Charging Flow Rate Research Articles

Transient evolution of thermal stratification and passive flow guidance inside a heat exchanger immersed thermal energy storage tank

Thermal stratification is being studied globally for thermal storage tanks while natural convection motion has a high impact on the phenomenon. Therefore, in this work, a conical guide geometry is introduced as a passive flow modifier to enhance the thermal stratification inside a cylindrical tank that is used for thermal storage purposes. The tank also has an immersed spiral coil heat exchanger in it. Transient evolution of thermal stratification inside the thermal storage tank is monitored for different charge flowrates and temperatures. The experimental data is used to benchmark a commercial computational fluid dynamics code relying on finite volume method. After seeing that the code simulates the transient thermal stratification with acceptable discrepancies, a conical guide geometry above the immersed heat exchanger is examined via the computational code for dimensional variations. The dimensions of the cone guide are defined based on thermal storage tank dimensions in order to have some degree of universality. The best performing cone guide in the simulations is then tested experimentally. It is validated that the proposed cone guidance enhanced thermal stratification evolution in the tank. An increase of 3.85 °C is obtained in the average tank temperature with the use of the cone guide after 3 h of charging. Approximate effectiveness of the heat exchanger coil is found about 90 % while a 7.6 % increase is realized by the utilization of the guide.

Thermal energy storage integration for increased flexibility of a power plant with post-combustion CO2 capture

Flexible operation of thermal power plants will become increasingly relevant in the coming years. This work evaluates the effect of integrating a steam accumulator into a 598 MW supercritical coal-fired power plant with moving bed temperature-swing adsorption CO2 capture. Charging the accumulator with reheat steam from the turbine train can reduce the net power output by up to 1.4 % (8.2 MW) for around 200 min. Small charging flow rates are recommended to maximize the final pressure of the accumulator. Covering the sorbent regeneration duty and meeting the demand of two feedwater heaters were considered as alternatives for discharging of the accumulator. Thermal storage discharging was found to give relative power plant load increases between 1.7 and 11.2 % (10.2–66.9 MW) for up to 37.5 min, which exceeds the requirement for primary reserve. Increases in the electrical energy output of 10.5–11 MWh were achieved. The flexibility modes studied in this work are compatible with high CO2 recovery rates.

Heat transfer and thermal resistance analysis under various heat transfer fluid flow rates based on a medium-temperature pilot-scale latent heat storage system

Assessments often rely on experimentally observed factors when examining heat transfer variations due to different heat transfer fluid (HTF) flow rates. To better comprehend limiting factors and guide operational parameter design for shell-and-tube latent heat system (LHS) systems, a quantitative analysis of thermal resistance hindering heat transfer is crucial. Hence, this article conducted experimental evaluations at various flow rates to critically analyze its thermal performance based on a large-capacity (1000 MJ) medium-temperature LHS system loaded with 4130 kg commercial nitrate mixture (peak melting temperature: 219.90 °C). The heat transfer coefficient and thermal resistance during charging and discharging were quantitatively investigated to identify the main factors influencing heat transfer and dominant mechanisms. The results suggested that augmenting the charging flow rate from 5 to 15 L/min resulted in 2.65 times increase in average power (from 24.01 to 63.64 kW). Besides, during charging, the overall thermal resistance primarily came from the phase change material (PCM) side initially. As PCM melted, the thermal resistance on the PCM side became equivalent to that on the HTF side. Increasing the charging flow rate enhanced heat transfer through two mechanisms: reducing the thermal resistance on the HTF side and increasing the driving force of heat transfer by elevating the average HTF temperature. During discharging, the overall thermal resistance was predominantly derived from the PCM side after solidification. Increasing the discharging flow rate caused a limited influence on decreasing thermal resistance. Enhancing the discharging flow rate only bolstered the driving force for heat transfer by elevating the average HTF temperature. This study provides valuable insights into the factors influencing heat transfer in LHS systems and contributes to optimizing LHS technology.

Experimental Investigation of Thermal Runaway Propagation in a Lithium-Ion Battery Pack: Effects of State of Charge and Coolant Flow Rate

Lithium-ion batteries (LIBs) are widely used as power sources for electric vehicles due to their various advantages, including high energy density and low self-discharge rate. However, the safety challenges associated with LIB thermal runaway (TR) still need to be addressed. In the present study, the effects of the battery SOC value and coolant flow rate on the TR behavior in a LIB pack are comprehensively investigated. The battery pack consists of 10 18650-type LIBs applied with the serpentine channel liquid-cooling thermal management system (TMS). The TR tests for various SOC values (50%, 75% and 100%) and coolant flow rates (0 L/h, 32 L/h, 64 L/h and 96 L/h) are analyzed. The retarding effect of the TMS on TR propagation is found to be correlated with both the coolant flow rate and the battery SOC value, and a larger coolant flow rate and lower SOC generally result in fewer TR batteries. Furthermore, the TR propagation rate, evaluated by the time interval of TR occurrence between the adjacent batteries, increases with the battery SOC. The battery pack with 100% SOC shows more rapid TR propagation, which can be completed in just a few seconds, in contrast to several minutes for 50% and 75% SOC cases. In addition, the impact of the battery SOC and coolant flow rate on the maximum temperature of the TR battery is also examined, and no determined association is observed between them. However, it is found that the upstream batteries (closer to the external heater) show a slightly higher maximum temperature than the downstream ones, indicating a weak association between the TR battery maximum temperature and the external heating duration or the battery temperature at which the TR starts to take place.

Experimental Study of Simultaneous Charging and Discharging Process in Thermocline Phase Change Heat Storage System Based on Solar Energy

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system.

Experimental study on the storage performance of the innovative spray-type packed bed thermal energy storage

• A 10 kW spray-type packed bed thermal energy storage test rig was built. • Effect of charging temperature, flow rate and cut-off temperature were discussed. • Charge and discharge behavior of thermal energy under different states were studied. • Energy and exergy efficiency achieved 96.06% and 54.29% over 5 cycles. Thermal energy storage (TES) has been recognised as an effective way to overcome the temporal mismatch between energy generation and users’ requirements. The innovative spray-type packed bed TES technology has promising development prospects owing to its advantages of high efficiency and low cost. In this study, a 10kW/10kWh spray-type packed bed TES test rig with aluminium spheres as storage media and thermal oil as the heat transfer fluid was established. The effects of parameters, including the charging temperature, flow rate, and cut-off temperature, as well as continuous-cycle experiments, on the heat storage performance were investigated. The experimental results show that the charging temperature and flow rate had little effect on the thermocline. A more even radial temperature distribution was obtained at a higher charging temperature and lower flow rate. The efficiency analysis indicated that increases in the values of the studied parameters promoted exergy efficiency, whereas only the flow rate was positive correlated with energy efficiency. Furthermore, energy efficiency was found to exceed 90% in most cases in this study. During continuous cycles, the energy and exergy efficiencies can reach 96.06% and 54.29%, respectively.

Experimental Energetic and Exergetic Performance of a Combined Solar Cooking and Thermal Energy Storage System

Most solar cookers usually perform a single task of solely cooking food during sunshine hours. Solar cookers coupled with thermal energy storage (TES) material for off-sunshine cooking are usually expensive and require complex engineering designs, and cannot be used for dual purposes, for example, solar water heating and cooking. In this paper, a solar cooker that can perform dual tasks of cooking as well as storing thermal energy to be used during off-sunshine periods is presented. The experimental setup is composed of a parabolic dish, a solar receiver coupled with a flat plate and an oil-circulating copper coil for charging and discharging a storage tank. The objective of the experiment is to evaluate the energy and exergy thermal performance parameters of the dual-purpose system during charging and discharging cycles. The effect of the flow rate and the mass of the load are investigated while using sunflower oil as both the heat transfer fluid and the storage material. Charging and discharging experiments are conducted using four different flow rates (2, 3, 4, 5 mL/s), and with different masses (0.5, 1, 1.5, 2.0 kg) with water and sunflower oil as the test loads. The charging results show that the average energy and exergy rates as well as their corresponding efficiencies increase with an increase in the charging flow rate. On the other hand, the increase in the mass load tends to decrease marginally the average charging energy and exergy rates for water, and their corresponding efficiencies. For sunflower oil, the average charging energy and exergy rates and efficiencies showed a more pronounced decrease with an increase in the mass. Water generally shows higher charging and discharging energy and exergy efficiencies compared to sunflower oil with an increase in the flow rate. For discharging results, the correlations between the energy and exergy thermal performance parameters with respect to the flow rate and the heating load are not well defined possibly due to different initial storage tank temperatures at the onset of discharging and the inefficient discharging process which needs to be optimized in future.

Influence of operating conditions on the removal of silica and hardness by continuous electrocoagulation

In this study we investigated the removal of silica and hardness by continuous electrocoagulation (EC), based on treatment of oil-sands produced water. The effect of operating parameters including charge loading, flow rate, current density and polarity reversal period were investigated. As expected, the removal of silica and hardness increased with charge loading. At a fixed charged loading, the flowrate was found to have only a slight impact on silica removal. With both Fe and Al electrodes, a slight decrease in contaminant removal was observed at high flow rates, likely due to the shear breakup of flocs. For the range of conditions studied, the removal of Si, Ca and Mg increased with the polarity reversal time (from 30 s to 10 min), while the cell voltage (and energy consumption) decreased. The cell voltage obtained with 10 min polarity reversal was significantly lower than that for DC-EC. More than 80 % silica removal was achieved using a current density of 8 mA cm–2, charge loadings of 1500 C L⁻1 and 1000 C L⁻1 with Fe and Al electrodes respectively. Al-EC was found to consume less electrode material and energy while achieving higher Si, Ca, and Mg removal compared to Fe-EC. Economic evaluation revealed that for >80 % Si removal the specific energy consumption was 1.13 and 0.70 kWh m–3, with a total operating cost C$0.54 and C$0.50 per m3 of water treatment, for Fe and Al-EC respectively.

Experimental investigation of heat dispatch controllability through simultaneous charging-discharging and stand-alone discharging operations in vertical cylindrical sensible heat storage tank

Using a vertical cylindrical thermal energy storage (TES) tank with helical discharging coil fitted inside, the present study experimentally investigates the scarcely studied simultaneous charging and discharging (SCAD) mode, as well as the discharging-alone operation following a substantial stand-alone period. The temperature distributions within the tank, coil outlet temperature and primary thermocline thickness serve as the key performance trackers for the storage tank. The primary thermocline thickness increases with increasing coil side flow rate during the SCAD operation. The SCAD operation exhibited the splitting of the primary thermocline, leading to the formation of a secondary thermocline in the lower half of the tank. The sustenance of secondary thermocline, thermal gradients across the tank height, and the discharging efficiency are found to decrease with increasing charging flow rate, whereas the coil outlet temperature and the primary thermocline thickness increase. The highest average discharging efficiency of 80.1 % is observed for the TES charging at 0.5 L/min at 70 °C, accompanied by the 2 L/min discharging flow rate. The average thermal energy stored is the maximum (1758 kJ) for the TES charging at 1.25 L/min at 70 °C, with discharging rate of 0.5 L/min. The stand-alone period prior to the discharging-alone operation exhibits the heat content retention capability of the storage and allows for the thermocline formation. The time required for thermal stratification is more with the higher initial charging temperature. The time required for the complete discharging of the TES storage tank decreases with increasing coil-side flow rate. These modes provide ample operational flexibility and heat content dispatch controllability, resulting in the versatility of the system.

Investigating the Role of Temperature on the Performance of Vanadium Redox Flow Batteries Using a Steady Validated Unit-Cell Model

Redox Flow Batteries (RFBs) are an evolved electrochemical energy storage technology crucial for the transition into a renewable energy future. Mainstream adoption of RFBs is subject to reduction of the capital and operation costs. In that sense, of particular importance is the optimization of the electrochemical stack, which affects the overall efficiency of the battery. Several studies have investigated the importance of thermal effects on the performance of vanadium redox flow batteries through transient non-isothermal models [1-2]. However, due to the simplified assumptions made by these authors some important temperature-dependent features are not included. Therefore, reliable and validated continuum models are also crucial to study the impact of the system temperature on all the fundamental physics in the electrochemical cells as well as to find the key aspects to optimize the stack.In this work, we present a 2D stationary model of a vanadium redox flow battery cell with a comprehensive and updated multiphysics description. The model was validated at a constant temperature of 25 ºC by polarization, conductivity, and open circuit voltage measurements. In a second step, the temperature was also included as a key operating variable in the model. Electrolyte properties, electrochemical rate constants, and H2SO4 dissociation equilibrium were described as a function of temperature as well as the state of charge (SoC) and the total vanadium concentration. The model is currently being validated through a second experimental campaign (see Fig. 1) conducted inside a climatic chamber imitating different environmental scenarios. The model can be used to explore the relevance of each phenomenon or element in the electrochemical stack and the influence of the operating conditions on them, e.g. temperature, state of charge and volumetric flow rate. By using the proposed model, we can elucidate the best temperature strategy to increase the performance of vanadium redox flow batteries in diverse operating scenarios.Figure 1. Open circuit voltage – SoC relation at different operating temperatures. References Al-Fetlawi, A.A. Shah, F.C. Walsh, Electrochimica Acta, 55, 78-89 (2009).Tang, S. Ting, J. Bao, M. Skyllas-Kazacos, Journal of Power Sources, 203, 165-176 (2012). Acknowledgments This work has been partially funded by the Agencia Estatal de Investigación (PID2019-106740RB-I00 and RTC-2017-5955-3/AEI/10.13039/501100011033). Figure 1

Heat transfer, energy conversion, and efficiency during cold discharge of a novel tetrabutylammonium bromide hydrate cold storage system

• External melting by internal heat exchange was used to study hydrate cold discharge. • Thermal buffering occurred due to energy balance caused by heat transfer. • Forced convection from gas disturbance reduced cold discharge time by 3 times. • Cold discharge efficiency can be maintained above 83 % under different conditions. • Time-efficiency number was proved to quantify the total cold discharge efficiency. Cold storage technologies using clathrate hydrates as working media have recently attracted more attention in the energy storage field because they undergo phase transitions with large latent heats and suitable temperatures for cold storage. However, the application of hydrate cold storage technologies is limited by the fact that the cold discharge mechanism is still unclear. Thus, this paper adopted the method of external melting by internal heat exchange to investigate the heat transfer, energy conversion and efficiency of a novel tetrabutylammonium bromide (TBAB) hydrate cold storage system during cold discharge. The system consisted of an internal circulating gas disturbance device and a metal spiral hydrate-on-coil heat exchanger. The heat transfer mechanism and cold discharge capacity, rate, and efficiency for different cold charge temperatures, flow rates and disturbance modes were compared and analyzed. A novel time-efficiency number was introduced to evaluate the comprehensive performance of the time, energy conversion and efficiency of cold discharge. The results showed that the heat exchange balance during the cold charge and discharge stages had a thermal buffering effect on the storage unit. Forced convection caused by gas disturbance resulted in a larger cold discharge capacity and reduced the discharge time by a factor of 3 compared to operation without gas disturbance. In addition, the cold discharge capacity gradually increased with decreasing cold charge temperature and increasing flow rate. The cold discharge efficiency was more than 83% under different conditions. A comparison showed that the time-efficiency number tended to be larger with gas disturbance. This study showed that the time-efficiency number can be used for quantitative comparison of the cold discharge time and efficiency in hydrate cold storage systems.

Prospect of modeling industrial scale flow batteries – From experimental data to accurate overpotential identification

A vast literature exists on modelling of small-scale single-cell experiments for flow batteries, but very few reports have been published on large stacks, consisting of tens of cells, each with an active area of hundred square centimeters. In this report, a large set of measurements taken on a kW-class vanadium test facility is used to develop an accurate ad-hoc physical model. Experimental data consist of polarization curves at a broad range of states of charge and electrolyte flow rates, as well as electrochemical impedance spectra. The model is capable to decouple three sources of voltage losses: activation, ohmic, and concentration overpotentials. In addition, a new numerical approach for identifying the main parameters of electrochemical kinetics and mass-transport has been proposed. To the best of our knowledge, this is the first time when a model for voltage losses analyses was developed and fitted to a data from large-scale flow battery, being validated with a sensitivity analysis study. Investigations showed that activation losses have a sophisticated nature in combination with mass-transport limitations and play an important role in a wide range of loading current densities. As a result, they must be included in a reliable model able to reflect a non-linear voltage behavior of large stacks. This work also highlights that, in the investigated case, activation losses are likely to be attributed to the positive electrode rather than to the negative one. The obtained results could facilitate the development of advanced simulation and design of large-scale flow battery stacks.

Temperature Regulation Model and Experimental Study of Compressed Air Energy Storage Cavern Heat Exchange System

The first hard rock shallow-lined underground CAES cavern in China has been excavated to conduct a thermodynamic process and heat exchange system for practice. The thermodynamic equations for the solid and air region are compiled into the fluent two-dimensional axisymmetric model through user-defined functions. The temperature regulation model and experimental study results show that the charging time determines the air temperature and fluctuates dramatically under different charging flow rates. The average air temperature increases with increasing charging flow and decreasing charging time, fluctuating between 62.5 °C and −40.4 °C during the charging and discharging processes. The temperature would reach above 40 °C within the first 40 min of the initial pressurization stage, and the humidity decreases rapidly within a short time. The use of the heat exchange system can effectively control the cavern temperature within a small range (20–40 °C). The temperature rises and regularly falls with the control system’s switch. An inverse relationship between the temperature and humidity and water vapor can be seen in the first hour of the initial discharging. The maximum noise is 92 and 87 decibels in the deflation process.

Origin of photo-enhanced hysteretic electrical conductance in nanostructured silicon-based heterojunction

Photo-enhanced hysteretic I–V curves have been observed under reverse bias in a p-i-n structure containing electrochemically etched nanostructured silicon (Si) sandwiched between p-Si and n-type a-Si:H layers. These curves have been found to depend on intensity of incident illumination and structural morphology of the nanostructured Si layer. The conductance in trace path is lower than that in retrace path. Charge transport mechanism in this structure has been interpreted using microscopic description of charge trapping and detrapping in the defect states present at the interface of nanocrystalline silicon core and oxide shell in the active layer. An applied voltage dependent probability distribution of trapping and detrapping has been calculated in light of classical random walk problem. The trapping/detrapping of charges leading to development/destruction of potential barriers in the path of charge flow shows an analogy with the river bed deposition/erosion. The rate of trapping has been considered to depend on the empty defect states whereas the rate of detrapping depends on the already filled defects. Moreover, the rate of both trapping and detrapping is expected to depend on the charge flow rate. All these considerations lead the I–V relations for trace and retrace paths in reverse bias fitting nicely with experimental I–V loops. The observed peaks in the voltage dependent dynamic conductance in trace and retrace paths have been explained as a consequence of development and destruction of two barriers in the active layer for electrons and holes separately. Best fit values of the fitting parameters indicates that the trace path is dominated by holes whereas the retrace path is dominated by electronic transport. The difference in mobility of electron and hole leads to different trapping and detrapping rates in the two paths resulting in the observed hysteresis.

A partially underground rock bed thermal energy storage with a novel air flow configuration

Low-cost, grid-level energy storage is key to maximizing the utilization of renewable energy production and decarbonizing the electricity sector. The design and testing of a high-temperature thermal energy storage based on rocks is presented. Important design features are the three electric heaters mounted on top of the storage and the inner pipe inside the rock bed, allowing for the first time a reversible vertical air flow configuration of a system which is partially underground. The rock bed storage is highly scalable and based on diabase which is abundant as well as low-cost in Northern Europe and other locations. A pilot plant with a storage capacity of 1 MWhth has been operated up to 675°C. The first law round-trip efficiency of 70.7% in an initial operation exceeds all efficiencies observed in a previously built thermal storage with horizontal flow configuration. By improving the operation with charge and discharge air flow rates of 140 and 300 Nm/h3, respectively, the first law round-trip efficiency increases to 80.7%. A maximum thermal output of 58.06 kW is achieved, of which 90% can already be provided within 6 min of start-up. This paper demonstrates that the novel medium-scale storage can operate with a satisfactory performance for several years with no failures to date.

Fault Detection Algorithm for Multiple-Simultaneous Refrigerant Charge and Secondary Fluid Flow Rate Faults in Heat Pumps

The detection and diagnosis of faults is becoming necessary in ensuring energy savings in heat pump units. Faults can exist independently or simultaneously in heat pumps at the refrigerant side and secondary fluid flow loops. In this work, we discuss the effects that simultaneous refrigerant charge faults and faults associated with the flow rate of secondary fluids have on the performance of a heat pump operating in summer season and we developed a correlation to detect and diagnose these faults using multiple linear regression. The faults considered include simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults (IFRFs), simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults (OFRFs) and simultaneous refrigerant charge, IFRF and OFRF. The occurrence of simultaneous refrigerant charge fault, IFRF and OFRF caused up to a 5.7% and 8% decrease in cooling capacity compared to simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults, and simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults, respectively. Simultaneous refrigerant charge fault, IFRF and OFRF resulted in up to an 11.6% and 5.9% decrease in COP of the heat pump unit compared to simultaneous refrigerant charge fault and IFRF, and simultaneous refrigerant charge fault and OFRF, respectively. The developed FDD correlations accurately predicted the simultaneous refrigerant charge and faults in the flow rate of the secondary fluid within an error margin of 7.7%.

Calculations for Coking Chamber Designs with Various Feedstock Charging Methods

The efficiency of various designs of devices for charging feedstock into coking chambers of delayed coking plants is analyzed by hydrodynamic and thermal modeling using ANSYS software. It is demonstrated that the design with two-way feedstock charging using expansible diffusers for reducing charge flow rate, which ensures uniform feedstock mixing, is most efficient.

Performance analysis of consolidated sorbent based closed thermochemical energy storage reactor for environmental sustainability

Adsorption thermochemical energy storage (TCES) is currently a momentous technique utilised for long-term energy storage due to the reversible gas-solid reaction under low-temperature. A novel 3D heat storage reactor, including two shaped columnar sorbent reactive beds is proposed. The heat charging (dehydration) and discharging (hydration) processes under different operating conditions are numerically investigated. The roughly uniform temperature and conversion degree evolutions of the bed during reaction suggest a good heat and mass transferability of the porous shaped sorbent bed. For reference cases, the time required to finish the dehydration and hydration processes are 328 and 748 min; the decreased condensation temperature and increased evaporation temperature promote dehydration and hydration kinetics. The charging power and thermal efficiency increase firstly and decline later till the end of dehydration, the final values are 212 W and 91.1%; while discharging power and efficiency decrease with the advancement of conversion degree, with thermal power and thermal efficiency of 93 W and 87.5%. Moreover, the overall thermal coefficient of performance of 80.9% and exergy coefficient of performance of 27.7% are achieved; and the coefficients of performance can be further optimised at specific charging temperature and flow rate of heat transfer fluid (HTF). All these satisfying performances of this model preliminarily confirm its feasibility in TCES.

Optimization Design and Numerical Investigation on Ball Valve of High Pressure Coal Slurry Pump

The charging flow rate fluctuation of the coal slurry pump was caused by the ball valve. In this study, the reconstruction was established to increase the circulation area surrounding the valve ball, the valve limiter was redesigned. The numerical simulation of the structure and performance of the ball valve is carried out with the new limiter structure, getting the flow resistance and the operational parameters The simulation results showed that the new limiter can effectively eliminate the flow fluctuation caused by the old limiter, the reform was successful to bring huge economic benefits to the plant.

Enhancing the efficiency of kW-class vanadium redox flow batteries by flow factor modulation: An experimental method

The paper presents a control method of the electrolyte flow factor in kW-class Vanadium Redox Flow Batteries that minimizes transport losses without affecting the battery's electrical performance. This method uses experimental data acquired on a 9 kW/27 kWh test facility at varying operating conditions. The effects of overpotentials on the polarization curves are then modeled as non-linear electrical resistances that vary with the stack current, state of charge and electrolyte flow rates. Our analysis of these variables shows that the optimal performance is found if the flow factor is modulated during operation according to stack current and the battery state, so as to minimize the overall flow-dependent losses. The optimal profiles have been identified as functions of the battery's operating conditions. Based on these results, a dynamic control for the electrolyte flow rates has been implemented at a software level (i.e. without modifying the hardware of the test facility), which is capable of maximizing the round-trip efficiency and exceeds the performance achieved with a constant flow factor strategy, as proposed in previous literature. The implementation of the optimal flow rate control requires a preliminary test campaign to collect performance data, which are then used in the control protocol to manage the battery's operation. This scheme is easily implementable at a software level in other industrial redox flow batteries.