Thermal Diffusivity Of Metals Research Articles

Is it Time to Demolish Current Mathematics?

Current mathematics in 3D geometric space plus real time t as an external control is incomplete and misleading. The dream of theoretical physicists and mathematicians to demolish all current mathematics and replace it with a single universal numerical statistical law in 4D is now within reach. In this paper, we first focus on the introduction and definition of the proposed unitary 4D space. Next, we introduce and explain what we call the modern Laplacian theorem in 4D unit space. Finally, we explain some unexpected and striking numerical results such as measuring the speed of sound in air at 330 m/s and that of light at 3 E8 m/s. There is an inherent relationship between the speed of sound in air and the diffusivity of sound waves in the sound room, similar to the relationship between the speed of light in a vacuum and the thermal diffusivity of metals when they all live two in a 4D unit. space.

Machining of sub-cooled low carbon tool steel by wire-EDM

ABSTRACTAISI P20 tool steel is a low-carbon steel which is widely used in plastic-molds, die holders, bolsters, backers, shaft and rail making industries. It undergoes metallurgical and microstructural changes when conventionally heat treated with sub-cooling. As Wire-Electro Discharge Machine (WEDM) has become an integral part of finishing most products, this paper gives the influence of sub-cooling of workpiece on its machinability. It also presents the effects of discharge current (I), Pulse on time (Ton), flushing pressure (Fp), wire speed (Ws) and wire tension (Wt) on individual machining response. Sub-cooled metal (SCM) is having more cutting speed (CS) and material removal rate (MRR), and less kerf width (KW), surface roughness (SR) and micro-hardness as compared to parent metal (PM), as both the electrical and thermal conductivities increases with full annealing followed by sub-cooling of metal which affects the thermal diffusivity of metal. It is observed that the machined surface of the SCM is having more spherical globules and smaller melted deposits as compared to that of PM. This is due to the difference in thermal and electrical conductivities, and driving energy with respect to the presence of different phases at the surface.

Entropy generation analysis on a heat exchanger with different design and operation factors during transient processes

Entropy generation analyses on the transient processes of heat exchangers can guide their designs and operations. A dynamic model of a typical recuperative heater is developed based on mass, energy, and momentum conservation equations. Dynamic behaviors of the heater during transient processes are analyzed based on the second law of thermodynamics. The real-time entropy generation rate due to the heat transfer between the work medium and metal surfaces, and the heat conduction in metals are presented and discussed. A cold fluid flow rate with 20% step increase is adopted as the boundary disturbance, and dynamic performances are obtained. Additional entropy is generated in the heater during the transient processes compared with stationary work conditions. Several design and operation factors of the heater are discussed. Calculation results show that the additional total entropy generation diminishes during the transient processes with the increase in the thermal diffusivity of metal. This rule is also suitable for the influence of thermal transfer resistance between the fluid and metal. By contrast, the metal thickness and specific heat capacity of hot work fluid have opposite influences on the total additional entropy generation of the heater during the transient processes.

Thermal diffusivity of metals determined by lock-in thermography

Lock-in infrared thermography is a well-established technique for measuring the thermal diffusivity of materials. A commonly-used method is to analyse the spread of a thermal wave along the surface of a thin sample or a filament, known as the slope method. In this work, an alternative technique is proposed, in which the phase delay of the thermal wave passing through sheets made of different metals is analysed using periodical laser heating. Different lock-in frequencies are used to obtain the frequency-dependent phase behaviour of thermal waves generated by the laser pulses. A subsequent curve fitting provides the coefficients required to determine the thermal diffusivity. To achieve a comparison with ambient conditions, the measurements are also performed in vacuum. A comparison with literature data substantiates that the proposed method is a robust approach for the determination of the thermal diffusivity in applications where the sample thickness exceeds the limits of the slope method.

Measurements of thermal diffusivity of spherical samples. Fe-Sn system

An experimental setup is described, which enables one to measure the thermal diffusivity of metals and alloys by the pulse method for spherical samples. Results are given of the investigation of thermal diffusivity of Fe-Sn alloy in the neighborhood of the solid st ate-liquid state transition; also give are X-ray electron spectra of valence bands of the Fe-S n system with different tin content.

Thermal wave methods in investigation of thermal properties of solids

A short review of thermal wave measuring methods is presented in the paper. Based on fundamental laws of heat transport, experimental methods for determination of thermal properties of solids are divided into two groups – steady flux techniques and variable flux ones. Special attention is paid to the wave methods belonging to the second group and methods used by the author in his experiments. The idea of Angstrom's method for determination of the thermal diffusivity of metals is reminded. Then different modifications of this classical technique using in investigations of bulk materials and thin films are described. Examples of a few thermal wave measurements are also presented.

Applicability of subpicosecond pulse lasers to determining thermal diffusivity of metals

The transient reflectivity change due to subpicosecond laser-pulse heating is measured for aluminum sheets and a gold film. While hot electron relaxation and/or diffusion seem to control the temperature relaxation in the gold film, the ordinary thermal diffusion seems to be responsible for that in the aluminum sheets. It is possible to determine the characteristic time of the thermal diffusion in the aluminum sheets by fitting a theoretical curve to the observed transient reflectivity. Its reliability is, however, somewhat questionable because of the asymptotic nature of the temporal dependence. Small thermal diffusivity as well as short thermalization time between electrons and phonons is required for the thermal diffusivity to be accurately determined.

High-Temperature Pyrometric Measurement of Thermal Diffusivity by a Flash Method: Co–Si and Co–Ge Systems

The paper deals with an automated system for measuring the thermal diffusivity of metals and alloys by a flash method involving the use of a contactless technique of recording the superheat temperature of a specimen. The solution of the heat equation for a cylinder with due regard for the Gaussian distribution of energy over the laser beam cross section forms the basis of the measurement method. The structural scheme of the experimental facility is described using an IBM PC and a GOR-100M type laser. The results of measuring the thermal diffusivity of Co–Si and Co–Ge systems in the temperature range of 300–1650 K are presented. The polytherms of the thermal diffusivity in the vicinity of the Curie point and in e → α structural transitions exhibit anomalies. These anomalies are smoothed out as the concentrations of Si and Ge increase, and are not observed at a concentration of admixtures higher than 10 at. %. The obtained results are in satisfactory agreement with the diagrams of state for Co–Si and Co–Ge alloys.

Automated apparatus for measuring the thermal diffusivity of metals by the thermal-wave method

Automated equipment for measuring the thermal diffusivity of metals by the thermal-wave method is described. The Seebeck effect is used to record the thermal waves. The thermal diffusivity of a number of metal samples 0.01–0.05 cm thick is measured with an error not greater than 10%.

Measurement of the thermal diffusivity of metals on the temperature interval 1100?2500�K

A method of measuring the thermal diffusivity of metals on the temperature interval 1100–2500°K is described. Values of the thermal diffusivity of tantalum, molybdenum, niobium, vanadium, and cobalt are presented.

金属の熱拡散率測定に対するパルス幅の影響

金属の熱拡散率測定に対するパルス幅の影響

A sensitive low inertia thermal resistor for helium temperatures

A low inertia, high sensitivity thermal resistor based on the superconducting transition is described. A sensitive element is obtained by simultaneous deposition in vacuum of lead and copper from separate evaporators. This resistor can be used to measure the thermal diffusivity of metals and alloys and to investigate rapidly varying thermal processes. (C.E.S.)

Measuring the Thermal Diffusivity of Metals at Elevated Temperatures

Abstract The Angström-bar method has been modified and adapted to the measurement of thermal diffusivity of metals for temperatures ranging from 300 to 1050 F. A small, sinusoidal temperature fluctuation is superimposed on the mean temperature of a thin-wall tubular specimen by means of simultaneous heating and cooling at one end. Thermal diffusivity was calculated from the phase shift and amplitude ratio of the temperature waves determined at two measuring stations. The effect of possible surface heat loss is considered. Measurements were made on AISI 1018, 1045, 3140 steels, and 1.1 per cent carbon tool steel. Results obtained for electrolytic tough-pitch copper and 2S aluminum showed good agreement with a recent theory of Storm concerning the variation of thermal diffusivity of simple metals with temperature.

Closure to “Discussions of ‘Measuring the Thermal Diffusivity of Metals at Elevated Temperatures’” (1956, Trans. ASME, 78, p. 820)

Closure to “Discussions of ‘Measuring the Thermal Diffusivity of Metals at Elevated Temperatures’” (1956, Trans. ASME, 78, p. 820)

Thermal Diffusivity of Metals at High Temperatures

Thermal Diffusivity of Metals at High Temperatures

Thermal diffusivity of metals at high temperatures

Thermal diffusivity of metals at high temperatures

Thermal diffusivity of metals at high temperatures

Thermal diffusivity of metals at high temperatures

Rapid Measurements of Thermal Diffusivity

Abstract An apparatus and a technique were developed for determining the thermal diffusivity of metals by a periodic heat-flow method. Measurements with a probable error of ± 6.8 per cent were made on specimens of Armco iron, titanium, zirconium, and Haynes Stellite 25 at temperatures of 456, 564, and 672 R.

Thermal Diffusivity of Metals at High Temperatures

A modified Ångström method for measuring thermal diffusivity and hence thermal conductivity of metals has been developed. Like previously reported dynamic methods, this method uses a heat source, whose temperature varies sinusoidally with time, located at one end of an effectively infinite rod. Unlike these methods, only one period of the heat pulse is required to eliminate the unknown coefficient determining the heat lost by radiation since both velocity and amplitude decrement of the heat pulse are measured. In addition to providing greater reliability at high temperatures by using only one period, the new method is faster in taking data and simpler in computation. The thermoelectric potentials from two thermojunctions are amplified and plotted on a Brown electronic recorder in order to obtain a permanent record of all necessary data for computing the thermal diffusivity. Results for copper, nickel, and thorium over the temperature range 0–500°C are given.