A Parametric Study of the Quasi-Steady State Temperature Field by a Moving Heat Source for Surface Treating

2000 ◽  
Author(s):  
Nicola Bianco ◽  
Oronzio Manca
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Heat Source ◽  
Peclet Number ◽  
Three Dimensional ◽  
Laser Source ◽  
Quasi Steady State ◽  
Péclet Number ◽  
Spot Center ◽  
Laser Heat Source

Abstract A three dimensional numerical analysis of a solid irradiated by a moving laser heat source in a quasi-steady state is carried out. The thermophysical properties of the material are considered to be temperature dependent. The dependence of the solution on the radiative and convective heat losses, the latter due to an impinging jet on the upper surface, is highlighted; the dependence of the temperature distribution on the Reynolds number of the jet is also presented. Different thicknesses and widths are shown to have discrepant influences on the induced thermal fields for a Gaussian laser source. The parametric analysis shows the thermal profiles to be strongly dependent on the jet Reynolds number. The thermal field is almost symmetric with respect to the spot center for a Peclet number equal to 0.1. The thermal penetration decreases as the Peclet number increases.

Approximate analysis of the containment of contaminated sites prior to remediation

2000 ◽  
Vol 42 (1-2) ◽  
pp. 319-324 ◽  
Author(s):  
H. Rubin ◽  
A. Rabideau
Keyword(s):  
Steady State ◽  
Peclet Number ◽  
Dimensionless Parameter ◽  
Contaminated Sites ◽  
Unsteady State ◽  
Péclet Number ◽  
Vertical Barrier ◽  
Time Period ◽  
Barrier Performance ◽  
Vertical Barriers

This study presents an approximate analytical model, which can be useful for the prediction and requirement of vertical barrier efficiencies. A previous study by the authors has indicated that a single dimensionless parameter determines the performance of a vertical barrier. This parameter is termed the barrier Peclet number. The evaluation of barrier performance concerns operation under steady state conditions, as well as estimates of unsteady state conditions and calculation of the time period requires arriving at steady state conditions. This study refers to high values of the barrier Peclet number. The modeling approach refers to the development of several types of boundary layers. Comparisons were made between simulation results of the present study and some analytical and numerical results. These comparisons indicate that the models developed in this study could be useful in the design and prediction of the performance of vertical barriers operating under conditions of high values of the barrier Peclet number.

Laser Lock-In Thermography for Fatigue Crack Detection

2013 ◽  
Vol 558 ◽  
pp. 76-83 ◽  
Author(s):  
Yun Kyu An ◽  
Ji Min Kim ◽  
Hoon Sohn
Keyword(s):  
Fatigue Crack ◽  
Heat Source ◽  
High Power ◽  
Crack Detection ◽  
Laser Source ◽  
Cw Laser ◽  
Laser Heat ◽  
Laser Heat Source ◽  
Fatigue Crack Detection ◽  
Lock In

This study proposes a new nondestructive evaluation methodology named laser lock-in thermography (LLT) for fatigue crack detection. LLT utilizes a high power continuous wave (CW) laser as a heat generation source for lock-in thermography instead of commonly used flash and halogen lamps. The advantages of the proposed LLT method are that (1) the laser heat source can be positioned at an extended distance from a target structure thank to the directionality and low energy loss of the laser source, (2) thermal image degradation due to surrounding temperature disturbances can be minimized because of high temperature gradient generated by the laser source and (3) a large target surface can be inspected using a scanning laser heat source. The developed LLT system is composed of a modulated high power CW laser, galvanometer and infrared camera. Then, a holder exponent-based data processing algorithm is proposed for intuitive damage evaluation. The developed LLT is employed to detect a micro fatigue crack in a metal plate. The test result confirms that 5 μm (or smaller) fatigue crack in a dog-bone shape aluminum plate with a dimension of 400 x 140 x 3 mm3 can be detected.

Numerical Analysis of Heat Transfer Enhancement in a Micro-Channel Due to Mechanical Stirrers

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
M. Sreejith ◽  
S. Chetan ◽  
S. N. Khaderi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Peclet Number ◽  
Periodic Case ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Fluidic Channel ◽  
Enhancement Of Heat Transfer ◽  
Péclet Number

Abstract Using two-dimensional numerical simulations of the momentum, mass, and energy conservation equations, we investigate the enhancement of heat transfer in a rectangular micro-fluidic channel. The fluid inside the channel is assumed to be stationary initially and actuated by the motion imparted by mechanical stirrers, which are attached to the bottom of the channel. Based on the direction of the oscillation of the stirrers, the boundary conditions can be classified as either no-slip (when the oscillation is perpendicular to the length of the channel) or periodic (when the oscillation is along the length of the channel). The heat transfer enhancement due to the motion of the stirrers (with respect to the stationary stirrer situation) is analyzed in terms of the Reynolds number (ranging from 0.7 to 1000) and the Peclet number (ranging from 10 to 100). We find that the heat transfer first increases and then decreases with an increase in the Reynolds number for any given Peclet number. The heat transferred is maximum at a Reynolds number of 20 for the no-slip case and at a Reynolds number of 40 for the periodic case. For a given Peclet and Reynolds number, the heat flux for the periodic case is always larger than the no-slip case. We explain the reason for these trends using time-averaged flow velocity profiles induced by the oscillation of the mechanical stirrers.

Steady Temperature in a Rotating Cylinder Subject to Surface Heating and Convective Cooling

1984 ◽  
Vol 106 (1) ◽  
pp. 120-126 ◽  
Author(s):  
B. Gecim ◽  
W. O. Winer
Keyword(s):  
Heat Source ◽  
Peclet Number ◽  
High Speed ◽  
Integral Transform ◽  
The Body ◽  
Cooling Zone ◽  
Dimensionless Numbers ◽  
Péclet Number ◽  
Heating And Cooling ◽  
Simultaneous Heating

This study utilizes an integral transform technique in order to solve the heat conduction equation in cylindrical coordinates. The major assumption is the high speed (i.e., large Peclet number) assumption. The boundary value problem is governed by the parabolic form of the heat equation representing the quasi-stationary state. The boundary conditions are a combination of Neumann and mixed type due to simultaneous heating and cooling on the surface of the cylinder. The surface temperature reaches a peak value over the heat source and gradually decreases to a nearly constant level over the cooling zone. Thermal penetration in the radial direction is shown to be only a few percent of the radius, leaving the bulk of the body at a uniform temperature. The width of the heat source and the total heat input are shown to be effective on the level of temperature whereas the input distribution is shown to be unimportant. The dimensionless numbers involved are the Biot and the Peclet numbers where the solution is governed by the ratio of the Biot number to the square root of the Peclet number.

Passive scalar statistics in high-Péclet-number grid turbulence

1998 ◽  
Vol 358 ◽  
pp. 135-175 ◽  
Author(s):  
L. MYDLARSKI ◽  
Z. WARHAFT
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Peclet Number ◽  
Passive Scalar ◽  
Structure Functions ◽  
Order Structure ◽  
Grid Turbulence ◽  
Temperature Derivative ◽  
Péclet Number ◽  
Transverse Temperature

The statistics of a turbulent passive scalar (temperature) and their Reynolds number dependence are studied in decaying grid turbulence for the Taylor-microscale Reynolds number, Rλ, varying from 30 to 731 (21[les ]Peλ[les ]512). A principal objective is, using a single (and simple) flow, to bridge the gap between the existing passive grid-generated low-Péclet-number laboratory experiments and those done at high Péclet number in the atmosphere and oceans. The turbulence is generated by means of an active grid and the passive temperature fluctuations are generated by a mean transverse temperature gradient, formed at the entrance to the wind tunnel plenum chamber by an array of differentially heated elements. A well-defined inertial–convective scaling range for the scalar with a slope, nθ, close to the Obukhov–Corrsin value of 5/3, is observed for all Reynolds numbers. This is in sharp contrast with the velocity field, in which a 5/3 slope is only approached at high Rλ. The Obukhov–Corrsin constant, Cθ, is estimated to be 0.45–0.55. Unlike the velocity spectrum, a bump occurs in the spectrum of the scalar at the dissipation scales, with increasing prominence as the Reynolds number is increased. A scaling range for the heat flux cospectrum was also observed, but with a slope around 2, less than the 7/3 expected from scaling theory. Transverse structure functions of temperature exist at the third and fifth orders, and, as for even-order structure functions, the width of their inertial subranges dilates with Reynolds number in a systematic way. As previously shown for shear flows, the existence of these odd-order structure functions is a violation of local isotropy for the scalar differences, as is the existence of non-zero values of the transverse temperature derivative skewness (of order unity) and hyperskewness (of order 100). The ratio of the temperature derivative standard deviation along and normal to the gradient is 1.2±0.1, and is independent of Reynolds number. The refined similarity hypothesis for the passive scalar was found to hold for all Rλ, which was not the case for the velocity field. The intermittency exponent for the scalar, μθ, was found to be 0.25±0.05 with a possible weak Rλ dependence, unlike the velocity field, where μ was a strong function of Reynolds number. New, higher-Reynolds-number results for the velocity field, which smoothly follow the trends of Mydlarski & Warhaft (1996), are also presented.

scholarly journals NUMERICAL AND HYDRAULIC EXPERIMENTS ON BORE PRESSURE DUE TO TSUNAMI

2018 ◽  
pp. 18
Author(s):  
Tatsuto Kimura ◽  
Masahiro Masuko ◽  
Naoki Fujii ◽  
Hideki Kaida ◽  
Naoto Kihara
Keyword(s):  
Steady State ◽  
Tsunami Wave ◽  
Three Dimensional ◽  
Tohoku Earthquake ◽  
Pressure Profile ◽  
Quasi Steady State ◽  
The 2011 Tohoku Earthquake ◽  
Wave Pressure ◽  
Pressure Profiles ◽  
State Regime

The 2011 Tohoku earthquake tsunami struck a wide area of the northeastern coast of Japan, and many coastal structures and buildings were damaged by the tsunami. Most of the buildings were damaged by the tsunami wave pressure. After the tsunami, characteristics of tsunami waive pressures have been investigated by many researcher, and are being clarified. As shown in previous studies, there are three regimes charactering the vertical pressure profiles. The first one is the impulsive pressure, which is observed just after the tsunami-bore impacted structures. In this regime, strong hydrodynamic pressures are generated by the fluid-solid impact process. After that, the bore pressure is observed, and both the hydrodynamic and hydrostatic pressures contribute the pressure profile. After that, the flow near the structures reaches a quasi-steady state, and the pressure profile becomes hydrostatic. Most of the evaluation equations of tsunami wave pressure proposed by the previous studies can be used against the impulsive pressures and the pressures in the quasi-steady-state regime. On the other hand, the characteristics and quantitative evaluations of the bore pressure remain immature. In this study, in order to clarify the characteristics of the bore pressure, experiments on the bore pressure are carried out, and furthermore, three-dimensional numerical simulations are also carried out.

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