Search

A microgrid (MG) is characterized by an arrangement of renewable energy sources (RES) and loads connected together to the distribution system. With the high dispersion of distributed generations (DG) in microgrids, which is inevitable, the distribution system will experience diverse challenges not only in its performance but also in the protection set-up. The lack of a comprehensive applicable protection scheme, which must be attuned to islanded and grid-connected modes of microgrid operation, is a key problem. The problem becomes more challenging and complex in an islanded operation of a microgrid (MG) due to limited fault current contribution by inverter based DGs. Therefore, conventional protection strategies cannot be applied in a radial distribution system with DGs. The lack of comprehensive protection schemes, which must be attuned with islanded and grid-connected modes of microgrid operation, is a challenging task to be implemented. To grasp the superlative protection scheme for MGs, the combined action of different protection strategies is required. Extensive research on the development of MG protection strategies reveals their incompetency to cater for protection of every component of the entire microgrid in its prevailing conditions being employed in solo-mode and also that no scheme is able to work without communication assistance. The current work proposes the comprehensive implementation of communication-less unified diverse protection schemes that include current differential relays, directional and non-directional overcurrent conventional IEC (International Electrotechnical Commission) standard-based overcurrent relays, and novel non-standard voltage-current relays. The assembly and graphical representation of proposed relays for each scheme are developed in MATLAB/Simulink during the simulation. The accomplished results of these diverse protection schemes are validated through simulations applied to the benchmark microgrid system using an industrial software package called ETAP (Electrical Transient Analyzer Program).

AbstractA global model is proposed to simulate the drying process of used nuclear fuel assemblies under vacuum drying conditions. The transient model consists of a coupled mass and energy conservation equation with appropriate source and sink terms. The classic Hertz-Knudsen expression is employed to resolve the evaporation rate and the associated water mass depletion in the system. Both latent heat of vaporization and residual decay heat are considered as sink and source in the energy conservation, respectively. The model is employed to simulate vacuum drying of spent nuclear fuel rod storage systems. Multistage stepwise vacuuming of the system is emulated, and several parametric studies are conducted to identify their role in the drying process. The predicted temporal profiles show that the proposed model is able to capture qualitative trends of the water removal rate, hence the dryness level of the system. The model prediction is also compared against experiments where the amount of residual water after a standard vacuum drying procedure is quantified. The predictions are found to compare favorably with the experimental measurements.

In this article, we investigate public support for eco-social policies combining goals of social justice and ecological sustainability. Eco-social policies contribute both to providing a social floor or redistributing resources to where they are needed and to respecting an ecological ceiling by keeping human activities within ecological limits. We discuss five such policies and highlight arguments for and against defining them as eco-social policies: a maximum income, a wealth tax, a basic income, a working time reduction and a meat tax. Asking what the social and individual determinants of supporting these policies are, we use 2020 data from a representative survey in Sweden containing information about how respondents evaluate the policies. We run regression analyses to estimate the effects on these evaluations and test for socio-economic, knowledge-based and value-based factors. Results show that (1) in Sweden a working time reduction is the most supported eco-social policy; (2) political left orientation increases support for all five eco-social policies; (3) socio-economic factors have effects on wealth tax, maximum income and working time reduction; and (4) knowledge-based factors are more associated with the meat tax. Thus, socio-economic and knowledge-based models have the most significance for policies that could be understood as being either social or environmental, while value-based models have significance across potentially perceived policy divides and hence to a greater extent explain support for policies targeting an ecological ceiling anda social floor.

The fracture system is the main transport channel of coalbed methane (CBM), and its quantitative characterization is crucial for the production of CBM. This paper takes the Lower Permian Shanxi Formation and Taiyuan Formation coals as examples; by the microscopic observation and mathematical analysis method, the development characteristics of the fracture system in the coal are systematically studied. The image processing technique is used to obtain the height resolution images (with an actual resolution of approximately 2 μm) of the fracture in the coal, then multifractal theory is used to study the microfracture structure, and an algorithm is proposed that can quantitatively characterize the multifractal characteristics of coal fractures and its corresponding steps. The quantitative characterization of the whole and part of the fracture structure’s heterogeneity combined with the description of the characteristic parameters calculated by the generalized dimension spectrum and the singularity spectrum. Our results show that the heterogeneity of fracture system distribution in samples collected from the Hunyuan area is stronger than that from the Puxian area. For the samples of various coal seams collected from Puxian, the heterogeneity of the distribution of the fracture system of 10# coal seam is the strongest, followed by that of 2# coal seam and 3# coal seam has the highest homogeneity.

Variability in precipitation results flooding and drought worldwide. The climate change has a close relationship with the precipitation and temperature pattern as well as river discharge. In this research, spatial and temporal rainfall variability have been analyzed. The rainfall data of seventeen meteorological stations for the period of 1980–2018 was acquired from China Meteorological Administration. To assess drought in the study area, the standardized precipitation index (SPI) was applied and to check the temporal drought trend the Mann–Kendall test was applied, while the data normality was checked through skewness, kurtosis, and standard deviation. The Mann–Kendall results shows decreasing rainfall and increasing drought trend in the study area. The study area southwest Xinjiang is an arid region and the decreasing rainfall trend will further aggravate the conditions of already endangered flora and fauna in the region. This study will provide a platform for decision makers to take proactive actions to mitigate the risk of increasing drought in the study area.

The combustion explosion fracturing of shale with in-situ methane is a revolutionary fracturing technique, but the modification characteristics of reservoir pores and fractures by combustion explosion energy level are still unclear. In order to study the transformation characteristics of micron-scale pore-fracture systems of marine shale reservoirs with different combustion explosion energies, this study selected a section of shale samples from the Longmaxi Formation in the Luzhou block in the southern Sichuan Basin to carry out different energy gradient combustion explosion test, named W1∼W5 (25–91 MPa). Based on micron CT scanning technology, the three-dimensional reconstruction of shale samples before and after combustion explosion was carried out to analyze the effect of combustion explosion energy on the transformation of the pore-fracture system characteristics. The results show that at the energy between 25 MPa and 45 MPa, the variation characteristics of cracks before and after explosion are not obvious. When the energy of the explosion is in the range of 61 MPa–91 MPa, the cracks gradually extend and become longer, and the distribution density of cracks becomes higher and more interconnected. After the explosion at 91 MPa, it can be seen that a number of annular cracks are generated at the edge of the sample, which are interconnected with radial cracks. Total porosity, connected porosity, pore number, and total pore volume of the shale increased after combustion explosion, where the total porosity at the combustion explosion energy of 91 MPa have the largest increment, while the connected porosity, pore number, and total pore volume in the combustion explosion energy of 71 MPa have the largest relative increments, indicating that there is a fracturing pressure value that strongly breaks through the bottleneck when the explosion pressure is between 61 MPa and 71 MPa. A comparison of different pore size sections before and after the combustion explosion pore volume share found that the explosion pressures of 25 MPa, 45 MPa and 91 MPa tend to expand from 100 to 200 μm pore size to form a larger volume share of >200 μm cracks, while at the explosion pressure of 71 MPa, more inclined to transform the 0–100 μm pores, so that the pores gradually transition to the 100–200 μm. Analysis shows that the gas explosion generates a large pressure, release a large amount of heat. Due to the high temperature and high pressure coupling effect, the pore-fracture in the shale changes significantly. Strong stress waves lead to stress concentration at the tip of shale and crack expansion and extension. At the same time, the local expansion force causes “pore expansion effect”. Various mineral particles in the shale undergo differential expansion, along the crystal rupture or through the crystal rupture. New pore fractures are also generated when the original pores keep expanding, which improves the shale pore connectivity. This understanding can provide a theoretical basis for the selection of the energy level of the in-situ methane combustion explosion in shale.

During the diagenetic processes of compaction and cementation, shale forms multiple beddings, significantly effecting the rock anisotropy. Therefore, it is important to study the effect of bedding on the mechanical properties of shale to guide fracturing engineering. To study the failure mode and fracture morphology of shale with bedding planes under different bedding dip angles, Brazilian disc splitting tests and finite element numerical simulations are performed for shale samples and the results are compared. (1) The bedding angle has a significant effect on the failure mode and tensile strength of shale, and the tensile strength tends to increase with increasing bedding angle. (2) The failure modes of shale under different bedding dip angles can be divided into three types: tensile failure along the bedding plane; comprehensive shear and tensile failure of the matrix and the bedding plane; and matrix tensile failure. (3) The direction of secondary cracks is mostly perpendicular to the bedding plane, and a smaller angle between the load application direction and the bedding direction results in a larger number of generated cracks with more complex shapes. (4) When the loading angle of the bedding is 30°, the tensile strength is low and the matrix and the bedding plane are comprehensively destroyed by shear and tension, resulting in a more complex joint mesh; conversely, when the bedding angle is greater than 60°, the tensile strength increases and the complexity of the seam mesh decreases. These findings can provide guidance for the selection of the bedding angle and the design of fracturing schemes in fracturing engineering.

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their potential applications in large-scale stationary energy storage. Early ZIBs research has primarily focused on searching for better cathodes and understanding cathodic Zn2+storage mechanisms. Only very recently has ZIBs research shifted to Zn anode. Here in this study, we report on insights into the interactions between Zn anode and aqueous Zn-salt electrolytes gained by a systematic investigation of bulk properties of electrolytes, surface properties of the reacted Zn, electrokinetics of Zn/Zn2+redox reaction and cycle stability of Zn/electrolyte/Zn symmetrical cells. We found that Zn metal surface, regardless of electrolyte, are always covered by a layer of Zn-containing layered double hydroxides (Zn-LDHs) upon contact with aqueous Zn-electrolytes. We show that “OH−production” pathway resulted from the dissolved oxygen in Zn-electrolytes is the root cause for the Zn-LDHs formation. The electrokinetic studies reveal that Zn/Zn(ClO4)2interface has the highest exchange current density, while the symmetrical cell tests show that Zn(OTf)2is the most stable electrolyte for Zn-metal anode.

The periodic generation and transmission of basic safety messages (BSM) place a heavy burden on the load of a vehicular ad hoc network (VANET), where there also remain multiple packet collisions undetected due to the hidden terminals. In this paper, we propose a distributed scheme that controls the spatial reuse distance to improve the efficiency of BSM transmissions in space-division multiple access (SDMA) based VANETs. With the proposed SDMA structure, only vehicles located sufficiently far apart are allowed to reuse the same time slot to send their BSMs. The signal interference is thus reduced while the hidden-node problem is essentially alleviated. Multiple transmissions per SDMA road segment or ‘cell’ are also enabled using the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), giving rise to a much better use of both space and bandwidth. To guarantee that the actual number of BSM transmissions does not exceed the maximum allowable in each SDMA cell, we further devise an adaptive scheme that adjusts the spatial reuse distance in accordance with the vehicle density. Because the global information of vehicle density is not available at individual vehicles, we propose a distributed algorithm that estimates the vehicle density and makes consensus to enhance the accuracy of spatial reuse distance estimation. As the transmission range is controlled accordingly, the mutual interference among the SDMA cells is further reduced. Importantly, the developed control algorithm can be distributively implemented by each vehicle with limited information exchange. To optimize the performance of the proposed solution, we also determine the optimal bandwidth utilization that maximizes the newly-defined criterion termed as ‘safe range,’ an important figure-of-merit in vehicular safety applications. Simulation results confirm the clear advantages of our proposal over the available approaches in terms of safety range, packet reception rate, end-to-end delay and BSM inter-arrival time in realistic network scenarios.

Carbon pricing as a key policy instrument for climate change mitigation it has now been implemented in many countries globally. However, existing systems differ significantly in design with regard to stringency, coverage and the use of the revenues collected through the system. In this literature study, we synthesise existing knowledge of how key factors affect the adoption, implementation, and design of carbon pricing systems. We find that the characteristics of actual political systems, the degree and nature of business influence and public opposition, as well as international influences, have impacted implementation. Obstacles to implementation have been overcome by adapting the design of the systems to meet different societal interests. Preferential treatment and tax exemptions are thus common, which makes the incentives for emission mitigation less coherent across sectors. The results are of practical relevance for policy makers when designing and implementing carbon policies and indicate that carbon pricing needs to be part of a policy package in order to secure both rapid mitigation and a long-term decarbonisation. Further research is needed on the nature of obstacles to carbon pricing policies in various contexts and on how to combine carbon pricing with other types of policies.

With the arrival of LTE standard, it is expected that the mobile voice services paradigm will shift from the circuit switched to fully packet switched mode supporting the VoIP services. VoIP services took quite a bit of time before they were accepted as the main stream telephony service in the fixed networks. To provide VoIP services over the LTE networks with appropriate QoS, it is necessary to analyse the performance of such services and optimise the network parameters. This paper analyses the performance of VoIP services on the LTE network using the FD and the SMP packet scheduling techniques. This work identifies and analyses the features of above LTE packet scheduling techniques to enhance the QoS of VoIP services. An OPNET-based simulation model is used to analyse the performance of VoIP services on the LTE network by incorporating G.711 and G.723 speech coders. The work also studied the performance of VoIP services in variable transmission channel conditions.

Vehicular ad hoc networks (VANETs) are expected to be used for the dissemination of emergency warning messages on the roads. The emergency warning messages such as post crash warning notification would require an efficient multi hop broadcast scheme to notify all the vehicles within a particular area about the emergency. Such emergency warning applications have low delay and transmission overhead requirements to effectively transmit the emergency notification. In this paper, an adaptive distance based backoff scheme is presented for efficient dissemination of warning messages on the road. The proposed scheme adaptively selects the furthest vehicle as the next forwarder of the emergency message based on channel conditions. The detailed performance figures of the protocol are presented in the paper using simulations in the OPNET network simulator. The proposed protocol introduces lower packet delay and broadcast overhead as compared to standard packet broadcasting protocols for vehicular networks.

AbstractThe thermal conductivity of the fuel in today’s light water reactors, uranium dioxide (UO2), can be improved by incorporating a uniformly distributed heat-conducting network of a higher-conductivity material: silicon carbide (SiC). The higher thermal conductivity of SiC along with its other prominent reactor-grade properties makes it a potential material to address some of the related issues when used in UO2(97% theoretical density). This ongoing research, in collaboration with the University of Florida, aims to investigate the feasibility and development of a formal methodology for producing the resultant composite oxide fuel. Calculations of the effective thermal conductivity (ETC) of the new fuel as a function of percent SiC for certain percentages and as a function of temperature are presented as a preliminary approach. The ETCs are obtained at different temperatures from 600 to 1600 K. The corresponding polynomial equations for the temperature-dependent thermal conductivities are given based on the simulation results. The heat transfer mechanism in this fuel is explained using a finite volume approach and validated against existing empirical models. FLUENT 6.1.22 was used for the thermal conductivity calculations and to estimate the reduction in centerline temperatures achievable within such a fuel rod. Later, the computer codes COMBINE-PC and VENTURE-PC were employed to estimate the fuel enrichment required to maintain the same burnup levels corresponding to a volume percent addition of SiC.

This paper presents a simple RLC/MAC protocol architecture for a wireless IP (Internet Protocol) network. In order to support IP-based multimedia services in a wireless network, two different approaches can be used. One approach is to transmit end-to-end IP packets in a multi-hop network, such as a cellular mobile telephone network. In this case IP packets can be transmitted on high data rate air interfaces using a suitable IP header compression technique. Another possibility is to transmit non-IP packets from a UE to a BTS using standard 2G/3G air interfaces. IP packets can be generated at a BTS by encapsulating received MAC packets on an uplink. On a downlink, an IP packet received from a RAN is fragmented at a BTS for further transmission using a standard air interface. This paper first reviews the end-to-end IP packet transmission strategy based on IP header compression techniques. Next a simple RLC/MAC protocol architecture for a wireless IP network is proposed. The proposed protocol architecture is suitable for generating IP packets at a BTS by encapsulating MAC packets. IP packet encapsulation delay at a BTS is minimized by using a reservation-based MAC protocol. The MAC protocol uses class-based reservation and priority queuing techniques to satisfy QoS needs of different classes of traffic. The RLC protocol is mapped onto the MAC protocol to minimize signaling overhead. The proposed RLC/MAC layer is simple, flexible, and generates minimum signaling load to maintain high QoS for multimedia traffic. Performance of the RLC/MAC protocol is analyzed using a simulation model.

Contaminant concentration estimates from simple models were compared with concentration fields obtained by computational fluid dynamic (CFD) simulations for various room and source configurations under steady-state conditions. Airflow and contaminant distributions in a 10×3×7-m room with a single contaminant source on a 1-m high table were simulated using CFD for steady, isothermal conditions. For a high wall jet inlet, simulations were performed for nine room air exhaust locations and eight source locations. For a ceiling diffuser inlet the impact of two exhaust locations and eight source locations were investigated. Because CFD treats determinants of contaminant transport explicitly and agreed well with experimental results, it was used as the standard for comparison. Parameters of the one- and two-zone completely mixed models (CM-1 and CM-2) and the uniform turbulent diffusivity model (UD) were determined from CFD simulation results. Concentration estimates from these were compared with CFD results in the breathing zone (BZ) plane (1.5 m above the floor) for the entire BZ, the source “near field,” and the source “far field.” In the near field the mean percentage difference between the model concentration estimates and the CFD results for all room configurations were -21.9, 32.3, and 126% for the CM-1, CM-2, and UD models, respectively, with standard deviations of 26.8, 111, and 103%. In the far field the mean percentage difference between the model estimates and CFD results were -4.8, -2.3, and -36.3%. The CM-1 model had generally the best performance for applications such as occupational epidemiology for the conditions and configurations studied. However, CM-1 tended to underestimate the near field concentration; thus, CM-2 was judged to be better in the near field when underestimation is undesirable, such as when determining compliance with occupational exposure limits. The agreement of CM-2 estimates with CFD results in the near field was more variable than that of the CM-1. The UD model performed poorly on average in both near and far fields, and the difficulty in accurately estimating the turbulent diffusivity presents a significant impediment to UD model use for exposure estimation.

PUT YOURSELF IN THIS SITUAtion. You have three drips to remix, your oscillator patient is starting to crash, and you have just been asked to work a double shift because the hospital is short staffed. The unit secretary informs you that the mother of one of your former primary patients is on the telephone and is hysterical. A physician at the neonatal follow-up clinic has just told her that her baby has cerebral palsy (CP). She wants reassurance, information, and input from you because you established a rapport with her when her infant was in the neonatal intensive care unit and she trusts you. You remember cerebral palsy from your pediatric rotation in nursing school, but you don’t see many actual diagnoses made in the NICU, and your recollection is foggy.

A numerical investigation has been carried out for conjugate forced convection heat transfer in tubes with multiple obstructions. The investigation included the ranges of Reynolds number Re, thermal conductivity ratio kr, and the distance between two obstructions d of 50-600, 0.3-3.0, and 2.0-8.0, respectively. A fluid Prandtl number Pr of 7.56 is used. The obstructions create recirculation flow / back flow in the tube with increase and decrease of local heat transfer rates. Reversal in the direction of heat transfer occurs at certain locations of the tube due to the presence of the obstructions. At high values of Re and d, reversal in the direction of heat transfer occurs on the outer wall after the second obstruction. The overall heat transfer rate decreases with the decrease of kr.

We describe a method that can be used to analyze chemical process flowsheets for waste minimization options for hazardous waste. The system is based on relating current waste minimization solutions to the waste generating unit operation. The system is simple and emphasizes EPA pollution prevention priorities. The system database contains numerous waste minimization solutions compiled from case studies, EPA reports, consultant reports and options identified during waste minimization visits. The database structure and the system which uses the database to analyze chemical process flow is described for two existing companies, a specialty chemical company and a plating company. A pollution prevention index (PPI) that emphasizes EPA pollution prevention priorities as well as economic and technical factors is proposed and is used by the system to rank solutions for a given process flowsheet. Analyses for the specific plating and specialty chemical companies examined are described in detail. It is shown that the new system and structure are effective in locating and providing an analysis of a chemical process flowsheet. The system has been applied to more than 16 South Carolina industries.

Increase in the heat transfer rate during melting and freezing of a phase change material (PCM) with a low thermal conductivity is demonstrated by inserting a high-porosity metal matrix into the PCM. A vertical annulus space (r1≤r≤r0, 0≤z≤h)homogeneously fitted with water and an aluminum matrix, is selected for this study. The Navier-Stokes equations are modified to account for Darcy's effect. For both the melting and freezing cases, the density inversion phenomenon of water is considered. The irregularity and time-varying nature of the solid and the liquid regions are accounted for by a geometric coordinate transformation. The numerical results are presented in the form of solid-liquid interface movements, isotherms, streamlines, and heat transfer rates for some representative cases. The heat transfer rates for enhanced cases show an order-of-magnitude increase over the base case, where no metal matrix is inserted.

The bandicoots,Bandicota bengalensis(Gray), tend to favour a varied diet, but the foods offered are not selected in a linear order. Unextracted flours of millet and maize, are readily accepted: only semolina is equally accepted among the forms of ground wheat. Among whole cereals, millet is preferred but equally preferred is polished rice. Rice is also markedly preferred when boiled to its dry alternative. Foods mixed with sugar or groundnut oil are similarly favoured over plain alternatives.

Mixed phytoplankton, zooplankton and Thermocyclops hyalinus collected from Fort Moat, at Aligarh (U.P.) India, were analysed for water, nitrogen and phosphorus. Results are generally in agreement with observations of earlier investigators.

The ionic composition offour very productive and one unproductive fishpond has been investigated. The concentration of various ions is typical of carbonate waters except in two ponds for reasons of pollution. Calcium and bicarbonate are the major cation and anion while inspite of high productivity potassium is not very abundant. Because of the geographical position the area enjoys, the carbonate content seems to be important in productivity evaluation. For the same, its equivalent ratio to calcium and bicarbonate is very significant.

•Swedish regions have increased public transport patronage through best practice measures.•Examples of measures are faster and straighter routes and more frequent departures.•Political support and communication to the public is important to introduce measures.•Trust between key actors is needed to develop collaboration and implement measures.•New collaboration arenas or forums have often been created.

The low‐power short‐range networks have gained prevalence in research fields such as machine‐to‐machine communications and the Internet of things. Given the large number of devices that may exist, the IPv6 over low‐power wireless personal area networks (6LoWPAN) standard is expected to be widely used. Although Contiki, NS‐3, and OMNeT++ have developed the 6LoWPAN model, it is still not available in optimized network engineering tools (OPNET) because it is extremely difficult to interface the built‐in IP module with the customized modules in OPNET. To bridge this gap, we first developed a preliminary 6LoWPAN model and implemented the header compression and header restoration functions to handle the incoming and outgoing packets in OPNET. To further improve the system performance, we also proposed an algorithm that aggregates packets, reduces intranetwork collisions and increases the packet delivery ratio. The model and algorithm in this work are free to download, so researchers from the OPNET community can easily extend this work for their own research in the future. How to make a 6LoWPAN simulation model in OPNET?

With the advent of machine‐to‐machine communications, various networking consumer industrial, and autonomous systems exchange messages in the real world in order to achieve their objectives. Parts of these systems are comprised of short‐range wireless networks in the form of clusters that collectively cover a large geographical area. In these clusters, the nodes that represent the cluster heads need to deal with two types of communications, ie, one is within the cluster and the other is from the cluster to the sink node. As the number of clusters increases, it takes multiple hops for the cluster head to forward data to the sink node, thus resulting in a low packet delivery rate (PDR) and throughput. To solve this problem, we propose a heterogeneous area network in which the cluster head is equipped with two types of radios, ie, the IEEE 802.15.4 and IEEE 802.11 radios. The former is for the devices within the cluster to communicate, whereas the latter is for the cluster heads to communicate to the sink node. Although the IEEE 802.11 links increase the link capacity, the IEEE 802.11 radio and the IEEE 802.15.4 radio might share the 2.4 GHz unlicensed band, thus giving rise to the internetwork collisions or interference. To tackle this problem and to maintain decent quality of service for the network, we subsequently present two interference mitigation techniques, in which a blank burst period is proposed so that the IEEE 802.15.4 radios can be suspended while the IEEE 802.11 radios are active. Simulation results show the proposed two methods can effectively mitigate the internetwork collisions and are superior to the existing technique, which uses an adaptive aggregation technique to mitigate the internetwork collisions. This paper presents a future scenario in which a heterogeneous LoWAN plays an important role in supporting IoTs. This paper also presents two innovative algorithms for mitigating the inter‐network collisions that is a potential obstacle. This paper also compared with an existing algorithm to show superiority.

Certain histologic subtypes of basal cell carcinoma (BCC) behave more aggressively and require more aggressive treatment.

In this paper, experimental investigation has been performed to characterize the heat transfer behavior of CuO–water and ZnO–water nanofluids. Nanofluids containing different volume percent (vol %) of nanoparticle concentrations flowed over a flat copper plate under a constant heat load. The constant heat flux was maintained using evenly placed cartridge heaters. The heat transfer coefficients of nanofluids were measured and compared with the results obtained from identical experiments performed with de-ionized (DI) water. In order to thoroughly characterize the nanofluids, nanoparticle size was investigated to inspect for possible agglomeration. The particle size was measured by using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS). Enhancement of convective heat transfer of nanofluids was 2.5–16% depending on the nanoparticle concentrations and Reynolds number. The plausible mechanisms of the enhanced thermal performance of CuO and ZnO nanofluids will be discussed in the following paper.

Control strategy plays a significant role in ensuring system stability and performance as well as equipment protection for maximum service life. This work is aimed at investigating the control strategies for start-up and part-load operating conditions of the solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system. First, a dynamic SOFC/GT hybrid cycle, based on the thermodynamic modeling of system components, has been successfully developed and simulated in the virtual test bed simulation environment. The one-dimensional tubular SOFC model is based on the electrochemical and thermal modeling, accounting for voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. Two operating conditions, start-up and part load, are employed to investigate the control strategies of the SOFC/GT hybrid cycle. In particular, start-up control is adopted to ensure the initial rotation speed of a compressor and a turbine for a system-level operation. The control objective for the part-load operation regardless of load changes, as proposed, is to maintain constant fuel utilization and a fairly constant SOFC temperature within a small range by manipulating the fuel mass flow and air mass flow. To this end, the dynamic electrical characteristics such as cell voltage, current density, and temperature under the part load are simulated and analyzed. Several feedback control cycles are designed from the dynamic responses of electrical characteristics. Control cycles combined with control related variables are introduced and discussed.

Control strategy plays a significant role in ensuring system stability and performance as well as equipment protection for maximum service life. This work is aimed at investigating the control strategies for start-up and part-load operating conditions of the solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system. First, a dynamic SOFC/GT hybrid cycle, based on the thermodynamic modeling of system components, has been successfully developed and simulated in the virtual test bed simulation environment. The one-dimensional tubular SOFC model is based on the electrochemical and thermal modeling, accounting for voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. Two operating conditions, start-up and part load, are employed to investigate the control strategies of the SOFC/GT hybrid cycle. In particular, start-up control is adopted to ensure the initial rotation speed of a compressor and a turbine for a system-level operation. The control objective for the part-load operation regardless of load changes, as proposed, is to maintain constant fuel utilization and a fairly constant SOFC temperature within a small range by manipulating the fuel mass flow and air mass flow. To this end, the dynamic electrical characteristics such as cell voltage, current density, and temperature under the part load are simulated and analyzed. Several feedback control cycles are designed from the dynamic responses of electrical characteristics. Control cycles combined with control related variables are introduced and discussed.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.