Heat Input Rate Research Articles

Study on crack generation at root of socket welds

Because a power generation facility is made up of structures that contain a large number of welds, the reliability of weld joints is important to ensure the safety of power plants. Surveys and research are conducted on special weld joints to verify the reliability of power plants. The results of the investigation to verify the relation between the welding conditions and quality of small-diameter socket joints are described. Some defects are observed in the roots of socket-pipe joints of carbon steel in this project. The authors investigate experimentally the effect of the welding parameters on the generation of defects. The defects of the root are found experimentally to be solidification cracking (hot cracking). It is also revealed that a higher heat input and lower wire feed rate generate more hot cracking at the root of a weld. The authors also give a hypothesis that explains the generation mechanism of hot cracks at the root of a socket-pipe joint, based on finite element modelling analysis and other information.

Heat and salt fluxes in the Atlantis II Deep (Red Sea)

The Atlantis II Deep is located on the Red Sea axial rift. It is a topographic depression enclosing a volume of about 17 km 3 between 1,900 m and 2,200 m depth that contains layered brines of temperatures up to 66°C and salinities up to 270‰. Previous geochemical investigations showed that the hot brines result from discharge of hydrothermal solutions that have exchanged heat and chemical components with the basaltic substratum. The last investigation of the Deep in 1992 showed that the brines occurred in four well mixed layers with the shallowest at a depth of 2,000 m. The temperature and salinity profiles describe a transition zone from 2,000 m to 1,900 m, above which Red Sea water occurs. The distribution of temperature and salt in this transition zone appears to be controlled by the topography of the Deep. The hydrographic structure of the brine column has been documented in the literature for seven time intervals between 1966 and 1992. Examination of these data shows that the system changed with time. The evolution of the entire package of brines that fill the Deep shows the following changes: (1) the temperature of the brines increased; (2) the salinity of the solutions increased; (3) the two brine layers described in 1966 still existed in 1992, but new layers appeared above them; (4) for 26 years, almost all additional heat and salt supplied in the Deep were confined to the depression and were not dispersed into the overlying seawater. The fourth point indicates that a heat and salt balance for the Deep can be calculated. The calculation of the heat that entered into the system was divided into two components: the temperature increase of the brines and the heat loss at the wall-rock; the latter component was negligible. The rate of heat input to the Deep was constant during the period considered, and amounted to 0.54 × 10 9 W. The salt input was also constant, and equalled 250–350 kg/s. During the period 1966–1992, heat and salt were most probably supplied by a hydrothermal solution with an average range of flow rate, temperature, and salinity of 670–1000 kg/s, 195–310°C, and 270–370‰, respectively.

ステンレス鋼と球状黒鉛鋳鉄の摩擦圧接に関する研究

Ductile cast iron (FCD450) and stainless steels (SUS304, SUS430) were friction-welded. Heat content of each joint was measured by calorimetry and tensile test was made.No defect was observed in joints of cast irons. In the present study, a simplified model has been proposed for calculating the heat input rate in dissimilar joints of friction welding using one dimensional thermal conductivity equation. If the burn-off rate is taken into consideration, a correlation between this heat input rate and tensile property of joints examined appeared to exist. In addition, the values obtained by modeling and measured ones were in good agreement.

Friction welding of cast iron and stainless steels

Ductile cast iron (FCD450) and stainless steels (SUS304, SUS430) were friction-welded. Heat content of each joint was measured by calorimetry and tensile test was made.No defect was observed in joints of cast irons. In the present study, a simplified model has been proposed for calculating the heat input rate in dissimilar joints of friction welding using one dimensional thermal conductivity equation. If the burn-off rate is taken into consideration, a correlation between this heat input rate and tensile property of joints examined appeared to exist. In addition, the values obtained by modeling and measured ones were in good agreement.

Temperature profile on a continuous moving surface subjected to a constant heat rate in a horizontal channel

This paper presents a theoretical analysis of the surface temperatures on conveyor borne materials in a typical manufacturing process, such as the preheat section of a PCB assembly line. The conveyor and materials are modelled as a continuous surface moving at a constant speed in a heated channel. The parameters studied include speed of the conveyor, the heat input rate and air flow over the surface.For problems of this nature, radiation interchange between the enclosed surfaces is significant in distributing the heat input, and losses due to radiation from the open ends of the channel may also account for about 15% of the total heat input. Often the airflow is only a small extraction flow, of about 0.2 m/s or less, to remove any toxic vapours, so that heat removal through convection is less important. The results show that, even for low conveyor speeds of 0.015 m/s or less, the heat outflow as a result of storage in the moving conveyor is the most significant portion, about 80% of the heat input. The temperature profile on the conveyor surface is then almost linear with maximum temperatures at the exit and is essentially proportional to the heat input rate. With a stationary surface, very high temperatures around the middle of the channel are observed.

Comparison of Emissions from Burning Hazardous Waste in a Dry-Process Cement Kiln with Emissions from Burning Conventional Fossil Fuels

During the past ten years, emissions data have been obtained from a dry process cement kiln. The kiln has been tested while burning various amounts of hazardous waste solvents. Supplemental fuel in the form of hazardous waste solvents has been used up to 40% of the heat input to the kiln, or up to 140 million Btu/hr of the maximum 351 million Btu/hr heat input rate. Three sets of tests have been performed on this unit that can be used to compare the emissions from the burning of conventional fossil fuels only, and approximately 15%, 25% and 40% of the heat input with hazardous waste solvents. The tests were performed in 1982, 1984 and 1989/1990. As might be expected, burning a solid fuel has the potential for greater organic emissions, or products of incomplete combustion (PICs) than does the liquid hazardous waste solvents. Additionally, other impurities such as metals and chlorine content can be controlled more fully in liquid hazardous wastes than in conventional fuels. Full scale data from the kiln indicate that emissions can be reduced when burning a hazardous waste solvent over a conventional solid fossil fuel. However, these data were not obtained under controlled conditions, which would be as expected for most full scale facilities. These data could be augmented by bench and pilot scale studies that examine emissions for various hazardous waste and conventional fuel feed rates under controlled conditions.

Geophysical characteristics of the hydrothermal systems of Kilauea volcano, Hawaii

Clues to the overall structure of Kilauea volcano can be obtained from spatial studies of gravity, magnetic, and seismic velocity variations. The rift zones and summit are underlain by dense, magnetic, high P-wave-velocity rocks at depths of about 2 km less. The gravity and seismic velocity studies indicate that the rift structures are broad, extending farther to the north than to the south of the surface features. The magnetic data give more definition to the rift structures by allowing separation into a narrow, highly-magnetized, shallow zone and broad, flanking, magnetic lows. The patterns of gravity, magnetic variations, and seismicity document the southward migration of the upper cast rift zone. Regional, hydrologic features of Kilauea can be determined from resistivity and self-potential studies. High-level groundwater exists beneath Kilauea summit to elevations of +800 m within a triangular area bounded by the west edge of the upper southwest rift zone, the east edge of the upper east rift zone, and the Koa'c fault system. High-level groundwater is present within the east rift zone beyond the triangular summit area. Self-potential mapping shows that areas of local heat produce local fluid circulation in the unconfined aquifer (water table). The dynamics of Kilauea eruptions are responsible for both the source of heat and the fracture permeability of the hydrothermal system. Shallow seismicity and surface deformation indicate that magma is intruding and that fractures are forming beneath the rift zones and summit area. Magma supply estimates are used to calculate the rate of heat input to Kilauea's hydrothermal systems. Heat flows of 370–820 mW/m 2 are calculated from deep wells within the lower east rift zone. The estimated heat input rate for Kilauea of 9 gigawatts (GW) is at least 25 times higher than the conductive heat loss as estimated from the heat flow in wells extrapolated over the area of the summit caldera and rift zones. Heat must be dissipated by another mechanism, or the heat input rate estimates are much too high.

Effect of heat input on the metallurgical properties of HSLA steel in multi-pass MIG welding

A special class of high strength low alloy (HSLA) steel developed for armour application is presently welded by SMAW. Here its weldability by AutoMIG welding using 309L electrode wire has been studied: this results in higher welding speeds and deposition rates and deeper penetration. HSLA steels are difficult to weld due to their higher carbon equivalent and consequent susceptibility to cold- and hot-cracking. The cooling rates are higher compared to SMAW, where the slag blanket produces low cooling rates of the weld beads. Similarly, the high welding speeds of AutoMIG welding causes airdrift into the weld zone, leading to its contamination. However, the multi-pass mode of welding produces bead tempering and lower residual stresses. The welding speeds can also be suitably selected to control the heat input, which is a major parameter affecting the microstructure and mechanical properties of the fusion zone. The heat input is defined by the expression: IV/1000 S in kJ/mm, where I is the welding current, V is the voltage and S is the welding speed in mm/s. Thus the heat-input rate can be varied by changing the voltage and current setting also, but this is not preferable. Higher voltages alter the bead geometry and fusion area, which affects the resultant microstructure, and can also destabilise the arc and produce spatter. Current variation is not adopted since for a particular wire the recommended range of current setting is small. In the present studies, therefore, the heat-input rate is varied by employing different welding speeds: these were selected in 6 steps between 250 to 600 mm/min, which resulted in the corresponding heat input range of 1.9 to 0.8 kJ/mm.

Evolution of particle clouds around ablating pellets in magnetically confined hot plasmas

Cryogenic hydrogen isotope pellets are being used for introducing fuel particles into the plasma interior in magnetic confinement fusion experiments. The spatial and the time evolution of the initially low-temperature, high-density particle clouds forming around such pellets are considered, with particular attention given to such physical processes as heating of the clouds by the energy fluxes carried by incident plasma particles, gas-dynamic expansion with j*B-produced deceleration in the transverse direction, finite-rate ionization and recombination processes, and magnetic field convection and diffusion. While the dynamic processes associated with the ionization and radial confinement processes are characterized by the relatively short Alfven time scale ( mu s range), the subsequent phase of axial expansion is associated with a notably larger hydrodynamic time scale defined by the heat input and gas-dynamic expansion rates (ms range). Data stemming from experimental measurements in toroidal confinement machines are compared with results of model calculations. Some similarities with extraterrestrial plasma scenarios, such as the earlier magnetospheric barium release experiments, are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Buoyancy-driven air flow in a stairwell model with through-flow

This paper is concerned with measurement of buoyancy-driven air flows between the two compartments of a half-scale model of a stairwell. The flow was maintained by a heater placed in the lower compartment. The results of earlier investigations are extended by considering a through-flow via two small openings, one in the lower and the other in the upper compartment. The stairwell model and its instrumentation are described. The results include velocity and temperature measurements, volume and mass flow rates of air circulating between the lower and upper compartments and rate of heat loss from the stairwell; all are presented for various heat input rates. For the range of experimental conditions and sizes of the openings considered, the through-flow mass flow was about 15% of the circulation flow rate. The results also include the rate of heat and mass transfer via the openings.

Investigation of a latent heat thermal energy storage system

An experimental investigation of a shell-and-tube heat exchanger concept for use in a latent thermal energy storage system for solar heating applications has been carried out. The thermal analysis provides the influence of the water inlet temperature and mass flow rate on the storage charging/discharging times and temperature gradients for heat flow into or out of two different storage substances: paraffin wax and asphalt. Results indicate the capability of the heat exchanger concept to operate within small temperature potentials (< 16 K) for realistic heat input rates.

A heat-transfer model for the rotary kiln: Part I. pilot kiln trials

A model for rotary kiln heat transfer, which accounts for the interaction of all the transport paths and processes, is presented in a three-part series. In this first paper, the pilot kiln facility is described, and the significant results from the heat-transfer trials are identified. Limestone, Ottawa sand, and pctroleum coke were heated using a range of firing rates, while other operating variables were held nearly constant. Measurements were made to obtain the net rates of heat transfer for the bed material, freeboard gas, refractory wall, and, unique to the study, the radial heat flux at the inside refractory surface as a function of circumferential position. High rates of net heat input to the bed material, occurring very near the feed end, were found to decline quickly with distance, and for an inert bed, leveled out at a value well below the rate of loss through the kiln wall. The onset of an endothermic bed reaction resulted in sharp increases in both the temperature cycling at the inside refractory surface and the net heat input to the bed, but no corresponding jump in the kiln wall heat loss. The temperatures of the bed material and inside refractory surface always were coupled closely, even in the presence of bed reaction. Regenerative heat transfer from the covered wall to the contacting bed material was not a major component of the net input to the bed, and for the inert bed, negative regeneration was en-countered beyond the kiln midpoint.

A heat-transfer model for the rotary kiln: Part II. Development of the cross-section model

A model of rotary kiln heat transfer, which accounts for the interaction of all the transport paths and processes, is presented in a three-part series. In this second paper, the development of a unified model for heat transfer at a kiln cross-section is described. Heat transfer within the kiln refractory wall was solved using a finite-difference approximation for one-dimensional transient conduction. A ray tracing technique was applied to derive coefficients for radiative heat transfer in the kiln freeboard, and the finite-difference model was extended into the contacting bed ma-terial in order to calculate the exchange between the covered wall and the bed. The cross-section model is shown to simulate the measured thermal performance of the pilot kiln for several feed materials: fine and coarse sand, limestone, and pctroleum coke. The interaction among the heat-transfer processes at cross-sections of the pilot kiln was examined, and explanations were made for both the observed close coupling of the bed and inside wall temperatures and the high rates of heat input to the bed occurring near the kiln entrance and in the presence of an endothermic bed reaction. Conclusions regarding the likely effects of kiln internal devices on heat transfer to the bed and the importance of preheaters are reached from the model predictions for a 4 m I.D. prototype kiln.

Thermal Instability in Buried Cable Backfills

Buried high voltage power cables generate heat when a current is passed through the conductor, and failure of the cable may occur if the conductor or insulation temperature exceeds the design limit. Thermal instability, a moisture migration phenomenon causing a decrease in soil thermal conductivity, has caused thermally induced failure of cables and may be a problem in the case of other buried heat sources as well. Thus accurate methods for predicting thermal instability are needed. Until recently, such problems have been mainly in the domain of electrical and mechanical engineers; however, geotechnical engineers are now frequently involved in the study of this problem. The Hartley and Black method, based on the assumption that the ratio of the time to instability to the diameter squared of the heat source is a constant for a given heat input rate, is investigated. Laboratory tests, scaled model tests, and field tests were used to provide a wide range in the diameter of the tubular heaters employed (1.6 t...

Chromospheric and coronal heating

From computations for a theoretical model chromosphere matched to the empirical model of Vernazza, Avrett, and Loeser published in 1981, it is concluded that the required magnitude and mass dependence of the heat input are compatible with heating by sound waves whose velocity amplitude is near the sound speed. However, the required rate of heat input per gram increases markedly at the top of the neutral chromosphere, and a different form of heating appears necessary in the corona and transition region. 24 references.

An experimental study of Buoyancy-driven flow in a half-scale stairwell model

This paper describes an experimental study of buoyancy-driven flows of mass and energy in a half-scale model of a stairwell. Two different geometries are considered. The stairwell model forms a closed system, within which the circulation of air is maintained by the continuous operation of a heater placed in the lower floor. The rig, its instrumentation and the computerized data-logging system are described in detail. The overall features of the flow are also described. The results include the velocity and temperature distributions and the circulating volume flow. The effects of heat input rate on these parameters are also discussed.

An Apparatus to Measure the Maximum Heat Transfer Rate in Heat Pipes

In an earlier investigation of evaporative heat transfer in low-temperature heat pipes, it was concluded, that nucleate boiling was the dominating mechanism for heat removal from the wall. Experimental data for vaporization of water and freon in screen wicks was shown to agree well with a boiling correlation. Data used in the correlation were obtained from Abhat and Seban for a water/screen wick vaporization experiment and from Ponnappan and Mahefkey for a copper/water double-wall artery heat pipe. During verification testing of this heat pipe, heat input to the evaporator was provided by electrical resistance heating. In such cases the evaporator wall heat flux is the independent parameter and the temperature drop across the evaporator is measured as a function of applied heat flux. The temperature drop is given by T{sub w} {minus} T{sub s}, where T{sub w} is the wall temperature and the T{sub s} is saturated vapor temperature. The criterion used to signify that the maximum heat flux had been reached was an observed evaporator temperature drop larger than 10C. In low-temperature heat pipes, before the boiling limit is reached, dryout will usually occur due to the inability of the wick to pump sufficient liquid to the evaporator (capillarymore » limit). The capillary limit Q{sub max} is a limitation on total heat input rate Q for a given heat pipe. Temperatures in the heat pipe evaporator increase rapidly if the maximum heat input rate is maintained, and the rise in internal pressure may cause failure of the container material. In this paper, a unique apparatus is used to control the wall temperature of the heat pipe evaporator independently. With this method, an increase in T{sub w} above that corresponding to Q{sub max} can only cause a decrease in Q. Although it is more difficult to control the temperature than the heat flux, this method allows a more accurate determination of Q{sub max} and precludes the possibility of runaway temperature.« less

Demystifying flash temperatures I. Analytical expressions based on a simple model

Equations by which flash temperatures at contact spots may be calculated in a straight-forward manner are presented and partly derived for the first time. They apply to arbitrary speeds and elliptical contact spots with axes A and B = A/ e in sliding direction and at right angles thereto, for cases in which (i) heat is evolved at the mathematically flat interface, (ii) the two materials are free of surface films and (iii) the two materials have the same temperature. With the characteristic dimension r = (AB) 1 2 /2 , with q the rate of heat input per unit area of contact spot, and with λ 1 the thermal conductivity of the substrate (side 1), the average value of the temperature increase at the interface is ΔT = f( Z, S) ΔT 0 where ΔT 0 = ( π/4) qr/ λ 1 is the value of ΔT for a circular contact spot at rest when the asperity (side 2) is an insulator. f( Z, S)⩽1 expresses the reduction in flash temperature due to motion (via the velocity function Z( ν r), due to ellipticity (via the shape function S( e, ν r)) and due to the finite heat conductivity of the substrate ( via λ r = λ 2/ λ 1). The velocities are expressed in terms of the relative velocities ν r = ν/ ν 0 where ν 0 = κ i / r with κ 1 the heat diffusivity of the substrate and κ 2 the heat diffusivity of the asperity side. In general, for a contact spot moving relative to both sides, ▪ and, to within about 3%, Z(ν r <2)= 1 1+ν r /3 ▪ ΔT max, the maximum value of the flash temperature at the interface, is about one-third larger than ΔT, i.e. ΔT max = (4/ π) ΔT for ν r ≪1 and ΔT max = 1.42 ΔT at high relative speeds. In the accompanying paper, Part II, the equations are applied to friction heat at plastically deformed contact spots and numerical values are presented which permit quick estimates to be made of the flash temperature in a wide range of cases. Also a more realistic model of the contact spot is considered in Part II, and an upper limit of the flash temperature which follows therefrom.

Explosive volcanic eruptions - VI. Ejecta dispersal in plinian eruptions: the control of eruption conditions and atmospheric properties

Summary. A simple model is developed to relate the maximum down-wind and cross-wind ranges of pyroclasts forming a plinian airfall deposit to the dynamic processes in the eruption cloud from which they fall and the atmospheric wind conditions in the area. The eruption cloud dynamics are in turn related to the eruptive conditions in the vent (vent radius, exsolved magmatic volatile weight fraction, velocity with which material passes through the vent, and mass eruption rate), some or all of which can be deduced if the appropriate field measurements can be made. Some aspects of the stability of convecting volcanic eruption clouds are investigated, and the effects on eruption cloud height of the local atmospheric temperature profile and the value adopted for the entrainment constant (which relates the horizontal flow speed of atmospheric air entering the column to the vertical rise speed of the column material) are explored. It is confirmed that eruption-cloud rise height and pyroclast dispersal are mainly controlled by the mass eruption rate (per unit length of active fissure in the case of linear vents) and, hence, the heat input rate to the cloud; but a significant subsidiary dependence on the amount of exsolved magma volatiles is also found. The eruption cloud model is validated by application to observed historic eruptions, and its use in the analysis of palaeo-eruptions is discussed.

Higher-Strength Steels Specially Processed for High Heat Input Welding

ABS Grade EH36 steel plates, specially formulated and produced with advanced metallurgical techniques, are shown to have a significantly greater resistance to weld heat-affected zone (HAZ) degradation that conventional EH36 steel. Welds made in these steels with the electroslag welding process at high heat input rates retained adequate toughness in the heat-affected zone at --4°F (-20°C); similar welds in conventional EH36 steel plate exhibit excessive HAZ toughness loss. This effect was confirmed on the basis of small-scale Charpy V-notch and large-scale explosion bulge testing. In view of their superior resistance to HAZ degradation, the steels should also be useful for applications where HAZ degradation is of particular concern, such as for American Bureau of Shipping (ABS), U.S. Coast Guard, and International Maritime Organization (IMO) weld requirements for liquefied gas carriers.