Research Papers: Conduction

Thermal Protection of a Ground Layer With Phase Change Materials

[+] Author and Article Information
X. Duan

Department of Mechanical and Manufacturing Engineering, University of Manitoba, 75A Chancellors Circle, Winnipeg, MB, R3T 5V6, Canada

G. F. Naterer1

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada


Corresponding author.

J. Heat Transfer 132(1), 011301 (Oct 26, 2009) (9 pages) doi:10.1115/1.3194764 History: Received September 13, 2008; Revised May 20, 2009; Published October 26, 2009

Conventional ground surface insulation can be used to protect power line foundations in permafrost regions from the adverse effects of seasonal freezing and thawing cycles. But previous studies have shown ineffective thermal protection against the receding permafrost with conventional insulation. In this paper, an alternative thermal protection method (phase change materials (PCMs)) is analyzed and studied experimentally. Seasonal ground temperature variations are estimated by an analytical conduction model, with a sinusoidal ground surface temperature variation. A compensation function is introduced to predict temperature variations in the foundation, when the ground surface reaches a certain temperature profile. Measured data are acquired from an experimental test cell to simulate the tower foundation. With thermal energy storage in the PCM layer, the surface temperature of the soil was modified, leading to changes in temperature in the foundation. Measured temperature data show that the PCM thermal barrier effectively reduces the temperature variation amplitude in the foundation, thereby alleviating the seasonal freezing and thawing cycles. Different thermal effects of the PCM thermal barrier were obtained under different air temperature conditions. These are analyzed via melting degree hours and freezing degree hours, compared with a critical number of degree hours.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Schematic of a simplified tower foundation—a metal rod buried in permafrost

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Figure 2

Daily averaged air and soil temperatures in Thompson, Manitoba, from the Canadian climate normals or averages data (1971–2000) (27)

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Figure 3

Ground surface temperature with a PCM layer

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Figure 4

Illustration of the compensation function method

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Figure 5

Schematic of the experimental system. 1: Container, 2: Thermal barrier, 3: Plate heat exchanger, 4: Circular heat exchanger and metal rod, 5: Temperature controlled baths, 6: Flow sensors, 7: Thermocouple analog input modules, 8: USB chassis for cDAQ-9172, 9: Computer and data logger program, ●: Thermocouples.

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Figure 6

Soil thermal conductivity and diffusivity at different temperatures (λsoil=16.5%)

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Figure 7

Measured and analytical results for one-dimensional transient heat conduction

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Figure 8

Variations in simulated air temperature above the PCM layer (TuPCM) and the soil surface temperature under the PCM layer (TbPCM)

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Figure 9

Effects of PCM layer thickness on its thermal protection performance

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Figure 10

Soil surface temperatures with a PCM thermal barrier of 20 mm, showing the effects of the PCM layer for different air temperature conditions

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Figure 11

Soil surface temperature under a PCM layer in the test cell, and the fitted sinusoidal temperature profile

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Figure 12

Comparison between predicted (compensation function method) and measured data

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Figure 13

Effects of PCM thermal barrier on temperature variations at two locations (R=7 mm and z=20 mm, and R=39 mm and z=20 mm) in the test cell




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