Improved method to calculate the critical conditions for drying out sandy soils around power cables

Groeneveld, Gino; Snijders, A.; Koopmans, G.F.; Vermeer, J.

doi:10.1049/ip-c.1984.0007

Cited by 21 publications

(26 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Smits et al (2010) demonstrated the sharp 12 decline in λs below residual water content for sands that they attributed to the disconnection of away from GHEXs during the cooling phase, when heat is injected into the ground. Moreover, previous 16 researchers ( Groeneveld et al, 1984;Salomone et al, 1984;Remund, 1988) developed methods to 17 measure soil thermal instability and worked toward developing predictive equations that could allow 18 engineers to estimate soil conditions that lead to poor heat transfer. Both Groeneveld et al (1984) and 19 Remund (1988) stressed the importance of initial moisture content in limiting the tendency of certain 20 soils to move toward thermal instability.…”

Section: Soil Moisture and Bulk Densitymentioning

confidence: 99%

“…Moreover, previous 16 researchers ( Groeneveld et al, 1984;Salomone et al, 1984;Remund, 1988) developed methods to 17 measure soil thermal instability and worked toward developing predictive equations that could allow 18 engineers to estimate soil conditions that lead to poor heat transfer. Both Groeneveld et al (1984) and 19 Remund (1988) stressed the importance of initial moisture content in limiting the tendency of certain 20 soils to move toward thermal instability. This highlights the need to couple field measurements that 21 quantify predominant soil moisture regimes with soil thermal properties.…”

Section: Soil Moisture and Bulk Densitymentioning

confidence: 99%

See 1 more Smart Citation

Spatiotemporal variability of ground thermal properties in glacial sediments and implications for horizontal ground heat exchanger design

2015

View full text Add to dashboard Cite

9Thorough characterization of the spatiotemporal variability in soil thermal properties can 10 facilitate better designs for horizontal geothermal heat pump (HGHP) systems by reducing ground heat 11 exchanger (GHEX) costs. Results are presented from a new monitoring network installed across a range 12 of glaciated terrains in Indiana (USA), including the first known observations of the dynamic range of 13 thermal conductivity that occurs at the depth of horizontal GHEX installations. In situ thermal 14 conductivity data can vary significantly on a seasonal basis in coarse-grained outwash sediments (0.8-151.4 W m -1 K -1 ), whereas clay-and silt-dominated moraine sediments have a dampened seasonal range 16 within 10% of the annual mean. Thermal conductivity across the network ranges from 0.8 to 2.0 W m -1 17 K -1 depending on soil parent material, climatic setting, and particularly, soil-moisture variability. Results 18 indicate that the standard industry practice to estimate thermal properties from soil type often leads to 19 suboptimal GHEX design (i.e., GHEX design lengths were 44% to 52% longer than necessary to meet 20 performance specifications). This research suggests that expanding the characterization of soil thermal 21 properties in specific settings where HGHPs are targeted will improve understanding of the dynamic 22 aspects of ground heat exchange and lead to more optimal HGHP system designs. 23 Keywords: soil thermal properties, geothermal heat pump, thermal conductivity, ground temperature, 24 soil moisture 25 © 2015. This manuscript version is made available under the Elsevier user license

show abstract

Section: Soil Moisture and Bulk Densitymentioning

confidence: 99%

Section: Soil Moisture and Bulk Densitymentioning

confidence: 99%

Spatiotemporal variability of ground thermal properties in glacial sediments and implications for horizontal ground heat exchanger design

2015

View full text Add to dashboard Cite

show abstract

“…The amount of the moisture filling the soil is inversely proportional to the dry density of the soil. The heat generated in different cable components flows into the soil, which causes moisture migration from the soil and formation of drying zone surrounding the cable, may be happened [26][27][28][29]. According to standards and from field experience, fine sands having small grain size are usually used as backfill material surrounding the cable, in this study sand grain size between 0.15 and 1.18 mm beside the percentage of clay to improve soil retention is tested to be used as backfill materials in the thermal study analysis.…”

Section: Experimental Workmentioning

confidence: 99%

“…2b. The general equation of the soil thermal resistivity ρ as a function of the moisture content, dry density and temperature is given according to [26].…”

Section: Experimental Workmentioning

confidence: 99%

Load cycling of underground distribution cables including thermal soil resistivity variation with soil temperature and moisture content

Gouda

Osman

Salem

et al. 2018

IET Generation, Transmission & Distribution

View full text Add to dashboard Cite

“…Our analysis points at combined domains of values for the van Genuchten parameter n and a specific dimensionless combination of parameters that we call a dynamic parameter, which efficiently counteracts the decrease in the critical temperature caused by ambient conditions. It has been known for well over two decades that the addition of fine-grained material to a coarse sand increases its critical temperature under certain conditions (CIGRE Study Committee 21, 1992) and the heat flux density under critical conditions (Groeneveld et al, 1984). However, a systematic quantification of the impact of hydraulic properties on the critical temperature of the backfill has been lacking.…”

mentioning

confidence: 99%

The Effect of Drying around Power Cables on the Vadose Zone Temperature

Hruška

Clauser

Doncker

2018

Vadose Zone Journal

View full text Add to dashboard Cite

The effects of moisture migration away from power cables depend strongly in most soils on whether the soil has reached the so-called critical conditions (e.g., critical temperature) for a dry-out. However, research on how to estimate this critical temperature has been limited. We solved numerically a differential equation for the planar case of steady-state coupled heat and mass transfer in porous media, using the van Genuchten-Mualem model for the hydraulic properties of the medium. The critical isotherm is assessed by the temperature at which the steepest change occurs in the moisture content with temperature. We considered the impact of the properties of the surrounding medium and of the ambient temperature and moisture content on the dry-out temperature. We found that seasonal variations in ambient conditions in a field in Italy have a greater impact on the critical temperature than the variations in soil properties in that field (under the assumption of a nearly uniform moisture content with depth). However, our analysis shows that, under certain conditions, a change in the van Genuchten parameter n and in a specific combination of parameters that we call a dynamic parameter can have as large an effect on the critical temperature. This suggests a direction in the optimization of backfill materials.Simultaneous transfer of heat and moisture is of interest for a wide variety of agricultural, industrial, and energy production processes. Drying of porous solids and soils, geothermal energy production, thermally induced oil recovery, underground high-level waste disposal, and heat transfer from buried pipelines and electrical cables are just some of the examples (Udell, 1985).The release of Joule heat from buried electrical cables increases the temperature of the ground in their vicinity and leads under certain conditions to the formation of a zone with a very low moisture content. Besides heat conduction through grain-to-grain contacts and the water bridges between the grains, heat is also transferred as a result of a "heat pipe cycle" (Groeneveld et al., 1984). Water evaporates in high-temperature areas and condenses in lower temperature regions, causing a gradient in moisture content. This results in liquid water flow in the opposite direction. At high heat fluxes, large gradients in temperature and moisture content develop. When certain critical conditions are exceeded, this results in almost complete drying out of the soil near the heat source (Groeneveld et al., 1984).Among the critical conditions, those involving the critical temperature are the most important for using standardized steady-state cable ratings. To prevent overheating in the cable insulation or the surrounding environment due to a low thermal conductivity caused by drying, the International Electrotechnical Commission recommended solution procedures for the steady-state rating and thermal analysis of power cables (CIGRE Study Committee 21, 1992; International Electrotechnical Commission, 2015). That analysis adopts a two-zone model-a steady...

show abstract

Improved method to calculate the critical conditions for drying out sandy soils around power cables

Cited by 21 publications

References 0 publications

Spatiotemporal variability of ground thermal properties in glacial sediments and implications for horizontal ground heat exchanger design

Spatiotemporal variability of ground thermal properties in glacial sediments and implications for horizontal ground heat exchanger design

Load cycling of underground distribution cables including thermal soil resistivity variation with soil temperature and moisture content

The Effect of Drying around Power Cables on the Vadose Zone Temperature

Contact Info

Product

Resources

About