Thermal conductivity, soil

A significant rise in temperature AT is calculated in a volume of soil at a distance up to 3 from the anode, where is the anode radius. Factors are the thermal conductivity of the soil, k, length of the anode, L, the grounding resistance, Rq, and the current, I. The rise in temperature can be calculated from these parameters [10]. For deep anodes it amounts to ... 

In many industrial halls, conduction inro the ground is a major factor for heat loss. Therefore, an adequate modeling of the floor slab and the underlying, thermally active, soil is very crucial for reliable simulation resuirs. In this case, the soil model in the TRNSYS model was established using results from an additionally performed finite-element program analysis. 

In the design of borehole heat exchangers accurate information on the soil thermal parameters, such as thermal conductivity, heat capacity and temperature, is essential for the design of an economically sized and well-functioning thermal energy store. Especially the soil thermal conductivity is critical, as... 

In the boreholes, which are placed at a parking lot, single U-pipes are installed. There is no back filling, but the holes are filled with ground water. The boreholes are drilled through 65 m of clayey soil and 135 m of shale. The thermal conductivity has been measured with a Thermal Response Test (TRT) to be approx. 2.8 W/m K. 

Thermal property is another critical property for furnace slag. Because of their more porous structure, blast furnace slag aggregates have lower thermal conductivities than conventional aggregates. Their insulating value is of particular advantage in applications such as frost tapers (transition treatments in pavement subgrades between frost-susceptible and nonfrost-susceptible soils) or pavement base courses over frost-susceptible soils. 

Thermal conduction (also referred to as electrical conductive heating or in situ thermal desorption) supplies heat to the soil through steel wells or with a blanket that covers the ground surface. As the polluted area is heated, the contaminants are destroyed or evaporated. Steel wells are used when the polluted soil is deep. The blanket is used where the polluted soil is shallow. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system. 

Air temperature variations are reasonably well-reflected in the soil surface but disappear rapidly in depth at 50 cm depth daily variations are hardly significant, and only seasonal temperature fluctuations are registered. Almost similar situations occur in hard consolidated rocks. Those, although having a somewhat higher thermal conductivity than loose materials, do not... 

Detectors range from the universal, but less sensitive, to the very sensitive but limited to a particular class of compounds. The thermal conductivity detector (TCD) is the least sensitive but responds to all classes of compounds. Another common detector is the flame ionization detector (FID), which is very sensitive but can only detect organic compounds. Another common and very sensitive detector is called electron capture. This detector is particularly sensitive to halogenated compounds, which can be particularly important when analyzing pollutants such as dichlorodiphenyltrichloroethane (DDT) and polychlorobiphenyl (PCB) compounds. Chapter 13 provides more specific information about chromatographic methods applied to soil analysis. 

Hyphenated methods can be divided into two types those that do and those that do not destroy the sample in the process of analysis. Spectrophotometric methods, thermal conductivity, and refractive index methods of detection do not destroy the sample. Chromatographic methods using flame ionization and similar detection methods destroy the sample as it is detected. Any hyphenated method that involves MS or thermal analysis (TA) will also destroy the sample. In most cases, the identification of the components in soil is most important, so the destruction of the analyte is of less importance. 

Vermiculites are formed by the decomposition of mica. They contain layers of water and magnesium ions in place the potassium ions. When heated to 800°C-1100°C, vermiculite expands because of the conversion of the water to gas. The expanded vermiculite has a low thermal conductivity and density, and is used as a thermal and sound barrier as well as an aggregate in lightweight concrete. It is also used as a moisture-retaining soil conditioner in planting. 

For this example, we will consider the soil surface as a boundary condition with an oscillating temperature, described by a cosine function. The soil will conduct heat from the surface, without flow. The only transport mechanism will be the thermal conduction of the soil matrix. 

A heat pump system utilizes a heat exchanger buried in water-saturated soil as a heat source. The heat exchanger basically consists of a series of vertical plates with height of 30 cm and a width of 10 cm. These plates are effective Is at a uniform temperature of 5°C. The soil can be assumed to have a permeability of 10 0 nr and apparent thermal conductivity of 0.1 W/m-K. The temperature of the saturated soil far from the heat exchanger is 30°C. Assuming natural convective flow and that there is no interference between the flows over the individual plates, find the mean heat transfer rate to a plate. 

A scheme is devised to measure the thermal conductivity of soil by immersing a long electrically heated rod in the ground in a vertical position. For design purposes, the rod is taken as 2.5 cm in diameter with a length of I m. To avoid improper alteration of the soil, the maximum surface temperature of the rod is 55°C while the soil temperature is 10°C. Assuming a soil conductivity of 1.7 W/m °C, what are the power requirements of the electric heater in watts ... 

Values of the thermal conductivity, k, have been determined in the present work with a thermal conductivity probe (24). It has long been known that sulfur has a low thermal conductivity although the values are even lower in such materials as PVC and expanded polystyrene. Sulfur-bonded composites made with inexpensive fillers such as soil and sand have thermal conductivities which are below those of typical portland cement concrete but with values higher than those of sulfur itself. The values for the composites are, however, still low as may be seen by comparison with the values for conductors such as steel and copper (Table II). 

These results suggest that sulfur-bonded composites may have uses in civil enginering where thermal insulation is required. General principles indicate that increased voids content or a stable retention of a noncrystalline form by the sulfur would reduce the thermal conductivities of the composites. A composite incorporating potters flint did have a fine void structure, but nonetheless its thermal conductivity was higher than that of sulfur (24) presumably a still larger void content is required. Use of moist fillers such as damp soil produced foaming, but a stable, well distributed system of voids was not produced the bubbles which formed collapsed under the conditions used. 

Soil has a substantial volumetric heat capacity, but it does not have a high thermal conductivity coefficient, Ks°l1. Heat is therefore not readily conducted in soil, where the heat flux density by conduction is... 

During the daytime, the surface of the soil can be considerably warmer than the underlying layers (Fig. 7-13), which leads to heat conduction into the soil. Because the soil exposed to the turbulent air tends to be drier than the underlying layers, the thermal conductivity coefficient can be lower near the soil surface. For the upper part of a fairly moist sandy loam, Z 50 1 may be 0.6 W m-1 °C-1 and dT/dz maybe —100°C m-1 (at least for the upper 0.05 m or so). Using Equation 7.27, the heat flux density by conduction into the soil then is... 

A 2.54-cm Styrofoam plastic foam with thermal conductivity of ca 0.03 W/(m-K) (0.21 (Btu-in.)/(ft-h- F)) is equivalent to 61 cm of gravel. Any synthetic foam having compressive strength sufficiently high and thermal conductivity sufficiently low is effective. However, the resistance of PS-type foams to water, frost damage, and microorganisms in the soil makes them especially desirable. An interesting and important appHcation of this concept was the use of Styrofoam in the constmction of the Alaska pipeline. In this case, the foam was used to protect the permafrost. 

A 30-m-long, lO-cm-diameter hot-water pipe of a district heating system is buried in the soil 50 cm below the ground surface, as shown in Fig. 3-49. The outer surface temperature of the pipe is 80 C. Taking the surface temperature I of the earth to be 10°C and the thermal conductivity of the soil at that location to be 0.9 W/m "C, determine the rate of heat loss from the pipe. 

Properties The thermal conductivity of the soil is given to be k = 0.9 W/m C Analysis The shape factor for this configuration is given in Table 3-7 to be... 

Arowof 1-m-long and 2.5-cni-dianieter used uranium fuel rods that are still radioactive are buried in the ground parallel to each other witli a cenler-to-center distance of 20 cm at a depth 4.5 m from the ground surface at a location where the thermal conductivity of the. soil is LI W/m "C. If the. surface temperature of the rods and the ground are 175 C and 1 S C, respectively, determine the rate of heat transfer from the fuel rods to the atmosphere through the soil. 

C How does the condensation or freezing of water vapor in the wall affect the effeclivene.ss of the insulalion in the wall How does the moisture content affect the effective thermal conductivity of soil ... 

Gases produced during soil and sludge incubations were analyzed by injections of headspace of the sample on a F M Scientific 700 gas chromatograph equipped with a thermal conductivity detector in... 

Under the conditions described in Example 10.5, what is the average rate of heat loss per unit area from the ground to the air during the 12-h period The thermal conductivity of soil is 0.7 W/m-°C. 

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