Thermodynamic design of cold storage-based alternate temperature systems

International audienc

A Traveling-Wave-Based Fault Location Scheme for MMC-Based Multi-Terminal DC Grids

This paper presents a novel fault location scheme of DC line in modular multilevel converter (MMC)-based multi-terminal DC (MTDC) grids. Considering the low-inertia characteristics and the meshed topology, the scheme, based on traveling-wave principle, is divided into three steps, namely, faulty pole identification, faulty segment determination and fault-distance calculation. With accurate amplitude, polarities and arrival times of the first arrival current traveling waves (FACTWs) collected from time-synchronized measurements taken just at the converter stations, the proposed scheme can correctly determine the faulty pole, the faulty segment and the precise fault location. The continuous wavelet transform (CWT) is deployed to extract the required features of the input signals at the DC lines. Since the scheme merely needs the features of FACTWs, the practical difficulties of detecting subsequent traveling waves are avoided. A four-terminal MMC-based high voltage direct current (HVDC) grid was built in PSCAD/EMTDC software to evaluate the performance of the fault-location scheme. Simulation results for different cases demonstrate that the proposed fault-location scheme has high accuracy, good adaptability and reliability. Furthermore, the algorithm can be used for a MMC-MTDC grid with any number of meshes

Thermo-Fluid Characteristics of High Temperature Molten Salt Flowing in Single-Leaf Type Hollow Paddles

A single-leaf type paddle heat exchanger with molten salt as the working fluid is a proper option in high temperature heating processes of materials. In this paper, based on computational fluid dynamics (CFD) simulations, we present the thermo-fluid characteristics of high temperature molten salt flowing in single-leaf type hollow paddles in the view of both the first law and the second law of thermodynamics. The results show that the heat transfer rate of the hollow paddles is significantly greater than that of solid paddles. The penalty of the heat transfer enhancement is additional pressure drop and larger total irreversibility (i.e., total entropy generation rate). Increasing the volume of the fluid space helps to enhance the heat transfer, but there exists an upper limit. Hollow paddles are more favorable in heat transfer enhancement for designs with a larger height of the paddles, flow rate of molten salt and material-side heat transfer coefficient. The diameter of the flow holes influences the pressure drop strongly, but their position is not important for heat transfer in the studied range. Other measures of modifying the fluid flow and heat transfer like internal baffles, more flow holes or multiple channels for small fluid volume are further discussed. For few baffles, their effects are limited. More flow holes reduce the pressure drop obviously. For the hollow paddles with small fluid volume, it is possible to increase the heat transfer rate with more fluid channels. The trade-off among fluid flow, heat transfer and mechanical strength is necessary. The thermo-fluid characteristics revealed in this paper will provide guidance for practical designs

Sep. Sci. Technol.

The essential oil was obtained by supercritical fluid extraction from dried roots of Ligusticum chuanxiong. Different solvent systems for high-speed counter-current chromatography (HSCCC) were compared. A system composed of n hexane-ethyl acetate-methanol-water-acetonitrile in the ratio of 8:2:5:5:3 (v/v) was found to be optimum for HSCCC of the essential oil. Z ligustilide and senkyunolide A were separated by HSCCC with purity of 98% determined by GC. The chemical structures of these two components were identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS).The essential oil was obtained by supercritical fluid extraction from dried roots of Ligusticum chuanxiong. Different solvent systems for high-speed counter-current chromatography (HSCCC) were compared. A system composed of n hexane-ethyl acetate-methanol-water-acetonitrile in the ratio of 8:2:5:5:3 (v/v) was found to be optimum for HSCCC of the essential oil. Z ligustilide and senkyunolide A were separated by HSCCC with purity of 98% determined by GC. The chemical structures of these two components were identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS)

A Novel Busbar Protection Based on the Average Product of Fault Components

This paper proposes an original busbar protection method, based on the characteristics of the fault components. The method firstly extracts the fault components of the current and voltage after the occurrence of a fault, secondly it uses a novel phase-mode transformation array to obtain the aerial mode components, and lastly, it obtains the sign of the average product of the aerial mode voltage and current. For a fault on the busbar, the average products that are detected on all of the lines that are linked to the faulted busbar are all positive within a specific duration of the post-fault. However, for a fault at any one of these lines, the average product that has been detected on the faulted line is negative, while those on the non-faulted lines are positive. On the basis of the characteristic difference that is mentioned above, the identification criterion of the fault direction is established. Through comparing the fault directions on all of the lines, the busbar protection can quickly discriminate between an internal fault and an external fault. By utilizing the PSCAD/EMTDC software (4.6.0.0, Manitoba HVDC Research Centre, Winnipeg, MB, Canada), a typical 500 kV busbar model, with one and a half circuit breakers configuration, was constructed. The simulation results show that the proposed busbar protection has a good adjustability, high reliability, and rapid operation speed

Heregulin-1β Promotes the Synergistic Effect Between Allogenic Skin-Derived Precursor Differentiated Schwann Cells (SKP-SC) and Acellular Nerve Allograft (ANA) in Peripheral Nerve Regeneration Through Inhibiting Mir-21

Previous studies in our lab found that heregulin-1β with SKP-SCs (neurons and Schwann cells differentiated from SKPs) / ANA (acellular nerve allograft) transplantation represented a powerful therapeutic approach, and facilitates the efficacy of ANA in peripheral nerve injury. In this study, our purpose is to explore the mechanism between them. Firstly we transplanted ANA + SKP-SC + heregulin-1β into rats with right sciatic nerve injury and then detected the miR-21 and SOX2 (SRY-like HMG box 2) levels. Then we transfected miR-21 inhibitor in SCs (Schwann cells) which induced in hypoxic condition before harvesting. Then we detected expression of miR-21 and SOX2 using real time-PCR and western blot assay. Results in vivo showed that the expression of miR-21 in rats was inhibited after transplantation of ANA + SKP-SC + heregulin-1β with induced SOX2 accordingly. Then we found miR-21 was increased time dependently in hypoxic SCs with decreased SOX2 accordingly. After miR-21 inhibitor transfection, miR-21 level was reduced and SOX2 was up-regulated. Meanwhile it was also showed that the miR-21 inhibitor induced the hypoxic SCs growth, decreased the apoptosis with cell cycle changing. In conclusion miR-21 and its target gene SOX2 played important role in peripheral nerve injury. Heregulin-1β may increase the synergistic effect between SKP-SC and ANA through inhibiting miR-21 in vivo

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Thermodynamic Performance of Molten Salt Heat Storage System Used for Regulating Load and Supplying High Temperature Steam in Coal-Fired Cogeneration Power Plants

In order to accept more electricity from renewable energy, cogeneration power plants are considering to reduce electricity production, which affects the heat supply. Here we present a molten salt heat storage system for coal-fired cogeneration power plants, which can supply high temperature steam to users and decouple the heat and electricity production. The first and second law-based analytical models for the cycle and a real device are built. Two water input methods are taken into account. The results show that the high and low temperatures in the two molten salt tanks influence the design of the components and the entropy generation distribution significantly. The pinch temperature difference in the discharge duration limits the lowest molten salt temperature. The device with real heat exchangers produces higher entropy generation and lower second law efficiency. Environmental water input requires more heat and entropy generation for the same steam supply. Recommendations are provided for practical designs