A Comprehensive Review of Heat Transfer Fluids and Their Velocity Effects on Ground Heat Exchanger Efficiency in Geothermal Heat Pump Systems

Khaled Salhein (), Abdulgani Albagul and C. J. Kobus
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Khaled Salhein: Game Above College of Engineering and Technology, Eastern Michigan University, Ypsilanti, MI 48197, USA
Abdulgani Albagul: Department of Control Engineering, College of Electronic Technology, Bani Walid 38645, Libya
C. J. Kobus: Department of Mechanical Engineering, School of Engineering and Computer Science, Oakland University, Rochester, MI 48309, USA

Energies, 2025, vol. 18, issue 17, 1-50

Abstract: This study reviews heat transfer fluids (HTFs) and their velocity effects on the thermal behavior of ground heat exchangers (GHEs) within geothermal heat pump (GHP) applications. It examines the classification, thermophysical properties, and operational behavior of standard working fluids, including water–glycol mixtures, as well as emerging nanofluids. Fundamental heat exchange mechanisms are discussed, with emphasis on how conductivity, viscosity, and heat capacity interact with fluid velocity to influence energy transfer performance, hydraulic resistance, and system reliability. Special attention is given to nanofluids, whose enhanced thermal behavior depends on nanoparticle type, concentration, dispersion stability, and flow conditions. The review analyzes stabilization strategies, including surfactants, functionalization, and pH control, for maintaining long-term performance. It also highlights the role of velocity optimization in balancing convective benefits with pumping energy demands, providing velocity ranges suited to different GHE configurations. Drawing from recent experimental and numerical studies, the review offers practical guidelines for integrating nanofluid formulation with engineered operating conditions to maximize energy efficiency and extend system lifespan.

Keywords: geothermal heat pump system (GHPS); ground heat exchanger (GHE); heat transfer fluids (HTFs) (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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