An analytical solution for heat extraction from shallow ground using a single-phase closed thermosyphon: A model for artificial ground freezing

Abstract

Artificial ground freezing can be costly. Except for drilling and installation costs, they may also include maintenance and electricity consumption. What if there is a possibility to build an apparatus that naturally works without a need for external energy? Closed thermosyphons filled with a working fluid (antifreeze) that has a proper thermal conductivity can be the solution whether there is a need for heat extraction for a greenhouse area or an intention to freeze the ground artificially. A portion of a vertical closed pipe is installed in the soil while the other is in contact with the ambient air. The heat transfers from the high-temperature zone, soil, to the low-temperature zone, wellbore, and is released into the air. The results show that increasing the target depth underground from 1.5 m to 3.5 m increases the freezing time from 5 days to 24 days. Expanding the length outside of the ground (cooling) from 1.5 m to 3.5 m improves the heat transfer by 10 W, decreasing the freezing time by 2.5 days. A slight growth in diameter allows for a larger soil-water mixture to be involved in freezing, and thus the freezing time increase; however, since it enhances the heat transfer rate, a larger amount of freezing storage is obtained (e.g., an increase from 3.9 in. to 5.5 in. shows a 150-kJ growth at the end of 60 days). A decrease of 10 °C in air temperature also shows a staggering growth in freezing storage by >1500 kJ.