Flow Inlet Pressure Research Articles

Experimental study on control of transverse jet mixing by arrayed plasma energy deposition

The efficient and prompt mixing of fuel is crucial in the operation of scramjet engines. This paper presents the findings from wind tunnel experiments that examined the influence of plasma energy deposition on transverse jets at a Mach number of 6.13. The study took into account various inlet flow total pressures and momentum flux ratios between the jet and the main flow. Utilizing a database containing time-resolved intensities from instantaneous schlieren images, we perform turbulence analysis employing various techniques such as the root mean square, fast Fourier transform, proper orthogonal decomposition, and the two-point correlation method. Specifically, we aim to compare and analyze the pulsation characteristics and spatial self-organization of the jet flow field, both with and without energy deposition control. The findings reveal that intermittent “hot bubbles” created by plasma energy deposition interact with the bow shock induced by the jet, resulting in the formation of an array of large-scale vortices. These vortices emerge as the dominant structures within the jet, effectively amplifying its pulsations. At low inlet flow pressures, energy deposition primarily disrupts the jet, causing large-scale vortices to propagate primarily within the jet plume region. However, at high inlet flow pressures, the impact of energy deposition extends to both the jet and the turbulent boundary layer, encompassing their respective disturbance ranges. Increasing the inlet flow pressure constraints the evolution of large-scale vortices, thus limiting the efficacy of energy deposition in governing the mixing process.

Experimental and numerical investigation on aerodynamic performance of biomimetic blade in steam turbine

Low load condition will cause the flow field in steam turbine to be complex, affecting the aerodynamic performance. We propose a biomimetic blade with bumpy leading edge to achieve better performance in low mass-flow conditions. The bumps on leading edge are inspired by the flipper of humpback whale. Both experiments and numerical simulation are conducted to discuss the function and mechanism of the biomimetic blade. The results from the experiment and simulation show high consistency. There exists a radial vortex on pressure side of original blade, blocking the energy exchange between blade and main flow. The bumpy leading edge generates streamwise vortex pairs to suppress the radial vortex. For the biomimetic blade, the pressure side from leading edge to the middle region has higher applied pressure because the streamwise vortices remains. The inlet flow pressure and the angle of attack have a significant influence on the vorticity of streamwise vortices. These two parameters should be in a certain range. The best value is inlet pressure of 1.09P0 and angle of attack of −40°. The current work uncovers the mechanism of bumpy leading edge in flow control and provides a new design for turbine blade.

Simulation and experimental measurements of 10-kW PEMFC passive hydrogen recovery system

Simulations are performed to examine the performance of a vacuum ejector in the hydrogen recovery loop of a 10-kW PEMFC system. The simulations commence by examining the effects of the primary flow fluid pressure and secondary flow temperature on the recirculation ratio and hydrogen stoichiometric ratio. Further simulations are then performed to investigate the temperature, pressure, velocity and Mach number distributions within the ejector for various values of the primary flow inlet pressure and temperature. A prototype ejector is fabricated using a 3D printing technique. Experiments are performed to evaluate the gas tightness and gas recovery performance of the ejector under realistic operating conditions. The simulation results show that the recirculation ratio and hydrogen stoichiometric ratio increase with a decreasing primary flow inlet pressure and secondary flow inlet temperature. As the primary flow inlet pressure increases, the pressure, velocity, and Mach number in the mixing chamber increase, and the hydrogen recovery performance decreases. Furthermore, as the temperature of the primary fluid flow increases, the stability of the isentropic flow condition within the ejector is enhanced. The experimental results show that the prototype vacuum ejector has a maximum gas leakage of just 0.7 psi and a minimum hydrogen recirculation rate of 59.3%. Consequently, it has significant potential for passive hydrogen recovery in large-scale fuel cell systems.

Adsorption of CO2 on ZSM-5 and Cu-MOF at room temperature and low pressure conditions for Carbon Capture and Storage (CCS) application

The application of Carbon Capture and Storage (CCS) is viewed as a key strategy to achieve CO2 reduction targets. In capturing CO2 process, both adsorption and absorption are promising techniques for CO2 capture, but adsorption processes using solid adsorbents are the prevailing technique nowadays. In this study, the performance of the prepared adsorbents on the CO2 capture capability is investigated and compared. Zeolite (ZSM-5) and copper metal–organic framework (Cu-MOF) are selected as adsorbents because of high surface area and the excellent performance in the adsorption process. The performance of both adsorbents in CO2 adsorption is evaluated in a fabricated setup consists of a metal cylindrical vessel equipped with flow of pure CO2 gas from a cylindrical tank. The efficiency of the adsorption system was explored as a function of the experimental parameters: effect of adsorbent dosage (0–500 mg) and inlet flow pressure (0–1 bar). Based on the findings from FTIR, EDX and XRD analyses, the results suggested successful formation of ZSM-5 and Cu-MOF. The highest particle size distribution and area for ZSM-5 were in the range of 25–66 µm and 1.7–442 µm2, while 102–149 µm and 1.7–1400 µm2 for Cu-MOF, respectively. SEM images show an agglomeration and flaky particles. From the TGA analysis, ZSM-5 tends to remain stable compared to Cu-MOF where lacks the ability to retain its framework at temperature above 400 °C. The optimum conditions obtained in the adsorption process for both adsorbents were 200 mg adsorbent dosage and 1 bar inlet pressure. Based on the results, ZSM-5 shows the best performance with high CO2 adsorption capacity as compared to Cu-MOF at the low pressure system. Under the optimum condition, 800 and 1000 mg/g adsorption capacity of Cu-MOF and ZSM-5 were achieved within 50 min of reaction to adsorb CO2.

Experimental and modeling studies of thermally-driven subcritical and transcritical ejector refrigeration systems

This paper presents an experimental and modeling investigation on thermally-driven subcritical and transcritical ejector refrigeration systems using refrigerant R32 as the working fluid. The performances of the ejector and its corresponding refrigeration system are studied under different ejector primary flow inlet temperatures, primary flow inlet pressures, and ejector outlet pressures. A theoretical model of the ejector is established and validated by experimental data. The results show that the physical properties of the working fluid significantly affect the performance of such ejectors. The mass flow rate of the primary flow exhibits a nonlinear change when the ejector inlet pressure or temperature is near the pseudo-critical state. At high primary flow inlet temperatures and pressures, the mass flow rate of the secondary flow of the transcritical ejector no longer increases with increasing primary flow inlet parameters, showing characteristics like the subcritical ejector. The optimal primary flow inlet pressure of the ejector refrigeration system increases with increasing primary flow inlet temperature, but remains unchanged after reaching about 7.1 MPa. The transcritical ejector refrigeration system exhibits a higher coefficient of performance than its subcritical counterpart at most primary flow inlet temperatures. The transcritical ejector has a better pressure lift performance, while the subcritical ejector exhibits a higher entrainment ratio only at low pressure lift ratios. Moreover, the transcritical system exhibits a unique oscillation phenomenon under some conditions, with the oscillation amplitudes in both the mass flow rates reaching up to 60% of their averages.

Inverse design of microfluidic concentration gradient generator using deep learning and physics-based component model

This paper presents a new paradigm of deep neural network (DNN) for the inverse design of microfluidic concentration gradient generators (µCGGs) with complex network topology. In this method, a concentration gradient (CG) and design parameters yielding the CG are, respectively, used as inputs and outputs of DNN, and the relationship between them is mapped. Several new elements are also proposed, including utilization of fast-running physics-based component model in the closed form to generate a large amount of data for DNN learning which otherwise is not available through computationally demanding computational fluid dynamics (CFD) simulation; and a divide-and-conquer strategy and DNN formulation combining classification and regression to mitigate many-to-one design complications for enhanced accuracy. Several DNN structures are investigated and developed, including single fully connected neural network (FCNN), convolutional neural network, and a new cascade FCNN for a divide-and-conquer implementation. Case studies are performed on a triple-Y µCGG to evaluate design performance of the proposed method in a six-dimensional space that only includes sample concentrations at inlet reservoirs as design parameters, and in a nine-dimensional design space, to which inlet flow pressures are also added. It is verified in high-fidelity CFD simulation that widely used CGs can be produced using DNN-predicted design parameters accurately with average error < 4% and < 8.5% relative to the prescribed CGs, respectively, in the six- and nine-dimensional design space. The learned design rules are packaged into the DNN model that allows to generate accurate µCGGs designs instantaneously (~ 3 ms) and eliminates requirements of simulation and optimization knowledge, facilitating distribution of the design capabilities to microfluidic end users.

Experimental Investigation on Ejector Performance Using R134a as Refrigerant

Ejector refrigeration has the advantage of low capital cost, simple design, reliable operation, long lifespan and almost no maintenance. The only weakness is the low efficiency and its intolerance to deviations from design operation condition. R134a used in ejector refrigeration system gives better performance in comparison with many other environmental friendly refrigerants as the generation temperature is from 75°C to 80°C. The present work experimentally investigated the on-design and off-design performance of the ejector with fixed geometry using R134a as refrigerant, and cycle performance of the ejector refrigeration system. The experimental prototype was constructed and the effects of primary flow inlet pressure, secondary flow inlet pressure and ejector back pressure on ejector performance and cycle performance were investigated respectively. The operation conditions are: primary flow inlet pressure from 2.2 MPa to 3.25 MPa, secondary flow inlet pressure from 0.36 MPa to 0.51 MPa, ejector back pressure from 0.45 MPa to 0.67 MPa. Conclusions were drawn from the experimental results, and the experimental data can be used for validation of theoretical model for both critical and subcritical mode.

Experimental study of the performance of an ejector system using Freon 134a

This paper presents experimental data of the entrainment ratio as a function of the outlet mixture pressure of an ejector. A single ejector geometry, manufactured from brass bore rods, is installed into a closed-circuit loop that uses Freon 134a as primary and secondary working fluids. Different inlet flow pressure conditions are applied for both the primary and secondary flows while the outlet mixture flow pressure is varied from 500 to up to 975 kPa. This range of the outlet pressure permitted on-design (i.e. formation of a first plateau on the diagram of the entrainment ratio as function of the pressure) and off-design operation conditions to be largely covered. It is thus, systematically observed that within the off-design zone there is formation of a secondary plateau which seems to indicate that the flow undergoes an unusual choking flow condition. A preliminary analysis of the data indicates that the off-design behavior is mainly controlled by the interaction between two currents of fluid without mixing, and the effect of the entropy on the speed of sound. The presence of a second plateau triggers a flow transition which can affect the on-design performance. The collected data were also compared with similar ones obtained by other research groups. Hence, these comparisons reinforce the trends of the actual experiments.

Experimental and numerical investigation on performance of a swirling jet reactor

In this work, a three-dimensional Computational Fluid Dynamic (CFD) analysis of a swirling jet reactor was implemented to gain a better understanding of fluid dynamics into the reactor. The effect of different geometries of the reactor, by considering different diameters of the injection slots of the reactor, on flow velocity and flow pressure distributions was investigated. Firstly, a one-phase model was implemented by considering only water into the reactor. Then, a two-phase model was defined including dissolved air into the water. The inlet flow pressure was set to 0.25 bar to consider non-cavitating conditions and, then, to get more accurate results on fluid dynamics into the reactor due to the absence of cavitating conditions. Data collected from experimental tests were used to calibrate and validate the model. Results of numerical simulations were in good agreement with experimental data, showing for all the geometries a rotating flow around the central axis of the reactor and at the exit of the double cone. The highest flow velocities and flow pressure drops were observed for the reactor geometry with the smallest injection slots diameters. Finally, noise measurements were performed during another set of experimental tests by considering different inlet flow pressures.

Visualization of two-phase flow in primary nozzle of a transcritical CO2 ejector

The two-phase flow in the primary converging-diverging nozzle of a transcritical CO2 ejector was investigated by a visualization measurement experiment using the direct photography method. The transition of the phase change position in the primary nozzle was discovered experimentally and analyzed theoretically based on the isentropic expansion process. The pressure distribution along the primary nozzle was measured by the pressure sensors simultaneously under different operating conditions. The expansion state of the primary flow and the nozzle outlet quality were studied by comparing the nozzle outlet pressure with the suction flow inlet pressure. The visualization images revealed that the phase change could start after or before the throat according to the operating conditions, which was consistent with the isentropic analysis results. In addition, the phase change position moved upwards when the primary flow inlet pressure and temperature decreased simultaneously. The pressure measurement results found that the nozzle outlet pressure was obviously higher than the suction flow inlet pressure in the experiment, which indicated that the primary flow was under-expanded in the primary nozzle. The nozzle outlet quality calculated with the nozzle outlet pressure was less than that calculated with the suction flow inlet pressure. The visualization experiment can be used to improve the CO2 ejector geometry and provide useful data for CO2 ejector model validation to better interpret the internal complex flow phenomena.

Transition from spray to roping in hydrocyclones

Although roping in hydrocyclones is a problem that has been studied by many researchers, we do not yet have a theory that relates all the variables involved. Several experimental works with different approaches such as mechanical energy balance, work on hydrocyclones with water only and hydrocyclone air core measurements with different instruments in the laboratory and plant have attempted to explain the roping phenomenon. They have addressed design variables such as apex to vortex diameters and different cone angles as well as operating variables such as inlet solid concentration, particle size, pressure and overflow and underflow flow rates and concentrations in order to understand their effect on the roping condition. In this paper we intend to verify some of the conclusions of these studies and establish inlet pressure and particle diameter as the variables that, in combination, lead from spray to roping. We present a computational model using Computational Fluid Dynamics (CFD) to study a 75-mm laboratory hydrocyclone operating at a variable flow rate and with three different particle diameters. The Reynolds Stress Model and Eulerian multiphase model were used to model the turbulence and interaction of phases, respectively. The solid particles are described with the kinetic theory of granular flows (KTGF). Physical coherence and accuracy were compared with experimental data, where errors are within the expected range for an engineering prediction. The results indicate that transition from spray to roping generates an increase in the inlet flow pressure and/or particle diameter at a constant solid concentration in the feed flow. For 20-µm-diameter particles an increase results in a decrease in the discharge angle, although it always has a spray shape, for 34-µm diameters increasing the inlet pressure generates a semi-rope discharge and for 70-µm-diameter particles a small increase in the inlet pressure generates a roping condition. Transition to roping is characterized by a decrease in the air core diameter and discharge angle due to slow rotational velocity when particle diameter increases or higher accumulation of the solid fraction in the apex when inlet pressure increases. The passage from spray to roping occurs with a change in the frequency spectrum of the pressure oscillations in the walls of the hydrocyclone, with high amplitudes at low frequencies for spray discharge and noisy signals in all spectrums and damped low frequencies for roping.

Experimental and analytical studies on the shock wave length in convergent and convergent–divergent nozzle ejectors

The shock cell structure and the entrainment were investigated for convergent and convergent–divergent nozzle ejectors. The shock wave structures after the nozzle with over-expanded supersonic flow were captured by optical Schlieren measurements at different inlet pressures and temperatures. The first shock wave length was analyzed by using an image processing method. An analytical model was then proposed to predict the wavelength of the first shock wave in both convergent and convergent–divergent nozzle ejectors. The model results agree well with the measurements for the first shock wave length with a maximum difference of 11%. The influence of the first shock wave length on the ejector entrainment performance was analyzed to show that the ejector entrainment performance decreases as the shock wave wavelength is increased at a given primary flow inlet pressure.

Experimental study and analysis of the purge gas pressure drop across the pebble beds for the fusion HCPB blanket

The lithium ceramic and beryllium pebble beds of the breeder units (BU), in the fusion breeding blanket, are purged by helium to extract the bred tritium. Therefore, the objective of this study is to support the design of the BU purge gas system by studying the effect of pebbles diameter, packing factor, pebble bed length, and flow inlet pressure on the purge gas pressure drop. The pebble bed was formed by packing glass pebbles in a rectangular container (56mm×206mm×396mm) and was integrated into a gas loop to be purged by helium at BU-relevant pressures (1.1–3.8bar). To determine the pressure drop across the pebble bed, the static pressure was measured at four locations along the pebble bed as well as at the inlet and outlet locations. The results show: (i) the pressure drop significantly increases with decreasing the pebbles diameter and slightly increases with increasing the packing factor, (ii) for a constant inlet flow velocity, the pressure drop is directly proportional to the pebble bed length and inlet pressure, and (iii) predictions of Ergun's equation agree well with the experimental values of the pressure drop.

A comparison study on the removal of suspended solids from irrigation water with pumice and sand–gravel media filters in the laboratory scale

In this study, different bed materials in media filter systems were examined. For this purpose a laboratory experiment was established to determine the solids removal efficiency, total outlet flow volume and outlet flow velocity of pumice that has numerous open spaces, vesicles and irregular cavity, sand–gravel and combination of pumice and sand–gravel. In the experiment, two different filter column diameters (150 and 200 mm) and two different inlet flow pressures (100 and 150 kPa) were used. The results show that the total outlet flow volumes increased logarithmically as the filtration test period progressed, while the outlet flow velocities and the outlet concentrations of suspended solids decreased logarithmically for all filter types. Pumice media filters provided higher total outlet flow volumes and lower solid removal efficiency in comparison with sand–gravel media filters. However, the highest average solid removal efficiency was determined by pumice plus a sand–gravel media filter at 90.5%. The average outlet flow velocity value for this filter type was 34.2 m3 h-1 m-2, which was higher than the other filter types at the same experimental conditions. Pumice plus sand–gravel media filters increased the filtration period according to the sand–gravel media filters as well.

A Lagrangian boundary element approach to transient three‐dimensional free surface flow in thin cavities

AbstractThe lubrication theory is extended for transient free‐surface flow of a viscous fluid inside a three‐dimensional thin cavity. The problem is closely related to the filling stage during the injection molding process. The pressure, which in this case is governed by the Laplace's equation, is determined using the boundary element method. A fully Lagrangian approach is implemented for the tracking of the evolving free surface. The domain of computation is the projection of the physical domain onto the (x, y) plane. This approach is valid for simple and complex cavities as illustrated for the cases of a flat plate and a curved plate. It is found that the flow behavior is strongly influenced by the shape of the initial fluid domain, the shape of the cavity, and inlet flow pressure. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Hydrodynamic Lubrication of Face Seal in a Turbulent Flow Regime

Abstract Models for thermohydrodynamic lubrication in the turbulent regime are developed for a mechanical end face seal with various combinations of asperity height and roughness pattern. A surface wear model, based on deformation, is established for mixed lubrication such that the displacement is at most equal to the mean asperity height. Only normal load is involved in the solution of asperity deformation, and the mean film thickness is determined based on a total volume conservation hypothesis, in conjunction with an elastic-exponential hardening model. The singularity problem, present in the expected form of the Reynolds equation for a seal surface with circumferentially-oriented roughness grain sphere grooves, is avoided by viewing the seal roughness as porous material, thereby introducing roughness permeability. Flow permeability is thus obtained by combining Darcy’s law for porous material with the average flow model developed by Patir and Cheng for mixed lubrication. The hydrodynamic pressure and thereby the hydrodynamic load support are relatively higher from a seal with radially-oriented roughness. Both the mean film thickness and the hydrodynamic load support are substantially elevated by increasing the composite rms roughness, raising the inlet-flow pressure, and decreasing the rotational speed. Good agreement has been obtained from the comparison between the results herein and Lebeck’s experimental results.

Side Thrust Control by Secondary Gas Injection into Rocket Nozzles

Directional control of rockets can be achieved by using secondary gas jets for providing side forces. The present investigation is concerned with the fact that a greater side force can be achieved by expanding the secondary gas into the supersonic region of the main nozzle than by expanding it directly to atmosphere. A laboratory test rig using ambient temperature air for the primary and secondary flows is described. Axial thrust and side force were measured using strain gauge force transducers. The experiments were performed on a small axisymmetric main nozzle with a 10° semi-angle of divergence and with sonic injection through circular ports placed normal to the main nozzle axis. The investigations centred principally on the effects of (1) varying the secondary port size at a given axial location in the nozzle and of (2) varying the axial location of a port of constant diameter. Side force and axial thrust augmentation characteristics were obtained for a range of primary and secondary flow inlet pressures. The results show the relative importance of the parameters on which side force depends, the maximum side force that may be produced and the interdependence of axial thrust augmentation and side force.