Intense Heat Source Research Articles

Heat transfer characteristics during melting of a metal spherical particle in its own liquid

There are manufacturing applications like surface modification and repair technologies where metal particles go into the superheated melt pool heated by an intense heat source and as the workpiece moves away from the energy source this pool solidifies to form a continuous built-up layer. In the present study two-dimensional axisymmetric Navier–Stokes and energy equations are solved using finite volume method to predict the time required for a metal sphere to melt in a melt pool of the same material. The effect of forced convection, characterised by Reynolds number, and superheat of the melt pool, characterised by Stefan number, has been studied in detail for material of different Prandtl numbers. Effect of buoyancy is neglected for the present investigation. It is found that the effect of convection on melting time is more pronounced if RePr/Ste 2/3 is high. The rate of melting of the metal sphere with time under different conditions is also presented. Finally, the heat transfer characteristic is represented by the correlation of Nusselt number with Reynolds number, Stefan number and Prandtl number.

Improvement of mechanical properties of gas tungsten arc and electron beam welded AA2219 (Al–6 wt-%Cu) alloy

Despite its excellent weldability characteristics, AA2219 suffers from poor fusion zone strength under the as welded condition. In the present work, it is attempted to increase the mechanical properties of the as welded fusion zone of this alloy by increasing the weld cooling rates and multipass welding. The cooling rate was increased with the use of high intense heat source, namely electron beam in a pulsed current mode. Multipass gas tungsten arc welding was carried out using direct current straight polarity. These techniques resulted in a significant improvement in fusion zone hardness and tensile properties, which is attributed to reduced copper segregation and natural aging as well as aging caused by heat of multipass welding.

A multifunctional heat pipe sandwich panel structure

A multifunctional sandwich panel combining efficient structural load support and thermal management characteristics has been designed and experimentally assessed. The concept is based upon a truncated, square honeycomb sandwich structure. In closed cell honeycomb structures, the transport of heat from one face to the other occurs by a combination of conduction through the webs and convection/radiation within the cells. Here, much more effective heat transport is achieved by multifunctionally utilizing the core as a heat pipe sandwich panel. Its interior consists of a 6061 aluminum truncated-square honeycomb core covered with a stochastic open-cell nickel foam wick. An electroless nickel plating barrier layer inhibited the chemical reaction between the deionized water working fluid and the aluminum structure, retarding the generation of non-condensable hydrogen gas. A thermodynamic model was used to guide the design of the heat pipe sandwich panel. We describe the results of a series of experiments that validate the operational principle of the multifunctional heat pipe sandwich panel and characterize its transient response to an intense localized heat source. The systems measured thermal response to a localized heat source agrees well with that predicted by a finite difference method model used to predict the thermal response.

Aerosol source plume physical characteristics from space‐based multiangle imaging

Models that assess aerosol effects on regional air quality and global climate parameterize aerosol sources in terms of amount, type, and injection height. The multiangle imaging spectroradiometer (MISR) aboard NASA’s Terra satellite retrieves total column aerosol optical thickness (AOT), and aerosol type over cloud‐free land and water. A stereo‐matching algorithm automatically retrieves reflecting‐layer altitude wherever clouds or aerosol plumes have discernable spatial contrast, with about 500‐m accuracy, at 1.1‐km horizontal resolution. Near‐source biomass burning smoke, volcanic effluent, and desert dust plumes are observed routinely, providing information about aerosol amount, particle type, and injection height useful for modeling applications. Compared to background aerosols, the plumes sampled have higher AOT, contain particles having expected differences in Angstrom exponent, size, single‐scattering albedo, and for volcanic plume and dust cloud cases, particle shape. As basic thermodynamics predicts, thin aerosol plumes lifted only by regional winds or less intense heat sources are confined to the boundary layer. However, when sources have sufficient buoyancy, the representative plumes studied tend to concentrate within discrete, high‐elevation layers of local stability; the aerosol is not uniformly distributed up to a peak altitude, as is sometimes assumed in modeling. MISR‐derived plume heights, along with meteorological profile data from other sources, make it possible to relate radiant energy flux observed by the moderate resolution imaging spectroradiometer (MODIS), also aboard the Terra spacecraft, to convective heat flux that plays a major role in buoyant plume dynamics. A MISR climatology of plume behavior based on these results is being developed.

Dynamic data‐driven finite element models for laser treatment of cancer

Elevating the temperature of cancerous cells is known to increase their susceptibility to subsequent radiation or chemotherapy treatments, and in the case in which a tumor exists as a well-defined region, higher intensity heat sources may be used to ablate the tissue. These facts are the basis for hyperthermia based cancer treatments. Of the many available modalities for delivering the heat source, the application of a laser heat source under the guidance of real-time treatment data has the potential to provide unprecedented control over the outcome of the treatment process [7, 18]. The goals of this work are to provide a precise mathematical framework for the real-time finite element solution of the problems of calibration, optimal heat source control, and goal-oriented error estimation applied to the equations of bioheat transfer and demonstrate that current finite element technology, parallel computer architecture, data transfer infrastructure, and thermal imaging modalities are capable of inducing a precise computer controlled temperature field within the biological domain.

Mathematical modeling of the process of warming up of a cylindrical surface by a moving intense heat source

A mathematical model of the process of warming up of a metal cylindrical surface by a moving point heat source has been proposed; the model allows for the presence of a thin absorbing coating on the metal surface and for the thermal resistance of the contact surface. An algorithm of calculation of a nonstationary temperature field has been constructed.; this algorithm makes it possible to find the values of the problem’s parameters ensuring local surface heating. An example of numerical calculation has been given.

Entropy generation analysis of turbulent transport in laser surface alloying process

A numerical formulation involving second law of thermodynamics is examined for analysis of three-dimensional surface tension driven turbulent transport during laser materials processing. A modified k–ϵ model is used to address turbulent melt pool convection in the presence of a continuously evolving phase change interface. Phase change aspects are addressed using a modified enthalpy–porosity technique. It is revealed that both energetic and exergetic efficiencies increase with increasing laser power, and remain insensitive to changes in powder feedrate over the range of parameters chosen. However, the energetic efficiency is found to increase with increasing laser scanning speed whereas the exergetic efficiency shows a reverse trend. Accordingly, a tradeoff in the laser scanning speed can be sought for while designing the process parameters, in order to ensure a maximum utilisation of the thermodynamic potential offered by the intense laser heat source.

Conditions leading to monsoon onset over Kerala and the associated Hadley cell

Monsoon onset over Kerala (MOK) is an important event in relation to the Asian Summer Monsoon and the global atmosphere and Ocean. It marks the beginning of an intense and large convective heat source north of the equator over the tropical Indian and west Pacific oceans and an intense low level jet stream that feeds moisture to the heat source, both having a life span of about 100 days from MOK. Using satellite data we are now able to monitor the slow evolution of this heat source which first forms near the equator over an area with large SST gradient (in the south-north direction) and slowly moves towards the warm pool over the southeast Arabian Sea.
 
 A Monsoon Hadley cell (MHC) is associated with this large convective heat source which is particularly strong over the south-east Arabian Sea at MOK. The ascending branch of the MHC is over this heat source and its descending branch is over the subtropical south Indian ocean. The low level branch of the MHC called V850 is a strong meridional southerly flow at 850 hPa crossing the equator between the longitudes 35° E and 55° E. The upper level branch V200 is a meridional northerly flow at 200 hPa over the south Indian ocean between longitudes 45° E and 75° E. The intensity of the MCH taken as (V850 -V200) is found to increase rapidly during the 10 day period prior to MOK.

ECRH at high heating power density in FTU tokamak

Plasma absorption at the fundamental EC resonance of e.m. waves at 140 GHz, 0.8 MW, Ordinary mode, provides in the FTU tokamak a localized (minimum δ r ≃2.5 cm) and intense (up to ≃100 MW/m 3) heat source for the electrons. It is shown that at high density (≃10 20 mγ− -3) ions are heated (Δ T i / T i =0.25) by collisional e−i energy transfer and assuming ion thermal diffusivity about three times larger (at most) than predictions in order to account for the observed T i . Off-center localization ( r abs/ a ≃0.2) of the ECRH heat source changes the electron temperature (and current density) profile in a way to fully stabilize sawteeth. On-axis absorption accelerates the sawtooth crash repetition rate if P ecrh⩽ P oh, but with P ecrh> P oh the sawtooth period is increased. A critical shear model for the sawtooth crash repetition rate is shown to be in agreement with its experimental dependence on resonance position and heating power. In discharges characterized by a flat temperature profile in the ohmic phase, ECRH may de-stabilize tearing modes of different order, with a strong degradation of core energy confinement.

Quasisteady thermal regime developing in periodic pulsed heating of cylindrical solid bodies

An oscillating component of the quasisteady cylindrical temperature field developing in the heating of solids by intense modulated heat sources is investigated.

Interannual Variability of the Onset of the Indian Summer Monsoon and Its Association with Atmospheric Features, El Niño, and Sea Surface Temperature Anomalies

Abstract The long-term mean date of the monsoon onset over Kerala (MOK) varies between 30 May and 2 June according to different estimates, with a standard deviation of 8–9 days. The earliest date of MOK, and the most delayed one, during the last 100 years differ by 46 days (7 May and 22 June, respectively). MOK switches on a spatially large and intense convective heat source over south Asia, lasting from June to September, whose moisture supply is made available through the cross-equatorial low-level jet stream. Superposed epoch analysis of 10 years of outgoing longwave radiation (OLR) data shows that MOK is a significant stage in the evolution of the OLR field in the tropics of the eastern hemisphere. At the time of MOK there is increased convection in a band about 5–10 degrees wide meridionally, extending from the south Arabian Sea to south China, and convection is suppressed all around, particularly in the western Pacific Ocean. In 1983 when MOK was delayed by about 3 pentads, OLR data showed that the ...

Large area diamond deposition in HFCVD technique employing convective flow of gases

Hot filament chemical vapour deposition technique is widely used for the synthesis of diamond at sub-atmospheric pressure. The normal procedure involves diffusional flow of the diamond precursor species and the atomic hydrogen, produced by the input gases at the heated filament. The active species are short lived and can therefore travel relatively small distances, in their lifetime, in an intrinsically slow diffusion controlled process. This restricts the distance between the filament and the substrate to ≲ 1 cm. In this communication, it is brought out that this shortcoming can be overcome, to a large extent, by using convective flow of gases. With minor modifications in the standard experimental set up, consisting of a single filament-jet assembly, it has been possible to deposit good quality diamond on zirconium substrate, placed at a distance ≈ 5 cms from the filament and over an area ≈ 7 cm 2. Besides deposition on larger area, this concept minimises the problems associated with the close proximity of an intense localized heat source to the substrate.

A survey of heat transfer phenomena in glass-to-metal seals

The present investigation through a survey of the literature aims to develop a basic understanding of the formation of glass-to-metal seals. The generic problem consists of a thin-walled cylindrical glass tube to be sealed on to a single or a pair of metallic conductors by a high intensity heat source employed in a suitably designed optical system to form a vacuum tight fusion seal. In the present investigation a generic form of the problem is considered and therefore the present synthesis will relate to applications outside the electronic industry.

Characteristics and Attributes of Char Forming Combustion Modified Flexible Foams Based on PHD Polyol

Combustion modified foams have been used in various applica tions for several years and they can be formulated to meet a variety of flam mability standards. Two general groups are commercially established: foams having margmal fire retardancy and foams having a high degree of resistance to ignition when exposed to high energy open flames such as two sheets of burning paper. The latter include melamine modified HR foams, which drip and develop molten polymer upon flame exposure, and the hydrate alumina modified HR foams that form a surface char upon flame exposure that protects the foam underneath against burning and reduces the rate of fire growth in fur nishings. Several types of latter foams have been developed, namely: high per formance COMBUSTION MODIFIED HIGH RESILIENCE (CMHR) foams that contain a sophisticated flame retardant system comprised of hydrated alumina and auxiliary flame retardants; MRC high resilience foams for medium risk category occupancies which also contain hydrated alumina and flame retardants; and ATH/HR that perform within the range bounded by Cali fornia 117 foams and CMHR foam—they are high resilience foams that contain only hydrated alumina and a liquid flame retardant. All of these are char formers-a very important attribute for fire safety in furnishings, transit vehicle seating, and other applications. Since all of the said char forming combustion modified foams based on PHD polyol contain organic materials, they are subject to decomposition and igni tion, and will sustain burning when exposed to a sufficiently intense heat source. Nevertheless, all of them represent a significant contribution to im proved fire safety in the end applications. Combustibility tests were conducted using specified controlled tests to measure the performance behavior of the material under these conditions. The data are not intended to reflect the hazards of this or any other material under actual fire conditions. This paper emphasizes the importance of char forming characteristics of foam in fire performance.

Determination of temperature distribution in laser welded heat exchangers with the aid of finite element methods

The determination of the thermal histories in a tube-plate combination when welded with a high intensity heat source is discussed in this paper. The influence of the geometry of the plate and the use of nitrogen gas during the welding process on the thermal histories is shown. With the thermal histories known, the distortion due to thermal stresses could be determined.

Rock failure mechanisms of flame-jet thermal spallation drilling—theory and experimental testing

Certain polycrystalline rocks will fracture into thin, disk-like fragments when exposed to rapid surface heating. Several current hard-rock drilling methods using supersonic flame-jets as heat sources exploit this behaviour for efficient granite quarrying or blasthole formation. The recent application of Weibull's theory of rock failure to quantitatively analyze rock spallation has been extended to allow prediction of chip size distributions and rock surface temperatures at spallation under any intense heat source. Therefore, with measured values of the Weibull distribution parameters, surface spallation temperatures can be estimated theoretically. However, finite-element analysis for intergranular stresses developed during transient heating prior to spall formation indicates that additional microcrack initiation will be favoured thereby altering Weibull parameters measured at room temperature. Nonetheless, experimentally observed spallation characteristics of Barre and Westerly granites are consistent with theory when mechanically determined Weibull parameters are substituted. Spallation temperatures induced by flame-jet heating were estimated to be below 520°C. In all cases, quartz or other mineral solid phase transitions are not expected at these conditions. Laser-induced spallation experiments were less successful, partially because extremely localized heating delivered by the beam greatly complicated the subsequent thermal stress analysis.

1979年における中国の梅雨前線付近の下層循環系の季節遷移と北半球夏モンスーン

The seasonal transition of the characteristics of the lower-level circulation systems around the Baiu front in China from spring to summer and their relation to the Northern Summer Monsoon are examined by using the observational data of 1979.The Baiu front in May (stage (A)) is the system within the baroclinic zone in middle latitudes. The surface high pressure belt with cooler air and large divergence is located just to the north of it and the subtropical high at the surface level to the south of the Baiu front is not so clearly found.The subtropical high with a strong lower-level southerly wind toward the Baiuu front around China was enhanced abruptly in the middle of June, nearly simultaneously with the onset of the Northern Summer Monsoon (the beginning of stage (C)). In stage (C) the low OLR area (intense heat source area) expands widely in South Asia (EQ-25°N/60°E-105°E). The pressure in the lower layer decreases there, which results in the geostrophic enhancement of the southerly wind in the subtropical high area around 120°E by producing the eastward pressure gradient. At the same time the belt-shaped low OLR area extending from India to Western Pacific region (-10°N/60°E-140°E) is formed, which intensifies the local Hadley cell with strong lower-level divergence around 20°N as its northern branch.It is concluded that the change in the lower-level wind structure of the subtropical high to the south of the Baiu front in the middle of June is due to the superposed effect of the two characteristics of the heat source distribution associated with the Northern Summer Monsoon. The additional analysis by using the pentad mean data from 1979 to 1983 supports this conclusion.

Melting of copper by an intense and pulsed heat source

The one-dimensional Stefan problem of heat conduction is solved including evaporation cooling i.e. for conditions similar to those occurring in vacuum arcs, when the current constricts. For high values of heating power density a quasi-stationary state is found, i.e. when the melting depth does no longer increase despite further heating. The dependence of this maximum on the heating power density and duration is discussed for copper.

LASEM — a novel combined device for laser modification in SEM

AbstractAn intense localized heat source inside a microscope could be useful in the improvement of electron microscopic in‐situ investigations. For this reason a JEOL scanning electron microscope was combined with a pulsed Nd‐glass laser which allowed power densities up to about 109 W/cm2 on the specimen under Q‐switch conditions. The mechanical and electrical adaptations necessary for the SEM‐to‐laser coupling, as well as some tests of the method involving the new equipment are discussed in detail in this paper. Various applications to materials are reviewed, including melting processes, thermal cracking and surface hardening of tungsten carbide alloys and other hard materials.

The Large-Scale Circulation and Heat Sources over the Tibetan Plateau and Surrounding Areas during the Early Summer of 1979. Part II: Heat and Moisture Budgets

Abstract The large-scale heat and moisture budgets over the Tibetan Plateau and surrounding area during a 40-day period from late May to early July 1979 are studied using the FGGE Level II-b data. During this period the general circulation over East Asia underwent a distinct seasonal change characterizing the onset of the summer monsoon circulation. The analyses of the horizontal distributions of the vertically integrated heat source and moisture sink reveal the major heat source regions and their different degrees of association with precipitation. The 40-day mean distributions show intense heat sources of 150–300 W m−2 with moisture sinks of nearly equal magnitude over the Assam–Bengal region and in a broad belt extending over the China Plain along the Mei-yu front. The heat source of ∼100–150 W m−21 over the eastern Tibetan Plateau is accompanied by a moisture sink with a magnitude about half as large. The heat sources over the western Plateau and the Takla Makan Desert are not accompanied by appreciab...