Amirkabir University of Technology Advances in Energy Sciences and Technologies 3115-9117 2 1 2026 07 01 Exact analytical modeling of a solar-ventilated modernized qanat for atmospheric water harvesting: Decoupling proof and closed-form solutions for Chabahar's humid climate 52 70 6162 10.22060/aest.2026.26301.1013 EN Saleh Ghassemi Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran 0009-0009-5023-6584 Journal Article 2026 07 20 Arid-coastal regions face a paradoxical coexistence of acute water scarcity and abundant atmospheric humidity, demanding low-carbon harvesting solutions. This study develops an exact one-dimensional analytical framework for a modernized, solar-ventilated underground Qanat equipped with horizontal aluminum fins, designed for passive atmospheric water harvesting in Chabahar, Iran—a hot-humid coastal city subject to Indian Ocean monsoons. Moving beyond conventional lumped-parameter and numerical approaches, we rigorously prove the mathematical decoupling of the sensible heat and species transport equations under constant ground-temperature boundary conditions, yielding explicit closed-form solutions for the spatial evolution of air temperature and humidity ratio. Applied to a 500-m finned tunnel at 20 m depth under peak summer conditions (40°C, 92% RH), the model reveals two critical design parameters: the thermal and mass penetration depths (𝛿_ℎ ≈ 218 𝑚 𝑎𝑛𝑑 𝛿_𝑚 ≈ 246 𝑚), demonstrating that over 99% of condensation occurs within the first 250 m of the tunnel. At an optimized airflow velocity of 1.5 m/s— analytically determined as the thermodynamic optimum balancing residence time and fan power—the system yields 𝟑𝟕𝟖 𝑳/𝒉 of freshwater, equivalent to 𝟏𝟑𝟔 𝒎³/𝒎𝒐𝒏𝒕𝒉 under 12 h/day operation. The specific energy consumption is merely 𝟎. 𝟑𝟕 𝑾𝒉/𝑳, over three orders of magnitude lower than conventional vaporcompression atmospheric water generators. A parametric sensitivity analysis confirms the robustness of the design and enables rapid optimization without computational fluid dynamics. The proposed modernized Qanat represents a scalable, off-grid, mathematically optimized solution bridging ancient Persian hydraulic heritage with modern renewable energy integration for the water-energy nexus in arid-coastal climates worldwide.

https://aest.aut.ac.ir/article_6162_6aaba9a124857622930ca4e50f5afed2.pdf