Pulsating Conditions Research Articles

Pulsatile Bi-Directional Aerosol Flow Affects Aerosol Delivery to the Intranasal Olfactory Region: A Patient-Specific Computational Study.

The nasal olfactory region is a potential route for non-invasive delivery of drugs directly from the nasal epithelium to the brain, bypassing the often impermeable blood-brain barrier. However, efficient aerosol delivery to the olfactory region is challenging due to its location in the nose. Here we explore aerosol delivery with bi-directional pulsatile flow conditions for targeted drug delivery to the olfactory region using a computational fluid dynamics (CFD) model on the patient-specific nasal geometry. Aerosols with aerodynamic diameter of 1 µm, which is large enough for delivery of large enough drug doses and yet potentially small enough for non-inertial aerosol deposition due to, e.g., particle diffusion and flow oscillations, is inhaled for 1.98 s through one nostril and exhaled through the other one. The bi-directional aerosol delivery with steady flow rate of 4 L/min results in deposition efficiencies (DEs) of 50.9 and 0.48% in the nasal cavity and olfactory region, respectively. Pulsatile flow with average flow rate of 4 L/min (frequency: 45 Hz) reduces these values to 34.4 and 0.12%, respectively, and it mitigates the non-uniformity of right-left deposition in both the cavity (from 1.77- to 1.33-fold) and the olfactory region (from 624- to 53.2-fold). The average drug dose deposited in the nasal cavity and the olfactory epithelium region is very similar in the right nasal cavity independent of pulsation conditions (inhalation side). In contrast, the local aerosol dose in the olfactory region of the left side is at least 100-fold lower than that in the nasal cavity independent of pulsation condition. Hence, while pulsatile flow reduces the right-left (inhalation-exhalation) imbalance, it is not able to overcome it. However, the inhalation side (even with pulsation) allows for relatively high olfactory epithelium drug doses per area reaching the same level as in the total nasal cavity. Due to the relatively low drug deposition in olfactory region on the exhalation side, this allows either very efficient targeting of the inhalation side, or uniform drug delivery by performing bidirectional flow first from the one and then from the other side of the nose.

Innovative pre-concentration technology for recovering ultrafine ilmenite using superconducting high gradient magnetic separator

To achieve the utilization of the abandoned ultrafine ilmenite (−20 μm) produced in the titanium magnetite processing plant in Panzhihua, the superconducting high-gradient magnetic separation (SMS) technology was proposed in this study. After optimizing the conditions of magnetic intensity, feeding and pulsation, an SMS concentrate with TiO2 grade of 16.03% and TiO2 recovery of 66.39% was obtained through one roughing–one cleaning pre-concentration flowsheet. The specific magnetic force and magnetic force were calculated and analysed to illustrate the pre-concentration mechanism, and the results revealed that the combination of high magnetic field and strong pulsating resulted in the effective pre-concentration of the ultrafine ilmenite in the SMS process. In addition, the magnetic force analysis indicated that the high magnetic intensity and high magnetic gradient are the key factors of the SMS technology. Furthermore, the EDS-Mapping detection certified that the ultrafine ilmenite was concentrated from the gangue minerals using SMS technology.

Evaluation of porous rib and flow pulsation on microchannel thermal performance using a novel thermal lattice Boltzmann method

In this study, a new thermal lattice Boltzmann model (TLBM) is developed to simulate conjugate heat transfer in a microchannel heat sink (MCHS) with porous ribs and pulsatile flow inlet. The examined parameters include the rib to channel height ratio (Hr*), Strouhal number (St), and Reynolds number (Re), which are varied from 0.25 to 0.75, 0 to 3.2, and 100 to 300, respectively. The proposed TLBM is based on the double distribution function framework and capable of addressing heat transfer in combined fluid and porous media conditions. The simulation data show that the flow pulsation inside MCHS with porous ribs not only improves the bulk mean temperatures but also eliminates the rib recirculation zones at some phases, which promotes both the local and overall heat transfer. For fixed Re, the overall Nusselt number (Nu‾/Nu0) and Fanning friction coefficient (f‾/f0) increase and then decrease with increasing St. The maximum values appear at St = 2. For fixed Re and St, the thermal performance factor (TPF) displays a single peak trend with Hr* and the optimal TPF of 2.2 occurs at Hr*=0.5. In addition, compared with the previous ribbed, baffled, and porous MCHSs, the proposed porous rib design under pulsating conditions reports the highest Nu‾/Nu0 of 13.4 in the range of f‾/f0≤200. Finally, the correlations of Nu‾/Nu0 and f‾/f0 with Re, St, and Hr* for the present MCHS are established for the first time, with average differences below 6.7% and 12.4%, respectively.

Study on Dispersed-Phase Axial Dispersion in an Agitated–Pulsed Solvent Extraction Column with a Step Tracer Injection Technique

In this work, the residence time distribution (RTD) of the dispersed phase (aqueous phase) and continuous phase (organic phase) in an agitated-pulsed extraction column (APC) was measured online with a step tracer injection technique and the axial dispersion was subsequently calculated via RTD analysis. It was found that both the agitation speed and the pulsation intensity had noticeable effects on the axial dispersion of the dispersed phase, which escalates with the increase in the agitation speed and this is especially authentic at high pulsation intensity. The dispersed-phase axial dispersion coefficient also becomes higher with the increase in the dispersed-phase velocity. Compared with the dispersed-phase axial dispersion in the APC, the continuous-phase axial dispersion is 2-3 times higher. Empirical equations have been proposed to correlate the dispersed- and continuous-phase axial dispersion coefficients for variation of both agitation and pulsation conditions in APC. This study could be valuable for assessing the dispersed-phase axial dispersion in liquid-liquid extraction columns.

Pulsating diffusion flames fed with biomass particles in counter-flow arrangement: Zeldovich and Lewis numbers effects

Natural and forced instabilities have a significant influence on the performance and efficiency of biomass-fueled combustion systems, where oscillatory behaviors cannot be ignored. This work concentrated on the analytical modeling of pulsating biomass-fueled diffusion flames in the non-premixed counter-flow arrangement, accounting for the effects of Lewis and Zeldovich numbers. Preheating, post-vaporization, reaction, and oxidizer zones were considered in the model derivation. In order to model the oscillatory characteristics, oscillations were mathematically modeled using a sinusoidal function. Transient mass and energy balance equations were formulated and analytically solved considering different Lewis and Zeldovich numbers. To preserve continuity and obtain the flame front position, jump conditions were given. After validating the derived analytical model, transient characteristics of flame temperature and position and time-varying distributions of reactants temperature and mass fraction were presented under pulsating conditions. Results show that Lewis number is the main parameter controlling the oscillatory and pulsating behaviors of the flame. Furthermore, Zeldovich number seems to escalate the effects of Lewis number.

Regulation of gas-liquid Taylor flow by pulsating gas intake in micro-channel

Bubble formation mechanism and slug flow characteristics have been studied in a T-junction rectangular micro-channel under pulsating gas intake conditions. A high-speed camera is used to track the trajectory of gas-liquid interface by the Lagrangian method, while the numerical simulation is used to acquire the flow field distribution at different moments using the Euler method. The dynamic pressure, shear stress and pressure difference across the forming bubble at the T-junction increase with the pulsation frequency and liquid velocity. Under pulsating gas intake conditions, none of these three types of force can be neglected, indicating a transition regime between squeezing and dripping regime. The evolution of bubble length under pulsating conditions is similar to the general gas-liquid flow, but with a shorter value, while the liquid slug length is longer than the latter. The slug flow is transformed into wave flow when the pulsation energy inputted to the system reaches a critical value. The bubble velocity varies periodically over time with a main fluctuation frequency equal to that of pulsation. The present work proves that the technique of pulsating gas intake enables precise control the gas-liquid Taylor flow pattern, which would be useful for future application in gas-liquid reactions.

Investigation on the unsteadiness of centrifugal compressor exposed to pulsating backpressure

Centrifugal compressor is exposed to pulsating backpressure due to the movement of intake valves in internal combustion engine. The performance of compressor deviates from the steady performance map, which affects the matching between turbocharger and engine. The behavior of compressor system at pulsation conditions are investigated via an in-house developed 1D unsteady code validated by experimental results. The influence of pulse frequency, magnitude and compressor characteristic curve on the compressor transient responses, including filling-emptying effect and wave dynamics, are analyzed. Results show that the strength of wave dynamics grows stronger with the increasing of pulse frequency, while the strength of filling-emptying effect increases first then decreases. The rise of pulse magnitude results in an almost linearly increasing of filling-emptying effect, while it can hardly affect the wave dynamics. Furthermore, the influence of pulsation magnitude and frequency represents the influence of local pressure gradient, and a correlation as quadratic curve can be evaluated between the pressure gradient and compressor unsteadiness. On the other hand, the influence of operating point, including the average mass flow rate and the slope of characteristic curve, is confirmed to be evidently smaller, comparing to the influence of pulsation frequency and magnitude. This study is helpful to estimate the behavior of compressor and the discrepancy of performance when operating at unsteady environment or matched with engine.

Large eddy simulation of the turbulence heat and mass transfer of pulsating flow in a V-sharp corrugated channel

The convective heat transfer and pressure loss characteristics of flow in a V-sharp Corrugated channel were studied using the LES numerical approach under pulsating inlet conditions. The A amplitude of the imposed pulsation did not exceed 100% of the mean velocity in order to avoid flow reversal (A≤1.0) while St dimensionless frequency was ranged from 0.0 to 0.79. The influence of the pulsating parameters (St, A) as well as Re are studied. Under pulsating condition, flow structures are favored and due to the imposed unsteadiness, heat transfer is enhanced. The 3D flow patterns also underline the driving of coherent structures within a pulsating period; everything occurs as if inlet pulsating conditions favored continuous oscillation between laminar and turbulent behavior. The results revealed that the overall thermal performance of pulsating flow has improved significantly compared with constant flow condition. As a result, pulsating conditions are more efficient in terms of thermal performance factor with values reaching 1.3 to 1.4 for pulsating corrugated channel while values ranging from only 0.9 to 1.17 are reached under constant flow condition.

Estimation of pulsatile flow and differential pressure based on multi‐layer perceptron using an axial flow blood pump

This study proposes a non-invasive method for estimating the pulsating flow and pressure difference, which uses the blood pump estimation model based on a multi-layer perceptron to calculate the flow and pressure difference under pulsating conditions. The model takes 11 parameters such as the rotational speed, power, and pulsation waveform of the blood pump as the input and uses the pressure difference and flow as the output. The experimental results of 119,590 sample data show that the flow error of the training set of the blood pump estimation model is 0.14 l/min and the pressure difference error is 7.50 mmHg; the flow error of the test set is 0.14 l/min and the pressure difference error is 7.50 mmHg. Compared with the traditional flow and pressure prediction method, this method has higher precision, which will provide a certain technical accumulation for accurately estimating the flow and pressure difference of the blood pump in the pulsating conditions.

Experimental study on unsteady flow field in a centrifugal compressor at pulsating backpressure conditions

Centrifugal compressor is confronted by pulsating backpressure when coupled with turbocharged internal combustion engine. Few studies have been reported on the understanding of pulsating flow field in the compressor although its performance is notably influenced by the strongly pulsating condition. This paper experimentally studies unsteady flow field in a centrifugal compressor at pulsating backpressure conditions. Experimental facilities and methodology are introduced firstly, followed by detailed discussions on experimental results of unsteady flow at different pulsating conditions. Results show that the pulses of pressure and mass flow rate are alleviated as the pulses propagate from compressor exit to the impeller, but then are enhanced remarkably in the impeller inducer. Flow field at compressor inlet manifests that the axial velocity and the incidence angle are evidently distorted in both circumferential and radial directions induced by the volute at both steady and pulsating conditions. Specifically, the incidence angle is higher in the region upstream the volute tongue than the values downstream the configuration. The patterns of distortions vary periodically with the pulsating backpressure. In particular, comparing with the variation near hub region, the incidence angle varies with the magnitude as about 10 degrees near 85% blade height, implying that the flow in spanwise direction responses to the pulsating backpressure with different sensitivity. The study experimentally demonstrates the clear evidence of the unsteadiness of the flow field in the compressor at pulsating backpressure conditions.

Experimental Evidence of the Influence of Recurves on Wave Loads at Vertical Seawalls

The role of recurves on top of seawalls in reducing overtopping has been previously shown but their influence in the distribution and magnitude of wave-induced pressures and forces on the seawall remains largely unexplored. This paper deals with the effects of different recurve geometries on the loads acting on the vertical wall. Three geometries with different arc lengths, or extremity angles (αe), were investigated in large-scale physical model tests with regular waves, resulting in a range of pulsating (non-breaking waves) to impulsive (breaking waves) conditions at the structure. As the waves hit the seawall, the up-rushing flow is deflected seawards by the recurve and eventually, re-enters the underlying water column and interacts with the next incoming wave. The re-entering water mass is, intuitively, expected to alter the incident waves but it was found that the recurve shape does not affect wave heights significantly. For purely pulsating conditions, the influence of αe on peak pressures and forces was also negligible. In marked contrast, the mean of the maximum impulsive pressure and force peaks increased, even by a factor of more than two, with the extremity angle. While there is no clear relation between the shape of the recurve and the mean peak pressures and forces, interestingly the mean of the 10% highest forces increases gradually with αe and this effect becomes more pronounced with increasing impact intensity.

The effect of flow pulsation on Al2O3 nanofluids heat transfer behavior in a helical coil: A numerical analysis

Nanofluids heat transfer in a helical coil under pulsation condition was numerically simulated. The dynamic single phase model which considered Brownian motion effect was utilized to study the Al2O3 nanofluids heat transfer in helical coils. The reliability test results were consistent with experimental results. Then, pulsation was further imposed. The influence of the pulsation frequency on the heat transfer performance was explored. And the changes of instantaneous h with frequency were further studied to interpret the results. The axial velocity contours, axial velocity distributions, and cross-section velocity vectors at various planes along the coil were examined. The results revealed that there was an optimum pulsation frequency for heat transfer augmentation within the scope of Re. The secondary flow generated in cross region and the counter-rotating vortex formed in the axial direction all devoted to the helical coil heat transfer augmentation under pulsation.

Unsteady performance of a mixed-flow turbine with nozzled twin-entry volute confronted by pulsating incoming flow

Turbine with twin-entry volute has advantage of utilising energy from pulsatile exhaust gas and improving low-speed torque of an internal combustion engine. This paper investigates unsteady performance of a mixed flow turbine with nozzled twin-entry volute confronted by pulsatile incoming flow. The turbine performance at pulsating conditions with different Strouhal numbers (St) is studied via experimentally validated numerical method. Results show that the unsteadiness of turbine performance is enhanced as Strouhal number increases. In particular, the cycle-average efficiency at St = 0.522 is about 3.4% higher than that of quasi-steady condition (St = 0). Instantaneous loss breakdown of the turbine shows that the entropy generation rate of turbine components reduces evidently at pulsating conditions as Strouhal number increases, especially for the nozzle. Specifically, the cycle-averaged reduction of the loss in the nozzle is 37.3% at St = 0.522 compared with that of St = 0. The flow analysis shows that secondary flow which contributes to the majority of loss in the nozzle, including flow separation, horseshoe vortex, and reversed flow near the leading edge, are notably alleviated as Strouhal number increases. The alleviation of the flow structures are resulted from two reasons: one is that the flow distortion at the nozzle inlet is evidently depressed by the pulsating conditions, the other is that the inertia of the low momentum flow in the nozzle damps flow evolution at pulsating incoming flow. Consequently, the loss is reduced and the turbine performance is benefited by the pulsating inflows.

Unsteady Flow Loss Mechanism and Aerodynamic Improvement of Two-Stage Turbine under Pulsating Conditions

The developments of two-stage turbocharging and turbocompounding promote the application of the two-stage turbine system in internal combustion engines. Since the turbine suffers from the pulsating exhaust, the performance deteriorates significantly from steady conditions. In the paper, the pulsating flow losses in the two-stage turbine are analyzed and a control method is proposed to improve the turbine performance. ANSYS CFX, which is a commercial software for computational fluid dynamic, is applied to resolve the three-dimensional unsteady flow problem. The accuracy of the simulation method is verified by the experimental data from each turbine. Firstly, the impacts of pulse amplitudes on transient loss of each component of the two-stage turbine are studied. Then flow field analysis is carried out to understand details of the unsteady flows. It is found that the variation of incidence angle at the low-pressure turbine (LPT) rotor tip is significantly larger than that at rotor hub, which causes severe flow loss near leading edge. As a result, the LPT performance drops down significantly. To improve the LPT performance, the blade shape at tip is modified. The aerodynamic performances of turbines with three different shapes under high- and low-load pulsating flow conditions are evaluated. It is found that increased inlet blade angle and medium thickness achieves good aerodynamic performance. The rotor averaged efficiency is improved by 2.27% under high-load pulsating condition.

Experimental study on performance of centrifugal compressor exposed to pulsating backpressure

Pressure fluctuations in intake manifold of Internal Combustion Engine introduce a pulsating boundary condition to the centrifugal compressor. In this study, the performance of centrifugal compressor exposed to pulsating backpressure is experimentally investigated. Unsteady performance and surge characteristic of the compressor at different pulsating conditions are analyzed. Results show that instantaneous performance of the compressor forms a hysteresis loop encapsulating steady performance. A correlation of compressor unsteadiness with pulse frequency, magnitude, and local slope of the characteristic curve is obtained based on measurements. The results show that cycle-average performance of the compressor is notably lower than that at constant conditions. Specifically, the averaged peak efficiency at pulsating condition drops by 3%–7%. Moreover, Fast Fourier Transformation method is applied to study surge characteristics at pulsating conditions. Results manifest that compressor surge is postponed remarkably by pulsating backpressure at the three speeds. As the compressor approaches to small mass flow rate, flow fluctuations decay quickly and then increase dramatically when the surge happens. This phenomenon is resulted from the influence of the slope of characteristic curve on the filling-empty effect and compressor stability. Larger slope produces weaker filling-empty effect and hence smaller size of the loop, but reduces the stability of compressing system and triggers compressor surge.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ИНТЕНСИФИКАЦИИ ТЕПЛОПЕРЕДАЧИ В ПЛАСТИНЧАТОМ ТЕПЛООБМЕННИКЕ ПРИ ПУЛЬСИРУЮЩЕМ ТЕЧЕНИИ ТЕПЛОНОСИТЕЛЯ

We conducted two sets of experiments, one is under steady-state conditions and the other under pulsating conditions. We focused on measuring the heat transfer characteristics of plate heat exchangers under different pulsation conditions. In the experiment, we control the mass flow of the hot fluid to circulate at a rate of 0.722 kg/s. The mass flow rate of the cold fluid is 0.05-0.18 kg/s, and the pulsation frequency is 0.45-2.23 Hz. We measured different mass flows at different pulsation frequency. The data analysis shows that when the pulsation frequency is 1.78 Hz, the heat transfer coefficient reaches a maximum of 4415.73 w/(m2·k), and the corresponding cold fluid mass flow rate is 0.155 kg/s, and compared with the heat transfer characteristics of the plate heat exchanger under steady flow, it is found that the average increase in the heat transfer coefficient during the transition to the pulsating mode was 20%.

Heat transfer enhancement and pressure drop by pulsating flow through helically coiled tube: An experimental study

Pulsating flow was applied as an active technique for heat transfer enhancement. Helically coiled tube was employed and convective heat transfer and pressure drop were experimentally investigated. Four helically coiled tubes with the same tube diameter and different coil curvature were fabricated and subjected to uniform wall heat flux. Distilled water was utilized as working fluid and its thermo-physical properties were estimated at mean temperature using available correlations. At first, Darcy friction factor and Nusselt number in steady laminar flow were compared with several correlations in the literature and the most accurate relations were found. Afterward, experiments were extended for pulsating laminar flow over a Womersly number range of 16–38 which corresponds to 2–10 Hz pulsating frequency, Reynolds number of 2000–9500, and Helical number of 350–2300. The results revealed that increment in pressure drop is nearly 3–7% in pulsating flow compared to steady one, while convective heat transfer enhanced up to 39%. Findings indicated that more heat transfer enhancement can be attained at low Reynolds numbers. Improvement in heat transfer rate and thermal performance was evaluated and discussed in detail. Also, a new correlation was proposed for Nusselt number in laminar pulsating flow. Among the four pulsating frequencies were studied in the current work, the optimum pulsating condition for achieving the best thermal performance was Wo ~ 24 (4 Hz).

Numerical study and POD snapshot analysis of flow characteristics for pulsating turbulent opposing jets

PurposeThe purpose of this study is to investigate the coherent structures of pulsed opposing jets by large eddy simulation (LES) model and proper orthogonal decomposition (POD) snapshot method. Flow pulsation as an active flow control method is considered for the enhancement of transport phenomena in impinging jets. The effect of flow pulsation parameters such as pulsation signal shape and frequency on the vortical coherent structures, the energy content of primary modes and their variation are studied numerically.Design/methodology/approachIn this study, flow field of turbulent pulsating opposing jets has been simulated using LES. The result of the simulation in different time steps (snapshots) are stored and POD is applied on the snapshots. In this study, the POD method and calculation of spatial modes has been done using OpenFOAM, and time coefficients have been calculated using a MATLAB code.FindingsThe results of this study show that the flow excitation has a great effect on the coherent structure formation and the energy containment of fundamental modes of the flow. When the flow was excited by a harmonic sinusoidal or step function, the turbulent kinetic energy accumulated in the set of primary modes. On the other hand, the pulsed opposing jets had more regularity compared to the steady jets. The shapes, patterns and energy values of dominant modes depended on the inlet pulsation signal. An increase in pulsation frequency leads to an augmentation in energy content of the primary modes.Research limitations/implicationsThe predictions may be extended to include various pulsation conditions such as: various amplitudes, Reynolds number and aspect ratio.Practical implicationsThe results of this study are a valuable source of information for active control of transport phenomena in opposing jet configurations which is used in different industrial applications such as cooling, combustion, reactors, heating and drying processes.Originality/valueIn this study, the coherent structures and energy content of primary modes was studied for the first time by LES model and POD snapshot method and a comprehensive discussion on numerical results is provided.

Numerical Study of Bubble Rising and Coalescence Characteristics under Flow Pulsation Based on Particle Method

Two-phase flow instability may occur in nuclear reactor systems, which is often accompanied by periodic fluctuation in fluid flow rate. In this study, bubble rising and coalescence characteristics under inlet flow pulsation condition are analyzed based on the MPS-MAFL method. To begin with, the single bubble rising behavior under flow pulsation condition was simulated. The simulation results show that the bubble shape and rising velocity fluctuate periodically as same as the inlet flow rate. Additionally, the bubble pairs’ coalescence behavior under flow pulsation condition was simulated and compared with static condition results. It is found that the coalescence time of bubble pairs slightly increased under the pulsation condition, and then the bubbles will continue to pulsate with almost the same period as the inlet flow rate after coalescence. In view of these facts, this study could offer theory support and method basis to a better understanding of the two-phase flow configuration under flow pulsation condition.

Fatigue behaviour of maraging steel samples produced by SLM under constant and variable amplitude loading

This paper addresses the fatigue behaviour of AISI 18Ni300 samples manufactured by selective laser melting under both constant- and variable-amplitude loading. The fatigue campaign encompasses a series of low-cycle strain-controlled fatigue tests performed under fully-reversed conditions at various strain amplitudes, and a series of high-cycle stress-controlled fatigue tests performed under pulsating conditions at various stress ranges considering both constant- and variable-amplitude loading spectra. Fatigue life predictions are performed on the basis of the SWT parameter along with the Miner’s law. This approach has demonstrated to be sufficiently reliable to predict the lifetime expectancy in maraging steel samples produced by selective laser melting.