Heat transfer by seepage in sand: Influence of saturated hydraulic conductivity and porosity

Heat transfer within the soil is a complex process in the presence of seepage flow. In such conditions, the soil’s thermal behavior is influenced by the thermal and hydraulic properties of the medium as well as the initial conditions and boundary conditions to which the medium is subjected. This paper presents the experimental and numerical studies of heat transfer within the sand subjected to the seepage flow. It focuses on the influence of saturated hydraulic conductivity and the porosity of medium on the heat transfer process. The temperature distribution within the sand was monitored by the optical fiber Distributed Temperature Sensor (DTS). The experiment was performed on three types of silica-dominated sands with different saturated hydraulic conductivities and different Soil Water Characteristic Curve (SWCC). In addition to the experimental study, a coupled hydrothermal numerical model was designed in FEFLOW software and validated by comparing its results with the experimental measurements. To determine the influence of porosity and saturated hydraulic conductivity on heat transfer, we analyzed the numerical models for different values of porosity and saturated hydraulic conductivity. The numerical and experimental studies showed that the thermal velocity is higher in sand with higher saturated hydraulic conductivity and temperature declination occurs more quickly due to the heat convection process. Saturated sand with larger porosity has an overall higher heat capacity, wherefore the temperature declination started later in the measuring points but dropped down lower close to the temperature of the upstream water.

Two-Dimensional Spatial Resolution in Plane Temperature Monitoring Based on Raman Distributed Temperature Sensor

Spatial resolution is an important parameter that characterizes the detection capability of a system, and there are extremely high requirements for spatial resolution in important fields such as the fossil energy industry and nuclear industry. In order to realize the high-precision distributed monitoring of the optical fiber distributed temperature sensing system (DTS), the factors affecting the spatial resolution of the DTS system were analyzed, and a two-dimensional planar temperature field distribution monitoring scheme based on Raman distributed temperature sensor (RDTS) was proposed. In this scheme, based on the layout of the two-dimensional RDTS heat source positioning system, multimode fiber was adopted. After comparing several sensing fiber routing schemes, the 45∘ skew 2D wiring method of sensing fiber was finally selected. According to the experimental results, the spatial resolution of the temperature field distribution in the monitoring area can break through the limitation of the system resolution. It has more application value than the traditional one-dimensional distributed temperature sensing system.