High-resolution Thermal Analysis Research Articles

POD-based reduced-order modeling study for thermal analysis of gas-cooled microreactor core

Small modular reactors require multi-physics coupling calculations to balance economy and stability, due to their compact structures. Traditional tools used for light water reactors are not effective in addressing the several modeling challenges posed by these calculations. The lumped parameter method is commonly used in the thermal analysis for its high computational speed, but it lacks accuracy due to the thermal model is one-dimensional. While computational fluid dynamics software (CFD) can provide high-precision and high-resolution thermal analysis, its low calculation efficiency making it challenging to be coupled with other programs. Proper Orthogonal Decomposition (POD) is one of the Reduced Order Model (ROM) methods employed in this study to reduce the dimensionality of sample data and to improve the thermal modelling of gas-cooled microreactors. In this work, a non-inclusive POD with neural network method is proposed and verified using a transient heat conduction model for a two-dimensional plate. The method is then applied to build a reduced order model of the gas-cooled micro-reactor core for rapid thermal analysis. The results show that the root mean square error of the reactor core temperature is less than 1.02% and the absolute error is less than 8.2°C while the computational cost is reduced by several orders of magnitude, shortening the calculation time from 1.5-hour to real-time display. These findings proved the feasibility of using POD and neural network in the development of ROMs for gas-cooled microreactor, providing a novel approach for achieving precise thermal calculation with minimized computational costs.

High-resolution thermal analysis at thermoplastic pre-impregnated acomposite interfaces

In situ consolidation of pre-impregnated thermoplastic composite requires as much as possible intimate contact as well as an appropriate molecular diffusion across the interface, where the intimate contact takes place. The last depends on the temperature that influences the molecular mobility. Thus, in order to evaluate the consolidation, first, we must describe accurately the composite surfaces and then, when placed in contact for manufacturing the laminate, a high-resolution simulation of the resulting thermal model must be accomplished to have access to the thermal history at the rough contact surface. In this paper, we proceed in three steps: (i) first the pre-preg surface is assimilated to a random process, a fractional Brownian motion, that can be characterized by two main descriptors, the topothesy and the fractal dimension; then, (ii) assuming the rough surface is represented by a Cantor set, the different parameters describing the fractal are determined from the statistical surface description; and finally, (iii) the resulting Cantor set representation will be considered as the geometrical support of a high-resolution thermal analysis accomplished within the proper generalized decomposition framework that allows exploring scales never until now attained.

Characterisation of High Temperature Phase Stability and Evaluation of Metallurgical Compatibility with SS 304L, of Indigenously Developed Alternate Shielding Material Ferro- Boron for Fast Reactor Applications

Abstract The high temperature phase stability and metallurgical compatibility of Ferro boron alloy which contain about 15 wt.% boron and some impurity elements like C(0.3),Si (0.29), P(0.006) etc, with 304 L SS have been evaluated using calorimetry and metallography. The X-ray diffraction of ferroboron revealed the presence of major FeB and minor Fe2B constituents, besides a small amount of Fe3(B, C). The thermal stability of this ferroboron alloy has been characterised up to melting by high resolution thermal analysis. In addition, the enthalpy increment measurements and hence specific heat estimates have been also made in the temperature range 400- 1200oC, using drop calorimetry. The high temperature metallurgical interaction between ferroboron and 304L SS clad has been simulated at temperatures 823 – 1073 K (550-800 oC) for reaction times up to 5000 h, using diffusion couples.

Decomposition of the synthetic hydrotalcites mountkeithite and honessite—a high resolution thermogravimetric analysis and infrared emission spectroscopic study

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer combined with infrared emission spectroscopy has been used to study the thermal decomposition of synthetic hydrotalcites honessite (Ni 6Fe 2(SO 4)(OH) 16·4H 2O) and mountkeithite (Mg 6Fe 2(SO 4)(OH) 16·4H 2O) and the cationic mixtures of the two minerals. High resolution thermal analysis shows the decomposition takes place in five steps. A mass loss step is observed over the 125–150 °C temperature range and is attributed to the mass loss due to dehydration. A second mass loss step is observed over the 260–330 °C temperature range and is attributed to dehydroxylation. The third mass loss occurs from 350 to 460 °C, and is assigned to a loss of oxygen. The fourth mass loss step is ascribed to the loss of sulphate from the hydrotalcite and occurs over the 676–820 °C temperature range. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and sulphur dioxide. The changes in the chemical structures are readily followed by infrared emission spectroscopy.

Decomposition of the synthetic hydrotalcites mountkeithite and honessite?a high resolution thermogravimetric analysis and infrared emission spectroscopic study

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer combined with infrared emission spectroscopy has been used to study the thermal decomposition of synthetic hydrotalcites honessite (Ni6Fe2(SO4)(OH)16·4H2O) and mountkeithite (Mg6Fe2(SO4)(OH)16·4H2O) and the cationic mixtures of the two minerals. High resolution thermal analysis shows the decomposition takes place in five steps. A mass loss step is observed over the 125–150 °C temperature range and is attributed to the mass loss due to dehydration. A second mass loss step is observed over the 260–330 °C temperature range and is attributed to dehydroxylation. The third mass loss occurs from 350 to 460 °C, and is assigned to a loss of oxygen. The fourth mass loss step is ascribed to the loss of sulphate from the hydrotalcite and occurs over the 676–820 °C temperature range. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and sulphur dioxide. The changes in the chemical structures are readily followed by infrared emission spectroscopy.

Thermal decomposition of synthetic hydrotalcites reevesite and pyroaurite

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni6Fe2(CO3)(OH)16·4H2O) and pyroaurite (Mg6Fe2(SO4,CO3)(OH)16·4H2O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. A. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide.

Thermal decomposition of the natural hydrotalcites carrboydite and hydrohonessite

A combination of high-resolution thermogravimetric analysis (HRTGA) coupled to a gas evolution mass spectrometer combined with infrared emission spectroscopy has been used to study the thermal decomposition of two Australian hydrotalcites carrboydite (Ni 6Al 2(SO 4,CO 3)(OH) 16·4H 2O) and hydrohonessite (Ni 6Fe 2(SO 4,CO 3)(OH) 16·7H 2O). High-resolution thermal analysis shows the decomposition takes place in five steps. Each step is related to the loss of water, hydroxyl units, carbonate and sulphate. Infrared emission spectroscopy clearly identifies the presence of these molecular species and the temperature at which they are lost. Minor amounts of carbonate are observed in the minerals. Water is in two states in the structure, namely weakly hydrogen bonded and strongly hydrogen bonded. The symmetry of the sulphate anion is reduced through this hydrogen bonding.

Controlled rate evolved gas analysis: 35 years of rewarding services

Abstract This paper reviews, in a chronological way, not avoiding a personal touch, a number of aspects of controlled rate evolved gas analysis (CR-EGA): principle, practical (and fortuitous) reasons for its start, difficulties encountered, main developments and specific applications, especially in the field of finely divided or porous materials, including high resolution thermal analysis, preparation of Taylor-made porous adsorbents and kinetical studies.

Shape memory alloys: from high-resolution thermal analysis to predictive modelling and simulation

Using high-resolution automatised equipment (close to 0.001 N, 0.1 μm and 0.005 K), detailed observations can be made of the surfaces stress, strain and temperature (σ, ϵ, T) of Cu-Zn-Al shape memory alloys. The analysis of the experimental curves allows a model of the behaviour of the alloy to be formulated. The model deals with a group of independent plates with a limited maximum growth and it separates the total friction into two parts: the nucleation of the domains of martensite or austenite (parent phase) and the friction of the movement of the interphases (the martensite growing-shrinking process). It is based on the existence of thermoelasticity/pseudo-elasticity. For local changes of composition and/or atomic order, the local temperature of transformation of the parent phase is assumed to be slightly different. The equation of Clausius-Clapeyron regulates the relationship between the external fields (temperature and stress). The results of the model with respect to changes in temperature and external stress, are consistent with the experimental measurements.

Martensitic transformations in shape-memory alloys: Successes and failures of thermal analysis and calorimetry

The development of adapted equipment for high-resolution thermal analysis (thermomicroscopy, acoustic emission, stress-strain and heat conduction calorimetry) provides macroscopically relevant information about the microscopic interactions and the effect of the defects in martensitic transformations of Cu-based shape-memory alloys, e.g., levels of resolution and evolution time scales, intrinsic thermoelasticity, separation between the effects of nucleation and friction. Furthermore, making direct measurements and applying a simple thermodynamic formulation directly relates the friction work (mechanical, analogous to the entropy production) with the width of the calorimetrically calculated hysteresis cycle. Thus, some thermodynamic difficulties found in the measurements and encountered in recent interpretations in the literature are avoided.

Study of the hysteresis cycle in Cu-Zn-Al shape-memory alloys by high resolution thermal analysis

A high resolution thermal analysis is used to study the martensitic transformation in Cu-Zn-Al shape memory alloys. The characteristics of the single-interface single-variant transformation induced either by temperature or by stress are analyzed and calorimetric measurements on this type of transformation are reported. Thermoelasticity, stabilization of martensite and recovery of the β phase, pinning points and coalescence of plates of the same variant appear as phenomena which prevent the reproducibility of the transformation path. The evolution of the spontaneous global transformation with cycling is measured calorimetrically and the effect of ageing at 373 K is estimated.

Shape memory alloys: Local and global transformations by high resolution thermal analysis

The use of high resolution automatised equipment (HRTA, conduction calorimetry, stress-strain-temperature) allows to study, locally and/or globally, the martensitic transformations of the alloys with memory (Cu-Zn-Al). The observations allow to establish the phenomenology of the effects of the cycling on the crystalline structure. Particularly, the formation of defects, the interactions between the interphases and the precipitates that change the relative stability of the phases, the effects of the nucleation and the growth. The experimental research of the area of coexistence of the two phases allows to set a phenomenological model coherent with the experimental observations.

Automatic equipment with improved performances (ATD and DSC) in shape memory alloys studies

We describe an experimental set-up of high resolution thermal analysis (HRTA) activated by Peltier effect and computer-controlled by the signal processing that allows a high resolution programming of the temperature and a reproducibility better than ±0.01 deg.The basic equipment is suitable for studying the behaviour of the shape memory alloys (i.e. Cu based alloys). We also describe the applications of the system, which allows to build up a calorimetric system (heat flux or conduction calorimetry) (resolution 1.5 μW) or a stress-strain-temperature system of 20 N of maximum charge (resolution around 1 mN and 0.1 μm.