Conductive Boundary Layer Research Articles

Observations of Multiphase, High-velocity, Shocked Gas in the Vela Supernova Remnant* *Based on observations made with the NASA/ESA Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on

We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O i, Si ii, Si ii*, C ii, C ii*, and Si iii. We also detect high-velocity components in the N v doublet and compare these features to observations of high-velocity O vi absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C ii and Si ii. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N v and O vi absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca ii absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR.

Unsteady Magnetohydrodynamic Radiative Casson Nanofluid within Chemically Reactive Flow over a Stretchable Surface with Variable Thickness through a Porous Medium

This study presents a mathematical investigation into the phenomena of radiative heat with an unsteady MHD electrically conducting boundary layer of chemically reactive Casson nanofluid flow due to a pored stretchable sheet immersed in a porous medium in the presence of heat generation, thermophoretic force, and Brownian motion. The surface is assumed to be not flat, and has variable thickness. The magnetic field is time-dependent, and the chemical reaction coefficient is inversely varied with the distance. The nanofluid’s velocity, heat, and concentration at the surface are nonlinearly varied. A similarity transformation is introduced, and the controlling equations are converted into nondimensional forms involving many significant physical factors. The transformed forms are analyzed numerically using a computational method based on the finite difference scheme and Newton’s linearization procedure. The impact of the involved physical parameters is performed in graphical and tabular forms. Some special cases of the current work are compared with published studies, and an excellent agreement is obtained. The main results of the present work indicate that the higher values of the Casson parameter cause an increase in both the shear stress and heat flux, but a decrease in the mass flux. Also, it is noted that the chemical reaction, the nanoparticles’ volume, and the permeability factor enhance the effect the of Casson parameter on both the shear stress and heat flux, while the variable thickness and thermal radiation field reduce it; on the other hand, the variable thickness and nanoparticles’ volume enforce the influence of the Casson parameter on mass flux, but thermal radiation, the permeability factor, and chemical reaction decrease it. The present study has important applications in mechanical engineering and natural sciences. In addition, it has significant applications in devices used for blood transfusion, dialysis and cancer therapy.

Self-similar analysis of the time-dependent compressible and incompressible boundary layers including heat conduction

We investigate the incompressible and compressible heat conducting boundary layer with applying the two-dimensional self-similar Ansatz. Analytic solutions can be found for the incompressible case which can be expressed with special functions. The parameter dependencies are studied and discussed in details. In the last part of our study we present the ordinary differential equation (ODE) system which is obtained for compressible boundary layers.

Mass Transfer Effects on the Mucus Fluid with Pulsatile Flow Influence of the Electromagnetic Field

The influence of pulsatile flow on the oscillatory motion of an incompressible conducting boundary layer mucus fluid flowing through porous media in a channel with elastic walls is investigated. The oscillatory flow is treated as a cyclical time-dependent flux. The Laplace transform method using the Womersley number is used to solve non-linear equations controlling the motion through porous media under the influence of an electromagnetic field. The theoretical pulsatile flow of two liquid phase concurrent fluid streams, one kinematic and the other viscoelastic, is investigated in this study. To extend the model for various physiological fluids, we postulate that the viscoelastic fluid has several distinct periods. We also apply our analytical findings to mucus and airflow in the airways, identifying the wavelength that increases dynamic mucus permeability. The microorganism’s thickness, velocity, energy, molecular diffusion, skin friction, Nusselt number, Sherwood number, and Hartmann number are evaluated. Discussion is also supplied in various sections to investigate the mucosal flow process.

Thermal evolution of Uranus and Neptune

Thermal evolution models suggest that the luminosities of both Uranus and Neptune are inconsistent with the classical assumption of an adiabatic interior. Such models commonly predict Uranus to be brighter and, recently, Neptune to be fainter than observed. In this work, we investigate the influence of a thermally conductive boundary layer on the evolution of Uranus- and Neptune-like planets. This thermal boundary layer (TBL) is assumed to be located deep in the planet and be caused by a steep compositional gradient between a H–He-dominated outer envelope and an ice-rich inner envelope. We investigate the effect of TBL thickness, thermal conductivity, and the time of TBL formation on the planet’s cooling behaviour. The calculations were performed with our recently developed tool based on the Henyey method for stellar evolution. We make use of state-of-the-art equations of state for hydrogen, helium, and water, as well as of thermal conductivity data for water calculated via ab initio methods. We find that even a thin conductive layer of a few kilometres has a significant influence on the planetary cooling. In our models, Uranus’ measured luminosity can only be reproduced if the planet has been near equilibrium with the solar incident flux for an extended period of time. For Neptune, we find a range of solutions with a near constant effective temperature at layer thicknesses of 15 km or larger, similar to Uranus. In addition, we find solutions for thin TBLs of a few km and strongly enhanced thermal conductivity. A ~ 1 Gyr later onset of the TBL reduces the present ΔTby an order of magnitude to only several 100 K. Our models suggest that a TBL can significantly influence the present planetary luminosity in both directions, making it appear either brighter or fainter than the adiabatic case.

Quantifying the Axial Magma Lens Dynamics at the Roof of Oceanic Magma Reservoirs (Dike/Gabbro Transition): Oman Drilling Project GT3 Site Survey

AbstractAt oceanic spreading centers, the interactions between the igneous system that builds the crust, and the hydrothermal system that cools it govern the plumbing system architecture and its thermokinetic evolution. At fast‐spreading centers, most of those interactions occur around the axial magma lens (AML) that feeds the upper crust, and possibly part of the underlying mushy igneous reservoir. Heat extracted from crystallizing AML is transferred through a conductive boundary layer to the overlying hydrothermal system. Quantifying the AML physical and thermal evolutions and its interactions with hydrothermal system is therefore essential to understand oceanic accretion. Those general issues were the rationale of drilling ICDP OmanDP Hole GT3A, and we present herein the geological, structural, and petrological data that were used as a site survey to select its location. GT3 area enables observations in three dimensions of fossilized AMLs and overlying dikes. The new field data and corresponding mineral compositions are used together with thermokinetic and thermodynamic models to deliver an integrated dynamic model for the AML/hydrothermal system interactions. Results attest that the isotropic gabbro interval is composite, with gabbro bodies intruding and reheating both gabbros and dikes (up to 1,040°C). We show that AMLs should be considered as transient igneous bodies that likely crystallize from primitive MORBs in decades, releasing heat to the intruded hosts, and feeding high temperature vents on the seafloor. We show for the first time that the thermal gradient recorded in AML roof is consistent with the heat fluxes reported at active hydrothermal vents.

Melting heat transfer of MHD stagnation point flow of non-Newtonian fluid due to an elastic sheet

This paper sheds light on the numerical investigation of 2D flow and melting heat transport of an electrically conducting boundary layer stagnation-point flow of Casson fluid in the direction of stretching sheet. Suitable changes are made in rehabilitating the flow governing partial differential equations into dimensionless ordinary differential equations and afterwards solved these ordinary differential equations by the fourth order Runge-kutta numerical method by utilising the most efficient shooting technique. The influence of melting heat transfer, magnetic field, Prandtl number, Rayleigh number and Schmidt number on velocity, energy and concentration distributions, are studied through graphically drawn results.

Entropy analysis for an MHD nanofluid with a microrotation boundary layer over a moving permeable plate

Entropy analysis of an electrically conducting boundary layer of a nanofluid with microrotation elements over a moving plate is presented in this article by applying the second law of thermodynamics. Two types of nanoparticles, copper oxide (CuO) and aluminum oxide (Al2 O3 ), are considered in addition to microstructure elements within a base fluid. The analysis is based on governing boundary layer equations associated with the linear and angular momentum as well as the energy transformed by introducing a suitable similarity transformation into a system of triple nonlinear differential equations that are solved analytically. On the physical side, this article examines the effect of the nanoparticle type and its concentration as well as the type of base fluid, whether Newtonian or non-Newtonian, on the rate of entropy generated and the rate of heat flux from the surface. This simulation involves the cooling stage of the metals during the heat treatment process, which controls the final mechanical properties of the plate, so controlling the entropy of the cooling system plays a great role on the results. The results obtained confirm that the entropy generation of the non-Newtonian fluids (fluids with microrotation elements) is higher than that of the Newtonian fluids and that the presence of nanoparticles in the cooling system increases the rate of entropy by 1–4% according to the type and concentration of the nanoparticles.

Magma-hydrothermal interactions at the Costa Rica Rift from data collected in 1994 and 2015

We use co-located CTD/transmissometry casts and multichannel seismic reflection surveys conducted at the Costa Rica Rift (CRR) to provide a better understanding of magma-hydrothermal processes occurring at an intermediate-rate spreading center. Water column observations reveal an ∼200 m thick plume head ∼650 m above the seafloor, which corresponds to a hydrothermal heat output of ∼200 ± 100 MW at the ridge axis. Assuming a hydrothermal vent temperature of 350°C and a discharge area between 104 and 105 m2, this heat output implies a mean crustal permeability within the discharge zone of between 2×10−14 and 6×10−13 m2, and a conductive thermal boundary layer thickness of ∼20 m. The volume of magma required to maintain the current hydrothermal heat output over the past two decades should result in an across-axis axial magma lens (AML) width between 270 and 1300 m, depending on the amount of cooling and crystallization. However, seismic reflection images, acquired in 1994 and 2015, while showing an apparent along-axis growth of the AML from 2.4 to 6.0 km between surveys, also suggest that, as of 2015, the AML has an apparent across-axis width of no more than 300 m, and that magma delivery at the intermediate spreading rate CRR may be episodic on time scales of tens of years. The data on magma-hydrothermal interactions at the CRR collected in 1994 and 2015 suggest that the hydrothermal system may have significantly cooled and crystallized the AML, primarily in the across-axis direction, and that this hydrothermal system may also episodically turn on and off. The current pattern of microseismicity supports this conclusion, with events not only mirroring the AML depth and location beneath the ridge axis, but also having a temporally varying focus.

Lead isotopes as tracers of crude oil migration within deep crustal fluid systems

Although Pb, U, and Th may be fractionated between crude oil and formation waters, Pb isotopes are not. This unique property makes Pb isotopes a particularly useful marker of hydrocarbon generation and migration. Here we show that Pb isotopes offer a new vision of long-range (secondary) oil migration relevant to the formation of oil fields. North Sea oils are largely generated from Jurassic black shales, yet their Pb isotopes are mixtures of Cenozoic to Proterozoic end-members. The same observation is made for crude oils from the Paris Basin, the Barents Sea, Libya, Kuwait, Kazakhstan, and Australia. Bulk Pb in crude oil therefore, for the most part, is foreign to its source rock(s). Our high-precision Pb isotope data on 195 crude oils worldwide, the first such data set in the published literature, and 17 Northern European black shales indicate that deep-seated Pb components originating beneath the source rocks are ubiquitous in crude oil. This implies that oil fields are embedded in basinal convective systems of hydrous fluids heated from below. Plumes of hot fluids rise from the lower thermal boundary layer, which Pb isotopes require douse the basement, into the core of the porous-flow convective cell where they dissolve the newly formed hydrocarbons sequestered in the source rocks. The fluids finally unload unmixed formation waters and crude oil at the base of the upper (conductive) boundary layer where they can be trapped in favorable sites. Based on these new insights we argue that Pb isotopes in crude oil constitute a good tracer of oil migration.

A Review of the Geological Constraints on the Conductive Boundary Layer at the Base of the Hydrothermal System at Mid‐Ocean Ridges

AbstractModels of high‐temperature hydrothermal systems at intermediate‐ to fast‐spreading mid‐ocean ridges have a conductive boundary layer (CBL) separating the magmatic heat source from the convecting hydrothermal fluid. Paleo‐CBLs preserved in the geological record provide a means to test theoretical models of the thermal, mechanical, and petrological evolution of this boundary. CBLs occur as metamorphic contact aureoles at or near the dike‐gabbro boundary where axial magma lenses (now plutonic rocks) intruded into the basal dikes, leading to their transformation into low permeability granulite and hornblende hornfels at >800 °C. Paleo‐CBLs are well documented in the Troodos and Oman ophiolites, and evidence of similar lithologies has been found at every location where the dike‐gabbro transition has been mapped and/or sampled in modern fast‐spreading crust (Hess and Pito Deeps, IODP Hole 1256D). Evaluation of the geothermometers used in studies of the thermal evolution of the CBL shows a lack of consistency that can be understood in terms of compositional controls. Peak temperatures are >900 °C in all areas at the base of the CBL, leading to partial melting, stoping, and disaggregation that facilitates thinning from below as required to maintain the high heat fluxes necessary to drive active black smoker systems. However, such thin CBLs are not the norm; steady state conditions must have thicker CBLs and smaller heat fluxes. In turn, global estimates of properties such as chemical fluxes for normal hydrothermal conditions may lead to substantially different element/heat fluxes than those based on active systems.

Analysis of activation energy in magnetohydrodynamic flow with chemical reaction and second order momentum slip model

This paper is communicated theoretically to study the collective effects of Arrhenius activation energy and binary chemically reactive species in the presence of the second order momentum slip model which has not been studied so far. To support these declaration in addition with electrically conducting boundary layer flow and heat transport have considered towards an exponential stretching sheet. The current study incorporates the impact of activation energy, temperature difference ratio parameter, 1st and 2nd order slip parameter, chemical reaction rate on fluid velocity, fluid temperature and concentration of chemical species are elaborated through graphically and discussed in detail. Appropriate transformations are betrothed to acquire nonlinear highly coupled ordinary differential equations (ODE's) from partial differential equations which are then solved numerically by employing finite difference collocation process that apply three-stage Lobatto IIIa scheme. The obtained results confirm that an excellent agreement is achieved with those available in open literature. It is found that concentration profile decreases in the presence of chemical reaction rate and temperature difference ratio parameter whereas opposite demeanour is seen for activation energy.

Effect of Radiation on MHD Free Convective Flow over a Stretching Sheet in the Presence of Heat Source/Sink

In this analysis, effects of viscous dissipation and thermal radiation on an electrically conducting boundary layer flow, heat and mass transfer of a fluid through a porous medium over a stretching sheet in the presence of heat source/sink is considered. The symmetry groups admitted by the corresponding boundary value problem are obtained by using symmetric transformations. These transformations are used to convert the partial differential equations of the governing equations into self-similar non-linear ordinary differential equations. These transformed ODEs are solved by employing Runge-Kutta fourth order with shooting method. Numerical results obtained for different thermo-physical parameters characterizes the flow phenomena are drawn graphically and effects of various physical parameters on velocity, temperature and concentration profiles are discussed. Numerical computation for skin friction, Nusselt number and Sherwood number are also obtained and presented in Tables.

Homogenous\u2013heterogeneous reactions in MHD flow of Powell\u2013Eyring fluid over a stretching sheet with Newtonian heating

This article addresses the effects of homogenous–heterogeneous reactions on electrically conducting boundary layer fluid flow and heat transfer characteristics over a stretching sheet with Newtonian heating are examined. Using similarity transformations, the governing equations are transformed into nonlinear ordinary differential equations. The constricted ordinary differential equations are solved computationally by shooting technique. The impact of pertinent physical parameters on the velocity, concentration and temperature profiles is discussed and explored via figures and tables. It is clear from figures that the velocity profile reduces for large values of fluid parameter B and Hartmann number H. Skin friction coefficient decreases for large values of Hartmann number H and fluid parameter B. Also, heat transfer rate monotonically enhances with conjugate parameter of Newtonian heating γ and Prandtl number Pr.

Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D

The formation of new ocean crust at mid-ocean ridges is a fundamental component of the plate tectonic cycle and involves substantial transfer of heat and mass from the mantle. Hydrothermal circulation at mid-ocean ridges is critical for the advection of latent and sensible heat from the lower crust to enable the solidification of ocean crust near to the ridge axis. The sheeted dike complex (SDC) is the critical region between the eruptive lavas and the gabbros through which seawater-derived recharge fluids must transit to exchange heat with the magma chambers that form the lower ocean crust.ODP Hole 1256D in the eastern equatorial Pacific Ocean provides the only continuous sampling of in-situ intact upper ocean crust formed at a fast spreading rate, through the SDC into the dike–gabbro transition zone. Here we exploit a high sample density profile of the Sr-isotopic composition of Hole 1256D to quantify the time-integrated hydrothermal recharge fluid flux through the SDC. Assuming kinetically limited fluid–rock Sr exchange, a fluid flux of 1.5–3.2×106 kgm−2 is required to produce the observed Sr-isotopic shifts. Despite significant differences in the distribution and intensity of hydrothermal alteration and fluid/rock Sr-isotopic exchange between Hole 1256D and SDC sampled in other oceanic environments (ODP Hole 504B, Hess Deep and Pito Deep), the estimated recharge fluid fluxes at all sites are similar, suggesting that the heat flux extracted by the upper crustal axial hydrothermal system is relatively uniform at intermediate to fast spreading rates.The hydrothermal heat flux removed by fluid flow through the SDCs, is sufficient to remove only ∼20 to 60% of the available latent and sensible heat from the lower crust. Consequently, there must be additional thermal and chemical fluid–rock exchange deeper in the crust, at least of comparable size to the upper crustal hydrothermal system. Two scenarios are proposed for the potential geometry of this deeper hydrothermal system. The first requires the downward expansion of the upper crustal hydrothermal system ∼800 m into the lower crust in response to a downward migrating conductive boundary layer. The second scenario invokes a separate hydrothermal system in the lower crust for which fluid recharge bypasses reaction with the sheeted dikes, perhaps via flow down faults.

MHD Boundary Layer Flow of Nanofluid over a Continuously Moving Stretching Surface

The present investigation provides an insight in the steady, incompressible and electrically conducting boundary layer flow of viscoelastic nanofluid flowing due to a moving, linearly stretched surface. The governing system of nonlinear partial differential equations is simplified by considering Boussinesq and boundary layer approximations. An analytical solution of the resulting nonlinear ordinary differential equations for momentum, energy and concentration profiles is obtained using the homotopy analysis method (HAM).

Numerical simulation of conjugate heat transfer and surface radiative heat transfer using the [formula omitted] thermal radiation model: Parametric study in benchmark cases.

A parametric investigation of radiative heat transfer is carried out, including the effects of conjugate heat transfer between fluid and solid media. The thermal radiation is simulated using the P1-model. The numerical model and the thermal coupling strategy, suitable for a transient solver, is described. Such numerical coupling requires that the radiative equation is solved several times at each iteration; hence, the computational cost of the radiative model is a crucial issue. The P1-model is adopted because of its particularly fast computation. First, a collection of benchmark cases is presented and used to carefully validate the radiation model against literature results and to analyse the model prediction limits. Despite the simplicity of the model, it satisfactorily reproduces the thermal radiation effects. Some lack of accuracy is identified in particular cases. Second, a number of benchmark cases are described and adopted to investigate fluid–solid thermal interaction in the presence of radiation. Three cases are designed, to couple radiation with: pure conduction, conduction and forced convection, conduction and natural convection. In all the cases, the surface radiative heat transfer strongly influences the system thermodynamics, leading to a significant increase of the fluid–solid interface temperature. The main non-dimensional numbers, related to the mutual influence of the different heat transfer modes, are introduced and employed in the analyses. A new conduction-radiation parameter is derived in order to study the conductive boundary layer in absence of convective heat transfer.

Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB

At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910°C and 970°C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

AbstractThe Lost City hydrothermal field (LCHF) is hosted in serpentinite at the crest of the Atlantis Massif, an oceanic core complex close to the mid‐Atlantic Ridge. It is remarkable for its longevity and for venting low‐temperature (40–91°C) alkaline fluids rich in hydrogen and methane. IODP Hole U1309D, 5 km north of the LCHF, penetrated 1415 m of gabbroic rocks and contains a near‐conductive thermal gradient close to 100°C km−1. This is remarkable so close to an active hydrothermal field. We present hydrothermal modelling using a topographic profile through the vent field and IODP site U1309. Long‐lived circulation with vent temperatures similar to the LCHF can be sustained at moderate permeabilities of 10−14 to 10−15 m2 with a basal heatflow of 0.22 W m−2. Seafloor topography is an important control, with vents tending to form and remain in higher topography. Models with a uniform permeability throughout the Massif cannot simultaneously maintain circulation at the LCHF and the near‐conductive gradient in the borehole, where permeabilities <10−16 m2 are required. A steeply dipping permeability discontinuity between the LCHF and the drill hole is required to stabilize venting at the summit of the massif by creating a lateral conductive boundary layer. The discontinuity needs to be close to the vent site, supporting previous inferences that high permeability is most likely produced by faulting related to the transform fault. Rapid increases in modelled fluid temperatures with depth beneath the vent agree with previous estimates of reaction temperature based on geochemical modelling.

Effect of radiation and porosity parameter on hydromagnetic flow due to exponentially stretching sheet in a porous media

The aim of this paper is to study the momentum and the heat transfer characteristics in incompressible electrically conducting boundary layer flow over an exponentially stretching sheet under the effect of magnetic field with thermal radiation through porous medium. The governing boundary layer equations are converted into self-similar nonlinear ordinary differential equations, using similarity transformations in exponential form and then solved numerically using shooting method. The velocity profile, skin friction-co-efficient and rate of heat transfer are computed numerically and then graphically studied with respect to similarity variable (η) for different cases of velocity ratio parameter (β) Keywords: Boundary layer, unsteady flow, exponentially stretching surface, porous medium, thermal radiationInternational Journal of Engineering, Science and Technology Vol. 6, No. 1, 2014, pp. 58-70