scholarly journals The effect of sediment thermal conductivity on vertical groundwater flux estimates

2019 ◽  
Vol 23 (8) ◽  
pp. 3305-3317 ◽  
Author(s):  
Eva Sebok ◽  
Sascha Müller
Keyword(s):  
Thermal Conductivity ◽  
Homogeneous Distribution ◽  
Temperature Profiles ◽  
High Flux ◽  
Water Interface ◽  
Heterogeneous Distribution ◽  
Groundwater Flux ◽  
Sediment Temperature ◽  
Spatially Distributed ◽  
Lagoon Environment

Abstract. Vertical sediment temperature profiles are frequently used to estimate vertical fluid fluxes. In these applications using heat as a tracer of groundwater flow, the thermal conductivity of saturated sediments (ke) is often given as a standard literature value and assumed to have a homogeneous distribution in the vertical space. In this study vertical sediment temperature profiles were collected in both a high-flux stream and a low-flux lagoon environment in sand- and peat-covered areas. ke was measured at the location of each temperature profile at several depths below the sediment–water interface up to 0.5 m with a measurement spacing of 0.1 m. In general ke values measured in this study ranged between 0.55 and 2.96 W m−1 ∘C−1 with an increase with depth from the sediment–water interface. The effect of using a vertically homogeneous or heterogeneous distribution of measured ke values on vertical flux estimates was studied with a steady-state HydroGeoSphere model. In the high-flux stream environment estimated fluxes varied between 0.03 and 0.71 m d−1 and in the low-flux lagoon between 0.02 and 0.23 m d−1. We found that using a vertically heterogeneous distribution of sediment thermal conductivity did not considerably change the fit between observed and simulated temperature data compared to a homogeneous distribution of ke. However, depending on the choice of sediment thermal conductivities, flux estimates decreased by up to 64 % or increased by up to 75 % compared to using a standard ke sediment thermal conductivity for sand, frequently assumed by previous local studies. Hence, our study emphasizes the importance of using spatially distributed thermal properties in heat flux applications in order to obtain more precise flux estimates.

scholarly journals The effect of sediment thermal conductivity on vertical groundwater flux estimates

2018 ◽  
Author(s):  
Eva Sebok ◽  
Sascha Müller
Keyword(s):  
Thermal Conductivity ◽  
Homogeneous Distribution ◽  
Temperature Profiles ◽  
High Flux ◽  
Water Interface ◽  
Heterogeneous Distribution ◽  
Groundwater Flux ◽  
Sediment Temperature ◽  
Spatially Distributed ◽  
Lagoon Environment

Abstract. Vertical sediment temperature profiles are frequently used to estimate vertical fluid fluxes. In these applications using heat as a tracer of groundwater flow, the thermal conductivity of saturated sediments (ke) is often given as a standard literature value and assumed to have a homogeneous distribution in the vertical space. In this study vertical sediment temperature profiles were collected both in a high-flux stream and a low-flux lagoon environment in a sand-, and peat-covered area. ke was measured at the location of each temperature profile at several depths below the sediment-water interface up to 0.5 m with a measurement spacing of 0.1 m. In general ke values measured in this study ranged between 0.55 and 2.96 W m−1 °C−1 with an increase with depth from the sediment-water interface. The effect of using a vertically homogeneous or heterogeneous distribution of measured ke values on vertical flux estimates was studied with a steady-state HydroGeoSphere model. In the high-flux stream environment estimated fluxes varied between 0.03 and 0.71 m d−1 and in the low-flux lagoon between 0.02 and 0.23 m d−1. It was found, that using a vertically heterogeneous distribution of sediment thermal conductivity did not considerably change the fit between observed and simulated temperature data compared to a homogeneous distribution of ke. However, depending on the choice of sediment thermal conductivities, flux estimates decreased by up to 64 % or increased by up to 75 % compared to using a standard ke sediment thermal conductivity for sand, frequently assumed by previous local studies. Hence, our study emphasizes the importance of using spatially distributed thermal properties in heat flux applications in order to obtain more precise flux estimates.

Development of TiB2 Dispersed Aluminum Composites by Spark Plasma Sintering

2016 ◽  
Vol 877 ◽  
pp. 601-605 ◽  
Author(s):  
Gen Sasaki ◽  
Takaaki Hirose ◽  
Yong Bum Choi ◽  
Kenji Sugio ◽  
Kazuhiro Matsugi
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Spark Plasma Sintering ◽  
High Performance ◽  
Homogeneous Distribution ◽  
Heterogeneous Distribution ◽  
Plasma Sintering ◽  
Low Thermal Expansion ◽  
Spark Plasma ◽  
Dispersed Aluminum

In order to obtain the high performance materials with high thermal conductivity, high electrical conductivity, low thermal expansion, good mechanical properties and low density, TiB2 particle dispersed aluminum (Al) composites was developed by spark plasma sintering. As these properties are affected by the dispersibility of the particles, the relationship among the dispersibility of dispersant and the thermal conductivity and mechanical properties was investigated, 20 vol. % TiB2 dispersed Al composites with different dispersibility were fabricated by spark plasma sintering (SPS). The dispersibility was estimated quantitatively by using the definition method of local number of particles (LN2DR method), and two composites having 6.884 and 4.839 for number of LN2DR was obtained. Thermal conductivity of the composites with homogeneous distribution of TiB2 particles was lower than that with heterogeneous distribution and clustering. On the other hand, the tensile strength of the composites improved as increasing temperature compared with Al block. Furthermore, strength of the composites with homogeneous distribution of TiB2 particles at 200°C and more was higher than that of the composites with heterogeneous distribution and clustering.

scholarly journals Behaviour of Metal(loid)s at the Sediment-Water Interface in an Aquaculture Lagoon Environment (Grado Lagoon, Northern Adriatic Sea, Italy)

2021 ◽  
Vol 11 (5) ◽  
pp. 2350
Author(s):  
Elisa Petranich ◽  
Matteo Crosera ◽  
Elena Pavoni ◽  
Jadran Faganeli ◽  
Stefano Covelli
Keyword(s):  
Sediment Cores ◽  
Fish Farm ◽  
Trophic Chain ◽  
Water Interface ◽  
Northern Adriatic Sea ◽  
Overlying Water ◽  
Northern Adriatic ◽  
In Situ Experiments ◽  
Diffusive Fluxes ◽  
Lagoon Environment

The cycling of metal(loid)s at the sediment–water interface (SWI) was evaluated at two selected sites (VN1 and VN3) in an active fish farm in the Grado Lagoon (Northern Adriatic, Italy). In situ experiments using a transparent benthic chamber and the collection of short sediment cores were performed, to investigate the behavior of metal(loid)s in the solid (sediments) and dissolved (porewaters) phases. Total and labile concentration of metal(loid)s were also determined in sediments, to quantify their potential mobility. Comparable total concentrations were found at both sites, excluding As, Mn, Pb and V, which were higher at VN3. Metal(loid) porewater profiles showed a diagenetic sequence and a close dependence with redox (suboxic/anoxic) conditions in the surface sediments. Positive diffusive fluxes along with benthic fluxes, particularly at the more oxic site, VN1, were found for almost all metal(loid)s, indicating their tendency to migrate towards the overlying water column. Despite sediments at two sites exhibiting high total metal(loid) concentrations and moderate effluxes at the SWI, the results suggest that they are hardly remobilized from the sediments. Recycling of metal(loid)s from the SWI would not constitute a threat for the aquatic trophic chain in the fish farm.

scholarly journals Thermal Conductivity, Heat Sources and Temperature Profiles of Li-Ion Batteries

2014 ◽  
Vol 58 (48) ◽  
pp. 145-171 ◽  
Author(s):  
O. S. Burheim ◽  
M. A. Onsrud ◽  
J. G. Pharoah ◽  
F. Vullum-Bruer ◽  
P. J. S. Vie
Keyword(s):  
Thermal Conductivity ◽  
Temperature Profiles ◽  
Heat Sources ◽  
Li Ion Batteries ◽  
Li Ion

Utilization of Thorium in LWR Fuels Aiming at Thermal Conductivity Improvements

2016 ◽  
Author(s):  
Jan Kubáň ◽  
Radek Škoda
Keyword(s):  
Thermal Conductivity ◽  
Uranium Dioxide ◽  
Nuclear Power ◽  
Fuel Pellet ◽  
Thorium Dioxide ◽  
Heterogeneous Distribution ◽  
Thermal Output ◽  
Homogenous Distribution ◽  
Limiting Parameters ◽  
Almost All

One of the main drawbacks of uranium dioxide, which is used in almost all nuclear power reactors, is its low thermal conductivity. As a consequence, temperature at the center of fuel pellet is relatively high, because heat is poorly conducted away. To reach a higher level of safety, maximal temperature in any fuel pellet is one of the main limiting parameters, which restrict the fuel thermal output. This paper deals with the use of thorium in LWR fuels with the objective of fuel pellet maximal temperature reduction. Research investigating homogenous distribution of thorium dioxide (thoria) in uranium dioxide fuel has already been done and did not lead to considerable thermal conductivity improvements. The aim of this study is to investigate heterogeneous distribution of thorium in commonly used uranium dioxide fuel in the form of uranium and thorium pellets placed together.

Study on Radial Temperature Distribution of Aluminum Dispersed Nuclear Fuels: U3O8-Al, U3Si2-Al, and UN-Al

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Jayangani I. Ranasinghe ◽  
Ericmoore Jossou ◽  
Linu Malakkal ◽  
Barbara Szpunar ◽  
Jerzy A. Szpunar
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Steady State ◽  
Temperature Gradient ◽  
Heat Conduction Equation ◽  
Conduction Equation ◽  
Temperature Profiles ◽  
Nuclear Fuels ◽  
State Heat ◽  
Steady State Heat

The understanding of the radial distribution of temperature in a fuel pellet, under normal operation and accident conditions, is important for a safe operation of a nuclear reactor. Therefore, in this study, we have solved the steady-state heat conduction equation, to analyze the temperature profiles of a 12 mm diameter cylindrical dispersed nuclear fuels of U3O8-Al, U3Si2-Al, and UN-Al operating at 597 °C. Moreover, we have also derived the thermal conductivity correlations as a function of temperature for U3Si2, uranium mononitride (UN), and Al. To evaluate the thermal conductivity correlations of U3Si2, UN, and Al, we have used density functional theory (DFT) as incorporated in the Quantum ESPRESSO (QE) along with other codes such as Phonopy, ShengBTE, EPW (electron-phonon coupling adopting Wannier functions), and BoltzTraP (Boltzmann transport properties). However, for U3O8, we utilized the thermal conductivity correlation proposed by Pillai et al. Furthermore, the effective thermal conductivity of dispersed fuels with 5, 10, 15, 30, and 50 vol %, respectively of dispersed fuel particle densities over the temperature range of 27–627 °C was evaluated by Bruggman model. Additionally, the temperature profiles and temperature gradient profiles of the dispersed fuels were evaluated by solving the steady-state heat conduction equation by using Maple code. This study not only predicts a reduction in the centerline temperature and temperature gradient in dispersed fuels but also reveals the maximum concentration of fissile material (U3O8, U3Si2, and UN) that can be incorporated in the Al matrix without the centerline melting. Furthermore, these predictions enable the experimental scientists in selecting an appropriate dispersion fuel with a lower risk of fuel melting and fuel cracking.

scholarly journals Heat loss analysis in a radiating slab of variable thermal conductivity

2018 ◽  
Vol 7 (2.23) ◽  
pp. 228 ◽  
Author(s):  
Ramoshweu S. Lebelo ◽  
Kholeka C. Moloi
Keyword(s):  
Differential Equation ◽  
Thermal Conductivity ◽  
Chemical Reaction ◽  
Combustion Process ◽  
Variable Thermal Conductivity ◽  
Temperature Profiles ◽  
Reactive Material ◽  
Loss Analysis ◽  
Exothermic Chemical Reaction ◽  
Rectangular Slab

This article investigates the transfer of heat in a stockpile of reactive materials, that is assumed to lose heat to the environment by radiation. The study is modeled in a rectangular slab whose materials are of variable thermal conductivity. The stockpile’s reactive material in this context is one that readily reacts with the oxygen trapped within the stockpile due to exothermic chemical reaction. The study of the combustion process in this case is conducted theoretically by using the Mathematical approach. The differential equation governing the problem is tackled numerically by applying the Runge-Kutta Fehlberg (RKF45) method coupled with the Shooting technique. To investigate the heat transfer phenomena, some kinetic parameters embedded in the governing differential equation, are varied to observe the behavior of the temperature profiles during the combustion process. The results obtained from the temperature profiles, are depicted graphically and discussed accordingly. It was discovered that kinetic phenomena such as the reaction rate parameter, accelerates the exothermic chemical reaction. However, the radiation parameter decelerates the exothermic chemical reaction by lowering the temperature profiles.  

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