Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150443

150443 - Numerical Analysis of Co2-Based Thermosyphons in Permafrost 

Global warming is accelerating degradation of permafrost in Arctic and Antarctic regions, which leaves many structures that are permafrost dependent at risk of destabilization. A common method of permafrost stabilization is the two-phase closed thermosyphon (TPCT), a type of passive heat exchanger. A TPCT consists of a pipe that is filled with a working medium (in this case, CO2) and is partly buried underneath the soil. The TPCT transfers heat out of the soil by the evaporation and condensation of the working fluid, and only does so when the air temperature is colder than the soil temperature. The goal of this research is to develop a numerical computational fluid dynamics model to accurately simulate the behavior of a CO2-based TPCT in ANSYS Fluent. Fluent utilizes computational fluid dynamics, a branch of physics that uses computers to simulate the movement and interactions of fluids. This is used to simulate the heat and mass transfer inside of the thermosyphon quantitatively with a great degree of accuracy and relative ease of use. To provide accurate results, a mesh convergence study was performed to find a computational mesh size that would accurately simulate the behavior of the TPCT while minimizing computation time and providing an independent solution. A computational mesh is a numerical technique that allows breakdown of a model into smaller parts for easier analysis. Mesh size is important because it determines the level of detail of the simulation: smaller mesh size means more elements, which in turn leads to greater accuracy but a longer computation time. Then, the mass-time transfer coefficients of the model were tuned based on experimental data. These important constants regulate the frequency of evaporation and condensation in the model. Evaporation and condensation are the main drivers of both heat and mass transfer, which is important to the accuracy of the model. Tuning the parameters provides a greater degree of control over the results and can be used to increase accuracy in the simulation. The results were compared with experimental data to verify their accuracy and provide a better understanding of how model constants can be tuned to reflect experimental data. This research allows for greater exploration of the possibilities of two-phase closed thermosyphons in foundational stabilization, and paves the way for future research to provide methodologies for testing and designing new thermosyphons that will provide robust stabilization for the lifetime of the structure while minimizing the effects of climate change. 

Presenting Author: Mercedes Chisholm Cornell College

Presenting Author Biography: Mercedes Chisholm is currently an undergraduate student at Cornell College studying general engineering with minors in computer science and applied mathematics. Her research this summer at Clarkson University focused on numerical analysis of carbon dioxide based thermosyphons using Ansys Fluent.

Authors:

Mercedes Chisholm Cornell College
Elizabeth Laughlin Clarkson University
Mohammad Abweny Clarkson University
Suguang Xiao Clarkson University