Flow and heat transfer were studied as part of the experimental investigation on hydro-thermo-mechanical properties of fractures in a granite. The hydraulic permeability of the fracture is found to decrease with increasing effective normal stress in a logarithmic form, and also decrease with increasing rock temperature. The heat convection coefficient is found to be a function of flow velocity. Laboratory results indicate that the heat convection coefficient vary from 5 to 200 W/m2°C, and is affected by rock fracture geometry and fracture surface characteristics.


Des etudes sur I'ecoulement et le transfert de la chayeur ont ete faites dans le cadre de la recherche sur les proprietes hydro-thermo-mechaniques des fractures du granite. II est demontre que la penneabilite hydraulique de la fracture decroit guand la pression effective normale s'accroit selon une formule logarythmique, et aussi qu'elle decroit quand la temperature de la roche s'accroit. Le Coefficient de convection de chaleur est en fonction de la vitesse du flot. Les resultsts de laboratoire indiquent que le coefficient varie de 5 a 200 W/m2°C, et depend de la geometric de la fracture ainsi que de ses caracteristiques de surface.


Als Teil einer experimental en Studie der hydro-thermo-mechanisehan Eigensohaften von Granitbruchen wurden Fliajiverhalten und Wanneubertragung untersucht. Man fand, daβ sich die Wasserdurchlassigkeit des Bruchs mit zunchmender tatsachlicher Normalbelastung in logarithmischer Form verringert und auch bei erhohter Erwarmung der Geoteino abnimmt. Der Koeffizient der Warmemitfubrung steht in Funktion zu der Durchfluβgeschwindigkeit. Laborergabnisse zeigten, daβ der Koeffizient zwischen 5 und 200 W/m2°C schwankt und auch durch geometrie und Oberflachenbeschaffanheit des Bruchs Beeinfluβt wird.


Transfer of mass and energy in fractured rock is of great interest to the development of hot dry rock geothermal energy. Although in an underground hot dry rock geothermal field at depth, conduction is tile dominant mechanism for heat transfer. However, the heat energy is extracted to the ground surface by convection of water flow through fractures in hot dry rock masses. Laboratory studies on a variety of discontinuities have been directed towards defining: a) the validity of theoretical flow laws, and, b) the effects of discontinuity geometry (e.g., Baker 1955; Louis 1969; Detournay 1980; Raven & Gale 1985; Zhao & Brown 1992a). Barton et al. (1985) related fracture roughness to fracture strength, deformation and hydraulic conductivity. Witherspoon et al. (1980) and Elliott et al. (1985) suggested that a factor should be introduced into the parallel plate theory to take account of the effects of fracture surface properties. In a coupled hydro-thermo-mechanical study of rock fractures, Zhao and Tso (1993) investigated phenomenon of heat convection of water flow through rough fractures in heated granite, and suggested that the rate of convection is governed by flow velocity and geometrical properties of the fractures.


When a liquid flows under differential pressure, the flow rate Q is related to the dimensionless hydraulic head gradient i, in the direction of flow.


The basic types or modes of heat transfer process relevant to hot dry rock geothermal studies are conduction, heat flow from a point to another within the rock body, and convection, heat transmission from rock to the water flow. Head conduction and analysis has been well studied and understood. Convection is the heat transfer mechanism which occurs in a fluid by the mixing of one portion of the fluid with another portion due to gross movement of the mass of fluid. The fluid motion may be caused by external means (e.g., by a fan, pump, etc.), in which case the process is called forced convection.

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