Local Heat Input Research Articles

Indirect measurement of nbti wire temperature field response to local heat input

Indirect measurement of temperature field profile on the NbTi multifilament wire locally heated by steady or transient thermal disturbance is presented. Contrary to point like measurements by thermometers glued upon the wire surface it can be applied for continual mapping of the T(x) profile. Especially useful may be the method in the case of tiny conductors where influence of gauge thermal conductivity and capacity may result in distortion of axial temperature field profile as well as its dynamics. Based upon experimental T c(B) data it can be applied both for steady local heating in I c(B,T) measurements or in monitoring of T(x,t) dynamics during superconductor recovery after transient heat input.

The thermal performance of heat pipes with localized heat input

The performance of heat pipes with localized heat input including the effects of axial and circumferential heat conduction under high and low working temperatures is investigated. The numerical results show that when heat pipes are spot heated, the peak temperature of the wall is greatly reduced and the surface can be protected from being burned out by the high heat flux. The boiling limitation becomes the most important limitation for this type of heat pipe. Numerical results for block heating a heat pipe with low working temperatures indicate a good agreement with existing experimental data. It is also shown that most of the input heat passes through the wall beneath the heated block.

On the two modes of operation of monolithic Ag-C brushes

The previously observed transition from low-temperature (mode I) to high-temperature (mode II) behavior in silver-graphite brushes can be explained either by changes of constriction resistance through the temperature dependence of electrical resistivity and hardness at negligible film resistivity and one to three contact spots, or by loss of graphite lubrication within the interfacial film. These two interpretations were tested by controlling the contact spot temperature: (1) by heating in an oven and (2) by local heat input through friction. Correlated studies of contact resistance, friction, wear rate, wear chip size, wear chip microstructure, and calculations of contact spot temperatures favor the second hypothesis. Micrographic evidence suggests that this occurs through desorption of water vapor from the graphite. It is found that primary wear particles form due to the wedge mechanism and by cutting by graphite fragments steeply inclined to the interface. Silver fragments may consolidate into secondary wear particles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power transmission capacity of As-S glass fiber on CO laser delivery

In this paper we describe the performance of CO laser power delivery over an As-S glass fiber, which has a fluorinated ethylene propylene resin (Teflon FEP) cladding, as well as kinetics of melting break off of the fiber on power delivery. The maximum fiber power output of 15.3 W with an intensity of 12.2 kW/cm2 was obtained by using a fiber whose core diameter was 400 μm and which was not forced cooled. Maximum transmission power was restricted by the thermal damage occurring at the end of the fiber. Kinetics of this thermal damage were investigated by measuring the temperature on the cladding surface and by estimating temperature distribution in the fiber through calculations. The localized heat input at the end of the fiber was estimated at approximately ten times higher than other portions of the fiber.

Nonstationary heat transfer in a channel containing saturated He II: stepped heat loading

Measurements have been made on the nonstationary temperature distribution in a channel containing saturated superfluid helium with local stepped heat input. A numerical method has been developed, which incorporates the variable thermophysical parameters for the helium.

Effect of heat input and preheating on hydrogen assisted weld joint cracking of a 0.13% C, 1.5% Mn, 0.032% Nb high strength steel of 50 mm plate thickness in the IRC test

The effects of preheating and heat input on hydrogen assisted weld joint cracking are investigated at a restraint intensity of 32 kN mm−2 of a 0.13% C, 1.5% Mn, 0.032% Nb high strength steel of 50 mm thickness in the IRC test, using a high hydrogen experimental electrode of 530 N mm−2 yield strength.For a heat input ranging from 0.6 to 1.05 kJ mm−1 a critical preheating temperature of 140°C for almost complete crack prevention, for a range from 1.5 to 2.05 kJ mm−1, 120°C were found respectively. Nominal stresses at the ends of the 70‐80 mm long welds at the start of extensive cracking increase with heat input and preheat, the crack propagating from the HAZ into the weld metal quickly. Under conditions without or close to cracking, however, final stresses after 18 h are reduced with heat inputs. Consequently, crack critical combinations of preheating and heat input are linked to stresses decreasing with heat input but increasing with preheat. From the established IRC‐test diagram required combinations of local preheat and heat input for either avoiding hydrogen cracking or overstressing of the weld metal can be determined. Currently used cracking prediction procedures do not consider the effect of heat input and preheat on stress sufficiently and, therefore, may provide unsafe conclusions.

Ductile strain and metamorphism in an extensional tectonic setting: a case study from the northern Snake Range, Nevada, USA

Summary In recent years considerable attention has focused on metamorphic core complexes of the Basin and Range Province of the western US Cordillera. These highly extended areas are characterized by an upper plate that has been brittlely attenuated by normal faults separated by a sub-horizontal detachment surface from a lower plate that has been ductilely thinned and stretched. A study of mesoscopic structures, finite strain, microstructures, quartz c -axis fabrics and 40 Ar/ 39 Ar geochronology was undertaken in order to characterize the nature, geometry, kinematic history and timing of ductile extension in the lower plate of the northern Snake Range metamorphic core complex in E-central Nevada. These data provide new insights into the processes of deep-seated ductile strain beneath supracrustal normal fault mosaics in highly extended regions. Mesoscopic structures and finite strain analyses indicate that the lower plate underwent plane strain with a sub-vertical Z-axis and a sub-horizontal WNW-ESE X -axis. The magnitude of strain increases dramatically from W-to-E, and is constant vertically. Bedding and foliation are everywhere parallel and bedding is thinned 30–90%. The nature and geometry of microstructures and c -axis fabrics changes progressively from W-to-E. Lower strain rocks on the W flank of the range are characterized by a single bedding-parallel foliation, defined by flattened detrital grains, globular grains which have their c -axes parallel to the Z -axis and symmetrical cross-girdle c -axis fabrics. Further E to slightly higher strains, the rocks are characterized by asymmetrical cross-girdle c -axis fabrics, although globular grains with their c -axes parallel to Z are still present. The high-strain rocks on the E flank of the range are characterized by C -planes, asymmetrical mica ‘fish’ and oblique quartz foliations, and asymmetrical single-girdle c -axis fabrics. These data suggest that the lower plate has not deformed entirely by either coaxial or non-coaxial strain, and we propose an evolutionary model whereby the lower plate deformed during an early period of coaxial strain followed by a later component of non-coaxial strain accompanied by coaxial strain on the E flank of the range. 40 Ar/ 39 Ar geochronology on lower-plate hornblendes and micas indicates that temperatures of deformation were &gt;280°C, but &lt;530°C, and increased with depth. Geochronological data suggest that lower-plate ductile strain is post-latest Cretaceous, and biotite and muscovite data indicate that ductile deformation was probably ongoing 22–26 Ma. Our data and regional geological relations suggest that ductile extensional deformation in the northern Snake Range occurred because of localized heat input to shallow levels of the crust, and together with seismic reflection data, indicate that lower-plate rocks probably represent the top of a regional metamorphic terrane of Tertiary age.

Role of brazing in repair of superalloy components – advantages and limitations

AbstractIn this paper, the different types of damage occurring in components of the hot section of gas turbines and the techniques used in their restoration are described. Brazing as a repair technique and its use on typical types of damage is discussed and illustrated. Welding is reported to be useful only when the damage is limited to small areas of blades or vanes, because of the composition of super alloys and the deformation caused by the local heat input. Brazing is discussed with respect to brittleness, erosion, corrosion resistance, and the size and shape of the defects to be repaired. Examples of slurry brazes are illustrated by pictures and micrographs and the parameters for such brazing are discussed briefly to show the interaction of brazing with the various steps in a repair and heat-treatment procedure.MST/100

Observations of melt rate as a function of arc power, CO pressure, and electrode gap during vacuum consumable arc remelting of Inconel 718

Statistically designed experiments were conducted at two different production melt shops to evaluate the influence of arc power, CO pressure, and electrode gap on melt rate. Approximately 11,000 kg of Inconel 718 alloy 0.4 m diameter electrodes were vacuum consumable arc remelted into 0.5 m diameter ingots. Analysis of the experimental results revealed that melting efficiency (melting rate/kW) was maximized when CO pressure and electrode gap were held at low levels. Under these conditions, the heat distribution (created by the vacuum arc) on the electrode tip and the molten pool exhibited macro uniformity. Increased CO pressure and/or electrode gap depressed the melt rate, and at 13.3 Pa (100 microns) and a 0.050 m electrode gap, this depression exceeds 46 pct. Increasing these parameters also changed the arc behavior to that of a constricted arc with a highly localized heat input. It is hypothesized that the change from the usual diffuse arc to this constricted arc results in intense Lorentz pumping in a localized region of the molten pool atop the ingot causing fluid flow transients. These transients could, in turn, create solidification defects.

Safety of superconducting magnets for fusion: Thermal analysis of large cryostable magnets

A thermal analysis program has been developed to study the response of a cryostable fusion magnet to abnormal conditions such as a localized heat input, overcurrent, or uncooled length of conductor. It performs a heat balance on each element. Variation of parameters with temperature, pressure, and magnetic field are incorporated. The program has been applied to a conductor with magnetic field variation along its length, carrying a high current as might occur in one toroidal field toil when a neighboring coil discharges rapidly. It is found that a stable normal region can develop, with possibly serious consequences.