Thermal Wedge Research Articles

Reconciling mantle wedge thermal structure with arc lava thermobarometric determinations in oceanic subduction zones

AbstractSubduction zone mantle wedge temperatures impact plate interaction, melt generation, and chemical recycling. However, it has been challenging to reconcile geophysical and geochemical constraints on wedge thermal structure. Here we chemically determine the equilibration pressures and temperatures of primitive arc lavas from worldwide intraoceanic subduction zones and compare them to kinematically driven thermal wedge models. We find that equilibration pressures are typically located in the lithosphere, starting just below the Moho, and spanning a wide depth range of ∼25 km. Equilibration temperatures are high for these depths, averaging ∼1300°C. We test for correlations with subduction parameters and find that equilibration pressures correlate with upper plate age, indicating overriding lithosphere thickness plays a role in magma equilibration. We suggest that most, if not all, thermobarometric pressure and temperature conditions reflect magmatic reequilibration at a mechanical boundary, rather than reflecting the conditions of major melt generation. The magma reequilibration conditions are difficult to reconcile, to a first order, with any of the conditions predicted by our dynamic models, with the exception of subduction zones with very young, thin upper plates. For most zones, a mechanism for substantially thinning the overriding plate is required. Most likely thinning is localized below the arc, as kinematic thinning above the wedge corner would lead to a hot fore arc, incompatible with fore‐arc surface heat flow and seismic properties. Localized subarc thermal erosion is consistent with seismic imaging and exhumed arc structures. Furthermore, such thermal erosion can serve as a weakness zone and affect subsequent plate evolution.

境界面の温度を考慮した分子気体潤滑 (t-MGL) 解析

In order to examine thermo-molecular gas film lubrication (t-MGL) characteristics with a temperature distribution at the disk or slider surfaces for spacings of several nanometers, the free molecular t-MGL equation considering temperature distributions and accommodation coefficients at the boundaries was established. By analyzing pressure generated by the wedge effect (slider inclination) and the thermal wedge effect (boundary temperature distributions), it is revealed that, as the accommodation coefficient, α0 , of the running disk or the boundary surface with a temperature distribution decreases, that is, as the ratio of specular reflection increases, the pressure generation decreases, whereas as the accommodation coefficient, α1 , of the stationary slider surface or the boundary surface without a temperature distribution decreases, the pressure generation increases.

The Relation Between Thermal Wedge and Thermal Boundary Conditions for the Load-Carrying Capacity of a Rectangular Pad and a Slider With Parallel Gaps

In order to understand the load-carrying mechanism of thermal wedge, numerical results for a rectangular pad and a slider with parallel gaps under four types of surface boundary temperature conditions are presented. Two assumptions of rigid-solid and smooth-surface were used to exclude the effects of both thermal deformation and micro-asperity. The relation between thermal wedge and thermal boundary conditions is revealed. The load-carrying mechanism of parallel gaps is explained with the thermal wedge derived not only from the surface temperature difference (STD) as proposed by Cameron but also from the film temperature gradient (FTG) independent of STD. It is also pointed out that in numerical analysis, the very small viscosity–temperature coefficient would result in high oil temperature and therefore, the predicted loading capacity from thermal density wedge would be extremely enlarged.

Study on the load-carrying mechanism of a parallel step bearing

In this paper, the load-carrying mechanism of a parallel step bearing was studied from two different viewpoints, i.e. step bearing and parallel bearing. It has a history of about 100 years that Rayleigh step bearing can give optimum load-carrying capacity for certain geometry. As to parallel bearing, several mechanisms have been proposed: the thermal wedge, the viscosity wedge, the thermal distortion, and the local hydrodynamic effect induced by surface irregularities. In this research, a custom-built fixed-incline slider-bearing test rig was used to measure the lubricant film thickness between a stationary parallel step slider and a rotating transparent disc. Film thickness was measured by interferometry at different sliding speeds. It is worth noting that both temperature and humidity were held constant in the experiments. Experimental results show that the measured curve of film thickness versus speed can be divided into two main distinct regions. One is the lower speed region, where the lubricant film is very thin and less dependent on the sliding speed. In addition, cavitation often occurs in lower speed region. The other is the higher speed region, where the lubricant film is thick and curves of film thickness versus sliding speed present linear relationship in the double logarithmic coordinate system. For different viscosities and loads, the experimental results are quite similar in spite of diverse transition speeds from lower speed region to higher speed region. Theoretical analyses indicate that the film-formation behavior in lower speed region can be attributed to the local hydrodynamic effect caused by the real surface irregularities on the smooth land of the step slider, while the load-carrying mechanism in higher speed region agrees well with the classical lubrication theory of Rayleigh step bearing.

A non-destructive method for testing non-flexible dual geomembrane seams using gas permeation

A non-destructive test is proposed to control in situ non-flexible geomembrane seams carried out by means of the thermal hot dual wedge method. It consists in pressurising the gap between the two welds by gas injection at a specific pressure and in monitoring the evolution of pressure over time. The migration of gas across the geomembrane is indicated by a decrease in pressure. A permeation parameter (the time constant) can then be estimated under unsteady-state conditions. Experiments were performed outdoors, under variable ambient conditions, to test the feasibility of the method in field conditions as well as in the laboratory, and under controlled ambient conditions to check the validity of the method. The results show that a poor seam from a mechanical point of view is also a poor seam from a permeation point of view. It is also shown that the non-destructive method presented here may be used in situ to test the entire seam. Hence the test is complementary to peel tests, because it reveals poor seams undetectable by the pressurised dual seam method, in pond applications where non-flexible geomembranes are placed.

How the orientation of the axes of an anisotropic KGW:Nd3+ crystal in the illuminator of a laser with self-cooling affects its maximum operating life with high pulse-repetition rates of the radiation

This paper presents the results of an investigation of the limiting operating regimes of a KGW:Nd3+ periodic-action laser with self-cooling. This showed that the operating life of a laser with large pulse-repetition rates of the radiation can be substantially increased by mounting the active element in the illuminator in such a way that the direction of the maximum temperature gradient in the anisotropic crystal that causes thermal wedge deformation in it corresponds to the minimum thermooptical constant. © 2004 Optical Society of America

Thermal pollution abatement with simultaneous wastewater treatment plants performance improvement

The beneficial effect of high wastewater temperature on treatment plant performance and effluent quality is shown, on the basis of full scale activated sludge plant data. The wastewater temperature may be regulated by cooling water reuse. The required cooling water flowrate is analytically and graphically determined. The disposal of the reused warm water into rivers and canals may cause density stratification. From the study of the stratified stream, analytical expressions and graphic presentations of the arrested thermal wedge dimensionless length and shape are given. The graphs are presented in appropriate form for practical applications.

Parallel Sliding Load Support in the Mixed Friction Regime. Part 2—Evaluation of the Mechanisms

When two parallel surfaces slide parallel to each other in the presence of a liquid, classical lubrication theory shows that no load carrying capacity should result. In Part 1 of this work the experimental data showing that such load support does occur are reviewed. In this paper several of the proposed mechanisms for parallel sliding load support are evaluated by combining the mechanism with a mixed friction model and comparing predictions to experimental results. Both water and oil type bearings are considered. While there are exceptions, it has been found that in general the thermal wedge, microasperity lubrication, microasperity collisions, and squeeze effects cannot account for the large apparent load support in the experimental cases studied. However, small deviations from parallel geometry have a strong effect and can easily account for the observed load support, but several questions remain. It is concluded that future investigations should be directed to developing a better understanding of how favorable macrogeometries might be developed and searching for other sources of pressure generation in parallel sliding.

Thermal Wedge with Penetrating Keratoplasty to Reduce High Corneal Cylinder

I devised a new technique using a thermal wedge resection at the time of keratoplasty to reduce excessive amounts of corneal astigmatism. Surface cautery was used to draw this thermal wedge of corneal tissue into the area to be trephined, and removed at surgery from the patient's cornea. The final result was the same as combining a surgical tissue wedge resection with keratoplasty. This new technique has resulted in reduction of the astigmatic error by as much as 8.5 diopters.

The Contribution of Fluid Film Inertia to the Thermohydrodynamic Lubrication of Sector-Pad Thrust Bearings

This paper is concerned with the load carrying capacity of thermohydrodynamic lubricating films in sector pad thrust bearings; it combines the effects of the thermal wedge and fluid film inertia in one analysis. Particular emphasis is placed on fluid film inertia in a rotational fluid film analysis. The nonlinear partial differential equations are transformed into finite difference equations and a successive over-relaxation method is used to obtain numerical solutions to the equations using a digital computer. The convergence of iterations is accelerated by introducing a relaxation factor. The analysis shows that fluid film inertia significantly affects the loading capacity (or pressure distribution), and velocity profiles. Temperature variance caused by fluid film inertia is insignificant.

An Experimental Investigation of a Heated Two-Dimensional Water Jet Discharge Into a Moving Stream

The experimental results are presented for a study of the behavior of heated and unheated two-dimensional water jets injected from the bottom of a moving water stream. The jet characteristics are described in terms of velocity and temperature profiles, velocity and temperature decay, jet width, jet trajectory, and jet turbulence. The conditions which favor the formation of an upstream thermal wedge are investigated.

Thermal Wedge Lubrication of Parallel Surface Thrust Bearings

The parallel surface thrust bearing has been studied both theoretically and experimentally. The general equations governing the laminar flow of a Newtonian fluid are presented and suitably reduced to describe the flow of lubricant through a plain collar bearing with sector pads. A computer solution of the resulting equations has been obtained in which the variations of density and viscosity with temperature are accommodated and the circumferential leakage of oil from the bearing is recognized. The resulting performance curves indicate that useful load-carrying capacities, produced by a “thermal wedge” effect, are possible with a parallel surface thrust bearing. The effect of the inlet oil temperature and bearing speed on the performance is shown. Tests were carried out on three, four, and five-pad bearings operating at 15,000 rpm. It was found that circumferential oil seals were required to insure stable operation. The results confirm that hydrodynamic lubrication may be achieved with a parallel surface thrust bearing. However, it was found that some practical limitations are imposed by high temperatures. A comparison between the theoretical load capacity of an optimum tilting pad bearing and that of a parallel surface bearing for equivalent pad dimensions, speed, and lubricant conditions revealed that the tilting pad bearing had the superior performance. Comparison of friction results with the findings of other workers shows good agreement.

Thermal wedge effect in hydrodynamic lubrication : J. Young, Eng. J. (Montreal), 45 (3) (1962) 46–54

Thermal wedge effect in hydrodynamic lubrication : J. Young, Eng. J. (Montreal), 45 (3) (1962) 46–54

Parallel Surface Thrust Bearing

The theory for the thermal wedge thrust pad is given assuming (a) all the heat is taken away by the oil and (b) the viscosity is constant across the thickness of the film. The viscosity is allowed to vary in the direction of motion. Solutions are obtained by both analytical and relaxation methods for infinite and finite pads. The viscosity is allowed to vary in the direction of motion and also a constant value is taken. The results are displayed non-dimensionally graphically.

On the Adiabatic Couette Flow of a Compressible Fluid

Abstract An investigation is made of the adiabatic flow of air between two parallel plates very close together in relative tangential motion with a pressure differential across the moving plate. The solution predicts the “thermal wedge” effect of hydrodynamically lubricated slider-pad bearings and gives a quantitative analysis of the more general problem where a pressure differential exists across the slider pad. The results indicate that the hydrodynamical pressure contribution is often negligible (for moderate speeds) in comparison to the hydrostatic pressures in the pressurized bearings. For the case of stationary plates, the adiabatic solution is identical with the isothermal solution and no temperature rise occurs.

The hydrodynamical theory of film lubrication

The equations of film lubrication are derived from the general equations of hydrodynamics assuming only that the motion is steady, and that it takes place between two surfaces, in relative motion, which are both close together and nearly parallel. Consideration of the relative magnitude of the various term sunder typical conditions as measured in a bearing shows that they are of very unequal orders of magnitude, and that in particular the inertia term s in the momentum and the dilatation and conductivity term s in the energy equation can be neglected. I t is shown that film lubrication is possible if, and only if, either the distance between the surfaces decreases in the direction of motion (the geometric wedge), or the density of the fluid decreases in the same direction (the thermal wedge). These types of film are approximately equal when compared on a basis of equal film thickness and equal decrease. With the geometric wedge a much greater decrease, and therefore load-carrying capacity, is possible, but the thermal wedge from its simpler mechanical construction should be able to equalize matters by running with a thinner film. The equations of film lubrication are derived from the general equations of hydrodynamics assuming only that the motion is steady, and that it takes place between two surfaces, in relative motion, which are both close together and nearly parallel. Consideration of the relative magnitude of the various terms under typical conditions as measured in a bearing shows that they are of very unequal orders of magnitude, and that in particular the inertia terms in the momentum and the dilatation and conductivity terms in the energy equation can be neglected. It is shown that film lubrication is possible if, and only if, either the distance between the surfaces decreases in the direction of motion (the geometric wedge), or the density of the fluid decreases in the same direction (the thermal wedge). These types of film are approximately equal when compared on a basis of equal film thickness and equal decrease. With the geometric wedge a much greater decrease, and therefore load-carrying capacity, is possible, but the thermal wedge from its simpler mechanical construction should be able to equalize matters by running with a thinner film. The equations are reduced to non-dimensional form and the equation of state discussed. For the general case the integration is probably a major computing operation and, in view of the uncertainties in the exact form of the equation of state, not worth while. For the infinite bearing, on the other hand, integration is comparatively simple and has been carried out in the Mathematics Division, N.P.L., for a series of representative cases. The results show that viscosity variation has a profound effect on the performance of the thermal wedge, and that the additional wedging action provided by change of density is likely to be small unless the lubricating surfaces are close together. On the other hand, for surfaces close together and a small variation of viscosity the thermal wedge altogether outclasses the geometric.

Thermal Wedge Theory of the Parallel Surface Thrust Bearing

Messrs. M. C. Shaw and C. D. Strang1 have criticized the thermal wedge explanation of the parallel surface thrust bearing put forward by A. Fogg in his paper2 describing his experimental work.