Changes In Flow Patterns Research Articles

South Atlantic Anomaly Areal Extent as a Possible Indicator of Geomagnetic Jerks in the Satellite Era

Geomagnetic jerks are sudden changes in the geomagnetic field secular variation related to changes in outer core flow patterns. Finding geophysical phenomena related to geomagnetic jerks provides a vital contribution to better understand the geomagnetic field behavior. Here, we link the geomagnetic jerks occurrence with one of the most relevant features of the geomagnetic field nowadays, the South Atlantic Anomaly (SAA), which is due to the presence of reversed flux patches (RFPs) at the Core-Mantle Boundary (CMB). Our results show that minima of acceleration of the areal extent of SAA calculated using the CHAOS-7 model (CHAOS-7.2 release) coincide with the occurrence of geomagnetic jerks for the last 2 decades. In addition, a new pulse in the secular acceleration of the radial component of the geomagnetic field has been observed at the CMB, with a maximum in 2016.2 and a minimum in 2017.5. This fact, along with the minimum observed in 2017.8 in the acceleration of the areal extent of SAA, could point to a new geomagnetic jerk. We have also analyzed the acceleration of the areal extent of South American and African RFPs at the CMB related to the presence of the SAA at surface and have registered minima in the same periods when they are observed in the SAA at surface. This reinforces the link found and would indicate that physical processes that produce the RFPs, and in turn the SAA evolution, contribute to the core dynamics at the origin of jerks.

Hydrokinetic piezoelectric energy harvesting by wake induced vibration

Piezoelectric energy harvesters capture various kinetic energy to power wireless sensors. A new hydrokinetic piezoelectric energy harvester using wake-induced vibration (WIV) is proposed in this paper. The mathematical model of the hydrokinetic energy harvester is established to consider the effect for different velocity regions. Circulating water-channel experiment is carried out to exam the performance of the harvester. The experimental results show that the model can predict the output power appropriately. Frequency analysis indicates that the performances in VIV region and WIV region are dominated by the wake vortex frequency and the natural frequency respectively. The flow pattern changes greatly under different spacings which are divided into extended-body, reattachment and co-shedding regions. The maximum output power of the harvester locates in the reattachment region. The maximum experimental power densities for the inverted D-shaped, circular and D-shaped cylinders are 570.3W/m3, 596.4W/m3, 1074W/m3, respectively. They are 43.2, 25.3, 31 times of that without wake interference. The corresponding optimal experimental spacing ratios are 5, 2.6 and 2, respectively. Compared with the case without wake interference, the output power of the hydrokinetic piezoelectric energy harvester using WIV is significantly improved.

Study on projects of bending shoal-cutting regulation for tidal river

By taking bending shoal-cutting of Water Conservancy park in Lingjiang as a case, the change of flow pattern in the curved channel before and after the shoal-cutting project is analyzed by numerical simulation, and application effect is analyzed. By analyzing the tidal level data of the engineering reach, the appropriate barrier clearance elevation is determined. The relationship between water level variation and different range of shoal-cutting is established, and the suitable range of shoal-cutting is recommended. It has an important reference for the management of bend in tidal river.

Effect of Silver Nanofluid on the Thermal Characteristics of Flat Plate Pulsating Heat Pipe

In this paper, the silver nanofluid with strong ion activity, low viscosity and excellent thermal conductivity is applied to the flat plate pulsating heat pipe (FP-PHP), the three-dimensional geometric model of FP-PHP with microchannel at the condensing section is established. A visual experiment platform is built independently to verify the reliability of the simulation results. The visualization phenomenon found that the types of bubbles of silver nanofluid are varied, including bubbly flow, plug flow, annular flow, semi-annular flow, and staggered cluster flow. With the increase of heating power, the stable cycle time gradually shortens, the flow pattern changes rapidly, and the cycle shortens. The thermal characteristics found that when the heating power reaches 110 W, the thermal resistance of nano silver fluid is the smallest, only 0.40 K/W. At this time, the heat transfer coefficient is 33% higher than that of the working fluid. The starting temperature of silver nanofluid is relatively low, only 35 ℃. Excellent temperature uniformity, after the heating power reaches 70 W, the overall temperature pulsation is only 1.2 ℃.

STABILITY ANALYSIS FOR EMBANKMENTS WITH GEOELECTRICITY

Abstract The collapse of the embankment is a problem that needs attention to find the right solution, so that the risk can be minimized. The condition of the embankment is influenced by the strength of the soil layer of the embankment, groundwater flow in the embankment, the condition of the water level of the embankment and human activities around the embankment. Changes in the quality of soil density in the embankment can form cavity zones within the embankment which cause changes in groundwater flow patterns in the embankment. The degradation of the soil layer of the embankment can cause piping, overtopping which is the cause of erosion of the embankment body and disturbs the stability of the embankment. Therefore, to determine the condition of the embankment soil layer, research on the stability of the embankment has been carried out using the geoelectric method at the location of the embankment in the Cipancuh and Penjalin reservoirs, so that an image of the embankment soil layer is obtained to determine the cavity zones in the embankment, the flow pattern in the embankment soil layer. Keywords: cavity zones, flow patterns, geoelectric methods, the stability of the embankment.

Experimental Research on Flow and Heat Transfer in Microchannel with Refrigerant HFO1234yf

An experiment was carried out to study the effect of refrigerant mass flow rate, heat flux density, and saturation temperature on boiling heat transfer coefficient and frictional pressure drop in microchannel. Flow patterns are captured by a high-speed camera. HFO1234yf was used in rectangular microchannels with a hydraulic diameter of 0.5 mm. The results showed that there were eight flow patterns in the experiment, and the change of flow pattern is closely related to the change of heat flux and mass flow rate. The higher the heat flux and mass flow rate, the more the flow patterns appear. Different flow patterns have different heat transfer mechanisms. The heat transfer mechanism is mostly nuclear boiling at the region of bubble flow, slug flow, elongated slug flow, and agitated flow; the heat transfer mechanism is film convection boiling at the region of annular flow, and it is vapor convection at the region of dryout flow. When the dryness is about 0.4, the heat transfer mechanism changes from nuclear boiling to film boiling. The friction resistance decreases with the increase of dryness and saturation temperature.

Pengaruh Liquid Hold-Up terhadap Transisi Pola Aliran 2 Fasa Air-Udara dari Stratified Ke Slug pada Pipa 50 mm

The slug flow pattern is one of the most avoiding factors in piping systems due to its destructive characteristics. Research on the criteria of the slug formation is still the concern. The present study focused on finding out the influence of liquid hold-up toward the transition of the flow pattern from stratified to slug pattern. It was conducted on a 50 mm-diameter horizontal acrylic pipe. The visual data was obtained from a fully developed area (180-210 D) by variations of liquid superficial rate (JL) of 0,03-0,3 m/s and gas superficial rate (JG) from 0,7 to 3,77 m/s. The high-speed camera with 2000 fps recording speed was the instrument to obtain the visual data. The measurement of the liquid hold-up is made by Constant Electric Current Method (CECM). The drastic decrement of liquid hold-up value on the wave growth mechanism (JG ≤ 1,88 m/s) indicated the changes in flow patterns from the stratified to the slug pattern, while on the wave coalescence mechanism (JG > 1,88 m/s) the liquid hold-up remains increases. The pattern change from pseudo slug to the slug pattern was not decreasing on its film thickness, yet, it tends to increase the frequency and the liquid slug length.

Breakup and coalescence of large and small bubbles in sudden expansions and contractions in vertical pipes

The present work studies the dynamics of large and small bubbles in sudden expansions and contractions in vertical pipes. The experimental apparatus was designed to permit changes in flow patterns through singularities provoked by an expansion followed by a contraction. The data were obtained through particle image velocimetry and the shadow sizer technique. Size and velocity distributions for small and long bubbles are presented for six vertical pipe positions and compared with existing theories for the motion of small and large confined bubbles. Results for the mean velocity profiles, local shear rate and turbulent kinetic energy of the continuous phase are also presented. Predictions on the permissible largest diameter of bubbles as a function of space coordinates and flow conditions based on phenomenological theories are compared with the experimental data. Results indicate that bubble breakup and coalescence are essentially ruled by the dynamic pressure forces of the turbulent motions, but shear induced breakup is also observed for the small and large bubbles. The formation of a gas pocket in the contraction is identified as an important promoter of bubble breakup.

Pressure Drop dan Pola Aliran Dua Fase (Air-Udara) Melewati Pipa Groove Vertikal

This research was conducted to observe the effect of adding grooves in the two-phase flow of water-air in the same direction through a vertical pipe to changes in pressure and fluid flow patterns. Test section in the form of pipes with grooves made of acrylic material with a length of 100 cm and an internal diameter of 2.54 cm. The geometric shape of the acrylic pipe is modified by giving a groove in the direction of the pipe along the test section. Grooves used amounted to 4 and 16 and pipes without grooves used as a comparison. Tests are carried out by flowing water and air that has been mixed through the inlet side upward. The ratio of air velocity to water velocity (VG / VL ) is 0.24-1.13. The method used in this study is experimental. Retrieval of pressure drops data is done by using a differential pressure transmitter. Visual observations are also made using a DSLR camera equipped with a flash and video observations using a smartphone with slow-motion mode. The results showed changes in flow patterns and pressure drop values. Slugs in pipes with grooves disappear faster and pressure drops are lower than pipes without grooves.

Analysis of flow pattern change in horizontal mini-channel under electric field force

In this paper, the phenomenon of the flow pattern in the channel changes when the electric field force exists. Through the visual observation in the experiment, it is found that the study found that the bubble behavior was suppressed by the electric field force. When the electric field is large enough, the working fluid in the channel will always maintain a single-phase liquid flow. However, When there is enough superheat at the bottom of the mini-channel, the liquid film at the bottom of the liquid phase changes to a vapor phase, and the dryout appears in the channel, and it rapidly changes into a mist flow as the heating power increases. This phenomenon of flow pattern change due to electric field force is referred to herein as a flow pattern special phenomenon. Due to the existence of this special flow phenomenon, the temperature difference between the inlet and outlet of the working fluid in the channel has a large change. Through calculation, it is found that the dimensionless temperature difference between the inlet and outlet at a voltage of 200 V is 1.67 times that of 0 V. At the same time, the channel heat transfer coefficient increases with the increase of voltage.

Changes in transvalvular flow patterns after aortic valve repair: comparison of symmetric versus asymmetric aortic valve geometry.

The aim of this study was to compare the effect of asymmetric versus symmetric bicuspid aortic valve (BAV) repair on transvalvular flow patterns and aortic wall shear stress (WSS). Four-dimensional flow magnetic resonance imaging was prospectively and consecutively performed in patients with congenital aortic valve (AV) disease before and after AV repair. The following MRI-based parameters were assessed: (i) flow eccentricity index, (ii) backward flow across the AV, (iii) grading of vortical and helical flow, and (iv) WSS (N/m2) in the proximal aorta. MRI-derived flow parameters were compared between patients who underwent 'asymmetric BAV repair' (n = 13) and 'symmetric BAV repair' (n = 7). A total of 20 patients (39 ± 12 years, 80% male), who underwent BAV repair, were included. In the asymmetric BAV repair group, circumferential WSS reduction was found at the level of the aortic arch (P = 0.015). In the symmetric BAV repair group, postoperative circumferential WSS was significantly reduced compared to baseline at all levels of the proximal aorta (all P < 0.05). Postoperative circumferential WSS was significantly higher in the asymmetric versus symmetric BAV repair group at the level of the sinotubular junction (0.45 ± 0.15 vs 0.30 ± 0.09 N/m2; P = 0.028), ascending aorta (0.59 ± 0.19 vs 0.44 ± 0.08 N/m2; P = 0.021) and aortic arch (0.59 ± 0.25 vs 0.40 ± 0.08 N/m2; P = 0.017). Segmental WSS analysis showed significantly higher postoperative WSS after asymmetric versus symmetric BAV repair, especially in the anterior aortic segment (P = 0.004). Symmetric BAV repair results in more physiological flow patterns and significantly reduces WSS, as compared to asymmetric BAV repair. From a haemodynamic point of view, symmetric AV geometry should be attempted in every congenital AV repair.

Thermodynamic Analysis of the Dryout Limit of Oscillating Heat Pipes

The operating limits of oscillating heat pipes (OHP) are crucial for the optimal design of cooling systems. In particular, the dryout limit is a key factor in optimizing the functionality of an OHP. As shown in previous studies, experimental approaches to determine the dryout limit lead to contradictory results. This work proposes a compact theory to predict a dryout threshold that unifies the experimental and analytical data. The theory is based on the influence of vapor quality on the flow pattern. When the vapor quality exceeds a certain limit (x = 0.006), the flow pattern changes from slug flow to annular flow and the heat transfer decreases abruptly. The results indicate a uniform threshold value, which has been validated experimentally and by the literature. With that approach, it becomes possible to design an OHP with an optimized filling ratio and, hence, substantially improve its cooling abilities.

Universal scaling laws of collective human flow patterns in urban regions

Detail observation of human locations became available recently by the development of information technology such as mobile phones with GPS (Global Positioning System). We analyzed temporal changes of global human flow patterns in urban regions based on mobile phones’ GPS data in 9 large cities in Japan. By applying a new concept of drainage basins in analogous to river flow patterns, we discovered several universal scaling relations. These include, the number of moving people in a drainage basin of diameter L is proportional to L^3 in the morning rush hour, which is surprisingly different from reasonable intuition of proportionality to the 2 dimensional area, L^2. We show that this unexpected 3 dimensional feature is related to the strong attraction of the city center to become a 3 dimensional structure due skyscrapers.

Experimental research on the influence of aviation fuel temperature on swirl nozzle velocity

The purpose of this research was to explore the effects of various fuel temperatures on the injection velocity of swirl nozzles. A phase Doppler particle analyzer (PDPA) and particle image velocimetry (PIV) were used to measure the velocity of fuel sprayed by an injector into the normal atmosphere. The flow characteristics and velocities of the droplet were studied at low to high temperatures (−40 °C to 80 °C). The results showed that: 1) the flow number (FN) and mass flow of the swirl nozzle decreased with the increase of the fuel temperature under the same supply pressure; 2) the existence of “pressure critical point” and “temperature critical point” makes the nozzle flow pattern and spray pattern change, thereby changing the distribution of droplet velocity and particle size in space; 3) the PDPA measurement results showed that under the same supply pressure, a larger droplet velocity on the fuel mist cone and a smaller Sauter Mean Diamter (SMD) were measured at high temperature of fuel.

Visualization study on the condensation in a propylene loop heat pipe operating at condenser temperatures between 153 and 283 K

A cryogenic loop heat pipe (CLHP) is an effective means of temperature control at low temperatures, but the physical properties of cryogenic working fluids are quite different from those of room-temperature working fluids, and their phase change and heat transfer characteristics need to be further studied. In this paper, a test system for evaluating the loop heat pipe (LHP) heat transfer performance and visualizing the condensation phenomenon in the condenser was fabricated. The performance of a propylene LHP with 20 W of heat exchange was tested as the condenser temperature was varied from 283 to 153 K, and the flow patterns and heat transfer characteristics during condensation were obtained. With the decreasing condenser temperature, slug flow disappeared, and pseudo-slug flow occurred and transitioned into wavy-annular flow, which was mainly caused by the increase of density ratio and viscosity ratio of the liquid to vapor. These change of flow pattern further affected the two-phase heat transfer and the performance of the CLHP. Pseudo-slug flow was observed at a condenser temperature of 273 to 203 K and it had a notable influence on the condensation pressure drop. The heat transfer coefficient of the two-phase region ranged from 2500 to 5500 W/m2K. When the condenser temperature ranged from 203 to 173 K, the transition of flow pattern and the fluctuation in the system caused a large deviation between the obtained and predicted heat transfer coefficients, and at other condenser temperatures, the obtained values were consistent with the predicted values for the corresponding flow patterns.

Effects of Secondary Currents on Turbulence Characteristics of Supercritical Open Channel Flows at Low Aspect Ratios

In this paper, we present secondary current effects on the turbulence characteristics of supercritical narrow open channel flows over a smooth fixed bed. The main hydraulic parameters are low channel width to flow depth ratios varying between 1 and 2, and Froude numbers (F) ranging from 2 to 4. Detailed profiling of instantaneous streamwise and vertical flow velocities was conducted in a laboratory flume using a 2D laser Doppler anemometry. The cross-sectional distributions of mean flow velocities, turbulence intensities, Reynolds, and bed shear stresses were obtained from the measurements. The mean streamwise and vertical flow velocity distributions reveal that four pairs of secondary current cells are formed: a pair of well-developed free-surface vortices near the water surface, a pair of bottom vortices near the bed, and two pairs of mid-vortices between the free-surface and bottom vortices. These secondary currents cause bulging of the contour lines of the streamwise velocities with respect to the water surface and the bottom corner bisectors resulting in an undulated pattern of the mean velocity distribution across the cross-section. Furthermore, they cause the velocity dip phenomenon, i.e., the maximum flow velocity occurs well below the surface, and redistribute the Reynolds and bed shear stresses in transverse direction. The results demonstrate that decreasing the aspect ratio increases the strength of the secondary currents causing a significant change in flow patterns with larger free-surface vortices compared to the bottom vortices. Compared to the aspect ratio effect, the Froude number only slightly impacts the flow characteristics as a result of flow non-uniformity. For all investigated aspect ratios and Froude numbers, bed shear stresses are concentrated at the flume center, and on average 5 to 10% higher than their mean values. The modified wake-log-law holds both in the inner and outer regions, matching well with the experimental data for all test conditions. The present findings are discussed with literature data, and their impact on engineering applications is demonstrated.

Experimental investigation of gas-liquid separation for two-phase flow within annular duct of an ESP skid

Although common in several sectors of the industry, undeveloped two-phase flow in annular ducts has yet to receive attention from researchers. This work investigates experimentally the gas-liquid separation phenomenon in the two-phase flows inside annular ducts. The experimental setup enables flow visualization and analysis through high-speed cameras. This experimental setup's design is based on a non-dimensional and similarity analysis with a real device (Electric Submersible Pump Skid or ESP Skid) in operation at an offshore oilfield in Brazil. The experiments were performed in 5°, 15°, 30° 45° and 60° slopes, horizontally. Flow patterns in the annulus were observed and analyzed. Also, vortices were observed in the intake region. The gas-liquid separation tests enabled the association of the measured separation efficiency with mixture velocities and, consequently, with dimensionless parameters (Froude number) and no-slip void fraction. As observed in the literature, the separation decreases as the mixture velocity increases. The results were qualitatively correlated with literature models, but with high quantitative discrepancies, mainly due to the disregard for radial slip in the models. Also, changes in the trend of separation efficiency were observed and these were caused by flow pattern changes.

Two-dimensional numerical modelling of strategies to avoid thermal stress induced flow channeling in fractured geothermal reservoirs

Thermal drawdown induced flow channeling in fractured geothermal reservoirs has been found to be inevitable in previous work. This hypothesis is questioned and found not to be true for all scenarios. We investigate flow in a simple two-fracture network to investigate the basic behavior of thermal drawdown induced flow pattern changes, using a Thermo-Hydro-Mechanical (THM) numerical model. In addition, we propose two operational interventions to mitigate the negative effects of uneven flow on geothermal production. We found that uneven flow is not inevitable, but dependent on several factors, including initial fracture aperture, the actual value of the aperture, and the total injection rate. A small difference in aperture, a higher aperture value and a larger total injection rate are all factors improving the chances for even flow. The operation interventions include variable injection rates, and sequential injection in the fractures before normal production. Both are shown to improve the chances for even flow and better production. Overall, changes in stress and pressure as a result of cooling, are found to have significant effects on flow pattern and production values, underlining the need for advanced numerical models capable of THM modeling for accurate geothermal production analysis in low permeability fracture networks.

Genetic diversity and differentiation of Olea europaea subsp. cuspidata (Wall. & G.Don) Cif. in the Hajar Mountains of Oman

Olea europaea subsp. cuspidata (Wall. & G. Don) Cif. is one of the six subspecies important for domestication of olive described as having valuable breeding traits. It is distributed from South Africa to the Middle East and the Mediterranean region to China mainly at mid to high altitudes with adequate precipitation. The currently rather fragmented Olea europaea subsp. cuspidata populations likely represent outposts of a formerly larger and more connected area and are hence vulnerable to additional stresses such as erratic weather extremes and anthropogenic influences. This may result in further fragmentation of stands, shifts in demography, increased clonal growth, lower genetic diversity, and higher differentiation between olive stands. In this study, we present data on Olea europaea subsp. cuspidata growing in the Hajar Mountains, Sultanate of Oman, a large area subjected to many anthropogenic disturbances. We used dendrological traits and genetic parameters to infer its stand and population genetic structure, levels of genetic diversity, and differentiation. To accomplish this, 366 individual trees in total were inventoried and 188 of them genotyped using 12 microsatellite markers. Dendrological measures indicated disturbances mainly due to human activities. Height and crown area of individuals averaged 3.7 m (ranging from 0.2 to 12 m) and 14 m (ranging from 1 to 18 m), respectively. The stand conditional index was mainly 50%. The identified genetic variation within the sampled areas was relatively moderate. The expected and observed heterozygosity equalled 0.55–0.58 and 0.62–0.64, respectively. All individual genotypes were unique indicating the absence of clones. Though significant genetic differentiation was found, there was no evidence of population substructure suggesting effective pollen and long-distance seed dispersal in the past. However, changes in gene flow patterns may be reflected in the next (sibling) generation. Further studies are necessary to detect any changes in the future and to develop sustainable conservation strategies for this species.

VP43.22: Longitudinal changes of umbilical artery Doppler flow patterns in monochorionic twins with selective fetal growth restriction

VP43.22: Longitudinal changes of umbilical artery Doppler flow patterns in monochorionic twins with selective fetal growth restriction