Thermal Transient Testing Research Articles

Thermal Transient Testing

Thermal issues are becoming increasingly serious with the scaling down of integrated circuits and the increasing density brought in by advanced packaging techniques. Consequently, thermal issues need to be considered during both design and test. The present paper addresses thermal testing, and more specifically thermal transient testing.

Proposal of a Strain Concentration Model of Welded Joints for Creep-Fatigue Evaluation of Welded Structures.

As the main causes of strength reduction in welded joints subjected to cyclic thermal transients, attention was given to (1) metallurgical discontinuity in which different deformation responses of base metal and weld metal can result in nonuniform stress and strain across the weldment, (2) structural discontinuity at penetration beads of unfinished welded joints, and (3) degradation of weld metal due to precipitation of dissolved metal. In order to evaluate the first two factors, an elastic follow-up model was applied. Thermal transient strength test results verified that the elastic follow-up model ensures adequate life in elevated-temperature component weldments. The proposed method was proven to be adequate in Type 304 SS, and to have safety margin in FBR grade Type 316 SS.

Proposal of a Strain Concentration Model of Welded Joints for Creep-Fatigue Evaluation of Welded Structures.

As the main causes of strength reduction in welded joints subjected to cyclic thermal transients, attention was given to (1)metallurgical discontinuity in which different deformation responses of base metal and weld metal can result in nonuniform stress and strain across the weldment, (2)peak strain concentration at penetration beads of unfinished welded joints, and (3)degradation of weld metal due to precipitation of dissolved metal. In order to evaluate the first two factors, an elastic follow-up model was applied. Thermal transient strength test results verified that the elastic follow-up model ensures adequate life in elevated-temperature component weldments. The proposed method was proven to be adequate in Type 304 SS, and to have safety margin in FBR grade Type 316 SS.

Transient creep of concrete under biaxial stress and high temperature

Understanding concrete behavior under transient high temperature is an important aspect of structural fire research. Consequently, many investigations have been performed under uniaxial loading conditions, but, only a few under biaxial states of stress. This report has two primary goals. The mechanical behavior of unsealed concrete and mortar was studied under biaxial stresses and transient temperature. Furthermore, the influence of the concrete composition was investigated for quartzitic concrete and mortar in thermal expansion tests and biaxial transient creep tests. Based on the test results a model of the transient creep of concrete under multiaxial loading is proposed. In combination with a suitable high temperature failure model, this model is applicable for concretes with different compositions.

Thermal buckling and progressive ovalization of pipes: experiences at the TTS sodium test facility and their analysis

Two remarkable thermally induced deformation mechanisms of pipes which may have serious effects on structural integrity, thermal buckling and progressive ovalization, were observed on the horizontal piping of the sodium test facility, called TTS, with which cyclic thermal transient tests of structures had been conducted. The thermal buckling, which was caused by thermal stratification, occurred at a circumferentially welded region of the pipe where a noticeable geometrical imperfection existed. The buckling was analyzed comprehensively for this pipe, using both the finite element method and a simplified method based on Gellin's analysis results. The predictions were reasonable and gave confidence in accounting for the sodium leakage encountered at the TTS. It was also demonstrated by the finite element analyses that the progressive ovalization of the pipe cross-section from a circular to a downward triangular shape can be caused by cyclic thermal stratification under the existence of cover gas in the pipe.

Application of fracture surface topographic analysis technique to thermal fatigue crack extension in stainless steel vessel

The fracture surface topographic analysis (FRASTA) technique is applied to investigate the propagating process of fatigue crack in a model vessel made of type 304 stainless steel due to repetitive thermal shocks for 1000 cycles. FRASTA is a procedure for reconstructing the process of crack extension by comparing topographic features of coupled areas of opposing fracture surfaces via computer. Based on the result, fracture mechanics analysis is made to estimate the relationship between crack depth and applied number of thermal cycles. During the thermal transient test, acoustic emission (AE) is monitored using four channel AE sensors. The estimated number of initiating cycles and propagating behavior of macroscopic crack by fracture mechanics analysis is compared with the result of AE monitoring examination, and the usefulness of the FRASTA technique is discussed.

Space-based LH 2 propellant storage system: subscale ground testing results

An orbital cryogenic liquid storage facility will be one of the essential elements of the US Space Program to realize the benefits of space-based cryogenic propulsion vehicles such as NASA's space transfer vehicle (STV) for transporting personnel and scientific packages from a space station in low earth orbit (LEO) to geosynchronous orbit (GEO), the moon and beyond. Long-term thermal control of LH 2 and LO 2 storage cryotanks is a key technical objective for many NASA and SDI programmes. Improved retention using refrigeration, boil-off vapour-cooled shields (VCSs), multilayer superinsulation (MLI) and para-ortho (P-O) hydrogen conversion are the required state-of-the-art techniques. The cryotank system level development testing (CSLDT) programme has supported the development of these technologies. Under the programme, trade studies and analyses were followed by the design and construction of a subscale LH 2 storage facility test article for steady-state and transient thermal tests. A two-stage gaseous helium (GHe) refrigerator was integrated with the test article and used to reduce boil-off and/or decrease the time required between passive test configuration steady-state conditions. The LH 2 tank, mounted in a vacuum chamber, was thermally shielded from the chamber wall by MLI blankets and two VCSs. The VCSs were cooled with either LH 2 boil-off gas (through an optional P-O converter) or refrigerated GHe. The CSLDT test article design, assembly and results from 400 hours of thermal tests are presented along with important conclusions. A comparison of predicted and measured steady-state boil-off rates is provided for 10 test configurations, and the system time constant is addressed. Also presented are some of the unique issues and challenges encountered during these tests that are related to instrumentation and control.

Non-destructive thermal evaluation of delaminations in a laminate: Part II—the experimental laplace transforms method

After initial attempts to identify the delamination parameters of a defective slab (thermal contact resistance and depth) presented in Part I, starting from an experimental thermal contrast curve, a new identification method is presented. The definition of a locally normalized contrast that allows us to process real experiments with the one-dimensional model, together with the calculation of Laplace transforms of this contrast, make the construction of identified contact resistance profiles (rear face) or of identified depth profiles (front face) possible. Results, after processing of transient thermal images produced by thermography, compare well with nominal delamination parameters and with measurement yielded on the same slab by an ultrasonic method. The various advantages of this very fast non-destructive transient thermal testing method are presented.

Parametric analysis of the reliability of igniter systems−PARIS

A fully automated improved thermal transient test set is used to measure the thermoelectrical response of a number of different fuze heads. The fitted wire model is used to describe the heat dynamics in the fuze head and to calculate a number of intrinsic thermal properties. These properties are used as input for a parametric analysis of the reliability of igniter systems (PARIS). Comparison of PARIS with firing levels obtained with the classical Robbins–Monro method has been used to validate this new way to estimate the sensitivity of fuze heads.

Crack Initiation and Growth Behavior Dissimilar Weld Joint of SUS304 and 2.25Cr-1Mo Steels Subjected to Cyclic Thermal Strains

Cyclic thermal transient fatigue tests of dissimilar weld joints of SUS304 and 2.25 Cr-1Mo steels with Inconel 82 buttering were performed in order to study the general behavior of crack initiation and growth, including crack locations, directions and densities under the respective loading conditions. The crack initiation sequence at different parts of the test models corresponded well with the result of analytical prediction using the finite element method. The results suggest that counter bore machining near the buttering boundary with 2.25 Cr-1Mo steel must be kept sufficiently apart from the joint area. The allowable number of thermal transient cycles according to the ASME CODE CASE N-47 and the elevated-temperature structural design guide developed by the PNC (Power Reactor and Nuclear Fuel Development Corporation)was shown to have a considerable Safety margin compared with the crack initiation data of 1 mm in depth at all parts of the pipe models.

Transient Liquid Crystal Measurement of Local Heat Transfer on a Rotating Disk With Jet Impingement

An experimental technique has been developed for measurement of local convection heat transfer characteristics on rotating surfaces, utilizing thin liquid crystal surface coatings in a thermal transient test procedure. The encapsulated liquid crystal coatings used are sprayed directly on the test surface and their response is observed and processed during the transient with automated computer vision and data acquisition systems. Heat transfer coefficients are calculated from the thermal transient response of the test surface, as determined from the color indication from the thin coating. A significant advantage of the method, especially for convection in disk/shroud cavities that may contain recirculating fluid regions, is that appropriate thermal boundary conditions are naturally imposed on all of the boundary surfaces. The method is also relatively fast and inexpensive, and allows the geometry of the disk and stator surfaces to be changed easily, without the expenses of mounting discrete heat flux and temperature sensors and equipment to transfer information to a stationary frame of reference. Application of the experimental technique is demonstrated with detailed radially local surface Nusselt number distributions acquired for cases involving jet impingement onto a smooth disk, rotating in close proximity to a parallel plane stator disk. A single circular jet, with nozzle exit flush mounted in the stator, is oriented normal to the disk surface at various radii and flow rates. Local Nusselt numbers are presented nondimensionally as functions of both disk and flow Reynolds numbers. The results indicate that the local radial heat transfer distribution can be controlled by varying the impingement radius, but maximum radially averaged heat transfer is obtained with impingement at the disk center.

Crack Initiation and Growth Behavior on SUS304 Steel Piping Components During Cyclic Thermal Transient Strains

A series of thermal transient fatigue tests on five SUS304 stainless steel straight pipe models with circumferential weld joints and a nozzle model were performed to study the general behavior of crack initiation and growth including crack locations, directions and densities under respective loading conditions. The crack initiation sequence at different parts of models corresponded well with the result of analytical prediction using the finite element method. The potential margin on the allowable number of thermal transient cycles according to the ASME CODE CASE N-47 and the Elevated Temperature Structural Design Guide developed by the Power Reactor and Nuclear Fuel Development Corporation was evaluated, and the result showed a considerable safety margin compared with the data on initiation of cracks of 1 mm in depth at all parts of pipe models including circumferential weldings, notches, and other structural discontinuities.

INITIATION AND GROWTH OF CRACK IN PIPINGS AND STRUCTURES OF SUS304 STEEL SUBJECTED TO CYCLIC TRANSIENT THERMAL STRAIN

Thermal transient fatigue tests of five straight pipe models with circumferential weld joints and a nozzle model made of SUS304 steel were performed. Crack locations, directions and densities were observed. Initiation sequences of cracks at different parts corresponded well with the result of analytical prediction using FEM. We evaluated the potential margin on the allowable number of thermal transient cycles according to the ASME Code Case N-47 and the elevated temperature structural design guide developed by the Power Reactor and Nuclear Fuel Development Corporation. The results show a considerable safety margin for the initiation of cracks of 1mm in depth.

Initiation and growth of crack in dissimilar weld joint of SUS304 steel and 21/4Cr-1Mo steel subjected to cyclic transient thermal strain.

Thermal transient fatigue tests of ten pipe models with SUS304 steel and 21/4Cr-1Mo steel dissimilar joints were performed. Transient temperature distributions and thermal stresses caused by sudden a temperature change of the internal fluid were analyzed using FEM. Using these data, we evaluated the potential margin of the allowable number of thermal transient cycles according to the ASME Code Case N-47 and the elevated temperature structural design guide by the Power Reactor and Nuclear Fuel Development Corporation. The results are as follows: (1) The sequence of crack initiation of various parts of the test models could be well predicted by the analysis. (2) The buttering boundary should be kept suffiently apart from any discontinuity caused by counter-bore machining. (3) A sufficient safety margin for initiation of a crack 1mm in depth is observed and compared with the result based on the design rule by PNC.

Analysis of the Functioning of Bridgewire Igniters based on the fitted wire model

AbstractThis paper contains the results of a study concerning the thermoelectrical response of a bridgewire fuze head to a d.c. pulse. The experimental part of the study has been performed using a home‐built, improved version of the Thermal Transient Test. The experimental temperature of the bridgewire fuze head as a function of time and current amplitude is described by means of the “fitted wire model”, an extension of the well‐known Rosenthal model. The experimental results are in excellent agreement with the results obtained with the fitted wire model. On the basis of this fitted wire model and postulating a critical temperature of the bridgewire, induction times and energy and power characteristics can be calculated. Furthermore, the model enables the evaluation of the effects of changes in the model parameters upon the functioning of the bridgewire fuze head.

Effects of Reynolds number and Richardson number on thermal stratification in hot plenum

Thermal transient water tests were performed using a simplified hot plenum model of a pool-type LMFBR to examine the fundamental characteristics of thermal stratification during reactor trips. These tests were divided into two series to clarify the effects of (1) Reynolds number and (2) Richardson number on the behavior of thermal stratification. The results of the first series indicated that the characteristics of thermal stratification were independent of Reynolds number in the range of Re > 10 4. It was concluded from the results of the second series that the rising speed of the thermal interface and the temperature gradient at the interface varied proportionally with Ri −1 2 and Ri 1 2 , respectively. In addition, large scale internal waves, called internal standing waves, were observed under the condition of Re > 10 4 and 1 < Ri < 5.

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.

Thermal Property Measurements On Oil Sands

Abstract Thermal conductivity and thermal diffusivity properties of oil sand have usually been measured on disturbed core material under ambient laboratory conditions and the measured values are not representative of field conditions at in-situ thermally stimulated production facilities. A transient state thermal test cell for thermal conductivity and thermal diffusivity testing of soil and rock cores has been devised by the authors. The test cell which is specifically designed for thermal property measurements of undisturbed oil sand and shale core samples, has an operational temperature range of 20 °C to 200 °C. Confining pressures up to 10 MPa can be applied to the sample to simulate overburden load and pore fluid pressures up to 10 MPa can be generated within the test cell to ensure fluid saturation of the sample throughout a test. A general description of the test apparatus is given and the thermal conductivity and thermal diffusivity theories and analytical methods used to interpret the test results are outlined. Experimental results for several samples of Athabasca oil sand material are given. Their specific hears are calculated from the results and from the weighted average method and the comparison shows that the test methods and analyses for the thermal conductivity and diffusivity are valid. Results are compared to previously published thermal conductivity measurements on Athabasca oil sands and the importance of the temperature and of the air-water-bitumen saturation is shown. Introduction In-situ thermal methods (such as steam stimulation and in-situ combustion) have been proven to be favorable for the recovery of heavy oil and bitumen from heavy oil and oil sand deposits in Alberta and elsewhere in the world. Many numerical and analytical models for reservoir simulation during heating are available in the petroleum industry. In order that these models can yield meaningful results, correct input parameters that characterize the reservoir are essential. Although the general physical properties of the oil sand deposits are relatively well defined, there appears to be a lack of information on the thermal properties of the materials, particularly at elevated temperature and pressure conditions. With the objective to determine thermal properties of natural oil sand core samples under simulated in-situ conditions, the authors and their coworkers have developed a transient state thermal test cell for the measurement of thermal conductivity and thermal diffusivity on oil sand, shale and limestone cores. Factors Affecting Thermal Properties Table 1 lists all the major factors that affect the three important thermal properties of oil sands, namely thermal conductivity, thermal diffusivity and specific heat. As recognized by many investigators, the material itself (mineral grains, soil structure and density), its degree of saturation and the temperature are significant factors that control the thermal properties of oil sands. There is, however, an uncertainty as to the effects of bitumen and water proportions on the thermal properties of oil sands. Some researchers suggest that there is no significant difference in thermal conductivity whether the non-water phase in the pores is oil or air while others argue that an oil/bitumen parameter should be included for a proper correlation analysis to be made.

Electrothermal Characterization for a Fusible Link

A low energy fusible link was characterized by its electrothermal analog model. Thermal transient testing apparatus, procedures, and methodology were used to determine the required parameters. The thermal time constant was determined by a novel comparison technique. Typical data and its relevance are presented.

Thermal transient simulation tests of a sodium valve

Abstract The feasibility of thermal transient testing of sodium components using a fluid other than sodium is considered. Simulation of thermal transient conditions that may exist in the sodium system is considered to be, in general, achievable in a special test fixture, if the thermal and hydraulic conditions of the fluid to be used are properly selected. This feasibility is demonstrated for the 28 in. FFTF hot-leg isolation valve by introducing a high-speed gaseous nitrogen flow into an annulus formed by the valve body and a cylindrical pipe insert. The structural wall temperature distributions were estimated first for the sodium system, and the simulation was established by equating the transient heat transfer rates as a function of time at key locations in both real sodium and simulating nitrogen systems. Remarkably good simulation test results were achieved.