Contour tracking of specularly reflecting surfaces

The aim of the presented work is to develop an ultrasonic imaging system for contour detection of specularly reflecting sheet metal surfaces and surface contour tracking during a continuous hydroforming process. Based on certain design considerations in context with hardware limitations to obtain on-line information about the state of forming during the whole process a sparsely filled ultrasonic 1D transducer array has been used with a limited number of transducer elements, operating at 2 MHz. It has been shown before, that "2.5D-geometries" (surface areas with curvatures independent of one direction) could be detected and tracked with a sufficient accuracy (linear aperture, 10 cm width, 21 transducers, error in sound propagation direction less than 1 mm). We now present the design and results of an imaging system for automated detecting and consecutive tracking of sheet metal surface contours during the forming process by means of an active contour model. To achieve a sufficient accuracy, a priori in process information, e.g., starting and final positions of the sheet metal, forming velocity, preceding instantaneous contour geometries are incorporated into the active model.     

Near-field radiative heat transfer between macroscopic planar surfaces

Near-field radiation allows heat to propagate across a small vacuum gap at rates several orders of magnitude above that of far-field, blackbody radiation. Although heat transfer via near-field effects has been discussed for many years, experimental verification of this theory has been very limited. We have measured the heat transfer between two macroscopic sapphire plates, finding an increase in agreement with expectations from theory. These experiments, conducted near 300?K, have measured the heat transfer as a function of separation over mm to μm and as a function of temperature differences between 2.5 and 30?K. The experiments demonstrate that evanescence can be put to work to transfer heat from an object without actually touching it.     

Sound propagation in street canyons: comparison between diffusely and geometrically reflecting boundaries

This paper systematically compares the sound fields in street canyons with diffusely and geometrically reflecting boundaries. For diffuse boundaries, a radiosity-based theoretical/computer model has been developed. For geometrical boundaries, the image source method has been used. Computations using the models show that there are considerable differences between the sound fields resulting from the two kinds of boundaries. By replacing diffuse boundaries with geometrical boundaries, the sound attenuation along the length becomes significantly less; the RT30 is considerably longer; and the extra attenuation caused by air or vegetation absorption is reduced. There are also some similarities between the sound fields under the two boundary conditions. For example, in both cases the sound attenuation along the length with a given amount of absorption is the highest if the absorbers are arranged on one boundary and the lowest if they are evenly distributed on all boundaries. Overall, the results suggest that, from the viewpoint of urban noise reduction, it is better to design the street boundaries as diffusely reflective rather than acoustically smooth.     

A kinetic theory of diffusely reflecting Brownian particles

An analysis is made of the motion of a spherical Brownian particle whose surface can diffusely reflect the molecules of an equilibrium host gas. The analysis is based on Newton's second law and a limiting form of Markov's method. It is shown, both for specular and diffuse reflections, that equipartition of energy is a consequence of the dynamics and randomness of the motion. In addition, it is demonstrated that the diffusion coefficient can depend on the temperature of the particle. The entire analysis is restricted to the case for which the Knudsen number of the particle is large compared to unity.Slinn's work was supported in part by Battelle Memorial Institute and in part by the U.S. Atomic Energy Commission contract AT(45–1)-1830. Shen's work was supported in part by the U.S. Air Force Office of Scientific Research contract 49(638)–1346. Mazo's work was supported in part by the National Science Foundation, NSF Grant GP–8497.     

Application of multidimensional scheme and the discrete ordinate method to radiative heat transfer in a two-dimensional enclosure with diffusely emitting and reflecting boundary walls

Radiative heat transfer is the dominant mode of heat transfer in many engineering problems, including combustion chambers, space, greenhouses, rocket plume sensing, among others. The aim of this study is to develop an efficient method capable of eliminating ray effects in complex 2D situations and to use the developed code for other problems including combined conduction and convection in connection with CFD codes. A complete genuinely multidimensional discretization in two-dimensional discrete ordinates method is formulated to solve radiative heat transfer in a rectangular enclosure composed of diffusely emitting and reflecting boundaries and containing homogeneous media that absorbs, emits and scatters radiation. A new genuinely multidimensional differencing scheme is used to solve the radiative transfer equation with S₄, S₆, S₈, T₆, T₇, T₈ and T₉ angular quadrature schemes. Different cases are analyzed and the results are compared when possible with those obtained by others researchers.     

Deformation measurements of specularly reflecting objects using holographic interferometry with diffuse illumination

It is demonstrated that, by using diffuse object illumination, deformation measurements with holographic interferometry can be performed on a specularly reflecting object without the use of any additional coating of the object surface. An analytical expression for the secondary fringe formation is found, and the system is demonstrated only to be sensitive to deformations along the surface normal. A method for carrying out topographic measurements on specularly reflecting surfaces is suggested. The fringe visibility is studied for a rigid rotation of the object by using matrix methods. It is found that maximum fringe visibility is obtained if the recording camera is focused on the surface of the object.     

The absorptivity of a specularly reflecting cone for oblique angles of view

The absorptivity of a specularly-reflecting conical cavity is a function only of the number of reflections, n, undergone by an incident ray before it is reflected out again. A simple general expression for n is derived which applies to oblique incident rays as well as paraxial rays. It is shown that as the point at which the incident ray first strikes the conical surface moves from the rim towards the apex. a point is reached beyond which n increases by one.     

Flow and heat transfer characteristics over rectangular blocked surfaces

Heat transfer and flow measurements were recorded over blocked surfaces to investigate the effects of flow velocity and block shape on flow separation and heat transfer. The results indicated that the flow separation occurred particularly on the first block and after the last blocks. The flow separation and block thickness resulted in higher turbulence and heat transfer, particularly in laminar flow. The average Stanton number increased as high as 125% in laminar, 80% in transitional, and 50% in turbulent flows above those of flat plate values. A new empirical equation indicated a good agreement with the experimental and numerical results.     

Neutralization of specularly reflecting ions on a clean (001) surface of SnTe

Neutral fractions of specularly reflected beams have been measured for the glancing-angle incidence of (0.2-0.5) MeV ions on a clean (001) surface of SnTe. The measured fractions have been compared with the results calculated by a classical model for charge exchanges and by a model based on the first-order perturbation theory. The experimental and calculated results have differed greatly. The disagreements are attributed to collisions with valence electrons on the surface. The electron capture cross-sections of (0.2-0.5) MeV ions for valence electrons have been derived, based on the measured neutral fraction and distribution of valence electrons for jellium background positive charges, and are found to be about ten times larger than those for the outermost electrons of Sn and Te atoms calculated by the classical model. Received: 23 October 1998     

Enhanced static evaporation heat transfer surfaces for compact two-phase heat exchangers

In the frame of the JOULE 1 R&D programme of the Commission of the European Communities this project has been carried out on enhanced evaporation heat transfer surfaces. The main goal of the project was to develop and investigate enhanced evaporation heat transfer surfaces for industrial compact two-phase heat exchangers. Planar and tubular surfaces have been investigated by IKE (structured planar and tubular surfaces), GRETh (covered planar surfaces) and NEL (covered tubular surfaces).     

Radiation heat transfer in axisymmetric quartz glass tubes

A mathematical model is proposed to describe the heat transfer in quartz glass axisymmetric tubes. Heat is transferred inside the glass by radiation and conduction. Scattering of thermal radiation inside the glass is ignored. At the boundaries of the tube the radiative intensity is specularly reflected. The spectral dependent radiative intensity and the temperature distribution inside the tube are determined. The model is applied to simulate the cooling process of a quartz glass tube. The calculated temperature is in agreement with that obtained from an experiment. Furthermore, steady-state temperature distributions in quartz glass tubes of different lengths have been determined.     

Near-field radiative heat transfer between two plane surfaces with one having a dielectric coating

The effect of a dielectric coating on the near-field radiative heat transfer between two plane surfaces is numerically studied in the framework of the fluctuational electrodynamics. The dielectric coating is assumed to be a SiC or SiO₂ film, which is on top of the emitter. The results show that the near-field radiative flux between the plane surfaces can be either diminished or enhanced by the dielectric coating, depending on the thermal radiative properties of the emitter and the receiver. Furthermore, the dielectric coating effect on the near-field radiative flux can be very different from that on the far-field radiative flux. Detailed analysis on the variations of the TE- and TM-wave components of the radiative flux by adding the dielectric coating is provided, along with the physical mechanisms that account for these changes. Dielectric coatings such as SiC and SiO₂ films are widely seen in microelectronic structures and nanofabrication devices. The results obtained in this work should be valuable for further study and nanotechnological applications of near-field radiative heat transfer.     

Effect of reflecting modes on combined heat transfer within an anisotropic scattering slab

Under various interface reflecting modes, different transient thermal responses will occur in the media. Combined radiative-conductive heat transfer is investigated within a participating, anisotropic scattering gray planar slab. The two interfaces of the slab are considered to be diffuse and semitransparent. Using the ray tracing method, an anisotropic scattering radiative transfer model for diffuse reflection at boundaries is set up, and with the help of direct radiative transfer coefficients, corresponding radiative transfer coefficients (RTCs) are deduced. RTCs are used to calculate the radiative source term in energy equation. Transient energy equation is solved by the full implicit control-volume method under the external radiative-convective boundary conditions. The influences of two reflecting modes including both specular reflection and diffuse reflection on transient temperature fields and steady heat flux are examined. According to numerical results obtained in this paper, it is found that there exits great difference in thermal behavior between slabs with diffuse interfaces and that with specular interfaces for slabs with big refractive index.     

Heat transfer expansion on outer surfaces of heat pipes

Some peculiarities of production technology for finned surfaces on round and flat heat pipes for heat exchangers are considered in the present paper. A comparison of different types of finned tubes is presented. The experimental investigation agrees with the data of the analysis.     

Contact heat transfer between dissimilar materials

The exact solution of the thermoelasticity problem obtained by the authors for a cylinder, one of whose end surfaces is heated while the other is cooled, is used for the first time to quantitatively describe the influence of the magnitude and direction of the heat flux on the contact thermal resistance. It is shown that appreciable macrowaviness of the original flat contacting surfaces can appear as a result of thermal expansion of the contacting samples when heat flows through the contact. Reversing the direction of the heat flux causes changes in the shape of the macrowaviness and in the contact thermal resistance. Zh. Tekh. Fiz. 67, 1–6 (February 1997)     

Relaxation of sound fields in rooms of diffusely reflecting boundaries and its application in acoustical radiosity simulation

The acoustical radiosity method is a computationally expensive acoustical simulation algorithm that assumes an enclosure with ideal diffuse reflecting boundaries. Miles observed that for such an enclosure, the sound energy decay of every point on the boundaries will gradually converge to exponential manner with a uniform decay rate. Therefore, the ratio of radiosity between every pair of points on the boundaries will converge to a constant, and the radiosity across the boundaries will approach a fixed distribution during the sound decay process, where radiosity is defined as the acoustic power per unit area leaving (or being received by) a point on a boundary. We call this phenomenon the "relaxation" of the sound field. In this paper, we study the relaxation in rooms of different shapes with different boundary absorptions. Criteria based on the relaxation of the sound field are proposed to terminate the costly and unnecessary radiosity computation in the later phase, which can then be replaced by a fast regression step to speed up the acoustical radiosity simulation.     

Transient coupled heat transfer in a rectangular medium with black surfaces

The main objective of this paper is to extend to two-dimensional (2-D) medium the ray tracing-node analyzing method, which has already been successfully used to solve one-dimensional (1-D) problem of coupled heat transfer in a semitransparent medium. For simplicity, an infinitely long rectangular semitransparent medium with four black opaque surfaces is chosen as our studying object. A control volume method in the implicit scheme is adopted for discretizing the partial transient energy equation. In combination with spectral band model, the radiative heat source term is calculated using the radiative transfer coefficients (RTCs), which are deduced by the ray tracing method. The Partankar's linearization method is used to linearize the radiative source term and the opaque boundary condition, and the linearized equations are solved by the ADI method. Effects of absorption coefficient, refractive index and conductivity on transient cooling process in the 2-D gray rectangular medium are investigated under the condition that the radiation and convection processes cool one side of the rectangular medium while heat the remaining three sides.