Thermal Analysis Methodology Research Articles

Study of the entropy and enthalpy of gamma irradiated TiC nanoparticles

The thermal characteristics of nanocrystalline titanium carbide (TiC) particles were systematically compared before and after gamma irradiation through the application of Differential Scanning Calorimetry (DSC) spectroscopy. Utilizing experimental findings, the Gibbs energy of titanium carbide nanoparticles was ascertained within the temperature range spanning from 300 to 1270 K. The investigation of potential phase transitions in nanoparticles and the amorphization processes induced by gamma radiation was investigated employing the Differential Thermal Analysis (DTA) methodology. The enthalpy and entropy of the system comprising nanocrystalline 3C-SiC particles were computed both before and after exposure to gamma irradiation, with theoretical calculations corroborated through comparison with experimental outcomes. The values derived from experimental results for all thermophysical parameters were compared both before and after exposure to gamma radiation.

Power Circuit Design and Analysis of Controller For High-Power Axial Flux PMSM

Designing a high-power controller having high efficiency for permanent magnet motors is a challenge for developers in recent times and very few techniques are available. Design and analysis of power electronic drive for a high-power axial flux permanent magnet synchronous motor is presented in this paper. The motor under consideration here is having two outer stators and single permanent magnet rotor to drive the shaft. Control schemes and methodologies are the major concentration for research. Present paper explains a method to estimate the operational drive parameters and loss calculation according the selected power switches. In addition to this, thermal modelling is also important for designing a controller for high power machines. The hardware selection for high current switching operations is very critical for reliable and robust operation. Parts like IGBT module, gate driver, DC link capacitor, snubbers, current sensor sensitivities and estimation of losses are also critical along with control logic and processor. The importance of thermal analysis for high current switching drives is discussed and methodology for thermal analysis of power electronic devices is explained. The current work focuses on hardware level design of high-power drive for 150kW axial flux PMS motor.

Thermal Network Modeling and Thermal Stress Evaluation for a High-Power Linear Ultrasonic Motor

This article presents a high-efficient thermal analysis methodology and outlines a set of useful design guidelines for high-power linear ultrasonic motors. A thermal network modeling technique is introduced to rapidly calculate the temperature rise for a typical high-power linear ultrasonic motor with a V-shaped stator. First, a six-terminal equivalent circuit for Langevin piezoelectric transducer considering the prestress bolt loss and all three losses in piezoelectrics is proposed to calculate the stator loss. Then, the calculated losses along with the friction loss are used as inputs into the developed thermal network model to calculate the temperature rise of critical parts of the motor. Furthermore, an analytical mechanical model combined with the proposed thermal network is established to calculate the temporal–spatial distribution of the stator thermal stress for evaluating its fatigue under the heating-up process. Finally, some experimental measurements and finite-element simulations are conducted to validate the theoretical analyses.

A new methodology for thermal analysis of geological disposal of spent nuclear fuel using integrated simulations of gamma heating and finite element modeling

A new methodology is illustrated, where the evolution of temperature in a geological disposal system for spent nuclear fuel is estimated by integrated calculations of a spatially distributed gamma heating source with conventional finite element thermal transport modeling. A case with one canister loaded with fuel assemblies with a cooling time of 30 years in a KBS-3 type repository illustrates the methodology. For this particular case, the effect of including distributed gamma heating rate in the modeling has a small impact on the temperature distribution compared to the conventional case of heat generated locally in the canister, resulting in a small decrease of the maximum temperature in the canister. A large proportion of gamma heating occurs inside the outer boundary of the copper canister for this case. Other potential consequences of radiation escaping the canister are discussed.

Temperature analysis of steel box girder considering actual wind field

Most existing studies on bridge thermal analysis have ignored the influence of wind on the resultant temperature distribution, in which a constant value of wind speed is applied to all structural surfaces. In fact, the wind blowing across the girder exterior surface significantly affects the heat-transfer convection coefficient and consequently influences the accuracy of the thermal analysis results. For the streamlined steel box girder in particular, the local wind speeds on different surfaces even under the same inflow wind speed could vary significantly, because the steel box girder is composed of multiple surfaces with different azimuth angles. In this paper, a novel thermal analysis methodology for predicting the temperature characteristics of steel box girders is proposed considering the actual wind field distribution around the girder. Validation studies are first performed to validate the applicability of the proposed methodology. Subsequently, the proposed thermal analysis methodology is applied to a typical bridge, with which the temperature distribution characteristics of its steel box girder is investigated in detail. Meanwhile, parametric analysis, including the inflow wind speed, the season, the geometry of box girder, and the influence of vehicle are conducted to identify their effects on the temperature distribution characteristics of the girder quantificationally.

Thermal-striping analysis methodology for sodium-cooled reactor design

Computational fluid dynamics simulations have been performed to study the applicability of engineering CFD methods for thermals striping analysis. Thermal striping is the fluctuating temperature profile in a solid caused by fluctuating fluid temperature, and the resulting thermal stresses cause high cycle fatigue and eventual material failure. This study presents the methodology for thermal striping analysis, including a transient conjugate heat transfer RANS simulation benchmarked against a sodium triple jet experiment. Multiphysics calculations are implemented to analyze the thermal stresses in the solid domain caused by the coupled heat transfer between the fluid and solid domains. Validation data from a liquid sodium triple jet experiment include time-averaged temperature measurements and power spectra of the temperature signal. The numerical results agree well with these experimental measures, demonstrating key features such as the dominant frequency of temperature fluctuations. The applicability of a low-cost wall treatment method is demonstrated, enabling key computational savings. Finally, the performance of two finite element stress analysis software packages is compared, and the validity of the lower-cost method is confirmed. These results demonstrate the applicability of engineering methods for computational thermal striping calculations, enabling thermal striping estimations in large fluid systems such as the core of a liquid metal-cooled nuclear reactor.

An approximate model of a multilayer wire-on-tube condenser operating with R134a and R600a: Experimental validation and parametric analysis

This study presents the development of a new approximate model for a multilayer wire-on-tube condenser used in the domestic refrigeration industry. This model is based on physical foundations and empirical correlations, as well as on the ε-NTU thermal analysis methodology. It has been designed for three zones according to the state of the refrigerant. The input parameters to the model correspond to typical geometric characteristics of this type of condenser and operating conditions. As output parameters, the emphasis was placed on the thermal capacity of the condenser, and the refrigerant side and air-side outlet temperatures. For its validation, tests were carried out with real refrigerators, one of them operating with R134a and the other with R600a. The model prediction showed maximum relative errors of ±5% for thermal capacity and ±0.5K for temperatures. Finally, a parametric study was carried out analyzing the effect of varying the main geometric parameters such as tube and wire diameters, and wire and tube pitches.

A solar regenerated liquid desiccant evaporative cooling system for office building application in hot and humid climate

In this paper, we provide the thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with fewer simplifying assumptions compared to earlier works; iii) large cooling capacity (~18.8 TR) under harsh climate; and, iv) a comprehensive year-round case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for year-long analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40 and 0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55–2017, throughout the year.

Pyrolysis performance of peat moss: A simultaneous in-situ thermal analysis and bench-scale experimental study

Peat moss in drained peatlands has become a non-negligible source of greenhouse gases (GHG) emission. Pyrolysis is a potential technique to convert carbon-emitting peat moss to carbon-storage materials. This work investigates the behavior of peat moss pyrolysis by a combined in-situ thermal analysis and bench-scale pyrolysis experiment methodology. The simultaneous thermal analyzer, which provides the simultaneous TG/DTA analysis, was employed to reveal the thermal decomposition behavior of peat moss. The samples were heated up to 900 °C with different heating rates of 10, 15, and 20 °C/min. Thereafter, pyrolysis experiments with peak temperatures of 450, 500, 550 and 600 °C were performed in a bench-scale pyrolyzer. It was found that there are four main stages and two micro stages of mass loss during peat moss pyrolysis from room temperature to 900 °C. Also, kinetic parameters were calculated based on the results of TG and DTG by the Kissinger-Akahira-Sunose (KAS) method and the Coats-Redfern (CR) method. In the bench-scale pyrolysis experiments, four phases, i.e., char, tar, aqueous phase, and gas, were obtained and characterized. The carbon distribution and the GHG emission from peat moss pyrolysis were determined.

Solar panel failure detection by infrared UAS digital photogrammetry: a case study

Infrared thermal photogrammetry is an attractive solution for the diagnosis of photovoltaic systems. Traditional systems often require high-end drones and expensive cameras, but more recently, low-cost thermal sensors on board of small-scale drone platforms suitable for digital photogrammetry have emerged as a promising approach. Nevertheless, studies evaluating its effectiveness can barely be found in the literature. Unlike many works in the literature that analyze individual images, through digital photogrammetry it is also possible to create orthomosaics of complete installations or high-resolution maps of segments that cannot be visualized and analyzed properly with single images. In this work, a photogrammetric thermal analysis methodology with a small-scale drone and a thermal camera is presented and a case of study is analyzed. To validate and quantitatively scale the results, functional tests on the panels were performed and temperature measurements with a thermocouple on the panels were carried out. The results from both single images and orthomosaics confirm that it is possible to obtain qualitative and quantitative information to detect failures in solar panel installations with a low-cost thermal sensor on board of small-scale drone platforms. These results may be useful for defining surveillance and maintenance procedures with low-cost equipment in photovoltaic installations, which can help for early detection of failures, operation with higher efficiency and to achieve longer lifetimes of the panels.

Methodology for thermal analysis of spent nuclear fuel dry cask using CFD codes

As the capacity in spent fuel pools is depleted, dry storage systems have been increasingly used. The key parameter for fuel cladding behaviour during dry storage is the temperature; that cannot surpass 400 °C based on NRC regulation. This paper proposes a new methodology to realistically calculate the thermal behaviour of cask/fuel system.In order to obtain realistic values, the methodology is divided in two steps. In the first step the outside part of the cask is simulated (from the inner surface of the interior cavity to the surrounding air). The second step is a fully fledge simulation of the inner cask (from the clad of the fuel assemblies to the exterior surface of the cask). This two-step approach shows some advantages compared to previous methodologies: the first step calculates a realistic boundary condition to apply in the second step and estimates the impact that the cask has on the near environment while the second step provides the temperature distribution for every single clad in each assembly.To ensure the validity of the methodology, several sensitivity analyses have been conducted, a grid independence study to the discretization error, a turbulence modelling has been applied to the outside and inner model and finally a study of the gaps between the canister and the inner cylinder has been carried out.Of these studies the gaps proved the most important one with changes in PCT of up to 28 °C. The changes in the size of the gaps not only change the overall temperature distribution but also the heat transfer mechanisms and the flow paths followed by the helium.

사용후핵연료 저장 캐니스터 구조물인 바스켓 디스크간 간극의 매질 종류 및 크기에 따른 열전달 연구

This study investigates numerically the heat transfer effects on gap media and size between the basket and disc in the spent fuel dry storage canister using Fluent 14.5 code. For helium gas, helium solid and stainless steel in media, maximum temperatures of fuel region were measured by varying the heights and width of gap, and the heat transfer phenomena in the gap were described in detail. It is found that the maximum temperature of fuel region is kept low in case the width of the gap is narrowed at the fixed heights of disc. Setting the medium to helium solid in the range of 2 to 10 mm leads to the similar results for the helium gas regardless of the disc heights, and the less time is required for convergence. From these results, it is considered that the medium of the gap may be applied as a helium solid rather than the helium gas in order to increase the efficiency of thermal analysis in terms of heat removal. The results of this study will be used as the theoretical basis for the thermal analysis methodology of the spent fuel dry storage system.

Validation of a methodology for thermal stratification analysis in sodium-cooled fast reactors

Thermal stratification phenomena usually occur in the upper plenum after a scram of sodium-cooled fast reactors, which should be closed concerned in the fields of structural integrity assessment and residual heat removal capacity. A 2-dimensional analysis program under cylindrical coordinate was developed for predicting the in-vessel thermal hydraulics. Non-orthogonal block-structured grids were generated to resolve the problems with complex structures. A second-order discrete scheme based on midpoint rule was applied to the spatial discretization of convection and diffusion terms. Two sets of experiments characterized by distinct shapes of their apparatuses were used for the validation, mainly from the viewpoints of vertical temperature distribution and rising behaviors of the stratification interface. Results show that RANS-type turbulent models make the significant impacts on different flow regimes. In the calculation of a scaled model with plenty of stagnant sodium in the upper region, the realizable k − ε model (RKE) considering the mean deformation rate gives better outcomes than the standard k − ε model (SKE). For the plant-type upper plenum with considerable flow rate along the entire height, buoyancy modeling is the crucial issue to follow the upward movement of the interface and the relaxation process of the temperature gradient. In this case, employment of the turbulent Prandtl number reflecting the damping effect by incorporating the local Richardson number well reproduced the experimental results.

Differential calorimetry scanning: current background and application in authenticity of dairy products

Dairy foods are consumed in a large scale by most age groups and social classes, because it is recognized benefits for the consumers’ health and the advantages considering a nutritional point of view. In this sense, they are intentionally subjected to different types of frauds (removal of some valuable ingredients or even substitution of ingredients by inferior substances) committed by industries in order to increase the profitability of the products’ sales. Thus, it is very important to have rapid, non-invasive and precise techniques to identify easily frauds in dairy food. Differential scanning calorimetry (DSC) is a simple thermal analysis methodology recognized as one of these techniques. In this review, the principles and its application for evaluating the authenticity of dairy products are presented.

Hydrogen Containment Process for Nuclear Thermal Engine Ground Testing

Nuclear thermal propulsion is an enabling technology for delivering large payloads to Mars, and ground testing of a nuclear thermal engine is an important part of the development. A critical issue in nuclear thermal engine ground testing is the presence of a large amount of hot hydrogen exhausted during the tests, which needs to be totally contained. A hydrogen containment process is proposed in this study in which an oxygen-rich burner and a tubular heat exchanger are employed for hydrogen containment. The objective of this effort is therefore to demonstrate that this new process could achieve the goal of total hydrogen containment for nuclear thermal engine ground testing. A multidimensional pressure-based multiphase computational fluid dynamics methodology was used to conceptually size the oxygen-rich burner, whereas a one-dimensional thermal analysis methodology was used to conceptually size the heat exchanger. Subsequently, a steady-state operation of the entire hydrogen containment process (from the pressure vessel through the nozzle, diffuser, burner, and heat exchanger) was simulated numerically, with the aforementioned computational fluid dynamics methodology. The computed results show that the exhaust hydrogen is reduced to meet the design goal at the end of the heat exchanger, demonstrating the hydrogen containment capability of the proposed process.

Mapping water status based on aerial thermal imagery: comparison of methodologies for upscaling from a single leaf to commercial fields

Aerial thermal remote sensing can provide a means for collecting spatial plant water status data. Many studies have shown their potential in irrigation management but the adaptation of this technology is not straight forward. In this paper, knowledge accumulated in recent years on thermal imagery analysis methodology for water status mapping is summarized aiming at indicating alternatives to calculate the Crop Water Stress Index (CWSI) for commercial scale water status mapping. Based on literature overview, four forms of wet-baselines to calculate CWSI were selected, namely: artificial wet reference surface, two theoretical calculations and a statistical bio-indicator. These baselines were used to calculate CWSI based on multi-temporal aerial thermal images of cotton fields. CWSI based on a statistical bio-indicator and one of the theoretical wet-baselines provided the best correlations. It is argued though that the statistical one is preferable since it includes the plant characteristics and it is farmer-friendly. Based on bio-indicators, leaf water potential maps of three commercial fields were produced on several dates through the season. Water status spatial patterns were not static and the effect of static factors like sandy soil patches also changed through the season. The maps show the importance of in-season variability mapping for rational irrigation management. To improve current variable-rate irrigation, the concept of in-season irrigation management zones (IMZ) based on thermal-images should be considered and integrated with the delineation of static irrigation IMZ.

A methodology for thermal analysis of complex integrated systems: Application to a micro-CHP plant

Thermal analysis and management studies are commonly conducted from early design stages of new products by numerical means. However, the application of three-dimensional tools for evaluating the thermal performance of multi-component systems, exhibiting high geometrical and phenomenological complexities may become unpractical in view of the long computational times. Therefore, a methodology for thermal analysis of complex thermal systems is developed to improve the overall numerical convergence rate. The methodology is based on an iterative two-way coupling procedure between two sets of simulations: simulation set where critical components are individual and fully simulated (component-level simulations); and simulation framework where the overall system is considered with hollow components (system-level simulation). A communication strategy between both simulation sets is established. The methodology can be readily applied for performing thermal management studies. A verification procedure for the suggested methodology is firstly carried out. Afterwards, the methodology is applied to investigate the thermal performance at the system-level of a fuel cell based μ-CHP unit, namely regarding the feasibility of components integration. The methodology application allowed the identification of critical hot-spots (with temperatures up to about 400°C) on the surface of the unit internal components, mainly due to an inadequate insulation thickness and shape.

Parametric Modeling of Welding Processes Using Numerical-Analytical Basis Functions and Equivalent Source Distributions

A general methodology for inverse thermal analysis of steady-state energy deposition in plate structures, typically welds, is extended with respect to its formulation. This methodology is in terms of numerical-analytical basis functions, which provide parametric representations of weld-temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and mechanical response. The extension of the methodology presented here concerns construction of numerical-analytical basis functions and their associated parameterizations, which permit optimal and convenient parameter optimization with respect to different types of weld-workpiece boundary conditions, energy source characteristics, and experimental measurements adoptable as weld-temperature history constraints. Prototype inverse thermal analyses of a steel weld are presented that provide proof of concept for inverse thermal analysis using these basis functions.

An Inverse Parameter Estimation Method for Building Thermal Analysis

The aim of this study is to introduce a new solution methodology for thermal parameter estimation in building engineering science. By defining a good numerical modeling, inverse algorithm provides us a chance to enhance design conditions in building thermal analysis. The definition of mathematical governing equations and a good solution method to solve them direct the analysis procedure to find temperature distribution using dynamic coding in the computational field. In fact, inverse algorithm utilizes known data resulted from numerical modeling in order to determine the unknown value of important thermal design properties in building problems. The results obtained from implementation of such algorithms demonstrate the accuracy and precision of this new thermal analysis methodology with those of real data resulted from experiments in building problems.

Investigation of a near mid-gap trap energy level in mid-wavelength infrared InAs/GaSb type-II superlattices

In this report, we present results of an experimental investigation of a near mid-gap trap energy level in InAs10 ML/GaSb10 ML type-II superlattices. Using thermal analysis of dark current, Fourier transform photoluminescence and low-frequency noise spectroscopy, we have examined several wafers and diodes with similar period design and the same macroscopic construction. All characterization techniques gave nearly the same value of about 140 meV independent of substrate type. Additionally, photoluminescence spectra show that the transition related to the trap centre is temperature independent. The presented methodology for thermal analysis of dark current characteristics should be useful to easily estimate the position of deep energy levels in superlattice photodiodes.