scholarly journals Technical Note: Simple formulations and solutions of the dual-phase diffusive transport for biogeochemical modeling

2014 ◽  
Vol 11 (1) ◽  
pp. 1587-1611
Author(s):  
J. Y. Tang ◽  
W. J. Riley
Keyword(s):  
Steady State ◽  
Tracer Diffusion ◽  
Technical Note ◽  
Analytical Models ◽  
Dual Phase ◽  
Soil Co2 ◽  
Near Surface ◽  
Solution Algorithms ◽  
Biogeochemical Models ◽  
Co2 Dynamics

Abstract. Representation of gaseous diffusion in variably saturated near-surface soils is becoming more common in land biogeochemical models, yet the formulations and numerical solution algorithms applied vary widely. We present three different but equivalent formulations of the dual-phase (gaseous and aqueous) tracer diffusion transport problem that is relevant to a wide class of volatile tracers in land biogeochemical models. Of these three formulations (i.e., the gas-primary, aqueous-primary, and bulk tracer based formulations), we contend the gas-primary formulation is the most convenient for modeling tracer dynamics in biogeochemical models. We then provide finite volume approximation to the gas-primary equation and evaluate its accuracy against three analytical models: one for steady-state soil CO2 dynamics, one for steady-state soil CO2 dynamics, and one for transient tracer diffusion from a constant point source into two different sequentially aligned medias. All evaluations demonstrated good accuracy of the numerical approximation. We expect our result will standardize an efficient mechanistic numerical method for solving relatively simple, multi-phase, one-dimensional diffusion problems in land models.

scholarly journals Technical Note: Simple formulations and solutions of the dual-phase diffusive transport for biogeochemical modeling

2014 ◽  
Vol 11 (14) ◽  
pp. 3721-3728 ◽  
Author(s):  
J. Y. Tang ◽  
W. J. Riley
Keyword(s):  
Steady State ◽  
Tracer Diffusion ◽  
Technical Note ◽  
Analytical Models ◽  
Dual Phase ◽  
Near Surface ◽  
Solution Algorithms ◽  
Biogeochemical Models ◽  
Volume Approximation ◽  
Multi Phase

Abstract. Representation of gaseous diffusion in variably saturated near-surface soils is becoming more common in land biogeochemical models, yet the formulations and numerical solution algorithms applied vary widely. We present three different but equivalent formulations of the dual-phase (gaseous and aqueous) tracer diffusion transport problem that is relevant to a wide class of volatile tracers in land biogeochemical models. Of these three formulations (i.e., the gas-primary, aqueous-primary, and bulk-tracer-based formulations), we contend that the gas-primary formulation is the most convenient for modeling tracer dynamics in biogeochemical models. We then provide finite volume approximation to the gas-primary equation and evaluate its accuracy against three analytical models: one for steady-state soil CO2 dynamics, one for steady-state soil CH4 dynamics, and one for transient tracer diffusion from a constant point source into two different sequentially aligned medias. All evaluations demonstrated good accuracy of the numerical approximation. We expect our result will standardize an efficient mechanistic numerical method for solving relatively simple, multi-phase, one-dimensional diffusion problems in land models.

Differential effects of wetting and drying on soil CO2 concentration and flux in near-surface vs. deep soil layers

2020 ◽  
Vol 148 (3) ◽  
pp. 255-269 ◽  
Author(s):  
Kyungjin Min ◽  
Asmeret Asefaw Berhe ◽  
Chau Minh Khoi ◽  
Hella van Asperen ◽  
Jeroen Gillabel ◽  
...  
Keyword(s):  
Co2 Concentration ◽  
Soil Co2 ◽  
Deep Soil ◽  
Wetting And Drying ◽  
Near Surface ◽  
Soil Layers ◽  
Differential Effects ◽  
Soil Co2 Concentration

scholarly journals Changes in the CO2 dynamics in near-surface cavities under a future warming scenario: Factors and evidence from the field and experimental findings

2016 ◽  
Vol 565 ◽  
pp. 1151-1164 ◽  
Author(s):  
C. Pla ◽  
S. Cuezva ◽  
E. Garcia-Anton ◽  
A. Fernandez-Cortes ◽  
J.C. Cañaveras ◽  
...  
Keyword(s):  
Near Surface ◽  
Warming Scenario ◽  
Future Warming ◽  
Experimental Findings ◽  
Co2 Dynamics

scholarly journals Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment

2011 ◽  
Vol 8 (5) ◽  
pp. 1333-1350 ◽  
Author(s):  
U. Gamnitzer ◽  
A. B. Moyes ◽  
D. R. Bowling ◽  
H. Schnyder
Keyword(s):  
Steady State ◽  
Isotopic Composition ◽  
Transport Model ◽  
Tracer Experiment ◽  
Atmospheric Co2 ◽  
Soil Co2 ◽  
Soil Air ◽  
Co2 Transport ◽  
Atmosphere System

Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δ13Cefflux) from soil is generally interpreted to represent the actual isotopic composition of the respiratory source (δ13CRs). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δ13Catm) or δ13CRs causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δ13Cefflux from δ13CRs (termed "disequilibrium effect"). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δ13Cefflux and δ13CRs in ecosystem respiration. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, and belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δ13Catm of −46.9 ‰ during daytime for 2 weeks. Nighttime δ13Cefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. Earlier work has shown that the δ13Cefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δ13CRs. Conversely, the δ13Cefflux measured using the closed chamber technique differed from these by −11.2 ‰. Most of this disequilibrium effect (9.5 ‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δ13Catm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6 ‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δ13CRs in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δ13CRs or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

scholarly journals Technical Note: Novel method for water vapour monitoring using wireless communication networks measurements

2009 ◽  
Vol 9 (7) ◽  
pp. 2413-2418 ◽  
Author(s):  
N. David ◽  
P. Alpert ◽  
H. Messer
Keyword(s):  
Wireless Communication ◽  
Water Vapour ◽  
Communication Networks ◽  
Weather Conditions ◽  
Technical Note ◽  
Base Stations ◽  
Propagation Path ◽  
High Temporal Resolution ◽  
Wireless Communication Networks ◽  
Near Surface

Abstract. We propose a new technique that overcomes the obstacles of the existing methods for monitoring near-surface water vapour, by estimating humidity from data collected through existing wireless communication networks. Weather conditions and atmospheric phenomena affect the electromagnetic channel, causing attenuations to the radio signals. Thus, wireless communication networks are in effect built-in environmental monitoring facilities. The wireless microwave links, used in these networks, are widely deployed by cellular providers for backhaul communication between base stations, a few tens of meters above ground level. As a result, if all available measurements are used, the proposed method can provide moisture observations with high spatial resolution and potentially high temporal resolution. Further, the implementation cost is minimal, since the data used are already collected and saved by the cellular operators. In addition – many of these links are installed in areas where access is difficult such as orographic terrain and complex topography. As such, our method enables measurements in places that have been hard to measure in the past, or have never been measured before. The technique is restricted to weather conditions which exclude rain, fog or clouds along the propagation path. Strong winds that may cause movement of the link transmitter or receiver (or both) may also interfere with the ability to conduct accurate measurements. We present results from real-data measurements taken from two microwave links used in a backhaul cellular network that show convincing correlation to surface station humidity measurements. The measurements were taken daily in two sites, one in northern Israel (28 measurements), the other in central Israel (29 measurements). The correlation between the microwave link measurements and the humidity gauges were 0.9 and 0.82 for the north and central sites, respectively. The Root Mean Square Differences (RMSD) were 1.8 g/m3 and 3.4 g/m3 for the northern and central site measurements, respectively.

scholarly journals Experimental and Numerical Analysis of Additively Manufactured Inconel 718 Coupons With Lattice Structure

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Sarwesh Parbat ◽  
Zheng Min ◽  
Li Yang ◽  
Minking Chyu
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Pressure Drop ◽  
Inconel 718 ◽  
Lattice Structure ◽  
Unit Cell ◽  
Common Vertex ◽  
Constant Wall Temperature ◽  
Near Surface ◽  
Smooth Channel

Abstract In the present paper, two lattice geometries suitable for near surface and double wall cooling were developed and tested. The first type of unit cell consisted of six ligaments of 0.5 mm diameter joined at a common vertex near the middle. The second type of unit cell was derived from the first type by adding four mutually perpendicular ligaments in the middle plane. Two lattice configurations, referred to as L1 and L2, respectively, were obtained by repeating the corresponding unit cell in streamwise and spanwise directions in an inline fashion. Test coupons consisting of these lattice geometries embedded inside rectangular cooling channel with dimensions of 2.54 mm height, 38.07 mm width, and 38.1 mm in length were fabricated using Inconel 718 powder and selective laser sintering (SLS) process. The heat transfer and pressure drop performance was then evaluated using steady-state tests with constant wall temperature boundary condition and for channel Reynolds number ranging from 2800 to 15,000. The lattices depicted a higher heat transfer compared with a smooth channel and both the heat transfer and pressure drop increased with a decrease in the porosity from L1 to L2. Steady-state conjugate numerical results revealed formation of prominent vortical structures in the inter-unit cell spaces, which diverted the flow toward the top end wall and created an asymmetric heat transfer between the two end walls. In conclusion, these lattice structures provided an augmented heat transfer while favorably redistributing the coolant within channel.

Closed-form expressions for the steady-state response of damped transmission line conductors considering their bending stiffness

2020 ◽  
Vol 26 (15-16) ◽  
pp. 1319-1329
Author(s):  
Marcelo A Ceballos ◽  
José E Stuardi
Keyword(s):  
Steady State ◽  
Transmission Line ◽  
Numerical Models ◽  
Mechanical Impedance ◽  
Steady State Solution ◽  
Bending Stiffness ◽  
Analytical Models ◽  
Dispersive Media ◽  
Overhead Transmission Line ◽  
Damper Design

This paper begins with a brief compilation of analytical models typically used to calculate the dynamic response of a conductor span belonging to an overhead transmission line, with a Stockbridge-type damper located near one of its ends. In most of analyses found in the literature, the calculation of the response is done through the superposition of waves that propagate in both longitudinal directions impinging and reflecting at the span ends and at the damper attachment points. The approach proposed in this paper allows obtaining the response as the steady-state solution of the governing differential equations providing suitable analytical expressions for conductors with bending stiffness, which are dispersive media for propagating waves. Using these analytical solutions, the influence of bending stiffness on the efficiency and on the optimal mechanical impedance of the damper, which are of great importance in damper design, can be described explicitly. At the same time, the proposed methodology avoids the need of numerical models or approximate formulas to calculate the bending strains in critical points of the conductor with a single damper.

A Comparative Analysis of Thermal Blood Perfusion Measurement Techniques

1987 ◽  
Vol 109 (3) ◽  
pp. 218-225 ◽  
Author(s):  
R. Kress ◽  
R. Roemer
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Time Window ◽  
Measurement Techniques ◽  
Temperature Response ◽  
Blood Perfusion ◽  
Analytical Models ◽  
Transient Temperature ◽  
Two Dimensional ◽  
Transient Heating

The object of this study was to devise a unified method for comparing different thermal techniques for the estimation of blood perfusion rates and to perform a comparison for several common techniques. The approach used was to develop analytical models for the temperature response for all combinations of five power deposition geometries (spherical, one- and two-dimensional cylindrical, and one- and two-dimensional Gaussian) and three transient heating techniques (temperature pulse-decay, temperature step function, and constant-power heat-up) plus one steady-state heating technique. The transient models were used to determine the range of times (the time window) when a significant portion of the transient temperature response was due to blood perfusion. This time window was defined to begin when the difference between the conduction-only and the conduction-plus-blood flow transient temperature (or power) responses exceeded a specified value, and to end when the conduction-plus-blood flow transient temperature (or power) reached a specified fraction of its steady-state value. The results are summarized in dimensionless plots showing the size of the time windows for each of the transient perfusion estimation techniques. Several conclusions were drawn, in particular: (a) low perfusions are difficult to estimate because of the dominance of conduction, (b) large heated regions are better suited for estimation of low perfusions, (c) noninvasive heating techniques are superior because they have the potential to minimize conduction effects, and (d) none of the transient techniques appears to be clearly superior to the others.

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