Hot Spot Effect Research Articles

The use of hydronic asphalt pavements as an alternative method of eliminating hot spots of underground power cables

It is well-known that a Hydronic Asphalt Pavement (HAP) system represents an alternative method to collect heat from the Sun. In case of installation above underground power cables whose trench is completely filled with high thermal conductivity bedding, the HAP system could also collect a portion of heat generated in the cables. By collecting heat from the Sun and cables, the HAP would behave as a cooler for the cables. The application of this method to a hot spot of underground power cables is regarded as a novelty. This paper considers the use of the proposed method for eliminating the negative thermal effect of an actual hot spot on the ampacity of a 110 kV cable line, which is installed in parallel with the group of four 35 kV cables and which crosses an underground heating pipeline. The mutual thermal effects between the underground installations are simulated using FEM-based models for specified environmental conditions. In addition, an appropriate experimental background, one reference FEM-based model and two required base cases are provided. Finally, it is found that the hot spot effect can be completely eliminated and that the ampacities of the 110 kV and 35 kV cables can be increased significantly.

A semi-empirical approach for modeling the vegetation thermal infrared directional anisotropy of canopies based on using vegetation indices

Measurements of the surface thermal infrared (TIR) radiance provides an estimate of the land surface temperature (LST). However, any TIR measurement must be acquired under a certain geometry observation, which may refer to strong directional anisotropies. Although physical radiative transfer models can provide high precision directional brightness temperature simulation, they are too complex for processing large volumes of satellite data. With the objective to compare TIR measures acquired under different viewing angles, the topic of angular normalization issue for retrieved LSTs could be treated based on semi-empirical modelling. In this paper, we consider such category of models to simulate the directional anisotropy of surface brightness temperatures in combination with visible and near-infrared (VNIR) data. In these models, the vegetation fraction and the hot spot effect are depicted by a vegetation index and a brightness factor, respectively. An evaluation of the method is performed with both synthetic and measured datasets. The directional anisotropies that are fitted by this semi-empirical model demonstrate good agreement with an extensive synthetic dataset that is generated with the Soil Canopy Observation, Photochemistry and Energy Fluxes (SCOPE) soil-vegetation-atmosphere transfer model. An evaluation using airborne multi-angle TIR data also reveals that this model performs well when predicting BT directional anisotropies, with root mean square errors (RMSEs) of less than 0.31 °C over a maize-planted area. Relative to Roujean-Lagouarde (RL) and Vinnikov models using only TIR data, the proposed model offers better performances. In addition, for future use with satellite data, the proposed model using observations at different times and the combination with VNIR BRDF model are also evaluated, and good results are obtained. It yields a promising approach for the angular normalization of LST and mosaics of fine-scale images.

Effects of human-made resource hotspots on seasonal spatial strategies by a desert pitviper

Habitat heterogeneity and local resource distribution play key roles in animal search patterns. Optimal strategies are often considered for foraging organisms, but many of the same predictions are applicable to mate searching. We quantified movement and space use by a pitviper to test whether Native Habitats (NH) and human-made Resource Hotspots (RH) facilitate alternative seasonal spatial strategies as a result of critical resources, including potential mating partners, being widely dispersed in NH and clustered in RH. Independent of habitat category, seasonal patterns resembled an intermediate mating system with elements of prolonged male mate-searching and female-defense. However, individuals using primarily NH or RH exhibited alternative strategies. NH rattlesnakes displayed greater movement and larger home ranges than RH rattlesnakes across behavioral seasons. NH males increased movement distances and home ranges during the mating season, while RH males displayed minimal or no seasonal shifts. NH females also elevated movement distances during the mating season, while RH females showed no significant seasonal differences. Despite contrasting spatial patterns, mating success and female-defense effort were not significantly affected by habitat category. This unique study system highlights the potential for interactions among sexual selection, habitat heterogeneity, and behavioral plasticity to facilitate divergent search tactics within populations.

Eliminating the effect of hot spots on underground power cables using cool pavements

It is well known that hot spots limit the ampacities of underground power cables. There are many commonly applied methods to control the thermal environment in hot spots of underground power cables. However, applications of cool pavements for this specific purpose would be a novelty in the field of power cable engineering. This paper considers the use of different cool pavements in combination with thermally stable bedding and/or pure quartz sand for mitigating or eliminating the thermal effect of an actual hot spot on the ampacities of a 110 kV cable line and a group of four 35 kV three-core cables installed in Belgrade, the Republic of Serbia. In the hot spot, the 110 kV cable line is installed in parallel with the group of 35 kV cables and crosses a district heating pipeline. All distances between these underground installations are lower than the recommended ones, and the 110 kV and 35 kV cables are laid at depths greater than required. The mutual thermal effects between the underground installations in the hot spot are simulated using FEM-based models for different environmental conditions. An experimental background is also provided. In comparison with the corresponding base cases, it has been found that the ampacities of the 110 kV cable line and group of 35 kV cables can be increased up to 25.1% and 60.9% in summer, and up to 62.8% and 170% in winter, respectively.

Long-range ordered silver nanoflower array structure for surface enhanced Raman scattering detecting

Surface enhanced Raman spectroscopy (SERS) is a key nondestructive detecting technology with a broad application demands. However, relative low stability and homogeneity of the SERS substrate hinder its practical applications. Here, a simple and flexible approach is proposed to achieve the arrayed SERS substrates with the periodicity and local randomness by directly growing silver nanoflowers on the patterned wafer fabricated by the optical interference method. By utilizing the hotspot effect of nanogaps within/between the Ag nanoflowers, the SERS substrates demonstrate the low detecting limit of 5 × 10−10 M and 5 × 10−9 M in one-dimensional (1D) and two-dimensional (2D) pattern structures for Rhodamine 6G (R6G) probe molecule, respectively. The periodicity assures the fabricated substrate a promising reproducibility and stability. After the 1D array structure is left for 21 days, the intensity of Raman signal of R6G maintains at 80%. Moreover, the proposed method has the advantages of simple preparation, low cost, flexible tunability, and easy-fabrication large scale substrate. The results indicate that the long-range ordered silver nanoflower array structures are promising candidates for the high performance SERS substrate in chemical analysis, medicine and environment monitoring.

Optimization of water-emulsified diesel preparation and comparison of mechanical homogenization and ultrasonic dispersion methods to study CI engine performances

ABSTRACT In this study, the stability of water-emulsified diesel (WED) prepared by different methods have been analyzed. In first phase, the optimum condition of Hydrophilic-Lipophilic Balance (HLB) value of the surfactant used for the preparation of emulsified diesel with respect to its stability has been determined. Different resultant HLB values have been obtained by mixing two surfactants in different proportion. The highest emulsion stability (ES) is found for WED prepared with the surfactant mixture of HLB value 8 which is obtained by mixing 65.5% Span 80 and 34.5% Tween 80. In second phase, WEDs containing 10% water and 2% surfactant mixture with resultant HLB value 8 have been prepared using mechanical homogenization as well as ultrasonication methods. In third phase, the emulsions are prepared adding 10, 20, and 30% water and 2% surfactant mixture with resultant HLB value 8 using ultrasonication process. The emulsion mixture has been kept in a cooled water bath to minimize hot spot effect during ultrasonication process. The polydispersity index (PDI), water particle size and auto correlation factor (ACF) of all four prepared WEDs have been measured by nano particle analyzer which works on dynamic light scattering (DLS) technique. These properties of the WEDs have been analyzed to investigate their stability behavior of the emulsion. Experimental investigations have also been carried out on performance and emission characteristics of a single cylinder, four-stroke diesel engine using WED prepared by both methods containing 10% water. At full load, the brake thermal efficiency is found to be marginally higher using emulsified diesel prepared using ultrasonicator compared to base diesel. The NOx and smoke emissions have been found to be lower for both types of emulsified diesel than pure diesel. The experimental results show more favorable emulsification, performance and emission characteristics for the emulsified diesel prepared by ultrasonic machine than that prepared by mechanical homogenizer. The density, viscosity, and calorific value of the emulsions prepared by the two methods have also been measured and compared with that of neat diesel.

Reduced-resolution RANS approach to grid spacer fuel assemblies

One of the main issues in the context of the safety assessment of liquid metal-cooled reactors is flow blockages in fuel sub-assemblies. CFD modelling may be used to predict the temperature and velocity fields inside a fuel assembly under blocked and unblocked conditions. However, the computational cost requirements make it infeasible to model the complete assembly using the resolved RANS, LES or DNS approaches. To this end, a reduced-resolution RANS approach of an assembly is presented and validated in this paper.In order to reproduce and compare with experimental data, the 19-pin hexagonal fuel assembly of the NACIE-UP facility at ENEA in Italy has been selected for the present simulation study. For the flow blockage, a 6-pin edge-type blockage is selected similar to that used in the experimental facility. During the pre-test simulation study, wall-resolved RANS simulations are performed for the unblocked flow conditions. Using the wall-resolved RANS simulations as reference, a mesh sensitivity is performed by subsequently reducing the wall and bulk resolutions. As the blocked flow condition requires transient simulations, the resolution study is only performed for the unblocked flow condition to reduce the computational effort. It is shown that the approach may be used to reproduce the temperature and velocity fields similar to that in wall-resolved simulations within tolerance limits, but at a fraction of the computational cost.Experimental data for unblocked and blocked flow conditions has been made available for the Blocked Fuel Pin Simulator (BFPS) section at the NACIE-UP facility. These experimental data are used to validate the reduced-resolution approach in the post-test analysis. The difference between the present results and the experimental data is attributed for and quantified. Consistent with the literature, two main effects of flow blockages are identified. A local temperature hotspot is observed in the wake of the blockage caused by the coolant recirculation zone. The global effect of temperature peak is observed at the end of the active length downstream of the blockage, caused by the lower mass flow rates in the blocked sub-channels. For the unblocked flow condition, the maximum difference compared to the experimental data is estimated to be 11%. While the error in prediction of the local temperature hotspot and peak temperature at the end of active length is estimated to be 25% and 12%, respectively, for the partially-blocked flow condition. Finally, based on the 19-pin model, the feasibility of the reduced-resolution approach for the complete 127-pin assembly of ALFRED demo reactor is demonstrated. In addition to the unblocked flow condition, the approach is also used for blocked grid spacer conditions. Consistent with the results of NACIE bundle, the two main effects – local and global – of the flow blockage are also observed here. The local effect of temperature hotspot behind the blockage is observed to be dominant for the larger blockage, while the global effect of peak temperature downstream of the blockage is observed to be proportional to the size of the flow blockage.

Assessment of the Hotspot Effect for the PROSAIL Model With POLDER Hotspot Observations Based on the Hotspot-Enhanced Kernel-Driven BRDF Model

The hotspot effect is a typical angular reflectance signature of vegetation canopies and contains important information for the retrieval of vegetation structural parameters. To date, the hotspot effect of various analytical bidirectional reflectance distribution function (BRDF) models (e.g., the PROSAIL model) has rarely been assessed by multiangular measurements with sufficient hotspot observations due to the lack of accurate hotspot measurements (for field measurements) or appropriate methods (for airborne and spaceborne measurements). In this paper, we develop a method to further improve the hotspot effect of the kernel-driven model and design a framework to utilize the improved kernel-driven model as a bridge to assess the hotspot effect of the PROSAIL model with Polarization and Directionality of the Earth Reflectance (POLDER) hotspot observations. The results indicate that the proposed method further improves the fits between the models and the observations in the vicinity of the hotspot direction, particularly in the rare situations where the geometric-optical scattering component governs the target reflectance. In addition, the hotspot signature indicated by the PROSAIL multiangular data shows a larger variability than that of POLDER observations. $C_{1}$ and $C_{2}$ in the improved kernel-driven model can be used as benchmarked parameters to qualify the amplitude and width of the hotspot effect for the simulated multiangular data of physical BRDF models and thus present the potential for the assessment and analysis of the hotspot effect of physical models, which, in return, helps retrieve the structural parameters of vegetation canopies from hotspot signatures.

Tunable Coffee Ring Formation on Polycarbonate Nanofiber Film for Sensitive SERS Detection of Phenylalanine in Urine.

A new method based on the coffee ring effect was developed for improving the sensitivity, simplicity, and robustness of surface-enhanced Raman scattering (SERS) in determining trace levels of analytes. In this method, a polyvinylpyrrolidone (PVP)-stabilized silver colloidal (AgC) solution was first prepared and mixed with a sample solution. Following deposition of the mixture solution on a solid substrate with a rough surface, a coffee ring was formed once the solvent had evaporated. The formation of a coffee ring not only concentrated the analyte but also reduced the space between silver nanoparticles (AgNPs) to strengthen the hotspot effect, thereby considerably improving SERS sensitivity. To strengthen the coffee ring effect further, the surface roughness of the solid support and PVP content of the AgC solution were investigated. The results indicated that an increase in surface roughness reduced the size of the coffee rings, whereas the addition of PVP not only stabilized the AgNPs but also improved the compactness of the coffee rings. When applying the proposed method to determine the phenylalanine (Phe) level in urine for rapid screening of the phenylketonuria disorder, strong chemical interference from uric acid (UA), which is a major component in urine, was observed. To minimize the interference from UA, ZnO powder was applied to the urine sample to adsorb UA prior to SERS detection. After cleaning by using ZnO, the SERS signals of Phe were revealed for quantitative purposes. Under the optimized conditions, both the sensitivity and reproducibility of SERS measurement considerably improved. Quantitative analyses revealed that the developed method is highly feasible for the rapid determination of Phe in real samples.

Hot spots policing of small geographic areas effects on crime.

In recent years, crime scholars and practitioners have pointed to the potential benefits of focusing crime prevention efforts on crime places. A number of studies suggest that there is significant clustering of crime in small places, or "hot spots," that generate half of all criminal events. Researchers have argued that many crime problems can be reduced more efficiently if police officers focused their attention to these deviant places. The appeal of focusing limited resources on a small number of high-activity crime places is straightforward. If crime can be prevented at these hot spots, then citywide crime totals could be reduced. To assess the effects of focused police crime prevention interventions at crime hot spots. The review also examined whether focused police actions at specific locations result in crime displacement (i.e., crime moving around the corner) or diffusion (i.e., crime reduction in surrounding areas) of crime control benefits. A keyword search was performed on 15 abstract databases. Bibliographies of past narrative and empirical reviews of literature that examined the effectiveness of police crime control programs were reviewed and forward searches for works that cited seminal hot spots policing studies were performed. Bibliographies of past completed Campbell systematic reviews of police crime prevention efforts were reviewed and hand searches of leading journals in the field were completed. Experts in the field were consulted and relevant citations were obtained. To be eligible for this review, interventions used to control crime hot spots were limited to police-led prevention efforts. Suitable police-led crime prevention efforts included traditional tactics such as directed patrol and heightened levels of traffic enforcement as well as alternative strategies such as aggressive disorder enforcement and problem-oriented policing. Studies that used randomized controlled experimental or quasiexperimental designs were selected. The units of analysis were limited to crime hot spots or high-activity crime "places" rather than larger areas such as neighborhoods. The control group in each study received routine levels of traditional police crime prevention tactics. Sixty-five studies containing 78 tests of hot spots policing interventions were identified and full narratives of these studies were reported. Twenty-seven of the selected studies used randomized experimental designs and 38 used quasiexperimental designs. A formal meta-analysis was conducted to determine the crime prevention effects in the eligible studies. Random effects models were used to calculate mean effect sizes. Sixty-two of 78 tests of hot spots policing interventions reported noteworthy crime and disorder reductions. The meta-analysis of key reported outcome measures revealed a small statistically significant mean effect size favoring the effects of hot spots policing in reducing crime outcomes at treatment places relative to control places. The effect was smaller for randomized designs but still statistically significant and positive. When displacement and diffusion effects were measured, a diffusion of crime prevention benefits was associated with hot spots policing. The extant evaluation research suggests that hot spots policing is an effective crime prevention strategy. The research also suggests that focusing police efforts on high-activity crime places does not inevitably lead to crime displacement; rather, crime control benefits may diffuse into the areas immediately surrounding the targeted locations.

Heating Behavior of Photovoltaic Panels and Front Side Water Cooling Efficiency

The use of solar energy is very promising for favorable Sun Belt countries. However, in these regions the hot climate leads to high temperatures which conduct to significant power losses in photovoltaic panels. In this paper we study the heating behavior of photovoltaic panels and front side water cooling efficiency. A standalone cooling system is designed as prototype which helps to proposal for a methodology for large-scale application through energy estimation of this system. Two typical situations were studied: the first one with a uniform distribution of the temperature and the second one with a non-uniform distribution of temperature under partial shadowing leading to hot spot effect. The gain in electrical power with cooling is about 45% in the case of a non-uniform distribution compared to 12% in the case of a uniform distribution at 30°C outdoor temperature. It was also noticed that temperature on hot spot point depends of the shadow type (direct and indirect). The estimation of the supplement of energy obtained from the cooling system demonstrates that the cooling system used in this study will be beneficial with using of string of PV panels with a minimum of three panels. This makes the autonomous cooling system very efficient.

Mitigating Hotspot Issue in WSN Using Sensor Nodes with Varying Initial Energy Levels and Quantification Algorithm

Abstract A typical Wireless Sensor Network (WSN) uses multihop communication rather than direct transmission. In a multi-hop communication, the sensor node communicates the sensed data to its neighbor node, which is comparatively closer to the sink and the receiving node will forward the data to its neighbor node. This process continues until the data reaches the sink. Due to the multihop communication, the nodes closer to the sink have to transmit and receive more data and control packets compared to other nodes. Hence, the nodes closer to sink may deplete their energy at a faster rate and may die soon. This may create network isolation. This issue is called as the Hotspot problem. In this paper, we are proposing a Quantification algorithm for Sensor Nodes with varying Initial Energy Level to mitigate the Hotspot effect.

Hot spots policing and crime reduction: an update of an ongoing systematic review and meta-analysis

This updated systematic review assesses the effects of focused police crime prevention interventions at crime hot spots. The review also examined whether focused police actions at specific locations result in crime displacement or diffusion of crime control benefits. Systematic review protocols and conventions of the Campbell Collaboration were followed to identify eligible hot spots policing studies, and meta-analytic techniques were used to assess the impact of hot spots policing on crime and investigate the influence of moderating variables. The search strategies identified 65 studies containing 78 tests of hot spots policing interventions. Meta-analyses revealed a small statistically significant mean effect size favoring the effects of hot spots policing in reducing crime outcomes at treatment places relative to control places. Crime displacement and diffusion effects were measured in 40 tests. Meta-analyses favored a small statistically significant diffusion of crime control benefits over displacement. The extant evaluation research provides fairly robust evidence that hot spots policing is an effective crime prevention strategy. Focused police intervention at hot spot locations does not seem to result in the spatial displacement of crime into areas immediately surrounding targeted locations. Rather, crime control benefits seem to diffuse into proximate areas.

PV-Battery Hybrid System with Less AH Capacity for Standalone DC Loads

Abstract Partial Shading Condition (PSC) is one of the key issues faced by Solar Photovoltaic (PV) systems. PSCs mainly occur due to clouds, shadows of trees/buildings, dust and so on. During the PSC, the shaded PV module acts like a sink and absorbs the power from highest irradiated modules in a string and leads to hotspot. This situation is highly vulnerable and has to be avoided. Bypass diodes are used in series configured PV modules to overcome the hotspot effect caused due to PSC. However, the use of bypass diodes leads to multiple peaks in the Power-Voltage (P-V) graph of a PV array. One among them is Global peak point, where PV array needs to operate under PSC. In such a case, some amount of power generated by the shaded modules gets wasted, which will lead to poor performance and efficiency of the overall system. Moreover, for standalone DC load applications an auxiliary supply also required to provide reliable supply to the load during night times and PSC. Normally, batteries are used in standalone systems as an auxiliary supply. To control the charging and discharging process of battery a bi-directional DC-DC converter is used as a charge/discharge controller. The amount of power that is being charged/discharged by batteries depends upon the load requirement and solar power availability. Under PSC, due to lack of extraction of PV power from shaded modules, batteries have to supply the deficient power to the load. This situation forces to increase the AH capacity of the battery to provide reliable supply. In this research article PV-Battery Hybrid system is proposed to improve the performance of PV under varying irradiance and load conditions with reduced AH capacity of battery for standalone DC loads. The performance assessment of proposed topology has been carried out with the comparison of percentage improvement in power extraction, percentage reduction in the average current consumption of battery and SoC delivered by battery with conventional methodologies of bypass diode and proposed methodology under PSC. The assessment is carried out on MATLAB/SIMULINK and results are presented.

Anisotropic characteristic of artificial light at night – Systematic investigation with VIIRS DNB multi-temporal observations

The released VIIRS DNB nightly images, also known as VIIRS DNB daily nighttime images, provide rich information for time series analysis of global socioeconomic dynamics. Anisotropic characteristic is a possible factor that influences the VIIRS DNB radiance at night and its time series analysis. This study aims to investigate the relationship between viewing angles and VIIRS DNB radiance of Suomi NPP satellite in urban areas. First, twenty-nine points were selected globally to explore the angle variation of Suomi NPP satellite views at night. We found that the variation of the satellite viewing zenith angle (VZA) is consistent (e.g. between 0° and 70°) since the range of VZA is fixed depending on the sensor design, and the range of viewing azimuth angle (VAA) increases with the increase of latitude. Second, thirty points in cities of Beijing, Houston, Los Angeles, Moscow, Quito and Sydney, were used to investigate the angle-radiance relationship. We proposed a zenith-radiance quadratic (ZRQ) model and a zenith-azimuth-radiance binary quadratic (ZARBQ) model to quantify the relationship between satellite viewing angles and artificial light radiance, which has been corrected by removing the moonlight and atmospheric impact from VIIRS DNB radiance products. For all the thirty points, the ZRQ and ZARBQ analysis have averaged R2 of 0.50 and 0.53, respectively, which indicates that the viewing angles are important factors influencing the variation of the artificial light radiance, but extending zenith to zenith-azimuth does not much better explain the variation of the observed artificial light. Importantly, based on the data analysis, we can make the hypothesis that building height may affect the relationship between VZA and artificial light, and cold and hot spot effects are clearly found in tall building areas. These findings are potentially useful to reconstruct more stable time series VIIRS DNB images for socioeconomic applications by removing the angular effects.

Study on decolorization of Rhodamine B by raw coal fly ash catalyzed Fenton-like process under microwave irradiation

Coal fly ash (CFA) catalyzed Fenton-like process was studied under microwave (MW) irradiation for the decolorization of Rhodamine B (RhB) wastewater. The physical-chemical properties of CFA were characterized, including the specific surface area, micromorphology, chemical and crystal components, and the distribution and chemical valence of metallic elements. The metallic oxidants in the CFA indicate CFA can work as Fenton-like catalyst and MW-absorbent simultaneously. The results reveal OH is more significant in the decolorization of RhB than HO2 and O2−. The generation of more OH in the MW-Fenton-like process (293–326 K) than that in the conventional heated Fenton-like process (326 K) reflects the function of hot spot effect and possible non-thermal effect of MW. Under the optimum condition ([H2O2] 2 mmol L−1, [CFA] 15 g L−1, pH 3, PMW 0.1 kW), the decolorization rate reaches 91.6% after 20 min. The intrinsic kinetic model of RhB decolorization is -dCRhBdt=1.76×10-4·CRhB·CH2O21.89·CCFA1.97-dCRhodamineB/dt=1.76×10-4·CRhodamineB·CH2O21.89·Ccoalflyash1.97. The loss of catalytic metallic elements causes the decline of catalytic capacity of CFA. The energy consumption (4313.3 kW·h kg−1 RhB) is a limitation for the MW-Fenton-like process, which can be overcame by the safe application of nuclear energy. The intermediates and the path of RhB decolorization were detected and proposed, respectively.

Evaluation of Four Kernel-Driven Models in the Thermal Infrared Band

Many physical models have been proposed to simulate the directional anisotropy in the thermal infrared (TIR) region over vegetation canopies to produce angular corrected directional brightness temperature or land surface temperature. However, too many input parameters obstruct their operational use. Semiempirical kernel-driven models are designed to be a tradeoff between physical accuracy and operationality. Recently, four kernel-driven models have been proposed: the first two are direct extensions of kernel models in the visible- and near-infrared region and the last two were directly designed for the TIR region. In this paper, 153 continuous and 153 discrete canopies with varying structures and temperature distributions were considered in order to evaluate their accuracies against two physical models (4SAIL and DART). Their error distribution, scatterplots, and directional anisotropy patterns are compared. LSF-Li model, followed by Ross-Li, Vinnikov, and RL model, gave the best fitting results for all the scenes. The $R^{2}$ of all four kernel models can reach up to 0.82 for discrete scenes; however, the kernel-driven models underestimate the hotspot effect from continuous scenes; therefore, further improvements are necessary for operational use with future TIR satellite missions.

Mesoporous Silica Nanospheres Decorated by Ag–Nanoparticle Arrays with 5 nm Interparticle Gap Exhibit Insignificant Hot-Spot Raman Enhancing Effect

Arrays of 20 nm silver nanoparticles (AgNPs) with tunable interparticle gaps have been grown on mesoporous silica (MPS) nanospheres to form AgNPs@MPS nanohybrids for surface-enhanced Raman scatteri...

Evaluation of the Snow Albedo Retrieved from the Snow Kernel Improved the Ross-Roujean BRDF Model

The original kernel-driven bidirectional reflectance distribution function (BRDF) models were developed based on soil-vegetation systems. To further improve the ability of the models to characterize the snow surface scattering properties, a snow kernel was derived from the asymptotic radiative transfer (ART) model and used in the kernel-driven BRDF model framework. However, there is a need to further evaluate the influence of using this snow kernel to improve the original kernel-driven models in snow albedo retrieval applications. The aim of this study is to perform such an evaluation using a variety of snow BRDF data. The RossThick-Roujean (RTR) model is used as a framework for taking in the new snow kernel (hereafter named the RTS model) since the Roujean geometric-optical (GO) kernel captures a neglectable hotspot effect and represents a more prominent dome-shaped BRDF, especially at a small solar zenith angle (SZA). We obtained the following results: (1) The RTR model has difficulties in reconstructing the snow BRDF shape, especially at large SZAs, which tends to underestimate the reflectance in the forward direction and overestimate reflectance in the backward direction for various data sources. In comparison, the RTS model performs very well in fitting snow BRDF data and shows high accuracy for all data. (2) The RTR model retrieved snow albedos at SZAs = 30°–70° are underestimated by 0.71% and 0.69% in the red and near-infrared (NIR) bands, respectively, compared with the simulation results of the bicontinuous photon tracking (bic-PT) model, which serve as “real” values. However, the albedo retrieved by the RTS model is significantly improved and generally agrees well with the simulation results of the bic-PT model, although the improved model still somewhat underestimates the albedo by 0.01% in the red band and overestimates the albedo by 0.05% in the NIR band, respectively, at SZAs = 30°–70°, which may be negligible. (3) The albedo derived by these two models shows a high correlation (R2 > 0.9) between the field-measured and Polarization and Directionality of the Earth's Reflectances (POLDER) data, especially for the black-sky albedo. However, the albedo derived using the RTR model is significantly underestimated compared with the RTS model. The RTR model underestimates the black-sky albedo (white-sky albedo) retrievals by 0.62% (1.51%) and 0.93% (2.08%) in the red and NIR bands, respectively, for the field-measured data. The shortwave black-sky and white-sky albedos derived using the RTR model for the POLDER data are underestimated by 1.43% and 1.54%, respectively, compared with the RTS model. These results indicate that the snow kernel in the kernel-driven BRDF model frame is more accurate in snow albedo retrievals and has the potential for application in the field of the regional and global energy budget.

On Subcool Control in SAGD Producers—Part II: Localized-Hot-Spots Effects and Optimization of Flow-Control Devices

Summary At the base of a steam-assisted-gravity-drainage (SAGD) steam chamber, a liquid pool is developed, which is a key component for bitumen production. A producer is placed in the liquid pool, and its production is mainly controlled by its liquid level and the temperature gradient across its depth. A “subcool control” or “thermodynamic steam-trap control” is a typical operating strategy to control steam coning to the producer. Part I of this study (Irani 2018) presented a methodology to evaluate the production rate for a given pressure drawdown and subcool in a SAGD liquid pool; and Part III (Irani and Gates 2018) modified such a formulation for a stability analysis of the Nsolv™ (Nenniger and Nenniger 2000, 2001) process that contained a large fraction of liquid butane. In this study, first, the effect of localized hot spots on well control is formulated as a virtual skin factor in the liquid-pool deliverability equation. The results of this work suggest that a longer hot spot will yield to lower differential pressure and make it more challenging to control the steam breakthrough by choking the well at a given rate. Another key finding is that the steam coning becomes less controllable for higher-permeability reservoirs. Flow-control devices (FCDs) have been used extensively in horizontal wells for conventional oil and gas production to prevent early water breakthrough or gas coning. Although FCDs are commonly installed to prevent steam coning after steam breakthrough and to manage hot spots as retrofit completions by SAGD operators, in recent years, FCDs have been often installed to improve SAGD well-pair performance as part of the initial completion. The benefits associated with this technology in the SAGD industry have been studied with reservoir simulations and validated with field experience, but a theoretical study that discusses the main factors for a correct FCD selection on the basis of operational conditions and reservoir heterogeneity is required. In this study, the liner-deployed FCD and liquid-pool systems are coupled, and two criteria are suggested for a design of liner-deployed FCDs on the basis of the pressure-drop ratio of the FCD relative to the liquid pool (ΔPFCD/ΔPpool) and the coefficient of variation (CoV) of inflow for the liner-deployed-FCD wellbore (CoVFCD). The results of this study show that in higher-permeability reservoirs, the ideal FCD design should have more ports to reduce the differential pressure to flow response. While FCDs will improve inflow conformance relative to completions without FCDs, the effect of permeability in this improvement is minimal. This improvement is larger in applications operating at lower target subcool values. Reducing the target-wellbore subcool value can improve well deliverability twofold: First, FCD-completed wells produce more at lower subcools and, second, reducing the subcool value helps to improve inflow uniformity along the length of the lateral. By effectively removing the fluids available to the producer, the growth of the steam chamber can be maximized through accelerated injection rates.