Numerical heat transfer model of a traditional ice cellar with passive cooling methods

Wendler, Kyle D.

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Abstract

Permafrost ice cellars have been used for generations by Arctic communities for subsistence food storage. Many of these ice cellars have been recently reported to be difficult or impossible to maintain due to thawing and water accumulation inside the cellar. The thesis objective is to investigate the effectiveness of implementing passive techniques to lower the surrounding permafrost temperature, ideally to 0°F, the USDA recommended temperature, throughout the year. Numerical finite element modeling was used to investigate the effects on permafrost temperature with the addition of two-phase, closed thermosyphons and/or ground insulation. Thermosyphon condensers installed both above and below ground were studied. The numerical models were created using Comsol Multiphysics. The modeling results indicated that the addition of thermosyphons and insulation caused a decrease in permafrost temperatures surrounding the ice cellar, although the target temperature of 0°F could not be maintained throughout the year by any of the methods studied. Subsurface insulation decreased the amplitude between the minimum and maximum temperature of the cellar wall 4.5°C. Air thermosyphons decreased the average temperature 8.5°C, and with additional insulation, 90C. Ground thermosyphons were less effective, decreasing the average wall temperature 2.4°C. Additionally, thermosyphon performance was found to be rate-limited by conduction through permafrost.

Description

Thesis (M.S.) University of Alaska Fairbanks, 2011

1. Introduction -- 1.1. Ice cellars -- 1.2. Cooling of permafrost -- 1.3. Objective and scope of thesis -- 2. Literature review -- 2.1. Ice cellars -- 2.2. Permafrost -- 2.2.1. Basics of permafrost -- 2.2.2. Northern Alaska permafrost conditions -- 2.2.3. Methods of cooling permafrost -- 2.2.4. Phase change material -- 2.3. Thermosyphons -- 2.3.1. Basics of thermosyphons -- 2.3.2. History of thermosyphons -- 2.3.3. Lab and test sites -- 2.3.4. Finite element modeling -- 2.4. Sub-surface insulation -- 2.4.1. Basics of insulation for permafrost preservation -- 2.4.2. Lab and test sites -- 2.4.3. Analytical and modeling solutions -- 3. Method of modeling and verification -- 3.1. Introduction -- 3.2. Methods -- 3.2.1. Volume fraction of water and ice -- 3.2.2. Latent heat effects -- 3.2.3. Sensible heat -- 3.2.4. Thermal conductivity -- 3.2.5. Density -- 3.2.6. Surface temperature (n-Factors) -- 3.2.7. Air-ground thermosyphons -- 3.2.8. Ground-ground thermosyphons -- 3.2.9. Model symmetry -- 3.3. Model verification -- 3.3.1. Stefan solution -- 3.3.2. Two dimensional base-case ice cellar verification -- 3.3.3. Three dimensional base ice cellar verification -- 4. Results and discussion -- 4.1. Introduction -- 4.2. Model parameters -- 4.2.1. Basic material properties -- 4.2.2. Constant model parameters -- 4.2.3. Barter Island climate averages -- 4.2.4. 2-D basic model geometric size -- 4.2.5. 3-D geometric size -- 4.2.6. Initial and boundary conditions -- 4.2.7. Mesh -- 4.3. Porosity study -- 4.3.1. Introduction -- 4.3.2. Effects -- 4.3.3. Conclusions -- 4.4. Subsurface insulation -- 4.4.1. Introduction -- 4.4.2. Effects -- 4.4.3. Conclusions -- 4.5. Heat transfer coefficient of air thermosyphons -- 4.5.1. Introduction -- 4.5.2. Effects -- 4.5.3. Conclusions -- 4.6. Air thermosyphon -- 4.6.1. Introduction -- 4.6.2. Effects -- 4.6.3. Conclusions -- 4.7. Air thermosyphons with sub-surface insulation -- 4.7.1. Introduction -- 4.7.2. Effects -- 4.7.3. Conclusions -- 4.8. Ground thermosyphon -- 4.8.1. Introduction -- 4.8.2. Effects -- 4.8.3. Conclusions -- 4.9. Comparison of different configurations -- 4.9.1. Air thermosyphons with and without insulation -- 4.9.2. Air and ground thermosyphons -- 4.9.3. Table of different configurations -- 5. Conclusions and future work -- 5.1. Conclusions -- 5.2. Future work --5.2.1. Natural convection -- 5.2.2. Governing equations for thermosyphons -- 5.2.3. Optimum radius for evaporator -- 5.2.4. Ground thermosyphons with insulation -- 5.2.5. Other considerations -- References.

Date

2011-12

Type

Thesis

Collections

Engineering