Thickness Of Solid Layer Research Articles

Criterion to control self-propagation high temperature synthesis for porous Ti–Al intermetallics

The criterion to control self-propagation high temperature synthesis for the fabrication of porous Ti–Al intermetallics was established from the prereaction model and the thermal balance condition. The criterion equation reflecting the relation between the solid reaction layer thickness correlation parameter and the ignition temperature was deduced to be p3 = C1/(Tad−T0)+C2, according to which the near net shaping synthesis of porous Ti–Al intermetallics was realised, which was significantly important for the industrial productions and applications of this high performance novel porous material. The slight difference between theoretical predictions and experimental data was analysed according to the model analysis.

G060072 2成分系水溶液を用いた垂直円筒周りの凝固プロセスに関する研究([G06007]熱工学部門一般セッション(7):蓄熱,および空調)

An experimental study of solidification is performed for a hypoeutectic sodium nitrate solution in a confined rectangular vessel with varying initial concentration. The experiments have been conducted by heating the lower wall of the vessel and cooling the vertical cylinder. We investigate the development of its temperature and concentration distribution in the liquid region during the solidification and its effect on the solid layer thickness formed around the cylinder. The growth of the solid layer, which accompanies solute ejection to liquid region, leads to double-diffusive convection and form a sharp density interface. Across the interface a drastic change of temperature and concentration is observed. Therefore, the solid layer thickness undergoes a dramatic change when the interface passes.

Stability of pressure-driven flow in a deformable neo-Hookean channel

The stability of pressure-driven flow in a rectangular channel with deformable neo-Hookean viscoelastic solid walls is analysed for a wide range of Reynolds numbers (from Re ≪ 1 to Re ≫ 1) by considering both sinuous and varicose modes for the perturbations. Pseudospectral numerical and asymptotic methods are employed to uncover the various unstable modes, and their stability boundaries are determined in terms of the solid elasticity parameter Γ = Vη/(ER) and the Reynolds number Re = RV ρ/η; here V is the maximum velocity of the laminar flow, R is the channel half-width, η and ρ are respectively the viscosity and density of the fluid and E is the shear modulus of the solid layer. We show that for small departures from a rigid solid, wall deformability could have a destabilizing or stabilizing effect on the Tollmien–Schlichting (TS) instability (a sinuous mode) depending on the solid-layer thickness. Upon further increase in solid deformability, the TS mode coalesces with another unstable mode (absent in rigid channels) giving rise to a single unstable mode which extends to very low Reynolds number (<1) for highly deformable walls. There are other types of instabilities that exist only due to wall deformability. In the absence of inertia (Re = 0), there is a short-wave instability of both sinuous and varicose modes arising due to the discontinuity of the first normal stress difference across the fluid–solid interface. For both sinuous and varicose modes, it is shown that inclusion of inertia is important even for Re ≪ 1, wherein a new class of long-wavelength unstable modes are predicted which are absent at Re = 0. These unstable modes are a type of shear waves in an elastic solid which are destabilized by the flow. These long- and short-wave instabilities are absent if a simple linear elastic model is used for the solid. At intermediate and high Re, upstream and downstream travelling waves of both sinuous and varicose modes become unstable. We show that sinuous and varicose modes become critical in different parameter regimes, thereby demonstrating the importance of capturing all the unstable modes. Inclusion of dissipative effects in the neo-Hookean model is generally shown to play a stabilizing role on the instabilities due to both sinuous and varicose modes. The predicted instabilities will be important for the flow of liquids (with viscosity ≥ 10−3 Pa s) in deformable channels of width ≤1 mm, and with shear modulus ≤ 105 Pa.

A scanning fluid dynamic gauging technique for probing surface layers

Fluid dynamic gauging (FDG) is a technique for measuring the thickness of soft solid deposit layers immersed in a liquid environment, in situ and in real time. This paper details the performance of a novel automated, scanning FDG probe (sFDG) which allows the thickness of a sample layer to be monitored at several points during an experiment, with a resolution of ±5 µm. Its application is demonstrated using layers of gelatine, polyvinyl alcohol (PVA) and baked tomato purée deposits. Swelling kinetics, as well as deformation behaviour—based on knowledge of the stresses imposed on the surface by the gauging flow—can be determined at several points, affording improved experimental data. The use of FDG as a surface scanning technique, operating as a fluid mechanical analogue of atomic force microscopy on a millimetre length scale, is also demonstrated. The measurement relies only on the flow behaviour, and is thus suitable for use in opaque fluids, does not contact the surface itself and does not rely on any specific physical properties of the surface, provided it is locally stiff.

Separation characteristics of clathrate hydrates from a cooling plate for efficient cold energy storage

Abstract To improve the coefficient of performance (COP) in air-conditioning systems, the liquid–solid phase change temperature of the cold energy storage material should be approximately 10 °C. Moreover, a thermal storage material that forms a slurry can maintain large heat capacity for the working fluids. Solids that adhere to the heat transfer surface form a thermal resistance layer and significantly reduce the cooling storage rate; therefore, it is important to avoid adhesion of a thick solid layer on the surface to realize efficient energy storage. Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate possesses the qualities of an efficient cold storage material. Therefore, it was used to examine the force required to remove solid phase from the heat transfer surface for a harvest-type cooling unit. The effects of TBAB concentration and surface properties on the scraping force required to remove adhered TBAB hydrate solid from the heat transfer surface were examined experimentally and comprehensively. Results showed that the required scraping force increased with TBAB concentration and was very small for the low-energy heat transfer surface.

Efficient and Tunable Light Trapping Thin Films

Using the discrete dipole approximation method, we demonstrated enhanced absorption efficiencies, which are close to 100%, at tunable wavelengths in a two-layer silver thin film. The film is composed of a 100 nm thick perforated layer facing the incident light and a 100 nm thick solid layer. Resonance wavelengths are determined by the distances between perforated holes in the first layer as well as the separation between the two layers. The resonance wavelengths shift to the red with increasing separation distance between the two layers or the periodic distance of the hole arrays. Geometries of conical frustum shaped holes in the first layer are critical for the improved absorption efficiencies. When the hole bottom diameter equals the periodic distance and the upper diameter is about one-third of the bottom diameter, close to unit absorption efficiency can be obtained. The simulations provide a proof of concept example for designing ultrathin antireflection films.

Adhesion and detachment characteristics of a TBAB hydrate solid on a heat transfer surface (Effect of concentration of TBAB solutions)

AbstractIn air‐conditioning systems, it is desirable that the liquid–solid phase change temperature of a cool energy storage material be approximately 10°C, with respect to improving the coefficient of performance (COP). Moreover, a thermal storage material that forms slurry can realize a large heat capacity of the working fluids. A solid that adheres to the heat transfer surface forms a thermal resistance layer and significantly reduces the rate of cold storage; therefore, it is important to avoid the adhesion of a thick solid layer on the surface so as to realize efficient energy storage. Considering a harvest type cooling unit, the force required for removal of the solid phase from the heat transfer surface was investigated. Tetra‐n‐butylammonium bromide (TBAB) clathrate hydrate was used as a cold storage material and the effect of the TBAB solution concentration on the scraping force required to detach the adhered TBAB hydrate solid from the heat transfer surface was experimentally examined. The TBAB hydrate solids were broadly categorized into two types, and the scraping force required for removal of these two types of TBAB hydrate solid was different. The scraping force required for removal of the solid increased due to the effect of increasing the concentration of the TBAB solution. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20254

Characteristics Detachment of Adhered Solid to Cooling Surface for Formation of Clathrate Hydrate Slurry (Effect of Concentration of TBAB Solutions)

In air-conditioning systems, it is desirable that the liquid-solid phase change temperature of a cool energy storage material is approximately 10°C from the perspective of improving coefficient of performance (COP). Moreover, a thermal storage material that forms slurry can realize large heat capacity of working fluids. Since the solid that adheres to the heat transfer surface forms a thermal resistance layer and remarkably reduces the rate of cold storage, it is important to avoid the adhesion of a thick solid layer on the surface so as to realize efficient energy storage. Considering a harvest type cooling unit, the force required for removing the solid phase from the heat transfer surface was studied. Tetra-n-butylammonium Bromide (TBAB) clathrate hydrate was used as a cold storage material. The effect of concentration of TBAB solutions on the scraping force for detachment of adhered solid of TBAB hydrate to the heat transfer surface was examined experimentally. The TBAB hydrate solids were categorized broadly into two kinds of solids. The scraping force of the TBAB hydrate solid on the heat transfer surface was different for the two kinds of the TBAB hydrate solids. The scraping force increased with the increase in the concentration of solution. It was confirmed that the concentration of solution had an effect on the scraping force required for removal of the solid.

An effect of scraper shapes on detachment of solid adhered to cooling surface for formation of clathrate hydrate slurry

AbstractIn air‐conditioning systems, it is desirable that the liquid– solid phase change temperature of a cool energy storage material is approximately 10°C from the perspective of improving the coefficient of performance (COP). Moreover, a thermal storage material that forms slurry can realize large heat capacity of working fluids. Since the solid that adheres to the heat transfer surface forms a thermal resistance layer and remarkably reduces the rate of cold storage, it is important to avoid the adhesion of a thick solid layer on the surface so as to realize efficient energy storage. Considering a harvest type cooling unit, the force required for removing the solid phase from the heat transfer surface was studied. Tetra‐n‐butylammonium bromide (TBAB) clathrate hydrate was used as a cold storage material. The effect of the scraper shapes on the scraping force for detachment of the adhered solid of TBAB hydrate to the heat transfer surface was examined experimentally. The TBAB hydrate solids were categorized broadly into two kinds of solids. The scraping force of the TBAB hydrate solid on the heat transfer surface was different for the two kinds of the TBAB hydrate solids. And the scraping force of the TBAB hydrate solid formed after scraping was improved by the modifying the scraper shape. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 489– 500, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20179

Predicting splat morphology in a thermal spray process

Splats formed during a thermal spray process may be either highly fragmented or intact and disk-like. To predict this change in splat morphology, a dimensionless solidification parameter ( Θ), which takes into account factors such as the particle diameter and velocity, substrate temperature, splat and substrate thermophysical properties, and thermal contact resistance between the two, has been defined. Θ is the ratio of the thickness of the solid layer formed in the splat while it is spreading, to the splat thickness. The value of Θ can be calculated from simple analytical models of splat solidification and spreading. If solid layer growth is very slow ( Θ ≪ 1), the splat spreads out to a large extent. Once it reaches maximum spread, it becomes so thin that it ruptures, producing fragmented splats. If, however, the solid layer thickness is significant ( Θ ∼ 0.1–0.3), the splat is restricted from spreading too far and does not become thin enough to rupture, resulting in disk splats. When solid layer growth is rapid ( Θ > 0.3), it obstructs liquid from flowing outward during droplet impact, producing splats with fingers around their periphery. Predictions from the model are compared with experimental data and found to agree well.

An Effect of Scraper Shapes on Detachment of Solid Adhered to Cooling Surface for Formation of Clathrate Hydrate Slurry

In air-conditioning systems, it is desirable that the liquid-solid phase change temperature of a cool energy storage material is approximately 10°C from the perspective of improving coefficient of performance (COP). Moreover, a thermal storage material that forms slurry can realize large heat capacity of working fluids. Since the solid that adheres to the heat transfer surface forms a thermal resistance layer and remarkably reduces the rate of cold storage, it is important to avoid the adhesion of a thick solid layer on the surface so as to realize efficient energy storage. Considering a harvest type cooling unit, the force required for removing the solid phase from the heat transfer surface was studied. Tetra-n-butylammonium Bromide (TBAB) clathrate hydrate was used as a cold storage material. The effect of the scraper shapes on the scraping force for detachment of adhered solid of TBAB hydrate to the heat transfer surface was examined experimentally. The TBAB hydrate solids were categorized broadly into two kinds of solids. The scraping force of the TBAB hydrate solid on the heat transfer surface was different for the two kinds of the TABA hydrate solids. And the scraping force of the TBAB hydrate solid formed after scraping was improved by the modifying the scraper shape.

Stability of two-layer Newtonian plane Couette flow past a deformable solid layer

The linear stability of two-layer plane Couette flow of Newtonian fluids (designated by labels A and B) of thicknesses (1−β)R and βR, and viscosities μa and μb past a soft, deformable linear viscoelastic solid of thickness HR, shear modulus G, and viscosity ηw is determined using a combination of low wavenumber asymptotic analysis and a numerical method. There are two qualitatively different interfacial modes in this system, viz., the two-fluid interfacial mode due to viscosity stratification [“mode 1;” C. S. Yih “Instability due to viscosity stratification,” J. Fluid Mech. 27, 337 (1967)], and the fluid–solid interfacial mode [“mode 2;” Kumaran, Fredrickson, and Pincus, “Flow induced instability of the interface between a fluid and a gel at low Reynolds number,” J. Phys II 4, 893 (1994)]. The respective effects of solid layer deformability and fluid viscosity stratification on mode 1 and mode 2 are analyzed in detail using both asymptotic and numerical methods. Results of our low wavenumber asymptotic analysis show that the deformability of the solid layer has a dramatic effect on the interfacial instability (mode 1) between the two Newtonian fluids: When the more viscous fluid is of smaller thickness (an unstable configuration for the two-fluid mode 1 instability), the solid layer could completely stabilize the two-fluid interfacial instability, when the nondimensional elasticity parameter Γ=Vμb/(GR) increases beyond a critical value. Here V is the dimensional velocity of the top moving plate. When the more viscous fluid is of larger thickness compared to the less viscous fluid (a stable configuration in rigid channels), it is shown that the solid layer could destabilize or stabilize the two-fluid interfacial mode, depending on the solid layer thickness H. Numerical results at finite values of wavenumber k reveal that the stabilization of the two-fluid interfacial mode predicted by the low wavenumber analysis extends to moderate values of k. For high values of k, the perturbations are localized near the two-fluid interface. Increase in Γ therefore does not have any effect on the high k unstable modes, which are stabilized by the presence of nonzero interfacial tension in the two-fluid interface. When Γ is further increased, the interfacial mode between fluid B and the solid layer becomes unstable. It is demonstrated here that the parameters Γ (representing the shear modulus of the solid), solid layer thickness H, and the solid layer viscosity ηw can be chosen such that both the interfacial modes are stabilized at all wavenumbers, for a fixed top plate velocity.

Effects of solid layer thickness and nominal composition on double-diffusive instabilities during solidification of a binary alloy cooled from the top

When a horizontal layer of fluid is cooled and solidified from the top, a cellular form of natural convection may occur inside the liquid, similar to that observed during classical Rayleigh–Benard convection. As a result of the interaction between the cellular convection and directional solidification, the phase-change interface tends to get wavy. The above situation can be mathematically represented by considering two horizontal parallel plates at z = 0 and z = h. The lower plate at z = h is fixed at temperature $T = T_1$ and the upper plate at z=0 is kept at a temperature $T = T_0$. Due to occurrence of solidification on account of cooling from the top, there is a solid–liquid interface at $z=\eta \leq \eta \leq h)$, which is assumed to be at a quasi-steady state. The physical situation is shown schematically in Fig. 1. As a result of interface perturbation on account of convection occurring below, the interface is likely to assume an irregular shape. It can be noted here that when the solidifying medium is a binary alloy that solidifies nonisothermally, the natural convection in the liquid is double-diffusive in nature (as a consequence of concentration and temperature gradients prevailing in the solidifying domain). Instabilities in thermo-solutal convection in such cases have attracted considerable attention in the literature [1,2]. However, the effects of nominal alloy composition and solid layer thickness on associated double-diffusive instabilities are yet to be addressed in the literature, to the best of our knowledge.

Wetting of van der Waals solid films on self-affine rough surfaces

In this work we investigate the influence of random self-affine substrate roughness on the solid layer thickness under conditions of triple-point wetting of adsorbed van der Waals films. Our calculations show that a significant solid film thickness ${\ensuremath{\lambda}}_{s}$ can be reached (in the nanometer range) for substrate roughness parameters $w/\ensuremath{\xi}l~0.05$ and/or $H\ensuremath{\approx}1$ with w the rms roughness amplitude, \ensuremath{\xi} the lateral roughness correlation length, and H the roughness exponent $(0l~Hl~1).$ Independent of substrate-particle and particle-particle interactions, with increasing roughness exponent H and/or decreasing ratio $w/\ensuremath{\xi}$ the solid film thickness ${\ensuremath{\lambda}}_{s}$ increases since the substrate surface becomes smoother. Finally, the solid layer thickness is shown to be sensitive to growth details of the substrate roughness as described in many cases in terms of dynamic scaling theory.

パルス通電圧接法(PCHP)により作製したNi/金属間化合物積層型複合材料の組織と機械的性質

Ni-aluminides reinforced Ni matrix composites were fabricated from 0.05 mm-thick Ni foils with 0.012 mm-thick aluminum foils, using pulsed current hot pressing (PCHP) process, and the effect of holding temperature on the properties of the composites was investigated. The microstructure of the composite was laminated structure composed of Ni and Ni-aluminides. With increasing holding temperature during PCHP, the thickness of Ni-rich Ni solid solution layer increased, while the thickness of Ni matrix layer decreased. Tensile tests at room temperature revealed that the mechanical properties of the composites depended on the holding temperature. The tensile strength and the elongation of the composite fabricated at 1373 K showed 500 MPa and 3.8%, respectively. These mechanical properties of the composite were higher than those by conventional vacuum hot pressing techniques. Microstructural observations of fractured specimens showed that the Ni layers effectively bridged numerous cracks formed in the Ni-aluminides in the composites.

Scaling analysis of momentum, heat, and mass transfer in binary alloy solidification problems

A systematic approach is developed for scaling analysis of momentum, heat and species conservation equations pertaining to the case of solidification of a binary mixture. The problem formulation and description of boundary conditions are kept fairly general, so that a large class of problems can be addressed. Analysis of the momentum equations coupled with phase change considerations leads to the establishment of an advection velocity scale. Analysis of the energy equation leads to an estimation of the solid layer thickness. Different regimes corresponding to different dominant modes of transport are simultaneously identified. A comparative study involving several cases of possible thermal boundary conditions is also performed. Finally, a scaling analysis of the species conservation equation is carried out, revealing the effect of a non-equilibrium solidification model on solute segregation and species distribution. It is shown that non-equilibrium effects result in an enhanced macrosegregation compared with the case of an equilibrium model. For the sake of assessment of the scaling analysis, the predictions are validated against corresponding computational results.

A macroscopic model of the diffusion and heat transfer processes in a periodically micro-stratified solid layer

A macroscopic mathematical model for the analysis of the diffusion and heat transfer processes in a bounded periodically micro-stratified thick solid layer will be derived. Contrary to the known asymptotic homogenization approach the proposed modelling method retains the microstructure length in a macroscopic description of the process. It will be shown that this effect makes it possible to formulate correctly boundary conditions on the boundaries which intersect the stratification and is responsible for certain transient and boundary layer phenomena.

Epitaxial deposition of InGaAsP solid solutions in the miscibility gap

Liquid-phase epitaxy of InGaAsP solid solutions isoperiodic with (001)GaAs substrates was studied in the miscibility gap. At the initial stage of deposition (first 1–2 s), thin (up to 0.15 µm) planar layers of homogeneous InGaAsP solid solutions are formed. This is aided by pronounced supercooling of the melt (by 10–15°C) and the resulting high growth rates. In further stages, growth becomes slower and a natural nanoheterostructure starts to form owing to decomposition of the solid solution. The formation of a nanoheterostructure comprising domains of different compositions with different lattice constants is accompanied by the appearance of an undulating relief on the sample surface, with the undulation magnitude increasing as the layer grows. Under the technological conditions employed, the thickness of InGaAsP solid solution layers containing a nanoheterostructure is limited to 0.5 µm.

A Scaling Analysis for Transport Phenomena during Alloy Solidification in a Rectangular Cavity

A scale analysis of the equivalent single phase continuum conservation equations for mass, momentum, heat and species transport is performed for flow inside the mushy zone for the freezing of a binary mixture in a rectangular cavity, which isothermally cooled from one vertical side. Certain terms in the full momentum equations turn out Co be relatively insignificant, and an analysis of the remaining terms leads to the establishment of an advection velocity scale. The energy equation is then analysed, resulting in an estimation of the solid layer thickness. Different regimes corresponding to different dominant modes of transport are simultaneously identified. Stale analysis of the species conservation equation reveals how a non-equilibrium solidification model affects solute segregation and species distribution. It is shown that non-equilibrium effects result in a more severe macro-segregation than that dictated by the rules of equilibrium solidification. It is also observed that, in spite of low velocities, solute transport is driven primarily by advection and less significantly by species diffusion. To test the validity of the scale analysis, numerical calculations using CFD techniques are performed, which confirm. the trends suggested by the sealing analysis.

Acoustic inspection of inertial confinement fusion targets

Acoustic cavity resonances were used to examine the interior surface geometry and gas fill pressures of various prototype inertial confinement fusion targets. A representative target consists of a millimeter-sized spherical beryllium shell filled to high pressure with deuterium/tritium (DT) gas at room temperature. Below the triple point of DT the gas forms a solid and redistributes itself symmetrically within the shell through a process known as beta-layering. The thickness of the solid DT layer, and the symmetry and smoothness of each surface must adhere to strict specifications for ignition to occur. Sound-speed measurements at room temperature provide the gas fill pressure and thus the solid DT layer thickness upon cooldown. These measurements rely upon an accurate equation of state. Degenerate-mode splitting of the cavity resonances provides interior surface geometry information. This technique was applied to a variety of deuterium and helium filled shells at pressures up to 356 atm. Several of these shells were manufactured with known interior surface perturbations. Measured mode splitting is compared with theory and the utility of the technique for cryogenic targets is examined.