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Title: Boiling radial flow in fractures of varying wall porosity

The focus of this report is the coupling of conductive heat transfer and boiling convective heat transfer, with boiling flow in a rock fracture. A series of experiments observed differences in boiling regimes and behavior, and attempted to quantify a boiling convection coefficient. The experimental study involved boiling radial flow in a simulated fracture, bounded by a variety of materials. Nonporous and impermeable aluminum, highly porous and permeable Berea sandstone, and minimally porous and permeable graywacke from The Geysers geothermal field. On nonporous surfaces, the heat flux was not strongly coupled to injection rate into the fracture. However, for porous surfaces, heat flux, and associated values of excess temperature and a boiling convection coefficient exhibited variation with injection rate. Nucleation was shown to occur not upon the visible surface of porous materials, but a distance below the surface, within the matrix. The depth of boiling was a function of injection rate, thermal power supplied to the fracture, and the porosity and permeability of the rock. Although matrix boiling beyond fracture wall may apply only to a finite radius around the point of injection, higher values of heat flux and a boiling convection coefficient may be realized with boiling in amore » porous, rather than nonporous surface bounded fracture.« less
Authors:
Publication Date:
OSTI Identifier:
896525
Report Number(s):
SGP-TR-166
TRN: US200708%%46
DOE Contract Number:
FG07-95ID13370; FG07-99ID13763
Resource Type:
Technical Report
Research Org:
Stanford University, Stanford, CA
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; ALUMINIUM; BOILING; CONVECTION; FRACTURES; GEOTHERMAL FIELDS; GRAYWACKE; HEAT FLUX; HEAT TRANSFER; NUCLEATION; PERMEABILITY; POROSITY; POROUS MATERIALS; GEOTHERMAL ENERGY Geothermal Legacy