Flux Partitioning Research Articles

Numerical investigation of flow and heat transfer characteristics of subcooled boiling in a single rod channel with/without spacer grid

A multiphase flow numerical model based on Eulerian is built to simulate the characteristics of subcooled boiling. The thermodynamic performance in a single rod channel with/without spacer grid are obtained by numerical simulation, and the influence of spacer grid on flow and heat transfer characteristics of subcooled boiling is studied. The model is verified by comparing with the experimental results. After passing through the spacer grid, the high-temperature zone departures from the surface of fuel rod moves towards the cold wall. This impact extends to a certain downstream distance, and then it gradually declines. The influence of different components in spacer grid on the pressure drop is detailed. The pressure drop with spacer grid is 5% higher than that without spacer grid, within the allowable design limitation. The maximum value of section average secondary flow can reach 13.5% of the inlet velocity, indicating that the mixing vanes have stronger ability to produce transverse flow. The influence length of spacer grid on heat flux partitioning is about 27Dh. The effect of spacer grid on the wall heat flux partitioning mainly lies in the decrease of the evaporation heat flux, benefited to reduce the risk of nuclear reactor approaching DNB.

Assessment of an Automated Calibration of the SEBAL Algorithm to Estimate Dry-Season Surface-Energy Partitioning in a Forest–Savanna Transition in Brazil

Evapotranspiration ( E T ) provides a strong connection between surface energy and hydrological cycles. Advancements in remote sensing techniques have increased our understanding of energy and terrestrial water balances as well as the interaction between surface and atmosphere over large areas. In this study, we computed surface energy fluxes using the Surface Energy Balance Algorithm for Land (SEBAL) algorithm and a simplified adaptation of the CIMEC (Calibration using Inverse Modeling at Extreme Conditions) process for automated endmember selection. Our main purpose was to assess and compare the accuracy of the automated calibration of the SEBAL algorithm using two different sources of meteorological input data (ground measurements from an eddy covariance flux tower and reanalysis data from Modern-Era Reanalysis for Research and Applications version 2 (MERRA-2)) to estimate the dry season partitioning of surface energy and water fluxes in a transitional area between tropical rainforest and savanna. The area is located in Brazil and is subject to deforestation and cropland expansion. The SEBAL estimates were validated using eddy covariance measurements (2004 to 2006) from the Large-Scale Biosphere-Atmosphere Experiment in the Amazon (LBA) at the Bananal Javaés (JAV) site. Results indicated a high accuracy for daily ET, using both ground measurements and MERRA-2 reanalysis, suggesting a low sensitivity to meteorological inputs. For daily ET estimates, we found a root mean square error (RMSE) of 0.35 mm day−1 for both observed and reanalysis meteorology using accurate quantiles for endmembers selection, yielding an error lower than 9% (RMSE compared to the average daily ET). Overall, the ET rates in forest areas were 4.2 mm day−1, while in grassland/pasture and agricultural areas we found average rates between 2.0 and 3.2 mm day−1, with significant changes in energy partitioning according to land cover. Thus, results are promising for the use of reanalysis data to estimate regional scale patterns of sensible heat (H) and latent heat (LE) fluxes, especially in areas subject to deforestation.

Impact of Soil Moisture on Winter 2-m Temperature Forecasts in Northern China

AbstractIn this study, the causes of the underestimated diurnal 2-m temperature range and the overestimated 2-m specific humidity in the winter of northern China in the Rapid-Refresh Multiscale Analysis and Prediction System–Short Term (RMAPS-ST) are investigated. Three simulations based on RMAPS-ST are conducted from 1 November 2016 to 28 February 2017. Further analyses show that the partitioning of surface upward sensible heat fluxes and downward ground heat fluxes might be the main contributing factor to the 2-m temperature forecast bias. In this study, two simulations are conducted to examine the effect of soil moisture initialization and soil hydraulic property on the 2-m temperature and 2-m specific humidity forecasts. First, the High-Resolution Land Data Assimilation System (HRLDAS) is used to provide an alternative soil moisture initialization. The results show that the drier soil moisture could lead to noticeable change in energy partitioning at the land surface, which in turn results in improved prediction of the diurnal 2-m temperature range, although it also enlarges the 2-m specific humidity bias in some parts of the domain. Second, a soil texture dataset developed by Beijing Normal University and the revised hydraulic parameters are applied to provide a more detailed description of soil properties, which could further improve the 2-m specific humidity bias. In summary, the combination of using optimized soil moisture initialization, an updated soil map, and revised soil hydraulic parameters can help improve the 2-m temperature and 2-m specific humidity prediction in RMAPS-ST.

The topographic control on land surface energy fluxes: A statistical approach to bias correction

Subsurface hydrodynamics are an important component of the hydrological cycle and a key factor in the partitioning of land surface water and energy fluxes. Because of computational reasons they are often neglected, or strongly simplified, in numerical weather prediction and climate models. Particularly in regions where the water table is shallow, soil moisture acts as a link between groundwater, land and atmosphere. Because of its long-term memory, groundwater represents a buffer for the effects of climate variability. To dynamically model this system we study the outputs of a variably saturated groundwater flow model (ParFlow) coupled with a surface model (CLM) and propose an empirical approach for the statistical correction of the bias of the energy fluxes in a highly-parametrized simulation. Corrections are based on a comparison of the simple scheme with the fully-coupled subsurface-land-atmosphere simulations. This simple dynamical scheme computes the potential latent heat flux in case of near saturation, while the fully-coupled simulations approximate the reality. Our statistical model examines the evapotranspiration surplus, i.e., the difference in latent heat flux between the two runs, and aims to correct the bias in the latent heat flux of the simple scheme, based on the characteristics of each point of the domain. In particular, we focus on the ability of topography-related indices, such as the topographic wetness index and the depth-to-water index, to provide information on the availability of water for evapotranspiration. Our results confirm that topographic indices are good predictors for moisture availability. While small-scale structures cannot be accurately reproduced by our model, large-scale biases of latent heat flux over the domain are effectively removed. Moreover, the bias corrected fluxes show a better agreement with the fluxes of the full modelling system than commonly used free-drainage simulations. Thus, the proposed approach can be useful in approximating the effect of groundwater on land surface water and energy fluxes in, e.g., regional climate models.

Biotic soil-plant interaction processes explain most of hysteretic soil CO2 efflux response to temperature in cross-factorial mesocosm experiment

Ecosystem carbon flux partitioning is strongly influenced by poorly constrained soil CO2 efflux (Fsoil). Simple model applications (Arrhenius and Q10) do not account for observed diel hysteresis between Fsoil and soil temperature. How this hysteresis emerges and how it will respond to variation in vegetation or soil moisture remains unknown. We used an ecosystem-level experimental system to independently control potential abiotic and biotic drivers of the Fsoil-T hysteresis. We hypothesized a principally biological cause for the hysteresis. Alternatively, Fsoil hysteresis is primarily driven by thermal convection through the soil profile. We conducted experiments under normal, fluctuating diurnal soil temperatures and under conditions where we held soil temperature near constant. We found (i) significant and nearly equal amplitudes of hysteresis regardless of soil temperature regime, and (ii) the amplitude of hysteresis was most closely tied to baseline rates of Fsoil, which were mostly driven by photosynthetic rates. Together, these findings suggest a more biologically-driven mechanism associated with photosynthate transport in yielding the observed patterns of soil CO2 efflux being out of sync with soil temperature. These findings should be considered on future partitioning models of ecosystem respiration.

Prediction of liquid hydrogen flow boiling critical heat flux condition under microgravity based on the wall heat flux partition model

Critical heat flux (CHF) of liquid hydrogen (LH2) flow boiling under microgravity is vital for designing space cryogenic propellant conveying pipe since the excursion of wall temperature may cause system failure. In this study, a two-dimensional axisymmetric model based on the wall heat flux partition (WHFP) model was proposed to predict the CHF condition under microgravity including the wall temperature and the CHF location. The proposed numerical model was validated to demonstrate a good agreement between the simulated and experimentally reported results. Then, the wall temperature distribution and the CHF location under different gravity conditions were compared. In addition, the WHFP and vapor-liquid distribution along the wall under microgravity were predicted and its difference with terrestrial gravity condition was also analysed and reported. Finally, the effects of flow velocity and inlet sub-cooling on the wall temperature distributions were analysed under microgravity and terrestrial gravity conditions, respectively. The results indicate that the CHF location moves upstream about 5.25 m from 1g to 10−4g since the void fraction near the wall reaches the breakpoint of CHF condition much earlier under the microgravity condition. Furthermore, the increase of the velocity and decrease of the sub-cooling have smaller effects on the CHF location during LH2 flow boiling under microgravity.

Regional Climate Impacts of Irrigation in Northern Italy Using a High Resolution Model

Irrigation is crucial for sustaining agriculture in certain regions; however, there are effects on the local climate. Previous studies discussed that the irrigation signal might depend on the geographical region as well as the synoptic and climatic conditions. The work presented here aims to investigate the mechanisms behind changes in the irrigation impact on the local conditions depending on synoptic changes. Different to previous works, this employs convection-permitting simulations. Irrigation processes are parameterized in three different ways depending on the evaporative loss. The region of focus is in northern Italy (Po Valley), which is of interest for both the soil-atmosphere coupling strength and widely used irrigation. The simulation period is Summer 2015 (May–July), which includes a heatwave month (July) and an average month (June). The results show how irrigation prevented the drying out of the soil layers during the heatwave. This influences the surface flux partition differently, by increasing moisture flux and decreasing the sensible heat flux. In general, the irrigation impact magnitude, with respect to the control simulation, is more than double in July compared to June. This study discusses climate implications for the region, such as the impact of widespread irrigation on the vegetation health, the heatwave feedback mechanism, atmospheric pollution, and human heat discomfort.

Critical heat fluxes for subcooled flow boiling in optimised microchannels

Critical heat fluxes (departure from nucleate boiling, DNB) for optimised rectangular microchannels were computed by carrying out simulations using computational fluid dynamics (CFD, ANSYS) non-equilibrium boiling model (the model is an extension of heat flux partitioning model for modelling up to departure from nucleate boiling) for subcooled flow boiling, at velocity ranges of 1.0-1.5 and 1.5-2.0 m/s and heat fluxes of 300 to 500 W/cm2. The flow was highly subcooled at inlet temperature of 25°C using deionised water as the cooling fluid and aluminium as the heat sink material. The results showed that the microchannels can be operated beyond the heat fluxes that they were optimised, up to their critical heat fluxes before the onset of departure from nucleate boiling or CHF. The numerical code for heat flux partitioning model (RPI) was validated by the available experimental data and the agreement showed the capability of the model to predict accurately subcooled flow boiling in microchannels.

Simulation of pool boiling of nanofluids by using Eulerian multiphase model

In the present work, a new simulation of nanofluid/vapor two-phase flow inside the 2-D rectangular boiling chamber was numerically investigated. The Eulerian–Eulerian approach used to predict the boiling curve and the interaction between two phases. The surface modification during pool boiling of silica nanofluid represented by surface roughness and wettability is put into the account in this simulation. New closure correlations regarding the nucleation sites density and bubble departure diameter during boiling of silica nanofluid were inserted to extend the boiling model in this work. Besides, the bubble waiting time coefficient which involved in quenching heat flux under heat flux partitioning HFP model was corrected to improve the results of this study. The numerical results validated with experimental works in the literature, and they revealed good agreements for both pure water and nanofluids. The results found that when improving the heat flux partitioning model HFP by considering the surface modification of nucleate pool boiling parameters, it will give more mechanistic sights compared to the classical model, which is used for predicting of boiling heat transfer of pure liquid.

Modeled Land Atmosphere Coupling Response to Soil Moisture Changes with Different Generations of Land Surface Models

An idealized study with two land surface models (LSMs): TERRA-Multi Layer (TERRA-ML) and Community Land Model (CLM) alternatively coupled to the same atmospheric model COSMO (Consortium for Small-Scale Modeling), reveals differences in the response of the LSMs to initial soil moisture. The bulk parameterization of evapotranspiration pathways, which depends on the integrated soil moisture of active layers rather than on each discrete layer, results in a weaker response of the surface energy flux partitioning to changes in soil moisture for TERRA-ML, as compared to CLM. The difference in the resulting surface energy flux partitioning also significantly affects the model response in terms of the state of the atmospheric boundary layer. For vegetated land surfaces, both models behave quite differently for drier regimes. However, deeper reaching root fractions in CLM align both model responses with each other. In general, differences in the parameterization of the available root zone soil moisture, evapotranspiration pathways, and the soil-vegetation structure in the two LSMs are mainly responsible for the diverging tendencies of the simulated land atmosphere coupling responses.

Ability of a soil–vegetation–atmosphere transfer model and a two-source energy balance model to predict evapotranspiration for several crops and climate conditions

Abstract. The heterogeneity of Agroecosystems, in terms of hydric conditions, crop types and states, and meteorological forcing, is difficult to characterize precisely at the field scale over an agricultural landscape. This study aims to perform a sensitivity study with respect to the uncertain model inputs of two classical approaches used to map the evapotranspiration of agroecosystems: (1) a surface energy balance (SEB) model, the Two-Source Energy Balance (TSEB) model, forced with thermal infrared (TIR) data as a proxy for the crop hydric conditions, and (2) a soil–vegetation–atmosphere transfer (SVAT) model, the SEtHyS model, where hydric conditions are computed from a soil water budget. To this end, the models' skill was compared using a large and unique in situ database covering different crops and climate conditions, which was acquired over three experimental sites in southern France and Morocco. On average, the models provide 30 min estimations of latent heat flux (LE) with a RMSE of around 55 W m−2 for TSEB and 47 W m−2 for SEtHyS, and estimations of sensible heat flux (H) with a RMSE of around 29 W m−2 for TSEB and 38 W m−2 for SEtHyS. A sensitivity analysis based on realistic errors aimed to estimate the potential decrease in performance induced by the spatialization process. For the SVAT model, the multi-objective calibration iterative procedure (MCIP) is used to determine and test different sets of parameters. TSEB is run with only one set of parameters and provides acceptable performance for all crop stages apart from the early growing season (LAI < 0.2 m2 m−2) and when hydric stress occurs. An in-depth study on the Priestley–Taylor key parameter highlights its marked diurnal cycle and the need to adjust its value to improve flux partitioning between the sensible and latent heat fluxes (1.5 and 1.25 for France and Morocco, respectively). Optimal values of 1.8–2 were highlighted under cloudy conditions, which is of particular interest due to the emergence of low-altitude drone acquisition. Under developed vegetation (LAI > 0.8 m2 m−2) and unstressed conditions, using sets of parameters that only differentiate crop types is a valuable trade-off for SEtHyS. This study provides some scientific elements regarding the joint use of both approaches and TIR imagery, via the development of new data assimilation and calibration strategies.

Numerical investigation of two-phase flow in a horizontal porous evaporator with localised heating using non-Darcian flow and two equations model

In this article, a new mathematical model, based on the modified enthalpy formulation of Two-Phase Mixture Model (TPMM), is developed by considering non-Darcy flow and Local Thermal Non-Equilibrium (LTNE) conditions to describe numerically the two-dimensional problems of the complete evaporation process inside an asymmetrically heated porous evaporator. The governing equations have been discretised using Finite Volume Method (FVM) on a fixed non-staggered grid layout. The in-house code has been validated against experimental data and the results show good agreement between them. Three different models have been employed for the partitioning of the wall heat flux. Only the effect of the heat flux has been analysed, while all other parameters and properties have been kept fixed during the present investigation. The numerical simulations indicated that the locally high heat flux significantly influences the working fluid flow performances, and lead to extend the superheated vapour region towards the exit of the evaporator. The results also show that the two-phase zone significantly expanded in the axial direction and does not occupy a large portion inside the channel due to the energy transport through the two-phase region is significantly higher in the flow direction as compared to the transverse direction, caused by the decrease in the effective diffusion coefficient in this region and higher axial velocity. Numerical analysis reveal that the different models for the partitioning of the wall heat flux have almost no influence on the overall predictions, except in the vicinity of the wall. The results clearly demonstrate that the numerical simulations with the modified h-formulation by considering non-Darcy law and LTNE model are indispensable for the problem of complete evaporation process, particularly under the high both heat flux and inlet velocity conditions.

Impact of a Multi‐Layer Snow Scheme on Near‐Surface Weather Forecasts

AbstractSnow cover properties have a large impact on the partitioning of surface energy fluxes and thereby on near‐surface weather parameters. Snow schemes of intermediate complexity have been widely used for hydrological and climate studies, whereas their impact on typical weather forecast time scales has received less attention. A new multilayer snow scheme is implemented in the European Centre for Medium‐range Weather Forecasts Integrated Forecasting System and its impact on snow and 2‐m temperature forecasts is evaluated. The new snow scheme is evaluated offline at well‐instrumented field sites and compared to the current single‐layer scheme. The new scheme largely improves the representation of snow depth for most of the sites considered, reducing the root‐mean‐square error averaged over all sites by more than 30%. The improvements are due to a better description of snow density in thick and cold snowpacks, but also due to an improved representation of sporadic melting episodes because of the inclusion of a thin top snow layer with a low thermal inertia. The evaluation of coupled 10‐day weather forecasts shows an improved representation of snow depth at all lead times, demonstrating a positive impact at the global scale. Regarding the impact on weather parameters, the multilayer snow scheme improves the simulated minimum 2‐m temperature, by decreasing the positive bias and improving the amplitude of the diurnal cycle over snow‐covered regions. However, the increased variability of the 2‐m temperature can have a detrimental impact in regions characterized by preexisting errors in the daily mean temperature, associated with errors in cloud processes or surface albedo.

A Recent Systematic Increase in Vapor Pressure Deficit over Tropical South America

We show a recent increasing trend in Vapor Pressure Deficit (VPD) over tropical South America in dry months with values well beyond the range of trends due to natural variability of the climate system defined in both the undisturbed Preindustrial climate and the climate over 850–1850 perturbed with natural external forcing. This trend is systematic in the southeast Amazon but driven by episodic droughts (2005, 2010, 2015) in the northwest, with the highest recoded VPD since 1979 for the 2015 drought. The univariant detection analysis shows that the observed increase in VPD cannot be explained by greenhouse-gas-induced (GHG) radiative warming alone. The bivariate attribution analysis demonstrates that forcing by elevated GHG levels and biomass burning aerosols are attributed as key causes for the observed VPD increase. We further show that There is a negative trend in evaporative fraction in the southeast Amazon, where lack of atmospheric moisture, reduced precipitation together with higher incoming solar radiation (~7% decade−1 cloud-cover reduction) influences the partitioning of surface energy fluxes towards less evapotranspiration. The VPD increase combined with the decrease in evaporative fraction are the first indications of positive climate feedback mechanisms, which we show that will continue and intensify in the course of unfolding anthropogenic climate change.

The eddy-covariance storage term in air: Consistent community resources improve flux measurement reliability

In the widely-used eddy-covariance (EC) technique, it is often assumed that the air storage term, i.e. the change of below-turbulence-sensor scalar abundance, is negligible or comprises a small part of net surface-atmosphere exchange (NSAE). Previous studies have demonstrated that this assumption is often violated where non-turbulent processes prevail, and thus it is important to measure and calculate air storage in flux measurements. However, the implementation of air storage measurement and calculation is not ubiquitous as EC standard turbulent flux. In most cases, air storage is not a standard data product or even neglected in EC flux tower measurements. In other cases, air storage term is calculated simply using only the measurements at the tower top. This gap between the ideal initiative and actual implementation motivates us to derive and release one of the first community resources to facilitate the consistent measurement and calculation of EC air storage across sites. These resources include (i) the standardized air storage term measurement setup design at National Ecological Observatory Network (NEON) sites; (ii) the development and public release of the eddy4R.stor open-source air storage R-package; (iii) the derivation and public release of storage term data products, measured and calculated consistently across 47 NEON sites; and (iv) exploration the scientific usefulness of these resources through example use cases, specifically the exploration of the bias of the air storage term when different measurement level intensity used and exploration of the air storage term pattern. We expect the consistent air storage measurement and calculation can better serve the overall purpose of the EC technique to provide more reliable measurement of NSAE for the community. This can further benefit the community accurate depiction of the sub-daily to diurnal cycle of surface fluxes in doing carbon cycle flux partitioning, land modeling, and studying ecosystem response to weather extremes.

Investigating effects of heating orientations on nucleate boiling heat transfer, bubble dynamics, and wall heat flux partition boiling model for pool boiling

Studying the nucleate pool boiling is an important research in the thermal science. Therefore, the pool boiling experiments are performed in this paper to investigate the effects of heating orientations on the characteristics of boiling heat transfer and bubble dynamics. Based on the measured data, the boiling heat transfer capability increases as the inclined angle of heating surface is elevated. This enhanced effect is pronounced in the lower heat flux region and is insignificant in the higher heat flux region, which is also reported in the previous works. The characteristics of bubble growth, departure, sliding, and coalescence as well as the corresponding timings can be clearly revealed in the frames taken from the high-speed videos. Based on the measurement and observation, the merged bubble diameter and departure frequency increase with the increasing heating orientation. However, the active nucleate site density is measured to be independent of the inclined angles. The relationship of bubble dynamics with the wall superheat and the heating orientation can be obtained using the least-square-error regression method. With the input of these regressed correlations, the wall heat flux partitioning model can be assessed with the present measured boiling curves under various heating orientations. Good agreement reveals that the measured results and the corresponding regression equations provided herein can assist in validation of other boiling heat transfer models. This is one of main contributions from the present work in addition to providing additional data to understand the boiling characteristics of pool boiling under variable heating orientations.

Sedimentary Organic Carbon Budget Across the Slope to the Basin in the Southwestern Ulleung (Tsushima) Basin of the East (Japan) Sea

AbstractWith the total sediment oxygen uptake rates measured using an in situ benthic chamber, vertical distributions of organic carbon, and sedimentation rates estimated by excess 210Pb across the slope to the basin sediment of the southwestern region of the Ulleung (Tsushima) Basin (UB), the partitioning of organic carbon fluxes in the sediment was estimated to understand the biogeochemical cycles of organic carbon in the high productivity marginal sea. The results of depth attenuation of total oxygen uptake (TOU) demonstrate that the organic carbon oxidation of the UB sediment was 2.5 times higher than that obtained from the empirical relationship of the global's depth attenuation of TOU. Similar to TOU, the high mass accumulation rates observed in the slope region were 9.5 times higher than the rate in the basin, indicating that the slope may act as the depocenter of organic carbon. The organic carbon budget with water depth gradient implies that a significant fraction of the organic carbon deposited into sediment is supplied by lateral transport down the slope. Definite increasing C/N ratio with water depth indicates that the refractory organic carbon seems to be successively transported later from shelf to slope. The total burial flux in the sediment of southwestern UB was estimated to be 0.46±0.04 Tg C/year, which is similar to the megadepocenter of the Congo River fan. Our results imply that the UB sediment may be an important biogeochemical reaction place not only for organic carbon but also materials linked to primary production.

Correlation-based flux partitioning of water vapor and carbon dioxide fluxes: Method simplification and estimation of canopy water use efficiency

The partitioning of water vapor and carbon dioxide (CO2) exchange between vegetation and the atmosphere remains a current research priority. A technique that has been proposed to simultaneously partition these fluxes, based on the correlation between their high-frequency concentration time series, has been the subject of recent empirical evaluations and theoretical advances. The method assumes that flux-variance similarity can be applied separately to stomatal exchange (transpiration for water vapor and net photosynthesis for CO2) and non-stomatal exchange (direct evaporation for water vapor and soil and stem respiration for CO2). Here, we present a mathematical simplification of this approach, from which the partitioned fluxes can be derived from routine eddy covariance measurements. The simplification arises from the fact that the transpiration and net photosynthesis fluxes are linearly related in solution space with respect to variable canopy water use efficiency, W. Conditions that are amenable to successful partitioning can now be determined a priori for a given averaging period. The simplified framework also has the benefit of providing a means for estimating W based on optimization theory. This allow for the estimation of W without any preconceptions of how the intercellular CO2 concentration, ci, varies as a function of ambient conditions. The simplified partitioning framework is applied to eddy covariance measurements collected over a mixed deciduous forests for three growing season. Aside from being more computationally efficient, the partitioned results exhibit less scatter compared with prior implementations.

Drainage water management effects on energy flux partitioning, evapotranspiration, and crop coefficients of corn

Over the past 20 years, marketplace demand for corn has prompted many farmers in the Red River Valley (RRV) of the north to include more corn in their crop rotations. With a very flat topography and heavy clayey soils, the RRV can have shallow water tables in the spring and fall but can be dry in the summer. Due to these field conditions, some farmers have installed subsurface drainage (SD) systems with structures for controlled drainage (CD, manage the water table in a field) and subirrigation (SI, add water to the field via the SD system) to improve corn production. In a CD + SI field, an eddy covariance system was used to measure and quantify energy flux components along with soil moisture content (SWC) and water table depth (WTD) measurements during four corn growing seasons in 2012, 2013, 2016 and 2017. The results show that the average SWC in 2012 was significantly different from the other three years. The SWC and WTD in 2016 were more stable compared to the other years. The CD practice had a positive effect during a wet year in 2013, which resulted in 26.7% higher yield than the county average. During the dry growing season of 2017, the use of subirrigation resulted in 6.6% higher yield than the county average. The corn evapotranspiration totals (ETa) were 468, 476, 551, and 537 mm for 2012, 2013, 2016, and 2017 growing seasons, respectively. The average crop coefficients were 0.49, 0.73, 0.88, 0.86, and 0.69 for the initial, development, tasseling, reproductive, and maturity stages, respectively. They were calculated from the daily ETa, values only from days with more than 45% of total available water in the root zone, and the ASCE-EWRI standardized grass-based reference evapotranspiration. This study showed that the SD along with the CD + SI system can be used for optimal water management of field corn during both wet and dry years.

Quantifying the impact of tissue metabolism on solute transport in feto-placental microvascular networks.

The primary exchange units in the human placenta are terminal villi, in which fetal capillary networks are surrounded by a thin layer of villous tissue, separating fetal from maternal blood. To understand how the complex spatial structure of villi influences their function, we use an image-based theoretical model to study the effect of tissue metabolism on the transport of solutes from maternal blood into the fetal circulation. For solute that is taken up under first-order kinetics, we show that the transition between flow-limited and diffusion-limited transport depends on two new dimensionless parameters defined in terms of key geometric quantities, with strong solute uptake promoting flow-limited transport conditions. We present a simple algebraic approximation for solute uptake rate as a function of flow conditions, metabolic rate and villous geometry. For oxygen, accounting for nonlinear kinetics using physiological parameter values, our model predicts that villous metabolism does not significantly impact oxygen transfer to fetal blood, although the partitioning of fluxes between the villous tissue and the capillary network depends strongly on the flow regime.