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Research Papers: Conduction

Ground Heat Transfer From a Varying Line Source With Seasonal Temperature Fluctuations

[+] 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. Naterer

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

J. Heat Transfer 130(11), 111302 (Aug 29, 2008) (10 pages) doi:10.1115/1.2955467 History: Received November 18, 2007; Revised February 22, 2008; Published August 29, 2008

In this paper, transient heat conduction between a line heat source and a semi-infinite medium (representing a foundation of a power transmission tower and the surrounding ground) is analyzed numerically and experimentally. The tower foundation is represented by a metal rod buried in a semi-infinite medium. Using an experimental test cell with a data acquisition system, heat transfer and temperature measurements within the domain are collected. The experimental studies are first applied to unidirectional heat conduction, wherein the analytical solutions are compared against measured temperature responses. Then two transient heat transfer cases are studied: one case with a steady heat input provided by an electrical heater and another with sinusoidal temperature variations achieved by temperature-controlled fluid in a heat exchanger. The analysis shows that a metal tower footing has significant thermal effects on the temperature response of the local half-space around the footing in the foundation. This thermal effect varies with time, as well as spatially at different positions around the tower footing. In particular, measured results from the case of sinusoidal temperature variations show that the tower footing introduces additional temperature increases in the “summer” periods and temperature decreases in the “winter” periods.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Annual temperature variations in the ground

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Figure 2

Schematic of a simplified tower foundation—a metal rod buried in the ground

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Figure 3

Schematic of a line heat source in a semi-infinite half-space

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Figure 4

Overview of the experimental system 1: container, 2: plate heat exchanger, 3-1: circular heat exchanger and metal rod, 3-2: electrical heater and metal rod, 4: Neslab temperature-controlled baths, 5: FTB603B flow sensors, 6: TAI module NI9211, 7: USB chassis for cDAQ-9172, 8: Computer and data logger program, ●: TCs

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Figure 5

Installation positions of the TCs

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Figure 6

Computer data acquisition system

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Figure 7

Schematic of insulation for the circular heat exchanger and heat losses/gains

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Figure 8

Measured and analytical results for a one-dimensional transient heat conduction

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Figure 9

Measured temperatures with a steady line heat source: (a) thermal response at two locations, (b) 127.5min after the heater is turned on, and (c) comparison with the model

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Figure 10

Measured temperature variations of circulating water through the heat exchangers and heat input to the circular heat exchanger (note: T(f) and Q(inf) refer to Tf and Qinf)

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Figure 11

Measured temperature variations at the inner wall of the circular heat exchanger and outer surface of the insulation layer (note: T(ins) and T(wi) refer to Tins and Twi)

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Figure 12

Comparison between predicted and measured temperatures at a point in the test cell

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Figure 13

Temperature response in summer (t=280min; curves with dashed lines) and winter (t=212min; curves with solid lines) at different positions around the buried rod

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