Heat Flow Conditions Research Articles

An experimental investigation of deformationinduced heating during tensile testing

An experimental investigation of deformation heating during uniaxial tensile testing is presented for Armco interstitial-free steel (I. F. steel) and stainless steel type 310 (310SS). Temperature distributions were measured along the specimen length for tests conducted at various strain rates and subjected to various heat flow conditions (in stirred water, in air, and with insulation). Maximum temperature rises of 75 °C and 118 °C were recorded in the neck. I.F. steel shows a decreasing failure strain from ∼45 pct to ∼40 pct when natural temperature gradients develop. 310SS shows a decreasing failure strain from ∼60 pct to ∼42 pct when natural heating is allowed. In 310SS, the developed temperature gradient accounts for about one-third of this ductility reduction while the uniform temperature rise accounts for about two-thirds. The uniform temperature rise influences ductilityvia a temperaturedependent work-hardening rate. These results have been qualitatively compared with finite element modeling of these tensile tests using constitutive equations generated previously. This study provides the basis for understanding several modified forming processes and demonstrates that care must be taken in interpreting data from “standard” tensile tests since such tests reflect the thermal properties of the material and environment as well as mechanical behavior.

Thermal history of ht-9 weldment heat-affected zones during welding

The microstructure in weldments of HT-9, a commercial 12Cr-1Mo ferritic steel, has been observed to vary over short distances as a function of the varying thermal history during welding. The mechanical behavior response of “local” weldment microstructures can be characterized by simulation of the structure in larger usable volumes of material, if the “local” thermal history during welding is known. An empirical equation for describing the thermal history of HT-9 weldment heat-affected zones during gas tungsten-arc welding is presented in this paper. Peak temperatures and cool-down cycles are both predictable at any location in the base metal heat-affected zone for welding of plate under conditions of two-dimensional heat flow anticipated for first wall component fabrication. Power input and preheat effects are included in the equation. The equation is expected to apply to materials having a chemistry and thermal properties similar to HT-9. This includes low activation alloys based on the composition of HT-9.

Mapping the Distribution of Buried Glacier Ice – An Example From Lago Delle Locce, Monte Rosa, Italian Alps

Techniques for mapping the distribution of buried glacier ice are discussed and the results, from a study carried out within the framework of flood protection work in the Italian Alps, are presented. Bottom temperatures of the winter snow cover (BTS) primarily indicate the heat flow conditions in the underlying ground and mainly depend on the presence or absence of an ice layer beneath the surface. Determination of BTS values is therefore an inexpensive method for quickly mapping the near-surface underground ice in areas where there is 1 m or more of winter snow cover. At greater depths, and/or when more detail is required, geoelectrical resistivity soundings and seismic refraction soundings are most commonly used to investigate underground ice. A combination of the two sounding techniques allows the vertical extent and the main characteristics (frozen ground, dead glacier ice) to be determined in at least a semi-quantitative way. Complications mainly arise from irregularity in the horizontal extension of the studied underground ice bodies, and they may have to be overcome by expensive core drillings and borehole measurements. Widespread occurrence of buried glacier ice was observed in morainic deposits, surrounding an ice-dammed lake near Macugnaga, Italy.

Mapping the Distribution of Buried Glacier Ice – An Example From Lago Delle Locce, Monte Rosa, Italian Alps

Techniques for mapping the distribution of buried glacier ice are discussed and the results, from a study carried out within the framework of flood protection work in the Italian Alps, are presented. Bottom temperatures of the winter snow cover (BTS) primarily indicate the heat flow conditions in the underlying ground and mainly depend on the presence or absence of an ice layer beneath the surface. Determination of BTS values is therefore an inexpensive method for quickly mapping the near-surface underground ice in areas where there is 1 m or more of winter snow cover. At greater depths, and/or when more detail is required, geoelectrical resistivity soundings and seismic refraction soundings are most commonly used to investigate underground ice. A combination of the two sounding techniques allows the vertical extent and the main characteristics (frozen ground, dead glacier ice) to be determined in at least a semi-quantitative way. Complications mainly arise from irregularity in the horizontal extension of the studied underground ice bodies, and they may have to be overcome by expensive core drillings and borehole measurements. Widespread occurrence of buried glacier ice was observed in morainic deposits, surrounding an ice-dammed lake near Macugnaga, Italy.

Conodont palaeobiogeography and thermal maturation in the Caledonides

Conodont elements are important in biostratigraphy, in palaeoenvironmental and palaeobiogeographical analyses, and in assessing the thermal history of Lower Palaeozoic strata throughout the Caledonian belt. The differentiation of Ordovician conodont faunas into the North Atlantic and North American Midcontinent provinces is not closely comparable with the provincial patterns shown by other faunal groups and does not relate clearly to criteria for recognizing continental separation across the Iapetus Ocean. Some species associations adapted to cool, normal marine waters were able to cross the ocean at the time of its presumed maximum extent. The colours of conodont elements reflect the thermal history of strata and can be used in studies of low-grade metamorphism. In S. Wales, for example, metamorphic temperatures indicated by conodont colour are too high to he accounted for by simple burial beneath the known stratigraphical overburden under normal heat flow conditions. Elsewhere, conodont colour trends also serve to constrain and test models of metamorphism that involve sedimentary burial in subsiding basins, tectonic burial under nappes, or the thermal effects of intrusions.

The Acadian Thermal History of the Merrimack Synclinorium in New Hampshire

The Acadian structural history of the Merrimack Synclinorium involves a phase of nappe emplacement and thrusting at 400 m.y.B.P. followed by a second thickening event before 370 m.y.B.P.; at the end of this phase the present erosion surface was buried at pressures of 6 to 8 kbar and subsequently experienced peak metamorphic temperatures in the range of 500°C to 650°C. The thermal history of the Acadian metamor-phism of the Merrimack Synclinorium is examined in a well-studied area of central New Hampshire to determine the conditions required for the high grade metamorphism of the region. Constraints are provided by metamorphic pressure estimates, by information on the erosional history, and by present day heat flow determinations in the Synclinorium. One-dimensional heat transfer calculations show that the high grade metamorphism could readily have been produced during thermal relaxation of the thickened continental crust under conditions of normal continental heat flow. These conditions also permit the melting of the lower continental crust between 50 and 100 m.y. after the end of crustal thickening, which could account for the generation of some of the post-tectonic Concord Series plutons (370-275 m.y.B.P.). If portions of the Acadian orogen experienced rapid erosion (faster than about 1 mm/yr) at the end of crustal thickening, then they would achieve peak metamorphic temperatures 100°C to 150°C lower than calculated here; this perhaps was the case for the Bronson Hill Anticlinorium to the west. Equally, if it can be shown that the Merrimack Synclinorium was eroded rapidly at the end of the Acadian, then an augmented heat supply during the metamorphism is required. More data on the rates of Paleozoic uplift and on the Pressure-Temperature-Time paths followed by these rocks are needed in order to place tighter constraints on the thermal history of the Acadian metamorphism.

Latent Heat of Frozen Saline Coarse‐Grained Soil

In recognition of the need to predict the thermal regime in arctic offshore structures, a laboratory research program was constructed to evaluate the latent heat of fusion of a coarse‐grained soil with saline pore water. Latent heat of fusion measurements were made by placing frozen soil specimens with saline pore water in an insulated cylinder and melting the specimens under steady‐state heat flow conditions. The specimen temperature and heat transfer through the cylinder as a function of time was recorded. The latent heat of fusion is equal to the heat supplied to the soil specimen in the time interval during which a phase change occurs. The results from the research program indicate that the latent heat released during thawing depends on the initial values of pore‐water salinity and subfreezing temperature. The latent heat released increases with decreasing pore‐water salinity. For the coarse‐grained soil employed in the research program, the latent heat released when thawing from a given subfreezing temperature was found to be equal to the latent heat released in a pure saline solution over a comparable temperature range.

Czochralski growth of silicon

The importance of Czochralski (CZ) grown silicon as a basic material for solid-state electronics is outlined. After that, a short review is given of the different possibilities for growing silicon crystals and the history of Czochralski technique. Details of the CZ pulling procedure are discussed. The different aspects of the process like starting material, crucible problems, heat and melt flow conditions, interface reactions, as well as incorporation and distribution of impurities in the crystals are considered. Examples are given of typical and exceptional impurity distributions. Oxygen is of supreme importance in CZ-Si and is dealt with in greater detail. Its origin, typical concentrations and distributions, and its influence on crystal quality are described. Finally, the technical aspects of current CZ-Si growth are outlined and the mechanical designs of the pulling apparatus, including recharging equipment, are illustrated.

Katalytischer wasserstoff-/sauerstoff-rekombinator mit selbstbegrenzung

Lead-acid cells evolve hydrogen and oxygen gasses during the charging mode, which results in a water loss. Gas recombination devices extend the water refilling periods due to the recombination reaction H 2 + 1 2 O 2 → H 2O The recombination devices consist of: aerosol retainer, charcoal filter, catalyst, condenser, gas storage and vents. Theoretical models describing the self-limiting behaviour of the catalyst and the heat flow conditions in the device were developed. Design specifications of component requirements for a 435-W recombination device, which is capable of recombining 182 l/h stoichiometric oxyhydrogen gas, were also developed. Tests with the system (recombination device-lead-acid cell) showed that a maintenance-free and nearly gastight operation was achieved. The use of catalytic recombination devices improves the economy and safety of battery operation.

A study of composite foams for diving suits subjected to high hydrostatic pressure

In order to obtain foams possessing flexibility and at the same time heat insulation under high hydrostatic pressure, composite foams with spherical rigid foams filled in flexible rubber foam at certain intervals were prepared and their thermal conductivity and flexural rigidity were studied. The following points were found: (1) With a unit model having a spherical rigid foam in the middle, the thermal conduction of a composite foam was analyzed under the conditions of steady one-dimensional heat flow. Theoretical equations giving overall coefficients of heat transmission under atmospheric and hydrostatic pressures were obtained, and the adequacy of these theoretical equations was confirmed by the measurement of overall coefficients of heat transmission of composite foams in an apparatus so constructed as to allow heat conduction experiments under pressures ranging from atmospheric to the hydrostatic pressure corresponding to 100-m depth in water. (2) The effect of the filled spherical rigid foams on heat insulation is notable under hydrostatic pressures corresponding to a 20-m depth or more in water. Under the hydrostatic pressure corresponding to a 100-m depth in water, the coefficient of heat insulation of the most closely filled composite foam used in the experiment was approximately 35% larger than that of the unfilled foam, while the theoretical most closely filled composite foam gives an approximately 110% increase. (3) Under the hydrostatic pressure corresponding to a 100-m depth in water, the flexural rigidity of the most closely filled composite foam used in the experiment was approximately one half that of an unfilled foam of the same heat insulating property.

Heat flow and heat transfer conditions in the bottom sediments of the equatorial indian ocean

The results are reported of heat flow determinations during the 10th and 11th cruises of the “Akademik Vernadsky”. Geothermal gradients were measured by the thermograd PTG-2MTB, with two temperature sensors of 1 or 1.2 m spacing. The temperature sensors were fixed to the coring tube. The lower sensor penetrated the sediment to a depth of 2.5 m. On board determinations of thermal conductivity were made by one of two methods: the needle probe method and analysis of water content in sediments. 21 heat flow measurements ranging from 4 to 120 mWm −2 have been obtained. The heat flow values depend on the type and granulometric composition of the sediments. High values are obtained on the southern slope of the Karlsberg Ridge, in the zones where bottom sediments have been found to have the maximum content of pelitic fraction and minimum of foraminifera. Low values of heat flow are due to a long-term effect of the ascending hydrothermal flow. This is confirmed by the traces of hydrothermal activity found in the sediments.

An Efficient Algorithm for Evaluating Arrays of Extended Surface

In the consideration of single longitudinal fins of rectangular, trapezoidal, and triangular profile and in arrays of extended surface composed of these fins, it is shown that conditions of heat flow and temperature excess at the fin or array tip induce conditions of heat flow and temperature excess at the fin or array base. In particular, there is a linear transformation between the aforementioned data at the fin tip and the fin base. The conventional fin efficiency is abandoned and single fins or arrays of extended surface are instead characterized by a single important parameter, the heat flow to temperature excess ratio, which is a function only of fin geometry and heat transfer parameters. Algorithms are provided for combining the effects of individual fins in arrays of extended surface. A modification of the procedures developed leads to an exact solution for the double stack with unequal heat distribution at opposite ends, a problem which has heretofore required iterative solution procedures.

Refinement of dendrite arm spacings in aluminum ingots through heat flow control

A model for heat flow during solidification of alloys is presented which treats the heat of fusion released during solidification separately for three distinct regions of a casting: portions released isothermally at the liquidus temperature, between the liquidus and solidus in a specified manner and the remainder released at the solidus. The model is solved numerically by a finite difference technique for unidirectional and two-dimensional heat flow in end-chilled thin plates. Effects of heat transfer coefficient at the chill, superheat, heat input, liquid convection and amount of sidewise heat loss are considered. Results are presented in terms of position of liquidus and solidus isotherms as a function of time, width of the mushy zone and local solidification time and secondary dendrite arm spacingvs distance from the chill. Results from experimental castings made under controlled heat flow conditions are compared with computer calculations. The local solidification time and resultant dendrite arm spacing are shown to decrease at a given location as a) the chill heat transfer coefficient increases, b) superheat increases, c) the gradient of temperature at the solidification front increases, and d) the multidimensionality of the heat flow path increases.

Al-Cu系合金の凝固時のみかけの固相域について

Some factors affecting the apparent thickness of the partially solidified layer on the original metal rod surface in the dip-forming process of the skin freezing process were investigated experimentally by dipping tests using 99.99%Al, Al-0.5%Cu, Al-2%Cu and Al-4.5%Cu alloy. Solid fraction was calculated by Scheil’s equation from the temperature distribution measured in the partially solidified region. The shear stress acting on the interface during the raise of the metal rod was estimated under some simple assumptions. The calculation of the solidification profile in this experiment was done by the finite difference method. The results obtained were as follows:(1) In pure Al and Al-Cu alloys without Ti, the apparent solid layer was columnar structure and corresponding to the position of 0∼30% solid fraction in Al-2%Cu alloy and 0∼15% in Al-4.5%Cu alloy.(2) The shear stress acting on the partially solidified region in raising the rod from the bath was much lower than the apparent strength of the region. Therefore the apparent thickness was decided by such a low solid fraction region.(3) Interface heat conductances h between the metall rod and the solid layer were obtained by comparing the experimental and calculated values. In the concentrated heat flow condition, h decreased with Cu content and increased with dipping time.(4) The apparent thickness was thicker with Cu content in the short dipping time and then this relation was reversed after a prolonged dipping time. This was caused by the difference in the partially solidified temperature range and in the thermal condition due to Cu content.

Heat balance and flow conditions for electron beam and laser welding

The conditions of energy and material flow during beam welding are investigated theoretically to determine the factors which govern the shape of the vapor cavity and of the molten zone. Flow conditions in the horizontal plane determine the dimensions of the weld. Material is moved around the advancing vapor cavity mainly by liquid flow, but there is some vapor flow across the cavity, providing the pressure which drives the liquid. The pressure inside the vapor cavity and its variation with depth is governed by surface tension, by the hydrostatic pressure in the liquid, and by the viscous forces acting on the vapor stream. These factors govern the radius of the cavity as a function of depth. The penetration is limited by the beam power or by the absorption of the beam. For the laser beam, absorption is decreased in the hot center, and beam penetration increases with power, but is insensitive to collimation. For electrons, absorption occurs mainly near the walls of the cavity, and the beam penetration depends on collimation and power. The balance between beam power and power dissipated by conduction, melting, and vaporization is discussed, and a self-consistent description is given of cavity formation and beam penetration.

The solidification of pure metals (and eutectics) under uni-directional heat flow conditions: II. Solidification in the presence of superheat

The generalized integral-profile method previously developed2 to predict the solidification rates of pure metals and eutectic alloys under a range of cooling conditions has been extended to treat solidification rates in the presence of super heat. Heat transfer within the liquid metal has been characterized in terms of a single parameter for which a heat balance on the liquid yields an ordinary nonlinear equation. This equation is additional to the two equations derived previously for the growth of the solid metal, and the three equations have been solved simultaneously using a Runge-Kutta technique. Solutions have been obtained for heat transfer conditions that can be reproduced accurately in laboratory experiments. The results of a series of such experiments are also presented and shown to agree very well with the theoretical predictions.

A Model for Seizure

Seizure may be defined as a large-scale mass flow. It requires a small variation of the shear strength with depth, i.e., a small temperature gradient. The temperature gradient in the upper layer can be calculated on the assumption that the mechanical energy input is dissipated as viscous friction. The calculation requires only the melting temperature and one limit value of the temperature range. The value adopted is the lower limit which, at the thermal steady state, can be easily deduced knowing the heat flux and the heat flow conditions. The knowledge of the temperature gradients leads to the conclusion that any change of conditions that lowers the surface temperature also reduces the shear strength gradient and may lead to seizure. In particular, it appears that seizure is very unlikely to occur during acceleration but is possible during deceleration. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE International Lubrication Conference held in New York City, October 9–12...

Density changes of helium II during heat flow through channels

We have measured temperature and density changes of helium II under heat flow conditions. No contribution to the density changes due to vortices could be detected; the density increase can be explained by the assumption of local thermodynamic equilibrium.

Strength, Fracture Mode, and Thermal Stress Resistance of HfB2and ZrB2

Zirconium diboride and hafnium diboride were fabricated by hot-pressing at 1800°C and 120,000 psi. Bend strengths were measured on the fully dense materials from 25° to 1400° C in an argon atmosphere. These diboride compounds do not exhibit any gross plastic flow in the temperature range studied. The bend strengths go through a maximum between 700° and 1000°C and vary from 39,000 to 68,000 psi for HfB2 and 30,000 to 56,000 psi for ZrB2. The maxima in strength correspond to maxima in the fraction of transgranular fracture. The bend strength and room-temperature elastic modulus measurements were combined with available thermal conductivity and expansion data to calculate thermal stress resistance parameters. Under steady-state heat flow conditions, the calculated thermal stress resistance parameters of the borides are higher than those calculated for other refractory compounds.

Thermal Stresses at Spherical Inclusions in Uniform Heat Flow

The thermal stresses in the vicinity of a spherical particle em bedded in an elastic matrix are investigated. An exact solution to the equations of thermoelasticity is presented for the case of a stationary heat flow. The results indicate that stress concentrations occur in a composite when the thermal properties of each of the constituents are different. These stress concentrations may be overlooked if one replaces the composite with an idealized thermal model.