Theoretical and experimental study of thermal conductance of wavy surfaces semiannual status report, nov. 1964 - jun. 1965

Contact area between two wavy rough surfaces and experimental determination of contact conductanc

Influence of surface roughness and waviness upon thermal contact resistance

This work deals with the phenomenon of thermal resistance between contacting solids. Attention is directed towards contiguous solids possessing both surface roughness and waviness. When two such surfaces are brought together under load, they actually touch at isolated microcontacts, and the resulting real area is the sum of these microcontacts. Because of the waviness the microcontacts are confined to a region called the contour area which may occupy some fraction of the total available area. The non-uniform pressure distribution over the contour area results in microcontacts which vary in size and density. In the absence of an interstitial fluid and negligible radiation heat transfer, all the heat crossing the interface must flow through the microcontacts. A thermal analysis, based on size and spatial distribution, results in a thermal resistance equation which differs from previously developed theories. The equation is verified by liquid analog tests which show that the size and spatial distribution are very significant.(cont.) A surface deformation analysis considers the influence of surface roughness upon the elastic deformation of a rough hemisphere. An equation is developed which shows the extent of the contour area as a function of the surface geometry, the material properties, and the applied load. The equation is compared with existing theories and qualitatively checked against experimental results. Experimental heat transfer data were obtained to verify the thermal and deformation theories. The agreement between theory and test is quite good over a large range of surface geometry and applied loads.Sponsored by the National Aeronautics and Space Administration DS

Laminar Flow Friction and Heat Transfer in Non- Circular Ducts and Channels Part II: Thermal Problem

A detailed review and analysis of the thermal characteristics of laminar developing and fully developed flow in non-circular ducts is presented. New models are proposed which simplify the prediction of Nusselt numbers for three fundamental flows: the combined entrance problem, the Graetz problem, and thermally fully developed flow in most non-circular duct geometries found in heat exchanger applications. By means of scaling analysis it is shown that the complete problem may be easily analyzed by combining the asymptotic results for short and long ducts. By means of a new characteristic length scale, the square root of cross-sectional area, the effect of duct shape has been reduced. The new model has an accuracy of ± 10 percent, or better, for most common duct shapes. Both singly and doubly connected ducts are considered

Thermal contact conductance in a vacuum

The object of this work is to develop analytically equations by which one could predict the thermal contact conductance between contiguous surfaces operating in a vacuum environment. In this work the solution to the problem is obtained by considering that any surface can be modelled as being either: 1) nominally-flat but rough, 2) a smooth surface having cylindrical waviness, 3) a smooth surface having spherical waviness, or 4) a surface having either cylindrical or spherical waviness plus roughness. Since the radiative heat transfer and the conduction through the interstitial fluid are negligible, the conduction of heat across the metal contact spots is the dominant mechanism. It is considered that the prediction of thermal contact conductance must be approached by: 1) examining the surface geometry, 2) proposing mathematical models for the solution of the heat transfer problem, 3) determining the surface parameters from deformation analysis, and 4) obtaining experimental data to substantiate the proposed models. The surface analysis is actually a critical examination of profiles of real surfaces as obtained by profilometers. From such profiles it is proposed that real surfaces can be idealized by assuming that any surface is a combination of a wavy and rough component. The thermal analysis is based upon the models proposed and the solutions for the steady-state condition are obtained for the various models and the appropriate boundary conditions. Certain surface parameters appear in the thermal contact conductance equations, which require that an analysis of the deformation of the surface under load be undertaken. The deformation analysis is separated into two regimes: 1) purely elastic and 2) purely plastic. The surface parameters are then determined as functions of the applied load for the proposed models under the restrictions of pure elastic or pure plastic deformation.Sponsored by the National Aeronautics and Space Administration DS

Models for Gaseous Slip Flow in Circular and Noncircular Microchannels,”

ABSTRACT Slip flow in noncircular microchannels has been examined and a simple model for normalized Poiseuille number is proposed to predict the friction factor and Reynolds number product fRe for slip flow. The developed model for normalized Poiseuille number has an accuracy of 4.2 percent for all common duct shapes. As for slip flow, no solutions or graphical and tabulated data exist for most geometries, the developed simple model can be used to predict friction factor, mass flow rate, and pressure distribution of slip flow in noncircular microchannels for the practical engineering design of microchannels such as rectangular, trapezoidal, doubletrapezoidal, triangular, rhombic, hexagonal, octagonal, elliptical, semielliptical, parabolic, circular sector, circular segment, annular sector, rectangular duct with unilateral elliptical or circular end, annular, and even comparatively complex doubly-connected microducts

Religion, politics and challenges of contemporary European identity

Yovanovich, H. N. M. Religion, politics and challenges of contemporary European identity / Yovanovich H. N. M. // Научный результат. Сер. Социология и управление. - 2020. - Т.6, №3.-С. 136-152. - Doi: 10.18413/2408-9338-2020-6-3-0-9. - Refer.: p. 149-152.The modern Europe (or more precisely - the European Union) builds its ideological matrix not on the foundations of its own Christian heritage, but on the foundations of agnostic secularism and liberalism, as inaugurated by the French Revolution, which places our topic in the domain of politology of religio

IMECE2005-79902 CONVECTIVE HEAT TRANSFER OF LAMINAR, SINGLE-PHASE FLOW IN RANDOMLY ROUGH MICROTUBES

Abstract Convective heat transfer of laminar, single-phase flow in rough microtubes is studied. Wall roughness and slope are assumed to possess Gaussian, isotropic distributions. Fractal concepts are used to model the rough microtube. It is shown that due to the existence of wall roughness, both cross-sectional and inside surface areas are increased. A new concept is defined as a figure of merit for assessing thermal performance of rough microtubes. As a result of increasing roughness, an enhancement is observed in the thermal performance of microtubes. The present model can be extended to analyze other geometries such as rectangular and trapezoidal microchannels. 1 Post-Doctoral Fellow. Mem. ASME. Corresponding author. Email: [email protected]. 2 Distinguished Professor Emeritus. Fellow ASME. 3 Associate Professor and Director of MHTL. Mem. ASME

IMECE2005-79902 CONVECTIVE HEAT TRANSFER OF LAMINAR, SINGLE-PHASE FLOW IN RANDOMLY ROUGH MICROTUBES

Abstract Convective heat transfer of laminar, single-phase flow in rough microtubes is studied. Wall roughness and slope are assumed to possess Gaussian, isotropic distributions. Fractal concepts are used to model the rough microtube. It is shown that due to the existence of wall roughness, both cross-sectional and inside surface areas are increased. A new concept is defined as a figure of merit for assessing thermal performance of rough microtubes. As a result of increasing roughness, an enhancement is observed in the thermal performance of microtubes. The present model can be extended to analyze other geometries such as rectangular and trapezoidal microchannels. 1 Post-Doctoral Fellow. Mem. ASME. Corresponding author. Email: [email protected]. 2 Distinguished Professor Emeritus. Fellow ASME. 3 Associate Professor and Director of MHTL. Mem. ASME