Document Lp52e7bnk093r8Qky9pp2EExw

172 CHAPTER 9 : - .1958 Guide i ' ' Heat Transmission Coefficients of Building'Materials 1731 causes an increase in thermal, conductivity... The rate of increase ill ;typical. soils - e was as follows:, average conductivities, in Btu per (square foot) .(hpur) (Fahren; heit degree per inch), 'of four sands at a density of 110 lb per cu ft worn': fi.8 at 2,5 percent moisture, 8.9 at 5 percent moisture, 112 at 10 percent moisture. - Five, soils ' of a fine texture at a density of 100 lb per cu ft) gave average conductivities of 6.7 at 10 percent moisture, and 9.6 at 20 percent. Thus, the doubling of moisture con- . tent within the ranges cited increases the conductivity by approximately. 30. or.yJO j' percent. . At higher moisture contents the percentage increase would be less. '.s': ; Effict of Soil Characteristics:' The thermal conductivity of the soil, at a given. density and- moisture content; varies in general with the texture of a soil, being rela'tively high for coarse-textured soils and relatively low for fine-textured-soils. The mineral composition of the soils also affects the conductivity. Quartz tends to give high values, whereas minerals such as plagioclase-feldspar and pyroxene, which arc constituents of basic rocks tend to give low values of thermal conductivity. These points'are illustrated by the values in Table 1 which lists seventeen soils'in approxi- V/ mate order of their-magnitude of thermal conductivity from greatest to least for seven different density-moisture content conditions. Some of the values in this ) table have been determined, by extrapolation'and are consequently, approximate), Blank spaces in the'table indicate that the density or moisture'content; or both, are such that no tests were possible for that condition or that no tests were sufficiently close to permit a reasonable extrapolation of the data. Granular, soils, particularly jp* those with high quartz contents, head the tabulation or have the greatest conduc- - ' 5> " Table 1. Thermal Conductivity (i) Values op Soils in Approximate Order of ! Decreasing Values* >: ;Mean Temperalure--It0t F ' "< Mechanical Analysis % by Weight ^ Moisture Content-^ Soil Designation Grav el Sand Silt Clay '"'4 ' ^'4 ' ` 4 10; 10' - 20 :: 20 Over 2.0 ram ! 0.5 to ,2.00. mm 0.005 Un-' to der 1 0.05. 0.005. mm' min 100 Dry Denbity-lb peb cu ft 110 120' 90' no ' 90 - 100 Fine Crushed Quartz Crushed Quartz Graded Ottawa Sand Fairbanks Sand Lowell Sand Chena River Gravel Crushed Feldspar Crushed Granite Dakota Sandy Loam Crushed Trap Rock Ramsey Sandy Loam Northway Fine Sand Northway Sand Hotly Clay Fairbanks Silt Loam Fairbanks Silty Clay Loam Northway Silt Loam 0.0 15.5 0.0 27.5 0.0. 100.0 79.0 99.9 70.0 100.0- 0.0 0.0 5.5 0.12.5 0.0 0.0 80.0 25.5 16.2 10.9 27.0 ' 19:4 70.3 77.0 . 57.9 63.0 0.6 N 4.2 6.8 21:2 10;0 10.0 0.4 53.6 0.0 97.0 3.0 97.0 0.0T ' 1.9 0.0 7.6 27.5 3.0 0.0 20.1 80.9 18.5 0.0 0.0 78:o 11.5 0.0 9.2 63.8 27.0 1.0 21.0 64.4 13.6 12.0 11.5 io.o ; 8.5 8.5 16.0 16.0 14.0 10.5 11.0 22.0 13.5 9.Chi 13.0 6.0 7.5 9.5 5.5 7.5 10.0 6.5 9.5 5.0 6.0 7.0 4.5 4.5 ' 4.5 !4.0 6.5 5:5 6.0 . 15.0' 13.5 13 10.0 . 8.5" 7.5 5.5 : 9.0 8.6 5.0 9.0 7.5 10.0 10.0 5.0 9.0i 7.5 9.5 4.01 7:0 -6.0 7.0 " A = Btu per (square foot) (hour) (Fahrenheit degree per inch). Fig. 2. Typical Variation op Thermal Conductivity with Mean Temperature TV 5.-'' tivity at a given condition. Sandy loam soils are midway in the table and fine X-', grained soils such as clay and silt loam are last. it' s Estimating Thermal Conductivity. The four diagrams Of Fig. 3 are presented to -` aid in the estimate of the thermal conductivity of any soil. Two of the charts are)., for sands or sandy soils, and two for silt and clay soils. One of the diagrams for.-v each,type of soils is for the frozen,,and the other for the.unfrozen condition. It is%fi expected that these charts will give conductivity, values with a precision of 25 per-)|^ bent. The effect of such factors as density, moisture content/freezing, or textureH., may be easily'approximated by use of these graphs. ! );!- Specific-Heat of Soils Tests to determine specific heat were run on twelve soils. On five of-.'fc the soils, tests were made at three or four mean temperatures varymg-.;/? from about 10 to 140 F. The specific heat values of all twelve soils Varied ':-;1 by only a small amount (about' 0.01), and averaged 0.19 at 140 F. TheS-i specific heat values of the soils decreased with a decrease in temperature, - f The average value at zero F would be about 0.16. . Values at temperatures between zero and 140 F can be estimated by considering a straight-line'; relationship between the two values given. ' Surface Conductance The surface conductance of a wall is the combined heat transfer to or) from the wall by radiation, convection'and conduction. Each of the three