Moisture-Temperature Realtionships in a Sand Due to Outward, Radial Freezing

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Author
Juel, Erling A.
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URI
http://hdl.handle.net/11122/10361
Abstract
A "clean" sand is commonly specified as backfill around the evaporator section of thermosyphons designed to maintain the thermal regime of pernnially, frozen, thaw-unstable soils. A series of laboratory tests were performed to determine the magnitude of moisture migration. The test results indicate the moisture migration can result due to outward radial freezing in a nonfrost susceptible sand possessing a low to moderate degree of saturation. Moisture did not migrate when the sand was saturated prior to freezing. The redistribution of moisture changes the thermal properties of the soil system which effects the maximum radius of freezing by desiccating soil at the outermost radius of influence and increasing the degree of saturation around the evaporator. The desiccated soil region will experience an accelerated rate of thaw due to a lower volumetric latent heat of fusion. In addition, the radius of freezing is reduced as moisture migrates towards the evaporator section. These effects warrant additional considerations that must be addressed when designing refrigerated foundations with thermosyphons.
Table of Contents
List of Figures - vi List of Tables - x Acknowledgements - xi Chapter 1 Introduction - 1 Chapter 2 Heat Transfer in Soils - 5 2.1 Modes of Heat Transfer - 6 2.1.1 Conduction - 7 2.1.2 Convection - 8 2.2 Thermal Properties of Soils - 10 2.2.1 Thermal Conductivity - 10 2.2.2 Volumetric Latent Heat of Fusion - 14 2.2.3 Specific Heat - 16 2.2.4 Heat Capacity - 17 2.2.5 Thermal Diffusivity - 19 2.2.6 Enthalpy - 20 2.3 Heat Transfer in Cylindrical Coordinates - 23 2.3.1 Steady-State Heat Flow - 24 2.3.2 Heat Transfer with Phase Change - 29 2.3.3 Explicit Finite Difference Technique - 37 Chapter 3 Moisture Migration in Freezing Soils - 41 3.1 Soil-Water Properties Effecting Moisture Migration - 44 3.1.1 Grain Size and Grain Size Distribution - 45 3.1.1.1 Specific Surface - 48 3.1.1.2 Soil Fabric - 50 3.1.1.3 Capillarity - 51 3.1.2 Soil Density - 56 3.1.3 Freezing Point Depression and Unfrozen Water - 57 3.1.4 Hydraulic Conductivity - 65 3.2 Environmental Factors Effecting Moisture Migration - 67 3.3 Moistrue Migration Mechanisms - 72 3.3.1 Transport Along Continuous Films - 73 3.3.2 Vapor Transport - 79 Chapter 4 Experimental Setup - 83 4.1 Freezing Tank and Equipment - 84 4.2 Soil Properties - 87 4.3 Temperature Measurements - 94 4.4 Pore Pressure-Moisture Measurements - 102 4.5 Test Procedure - 105 Chapter 5 Experimental Results - 108 5.1 Test Properties and Controls - 109 5.2 Soil Temperatures - 112 5.2.1 Complete Phase Change - 118 5.2.2 Steady-State Temperatures - 121 5.2.3 Freezing Isotherm Velocities - 127 5.3 Soil Suction Measurements - 134 5.4 Moisture Redistribution - 140 Chapter 6 Summary - 149 6.1 Discussion - 149 6.2 Recommendations - 152 6.3 Conclusions - 153 References - 155
Date
1989-05
Type
Technical Report
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