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ABSTRACT
The thermal performance of different cross-sectional areas of a U-shape ground-coupled heat exchanger (GCHE) is numerically investigated for summer and winter conditions in the present paper. The four different cross-sectional tubes, viz. square, circular, triangular, and rectangular, of fixed hydraulic diameter and length are considered. Numerical simulations are carried out for different velocities ranging from 2 m/s − 5 m/s using K-epsilon turbulent model. It is found that the rectangular cross-sectional area GCHE provides a more stable air temperature for both summer and winter conditioning, and a maximum temperature drop/rise is observed at a shorter length in this condition. The temperature drop of 14.2 K is observed at a length of 12.6 m in the case of GCHE with rectangular cross-section, while the same drop is reported at 19.2 m, 17.4 m, and 16.5 m for circular, square, and triangular cross-sectional areas, respectively. A maximum temperature rise of 8.3 K is reported at 14.8 m, 20.7 m, 18.2 m, and 17.5 m in rectangular, circular, square, and triangular cross-sectional GCHE for heating conditions. Therefore, the rectangular cross-section GCHE may be preferred for space constraints. The net temperature difference is found to be dependent on inlet air temperature. It increases with an increase in the inlet air temperature for summer cooling conditions and reverses in winter conditions. The inlet velocity greatly influences the thermal performance of GCHE, and optimum performance is found at a lower velocity of 2 m/s due to the more settling time. The effectiveness is found to increase initially along the length, and it attains a maximum value at a shorter length in the case of rectangular cross-section compared to other sections. The maximum effectiveness is achieved between 14 m to 15 m length of the pipe for the case of rectangular cross-sectional GCHE.
Nomenclature
| u | = | Airflow rate |
| A | = | Area of the cross-section of GCHE |
| Cv | = | Constant volume heat capacity |
| Dh | = | Hydraulic-diameter |
| ma | = | Mass flow rate of air |
| U | = | Overall heat transfer coefficient |
| L | = | Pipe length |
| T | = | Temperature |
| k | = | Thermal conductivity |
| Subscripts | = | |
| ai | = | Inlet air |
| ao | = | Outlet air |
| s | = | Soil |
| Dimensionless parameters | = | |
| Nu | = | Nusselt number |
| Re | = | Reynolds number |
| Pr | = | Prandtl number |
| f | = | Friction factor |
| e | = | Effectiveness |
| Greek letters | = | |
| ρ | = | Air-density |
| υ | = | Kinematic viscosity |
| µ | = | Dynamic viscosity |
Disclosure statement
No potential conflict of interest was reported by the authors.
Additional information
Notes on contributors
Sudhir Kumar
Mr. Sudhir Kumar is a Ph.D. scholar in Mechanical Engineering department at MANIT Bhopal, India since 2020. He works in the area of heat transfer analysis through Ground-coupled heat exchangers.
Narendra Gajbhiye
Dr. Narendra Gajbhiye is an assistant professor in Mechanical Engineering Department at Maulana Azad National Institute of Technology Bhopal, Madhya Pradesh, India since 2019. He obtained his Ph.D. degree from Indian Institute of Technology Kanpur, Uttar Pradesh in 2016. He did Master of Technology in Mechanical Engineering (CFD and Heat Transfer) from National Institute of Technology Hamirpur, Himachal Pradesh in 2008 and Bachelors of Engineering in Mechanical Engineering from RTM Nagpur University in 2006. He was Post-Doctoral Fellow at IIT Hyderabad on SERB sanctioned project. He works in area of Computational fluid flow and heat transfer with a focus on understanding the flow physics and heat transfer characteristics of the complex problem in presence of magnetic field.