نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی آب، دانشکده آب و خاک، دانشگاه زابل، زابل، ایران
2 بخش آبیاری و زهکشی، موسسه تحقیقات فنی و مهندسی کشاورزی، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Heat transfer in porous media is a complex nonlinear process due to interactions among solid, liquid, and gas phases. In soils, this process is characterized by thermal conductivity (λ), a critical parameter with significant applications in civil and environmental engineering, soil science, agriculture, and water resources. Previous research has established the influence of factors such as soil texture, moisture content, density, and salinity on λ. Given the increasing water scarcity and soil salinity in arid regions, understanding the behavior of λ's under combined moisture and salinity stress is essential. This study investigated the effects of moisture content, salinity, and matric suction on the thermal conductivity of two soil textures (loam and sandy-loam) from the drought-affected Sistan Plain. Soil water retention curves were modeled using the van Genuchten equation. Thermal conductivity was measured across a suction range (1 to 1500 kPa) and various moisture at levels during both wetting and drying cycles. The results demonstrated that soil thermal conductivity behavior in response to moisture and suction changes cannot be described by a simple function. Instead, the interaction between salinity, particle geometry, moisture level, and the soil moisture path (hysteresis) is determinant factors in λ's performance at any given state. These findings are crucial for accurately modeling soil heat transfer and for designing efficient water resource management, irrigation, and drainage systems in arid and saline environments.
کلیدواژهها [English]
Heat transfer in unsaturated porous media is a complex, nonlinear process critical to numerous engineering and environmental applications, from geothermal systems to agricultural water management. Soil thermal conductivity (λ) is the key property governing this process. While the influence of factors like soil texture, moisture content, and density on λ is well-documented, the role of salinity—particularly under the combined stress of drought and salinization prevalent in arid regions like Iran—remains less understood and often contradictory in the literature. This study aims to comprehensively investigate the simultaneous effects of matric suction, moisture content, and salinity levels on the thermal conductivity of two dominant soil textures (loam and sandy-loam) from the drought-affected Sistan Plain. The research seeks to address a critical knowledge gap by analyzing how the interaction of these factors, alongside wetting and drying paths, influences heat dynamics, providing essential data for improving thermal models in saline, arid environments.
A comprehensive experimental study was conducted on soils from the Sistan Plain. Undisturbed and disturbed soil samples were collected from two dominant soil textures: loam and sandy-loam. Samples were prepared with three levels of salinity (approximately 2, 4, and 6 dS/m). Standard methods were employed to characterize the physical and chemical properties of the soils, including particle size distribution (hydrometer method), bulk density, organic matter content (Walkley-Black method), pH, and electrical conductivity (EC). The soil water retention curves (SWRCs) for both drying and wetting paths were determined using a combination of a sandbox apparatus (for low suction ranges from 0 to 100 cm) and pressure plate extractors (for higher suction ranges up to 15,000 cm). The van Genuchten model was fitted to the SWRC data. Thermal conductivity (λ) was measured directly using a KD2 Pro thermal properties analyzer (Decagon Devices, USA). Measurements were taken at various matric suction levels (equivalent to a water pressure range of 1 to 70 cm) during both the drying and wetting processes, allowing for the analysis of hysteresis effects. The experimental design facilitated a detailed examination of the interplay between soil texture, salinity, moisture path, and suction on thermal conductivity.
The results revealed a complex, non-linear relationship between thermal conductivity and the studied parameters. Key findings include:
Interactive Effects: The behavior of λ could not be described by a simple function of moisture or suction alone. Instead, it was determined by the complex interactions between salinity, particle geometry, moisture level, and the moisture path (hysteresis).
Effect of Salinity: The influence of salinity was highly dependent on soil texture. In loam soil, increased salinity generally led to a decrease in λ, particularly during the wetting path. In contrast, sandy-loam soil showed a more variable response; medium salinity sometimes increased λ (potentially due to salt crystallization improving particle contact), while higher salinity levels could reduce it.
Hysteresis Effect: A clear hysteresis was observed in the λ-moisture-suction relationships. The values and patterns of λ differed significantly between the drying and wetting paths for both soil types, emphasizing that the hydraulic history of the soil is a crucial factor.
Texture Dependence: Sandy-loam soil exhibited greater stability and less pronounced changes in λ with varying salinity compared to the more sensitive loam soil. This is attributed to the coarser pore geometry and lower specific surface area of the sandy-loam, making its thermal properties less susceptible to changes induced by salt concentration.
This study demonstrates that soil thermal conductivity in saline, unsaturated soils is governed by a dynamic interplay between salinity, moisture content, matric suction, and soil texture, all mediated by the moisture path. The findings move beyond simplistic models and highlight that predictive models for heat transfer in arid, saline environments must incorporate these interactions to be accurate. The results have direct practical implications for improving the design and management of agricultural systems (e.g., irrigation and drainage), geothermal systems, and environmental modeling in regions facing water scarcity and soil salinization. Future work should employ advanced multi-scale modeling approaches to further elucidate the mechanisms behind these complex interactions.
M.A. (PhD Student) conducted the investigation, performed the experiments, curated the data, and wrote the original draft. M.D. (Supervisor) conceived the research idea, acquired funding, supervised the project, and reviewed & edited the manuscript. F.A. and P.A. (Advisors) contributed to the methodology, validation, and reviewing & editing of the manuscript
Data are available on request from the authors.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare no conflict of interest.
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