| Summary: | Subgrade cooling methods to prevent thermal degradation of permafrost in cold regions include the use of thermosyphons with inclined evaporator sections. This laboratory study was conducted to determine the thermal performance characteristics of two commercially available thermosyphons. Evaporator inclination angles ranged from 0(degrees) to 12(degrees) from the horizontal, and air speeds ranged from 0 to 13.4 miles per hour over the finned condenser sections. Two standard full size thermosyphons, one charged with CO2, carbon dioxide and the other with NH3, anhydrous ammonia, were tested in CRREL's atmospheric wind tunnel. Empirical expressions are presented for heat removal rates as a function of air speed, ambient air temperature and evaporator inclination angle. An analytical method is also presented to approximate thermal design of foundations using thermosyphons under buildings with a slab-on-grade. We present heat gains from the slab and pad to the thermosyphon as well as the evaporator temperature as functions of time. List of Figures - iv List of Tables - vi Abstract - vii Nomenclature - viii Introduction - 1 History - 3 Working Fluid - 8 Container - 14 Thermosyphon Conductance - 16 Heat Transfer from the Finned Section - 19 Tests - 30 Test Results - 33 Foundation Design with Thermosyphons - 48 Conclusions - 54 Acknowledgments - 58 References - 58
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