In this paper, the controllability issue of complex network is discussed. A new quantitative index using knowledge of control centrality and condition number is constructed to measure the ...controllability of given networks. For complex networks with different controllable subspace dimensions, their controllability is mainly determined by the control centrality factor. For the complex networks that have the equal controllable subspace dimension, their different controllability is mostly determined by the condition number of subnetworks’ controllability matrix. Then the effect of this index is analyzed based on simulations on various types of network topologies, such as ER random network, WS small-world network, and BA scale-free network. The results show that the presented index could reflect the holistic controllability of complex networks. Such an endeavour could help us better understand the relationship between controllability and network topology.
•We present an accurate and convenient 1D transient thermal energy storage model.•The model was introduced with an extended lumped capacitance method.•Results from a comprehensive CFD analysis were ...used to verify the model.•The agreement was excellent and the model is recommended for general application.
With an extended lumped capacitance method applied to account for the internal heat conduction resistance in a solid (for Biot number larger than 0.1), a general model of thermal energy storage with various solid–fluid structural combinations is presented and verified using numerical results. The thermal energy storage system has a heat transfer fluid (HTF) flowing through a packed bed of solid materials structured in different configurations, such as in the form of solid pebbles, parallel plates, solid rod-bundles, or solids with fluid tubes imbedded through them. The model of energy conservation in the liquid and solid is transient, one-dimensional in nature, due to the introduction of a modified lumped capacitance method that counts for the effect of three-dimensional heat conduction in the solid structures. The computational workload using this modified model is significantly less compared to that of a comprehensive CFD analysis. Numerical results obtained from a CFD analysis of the thermal energy storage in the solid and liquid are used to verify the model. The CFD simulated results of temperatures of HTF are compared with the 1D model results, and they show excellent agreement. In conclusion, the 1D model is recommended as a convenient and accurate tool for general analysis and sizing of thermal energy storage containers that have various solid–fluid structural combinations.
This study focuses on altering the diffusion combustion characteristics of the self-reflux burner by optimizing the burner nozzle structure. By adjusting the jet angle of each nozzle, enhancing the ...diffusion effect of fuel and air in the combustion chamber, a low-oxygen combustion atmosphere is formed in the high-temperature zone of the combustion chamber, avoiding local high temperature caused by fuel accumulation and combustion, reducing the combustion rate of nitrogen, and then the thermal NOx emission is reduced. Parallel, inwardly inclined, and outwardly inclined jet angles are studied in simulation, and five working conditions (-10°, -5°, 0°, 5°, and 10°) are calculated, compared, and analyzed. The cooperative coupling mechanism between multiple fields (velocity, concentration, and temperature) is compared and analyzed. We use the diffusion effect to reduce the oxygen concentration in the central axis and achieve the goal of reducing NOx by reducing the maximum combustion temperature. The simulation results show that the maximum and average temperatures of the combustion chamber are reduced by 28.9 K and 15.38 K, respectively, when the jet angle is outwardly tilted by 5°, which reduces the local high temperature; and NOx emissions are in turn reduced by 104.72 ppm.
•Low-oxygen combustion technology applies to the self-reflux burner.•We studied the effects of jet angle on the thermal process of diffusion combustion.•We studied the effect of different jet angles on low NOx combustion performance.•We recommend adjusting the jet angle to maximize the self-reflux burner performances.
The extensive researches of flexible phase change materials (FPCMs) provide a new way for the coupling of heating system and latent heat storage technology to improve the limited thermal inertia of ...heating system. In this study, FPCMs were prepared with styrene ethylene butylene styrene (SEBS) as flexible supporting material, expanded graphite (EG) as thermal conductivity additive and paraffin as PCMs. The prepared materials with 8 wt% EG, enthalpy of 181.22 kJ kg−1 and thermal conductivity of 0.78 W m−1 K−1 was selected to couple with secondary heating pipe. The stability and indoor thermal comfort of heating system coupling with FPCMs and heating pipes were analyzed in detail by simulation. The results show that, for the object system, the addition of 53 mm FPCMs to heating pipe has the best economic applicability, which reduces the fluctuation of supply temperature by 20.99% (1.70 °C) and that of indoor temperature by 22.92% (0.11 °C). Besides, from the simulation results of 1–5 h non-heating condition, the secondary heating pipe using FPCMs can provide at least 3 h for the repair of heating equipment or boiler in primary pipe network. The results also provide technical support for the matching application of high proportion renewable energy, which is unstable and intermittent, and flexible latent heat storage in heating system.
•Preparation of flexible and form stable phase change materials (FPCMs).•Thermal property of FPCMs with various expanded graphite contents was studied.•The stability of heating system is improved by coupling FPCMs with heating pipes.•The addition of FPCMs provides time for the equipment repair in primary network.
Based on the design concept of a fourth-generation smart pipe network system, this paper innovatively proposes a new TOTS (Two-supply/One-return, triple pipe structure) arrangement method for ...district heating systems. Moreover, to accurately predict the heat loss due to the pipeline operation of the multi-pipe system, based on the multipole calculation method, a new heat loss theoretical analytical model for the TOTS was created; additionally, a corresponding three-dimensional numerical simulation model was established, which was analyzed and numerically solved. The results showed that in comparison with thermal loss data measured by Danfoss et al., the above analytical and numerical models have a high accuracy, and the deviation is within 2%. Additionally, through calculations, it was found that the distance between the heating pipes is an important factor that affects the total heat loss from the new multi-control heating system and the actual heat exchange between pipes.
•A new type of TOTS arrangement method is proposed.•A mathematical model of the heat loss for the multi-tube system was established.•A 3D numerical simulation model for the multi-pipe system was established.•The effects of the water supply pipes spacing on heat loss were studied.
•Shell-and-tube thermochemical reactor was used in discharging process of open system.•Increasing inlet temperature was used to markedly increase the discharging rate.•Parallel flow can achieve ...higher discharging temperature and rate than counter flow.
Thermochemical energy storage (TCES) has attracted significant attention in recent years due to some unique features of the technology such as very high energy density and negligible heat loss during storage. The TCES, however, is still at its early stage of development currently at a technology readiness level of 1–3. Major technical challenges of the TCES include materials stability, charge/discharge kinetics and limited temperature lift. Here we firstly studied the application of shell-and-tube thermochemical reactor with silica gels as heat storage material in open TCES system by experimental method. And then validated model (the maximum root mean square percentage error of 13.62% between the modeling and experiments) of single tube reactor containing 0.29 kg silica-gel was established to numerically investigate the discharging behavior of the thermochemical reactor under different operating conditions and flow directions of air and water. The numerical simulation results showed inverse heat transfer occurred for a counter-flow of air-water. The problem could be solved by changing the counter-flow of air and water to the parallel-flow. Thus, the water outlet maximum temperature limit was broken through. The total heat uptake increased by at least 24.14% when water flow rate was less than 0.36 kg/h and 11.93% when air flow rate was more than 1.07 kg/h, respectively. By increasing the inlet temperature of air and water from 23 °C to 38 °C, the maximum temperature lift could be significantly increased by 79.94% for air and 80.81% for water, respectively. Meanwhile, the total heat uptake increased by 107.44%. For a completely charging and discharging process, the discharging rate of parallel-flow was faster than that of counter-flow.
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Abstract
Although ceramic-based oxygen transport membranes (OTMs) have irreplaceable advantages over traditional oxygen production technologies, their oxygen permeability and stability need to be ...further improved. Based on the theoretical starting point of increasing the three-boundary reaction zone and reducing blocking effect, a set of new dual-phase membranes 75wt%Ce
0.8
Sm
0.1
Cu
0.1
O
2-δ
-25wt%-Sm
0.8
Sr
0.2
Co
0.8
Fe
0.2
O
3-δ
(CSC-8282) and 75wt%Ce
0.8
Sm
0.1
Cu
0.1
O
2-δ
-25wt%Sm
0.3
Sr
0.7
Co
0.8
Fe
0.2
O
3-δ
(CSC-3782) with different strontium contents were prepared by a one-pot sol-gel method ensuring that each element has the same chemical potential. The surface morphology, crystal structure and element distribution are systematically studied by SEM, XRD and EDS, which confirms that the synthesized membranes have an obvious dual-phase structure and excellent compactness. The results of the oxygen permeability experiment show that the oxygen permeability of CSC-3782 is always higher than that of CSC-8282 under any conditions due to the inducing effect of strontium on oxygen vacancies, and flow rate of CSC-3782 at 960°C reached 0.64 and 0.22mL⋅cm
-2
⋅min
-1
for He and CO
2
as a sweep gas, respectively. The final long-term stability test confirmed that the dual-phase composite membrane with great prospects for development has high temperature stability and CO
2
-tolerant property, and the doping of strontium to A-site of perovskite contributes to the improvement of its performance.
Distributed generation (DG) has gradually become significant in the power system owing to energy shortages and environmental pollution. However, the traditional structure of power systems is changed ...with the advent of DG, and the output power of DG has the characteristic of randomness due to relying on renewable energy, which will cause risks in the power system. This paper studies the issue of economic dispatch while not only considering the power system's controllable DG but also taking uncontrollable DG with single or multiple generator failures into account. Firstly, we built the random power output models of distributed generators including wind power, solar power, fuel cell and diesel. Considering random power output of DG, then we present dynamic energy dispatching strategies to keep voltage deviation, active power loss and fuel cost to a minimum. In addition, we presented three improved bare-bones particle swarm optimization (BBPSO+) algorithms to adopt the model presented in the paper. Finally, this paper evaluates the improved method's performance through the IEEE 118-bus system and also compares solution quality and convergence performance of the BBPSO+ with genetic algorithm (GA), PSO, random drift PSO (RDPSO) and BBPSO. The experimental result indicates that in case of considering both controllable and uncontrollable DG, the BBPSO+ algorithm solves problems more effectively and is promising to be applied in a power system.
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