Oral Presentation Australasian Groundwater Conference 2017

Effect of turbulent flow on heat transfer in a real fracture (#110)

Hamid Roshan 1 , Gabriel Rau 1 , Martin S Andersen 1
  1. UNSW, Sydney, NSW, Australia

An understanding of heat transfer in fractured systems is vital in many engineering applications such as heat extraction from geothermal systems, thermal enhanced oil recovery and heat transport through karst systems.

The heat transfer in fracture systems greatly depends on the rock and fluid thermal interactions, in particular the flow regime. The fluid flow in fracture systems is often considered laminar where the fracture flow is coupled with heat transfer to investigate the heat exchange between the matrix and fracture. However, it has been documented that the fluid flow approaches the turbulent regime in many natural systems. The effect of turbulent flow on heat transfer within the fracture system remains poorly understood.

To understand the implications of turbulent flow on the heat transfer in fracture systems, a coupled 3D turbulent flow and heat transfer model has been constructed based on realistic fracture properties. The variables controlling flow, such as fracture aperture, fluid velocity/flow regime and surface roughness, are varied to investigate the effect of turbulence flow on fluid-matrix heat exchange. The obtained results are then compared with that of a coupled laminar flow and heat transfer model commonly implemented in commercial numerical simulators.

The results of the numerical experiments showed that turbulent flow can considerably enhance the heat transfer in a fracture with surface roughness mainly due to flow localization. It was found that the fracture surface roughness, fracture flow and aperture are the key factors controlling the heat exchange between the matrix and fluid. The influence of the fracture aperture becomes more significant at relatively low Reynolds numbers (Re<10). Despite common expectation of an increasing difference in heat transfer with increasing Re, the difference in heat transfer between laminar and turbulent flow is more pronounced at relatively low Re.

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