Effects Of Gravitational Forces Research Articles

Influence of slug flow on sand dune transport in a 3.6° upward inclined pipeline

AbstractThis study presents an experimental investigation of sand conveying from a stationary flatbed through two‐phase liquid–gas flows as a function of the fluids flow rates and pipeline orientation (α = 0°, and α = +3.6°). The characteristics of sand particle transportation by saltation, sand dune formation process and morphologies are visualized using a transparent cylindrical acrylic pipeline and digital photography. It was observed that slug flow regime was the dominant mechanism to lift the sand particles for both horizontal and upward inclinations. It was also found that sand dunes deconstructed more quickly at an upward inclination than horizontal position. For the upward inclination, the conveying phenomenon is characterized by sand bed lifting, suspension, and backward entrainment below the air bubble in the water film. Due to the increased liquid flow rates, higher dune velocity is recorded for the inclined condition. The dune pitch length grew for the horizontal configuration after the transient phase, as a result of the gravitational force effect, while it remained constant for the inclined orientation. In both conditions the slip face angle decreased with time; however, for the inclined configuration, this angle was lower because of the higher upstream liquid flow rate. These results provide important insights into the effect of pipe inclination on bed‐load mode solid transport by two‐phase flow inside a closed circular conduit. The obtained experimental data can be used to validate future numerical investigations.

The Effect of Gravity on Marginal Integrity of Different Flowable Bulk-Fill Resin Composites.

Background and Objectives: The aim of this quantitative research was to investigate the effect of gravitational forces on the marginal integrity of different bulk-fill composites by micro-CT imaging. Materials and Methods: Fifty caries-free human third molars extracted for prophylactic purposes were used in this study. Each tooth was prepared with two proximal box cavities, with dimensions of 3 mm × 3 mm × 5 mm. Five distinct groups, each comprising 20 cavities, thus totaling 100 cavities for this study: (1, Group CON): Clearfil Majesty Flow + Clearfil Majesty Esthetic (as the control); (2, Group FBR): Filtek Bulk-fill Flowable Restorative + Clearfil Majesty Esthetic; (3, Group XTB): Voco Extrabase + Clearfil Majesty Esthetic; (4, Group SDR): SDR + Clearfil Majesty Esthetic; and (5, Group SNC): Sonicfill. When restoring the mesial cavities, the occlusal surfaces of the teeth in the mold were positioned upwards, counteracting the force of gravity. In contrast, for the restoration of the distal cavities, the occlusal surfaces were aligned downwards, to be parallel with the gravitational pull. After restorative procedures, each tooth was treated with 5000 thermal cycles. A solution of ammoniacal silver nitrate (AgNO3) was employed as a tracing agent. The micro-CT scans were conducted and the total volume of silver nitrate and the total volume of restorations within the relevant region of interest were calculated in "mm3" with software. Two-way ANOVA and Tukey tests were performed at a significance level of p = 0.05 with Graphpad Prism v 8.2.1 software. Results: Both gravity effect and interaction showed no statistical differences (p > 0.05). Statistically significant differences were observed in the restorative materials (p < 0.05). Conclusions: Gravitational forces do not emerge as a major factor affecting the marginal integrity of flowable bulk-fill composites in class II restorations. The chemical composition of the composites plays a more crucial role, with the XTB composite showing higher microleakage ratios compared to the others.

Confront f(R,T)={mathcal {R}}+beta T modified gravity with the massive pulsar {textit{PSR J0740+6620}}

Many physically inspired general relativity (GR) modifications predict significant deviations in the properties of spacetime surrounding massive neutron stars. Among these modifications is f({mathcal {R}}, {mathbb {T}}), where {mathcal {R}} is the Ricci scalar, {mathbb {T}} is the trace of the energy–momentum tensor, the gravitational theory that is thought to be a neutral extension of GR. Neutron stars with masses above 1.8 M_{odot } expressed as radio pulsars are precious tests of fundamental physics in extreme conditions unique in the observable universe and unavailable to terrestrial experiments. We obtained an exact analytical solution for anisotropic perfect-fluid spheres in hydrostatic equilibrium using the frame of the linear form of f({mathcal {R}},{mathbb {T}})={mathcal {R}}+beta {mathbb {T}} where beta is a dimensional parameter. We show that the dimensional parameter beta and the compactness, C=frac{2GM}{Rc^2} can be used to express all physical quantities within the star. We fix the dimensional parameter beta to be at most beta _1=frac{beta }{kappa ^2}= 0.1 in positive values through the use of observational data from NICER and X-ray Multi-Mirror telescopes on the pulsar {textit{PSR J0740+6620}}, which provide information on its mass and radius. The mass and radius of the pulsar {textit{PSR J0740+6620}} were determined by analyzing data obtained from NICER and X-ray Multi-Mirror telescopes. It is important to mention that no assumptions about equations of state were made in this research. Nevertheless, the model demonstrates a good fit with linear patterns involving bag constants. Generally, when the dimensional parameter beta is positive, the theory predicts that a star of the same mass will have a slightly larger size than what is predicted by GR. It has been explained that the hydrodynamic equilibrium equation includes an additional force resulting from the coupling between matter and geometry. This force partially reduces the effect of gravitational force. As a result, we compute the maximum compactness allowed by the strong energy condition for f({mathcal {R}}, {mathbb {T}})={mathcal {R}}+beta {mathbb {T}} and for GR, which are C = 0.757 and 0.725, respectively. These values are approximately 3% higher than the prediction made by GR.. Furthermore, we estimate the maximum mass Mapprox 4.26 M_{odot } at a radius of Rapprox 15.9 km for the surface density at saturation nuclear density rho _{text {nuc}} = 2.7times 10^{14} g/cm^3.

A seesaw-inspired bistable energy harvester with adjustable potential wells for self-powered internet of train monitoring

Energy harvesting provides a potential solution to power distributed sensors for train condition monitoring in a self-sustained manner, but the broadband and random nature of the available vibration energy makes effective energy harvesting very challenging. In this paper, a novel seesaw-inspired bistable energy harvester is developed to facilitate self-powered monitoring of trains and the realization of the Internet of Trains. The seesaw-inspired nonlinear harvester is realized for the first time using the attractive magnetic forces between a moving magnet and two fixed magnets to implement the gravitational force effect in seesaws and the restoring spring forces from limit springs to realize the supporting effect of legs to prevent seesaws from being hitting on the floor. A theoretical model is established to describe the dynamics of the whole systems, and the dynamics of the bistable energy harvester are numerically studied for different structural parameters to explore is potential well adjustability and its impact on energy harvesting performance. Through the numerical analysis, it is identified that different fixed magnet positions and spring lengths correspond to different harvesters’ potential well distribution, operational frequency ranges, and changing the coil positions also affects the output power. The results of the theoretical model are validated by a developed prototype and experimental results. The bistable energy harvester performs well over a wide frequency range of 18–38 Hz. An output power of 7.4 mW was obtained at 38 Hz with a 600 Ω load resistor. Finally, this energy harvester is used to fully power a wireless sensor node with a micro-controller, a Bluetooth module and an accelerometer, showing its capability in realizing self-powered condition monitoring of trains.

Fundamentals of Force Balance in Liquid Films and Transition from Macro- to Microchannels in Flow Boiling

Microchannel heat exchangers play a critical role in development of more efficient and environmentally friendly energy systems. Thus, understanding the underlying physics that govern their heat transfer performance is of paramount importance. The most fundamental question is what is considered a microchannel, and what channel size, fluid properties, and flow conditions warrant use of a micro- versus macrochannel model. There have been extensive discussions in the literature regarding the appropriate definition of a microchannel; however, a clear, physics-based distinction of micro- from macrochannels has not emerged. This study analyzes this outstanding scientific question from the perspective of confinement effect on liquid films through investigating the effect of gravity on liquid films thickness. A set of experimental studies are conducted to determine the effect of gravitational force on liquid film asymmetry. The experimental findings are utilized to evaluate the existing criteria for transition from macro- to microchannels. Our analysis suggests that confinement numbers greater than 1.0 distinguish micro- from macrochannels in terms of liquid film symmetry. This analysis is supported by a force balance that shows gravitational force on liquid films exceeds the surface tension force in macrochannels.

Simplified model to consider influence of gravity on impacts on structures: Experimental and numerical validation

Traditionally, the effect of gravitational force has not been considered in the study of impacts on structures, partly due to lack of knowledge. In most cases, it may be reasonable to disregard this effect, but it is not clear where the limit is and, therefore, in which cases its effect should be considered. Is this limit the same regardless of the type of structure? What criterion should be adopted? This paper develops a simplified model that allows, through a simple formulation, the calculation of the displacement and contact force in an impact considering the effect of the force of gravity on the structural response. In this article, the formulation has been validated with experimental impact tests on beams and also with finite element models. In addition, a coefficient is proposed which enables the evaluation, prior to any analysis, of whether the impact will be significantly influenced by the force of gravity, whatever the structure under study.

Analysis of bubble dynamics and thermal destratification induced by gas bubbles in cylindrical liquid storage tanks

• OpenFOAM code is modified to incorporate temperature-dependent transport properties. • A new parameter to estimate the extent of the destratification is introduced. • The destratification index increased by 25.29% as the diameter ratio is increased. • Bubble in square pitch with p/d =4 gives higher effectiveness for thermal destratification. • The destratification index increased by 44.65% as the gravity ratio is increased. Thermal stratification is of great concern for liquid propellant storage tanks of space vehicles. The present study's primary objective is to better understand the bubble dynamics on thermal destratification, quantify the extent of destratification and propose a scheme for destratification. This study investigates the effect of different geometric parameters on the destratification of thermally stratified layers of liquid using the volume of fluid and interface compression method of OpenFOAM CFD code. The OpenFOAM code is modified to incorporate temperature-dependent fluid properties. Different values of bubble diameter, spacing between the bubbles, and arrangement of bubbles in triangular and square fashion with different pitches are considered. The effect of gravitational forces on thermal destratification is also reported. For all these cases, the effectiveness of thermal destratification is quantified in terms of the destratification index ( I d ). The average destratification index ( I davg ) value increased by 25.29% as the ratio of bubble diameter to tank diameter ( d/D ) increased from 0.10 to 0.16. When the pitch to bubble diameter ratio ( p/d ) of triangular and square arrangements is reduced from 8 to 4, the I davg increases by 14.59% and 22.97%, respectively. The average destratification index increased by 44.65% when the g/g e ratio changed from 0.3 to 3. These studies give an overall idea of the sparger design for getting the correct gas flow rate for thermal destratification within the liquid propellant storage tanks.

Impact of Rastall Gravity on Mass, Radius, and Sound Speed of the Pulsar PSR J0740+6620

Millisecond pulsars are perfect laboratories to test possible matter–geometry coupling and its physical implications in light of recent Neutron Star Interior Composition Explorer (NICER) observations. We apply Rastall field equations of gravity, where matter and geometry are nonminimally coupled, to Krori–Barua interior spacetime whereas the matter source is assumed to be anisotropic fluid. We show that all physical quantities inside the star can be expressed in terms of Rastall, ϵ, and compactness, C = 2GM/Rc 2, parameters. Using NICER and X-ray Multi-Mirror Newton X-ray-observational constraints on the mass and radius of the pulsar PSR J0740+6620, we determine the Rastall parameter to be at most ϵ = 0.041 in the positive range. The obtained solution provides a stable compact object; in addition the squared sound speed does not violate the conjectured sound speed unlike the general relativistic treatment. We note that no equations of state are assumed; the model however fits well with linear patterns with bag constants. In general, for ϵ > 0, the theory predicts a slightly larger-size star in comparison to general relativity for the same mass. This has been explained as an additional force, due to matter–geometry coupling, in the hydrodynamic equilibrium equation, which contributes to partially diminishing the gravitational force effect. Consequently, we calculate the maximal compactness as allowed by the strong energy condition to be C = 0.735, which is ∼2% higher than general relativity prediction. Moreover, for the surface density at saturation nuclear density ρ nuc = 2.7 × 1014 g cm−3, we estimate the maximum mass M = 4M ⊙ at radius R = 16 km.

Buoyancy-modulated Lagrangian drift in wavy-walled vertical channels as a model problem to understand drug dispersion in the spinal canal.

This paper investigates flow and transport in a slender wavy-walled vertical channel subject to a prescribed oscillatory pressure difference between its ends. When the ratio of the stroke length of the pulsatile flow to the channel wavelength is small, the resulting flow velocity is known to include a slow steady-streaming component resulting from the effect of the convective acceleration. Our study considers the additional effect of gravitational forces in configurations with a non-uniform density distribution. Specific attention is given to the slowly evolving buoyancy-modulated flow emerging after the deposition of a finite amount of solute whose density is different from that of the fluid contained in the channel, a relevant problem in connection with drug dispersion in intrathecal drug delivery (ITDD) processes, involving the injection of the drug into the cerebrospinal fluid that fills the spinal canal. It is shown that when the Richardson number is of order unity, the relevant limit in ITDD applications, the resulting buoyancy-induced velocities are comparable to those of steady streaming. As a consequence, the slow time-averaged Lagrangian motion of the fluid, involving the sum of the Stokes drift and the time-averaged Eulerian velocity, is intimately coupled with the transport of the solute, resulting in a slowly evolving problem that can be treated with two-time-scale methods. The asymptotic development leads to a time-averaged, nonlinear integro-differential transport equation that describes the slow dispersion of the solute, thereby circumventing the need to describe the small concentration fluctuations associated with the fast oscillatory motion. The ideas presented here can find application in developing reduced models for future quantitative analyses of drug dispersion in the spinal canal.

Thermal destratification of cryogenic liquid storage tanks by continuous bubbling of gases

This paper focuses on thermal destratification and pressurisation inside thermally stratified storage tanks by continuous gas bubbling. The primary purpose of doing these studies is to better understand the effect of bubble dynamics on thermal destratification and quantify the extent of destratification. The volume of fluid and interface compression method of OpenFOAM CFD code is utilised for the present analysis. Different values of inlet gas velocities (Vg), orifice diameters (do), and arrangement of the orifices in triangular and square fashion with different pitches (p/do) are considered. In addition, the effect of gravitational forces (g/ge) on thermal destratification is also reported. For all these cases, the effectiveness of thermal destratification is quantified in terms of a newly defined parameter, the destratification index (Id). For Vg = 1 m/s, the Id value is maximum compared to lower Vg values. It is seen that when the gas velocity increased from 0.3 m/s to 1.0 m/s, the average effectiveness in thermal destratification (Idavg) and pressure at the ullage increased by 44.38% and by 64.81%, respectively. The Idavg and pressure at ullage increased by 96.29% and 14.91%, respectively, when the g/ge ratio changed from 0.3 to 3. Compared to the triangular arrangement with p/do = 10, the calculated Idavg increased by 30.67% when gas inlets were arranged with a square pitch of 10. For p/do = 4, 6 and 8, the increments in Idavg are of the order of 12.86%, 19.43% and 21.92%, respectively, for gas inlets arranged in a square fashion as compared to the triangular arrangement. It is found that continuous bubbling with gas inlets arranged in square pitch p/do = 10 gives higher effectiveness in thermal destratification. Thus, by these studies, one can develop a thermal destratification mechanism with continuous bubbling for optimum performance. Also, these studies give an overall idea of sparger design for getting the correct gas flow rate for thermal destratification within the cryogenic liquid storage tanks.

Biomechanics Specialization in Aging Science and Research: Biomechanical Gerontology or Geronto-Biomechanics?

Aging process becomes a miserable phase of lifespan of various individuals. Gerontology and Geriatrics exclusively deal with researching complex human ailments pertinent to old age in order to overcome the challenges posed by several irreversible physiological changes occurring with aging. Inevitably, homeostasis declines and massive allostasis gets organized during aging to destroy the functional independence and survival potential. Controlling the rate of aging process is the only possible self-regulating strategy available to each individual to enjoy Morbidity-Attenuated Life Years (MALYs) but maintaining an optimal fitness competence to travel along the healthy aging trajectory is not effortlessly feasible regardless of the socioeconomic conditions. Fitness evaluations on different age groups enhances the understanding that the aging process might be a premature event among several individuals at an early age itself due to multifactorial reasons, and the biomechanical constraints displayed by such individuals expose the probable wide spectrum of postural and movement dysfunctions or disabilities of unhealthy older adults. Many such health-ruining erroneous postures and movements remain asymptomatic perilously, which when addressed during appropriate stage in life, could repair the impaired physical efficiency to sustain the abilities to counteract the effects of gravitational force on the body. The importance of early detection and rectification of such peculiar biomechanical dysfunctions should become an integral part of public health prophylaxis. The repertoire of biomechanical dysfunctions of premature unhealthy aging needs to be strongly merged with gerontology to strengthen the pursuits to retard unsuccessful aging and accomplish successful aging. Keywords: Biogerontology, Biomechanics, Ageing Trajectory, Compression of Morbidity, Polypharmacy, Comorbidities, Successful Aging, Unsuccessful Aging.

Study of Gravitational Force Effects, Magnetic Restoring Forces, and Coefficients of the Magnetic Spring-Based Nonlinear Oscillator System

The aim of this article is to analyze the design of a magnetic spring-based nonlinear oscillator system and investigate its magnetic properties, the effect of gravitational force, the accuracy of the modeled magnetic restoring force, the coefficient of the magnetic restoring force, and the nonlinear response of the proposed system. The proposed magnetic spring-based nonlinear oscillator system consists of a nonmagnetic shaft, floating magnet, and two fixed magnets where all magnets are placed in such a way that each magnet can repel the other. The magnetic properties of the proposed system are studied numerically and analytically to provide insight into its role in the nonlinear oscillatory behavior of the system. The effect of the gravitational force, which changes the equilibrium position and the nonlinear behavior of the magnetic spring, is studied. The numerical analysis of the magnetic flux density and magnetic restoring force is validated using an analytical and experimental analysis. Different orders of polynomial curve fittings, such as cubic and quintic, are used to model the magnetic restoring force between the moving magnet and the two fixed end magnets. Finally, the linear and nonlinear coefficients of the magnetic spring-based system for different positions of the floating magnet are investigated.

Mathematical modeling of nano-particle transport in oil well cement cracks

Transport of nanoparticles (NPs) in fluids was analyzed in this study for sealing cement and micro-annuli fractures with nano-silica gels. Analytical models were developed to analyze NPs transport in cracks. The effects of gravitational, capillary, and viscous forces on NPs transport in oil well cement sheath cracks were investigated. It was found that the effect of gravitational force on the NPs transport in cracks is negligible owing to the small particle size. Gravity should not cause segregation of solid and liquid phases. Capillary force can induce spontaneous imbibition of nano-fluids that carries NPs into cement cracks. The imbibition rate is crack size-, fluid viscosity- and time-dependent. NPs can be effectively carried into cracks by viscous force. The viscous pressure gradients required for transporting NPs into the cement cracks are in the range between 0.04 psi/ft and 0.1 psi/ft at a convection flow rate of 1 gpm, depending on crack width and fluid viscosity. For a 500-ft long crack, the viscous pressure drop should be in a range from 20 psi to 50 psi, which is manageable in field operations.

Role of gravitational force on mechanical entrainment of nonmagnetic particles in high gradient magnetic separation

Mechanical entrainment is an important mechanism responsible for the low selectivity in high gradient magnetic separation (HGMS). Previous studies on mechanical entrainment mainly focused on particle motion behaviors or interparticle forces, a very important factor attributing entrainment was neglected, namely the effect of gravitational force. In this paper, the role of gravitational force on mechanical entrainment was systematically investigated with varying feeding direction, fluid velocity, size and density of nonmagnetic particles. Results indicated that gravity played a vital role in mechanical entrainment. Nonmagnetic particles were preferentially entrained in deposits of upper surface (relative to gravity direction) rather than upstream surface (relative to flow direction) due to gravity. Mechanical entrainment became more serious with increasing gangue mineral density. Mechanical entrainment of low-density gangue could easily be eliminated with moderate fluid velocity or pulsating frequency, but that caused by large density gangue in upper deposit could hardly be eliminated, even with high fluid velocity or high strength pulsating. Weakening the effect of gravity with nonmagnetic heavy medium (or heavy suspension) should be promising method to enhance selectivity in HGMS, which will be conducted theoretically and experimentally in near future.

Photon Characteristics and Behavior under Refractive Index

The effective mass, energy and momentum of photon in medium is described. The photon has both kinetic and potential energy and displays an effective mass when travelling through a medium. The photon is a type of elementary particle that serves as the quantum of the electromagnetic field and is explained through equations to have an elastic constant, volume, momentum, force, power and zero rest mass. The theory that photons a massless only applies to rest mass. A photon undergoes different dynamics such as strain and changes in effective mass under the influence of the refractive index that gives rise to a refractive force. This study synthesizes some properties of energy such as elastic constant, weight, and volume in order to explain the nature of photons and photon dynamics under refractive index. In this study, a helical spring model has been used to describe the behavior of a photon in the medium. The model connects together the exhibited properties such as energy, effective mass, spin, elastic constant and volume. Further explanation is given to the effect of gravitational force on wavelength and refractive index of air, and how gravitational force causes red and blue shifts in photon propagation. The quantization of energy has been extended to the quantization of space, time and matter. This study is consistent and consolidates the existing classical and quantum theories. There are further potential applications in optical communication, quantum cryptography, quantum optics, and medicine, especially in the use of two-photon excitation microscopy and photodynamic therapy.

Insights into the flow behaviour of the pre-generated polymer enhanced foam in heterogeneous porous media during tertiary oil recovery: Effect of gravitational forces

Over the past few decades, foam flooding has emerged as a decent option for diverting flow from high permeable layers toward dense layers. Here, a visualization study of the conventional foam and polymer enhanced foam (PEF) behavior in the heterogeneous porous media is presented and the PEF performance in horizontal and vertical injection modes is evaluated. A heterogeneous porous medium made of transparent plexiglass packed with two different layers of glass beads to attain a heterogeneity ratio of 4:1 was used in various flooding experiments. The results of dynamic tests in the absence of oil showed that the presence of polymer in the foaming solution increases the flow resistance of foam in the porous medium and prevents foam fingering in the low-permeable layers. Horizontal oil displacement experiments showed that PEF flooding has an excellent plugging capacity and oil recovery increased by 72.5% of water flooded residual oil (S*or), which was 19.1% more than that of conventional foam injection. Comparison between vertical and horizontal PEF flooding proved that due to the positive gravity effect, the performance of PEF in vertical mode was better than that in horizontal mode, and the recovery factor increased to 78.3% water-flooded residual oil.

Investigation of liquid marble shell using X‐ray: shell thickness and effective surface tension

AbstractLiquid marble is a non‐wetting droplet encapsulated by micro‐ or nano‐sized hydrophobic particles. Recently, liquid marble has been emerging as a tool for digital microfluidics. Thus, a detailed understanding of the fundamentals of liquid marble is essential. The shell of a liquid marble has an opaque and fuzzy appearance which hinders in‐depth investigation using conventional optical microscopy. We used X‐ray computerized microtomography (CMT) to generate an image with a visible interface between the core liquid and the shell to overcome this problem. The interface facilitates accurate measurement of the shell thickness and the effective surface tension. This work investigates the effect of liquid marble preparation methods and liquid marble volumes on shell thickness and effective surface tension. We found that increasing the revolution speed during liquid marble preparation increases shell thickness. A liquid marble shell has a uniform packing when the revolution speed is 200–300 rpm. We also found that the effective surface tension of liquid marbles decreases with increasing volume. This could be due to a stronger effect of gravitational force for a large liquid marble. The findings from this work could provide a new insight into the characterization of liquid marble and open up a new direction of fundamental research of liquid marble shell.

Shape estimation of a large workspace continuum manipulator with fusion of inertial sensors

This paper focuses on shape estimation of a novel multi-section continuum and compliant robotic manipulator with large workspace. Real-time shape estimation is important for closed-loop control of continuum robots. However, due to the continuum deformation of such manipulators, it is not feasible to use conventional angular sensors. On the other hand, in order to increase the motion range in the proposed manipulator structure, each flexible link includes several serially connected sections. Because of the effect of gravitational forces, each section in these long size links could have different curvatures which makes the shape estimation more challenging. In this study, inertial sensors are utilized to estimate the overall shape of the large scale continuum manipulator. MEMS based inertial measurement units (IMUs) including gyroscopes, accelerometers, and magnetometers are installed on each section and the shapes of the sections are determined with Extended Kalman Filter (EKF) fusion algorithm. But the effect of unwanted external disturbances including translational accelerations and magnetic interferences on the observation model of the EKF, severely affects the estimation performance. So, a disturbance rejection algorithm (DRA) is proposed which can detect the presence of disturbances in each measurement axis and excludes that sensor axis from estimation procedure. Performance of the proposed shape estimation method is validated experimentally on the implemented manipulator.

An investigation of horizontal and vertical flow boiling in a single channel with a confinement number beyond the threshold of micro-scale flow

The gravitational force effect is of concern when designing flow boiling systems deployed on Earth and in space. A study of the R-134a flow boiling inside the horizontal and vertical channels was experimentally performed to explore the flow orientations' effect on flow pattern and heat transfer characteristics. The test section was a 0.5 mm diameter tube from which the corner effect was excluded. The single channel was used to avoid disturbances that flow maldistribution could possibly cause in the multiple channels. The experimental two-phase flow corresponded to a 1.75 confinement number, which was above the threshold for micro-scale flow. The results indicated the flow regime map, which was less affected by the channel orientation except for that slug flow pattern that was unable to survive during the vertical downflow and vertical upflow. Also, based on the present micro-scale flow, the heat transfer results were mostly independent of the gravitational force effect, and the nucleate boiling and convective mechanisms tended to govern them.

Impact of Wettability and Gravity on Fluid Displacement and Trapping in Representative 2D Micromodels of Porous Media (2D Sand Analogs)

AbstractThe combined effects of gravitational forces and wettability on displacement and trapping have not previously been investigated experimentally in realistic 2D porous media. Here we report the first use of representative 2D micromodels that accurately reproduce characteristic geometric, morphological, and topological properties of 3D sand packs. We use these representative micromodels to compare the wettability dependence of displacement front morphology and trapping processes using selected fluid pairs at capillary numbers between 10−6 and 10−5. The contact angles studied ranged from 30° (normal imbibition) to 150° (strong drainage). The impact of gravity was dramatic: In the horizontal flow case, only one finger developed, that is longitudinal displacement was always favored, whereas gravity created a more compact displacement front with broad lateral extension, and this lateral movement created loops, leading to by‐pass trapping. As a result, the trapping efficiency rose from 7% to 29%. We observed universal scaling of the cluster size distribution demonstrating that our micromodels are statistically representative. The universal 2D‐scaling exponent of 2.05 was obtained with an acceptable error smaller than 5%. Our experimental results obtained by fluorescence microscopy showed (a) precursor corner flow for weak imbibition at θ = 51°, that is above the critical contact angle of αc = 45° (Zhao et al., 2016, https://doi.org/10.1073/pnas.1603387113), and (b) a new wetting transition from corner flow to full duct flow under neutral wettability conditions, that is at θc ≈ 90°; and (c) above this second critical contact angle, that is under strong drainage conditions, we again observed corner flow (specifically, core‐annular flow).