Transient Temperature Conditions Research Articles

Modelling steel behaviour

When modelling material mechanical behaviour, an analytical description is required of the relationship between stresses and strains. A computer-oriented mechanical behaviour model for steel is described. The model is based on the fact that the deformation process at transient high temperature conditions can be described by three strain components which are separately found in different steady-state tests. It is shown that a behaviour model based on steady-state data satisfactorily predicts behaviour in transient tests under given fire process, load and strain history. The test method used for determining strength properties is of great importance for the obtained result. By using the model a procedure is shown of how to couple steady-state and transient-state results and make them comparable for design. Sometimes the behaviour model for design purposes is simplified by using constructed stress-strain curves based on transient-state results. This means that creep from the transient test is included in an approximate way in the stress-strain curves. The consequence of this simplification in a computation is illustrated for steel structures approaching creep failure under fire attack.

Oxidation kinetics and related phenomena of zircaloy-4 fuel cladding exposed to high temperature steam and hydrogen-steam mixtures under PWR accident conditions

With respect to the behavior of Nuclear Pressurized Water Reactor fuel cladding during accidents the oxidation kinetics of Zircaloy-4 tubing in steam and hydrogen-steam mixtures and the related changes in the mechanical properties have been investigated. Short tube sections were exposed to steam in surplus between 600 and 1600°C under isothermal and temperature transient conditions and to steam of limited supply and hydrogen-steam mixtures between 800 and 1300°C under isothermal conditions. Tube capsules were creep-rupture tested in steam under isothermal/isobaric (600–1300°C, 7–150 bar) and various temperature/pressure transient conditions. The oxidation kinetics of Zircaloy-4 is described in case of short-term reaction by simple rate laws. The long-term behavior is proved to be highly influenced by the breakaway transition and finally by total consumption of the tube wall. On the basis of the isothermal behavior the short-term temperature transient case can be understood and also modelled. Deviations from predictable behavior are the consequences of Zr- and ZrO 2-phase transformations. The protective character of preexistent scales is lost above 1100°C for the same reason. The limits of steam supply rate dependent oxidation and its interrelation with the competing hydrogen take-up are described. The consequences of oxidation on the mechanical properties are increased strength and decreased ductility, whereas the response to creep deformation is an overall increase in oxidation due to oxide cracking.

Failure Correlation for Zircaloy-2 Fuel Cladding under High Temperature Transient Conditions

Failure Correlation for Zircaloy-2 Fuel Cladding under High Temperature Transient Conditions

Failure correlation for zircaloy-2 fuel cladding under high temperature transient conditions.

Thermal transient and isothermal tests on unirradiated Zircaloy-2 fuel cladding were conducted by determining short-term failure behaviors depending on temperature transients under constant differential internal pressure conditions. Failure data for constant heating rate transient tests were converted to Larson-Miller Parameter (LMP) values on the basis of the life-fraction rule. It was found that failure data for both the transient and isothermal tests were reduced to a single curve described by a correlation between LMP and initial hoop stress. Also, the failure strength during isothermal holdings after thermal transients was successfully evaluated by summing up life-fractions corresponding to each temperature process, using the LMP correlation. The LMP correlation approach could be used to predict the transient mechanical response of fuel cladding under high temperature conditions.

Megalopolis lignite drying kinetics based on TGA experimental results

Lignite drying kinetic data are of critical importance for the design of drying and occasionally gasification process equipment because of the particularly high (55–60%) moisture content held in the lignite particles. A lumped kinetic model, R d( t) = η k d( T)( W * - W( t)) n d( T) , describing the dependence of the drying rate upon the residual moisture content (dry basis) of lignite single-particle systems is proposed in this paper. The mathematical analysis is based on data obtained from TGA experimental studies carried out on lumps or on samples of pulverized Greek (Megalopolis) lignite in a nitrogen atmosphere under transient temperature conditions. (A rate of temperature rise 20°C/min, up to 100°C, was applied.) The temperature dependence of both the relevant rate constant and the kinetic order was determined by the best fit of the theoretical model to the relevant experimental data. Megalopolis lignite drying can be described satisfactorily by the kinetic equation ▪ η = f( d p) and T = f′( t) are described graphically in the text.

Transition Boiling Heat Transfer on a Vertical Surface

Transition boiling heat transfer on a vertical surface in a pool of saturated water is investigated experimentally. Local heat transfer rates are obtained on a 6.3-cm-wide and 10.3-cm-high surface which was machined from a large block of copper. Experiments conducted with water show that even for relatively slow transient cooling rates (|dT/dt| < 11 K/s), the transient maximum heat fluxes are as much as 60 percent lower than the maximum steady-state heat fluxes. It is found that transition boiling heat transfer is very sensitive to the surface condition as well as to the history of the process. Two distinct transition boiling curves are observed during transient heating and cooling of clean surfaces. However, the difference between the two curves diminishes as the wettability of the surface increases. A correlation is developed to relate the transient quenching and steady-state peak heat fluxes for the range of temperature transient rates and surface conditions used in this investigation. Although the transient transition boiling curves obtained during heating and cooling are distinct because of different initial conditions, it is found that they possess the same rate of change of heat transfer coefficient with surface temperature when a correction factor equal to the ratio of steady to transient maximum heat fluxes is used.

The oxidation behavior of Zircaloy‐4 in steam between 600 and 1600°C

AbstractWith respect to the behavior of Nuclear Pressurized Water Reactor fuel cladding during accidents the oxidation kinetics of Zircaloy‐4 tubing in steam and the related changes in the mechanical properties have been investigated. Short tube sections were exposed to steam between 600 and 1600°C under isothermal and temperature transient conditions. Tube capsules were creep‐rupture tested in steam under isothermal/isobaric (600–1300°C, 7–150 bar) and various temperature/pressure transient conditions.The oxidation kinetics of Zircaloy‐4 is described in case of shortterm reaction by simple rate laws. The long‐term behavior is proved to be highly influenced by the breakaway transition and finally by total consumption of the tube wall. On the basis of the isothermal behavior the short‐term temperature transient case can be understood and also modelled. Deviations from predictable behavior are the consequences of Zr‐ and ZrO2‐phase transformations. The protective character of preexistent scales is lost above 1100°C for the same reason.The consequences of oxidation on the mechanical properties are increased strength and decreased ductility, whereas the response to creep deformation is an overall increase in oxidation due to oxide cracking.

UO 2/Zircaloy-4 chemical interactions from 1000 to 1700°C under isothermal and transient temperature conditions

Chemical interactions between UO 2 fuel and Zircaloy-4 cladding under isothermal and transient temperature conditions up to the melting point of zircaloy (Zry) are described. The tests were conducted in inert gas (1 to 80 bar) with 10 cm long zircaloy cladding specimens filled with UO 2 pellets. In the isothermal tests, the annealing temperature varied between 1000 and 1700°C and the annealing period between 1 and 150 min. The transient experiments were conducted from 1000°C to maximum temperatures of 1400, 1500, and 1600°C. The extent of the chemical reaction depends decisively on whether or not good contact between UO 2 and zircaloy has been established. If solid contact exists, zircaloy reduces the UO 2 to form oxygen-stabilized α-Zr(O) and uranium metal. ZrO 2 does not form. The uranium reacts with zircaloy low in oxygen to form a (U, Zr) alloy which is liquid above about 1150°C and lies between two α-Zr(O) layers. The isothermal UO 2/zircaloy reaction obeys a parabolic rate law. The growth of the reaction layers can be represented in an Arrhenius diagram.

Heat-Stress Proteins and Thermal Resistance in Rat Mammary Tumor Cells

Exposure of clone MTC rat 13672NF mammary adenocarcinoma cells to continuous heating at 42 degrees C or to heating for 20 min at 45 degrees C followed by incubation at 37 degrees C induced or enhanced synthesis of several heat-stress proteins (hsp) detectable by [3H]leucine pulse labeling, gel electrophoresis, and fluorography. Hsp synthesis occurred during development and expression of thermal resistance. For example, continuous heating of MTC cells at 42 degrees C after a rapid temperature transient (about 4 min) produced thermal resistance within 4 to 5 hr of initiation of heating. Hsp synthesis was observed within 2 hr of the cells reaching 42 degrees C and continued throughout 8 hr of heating; four major hsp appeared at nominal molecular weights of 112, 90, 70, and 22 kDa. A slow temperature transient from 37 degrees to 42 degrees C over a 3-hr period increased thermal resistance by a factor of about 2 relative to a rapid transient or "shock" to 42 degrees C. However, hsp synthesis was not significant during the slow heat transient and was either reduced (at 70 and 22 kDa) or not increased (at 112 and 90 kDa) compared with the rates of hsp synthesis at the same time intervals after the rapid transient to 42 degrees C. In these mammary tumor cells, no differences in the number of hsp were detected during heating at 42 degrees or after 45 degrees C heating. Other proteins did not appear to change their relative rates of synthesis, with the exception of a clear decrease in proteins with nominal molecular weights of histones H2A, H2B, H3, and H4. Hsp synthesis was not triggered by cold shock to 23 degrees or 0 degree C, or by radiation of from 2.5 to 10 Gy. Thus hypothermic stress did not enhance hsp synthesis nor were hsp nonspecifically associated with eventual cell lethality. In these experiments, the synthesis of hsp was generally correlated with the development of thermal resistance. Determining the quantity, function, and location of stress proteins may identify targets for thermal killing and resistance. However, one paradoxical observation remains to be resolved. Under the slow temperature transient conditions, the tumor cells attained more thermal resistance with generally reduced rates of hsp synthesis. These results have two possible implications: (a) one or more hsp were not directly related to thermal resistance, or (b) hsp were involved in thermal resistance but their relative rate of synthesis depended on the severity of the heat transient. The latter would imply that the cells made other regulatory or metabolic adjustments and either utilized the hsp more effectively or required less additional hsp.

Effects of Impurities and Supporting Electrolytes On SCC of 304 Stainless Steel in High Temperature Aqueous Environments

Abstract The effects of impurities in high temperature water has been examined on sensitized 304 stainless steel under both constant temperature and transient temperature conditions. As-welded, low...

HEAT EXCHANGER FOR IN-GROUND HEAT STORAGE

The first phase of a research project using undisturbed soil for sensible heat storage is described. A laboratory scale model of a heat exchange system was constructed and tested. Thermal charging and recovery rates, modes of heat transport and transient temperature conditions, as well as over-all heat storage performance of the unit are given. The experimental results are compared with predictions of a numerical model based on mass and heat transport. A prototype field installation has been constructed and preliminary results are presented.

A Short-Time, High Temperature Mechanical Testing Facility

Abstract Design and performance details are given for a facility developed to obtain the mechanical properties of materials under high heating rate or transient temperature conditions and medium strain rates. The system uses self-resistance heating and is applicable to materials possessing electrical resistivities ranging from that of aluminum to that of graphite. Heating rates as high as 2000 K/s in graphite are attained under controlled conditions. Methods of measuring temperature and the effects of expected temperature distributions are discussed. A method for measuring strain during transient temperature conditions to 3000 K is described. Finally, results are presented for the stress-strain behavior of Type 316 stainless steel and ATJ(S) graphite obtained for heating times of few seconds.

Behaviour of concrete under thermal steady state and non‐steady state conditions

AbstractStress–strain behaviour of concrete at elevated temperatures is extremely complex and is not completely understood up to now. The creep properties of concrete at temperatures up to 300°C thus need to be determined, as well as the thermal stability of concrete during repeated cycles of heating and cooling. In this report the results of recent high temperature experiments with normal concrete specimens are presented. The main objectives of the tests were to investigate the dependence of strength and elasticity on temperature and to study the creep and deformation characteristics of concrete at temperatures up to 450°C. Transient creep data, i.e. data derived under transient temperature conditions, are compared with creep data which were measured at constant elevanted temperatures. The results suggest that transient creep values and steady state creep values in some cases may be of the same magnitude.The creep measurements appear to be in good agreement with data presented by other workers. However, the scatter in all data increases significantly with increasing temperature and differences of more than 100% can be observed. When loaded concrete specimens were cooled down to ambient temperature exptraordinarily large compressive strains can be observed. The experiments indicate clearly the considerable strain capacity of normal structural concrete can be used at temperatures higher than 100°C. In areas of high stress concentrations a tures. On the other hand, with respect to the whole structure it is necessary to limit the deformations. For a constant maximum temperature this can only be done by limiting the admissible stresses. The test results permit an initial estimation of maximum permissible stress and temperature values.

Causes of the shell and core structure and layered inhomogeneity in iron ore pellets

Equations for a multiple shell model of a sphere where induration occurs under transient temperature conditions are written and solved on a digital computer using a repeated extrapolation technique. Parameters representative of industrial induration and shrinkage-kinetic data for a commercial magnetite concentrate are used in the calculations. Results show that large temperature gradients within pellets are characteristic of the more severe heating conditions, which in turn can lead to large shrinkage gradients in the radial direction from pellet surface to the core and result in the defective pellet texture. Experimental evidence is discussed and a “propensity index,” derived from the calculations, is introduced and compared with experience.

Elasto-Plastic Creep Analysis of Axisymmetric Thick Shells under Transient Temperature Conditions by Finite Elements

Elasto-Plastic Creep Analysis of Axisymmetric Thick Shells under Transient Temperature Conditions by Finite Elements

The Effect of Temperature On Stimulation Design

During hydraulic fracturing, fluid viscosity, acid spending times, and inhibitor performance are adversely affected by the high temperatures existing in deep wells. However, when fluids are pumped down tubing at normal rates, tubing temperature drops drastically. Presented here is a method of predicting the dynamic temperature changes that occur during stimulation. Introduction Many producing oil and gas wells requiring stimulation treatments have high bottom-hole temperatures. This is illustrated in Table 1, which lists the approximate well depths where formation temperatures reach or exceed 200 degrees F. In almost all of these areas, wells of these depths are being, or soon will be stimulated either by hydraulic fracturing or by acidizing techniques. In fact, stimulation of wells having bottom-hole temperatures of about 350 degrees F has already begun in some areas. In order for these types of treatments to effect the greatest production increases, the thermal environment must be understood, and its effect on treatment fluids, chemicals, and additives must be considered. It is important, for instance, to know the relationship between the effects of the thermal environment during treatment and fracture fluid viscosity, fracture proppant settling rates, solid blocking agent performance, proppant settling rates, solid blocking agent performance, acid reaction rates, and acid retarder requirements. In designing methods of stimulation, the effect that transient temperature conditions will have on these properties has not been considered. This neglect will properties has not been considered. This neglect will cause considerable error, which will be demonstrated by comparisons in this paper. Before the effects of temperature-dependent factors on stimulation design can be accurately established, it is first necessary to determine what the thermal environment actually is during a fracturing operation. With existing technology it is impossible to measure temperatures in the fracture passages themselves. It is possible, however, to measure the temperature in the wellbore during or immediately after a stimulation operation. Such measurements show that the wellbore walls are cooled dramatically by the passage of cool fluids. This result has been predicted by Ramey as well as others in their analytical approaches to this problem. Good correlations have been made between problem. Good correlations have been made between theoretical and field-measured data. Although it is known that wellbore cooling takes place during the fracturing process, attempts to place during the fracturing process, attempts to calculate the temperature in the fracture itself during stimulation had not been published until the early work presented in Ref. 6. That study was the first, presented in Ref. 6. That study was the first, somewhat elementary, but important step in the development of a representative thermal model. Since then, a much more representative thermal model bas been developed to describe the temperature in a vertical fracture and the adjacent formation. The following discussion describes the development of this thermal model. The analytical solution, obtained through the introduction of some simplifying assumptions, bas the convenience of being usable without the need of numerical analysis techniques and digital computing equipment. Development of the Solution The hydraulic fracturing of a formation involves applying sufficient fluid pressure in the wellbore to overcome the stresses in the formation. In wells that have high temperatures, the least principal stresses generally are in the horizontal plane. This will cause vertical fractures to occur. JPT P. 493

A generalized method for photoelastic studies of transient thermal stresses

This paper describes the apparatus and experimental method which was developed for generalized studies of transient thermal stresses in photoelastic models of many different shapes under a variety of steady-state or transient temperature conditions. It explains how the desired temperature gradients are established in the models and how rapidly changing temperature and stress profiles are monitored during a test.

TVA Experience with Concrete Chimney Linings

The condition of the concrete lining for TVA’s Bull Run chimney after 15 months of operation is described together with the effects of insulation, temperature change, drying out, and acid attack. Temperature gradients and thermal stresses for startup and shutdown cycles are computed and used to predict as well as explain the cracks found in the lining. The results of sonic tests and core analyses are given to show that drying out and acid attack have had little detrimental effect, and even with vertical cracks the lining is in no structural danger. Shrinkage stresses are shown to be much more critical for the transient temperature conditions than for the steady state. At Bull Run the condition was improved by controlling the draft in the annulus. At Paradise where a similar chimney was completed in 1968 changes in the design of the concrete lining were made to better control shrinkage cracks. Inspections and tests in both chimneys will be made periodically.

Temperature Anomalies in Wells Due to Cementing of Casing

Abstract Temperature measurements were made in the surface portion of a test well drilled in Central Texas. The well portion of a test well drilled in Central Texas. The well was drilled to 304 ft by the cable tool method and surface casing was set and cemented. Temperature observations were made in the 25-hour interval between termination of drilling and installation of casing. Subsequently, temperature data were obtained, at progressively longer time intervals, to a total time of 280 hours after cementing of the surface casing when deepening of the hole by the rotary method commenced. Field observations indicated that a hole drilled by the cable tool method is heated (the maximum observed anomaly was about 5F); and hydra- tion of the cement leads to a general heating of the well. A maximum temperature of about 15F was, observed 14 hours after cementing was complete. Field measurements were supplemented by a laboratory study. Both the thickness of the cement annulus and the thermal diffusivity of the surrounding formation were varied. Results indicated that both parameters have a pronounced influence on the resulting temperature pronounced influence on the resulting temperature anomaly. Thus, an interpretation of the temperature log in terms of cement thickness behind the casing is permissible only when the lithology of the formation is reasonably uniform. Introduction The test well, Bill Stribling No. 3 (Fig. 1 ), is located in Central Texas over the Llano uplift where the sedimentary cover over the igneous basement is about 1,240 ft. The well was cable tooled to 304 ft between Sept. 22 and Oct. 27, 1964. The cable tool method was chosen since cavernous zones posed serious problems in a previous attempt with the rotary method (the bit dropped 6 ft previous attempt with the rotary method (the bit dropped 6 ft at one stage and circulation loss could not be controlled); 13-in. casing was set to 80 ft and 10-in. casing to 128 ft.. but neither casing was cemented. At noon on Oct. 27, drilling was suspended. Instrumentation All field measurements were taken with a 1,500-ft multiconductor rubber cable. Twelve glass bead thermistors are molded into the lower part of this cable at 25-ft intervals. Over the range of temperatures encountered in the shallow subsurface, these thermistors show a change of electrical resistance of about 100 ohm/ deg. F, Resistance for each thermistor is measured while the cable is at rest. Measurements are made with a four-digit bridge and an electronic direct-current null detector. Accuracy of the measurement is within 1/2 ohm. The cable resistance is measured separately for each cable position and subtracted from the reading. After the resistance of all thermistors has been determined, the cable is moved the desired distance-generally not less than 5 ft-and the next sequence of measurements is taken. Since the thermistors are insulated from the borehole fluid by about 0.1 in. of rubber, their time constant (95 percent recovery) is several minutes. Thus, a waiting period of 5 to 10 minutes is necessary before reliable measurements can be taken. As a result, each temperature log took about an hour to complete. This makes the tool ill-suited for the observation of transient temperature conditions as described in this article. A continuous logger such as the High Resolution Thermometer* or the one described by Simmons would be superior. Field Measurements Temperature measurements in the Stribling No. 3 well are summarized in Fig. 2. JPT P. 147

The Fundamentals of Infrared Hotbox Detection

Existing data on railroad car plain bearing temperatures are presented and interpreted by means of equivalent thermal circuits. Analyzing the radiation from the car truck, relating it to the characteristics of infrared measuring equipment, and discussing the handling of resulting data-all suggest approaches to more efficient use of wayside hotbox detectors. Effects of some ambient phenomena are presented, and further study of transient temperature conditions following lubrication failure is suggested.