Numerical Simulation on Thermal Analysis of a Single Borehole U-Tube
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Department of Mechanical and Production Engineering(MPE), Islamic University of Technology(IUT), Board Bazar, Gazipur-1704, Bangladesh
Abstract
Ground source heat pumps (GSHPs) have emerged as a promising solution for effectively
harnessing renewable energy sources. However, their efficiency can be compromised by
the accumulation of heat in the soil, posing a challenge to their optimal utilization. To
mitigate temperature swings, innovative borehole ground heat exchangers (BGHE)
incorporating shape-stabilized phase change material (SSPCM) backfill have gained
attention. Despite a lack of experimental research, a comprehensive investigation
combining meticulous research studies and cutting-edge computer modeling aimed to
address the crucial question: How does the choice of backfill material affect soil
temperature? Remarkably, sand-SSPCM mixtures demonstrated the superiority of
SSPCM over traditional sand backfill, reducing temperature swings by an impressive
10°C near the heater wall. This finding is of paramount significance as maintaining a
consistent temperature during the cooling process substantially enhances GSHP system
efficiency.
The study further explored heat transfer rates, recognizing their pivotal role in optimizing
energy utilization within GSHP systems. Numerical modeling showcased a remarkable
16.5% reduction in the heat influence radius after just one operational cycle with the
innovative SSPCM backfill. Even after a prolonged 14-hour shutdown, SSPCM
consistently maintained a higher temperature compared to its conventional counterpart,
highlighting its resilience and capacity to retain thermal properties over an extended
period. However, cost-effectiveness must be considered, as the study revealed a decline
in cost-effectiveness with increased mass ratios of SSPCM. Designers and engineers face
the challenge of weighing the advantages of SSPCM against implementation expenses
while striving for the optimal balance.
In the domains of heat transfer rate and borehole design, numerous hurdles exist for
designers of GSHP thermal equipment. To address these challenges comprehensively, a
novel mathematical and numerical methodology was devised. This approach enabled the
evaluation of thermal efficiency and performance in U-tube heat exchangers utilizing
two distinct backfill materials: grout and SSPCM. Numerical simulations using
COMSOL Multiphysics software analyzed the intricate heat transfer processes within a
cylindrical borehole configuration, where a U-tube circulating water acted as the working
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fluid for heat exchange with the surrounding ground. The simulations revealed a 14.6%
increase in the total mean resistance of the single U-tube borehole with SSPCM backfill,
indicating the enhanced effectiveness of this innovative approach. The research
conclusively demonstrated that SSPCM backfill significantly augments the effectiveness
and functionality of GSHP systems, emphasizing the need for meticulous design and
optimization to strike the delicate balance between benefits and costs.
The continued advancement and widespread adoption of GSHP technology are vital to
meet escalating energy demands while mitigating adverse environmental effects. As the
world increasingly turns to renewable power sources, the significance of this progress
cannot be overstated. By leveraging the untapped potential of ground source heat pumps
and capitalizing on innovative approaches like SSPCM backfill, a sustainable future
becomes an achievable reality.
Description
Supervised by
Prof. Dr. Shamsuddin Ahmed,
Department of Production and Mechanical Engineering(MPE),
Islamic University of Technology (IUT)
Board Bazar, Gazipur-1704, Bangladesh
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Citation
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