The Relationship Between Thermal Conductivity And Other Rock Properties

Author : Steven A. Johnson
Publisher :
ISBN 13 :
Total Pages : 104 pages
Book Rating : 4.:/5 (15 download)

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Download or read book A Comparison of Thermal Conductivity with Elastic Properties for Six Igneous Rock Types written by Steven A. Johnson and published by . This book was released on 1974 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objectives of this research were: 1) to investigate the relationship between thermal conductivity of rock and the 11engineeringll properties (Young's modulus and dynamic elastic constants) and 2) to evaluate a .point source technique; the Thermal Comparator", as a1i-c alternative to the divided bar for measuring thermal conductivity of rock. A suite of six rock types including a gabbro, granodiorite, dunite, dacite, serpentinite and tholeiitic basalt from the U.S. Bureau.-, of Mines' NASA suite comprised the test samples. These rocks were· previously documented and described petrographically by the Bureau of Mines and as a group represented a wide range of texture and igneous- rock composition. Thermal conductivity measurements of the NASA suite rocks were made at 25°C under saturated and unsaturated conditions using the divided bar and the Thermal Comparator methods. Samples measured in the divided bar ranged in number from 35 for the dacite to 12 for the gab bro yielding thermal conductivity values from O. 77 Wm-l K-l for dacite to 3.63 Wm -1K-1 for dunite, both in the dry state. Compressional and shear wave velocity measurements of saturated and unsaturated specimens at one bar using the ultrasonic pulse velocity method varied from a high of 7.0 km/sec for the compressional wave velocity (saturated dunite) to a low of 1.5 km/sec for the shear wave velocity (saturated dacite). Seismic wave velocities and densities for the saturated and unsaturated samples were used to calculate Young's 1DOdulus; values ranged from 2.0 x 1011 dyne cm-2 (unsaturated dunite) to 1.35 x 1011 dyne cm-2 (unsaturated dacite). A linear regression analysis of thermal conductivity data as the dependent variable for the saturated and unsaturated conditions was. accomplished by inputing the dynamic and static mechanical test result as independent variables. Twelve equations relating thermal conductivity to seismic velocities and the dynamic and static elastic moduli resulted. These equations were tested using a list of ten rock type with known seismic velocities, densities and thermal conductivities and inputing these data to predict their thermal conductivities using the equations from regression analysis. Thermal conductivity values were predicted to within ± 30% for four of the ten rock types; the variation was greater than ± 30'% for the remainder. Best results were obtained from the equations relating shear wave velocity and shear modulus to· thermal conductivity. K-Saturated = (0.916 ± 0.348)V s - 0.477 K-Saturated = (0.559 ± 0.182)G + 0.698 where: K= thermal conductivity, Wm-1 K-1 V = shear wave velocity, km sec-1 G= shear modulus, dyne cm -2 x 10 -11 When seismic velocities measured at 1000 bars were substituted into the equations, the predicted thermal conductivities were within ± 30%for seven of the ten rocks. This suggests some of the scatter in the predicted values is due to variability in seismic velocities and thermal conductivities at pressures less than 1000 bars. It is therefore concluded that elastic moduli measured at one bar cannot consistently predict accurate values for thermal conductivity of rock. Comparison of thermal conductivity data from the Thermal Comparator and the divided bar indicated the Thermal Comparator could be u1ed for accurate determination of thermal conductivity for rocks in the saturated state which poses a mean grain size less than 0.2 mm, pro vided a large number of readings were made (approximately 100) and the surface finish of the calibration references matched those of the sample. The difficulty of preparation and consequent time expenditure for numerous reading shows the Thermal Comparator method to be less efficient than the divided bar for determining thermal conductivity of rock.