Wide Range Of Operating Conditions Research Articles

Control of superheat of organic Rankine cycle under transient heat source based on deep reinforcement learning

The organic Rankine cycle (ORC) is a promising technology for engine waste heat recovery. During real-world operation, the engine working condition varies frequently to satisfy the power demand; thus, the transient nature of engine waste heat presents significant control challenges for the ORC. To control the superheat of the ORC precisely under a transient heat source, several optimal control methods have been used such as model predictive control and dynamic programing. However, most of them depend strongly on the accurate prediction of future disturbances. Deep reinforcement learning (DRL) is an artificial-intelligence algorithm that can overcome the aforementioned disadvantage, but the potential of DRL in control of thermodynamic systems has not yet been investigated. Thus, this paper proposes two DRL-based control methods for controlling the superheat of ORC under a transient heat source. One directly uses the DRL agent to learn the control strategy (DRL control), and the other uses the DRL agent to optimize the parameters of the proportional–integral–derivative (PID) controller (DRL-based PID control). Additionally, a switching mechanism between different DRL controllers is proposed for improving the training efficiency and enlarging the operation range of the controller. The results of this study indicate that the DRL agent can satisfactorily perform the control task and optimize the traditional controller under the trained and untrained transient heat source. Specifically, the DRL control can track the reference superheat with an average error of only 0.19 K, whereas that of the traditional PID control is 2.16 K. Furthermore, the proposed switching DRL control exhibits excellent tracking performance with an average error of only 0.21 K and robustness over a wide range of operation conditions. The successful application of DRL demonstrates its considerable potential for the control of thermodynamic systems, providing a useful reference and motivation for the application to other thermodynamic systems.

Influencing factors on flow boiling of carbon dioxide in enhanced tubes and comparison with correlations

Carbon dioxide two-phase flow characteristics are different from those of conventional refrigerants, due to the CO2 particular thermodynamic and transport properties obtained by working at high reduced pressures. Moreover, the use of peculiar heat transfer surfaces such as grooves and internal fins are often preferred to enhance the boiling heat transfer performance. This paper collects CO2 flow boiling heat transfer coefficient data from different independent databases available in scientific literature, regarding both smooth and enhanced geometries and a wide range of operative conditions, that are typical of refrigeration systems and heat pumps. The database for enhanced tubes covers internal diameters from 0.8 to 8.92 mm, saturation temperatures from -30 to +20 °C, imposed heat fluxes from 1.67 to 60 kW/m2 and mass velocities from 75 to 800 kg/m2s, collecting more than 800 points. Heat transfer data for smooth and enhanced surfaces under the same conditions are collected, in order to measure the enhancement and to correlate it to the geometry augmentation. The assessment of quoted prediction methods explicitly developed for carbon dioxide is finally carried out, with a proposal for a correction factor.

Diagnosis of hydrous ethanol combustion in a spark-ignition engine

By evaluating combustion duration and flame development, it is possible to evaluate the effects of utilizing a new type of fuel. This allows for optimization of the operational parameters such as the ignition timing, air–fuel ratio, and throttle opening with respect to efficiency, knock, emissions, and performance. In this work, the combustion of a Brazilian hydrous ethanol fuel was evaluated in a commercial flexfuel engine. Investigations were conducted by performing a heat release analysis of the experimental data and providing combustion characteristics. The experimental design comprised of variations in engine speed, load, ignition timing, and air–fuel ratio under lean condition. The results indicated the relationship between the engine parameters and combustion characteristics under a wide range of operational conditions, and identified the relationship between the physical characteristics of the fuels and their combustion in the commercial engine. For high engine speed, lean combustion presented a similar duration to the stoichiometric combustion duration. When comparing the combustion characteristics obtained for the hydrous ethanol with gasoline combustion, the main differences noted were reduced sensitivity to detonation and a shorter duration of combustion, although the temperature at the start of combustion was lower for ethanol. In addition to shorter combustion duration, ethanol presented a lower value for the Wiebe exponent. The results obtained from the combustion duration values and Wiebe function parameters enable the composition of a set of data required for a simplified combustion simulation.

Mass transfer in coalescent batch fermenters with mechanical agitation

Volumetric mass transfer coefficient (kLa), is the critical transport characteristic in the design of mechanically agitated contactors. Prediction of kLa is nowadays mostly based on literature correlations. Our aim is to establish suitable kLa correlations for different types of devices that would be based on the experimental data set. In our previous work, the correlation for kLa prediction in coalescent batch were described only for Rushton turbines (Petříček et al., 2019). Now, we aim at the description of one universal correlation that would be viable for mechanically agitated contactors in coalescent batch for several impeller types with different diameters and their combinations on a common shaft. The measured transport characteristics were summarized into correlations. This correlation shape can be used to predict transport characteristics in industrial-scale vessels under a wide range of operational conditions.

Performance evaluation of a retrofitted multi-cyclone using computational fluid dynamic

Multi-cyclone is widely used in industries as air pollution control device due to several advantages over other available separation units such as its low capital, operating, and maintenance cost and as well as its usability under a wide range of operational conditions. However, it is merely a pre-cleaner as it is inefficient in collecting fine particulate especially, particulate matter with size less than 10 µm (PM10) and below. Hence a simple, cost-effective retrofit on a Conventional Multi-cyclone (CMC) with the motivation of increasing its overall performance on fine particulate emission control was carried out. The retrofit was performed by creating higher negative pressure inside the dust hopper of the CMC by extracting 10% and 24% from the total volumetric airflow rate of the unit with the means of an external Induced Draft Fan. The Computational Fluid Dynamics (CFD) with Reynold Stress Model (RSM) turbulence model was performed and validated using experimental data to gain a better understanding in pressure distribution, velocity profile and particulate movement between the CMC and the Retrofitted Multi-cyclone (RMC). The CFD results show deviation between 0% to 8% for pressure at inlet and outlet of cyclone compared to the experimental results. In addition, CFD results depict that the RMC has higher pressure at the inlet and lower pressure inside dust hopper of CMC, which cause the finer particle to be pulled in through suction outlet. Also, the emission of fine particulate is reduced in RMC by 9% to 16%. compared to the CMC. Moreover, the phenomena at the suction duct can be clearly explained with the usage of CFD. The finding suggests that a simple, cost-effective retrofit at the multi-cyclone has increased the overall performance in the fine particulate collection, and the understanding of the phenomena could be enhanced by the CFD.

Modulation and Capacitor Voltage Balancing Control of Multilevel NPC Dual Active Bridge DC–DC Converters

The present paper provides a solution to operate multilevel dual active bridge (ML-DAB) converters built upon neutral point clamped switching legs in a full-bridge disposition and with any number of levels on either side of the converter. The main issue of such converters is addressing the inherent unbalance of the dc-link capacitor voltages, which hinders the proper operation and optimum utilization of the converter. The proposed solution comprises a generalized to N levels modulation and control scheme that allows operating these converters, while guaranteeing the proper balance of the dc-link capacitor voltages. The suitability of the proposed solution is verified through simulation and experimental tests performed in five different converter configurations, three of them with an asymmetric number of voltage levels, proving that capacitor voltage balance is achievable in a wide range of operation conditions. Moreover, the efficiency of the ML-DAB converters is demonstrated to be superior to the conventional two-level DAB case.

Cost analysis based on bioreactor cultivation conditions: Production of a soluble recombinant protein using Escherichia coli BL21(DE3)

The impact of cultivation strategy on the cost of recombinant protein production is crucial for defining cost-effective bioreactor operation conditions. This paper presents a methodology to estimate and compare cost impacts related to utilities as well as medium composition, using simple design equations and accessible data. Data from batch bioreactor cultures were used as case study involving the production of pneumococcal surface protein A, a soluble recombinant protein, employing E. coli BL21(DE3). Cultivation strategies and corresponding process costs covered a wide range of operational conditions, including different media, inducers, and temperatures. The core expenses were related to the medium and cooling. When the price of peptone was above the threshold value of US$ 30/kg, defined medium became the best choice. IPTG and temperatures around 32 °C led to shorter cultures and lower PspA4Pro production costs. The procedure offers a simple, accessible theoretical tool to identify cost-effective production strategies using bioreactors.

Parametric Reduced-Order Modeling of the Unsteady Vortex-Lattice Method

A method for frequency-limited balancing of the unsteady vortex-lattice equations is introduced that results in compact models suitable for computational-intensive applications in load analysis, aeroelastic optimization, and control synthesis. The balancing algorithm relies on a frequency-domain solution of the vortex-lattice equations that effectively eliminates the cost associated to the wake states. It is obtained from a transform of the underlying discrete-time equations, and it requires no additional geometrical or kinematic assumptions for the lifting surfaces. Parametric reduced-order modeling is demonstrated through interpolation over 1) projection matrices, 2) state-space realizations, and 3) transfer functions, which trade accuracy, robustness, and cost. Methods are finally exemplified in the dynamic stability of a T-tail configuration with varying incidence. Numerical studies show that a very small number of balanced realizations is sufficient to accurately capture the unconventional aeroelastic response of this system, which includes in-plane kinematics and steady loads, over a wide range of operation conditions.

Investigation on millimeter-scale W1/O/W2 compound droplets generation in a co-flowing device with one-step structure

Millimeter-scale W1/O/W2 compound droplets generation in a co-flowing microfluidic device with one-step structure was symmetrically observed through experiments, and the formation process is distinguished according to the variation law of thread tip velocity. Specially, under a wide range of operation conditions, W1/O/W2 compound droplets form accompanying with the generation of oil phase droplet. The formation ratio of compound droplets to oil phase droplet always depends on the outer phase Capillary number, Caw2, and the flow rate ratio, R, of middle to inner phases, and thus the flow pattern diagram is obtained. Further the influences of all phases flow rates, outer phase viscosity as well as the interfacial tension on the formation period and geometric sizes are extensively studied. Finally, a prediction correlation for dimensionless inner and outer diameters with several dimensionless numbers is also obtained. The results could provide an experimental basis for controllably preparing monodisperse compound droplets with millimeter-scale.

Feature Extraction of Oscillating Flow With Vapor Condensation of Moist Air in a Sonic Nozzle

The sonic nozzle is commonly used in flow measurement. However, the nonequilibrium condensation phenomenon of moist air in the nozzle has a negative effect on the measuring accuracy. To investigate this complex phenomenon, the experiments on the oscillating condensation flow of moist air were conducted by an adjustable humidification apparatus with different relative humidities (0%-100%), temperatures (30-50°C), and carrier gas pressures (1-6 bar), where the microsize pressure measuring system was designed by Bergh-Tijdeman (B-T) model. The accurate mathematical model of nonequilibrium condensation was also built and validated by the experimental data of time-averaged pressure distribution. Then, the frequency and intensity of pressure fluctuation of oscillating flow at a wide range of operation condition were obtained combining experimental data and physical simulation model. Importantly, a new semiempirical relation of dimensionless frequency deduced from dimensionless analysis was identified accurately by experimental data. Finally, the signal nonstationarity was also observed using the continuous wavelet transform (CWT). The instantaneous frequency saltation and the energy attenuation of pressure signals were observed in the condensation flow.

Validation of Actuator Line and Vortex Models Using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine

Vertical Axis Wind Turbines (VAWTs) are characterized by complex and unsteady flow patterns resulting in considerable challenges for both numerical simulations and measurements describing the phenomena involved. In this study, a 3D Actuator Line Model (ALM) is compared to a 2D and a 3D Vortex Model, and they are validated using the normal forces measurements on a blade of an operating 12 kW VAWT, which is located in an open site in the north of Uppsala, Sweden. First, the coefficient power ( C P ) curve of the device has been simulated and compared against the experimental one. Then, a wide range of operational conditions for different tip speed ratios (TSRs), with λ = 1.84, 2.55, 3.06, 3.44, 4.09 and 4.57 were investigated. The results showed descent agreement with the experimental data for both models in terms of the trend and magnitudes. On one side, a slight improvement for representing the normal forces was achieved by the ALM, while the vortex code performs better in the simulation of the C P curve. Similarities and discrepancies between numerical and experimental results are discussed.

Active SHM for composite pipes using piezoelectric sensors

Composite materials, in addition to the high specific mechanical properties, have properties enabling their applications in high-pressure, high-temperature (HPHT) and corrosive environment as occurs in deep water. Their use for manufacturing pipelines and offshore risers can provide relevant performance advantages over steel such as lower weight, improved fatigue capacity, corrosion resistance and higher strain limits. However, composite materials are more complex to use in design than metallic materials due to their anisotropic properties and lack of accurate failure prediction models. Thus, a continuous in-situ and in real-time Structural Health Monitoring (SHM) of composite components would be necessary and useful to promote their use in a wider range of operational conditions. In this work, an FRP pipe sample was instrumented with Piezoelectric Wafer Active Sensors (PWAS) used either as passive receivers or as transmitters of guided waves for active health monitoring in pitch-catch configuration. The propagation properties of guided waves in glass fibres reinforced composites were studied by developing MATLAB scripts, running FE simulation and experiments. The numerical and experimental signals were post-processed in MATLAB by Short Time Fourier Transform (STFT) in order to evaluate their frequency and time-frequency content. Furthermore, the guided waves were used to detect artificial defects imposed on the structure identifying their location. Several testcases were studied to find out the limitations and the most suitable conditions of using guided waves for defects monitoring in a composite pipe. The work proposes effective methods for pipe structural health evaluation by non-destructive techniques and ultrasonic guided waves.

Robust computational modelling of the sodium adsorption ratio using regression analysis and support vector machine

In present study, two new methods including least-square support vector machine (LSSVM) and regression-based model, were created for accurate estimation of the adsorption ratio of sodium in terms of ionic concentrations of calcium (Ca2+), magnesium (Mg2+), and sodium (Na+); the bicarbonate (HCO3-) to Ca2+ ratio; and salinity/conductivity of the used water so as to explain the impact of water quality on the irrigation water using a reliable literature database. The results of the developed models were compared with a commonly used model in literature using visual and statistical parameters. Consequently, the supremacy of the regression-based approach is demonstrated with the average absolute relative deviations (AARDs) of 0.06% for HCO3-/Ca2+ ratio ≤1 and 0.28% for HCO3-/Ca2+ ratio >1. Finally, it should be mentioned that the proposed methods are easy-to-apply and sufficiently accurate which require the less calculations leading to the rapid estimation of sodium adsorption ratio (SAR) in wide range of operational conditions.

Online optimal stationary reference frame controller for inverter interfaced distributed generation in a microgrid system

This paper presents a novel optimal real-time controller for inverter-based distributed generation units in an islanded microgrid. With respect to the fact that the microgrid has a completely nonlinear structure and its dynamics is constantly changing, the linear controllers with constant and inflexible coefficients cannot maintain proper response in a wide range of operation conditions. Hence, an optimal nonlinear controller that theirs coefficient are adjusted in a real-time manner based on fuzzy logic is presented. To improve the performance of the proposed real-time controller, its fuzzy system parameters are determined using an offline particle swarm optimization algorithm for various operation conditions. In the proposed real-time controller, proportional-resonant controllers are used due to their advantage in the stationary reference frame for controlling the voltage and current of distributed generation units in the microgrid. Capability and efficiency of the proposed real-time controller are evaluated in different operation scenarios in MATLAB/Simulink environment. The simulation results shows that changing the control coefficients online with respect to operation condition leads to achievement of an optimum answer for voltage during the occurrence of islanding condition and also in case of load variation in the islanded microgrid.

Validation and uncertainty analysis of a stormwater biofilter treatment model for faecal microorganisms

Stormwater biofilters, also known as rain gardens or bioretention systems, are effective stormwater treatment systems. This paper presents the validation, sensitivity and uncertainty analyses of a model for microbial removal in stormwater biofilters. The model, previously developed based on a rather limited laboratory study, was fully validated using the data collected in extensive laboratory experiments and field tests. The lab-scale and field-scale systems used for validation were of various designs (e.g., system size, plant type, media type), and have been operated under a wide range of operational conditions (e.g., length of antecedent dry period, and the inflow volume and concentration). For each tested biofilter design, the predicted E. coli concentrations in biofilters' outflow showed relatively good agreement with the measured ones: e.g., Nash-Sutcliffe Efficiency (Ec) ranged from 0.50 to 0.60 for the laboratory tests, and Ec = 0.55 for the field system. The results from sensitivity analysis confirmed the significance of adsorption and desorption processes, and also revealed the impact of temperature on microbial die-off (which was not fully represented in the model development stage). Finally, parameter transferability from one system to another with similar design was examined, achieving generally promising Ec values (0.04–0.56 with the best-fit parameter set for the other system; maximum value: 0.46–0.63) and acceptable uncertainties (intersection between prediction uncertainty band and observation: 50%–97%). Most importantly, the prediction of E. coli outflow concentrations from the field system was reasonably good when laboratory-determined parameter values were adopted: with the best-fit parameter set for the lab-scale system, Ec = 0.39; maximum Ec = 0.55; intersection between prediction and observation = 83%. These results suggested that the very rare biofilter model for microbial removal could provide reliable prediction for large scale field systems, by simply calibrating parameters with limited laboratory-scale experiments.

Combustion of solid recovered fuels within the calcium looping process – Experimental demonstration at 1 MWth scale

The calcium looping (CaL) process is an efficient post-combustion CO2 capture technology based on the reversible carbonation-calcination reaction of natural lime. This work presents the results obtained during long-term operation at the 1 MWth CaL pilot plant at Technische Universität Darmstadt. During more than 230 h of representative CaL operation, the calciner was heated by oxy-fuel combustion of waste derived fuels. During the experimental investigation, two types of solid recovered fuels (SRF) were utilized. Both types of SRF were fed to the process in the form of raw fluff, similar to typical industrial applications. The flue gas to be decarbonized in the carbonator, was supplied by an on-site combustion chamber. The CO2 concentration was kept between 9.5 and 10.5 vol% as typical value for waste-to-energy (WtE) plants fueled by municipal solid waste (MSW). Over a wide range of operation conditions, CO2 absorption rates of 80% and total CO2 capture rates over 90% were achieved. Within this work, exemplary long-term data plots of relevant CaL process parameters are shown for each type of SRF. A chlorine balance for a representative operation period is established based on the relevant effluent streams from the CaL system. Thereby, it was found that the calciner fly ash represents the major chlorine effluent. Furthermore, the retention rate of chlorine was above 82% throughout all test points, respectively. When taking into account the organic waste fractions typically contained in SRF and MSW, this work successfully demonstrates the feasibility of net negative CO2 emissions by means of the CaL process at semi-industrial scale.

Mechanistic Description of Convective Gas-Liquid Mass Transfer in Biotrickling Filters Using CFD Modeling.

The gas-liquid mass transfer coefficient is a key parameter to the design and operation of biotrickling filters that governs the transport rate of contaminants and oxygen from the gas phase to the liquid phase, where pollutant biodegradation occurs. Mass transfer coefficients are typically estimated via experimental procedures to produce empirical correlations, which are only valid for the bioreactor configuration and range of operational conditions under investigation. In this work, a new method for the estimation of the gas-liquid mass transfer coefficient in biotrickling filters is presented. This novel methodology couples a realistic description of the packing media (polyurethane foam without a biofilm) obtained using microtomography with computational fluid dynamics. The two-dimensional analysis reported in this study allowed capturing the mechanisms of the complex processes involved in the creeping porous air and water flow in the presence of capillary effects in biotrickling filters. Model predictions matched the experimental mass transfer coefficients (±30%) under a wide range of operational conditions.

Application of grid partitioning based fuzzy inference system as a novel predictor to estimate dynamic viscosity of n-alkane

The oil recovery and rate of production are highly dependent on viscosity of reservoir fluid so this term becomes one of the attractive parameters in petroleum engineering. The viscosity of fluid is highly function of composition, temperature, and pressure so in this article, Grid partitioning based Fuzzy inference system approach is utilized as novel predictor to estimate dynamic viscosity of different normal alkanes in the wide range of operational conditions. In order to comparison of model output with actual data, an experimental dataset related to dynamic viscosity of n-alkanes is gathered. The graphical and statistical comparisons between model outputs and experimental data show the high quality performance of predicting algorithm. The coefficients of determination (R2) of training and testing phases are 0.9985 and 0.9980, respectively. The mentioned statistical indexes represent the great accuracy of model in prediction of dynamic viscosity.

Coverage-dependent acrylonitrile adsorption and electrochemical reduction kinetics on Pb electrode

Electrochemical dimerization of acrylonitrile (AN) is an environmentally friendly approach to manufacture adiponitrile (ADN), the key raw material of nylon-6,6. Despite its significance in industry, the studies on the mechanism and kinetics of AN conversion on cathode are relatively limited. Herein we investigated the adsorption and electrochemical reduction of AN on Pb electrode under different coverage by the combination of experiments and density function theory (DFT) calculations. Under various reaction conditions, it was observed that when decreasing the bulk concentration of AN, the generation of ADN decreases as expected while that of the saturated propionitrile (PN) increases on the contrary, indicating a coverage-dependent kinetic behavior. Theoretical analysis revealed high AN coverage on Pb surface could inhibit the formation of H and repel the contacting of C=C with active site, both of which is against the generation PN and favorable for ADN. A kinetic model was then developed for the cathodic reaction by taking the impact of temperature, potential and surface coverage into account, which gives good agreement in a wide range of operation conditions.

Turbine Cascades of Last Stage Blades for Wide Range of Operating Conditions

Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades.