Intermediate Flow Rates Research Articles

Robust Control of Heat Exchangers in Stratified Storage Systems – Simulation and Experimental Validation

Since many industrial processes are not operated continuously, large shares of the heat recovery potential in those processes can only be achieved indirectly. While conceptual design methods to integrate stratified thermal energy storage systems are being developed, the control of the resulting systems is addressed in this paper. The main challenge of the control of heat exchangers in stratified storage systems is the fact that both outlet temperatures of the heat exchanger need to be maintained at their setpoint. A simulation model describing plate heat exchangers and based on this a control strategy are presented. The simulation model is experimentally validated and represents the real heat exchanger with a steady state error within the bounds of ± 0.31 K. The control strategy contains a feed forward path using measured disturbances and a lookup table to set the intermediate loop-sided mass flow rate. Furthermore, one feedback PI controller is used to control one outlet temperature by adjusting the intermediate loop-sided inlet temperature with a mixing valve. As the lookup table is based on a sufficiently accurate description of the heat exchanger characteristics, the second outlet temperature (process-side) is maintained within bounds of ± 0.5 K. For further development, the measurement effort is recommended to be reduced by means of state and disturbance estimation. The rather rigid control algorithm might be replaced with a multivariable control approach such as model predictive control in order to increase the versatility of the system.

Photoselective nets impact apple sap flow and fruit growth

•A red net shading 50% increases apple tree water use, limiting fruit growth.•A red net shading 50% is not advisable for apple production when water is limited.•A white net shading 50% lowers crop water use, representing a useful tool to save water.•A blue net shading 50% improves fruit growth, despite intermediate sap flow rates.

Experimental and theoretical investigation on pool entrainment under small air flow rate

The liquid entrainment is a ubiquitous phenomenon in nuclear engineering. In the scenario of SBLOCA, liquid entrainment plays an important role threatening the core safety. Numerous research has been conducted on the mechanism of pool entrainment. Part of experiment data could be predicted well by Kataoka-Ishii entrainment correlation which has been widely used. However, most research focused on the pool entrainment is conducted under intermediate or high gas flow rate. The Kataoka-Ishii correlation is also less accurate when air flow rate is small. Therefore, an experimental investigation under small air flow rate is important to conduct. This paper demonstrates experiment apparatus, instrumentation, experiment phenomenon as well as relevant analysis. An entrainment correlation is proposed based on the experiment data. The relative uncertainty of fitting entrainment correlation based on the experiment data is within ±30%. Entrainment factor influenced by exit effect of different location is specifically deducted. The transition region of pool entrainment is analyzed and can be estimated by flow pattern map. Some typical entrainment patterns under different air flow rate are also illustrated and described.

Numerical study on inertial effects on liquid-vapor flow using lattice Boltzmann method

Liquid-vapor flow in porous media is studied in this article. To fulfill this goal, a double-distribution-function lattice Boltzmann (LB) model is proposed based on the separate-phase governing equations at the representative elementary volume (REV) scale. Importantly, besides the Darcy force and capillary force, which were commonly included in previous studies, the LB model in this article also considers the inertial force characterized by the Forchheimer term. This feature enables the model to offer an effective description of liquid-vapor flow in porous media at low, intermediate and even high flow rates. We validated the LB model by simulating a single-phase flow in porous media driven by a pressure difference and found its results are in good agreement with the available analytical solutions. We then applied the model to study water-vapor flow in a semi-infinite porous region bounded by an impermeable and heated wall. The numerical simulation reveals the flow and mass transfer characteristics under the compounding effects of inertial, Darcy and capillary forces. Through a comparison with the results given by the generalized Darcy’s law, our numerical results directly evidence that the inertial force is a dominating factor when a fluid passes through porous media at an intermediate or high flow rate.

Development of a control-oriented power plant simulator for the molten salt fast reactor

In this paper, modelling and simulation of a control-oriented plant-dynamics tool for the molten salt fast reactor (MSFR) is presented. The objective was to develop a simulation tool aimed at investigating the plant response to standard control transients, in order to support the system design finalization and the definition of control strategies. The simulator was developed employing the well tested, flexible and open-source object-oriented Modelica language. A one-dimensional modelling approach was used for thermal-hydraulics and heat transfer. Standard and validated thermal-hydraulic Modelica libraries were employed for various plant components (tubes, pumps, turbines, etc.). An effort was spent in developing a new MSR library modelling the 1D flow of a liquid nuclear fuel, including an ad-hoc neutron-kinetics model which properly takes into consideration the motion of the Delayed Neutron Precursors along the fuel circuit and the consequent reactivity insertion due to the variation of the effective delayed fractions. An analytical steady-state 2-D model of the core and the fuel circuit was developed using MATLAB in order to validate the Decay Neutron Precursors model implemented in the plant simulator. The plant simulator was then employed to investigate the plant dynamics in response to three transients (variation of fuel flow rate, intermediate flow rate and turbine gas flow rate) that are relevant to control purposes. Simulation outcomes highlight the typical reactor-follows-turbine behavior of the MSFR, and they show the small influence of fuel and intermediate flow rate on the reactor power and their strong effects on the temperatures in their respective circuits. Starting from the insights on the reactor behavior gained from the analysis of its free dynamics, the plant simulator here developed will provide a valuable tool in support to the finalization of the design phase, the definition of control strategies and the identification of controlled operational procedures for reactor startup and shutdown.

Microfluidic Manufacturing of SN-38-Loaded Polymer Nanoparticles with Shear Processing Control of Drug Delivery Properties.

Two-phase gas-liquid microfluidic reactors provide shear processing control of SN-38-loaded polymer nanoparticles (SN-38-PNPs). We prepare SN-38-PNPs from the block copolymer poly(methyl caprolactone- co-caprolactone)- block-poly(ethylene oxides) (P(MCL- co-CL)- b-PEO) using bulk and microfluidic methods and at different drug-to-polymer loading ratios and on-chip flow rates. We show that, as the microfluidic flow rate ( Q) increases, encapsulation efficiency and drug loading increase and release half times increase. Slower SN-38 release is obtained at the highest Q value ( Q = 400 μL/min) than is achieved using a conventional bulk preparation method. For all SN-38-PNP formulations, we find a dominant population (by number) of nanosized particles (<50 nm) along with a small number of larger aggregates (>100 nm). As Q increases, the size of aggregates decreases through a minimum and then increases, attributed to a flow-variable competition of shear-induced particle breakup and shear-induced particle coalescence. IC25 and IC50 values of the various SN-38-PNPs against MCF-7 cells show strong flow rate dependencies that mirror trends in particle size. SN-38-PNPs manufactured on-chip at intermediate flow rates show both minimum particle sizes and maximum potencies with a significantly lower IC25 value than the bulk-prepared sample. Compared to conventional bulk methods, microfluidic shear processing in two-phase reactors provides controlled manufacturing routes for optimizing and improving the properties of SN-38 nanomedicines.

Variable speed liquid chiller drop-in modeling for predicting energy performance of R1234yf as low-GWP refrigerant

This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant.

IMPACT OF THE HYDRAULIC LOADING RATE ON THE HYDRODYNAMIC CHARACTERISTICS OF AN ANAEROBIC FIXED BED REACTOR TREATING CATTLE SLAUGHTERHOUSE WASTEWATER

The hydrodynamic behavior of an anaerobic fixed bed reactor (AFBR) was evaluated in the treatment of cattle slaughterhouse wastewater. The AFBR was operated at hydraulic retention time (HRT) of 14, 11 and 8 h. Stimulus-response assays were carried out with eosin Y and the experimental data were adjusted to the single-parameter theoretical models of dispersion and N-continuous stirred tank reactors in series. The experimental results of the residence time distribution curves showed that at lower flowrate, the reactor showed plug flow behavior with R2 of 0.88 and number of dispersion of 0.2 for high dispersion (HD). However, at higher and intermediate flowrates, the AFBR behave as a complete mixture flow, with R2 of 0.94 and 0.96, respectively. Residence time distribution curves in the AFBR showed a good approximation of the complete mixing model at hydraulic residence time of 11 h and 8 h, with 5 and 2 N-CSTR reactors in series, respectively. The volume of dead zones corresponding to 43.0%, 37.4% and 11.2% of the volume of the reactor for HRT of 14 h, 11 h and 8 h, respectively, was noted, and hydraulic short-circuiting were not confirmed.

Investigating the influence of flow rate on biofilm growth in three dimensions using microimaging

Abstract We explore how X-ray computed microtomography can be used to generate highly-resolved 3D biofilm datasets on length scales that span multiple pore bodies. The data is integrated into a study of the effects of flow rate on three-dimensional growth of biofilm in porous media. Three flow rates were investigated in model packed-bed columns. Biofilm growth was monitored during an 11-day growth period using a combination of differential pressure and effluent dissolved oxygen measurements. At the end of the growth period, all columns were scanned using X-ray computed microtomography and a barium sulfate-based contrast agent. The resulting images were prepared for quantitative analysis using a novel image processing workflow that was tailored to this specific system. The reduction in permeability due to biofilm growth was studied using both transducer-based pressure drop measurements and image-based calculations using the Kozeny–Carman model. In addition, a set of structural measures related to the spatial distribution of biofilms were computed and analyzed for the different flow rates. We generally observed 1 to 2 orders of magnitude decrease in permeability as a result of bioclogging for all columns (i.e, across flow rates). The greatest average permeability and porosity reduction was observed for the intermediate flow rate (4.5 ml/h). A combination of results from different measurements all suggest that biofilm growth was oxygen limited at the lowest flow rate, and affected by shear stresses at the highest flow rate. We hypothesize that the interplay between these two factors drives the spatial distribution and quantity of biofilm growth in the class of porous media studied here. Our approach opens the way to more systematic studies of the structure-function relationships involved in biofilm growth in porous media and the impact that such growth may have on physical properties such as hydraulic conductivity.

Parametric analysis of a solar Organic Rankine Cycle trigeneration system for residential applications

In this paper, the potential of a small scale concentrated solar Organic Rankine Cycle unit coupled with an absorption chiller for trigeneration purposes is investigated using a simulation analysis.At the moment, only few research works encompass small-scale solar trigeneration systems and most of them do not refer to real plant. On the contrary, in this work electric, heating and cooling maximum generation of a real and experimental small scale prototype system composed of a 50 m2 CPC solar field, a 3.5 kWe ORC plant and a 17 kWc absorption chiller is investigated by means of TRNSYS. In particular, this work relies on the evaluation of the dynamic performance of the mentioned plant varying some selected system parameters to provide proper modifications of its design configuration and operation.More precisely, working temperature ranges, heating and intermediate fluid flow rates as well as volume of the storage tanks and size of the solar field have been varied within the simulation model. Results have shown that operating temperature ranges of the storage tanks considerably affect the overall performance of the system; by appropriately choosing these ranges the primary energy production can be increased by 6.5% compared to the baseline configuration without any additional investment costs. Moreover, setting suitably some design parameters can significantly contribute to extend the operating hours and the feasibility of a such small scale integrated system for residential applications.

Study on the Large Area Diamond Film Deposition in a Self- built Overmoded Microwave Power Chemical Vapor Deposition Device

With a self-built overmoded microwave plasma chemical vapor deposition device, the effect of the gas flow rate variation on the uniform deposition of diamond films on molybdenum of 100 millimeter diameter was studied. The plasma density was 1.0×1019/m3 when the microwave power was 5.0 kW and the gas pressure was 10.0 kPa. The ovemoded MPCVD device presented good stability of the gas flow rate field distribution. The substrate surface can be well covered when the hydrogen flow rate varied from 50 to 800 sccm. The uniform diamond film with good quality was obtained at an intermediate gas flow rate, 300 sccm. The diamond film with good quality, 5.74 cm-1 as FWHM value and high growth rate, 5.8 μm/h was deposited when the gas flow rate was 300 sccm.

Room temperature self-assembled growth of vertically aligned columnar copper oxide nanocomposite thin films on unmatched substrates

In this work, we report the self-assembled growth of vertically aligned columnar Cu2O + Cu4O3 nanocomposite thin films on glass and silicon substrates by reactive sputtering at room temperature. Microstructure analyses show that each phase in nanocomposite films has the columnar growth along the whole thickness, while each column exhibits the single phase characteristics. The local epitaxial growth behavior of Cu2O is thought to be responsible for such an unusual microstructure. The intermediate oxygen flow rate between those required to synthesize single phase Cu2O and Cu4O3 films produces some Cu2O nuclei, and then the local epitaxial growth provides a strong driving force to promote Cu2O nuclei to grow sequentially, giving rise to Cu2O columns along the whole thickness. Lower resistivity has been observed in such kind of nanocomposite thin films than that in single phase thin films, which may be due to the interface coupling between Cu2O and Cu4O3 columns.

Controlling Structure and Function of Polymeric Drug Delivery Nanoparticles Using Microfluidics.

We demonstrate control of multiscale structure and drug delivery function for paclitaxel (PAX)-loaded polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) polymeric nanoparticles (PNPs) via synthesis and flow-directed shear processing in a two-phase gas-liquid microfluidic reactor. This strategy takes a page from the engineering of commodity plastics, where processing rather than polymer chemistry provides an experimental handle on properties and function. PNPs formed from copolymers with three different PCL block lengths show sizes, morphologies, and loading efficiencies that depend on both the PCL block length and the microfluidic flow rate. By varying flow rate and comparing with a conventional bulk method of PNP preparation, we show that flow-variable shear processing provides control of PNP sizes and morphologies and enables slower PAX release times (up to 2 weeks) compared to bulk-prepared PNPs. Antiproliferative effects against cultured MCF-7 breast cancer cells were greatest for PNPs formed at an intermediate flow rate, corresponding to small and low-polydispersity spheres formed uniquely at this flow condition. Formation and flow-directed nanoscale shear processing in gas-liquid microfluidic reactors provides a manufacturing platform for drug delivery PNPs that could enable more effective and selective nanomedicines through multiscale structural control.

Investigation of an IC Engine Intake Flow Based on Highly Resolved LES and PIV

To reduce emissions and fuel consumption, the current generation of gasoline engines uses technologies such as direct injection, downsizing and supercharging. All of them require a strong vortical in-cylinder charge motion, usually described as “tumble”, to improve fuel-air mixing and enhance flame propagation. The tumble development strongly depends on the flow field during the intake stroke. This flow field is dominated by the intake jet, which has to be captured well in the simulation. This work investigates the intake jet on a steady-state flow bench, especially in the vicinity of the intake valve. At first, the general flow dynamics of the intake jet for three different valve lifts and three different mass flows were investigated experimentally. For the smallest valve lift (3 mm), flow-field measurements using Particle Image Velocimetry (PIV) show that the orientation of the intake jet significantly depends on the air flow rate, attaching to the pent roof for low flow rates. This phenomenon is less pronounced for higher valve lifts. An intermediate valve lift and flow rate were chosen for further investigations by scale-resolving simulations. Three different meshes (coarse, medium and fine) and two turbulence models (Sigma and Detached Eddy Simulation-Shear Stress Transport (DES-SST)) are applied to consider their effect on the numerical results. An ad-hoc post-processing methodology based on the ensemble-averaged velocity field is presented capturing the jet centerline’s mean velocity and velocity fluctuations as well as its orientation, curvature and penetration depth. The simulation results are compared to each other as well as to measurements by PIV.

On the Phase Shifts in the Dynamics of the H2O2–Na2S2O3–H2SO4–CuSO4 Oscillator Revealed by Comparison of Potentiometric Responses of Different Indicator Electrodes

ABSTRACTThe dynamics of the H2O2–Na2S2O3–H2SO4–CuSO4 homogeneous pH oscillator was studied in the flow reactor potentiometrically using different sensors: platinum electrode, Cu(II) ion‐selective electrode (Cu‐ISE), and pH‐electrode. It was found that for the flow rates close to two bifurcation values, between which the oscillations exist, there is a detectable phase shift between the response of the Cu‐ISE and other electrodes, while it practically vanishes for the intermediate flow rates. To explain both the oscillations of the Cu‐ISE potential and the relevant phase shift, the system's dynamics was studied both experimentally and numerically. The literature kinetic mechanism of the pH oscillator was extended for the dynamics of the copper(II) and copper(I) species in the form of thiosulfate complexes, and kinetic parameters of the redox equilibria, ensuring the oscillations, were estimated. It was found that the phase shift at the relatively low flow rates occurs due to limited efficiency of the supply of CuSO4 catalyst, as the species of lowest concentration, to the reactor, and therefore it can be minimized either by increasing the flow rate of all reactants or, alternatively, by enhancing the model concentration of CuSO4 in the feeding stream, for its fixed flow rate. This work is one more proof that it is useful to monitor the dynamics of the homogeneous oscillatory systems with more than one electrode, if the experimental potential–time courses are to be explained in terms of an appropriate kinetic mechanism.

Studies on the Effect of Staggering the Rear Rotor in a Counter Rotating Turbine with Respect to Flow and Performance Parameters

Abstract Counter rotating turbine is an axial turbine with nozzle followed by a rotor and another rotor that rotates in the opposite direction of the first one. Absence of the second guide vane makes it more beneficial. Present work involves computationally studying the performance and flow pattern of CRT with different stagger angles ranging from 8 to 13° in case of rotor 2. Equivalent mass flow rates of 0.091 to 0.137 are considered. Turbine components nozzle, rotor 1 and rotor 2 are modeled for the cases of CRT with and without staggering. Total pressure, entropy and TKE distributions across the blade rows are used to describe the flow through CRT. Results show that the flow composition at the inlet of rotor 2 is improved for staggering cases. Due to this, the performance of rotor 2 and CRT increased with staggering. For the intermediate mass flow rate of 0.108, the efficiency of CRT stage is found to be increasing by 1.2, 2.1 and 1 % for the staggering cases. The beneficial aspect of staggering the rear rotor is thus confirmed that can provide long-term design solutions in terms of reducing weight, losses and improving the performance.

Chemiluminescence imaging of an optically accessible non-premixed rotating detonation engine

The detonations propagating through the annular channel of an optically accessible rotating detonation engine (RDE) operating on hydrogen–air are visualized using OH* chemiluminescence imaging. The images are useful for observing the instantaneous size and shape of the detonation structure, oblique shock wave, and possible presence of deflagration between the fuel-fill zone and expansion region containing detonation products. The detonation increases in height as the air flow rate is increased for low flow rates, experiences subtle changes for intermediate flow rates, and transitions from one to two waves for higher flow rates. The two detonation waves typically propagate in the same azimuthal direction. Counter-rotating waves resulting in detonation–detonation interactions are observed for some configurations with a reduced number of fuel injection jets. Time-dependent static pressure measurements show that acoustic interactions between the detonation channel and air plenum are important for low air flow rates and large air injection areas. The OH* chemiluminescence images, pressure, and wave speed measurements provide benchmark data that are useful for evaluating RDE models and simulations, improving fundamental understanding of the detonation structure in RDEs, and identifying critical design parameters that influence RDE operation and performance.

2D reactive transport modeling of the interaction between a marl and a CO2-rich sulfate solution under supercritical CO2 conditions

The circulation of CO2-rich solutions through fractured marl cores (caprock) under different flow rates and supercritical CO2 conditions (PTotal=150bar, pCO2=61bar and T=60°C) led to mineral changes caused mainly by calcite dissolution and to a lesser extent by aluminosilicate dissolution, and by gypsum precipitation adjacent to the fracture walls. Another significant result was the formation of the altered and highly porous zone (Dávila et al., 2016a). Dissolution structures ranged from face to uniform dissolution and wormhole formation depending mainly on the flow rate.2D reactive transport models were used to interpret the results of the percolation experiments (except at 60mLh−1). They reproduced the variation in the outflow composition with time and the observed width of the altered zone along the fractures. A good match was achieved by using initial Deff values in the rock matrix that ranged from 1×10−13m2s−1 to 3×10−13m2s−1 under slow flow rates. The Deff value was higher by a factor of 20 (6×10−12m2s−1) under fast flow. Moreover, a slight variation in the calcite reactive surface areas contributed to the fit of the model to the experimental data.The modeling results reproduced major dissolution of calcite and gypsum precipitation, and minor dissolution of clinochlore. Calcite dissolution was boosted by increasing the flow rate and gypsum precipitation increased at intermediate flow rate (1mLh−1). Minor precipitation of dolomite, kaolinite, boehmite and three zeolites (mesolite, stilbite and smectite) along the altered zone occurred. The magnitude of these reactions was consistent with the measured increase in porosity over the altered zone.

Augmenting numerical stability of the Galerkin finite element formulation for electromagnetic flowmeter analysis

Due to the complexities in handling liquid metals, theoretical evaluation of the sensitivity of magnetic flowmeters forms an attractive and preferred choice. The classical Galerkin finite element formulation is generally opted for the required evaluation. However, it is known to lead to numerical oscillations at higher flow rates. To overcome this, modified methods like upwind/Petrov–Galerkin schemes are generally suggested in allied areas like fluid dynamics. However, it requires the evaluation of stabilisation parameter and this parameter is not readily available for elements of order beyond quadratic. After a careful analysis of the numerical instability through a reduced one-dimensional problem, an elegant and stable approach is devised. In this scheme, the input magnetic field is restated in terms of the associated vector potential and the classical Galerkin finite element method is employed without any modification. The analytical solution of the associated difference equation is employed to show: (i) the stability of the proposed approach at higher flow rates and (ii) quantification of the small oscillations remnant at intermediate flow rates. It is then applied to the original flowmeter problem and the stability of the numerical solution is clearly demonstrated.

Distribución espacial y temporal de la salinidad en la columna de agua del sector estuarino del Humedal Nacional Térraba Sierpe, Costa Rica

El análisis de la salinidad durante tres campañas de monitoreo (2002-2004, 2005-2008 y 2011-2012), permite establecer que el sector estuarino del HNTS se divide en una zona norte con una fuerte influencia del Río Grande de Térraba y características de un estuario parcialmente mezclado durante el periodo de caudales bajos (diciembre-abril), mientras que se asemeja a un estuario estratificado de cuña salina durante los caudales intermedios (mayo-agosto) y caudales altos (setiembre-noviembre). La zona central, con una mayor influencia marina, presenta características de un estuario bien mezclado o verticalmente homogéneo, mientras que la zona sur del estuario, bajo la influencia del Río Sierpe, se mantiene parcialmente mezclado a lo largo del año. Los primeros siete kilómetros aguas abajo de Ciudad Cortés presentaron una condición fluvial muy bien definida con salinidades inferiores a 1ups, a partir del kilómetro 14 se observa un incremento gradual de los valores de salinidad hasta 30ups hacia la desembocadura, reflejando una mayor influencia de las mareas en este último tramo (F1,47=2.5, p&lt;0.001). El eventual desarrollo del Proyecto Hidroeléctrico El Diquís podría ocasionar un incremento en el aporte de agua dulce entre un 82 y 66% de los valores mínimos promedio y máximos promedio sobre la zona norte del sector estuarino del HNTS durante el periodo de caudales bajos, lo cual generaría condiciones semejantes a las registradas durante el periodo de caudales intermedios. El monitoreo de las relaciones entre los aspectos físicos-químicos y biológicos es esencial para entendimiento de los posibles cambios en el sector estuarino del HNTS.