Hot-wire Heating Research Articles

各種ワイヤを用いたホットワイヤ適正加熱電流値の導出 -高出力半導体レーザとホットワイヤとを組み合わせた高能率AM 技術の開発(第3報)-

各種ワイヤを用いたホットワイヤ適正加熱電流値の導出 -高出力半導体レーザとホットワイヤとを組み合わせた高能率AM 技術の開発(第3報)-

Statistical analysis of pulsed laser beam welding repair strategies of nickel-base superalloys

Pulse shaping is a suitable option to adapt energy input and temperature gradients in the base material during filler wire assisted laser beam welding, although the influence on the temperature-depended microstructure and γ’-precipitation strengthening of Nickel-base superalloys as well as the process windows are not sufficiently understood so far. Therefore, the influence of pulse parameters, preheating temperature, hot-wire heating power and wire feeding rate on the deposition process and the resulting macro- and microstructure of similar Nickel-base superalloy joints of Inconel 738 low carbon (IN 738 LC) with Haynes (HS 282) filler are investigated. The statistical analysis of the multidimensional parameter space with respect to the geometric properties of the weld seams (dilution, aspect ratio and wetting angle) and hot-crack formation revealed high reliability and predictability concerning individual choice of suitable parameters in field repair application.

Complex 1D-spatio-temporal behaviour generated by hot-wire heating below an interface

The existence of complex 1D-spatio-temporal behaviour generated by hot-wire heating below an interface is reported. This complex behaviour is associated with wave propagation on the liquid interface, with spatial domains isolated by defects (sources and sinks). It is believed that these experiments, after implementing some modifications, should allow the observation of genuine 1D-spatio-temporal chaos.

Instabilities produced by hot-wire heating below a free surface with emphasis on relationships between temporal and spatial dynamics

Bifurcations up to the appearance of temporal chaos are observed when hot-wire heats below a free surface. New obwrvations are reported, and some emphasis is laid on the relationships between temporal dynamics produced by signal~ averaged along the hot-wire and spatial behaviour of waves generated above it.

A numerical study of the effect of Coriolis force on the fluid flow and heat transfer due to wire heating on centrifuge

The effects of the Coriolis force on a flow field, and on temperature increase during transient hot-wire heating, were studied by three-dimensional and time-dependent calculation as compared to the experimental result. We have found that the Coriolis force drastically changes the flow field as well as the heat transfer tendencies of mercury on a centrifuge. The origin of these changes is that the Coriolis force reduces the component of velocity parallel to the effective gravity, and increases the radial and azimuthal components normal to the direction of the effective gravity on the centrifuge. The order of the effect of the Coriolis force depends on the configuration and the characteristic length of the specimen.

Simultaneous estimation of thermophysical properties by periodic hot-wire heating method

A new unsteady heat flux method is proposed to measure thermal conductivity and diffusivity simultaneously, the principle based on an analytical solution for an infinite hollow cylindrical system with a periodic heat source in the center. Thermal conductivity and diffusivity are determined from the amplitude and phase lag of the temperature response within the cylinder. The method also makes it easy to measure the temperature dependency of thermal properties during a continous heating process. The measurement errors caused by the finite specimen size and the displacement of the thermocouple location are estimated numerically to confirm the accuracy of the measurement method. Effective thermal conductivity and diffusivity for the packed beds of aluminum oxide particles and potassium perchlorate particles are measured. The thermophysical properties measured by this method agree well with those measured by conventional methods such as the hot-wire, periodic heating, and continuous heating methods.

Oscillatory Instabilities Produced by Laser or Hot-Wire Heating Below an Interface

A review concerning oscillatory instabilities produced by laser (thermal lens oscillations, optical heartbeats) or hot- wire heating below an interface is given. The dynamical states and bifurcations observed in thermal lensing are described. For the hot-wire experiments, critical quantities for the onset of overstability (Hopf bifurcation) are given and discussed. Three theoretical approaches are developed in order to understand these instability phenomena and recover experimental results : numerical analysis, examination of possible analogies with simpler systems and design of very simple models. The systems under discussion indicate a new candidate for systematic studies in the framework of nonlinear dissipative dynamical systems.

Examination of an analogy toward the understanding of thermal lens oscillations

The overstability for surface tension and coupled buoyancy-driven instability in a horizontal liquid layer, with very general conditions, is studied. A linear formulation to compute the critical quantities is established. Numerical results are given and compared with experiments in which a free surface is heated by a controlled hot-wire located near and below it. When correctly presented in terms of well-chosen reduced quantities, theoretical and experimental results agree very well, showing that there is an analogy between the theoretical problem (horizontal liquid layer, basic conductive state) and the experimental situation (hot-wire heating, basic convective state). Disagreements are pointed out to stress the limitations of the analogy. The original motivation of the work is the understanding of thermal lens oscillations produced when heating below the free surface is carried out using a laser beam.

An Apparatus for Removing Tropical Rat Mites from Large Quantities of Bedding Materials

For certain experiments involving the use of the tropical rat mite, Liponyssus bacoti, as vector of the cotton rat filaria, Litomosoides carinii, it has been necessery to make rapidly available several thousand adult mites from a single source. A method for producing the required number of mites by raising them on a white rat or a cotton rat in a metal tank containing wood shavings and hay has already been described (Scott, Stembridge, and Sisley, 1947). The apparatus shown in Fig. 1 has been constructed for the purpose of extracting within a single working day this large number of adult mites and the even larger number of accompanying nymphs from approximately 4000 cc of wood shavings and an equal volume of hay. The principal on which the apparatus is based is that used by Bertram (1946) in an apparatus for removing mites from small quantities of sawdust, namely that of driving the mites ahead of a wave of heat. Because of the problem of condensation of moisture the closed system of Bertram was replaced by an open trough of galvanized sheet iron surrounded by a moat containing water. Instead of a hot wire heating element there was substituted an infra red bulb of 250 watts, the back of which is reflector coated. This bulb is mounted on a carriage containing two pulleys which run on a wood track at a sufficient height above the trough to cause the principal heating area to slightly more than cover the width of the trough. The motive power is provided by a small electric motor turning a glass tube. A heavy cotton cord from the lamp carriage is wound twice around this tube, then passed through a pulley and attached to a weight. The length of the cord is adjusted so that the weight will rest on the floor just before the lamp reaches the end of the tank, relieving the tension and allowing the cord to slip. Thus if the operator is absent there will be no damage to the mechanism and any mites remaining at the end of the trough will not be killed by excessive application of heat. The lamp moves at the rate of ? inch per hour and will heat a 1 inch layer of sawdust or a 4-inch layer of loose hay. It was found that by the time mites stranded on the end of a piece of hay were forced to drop off, the metal bottom was so hot that they were killed. The bottom of the trough was therefore lined with a ?-inch sheet of hard asbestos-cement composition board to delay conduction of heat along the bottom. An auxiliary hot wire heater can be hung from the lamp carriage beneath the trough and just behind the center of the lamp so as to heat a thicker layer of sawdust from beneath. When the mites are not too numerous they can be removed from the inner top edge of the trough by means of a suction bottle. One hole of the rubber stopper in this bottle is covered with bolting silk and attached by rubber and glass tubes to a suction pump, while the other hole is provided with a tapered and bent glass tube into which the mites are sucked. Some mites will fall into the water and can be