Characteristics of heat fluxes of an oil pipeline armed with thermosyphons in permafrost regions. (25th May 2021)

• Record Type: Journal Article
• Authors: Chen, Lin; Yu, Wenbing; Lu, Yan; Wu, Pan; Han, Fenglei
• Is Part Of: Applied thermal engineering. Volume 190(2021)
• Publication Date: 2021-05-25
• Subjects: Buried oil pipeline -- Permafrost degradation -- Talik formation -- Heat flux -- Snow insulation -- Two-phase closed thermosyphon; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.116694
• Languages: English
• ISSNs: 1359-4311

Abstract

Graphical abstract: Heat flux dissipated by the buried warm-oil pipeline causes the accelerated and potentially irreversible permafrost thaw. The mean annual heat flux exponentially decreases with increasing insulation thickness, while have a logarithmical increase with the increase of the thermal conductivity of insulation material. Two-phase closed thermosyphons (TPCTs) can be an excellent strengthen measures to mitigate permafrost thaw by increasing the heat extraction on an average 0.5 W/m 2 . Highlights: The amount of heat dissipated by a warm oil pipeline was quantified. Heat flux exponentially decreased with the increase of the thermal resistance. Insulation material cannot protect permafrost degradation in the service life. Thermosyphons largely increase heat extraction by a daily average of 0.5 W/m 2 . Abstract: Permafrost degradation negatively affects the thermal stability of northern infrastructure. The quantification of heat loss through a buried oil pipeline is imperative to determine the thermal interaction between the pipe and underlying permafrost. However, the magnitudes and patterns of heat flux have not been studied methodically. This study quantifies how lateral and vertical heat fluxes from a buried warm oil pipeline increase the permafrost thawing rate and promote talik ( i.e., bodies or layers of unfrozen ground in permafrost areas) development in subarctic regions by employing a three-dimensional conductive heat transfer model. In addition, the sensitivities of daily and annual heat fluxes to insulation thickness and its thermal conductivity were determined. Simulated results indicate that the heated oil pipeline acts as a heat source with the maximum daily heat flux of 6.7 W/m 2 and maximum annual heat flux of 4.3 W/m 2 . The mean annual heat flux exponentially decreases with increasing insulation thickness, while has a logarithmical increase with the increase of the thermal conductivity of insulation material. For an insulated (0.04-m thickness) oil pipeline, a fast-growing talik initiates and enlarges laterally and vertically over time. By contrast, two-phase closed thermosyphons can be used as a remedying measure to mitigate the accelerated permafrost thaw around a buried oil pipeline. Thermosyphons increase the lateral daily heat flux by an average of 0.5 W/m 2 and lower mean annual soil temperature at depth by an average of 2 °C. Within the context of climate warming, we expect that talik beneath the oil pipeline will enlarge faster than previously estimated in the coming decades due to the adverse effects of the subsurface water flow. The net founding of our results is applicable to improve the engineered design and assess the vulnerability of the oil pipeline in cold regions.