Effect of tube-in-tube configuration on thermal performance of coaxial-type ground heat exchanger

Seokjae Lee, Sangwoo Park, Minkyu Kang, Kwanggeun Oh and Hangseok Choi

Renewable Energy, 2022, vol. 197, issue C, 518-527

Abstract: Among various types of ground heat exchangers (GHEXs or GHEs), a coaxial-type GHEX exhibits outstanding thermal performance owing to the geometric characteristics of the concentric tube-in-tube configuration. In this study, the unique configuration of the coaxial-type GHEX was investigated through parametric studies, which provided the energy efficient configuration. A computational fluid dynamics (CFD) model was developed and verified by using the field test results for the coaxial-type GHEX constructed in a test bed. Then, the parametric studies were conducted using the developed CFD model for various influential factors (i.e., flow rate of a circulating fluid, hydraulic diameter, and thermal conductivities of inner pipe and bentonite grout), which were selected considering the tube-in-tube configuration. The thermal performance of the coaxial-type GHEX increased with an increase in the flow rate of a circulating fluid and the thermal conductivity of bentonite grout. In addition, the inner pipes of the coaxial-type GHEX should be composed of materials with a thermal conductivity lower than 0.025 W/(m⋅K) to relieve thermal interference between the outer and inner pipes. Notably, it was concluded that the coaxial-type GHEX should be designed to secure the sufficient heat exchangeable area and retention capacity of the circulating fluid.

Keywords: Coaxial-type ground heat exchanger (GHEX); Turbulent flow; Thermal performance; Computational fluid dynamic (CFD) model; Parametric study (search for similar items in EconPapers)
Date: 2022
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Persistent link: https://EconPapers.repec.org/RePEc:eee:renene:v:197:y:2022:i:c:p:518-527

DOI: 10.1016/j.renene.2022.07.088

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