Performance Analysis and Optimization of a Ground Source Heat Pipe with Carbon Dioxide for Thermal Management of Engineered Pavements and Turf

Date of Award

2022

Degree Name

Ph.D. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Andrew Chiasson

Abstract

A fully wicked ground source heat pipe (GSHP) is employed to passively transfer stored Earth energy from the underground to the ground surface. The novel design of the GSHP system enhances the heat exchange between the vertical underground section and the top part of the system. The top part is built with a disk-shaped heat pipe connected from the center to a cylindrical pipe representing the part buried in the ground. Carbon dioxide was utilized as the working fluid to transfer heat along the heat pipe with the heat of vaporization equivalent to 200 kJ/kg at 283 K saturation temperature. The GSHP system was constructed virtually using a finite element method in the two-dimensional axisymmetric model in COMSOL software. The system performance was numerically investigated to reduce the temperature fluctuation in the pavement. The numerical result was validated with published experimental and numerical work. The steady-state results were applied as initial values in a transient simulation where the study period represented cold weather conditions from December 2nd to January 31st, equivalent to 60 days period. The effect of the heat pipe length and radius of the condenser under different climatic conditions were investigated. To simplify results visualization, the minimum-maximum normalization method was applied to scale the values of various parameters. The temperature distribution in the system's surroundings reduced the amount of thermal energy released below the pavement due to the heat dissipation below the disk part. Adding insulation to several positions was found to avoid thermal energy loss at the side of the unheated surface. The heat pipe surroundings can be divided into zones based on the temperature fluctuation into pavement zone: high-temperature fluctuation (HTF) zone, and low-temperature fluctuation (LTF) zone. The HTF zone represents the ground below the disk shape and extends to a 10 m depth; the temperature is effect by the low ambient temperature on the unheated surface. Thus, adding an insulation wall at the end of the disk part to a 10 m depth reserves the HTF zone heat to be used as needed. The pavement zone was found to have a relatively high thermal resistance, and as a result, copper nanoparticles were added to the pavement to increase the thermal conductivity below the surface. The GSHP system can be viably utilized to melt snow accumulated on pavement surfaces at different geographic locations. To rapidly recover heat absorbed by the GSHP system, copper nanoparticles may also add to the soil in the LTF zone and the lower half of the HTF.

Keywords

Mechanical Engineering, Heat pipe, Pavement, Temperature Fluctuation, Nanoparticles, Snow Melting

Rights Statement

Copyright © 2022, author

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