VWC increase with the increasing heat source temperature at the same initial VWC and increase with the increasing initial VWC at the same heat source temperature as well. The heat source temperature is a main factor affecting the peak soil temperature and peak VWC, while the initial VWC has little impact on them.

EFFECT OF PHASE COMPOSITION ON THE PARAMETERS OF NON-ISOTHERMAL MOISTURE TRANSFER IN UNSATURATED SANDY SOILS

This paper considers the influence of phase composition on the parameters of non-isothermal moisture transfer in unsaturated sandy soils. The technique of study options non-isothermal moisture transfer to disperse soil of disturbed structure. The exploratory procedure of the parameters in disperse soils having disturbed structure in the wide range of their phase composition using triangular diagrams is expounded. Shown that the parameters non-isothermal moisture transfer depend on moisture content and soil composition density. Established that for the sandy soil there is the “optimal” range of moisture content and density at which the non-isothermal moisture transfer is most efficient. The dynamics of the field moisture content of sand in time is identified.

Cauchy Problem in the Non-Classical Treatment for One Pseudoparabolic Equation

In the paper, we consider the Cauchy problem for a fifth order pseudoparabolic equation that appears in studying the issues of fluid filtration in fissured media, the moisture transfer in soils and etc. The Cauchy problem with non-classic conditions not requiring the agreement conditions are studied for a discontinuous coefficient pseudoparabolic equation. The equivalence of these conditions with the Cauchy classic condition is substantiated in the case when the solution of the stated problem is sought in S.L.Sobolev anisotropic space ( ) ( ) 3,2 p WG .

Comprehesive Solution of Heat Conduction Problem Using Mathematical Model of Heat and Mass Transfer in Permafrost Soils

Technical solutions are proposed for the beds and foundations of buildings and structures on permafrost soils, which are designed with use of a software package for modeling heat and moisture transfer in soils by the method of thermal and hydraulic resistances.

The Influence of Heat and Moisture Transfer in Soil on the Performance of the Ground Heat Exchanger

In this paper, a numerical heat and moisture transfer model (HMTM) and a pure conduction model (PCM) were established separately for unsaturated soil around the ground heat exchanger (GHE) and were numerically solved by finite volume method. The simulation results indicate that rejecting heat into soil can reduce moisture content in the vicinity of the borehole wall. When the initial moisture content is high, moister transfer has little effect on soil thermal properties. In this case, the results of the HMTM and the PCM are basically identical. On the contrary, when the initial moisture content is low, the thermal effect has significant influence on moisture transfer around the borehole wall, and the soil thermal properties will change correspondingly. In this case, there is a large difference between the results of these two models.

A new coupled heat, moisture and air transfer model in unsaturated soil

After a spacious research and consideration on various approaches of thermal coupled formulations in porous media, a new mathematical form of coupled heat, moisture, and air transfer in unsaturated soil is proposed upon taking the effect of combined volumetric moisture content and temperature gradients and air pressure changes. In this matter, in the convective flows through the unsaturated heated soil, the effects of sensible and latent heat of vapor are also composed with the water and dry air fluxes. Thus in this aspect, some new material parameters are defined for the derived equations, which are related to thermodynamic specifications of soil and the soil-water characteristic curve. After that, the application of the model is presented with a numerical example of a ground heat exchanger which is buried in the earth vertically. It could be considered as an interior heating source which operates in extracting saved energy from the earth or emitting heat to the ground. Then, by using some thermal graphs, the influence of the different operating ratio is investigated which are compared with the full operating mode at all times. Meanwhile, the mode1 is verified by comparing its results against those established by other researchers. By the results, it was found that the volumetric water content and specific heat capacity are the main factors could be effective to generate directly the thermal and isothermal diffusivities and conductivities in terms of the thermodynamic properties.

Numerical Simulation and Analysis on the Heat Transfer of the Vertical Ground Heat Exchanger in Hydrous Soil

Based on the law of mass and energy conservation and the one-dimensional model of heat transfer, a heat and moisture transfer line source model for the ground-source heat pump system has been developed. Numerical simulation results in summer working conditioning indicate that the affect of moisture transfer in soil was mainly around the U-type tube. When the soil moisture content is high, the capacity of heat transfer in soil is good. The heat transfer capacity of the ground heat exchanger calculated by the model in this work is lower than those which are calculated by the common heat transfer model. When the initial soil moisture content is about 0.1, the difference calculated by the two model is about 18%.

Multivariate analysis of soil moisture history for a hillslope

Summary In this study, the spatial distribution of measured soil moisture was analyzed on the platform of multivariate modeling. Soil moisture time series for two seasons were selected and used for analysis to reveal similarities and differences in soil moisture responses for a few rainfall events. The development of a soil moisture transport process that considers the representative element volume and uncertainty of soil media provides the hydrological basis for time series modeling. The systematic procedure of Box–Jenkins with noise modeling was used to delineate the final models for all monitoring points. The physical basis of mass balance and the continuity in inflow contribution, as well as statistical criteria, were used in the model selection procedure. Heuristic approaches provide the spatial distribution of selected models along the transect of a hillside. Comparative analysis for two different depths and seasons provide an understanding of the variation in soil moisture transfer processes at the hillslope scale. Differences in soil moisture models for both depths and seasons are associated with eco-hydrological processes. The relationships between distributed topographic features and modeling results were explored to configure dominant hydrological processes for each season.

Application of a three-dimensional model for assessing effects of small clear-cuttings on radiation and soil temperature

A three-dimensional model Mixfor-3D of soil–vegetation–atmosphere transfer (SVAT) was developed and applied to estimate possible effects of tree clear-cutting on radiation and soil temperature regimes of a forest ecosystem. The Mixfor-3D model consists of several closely coupled 3D sub-models describing: forest stand structure; radiative transfer in a forest canopy; turbulent transfer of sensible heat, H 2O and CO 2 between ground surface and the atmospheric surface layer; evapotranspiration of ground surface vegetation and soil; heat and moisture transfer in soil. The model operates with the horizontal grid resolution, 2 m × 2 m; vertical resolution, 1 m and primary time step, 1 h. The model was tested against meteorological data obtained at a small clear-cutting area in Otterbach in central Germany during summer 2005. The meteorological data including air temperature and humidity, precipitation, solar radiation, wind speed and direction, soil temperatures at 10 and 20 cm depth were measured by five automatic stations within the clear-cut area. One reference station was placed about 100 m from the clear-cut inside the forest stand. Comparisons of modelled and measured solar radiation fluxes and soil temperature profiles showed that the model adequately describes the spatial heterogeneity and dynamics of these variables under different weather conditions. The model can be used to explore solar radiation and soil temperature patterns within heterogeneous forest plots, with applications to various silvicultural tasks.