Conventional Thermal Analysis Research Articles

Analysis and experimental research of transient temperature rise characteristics of high-speed cylindrical roller bearing

In this paper, on one hand, the time-varying characteristics of the heat source and thermal boundary conditions of the high-speed spindle system were analyzed considering the thermal-structural coupling effect. And a transient bearing temperature field prediction method combining the thermal network method and finite element method was proposed. Furthermore, the relationships between time step, calculation efficiency and calculation results were analyzed. On the other hand, a online real-time monitoring system of the transient temperature of the cylindrical roller bearing inner ring for maximum speed of 13,000 r/min was designed and implemented using fibre optic sensing technology. Comparing with the conventional static thermal analysis results, it is verified that the simulation method proposed in this paper has higher accuracy. This paper provides a new approach for analysing and testing the thermal characteristics of high-speed spindle system.

An equivalent winding thermal model considering fill factor and void ratio for multiphysics coupling analysis of permanent magnet linear motors

Accurately clarifying thermal characteristics and acquiring thermal limits of permanent magnet linear motors (PMLMs) is significant for system safety, which is often evaluated by computational thermal analysis. However, conventional thermal analysis methods are faced with the contradiction between the complexity of modeling and the accuracy of computation. To fix the problem, a new two-way multiphysics coupling method is developed by proposing an improved equivalent homogeneous winding thermal model. The energy consumption distribution is used as the heat source for thermal field calculation, and the material properties are determined by temperature in the electromagnetic field. To further reduce the complexity of winding region modeling and ensure the accuracy of calculation, an improved equivalent homogeneous winding thermal model is established by considering the fill factor and void ratio. The new coupling method is verified by temperature rise experiments on a single winding sample and a PMLM prototype. The error between the simulation and experiment of the single winding sample is less than 3 %, which indicates the high accuracy of the improved equivalent model. Meanwhile, the low error (less than 6 %) on the PMLM case indicates the high accuracy of the new multiphysics coupling method. Then, the temperature distribution of PMLM is analyzed, and the effect of the fill factor and void ratio on the temperature rise of PMLM is studied with the effect of the void ratio on the limiting temperature and continuous working time of PMLM discussed. It is demonstrated that both fill factor and void ratio affect the temperature rise of winding, and thus impact the temperature rise of the PMLM. The continuous working time decreases rapidly with the increase of the void ratio, and this effect will be more significant with a higher effective current. The results can provide references for improving the precision of temperature estimation and selecting a reasonable current density. This also demonstrates the high accuracy and efficiency of the new coupling method.

Evaluation of the Critical Times for the Crack Susceptibility Coefficient Calculation

The objective of the present study is to evaluate the hot tearing tendency based on the Clyne and Davies model by evaluating the critical times which can be obtained using a newly developed method. A method to determine the critical times required to calculate the crack susceptibility was presented based on the measurement results with Al–Si alloys, and the method to calculate the crack susceptibility coefficient was presented. In the newly developed method named “Signal intensity method,” signals were generated by tapping the edge of a waveguide which is immersed in molten and solidifying sample and the critical solid fractions were obtained from the signal intensity change. The conventional thermal analysis was also performed simultaneously and the corresponding critical points were identified. The method shown in the present study will enable the determination of the crack susceptibility coefficient with higher accuracy.

Innovation in lifetime prediction of rigid polyurethane foam through random vibration and comparison with conventional methods

As the filling material for the new nuclear fuel transport cask, the rigid polyurethane foam plays an important role in the safe transportation of the nuclear fuel assemblies, and therefore its reliability deserves special attention. Thermal analysis and long-term ageing test are commonly used to predict the service lifetime of rigid polyurethane foams, but they cannot fully consider the influences of mechanical loads like vibration, collision, and impact etc., which is not satisfactory for the transportation application. Herein, in addition to the conventional thermal analysis and long-term ageing methods, the random vibration testing was particularly conducted on the rigid polyurethane foam that has been used in the new nuclear fuel transport cask for the nuclear power plants in China, and its service lifetime was innovatively predicted by the intrinsic property of material, the resonance frequency. The result which can be easily obtained from the acceleration data through fast Fourier transform without additional test and treatment was in the same order of magnitude with that from the conventional methods, and is more rational and convenient, deserving recommended for the rigid polyurethane foams that are used in other applications involving mechanical loads.

Infrared Spectroscopic Investigations of Calcium Oxalate Monohydrate (Whewellite) Dehydration/Rehydration

Variable-temperature infrared spectroscopy is employed to monitor molecular vibrations during dehydration of calcium oxalate monohydrate (COM) and hydration of anhydrous calcium oxalate (COA). A unique variable-temperature infrared spectroscopy approach combines precise sample temperature control and rapid (2 °C s−1) heating/cooling with high-sensitivity infrared analysis. Infrared spectra are obtained at specific isothermal sample temperatures, while applying linear temperature versus time heating and cooling ramps, and in coordination with programmed temperature steps. Spectrum vibration bands provide information regarding the symmetry and local environments of solid-state water molecules and oxalate anions. When COM is heated, water molecules liberated from different crystallographic sites are selectively detected. Subtle oxalate anion configuration changes associated with water losses are detected based on infrared vibration band shapes and wavenumber trends. Dehydration and rehydration processes occur at lower temperatures and over narrower temperature ranges than conventional thermal analysis methods because samples consist of thin layers of small particles. Reversible and irreversible sample changes are distinguished by using a step heating/cooling temperature program and spectral subtractions. COA temperature-dependent structure variations that occur while heating and cooling samples in an atmosphere with a low water vapor concentration are characterized.

Novel ((E)-((2-hydroxynaphthalen-1-yl)methylidene)amino)urea ligand and its Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes: Synthesis, characterization, molecular docking, and anti-cancer activities

The ligand ((E)-((2-hydroxynaphthalen-1-yl)methylidene)amino)urea (HL) and its Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes have been synthesized and characterized by conventional spectroscopic methods, elemental analysis, molar conductivity, and thermal analysis. The complexes show that the ligand disposes of as tridentate anionic (ONO) donor via deprotonated (OH)ring, (C = N)azomethine, and (C = O) functions with a ratio of metal:ligand (1:2) with Mn(II) and Co(II) ions. While, in Ni(II), Cu(II), and Zn(II) complexes, HL acts as monobasic bidentate (NO) donor ligates through deprotonated (OH)ring and (C = N)azomethine with metal:ligand of 1:2. Zn(II) complex adopts tetrahedral and other complexes adopt octahedral geometry. DFT in the material studio package validates the geometry of ligand and metal complexes by measuring bond lengths and angles, HOMO, and LUMO. The thermodynamic and kinetic parameters were estimated from TGA-DTG curves. These complexes provide better activities against human prostatic cell line PC-3 than free ligand which is further verified by molecular docking studies.

Thermotics As an Alternative Nonequilibrium Thermodynamic Approach Suitable for Real Thermoanalytical Measurements: A Short Review

Abstract The general concept of temperature is thermodynamically defined in equilibrium somehow predictable even for non-equilibrium; however, it presents some still controversial aspects, as has been shown in a number of studies and reviews that have been published so far. Equilibrium concepts are often extrapolated to apply in micro-localized equilibrium and then appended to non-equilibrium in its entirety, which helps to define out-of-equilibrium temperature on both the macroscopic and microscopic bases. Unfortunately, these theoretical analyses do not provide any guidance on how to assess and understand temperature in practical measurements, such as for conventional thermal analysis. Insufficient use of alternative thermodynamic attitudes is evident especially in the field of thermophysical studies, which do not use static measurements, because they usually involve heating from an external source, i. e., the effect of thermal dynamics on the laboratory sample. This paper presents the applied nonequilibrium thermodynamic concept, historically known as thermotics. This approach takes into account the existence of gradients and heat fluxes, which it assesses from the point of view of the average user, and considers additional influences, going beyond the description of thermodynamics in traditional textbooks. The goal is to extend their validity, even to the state of constant first-time derivatives. At the same time, it points to changes in the temperature due to thermal inertia, which has long been ignored, suggesting that the heat spreads immediately. Moreover, special techniques enabling measurements during its extreme changes probably then require an alternative concept for temperature (tempericity). This opinion paper may provide stimuli for further discussion with regard to the practice of measurements done in the customary nonisothermal mode.

Analysis of dissolved titanium concentration and phase transformation in molten Al[sbnd]Ti alloy using laser-induced breakdown spectroscopy

We report Ti concentration measurements in dilute AlTi alloys, acquired from direct analysis of the molten metal by laser-induced breakdown spectroscopy (LIBS). The LIBS analysis showed approximately constant Ti concentrations at melt temperatures above the liquidus, while at lower temperatures the measured concentration followed the L/(L + Al3Ti) liquidus of the phase diagram, confirming that the LIBS measurement accurately detects the dissolved Ti concentration in the melt. The LIBS measurements furthermore demonstrated that the Al3Ti phase forms or dissolves within minutes when the melt temperature is decreased or increased, respectively. For the first time, the liquidus line at low Ti concentrations in the AlTi phase diagram has thus been mapped using LIBS analysis instead of the more conventional but time-consuming thermal analysis methods. We conclude that LIBS analysis of molten metal offers a unique opportunity to monitor accurately the chemical composition of the liquid phase and reveal the formation of solid precipitates in real time.

Unveiling meloxicam monohydrate process of dehydration by an at-line vibrational multi-spectroscopy approach

Meloxicam (MLX) is a non-steroidal anti-inflammatory drug, extensively used for inflammatory diseases and pain treatments, which exhibits five known solids forms. Form IV of MLX, a zwitterionic monohydrate (MH), is an emblematic hydrate case with promissory dissolution properties in a poorly soluble drug. However, the lack of information about MH stability regarding the dehydration process and phase transition impedes the development of further stability studies.A multi-spectroscopic/chemometric approach was implemented coupling middle- (MIR), near-infrared (NIR) and Raman spectroscopies to monitor the heat-mediated dehydration process of MH. The application of multivariate curve resolution-alternating least squares (MCR-ALS) to multi-source spectra by data fusion allow a complete view of the phenomena, improving the selectivity and precision to establish the transition temperatures and to identify involved species.It was revealed a two-step mechanism, where MH changes to Form V at 90 °C obtaining its complete dehydration at 130 °C, Form V remains unchanged during the temperature range 130−190 °C and then the polymorphic conversion to Form I starts, which reaches 100 % at 230 °C before melting MLX (248 °C). The findings of this work allow set targets in the process control of products using MH. Additionally, MCR-ALS detected an event not evidenced by conventional thermal analysis, the transformation of Form V to Form I.

Predictions of polymer thermal degradation: relevance of selecting the proper kinetic model

Making predictions, such as lifetime estimations, is one of the main objectives of kinetic studies. Thus, from conventional thermal analysis experiments, the behavior of polymeric materials under processing or application conditions, usually far away from those used in the laboratory experiments, could be estimated. Conventional prediction procedures usually make use of oversimplified equations based on simple approaches. One of the most common approaches is the assumption of a first, or n-order, kinetic model for the process. However, recent studies have shown, for a number of polymers, that random scission kinetic models are not only physically sound, but more reliable in terms of describing the degradation kinetics. In this paper, the consequences of selecting an erroneous kinetic model on lifetime predictions is discussed. It is demonstrated, using both simulated and experimental data, that any kinetic analysis of a chain scission driven reaction performed assuming a first-order model entails enormous deviations in predictions. This occurs despite the fact that the first-order kinetic model can fit experimental data from chain scission driven reactions with significant correlation coefficients, and even lead to a reasonably good reconstruction of the original experimental curves.

Towards significant enhancement of structural and optoelectronic properties of porphyrin palladium(II) complex: A theoretical and experimental analysis

In the present investigation, the nanostructure of porphyrin palladium(II) complex thin films was fabricated by low-cost conventional thermal analysis. The experimental and simulation investigations were used for the analysis of the structure and the unique optical characteristics for optoelectronic applications. The simulation processes using TD-DFT/ B3LYP were implemented to extract the distinguished geometry optimizations and other related parameters. The quantum theory of atoms in molecules (QTAIM) was additionally applied for the studied complexes to evaluate their peculiar electronic features. An indexation of XRD was performed to give a full identification of the crystal structure and supported by the results of transmission electron microscopy images. The investigation of the surface morphology and its quality for the optical applications was established using the atomic force microscopy, AFM supported surface topography mapping images. The optical properties confirm two main direct transitions with determined band gaps of 2.31 and 2.98 eV. The experimental optical gap was comparable with those theoretically extracted using DFT. The characteristics of the current density-voltage measurements verified rectification in the dark and under different values of illuminations. The device showed remarkable rectification characteristics with good responsitivity under illumination conditions. The maximum external quantum efficiency of 9.8% was obtained and compared to other organic-based devices.

New insights of the peritectic phase transition in steel through in-situ measurement of thermal response in a high-temperature confocal microscope

The topic of peritectic phase transition in steel has been widely studied using various in-situ experimental techniques including visual observation on a surface of a sample in a high temperature microscope and measurement of the thermal response from the bulk of the sample using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These two different techniques have inherent limitations leading to difficulties in interpretation of the results in the case of complex phase transformations such as the peritectic reaction, and there have been discrepancies among the interpretations from many previous studies of the peritectic transition in steel. A new technique was developed through a spatial combination of a DTA apparatus and a high-temperature laser-scanning confocal microscope to overcome these limitations. Solidification experiments with carbon steels of 0.061, 0.182 and 0.451 wt%C were conducted under conditions typical of conventional thermal analysis experiment, i.e. 90 mg of sample mass and 10 °C/min cooling rate, and the findings of earlier studies were revisited. We concluded that whether or not a peritectic reaction in a steel specimen of peritectic composition occurs, largely depends on the size of the sample used in the experiment. Deep undercooling for austenite nucleation can be experienced, in the absence of the occurrence of a peritectic reaction as a result of constrained nucleation of austenite, due to a limited number of nucleation sites in the small samples used.

Quartz Enhanced Conductance Spectroscopy for Polymer Nano-Mechanical Thermal Analysis

A fast and highly sensitive polymer nano-mechanical thermal analysis method for determining the melting temperature (Tm) of polymer microwires was proposed. In this method, a small-size, low-cost quartz tuning fork was used as a piezoelectric transducer to analyze the thermodynamics of polymer microwires at the nanogram level without changing its own properties. Due to the thin wire sample, which has a length of 1.2 mm and a diameter of ~5 µm, which is bridged across the prongs of the tuning fork, the nanogram-level sample greatly reduces the thermal equilibrium time for the measurement, resulting in a fast analysis for the melting temperature of the polymer sample. Compared with the traditional method, the analysis method based on the quartz enhanced conductivity spectrum (QECS) does not require annealing before measurement, which is an essential process for conventional thermal analysis to reduce the hardness, refine the grain, and eliminate the residual stress. In this work, the melting temperatures of three of the most commonly used polymers, namely polymers polymethyl methacrylate, high-density polyethylene, and disproportionated rosin, were obtained under the temperature from room temperature to >180 °C, proving the QECS method to be a useful tool for nano-mechanical thermal analysis.

Study of the Degree of Cure through Thermal Analysis and Raman Spectroscopy in Composite-Forming Processes.

The curing of composite materials is one of the parameters that most affects their mechanical behavior. The inspection methods used do not always allow a correct characterization of the curing state of the thermosetting resins. In this work, Raman spectroscopy technology is used for measuring the degree of cure. The results are compared with conventional thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). Carbon fiber specimens manufactured with technologies out of autoclave (OoA) have been used, with an epoxy system Prepreg System, SE 84LV. The results obtained with Raman technology show that it is possible to verify the degree of polymerization, and the information is complementary from classical thermal characterization techniques such as TGA and DSC; thus, it is possible to have greater control in curing and improving the quality of the manufactured parts.

A Simple Equivalent Temperature Rise Test Method Suitable for Safely Evaluating Thermal Limits of Motors and Power Devices Without Model Dependence

Accurately getting thermal limits (peak capacity and duration, maximum temperature, thermal dynamic, etc.) is very useful to avoid damage, verify reliability, reduce size, and determine overloading capability of motors and power devices. Conventional model-dependent thermal analysis often leads to complexity and requires empirical knowledge. If feasible, experimentally evaluating one thermal behavior through another test is not only simple but also fast and accurate. By exploring model basic properties not a precise model, this article provides a “superposition-based” simple equivalent temperature rise test method. Unlike conventional experiments with persistent loading until the stable high-temperature point, the proposed method is able to reconstruct high-temperature data from much lower temperature data by short-term loading, avoiding the risk of permanent damage and reducing the energy consumption. It works for various heat transfer relations, cooling conditions, and loss compositions, as validated by the experimental results. No cumulative error occurs. The nonlinearity influence and the corresponding linear approximation are analyzed in detail. Discussions on inherent nonlinearity influence reduction are provided. Two “superposition-based” accuracy improvements for the nonlinear heat transfer coefficient and variant power loss are also provided. It could be suitable for evaluating the overloading ability or thermal limits without damage risk and with reduced energy consumption.

Effect of Backbone Rigidity on the Glass Transition of Polymers of Intrinsic Microporosity Probed by Fast Scanning Calorimetry.

Polymers of Intrinsic Microporosity (PIMs) of high performance have developed as materials with a wide application range in gas separation and other energy-related fields. Further optimization and long-term behavior of devices with PIMs require an understanding of the structure-property relationships, including physical aging. In this context, the glass transition plays a central role, but with conventional thermal analysis a glass transition is usually not detectable for PIMs before their thermal decomposition. Fast scanning calorimetry provides evidence of the glass transition for a series of PIMs, as the time scales responsible for thermal degradation and for the glass transition are decoupled by employing ultrafast heating rates of tens of thousands K s-1. The investigated PIMs were chosen considering the chain rigidity. The estimated glass transition temperatures follow the order of the rigidity of the backbone of the PIMs.

Exploring Novel Cocrystalline Forms of Oxyresveratrol to Enhance Aqueous Solubility and Permeability across a Cell Monolayer.

Oxyresveratrol (ORV) is a naturally extracted compound with many pharmacological activities. However, information about the crystalline form is not known when considering the development of a form for oral dosage. Cocrystal engineering offers drug molecular understanding and drug solubility improvements. Thus, we attempted cocrystallization of ORV using 10 carboxylic acids as a coformer at a 1:1 M ratio. Each combination was processed with liquid-assisted grinding, solvent evaporation and a slurry method, then characterized by powder X-ray powder diffraction (PXRD), conventional and low-frequency Raman spectroscopy and thermal analysis. The solubility, dissolution and permeation studies across Caco-2 cell monolayers were conducted to evaluate the ORV samples. A screening study revealed that an ORV and citric acid (CTA) cocrystal formed by ethyl acetate-assisted grinding had characteristic PXRD peaks (14.0 and 16.5°) compared to those of ORV dihydrate used as a starting material. Low-frequency Raman measurements, with peaks at 100 cm-1, distinguished potential cocrystals among three processing methods while conventional Raman could not. An endothermic melt (142.2°C) confirmed the formation of the novel crystalline complex. The solubility of the cocrystal in the dissolution media of pH 1.2 and 6.8 was approximately 1000 µg/mL, a 1.3-fold increase compared to ORV alone. In vitro cytotoxicity studies showed that the cocrystal and physical blend were not toxic at concentrations of 25 and 12.5 µM ORV, respectively. The ORV-CTA cocrystal enhanced the cellular transport of ORV across Caco-2 monolayers. Therefore, cocrystallization could be used to improve aqueous solubility and permeability, leading to better oral bioavailability of ORV.

Simulation Research on the Effect of Coupled Heat and Moisture Transfer on the Energy Consumption and Indoor Environment of Public Buildings

A building envelope is a multi-layer porous structure. It transfers heat and moisture to balance the indoor and outdoor temperature difference and water vapor partial pressure difference. This is a typical coupled heat and moisture migration process. When the space is filled with moist air, water or ice, it will directly affect the thermal properties of the material. With respect to moisture coming through the wall into the indoor building, it will also affect the indoor environment and the energy consumption due to the formation of latent heat. However, the moisture transfer process in the building envelopes is not taken into account in the current conventional thermal calculation and energy consumption analysis. This paper analyzes the indoor thermal and humidity environment and building energy consumption of typical cities in Harbin, Shenyang, Beijing, Shanghai, and Guangzhou. The results show that it is obvious that the coupled heat and moisture transfer in the building envelopes has an impact on the annual cooling and heating energy consumption, the total energy consumption, and the indoor thermal and humidity environment. The geographical location of buildings ranging from north to south influences the effect of coupled heat and moisture transfer on the annual energy consumption of the building, moving from positive to negative. It is suggested that the additional coefficient of the coupled thermal and moisture method can effectively correct the existing energy consumption calculation results, which do not take the consumption from the coupled heat and moisture in the building envelopes into account.

A Novel Approach for Reliability Investigation of LEDs on Molded Interconnect Devices Based on FE-Analysis Coupled to Injection Molding Simulation

Due to many advantages, such as cost-effective production, design freedom, and weight reduction, plastics have replaced metals and ceramics in many fields. However, engineering plastics are good thermal insulators. This characteristic, although beneficial in certain applications, poses many challenges in many heat-generating applications. This can lead to hot spots or even to an increase in the device temperature. Along with the increasing demand for plastics in areas of the lighting technology or in the automotive field due to the free shaping potential, the requirements are becoming more challenging. Driven by the trend of miniaturization, applications with high heat generation often have to operate in the tightest of spaces. Since not always sufficient space for complex cooling systems is given, the housing or the substrate should assume the task of thermal management. In regard to this fact, the use of thermally conductive thermoplastics seems to be very appealing. Quality loss, poorer reliability, loss of performance, and even failure can occur in case of insufficient heat dissipation. In order to improve the properties of these polymers, highly heat-conducting fillers are added in order to improve the thermal conductivity of the compound. Another technology trend that has been prevalent for years is the use of simulations. Due to shorter product life cycles and therefore shorter development times, simulation has become an indispensable part of the chain of product development. Time-consuming and costly test series make the simulation more and more important as a tool for material and product design. In this context, this paper presents a novel approach for reliability investigation and lifetime estimation, based on simulation. Therefore, a simulative method based on coupling the results from the process simulation (injection molding simulation) to finite element analysis was developed and explained. This coupled method makes it possible to take into account the manufacturing process and its engendered filler orientation. The obtained findings are compared to conventional thermal steady-state analysis and used in order to better predict the lifetime of LEDs mounted on thermoplastic substrates, the so-called molded interconnect devices. It is demonstrated that it is necessary to consider the filler orientation, especially in the case of 3D substrates.

Thermal property measurement of thin plate by a modulated laser and IR thermography

Accurate thermal conductivity measurements using conventional thermal analysis techniques may be difficult for thin plates with thicknesses less than 0.2 mm. In this study, the two-dimensional temperature of a thin plate heated using a modulated laser beam is observed through infrared thermography. The temperature variations depending on the distance from the laser spot and time are analysed from the obtained temperature images. The thermal conductivities of stainless steel and slide glass samples are calculated by fitting the experimental results to the theoretical values. The measured thermal conductivity agrees with the table values within 10%.