Effect Of Surface Motion Research Articles

Effect of Surface Motion on Heat Transfer and Pressure Force from Multiple Impinging Jets– A Numerical Study

The effect of jet arrangement, jet Re number, jet exit angle (θ), the nozzle-to-surface distance (H/d), jet-to-jet spacing (S/d) on the heat transfer, and pressure force performance from multiple impinging round jets on a moving flat surface have been numerically evaluated. There is a minor difference between in-line and staggered arrangements on a moving flat surface. The averaged Nusselt number on a moving flat surface reduces with an increase in the relative velocity (VR). The surface motion effects become more pronounced on the local Nu distribution at low Re, small S/d, large H/d, and angled jets for a moving flat surface. The pressure force coefficient on a moving flat surface is highly dependent on the H/d and θ but relatively insensitive to the VR, Re, and S/d within the range examined. Two correlations are developed and validated for the average Nu and force coefficient and the agreement between the CFD and correlation is found to be reasonable.

A Numerical Study of Heat Transfer From an Array of Jets Impinging on a Flat Moving Surface

Abstract A numerical study of heat transfer between circular jet arrays and the flat moving surface is carried out. Two jet patterns, inline and staggered, are chosen. A total of nine circular jets are used in both jet patterns. The analysis is carried out for steady and transient conditions with the turbulent flow of jet fluid. The steady-state analysis analyzes the effect of surface motion on the flow field and heat transfer through the jet arrays. The surface-to-jet velocity ratio (r) varies from 0 to 2. In transient analysis, the effect of jet pattern on the cooling of hot moving plate is analyzed. The two-equation shear stress transport (SST) k–ω turbulence model is used to solve Reynolds-averaged Navier–Stokes (RANS) equations of conservation of mass, momentum, and energy for incompressible turbulent flow. The steady-state analysis shows that surface motion has a significant effect on the flow field and heat transfer. The results of the transient analysis show that a staggering jet pattern cools the plate more uniformly than an inline jet pattern.

Stormtime Energetics: Energy Transport Across the Magnetopause in a Global MHD Simulation

Coupling between the solar wind and magnetosphere can be expressed in terms of energy transfer through the separating boundary known as the magnetopause. Geospace simulation is performed using the Space Weather Modeling Framework (SWMF) of a multi-ICME impact event on February 18–20, 2014 in order to study the energy transfer through the magnetopause during storm conditions. The magnetopause boundary is identified using a modified plasma β and fully closed field line criteria to a downstream distance of −20Re. Observations from Geotail, Themis, and Cluster are used as well as the Shue 1998 model to verify the simulation field data results and magnetopause boundary location. Once the boundary is identified, energy transfer is calculated in terms of total energy flux K, Poynting flux S, and hydrodynamic flux H. Surface motion effects are considered and the regional distribution of energy transfer on the magnetopause surface is explored in terms of dayside X>0, flank X<0, and tail cross section X=Xmin regions. It is found that total integrated energy flux over the boundary is nearly balanced between injection and escape, and flank contributions dominate the Poynting flux injection. Poynting flux dominates net energy input, while hydrodynamic flux dominates energy output. Surface fluctuations contribute significantly to net energy transfer and comparison with the Shue model reveals varying levels of cylindrical asymmetry in the magnetopause flank throughout the event. Finally existing energy coupling proxies such as the Akasofu ϵ parameter and Newell coupling function are compared with the energy transfer results.

Quench cooling of fast moving steel plates by water jet impingement

Quench cooling of steel on the Run Out Table presents great complexity arising from the high speed of the steel slabs and the violent nature and short time scale that characterize the involved boiling regimes. Until now experimental studies on quenching of moving surfaces have reported surface speeds up to 1.6 m/s. This is far from the real Run Out Table operation conditions, where the steel slabs move between 2 and 22 m/s. In this study, a new experimental setup is presented that allows quenching of steel surfaces at speeds between 0 and 8 m/s. For the first time direct visualization of the boiling activity in the stagnation zone during quenching of a moving surface is presented and the effects of surface speed and water jet temperature are analyzed. The results show a change in the trend of the cooling history and boiling curves that depends on plate speed. This change is a consequence of the effect of surface motion on the viscous and thermal boundary layers. The direct visualization of the stagnation zone confirms that this change in trend corresponds to progressive suppression of boiling activity and enhancement of explosive boiling and film boiling with increasing surface speed.

Single- and two-phase water jet impingement heat transfer on a hot moving surface

In this study, the laminar flow and heat transfer of water jet impingement on a hot moving plate is investigated. A similarity solution is applied to momentum and energy equations formulating the single-phase forced convection in order to determine the flow velocity and heat transfer. The heat flux in flow boiling regime is predicted by a superposition approach which is based on the combination of the single-phase and nucleate pool boiling components. The effects of surface motion and arbitrary surface temperature distribution on important forced convection and nucleate boiling heat transfer parameters for both stationary and moving plates are examined in the stagnation line and its nearby region. The results show that surface motion does not affect the rate of heat transfer in stagnation region when surface temperature is constant, while this motion is found to decrease heat transfer for a non-uniform surface temperature distribution state. However, it is observed that in fully developed nucleate boiling regime, the parameters including the surface velocity, the surface temperature gradient and the local distance from the stagnation line have negligible effect on the rate of heat transfer from the surface.

Effects of surface motion and electron-hole pair excitations in CO2 dissociation and scattering on Ni(100).

The energy transfer between different channels is an important aspect in chemical reactions at surfaces. We investigate here in detail the energy transfer dynamics in a prototypical system, i.e., reactive and nonreactive scattering of CO2 on Ni(100), which is related to heterogeneous catalytic processes with Ni-based catalysts for CO2 reduction. On the basis of our earlier nine-dimensional potential energy surface for CO2/Ni(100), dynamical calculations have been done using the generalized Langevin oscillator (GLO) model combined with local density friction approximation (LDFA), in which the former accounts for the surface motion and the latter accounts for the low-energy electron-hole pair (EHP) excitation. In spite of its simplicity, it is found that the GLO model yields quite satisfactory results, including the significant energy loss and product energy disposal, trapping, and steering dynamics, all of which agree well with the ab initio molecular dynamics ones where many surface atoms are explicitly involved with high computational cost. However, the GLO model fails to describe the reactivity enhancement due to the lattice motion because it intrinsically does not incorporate the variance of barrier height on the surface atom displacement. On the other hand, in LDFA, the energy transferred to EHPs is found to play a minor role and barely alter the dynamics, except for slightly reducing the dissociation probabilities. In addition, vibrational state-selected dissociative sticking probabilities are calculated and previously observed strong mode specificity is confirmed. Our work suggests that further improvement of the GLO model is needed to consider the lattice-induced barrier lowering.

RADARSAT-2-based digital elevation models derived from InSAR for high latitudes of northern Canada

The accuracy of digital elevation models (DEMs) plays an important role in many terrain-related applications, particular in high northern latitudes where there is uncertainty in DEMs. Using the interferometric synthetic aperture radar techniques, this study examined how different RADARSAT-2 beam modes can be used to generate DEMs with high accuracy. Using a conventional interferometry method, the Spotlight DEM shows the highest accuracy among all studied DEM products, with the root-mean-square error (RMSE) ranging from 13.9 to 17.4 m, followed by the F0W3 DEM and U26W2 DEM. The error sources in DEM generation due to uncertainty in perpendicular baseline and atmospheric delay are likely more important than the random phase noise caused by volume scattering and environmental changes during synthetic aperture radar (SAR) acquisitions. The small baselines subset (SBAS) method did not significantly improve DEM quality due to the limitation of the number of SAR images in this study. The integration of both Spotlight conventional DEMs and SBAS DEM considerably improved results yielding high-quality DEMs for the study area, with an RMSE of 9.7 m. Further studies are necessary to quantitatively evaluate the effects of surface motion as well as the orbital and atmospheric errors on the DEM accuracy. The Slave River Delta in the Northwest Territories of Canada was used as a test case.

Modeling surface motion effects in N2 dissociation on W(110): Ab initio molecular dynamics calculations and generalized Langevin oscillator model.

Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics.

N2 dissociation on W(110): An ab initio molecular dynamics study on the effect of phonons.

Accurately modeling the chemisorption dynamics of N2 on metal surfaces is of both practical and fundamental interest. The factors that may have hampered this achievement so far are the lack of an accurate density functional and the use of approximate methods to deal with surface phonons and non-adiabatic effects. In the current work, the dissociation of molecular nitrogen on W(110) has been studied using ab initio molecular dynamics (AIMD) calculations, simulating both surface temperature effects, such as lattice distortion, and surface motion effects, like recoil. The forces were calculated using density functional theory, and two density functionals were tested, namely, the Perdew-Burke-Ernzerhof (PBE) and the revised PBE (RPBE) functionals. The computed dissociation probability considerably differs from earlier static surface results, with AIMD predicting a much larger contribution of the indirect reaction channel, in which molecules dissociate after being temporally trapped in the proximity of the surface. Calculations suggest that the surface motion effects play a role here, since the energy transfer to the lattice does not allow molecules that have been trapped into potential wells close to the surface to find their way back to the gas phase. In comparison to experimental data, AIMD results overestimate the dissociation probability at the lowest energies investigated, where trapping dominates, suggesting a failure of both tested exchange-correlation functionals in describing the potential energy surface in the area sampled by trapped molecules.

Different response of articular chondrocyte subpopulations to surface motion

To investigate the effect of surface motion on the gene expression of proteoglycan 4 (PRG4), hyaluronan synthases (HAS1, HAS2) and on the hyaluronan (HA) and proteoglycan 4 (PRG4) release of chondrocytes from different zones of bovine articular cartilage. Superficial zone, deep zone, full thickness, and superficial/deep 1:1 mixed chondrocytes were seeded into 3D polyurethane scaffolds and stimulated using our bioreactor that approximates kinematics and surface motion characteristics of natural joints. One hour of surface motion superimposed on cyclic compression was applied twice a day over 3 consecutive days. Scaffolds were cut into top and bottom sections and analyzed for gene expression of PRG4, HAS1, and HAS2. Depending on the cell population, the gene expression levels increased within 8 days of culture in unloaded scaffolds, with a stronger increase in the top compared to the bottom sections. Mechanical loading further enhanced the messenger RNA (mRNA) levels in all cell types, with most pronounced up-regulations observed for the PRG4 expression in deep zone and the HAS2 expression in superficial zone cells. The effect of the biochemical and biomechanical environment appeared to be additive, resulting in highest mRNA levels in the top sections of loaded constructs. Bioreactor stimulation also enhanced the HA release in all cell populations. Full thickness chondrocytes experienced the greatest effect on HAS1 mRNA expression and HA release, indicating that the interaction between cell populations may promote HA synthesis compared to subpopulations alone. Reciprocating sliding can be an efficient tool for generating tissue-engineered constructs from various chondrocyte populations by providing a functional cartilage-synovial interface.

Effect of Surface Motion on Transport Processes Due to Circular Impinging Jets—A Numerical Study

This article presents a numerical study of transport phenomena under impinging circular jet banks over a moving surface by solving three-dimensional Navier-Stokes equation in both the laminar and the turbulent regime. A periodic element of the jet bank was used with jet pitch of 10d, span of target surface as 10d, and jet height of 2d, where d is the jet diameter. For the turbulent closure, a realizable k-ε model was used. The distributions of the Nusselt number and the skin friction coefficients were computed from the analyzed data. The surface velocity was found to influence strongly the flow structure over the impinging surface, leading to reduction in heat transfer.

Interactions between spatial and spatiotemporal information in spatiotemporal boundary formation.

The surface and boundaries of an object generally move in unison, so the motion of a surface could provide information about the motion of its boundaries. Here we report the results of three experiments on spatiotemporal boundary formation that indicate that information about the motion of a surface does influence the formation of its boundaries. In Experiment 1, shape identification at low texture densities was poorer for moving forms in which stationary texture was visible inside than for forms in which the stationary texture was visible only outside. In Experiment 2, the disruption found in Experiment 1 was removed by adding a second external boundary. We hypothesized that the disruption was caused by boundary assignment that perceptually grouped the moving boundary with the static texture. Experiment 3 revealed that accurate information about the motion of the surface facilitated boundary formation only when the motion was seen as coming from the surface of the moving form. Potential mechanisms for surface motion effects in dynamic boundary formation are discussed.

Dynamics of oxygen adsorption on Ag(110): surface motion effects

The study of the adsorption of oxygen on silver surfaces is particularly important because it is a fundamental step in the catalytic partial oxidation of ethene. This gas-surface system is characterized by physisorption at low temperatures, molecular and dissociative chemisorption at higher temperatures, and by the presence of a subsurface state. Starting from the results of recent molecular beam experiments, a theoretical study of the dynamical aspects of the process was initiated within the framework of a quasi classical trajectory approach. The reactive scattering of an O 2 beam on the Ag(110) surface was simulated by using a model potential which accounts for the electronic charge transfer from the metal surface to the incoming O 2 molecule and for the vibrational motion of the Ag atoms. The dependence of the initial sticking coefficient on the O 2 translational and rovibrational energies, on the incidence angles of the beam, and on the surface temperature was investigated.

NUMERICAL ANALYSIS OF CONVECTIVE HEAT TRANSFER FROM A MOVING PLATE COOLED BY AN ARRAY OF SUBMERGED PLANAR JETS

Abstract A numerical model is developed to determine convective heat transfer distributions for an array of submerged planar jets impinging on a uniform heat flux or constant temperature moving surface where the surface motion is directed perpendicular to the jet planes. Unlike prior related work, the model accounts for the interaction between neighboring jets in the array without imposition of an imposed cross flow. The effects of surface speed, nozzle separation distance within an array, nozzle height, and Reynolds number on the flow field, coefficient of friction, and Nusselt number are investigated. Results suggest that neglecting surface motion effects can lead to overestimates of heat transfer.

Nonuniqueness of solutions to extended Kirchhoff integral formulations

This paper examines the nonuniqueness of solutions to an extended Kirchhoff integral formulation at certain discrete frequencies corresponding to the eigenfrequencies of the related interior boundary value problem. In particular, effects of surface motion and interaction between turbulence and vibrating surface in motion on nonuniqueness difficulties are investigated. It is shown that surface motion affects nonuniqueness difficulties in two ways: (1) it shifts the eigenfrequencies of the related interior boundary value problem and (2) it excites more eigenfrequencies at which nonuniqueness difficulties occur than the corresponding stationary case. The interaction between turbulence and vibrating surface in motion further shifts the eigenfrequencies. Although changes in these eigenfrequencies are small at low Mach numbers, they increase with the Mach number. It is also demonstrated that although an extended Kirchhoff integral equation fails to yield a unique solution at certain discrete frequencies, a combined extended surface Kirchhoff integral equation and an extended interior Kirchhoff integral equation always yield a unique solution for all frequencies. This is because there is only one set of solutions that satisfy both an extended surface Kirchhoff integral equation and an extended interior Kirchhoff integral equation.

Spray and jet cooling in steel rolling

Prediction and control of roll and strip cooling are necessary in modern steel mills because they not only affect the process efficiency but also strongly influence the quality of rolled products. In this article, relationships among metallurgy, heat transfer, and control of the cooling system in steel rolling are first discussed. Heat transfer characteristics associated with the water spray and jet cooling used in rolling processes are then studied. The effects of important convective heat transfer parameters on cooling perormance for both stationary and moving surfaces are examined. Results indicate that local heat fluxes up to 20 × 10 6 W/m 2 are observed in the nucleate boiling regime. The present results are compared with typical boiling heat transfer studies in terms of heat fluxes, heat transfer coefficients, spray rate, and cooling efficiency. The effect of surface motion is found to increase the cooling efficiency of roll and strip cooling. Finally, implementation of the present finding in roll and strip cooling to thermomechanical processing in steel rolling is proposed.

A laminar boundary layer model of heat transfer due to a nonuniform planar jet impinging on a moving plate

A theoretical model is developed of planar jet impingement heat transfer on a moving plate. Boundary layer equations in their integral forms are used in order to include, both near and away from the stagnation line, the effects of surface motion directed perpendicular to the jet plane, an arbitrary surface temperature variation, and nonuniform jet discharge velocity profiles. The validity and accuracy of the approximate solution is assessed by comparison to an exact solution restricted to regions near the stagnation line. Results indicate that the influence of a nonuniform jet discharge velocity decreases with distance from the stagnation line. Surface motion affects heat transfer at regions away from the stagnation line, but has little influence near the stagnation line when the surface temperature is constant.

Impingement heat transfer under a confined slot jet. Part II: Effects of surface motion and throughflow

AbstractLocal and average heat transfer coefficients were measured for a confined turbulent slot jet impinging on a moving surface at which there may be throughflow. Profiles of the local convective coefficient at the impingement surface were obtained using a fast responding, highly sensitive porous heat flux sensor. The decrease in average heat transfer with surface motion is not negligible, ∼20%, at values of the surface motion parameter, Mvs, comparable to those used in industry. The enhancement of heat transfer by throughflow at a moving impingement surface is linearly additive and, when expressed as δSt, is proportional to only the throughflow parameter, Mus, with a proportionality constant of 0.17 which is independent of Re, Mvs or extent of the heat transfer surface.

Method and apparatus for measuring heat transfer distributions on moving and stationary plates cooled by a planar liquid jet

An experimental method and apparatus were developed to measure local heat transfer distributions on moving and stationary plates. The apparatus can be used to study the effect of surface motion where a flat plate geometry is important. Such cases arise when different heat transfer regimes, such as single-phase forced convection, nucleate boiling, and film boiling, occur in close proximity on moving strips and plates cooled by planar liquid jets. In these cases, surface motion is either in or opposite to the flow direction. Versatility is an important feature of the apparatus because both moving and stationary plates can be considered. Surface temperatures of a test specimen were measured and used with a numerical solution of the energy equation for the specimen to determine local heat transfer coefficients in the vicinity of a planar jet. Experimentes were performed for plate speeds less than one-half of the impingement velocity. For single phase forced convection, heat transfer coefficients near the stagnation point were not appreciably affected by surface motion. In addition, transition to a turbulent boundary layer was delayed when the surface motion was in the flow direction. In nucleate boiling, the peak heat transfer coefficient was shifted in the direction opposite to the plate motion where surface temperatures were higher.

The Effect of Surface Motion on Forced Convection Film Boiling Heat Transfer

The growth in demand for high-quality metallic alloys has placed greater emphasis on the predictability of cooling methods used in manufacturing processes. Several methods involve forced convection film boiling, which can occur on metallic strips or plates cooled by water jet impingement or on strips inside cooling jackets of continuous annealing processes. Since surface temperatures are typically well above the boiling point of water, a substantial portion of the surface area can involve film boiling. The strip or plate speed often exceeds the water velocities and strongly influences boundary layer development in the vapor and liquid. The purpose of this paper is to estimate the effect of plate motion on heat transfer in the film boiling regime. Conservation equations for mass, momentum, and energy have been solved by the integral method for film boiling in forced convection boundary layer flow on a flat isothermal plate in motion parallel to the flow direction. Unlike previous studies, which have shown that heat transfer is chiefly governed by the plate and subcooled liquid temperatures, heat transfer is shown to also depend on the plate velocity. For large velocities, the importance of radiation heat transfer across the vapor layer is reduced. However, when the velocities of the plate and liquid are oppositely directed and of nearly equal magnitude, radiation across the vapor layer can become significant, even at low plate temperatures.