Low Temperature Thermal Cycling Research Articles

ADVANCED HYBRID SOLAR THERMOELECTRIC GENERATOR THEORETICAL ANALYSES

Due to the fact that much of the world’s best solar resources are inversely correlated with population centers, significant motivation exists for developing the technology, which can deliver reliable and autonomous conversion of sunlight into electricity. Thermoelectric generators (TEG) are gaining incremental ground in this area due to its extensive use in solar thermal application as power generators, known as solar thermoelectric generators (STEG). STEG systems are gaining significant interest in both, concentrated and non-concentrated systems and have been employed in hybrid configurations with the solar thermal and photovoltaic systems. In this dissertation, mainly studies of Hybrid Solar Thermoelectric Generators (HSTEG) configuration are presented. HSTEG systems are much less studied both experimentally and theoretically, despite their clear technoeconomic advantages. There is a scope for significant improvement in the performance (efficiency) and a need for detailed performance analysis to understand the fundamentals of the energy transfer process. HSTEG systems (conventional) reported till date, initially the solar energy is utilized by the TEG for generating electricity and then transferred to other low temperature thermal cycles (heating or cooling). As an alternative one can design an advanced HSTEG system, in such way to first utilize the solar energy in the heat transfer fluid (HTF), which can run high temperature thermal cycle for heating or cooling or power generation) and then generate electricity by using TEG. Further, there is no advanced HSTEG system is available in the literature, which could deliver high temperature heat output from the hot side of the HSTEG system. Key Words: optics, photonics, light, lasers, stencils, journals

Quantification of tiny damage variation in asphalt mixture during the low-temperature thermal cycle

The performance evaluation of asphalt materials during low-temperature thermal cycles remains a challenge, particularly in quantifying the early tiny damage development and recovery processes. To address this issue, a high-sensitivity nonlinear ultrasonic method - the second harmonic generation (SHG) technique in the form of Rayleigh surface waves, is proposed to investigate these behaviors in asphalt mixture. The decrease in thermal contraction value and stiffness modulus with cycles verifies the damage behavior at the macro level. Turning points in crack length, crack density, and nonlinear parameter during the thermal cycle indicate the generation of cracks from − 20 ℃ to − 30 ℃ during the cooling process. The decrease of crack length and crack density in the heating phase demonstrates the recovery of asphalt. The nonlinear ultrasonic parameter β'(c) caused by crack is successfully separated from the total nonlinear parameter β', and the recovery index (RI)is defined to quantify the recovery behavior. Both of them are highly consistent with crack length and crack density. While the sensitivity index (SI) of nonlinear parameter is hundreds or thousands of times greater than other measurements of damage development. Furthermore, a qualitative correlation between the nonlinear parameters and plastic strain has been established. This breakthrough widens the scope of studying low-temperature weak damage in asphalt mixtures, moving beyond the confines of crack analysis.

Enhancing the performance of composite phase change materials using novel triply periodic minimal surface structures

Organic phase change materials (PCMs) are widely used in thermal management applications owing to their high latent heats of fusion and low cost. Unfortunately, their poor thermal conductivities severely hamper the thermal transport process. Hence, PCMs are often hybridized with high thermal conductivity materials that promote phase change for time-sensitive applications and potentially increase the power density of thermal energy storage (TES) devices. Optimized thermally conductive networks with high-latent-heat PCM matrices are critical in the thermal management of high heat flux applications. With advancements in additive manufacturing, it has become easier to create complex topologies, such as triply periodic minimal surfaces (TPMS), that can further augment the performance of composite PCMs. TPMS surfaces have shown great promise in improving thermal transport performance but investigations into their thermal properties remain limited. In this study, the thermal performances of PCM infused TPMS structures of wall thicknesses varying from 0.4 mm to 0.8 mm were systematically investigated. The TPMS structures were designed using level-set equations, and each system of structures was fabricated by selective laser melting, a metal additive manufacturing technique. Numerical investigations were performed to understand the phase change dynamics of PCM in TPMS cells and experiments were performed to determine their thermal properties and phase change performance for thermal energy storage applications. Our simulations revealed that for structures with uniform wall thickness of 0.4 mm, the novel Neovius structure resulted in the highest effective thermal conductivity enhancement. For a given thickness, it is thus hypothesized that more complex TPMS topologies have higher surface areas and volumes which enhance their thermal conductivities. However, the complex shape of the Neovius structure could not be further uniformly thickened without self-intersecting geometries. Ultimately, a balance of both the surface area and thickness of the TPMS cell determines the thermal conductivity enhancement. Overall, the 0.6 mm thick IWP cells had the highest thermal conductivity of 13.84 W/m K, which was consistently verified in experiments. This is likely due to the fact that it has a larger surface area than the P structure but is also thicker than the 0.4 mm Neovius structure. To further demonstrate the potential application of our PCM-based TPMS design, low temperature thermal cycling tests were performed. Our results showed the IWP cell structure promoted a more uniform temperature distribution as compared to the P cell. Phase change in the 0.6 mm thick IWP cell structure was completed 1.4 times faster than the 0.8 mm thick P cell and 1.8 times faster than the 0.6 mm thick P cell. The purpose of this study is to provide useful guidelines for the selection of TPMS structures for various applications such as battery packs and spacecraft and to open doors for the co-optimization of materials and device geometry for enhanced energy and power density.

The effect of multiple thermal cycles on Ti-6Al-4V deposits fabricated by wire-arc directed energy deposition: Microstructure evolution, mechanical properties, and corrosion resistance

Thermal cycles have an important effect on the microstructure and properties of the components fabricated by wire-arc directed energy deposition (wire-arc DED). In this study, a Gleeble thermal-mechanical simulator was adopted to create closer-to-reality thermal cycles with the assistance of a numerical simulation model and experimental Ti-6Al-4V deposition. Step-by-step microstructure evolution, including αm, retained β, and GB α, microhardness gradual variation, and the corrosion resistance change before and after the entire thermal cycle were investigated. Therefore, combining phase orientation and high-magnification morphology, transformed and untransformed α that occurred in low- and medium-temperature thermal cycles can be distinguished. After the entire thermal cycle, αm laths coarsened from ∼1 µm to ∼1.2 µm, and the content of retained β phase became more and more. The αm formed around grain boundaries partially disappeared and was occupied by α laths from the inner grain. GB α was more continuously distributed along prior β grain boundaries due to its lower formation temperature during the subsequent thermal cycles that were occurring incomplete α→β transformation. The severe preferential orientation of α phases formed after the deposition and high-temperature thermal cycle was also alleviated through the twice low-temperature thermal cycles. Besides, the microhardness decreased from 318.78 ± 7.5 HV to 285.17 ± 5.3 HV after the high-temperature thermal cycle but eventually increased significantly to 330.5 ± 6.4 HV after experiencing the final low-temperature thermal cycle. The corrosion resistance decreased after the entire thermal cycle, indicating a performance difference between the top and bottom regions of the Ti-6Al-4 V component fabricated by wire-arc DED.

Enhanced dynamics in deep thermal cycling of a model glass.

We investigate the effect of low temperature (cryogenic) thermal cycling on dynamics of a generic model glass via molecular dynamics simulations. By calculating mean squared displacements after a varying number of cycles, a pronounced enhancement of dynamics is observed. This rejuvenation effect is visible already after the first cycle and accumulates upon further cycling in an intermittent way. Our data reveal an overall deformation (buckling of the slab-shaped system) modulated by a heterogeneous deformation field due to deep cryogenic thermal cycling. It is shown via strain maps that deformation localizes in the form of shear-bands, which gradually fill the entire sample in a random and intermittent manner, very much similar to the accumulation effect observed in dynamics. While spatial organization of local strain may be connected to the specific geometry, we argue that the heterogeneity of the structure is the main cause behind rejuvenation effects observed in the present study.

Rejuvenation in Deep Thermal Cycling of a Generic Model Glass: A Study of Per-Particle Energy Distribution.

We investigate the effect of low temperature (cryogenic) thermal cycling on a generic model glass and observe signature of rejuvenation in terms of per-particle potential energy distributions. Most importantly, these distributions become broader and its average values successively increase when applying consecutive thermal cycles. We show that linear dimension plays a key role for these effects to become visible, since we do only observe a weak effect for a cubic system of roughly one hundred particle diameter but observe strong changes for a rule-type geometry with the longest length being two thousand particle diameters. A consistent interpretation of this new finding is provided in terms of a competition between relaxation processes, which are inherent to glassy systems, and excitation due to thermal treatment. In line with our previous report (Bruns et al., PRR 3, 013234 (2021)), it is shown that, depending on the parameters of thermal cycling, rejuvenation can be either too weak to be detected or strong enough for a clear observation.

Decelerated aging in metallic glasses by low temperature thermal cycling

The work presents a combined study on the impact of cryogenic thermal cycling in terms of differential scanning calorimetry measurements on bulk metallic glasses and extensive molecular dynamics simulations of a generic model glass former.

Integration of a Testbench for the Optical and Thermal Characterization of Near-Infrared Detectors Used in Ground and Space-Based Astronomy

The mercury–cadmium–tellurium (MCT) sensors are considered the ideal infrared detectors to equip the focal plane arrays (FPAs) of astronomical scientific missions. To tackle Europe to be self-sufficient on this technology and promote to reach the same maturity level attained by the current MCT sensors market leaders, the Astronomy European Infrared Detector (ASTEROID) project aims to provide Europe with the capability to manufacture high-performance infrared FPAs devoted to scientific use, space astronomy, and ground-based telescope infrastructures. The resulting detector will be a hybridized MCT array with a CdZnTe substrate of 2k $\times2\text{k}$ pixels and 15 $\mu \text{m}$ of pixel pitch. The Institut de Fisica d’Altes Energies (IFAE) will lead the task to validate the detector performance with respect to the hybridization reliability between the readout integrated circuit (ROIC) and the MCT detector by submitting it to several low-temperature thermal cycles. After every thermal stress, the detector will be optically characterized in order to measure any performance degradation and possible problems with the pixel operability. To perform such tasks, two custom setups, focused on optical and cryo-vacuum aspects, were developed, which, used in conjunction, allows to cool down the detector from the room temperature up to ~30 K, while it is electro-optically characterized in terms of linearity, gain, quantum efficiency, and cosmetics defects, among others. The whole cryo-vacuum system and the optical setup are fully described in this article as part of the work packages assigned to IFAE to test the hybridized detector to assess the reliability at operating temperature and after several thermal cycles.

Effects of Test Temperature and Low Temperature Thermal Cycling on the Dynamic Tensile Strength of Granitic Rocks

This paper presents an experimental procedure for the characterization of the granitic rocks on a Mars-like environment. To gain a better understanding of the drilling conditions on Mars, the dynamic tensile behavior of the two granitic rocks was studied using the Brazilian disc test and a Split Hopkinson Pressure Bar. The room temperature tests were performed on the specimens, which had gone through thermal cycling between room temperature and − 70 °C for 0, 10, 15, and 20 cycles. In addition, the high strain rate Brazilian disc tests were carried out on the samples without the thermal cyclic loading at test temperatures of − 30 °C, − 50 °C, and − 70 °C. Microscopy results show that the rocks with different microstructures respond differently to cyclic thermal loading. However, decreasing the test temperature leads to an increasing in the tensile strength of both studied rocks, and the softening of the rocks is observed for both rocks as the temperature reaches − 70 °C. This paper presents a quantitative assessment of the effects of the thermal cyclic loading and temperature on the mechanical behavior of studied rocks in the Mars-like environment. The results of this work will bring new insight into the mechanical response of rock material in extreme environments.

A new method to improve the tribological performance of metal nitride coating: A case study for CrN coating

Taking CrN coating as an example, a new refinement method was performed to improve the tribological performance of metal nitride coatings in the low temperature thermal cycling in humidity condition. After the low temperature thermal cycling post-treatment of −20 to 60 °C in high humidity environment of 80%, the structural and performance changes of the monolayer CrN coating fabricated by the multi-arc ion plating deposition technique were evaluated by using high-resolution transmission electron microscopy, scanning electron microscope equipped with EDS analyzer, X-ray diffraction, X-ray photoelectron spectroscopy and ball-on-disk tribometer. TEM observations and inverse Fourier-filtered images revealed dislocation-mediated mechanism in the treated state CrN coating, which was a key mechanistic process to enhance mechanical properties and wear resistance of CrN coatings after low temperature thermal cycling treatment. Moreover, the more physisorption and chemisorption of oxygen in treated CrN coating can be released and then pass through the defects and the channels between columnar crystal structure, finally arriving at the surface of coating to continuously participate in the tribo-contact interface reaction and produce more oxides as lubricants to effectively reduce friction coefficient and wear rate during dry-sliding.

Exergetic Analysis of Hybrid Photovoltaic - Thermal Solar Collectors Coupled to Organic Rankine Cycles

In this work, the application of hybrid solar modules that combine photovoltaic panels and solar thermal collectors coupled with a low-temperature thermal cycle such as the Organic Rankine Cycle is discussed, their main purpose being an increase in the total electric power production per available area. This work will study the thermal and electrical power production efficiency of the hybrid system, the increase in the PV module electric conversion efficiency due to their cooling through heat transfer to the thermal cycle and the total exergetic efficiency of the system. A simplified simulation of the system in steady state conditions based on a thermal efficiency model will be performed with the aid of the EES (Engineering Equation Solver) software using climate data from Campinas, São Paulo, Brazil. The study shows that while the PV/T+ORC system does fulfill the purpose of increasing the electrical power generation both from the generator coupled to the thermal cycle and from the increase in the PV module efficiency due to its cooling. Thus, there is an increase the overall exergy efficiency of the system compared to uncoupled PV/T collectors.

The shape-stabilized light-to-thermal conversion phase change material based on CH3COONa·3H2O as thermal energy storage media

Latent thermal energy storage using phase change material (PCM) is an effective way to store and transport thermal energy. In this work, a shape-stabilized light-to-thermal conversion composite PCM containing 72.5 wt% CH3COONa·3H2O (SAT), 0.4 wt% Na2HPO4, 17.1 wt% expanded graphite (EG) and 10 wt% CuS was prepared using a physical blending and impregnation method. Experimental results showed that Na2HPO4 was an effective nucleating agent, greatly promoting SAT crystallization. EG as supporting material played an important role in preventing melting PCM from leakage. The addition of CuS can increase the light-to-thermal conversion efficiency from 66.9% to 94.1%. The resultant composite PCM had high phase change enthalpy of 194.8 J/g, low supercooling temperature and good thermal cycling performance. After 150 thermal cycles, the melting enthalpy and light-to-thermal conversion efficiency were decreased by only 5.9% and 2.6%, respectively. This material could be suggested as a potential candidate for storage of thermal energy in solar energy utilization.

Development of the low temperature thermal cycle with amine solution and CO<sub>2</sub>

Development of the low temperature thermal cycle with amine solution and CO<sub>2</sub>

Effects of low-temperature thermal cycling treatment on the microstructures, mechanical properties and oxidation resistance of C/C-ZrC-SiC composites

Carbon/Carbon (C/C) composites modified with ZrC and SiC particles were prepared by precursor infiltration and pyrolysis (PIP) process. Effects of the simulated low earth orbit environment including the vacuum environment (under the high-vacuum state of 1.3 × 10−3 Pa) and low-temperature thermal cycling (the temperature is ranged from 153 K to 393 K for 200 times) on C/C-ZrC-SiC composites were investigated. These results show that the significantly generated microcracks, interspaces and interface debondings contributed to the increase of open porosity. The interfacial damages of C/C-ZrC-SiC composites caused by low-temperature thermal cycling in short-cut webs and non-woven webs were generated at fiber/matrix interface and fiber bundle/matrix interface, respectively. The flexural strength of C/C-ZrC-SiC composites increased by 9.35% after 100-time thermal cycles and then decreased dramatically to 83.99% of pristine strength after 200-time thermal cycles, accompanied by the transformation of fracture behavior from the brittle fracture mode into the pseudo-plastic fracture mode. In addition, the defects induced by the low-temperature thermal cycling accelerated the oxidative damage of C/C-ZrC-SiC composites during thermal shock between 1773 K and room temperature.

A 'degradable' poly(vinyl alcohol) iron oxide nanoparticle hydrogel.

This manuscript explores the stability of an iron oxide nanoparticle (IONP)-containing, physically crosslinked poly(vinyl alcohol) (PVA) hydrogel. The PVA-IONP hydrogel's stability is imparted through crosslinks created through a low temperature thermal cycling process and through the IONPs. Subsequent IONP removal reduces crosslinks so material dissolution can occur, resulting in a 'degradable' and multifunctional biomaterial. PVA-IONP films were fabricated, characterized and evaluated in terms of dissolution in solutions of varying pH and in the presence of chelating agents. Iron release, mass loss, and mechanical testing data demonstrate the ability of the PVA-IONP biomaterial to 'degrade' over time. This degradability has not yet been demonstrated for crosslinked PVA hydrogels. These results are relevant to the development of degradable multifunctional drug carriers, image contrast agents, or magnetic scaffold materials.

Study on the low temperature thermal cycle with amine solution and CO<sub>2</sub>

Study on the low temperature thermal cycle with amine solution and CO<sub>2</sub>

Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements

Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the sub-micrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.

Stability of a Ni-rich Ni-Ti-Zr high temperature shape memory alloy upon low temperature aging and thermal cycling

The thermal stability of Ni50.3Ti29.7Zr20 with aging in austenite at 250°C has been studied for three distinctive microstructures obtained after selected thermal treatments: precipitate free and containing two different sizes and densities of H-phase nanoprecipitates. The martensitic transformation is suppressed after 1–3weeks aging, depending on the initial microstructure, due to a B2 phase instability in the form of short range atomic reordering within the Ti+Zr sublattice, considered to be precursor to the H-phase precipitation. Thermal cycling leads to notable changes in the transformation temperatures, which strongly depends on the starting microstructure.

Elementary Process for CVD Graphene on Cu(110): Size-selective Carbon Clusters

Revealing the graphene growth mechanism at the atomic-scale is of great importance for achieving high quality graphene. However, the lack of direct experimental observation and density functional theory (DFT) verification hinders a comprehensive understanding of the structure of the carbon clusters and evolution of the graphene growth on surface. Here, we report an in-situ low-temperature scanning tunneling microscopy (LT-STM) study of the elementary process of chemical vapor deposition (CVD) graphene growth via thermal decomposition of methane on Cu(110), including the formation of monodispersed carbon clusters at the initial stage, the graphene nucleation and the ripening of graphene islands to form continuous graphene film. STM measurement, supported by DFT calculations, suggests that the carbon clusters on the surface are C2H5. It is found that graphene layers can be joined by different domains, with a relative misorientation of 30°. These graphene layers can be decoupled from Cu(110) through low temperature thermal cycling.

Determination of Thermal Spray Coating Property with Curvature Measurements

Real-time curvature measurement of a coating-substrate system during deposition has facilitated the monitoring of coating stresses and provided additional insights into thermal spray deposition mechanisms. However, the non-equilibrium state of coating formation along with harsh spray booth environment introduces complexity not only in data interpretation but also in the coating properties estimation. In this paper, a new procedure is proposed to estimate the elastic modulus of thermal sprayed ceramic coatings using in situ curvature and temperature measurements. In order to correlate the measurable parameters to coating elastic modulus, a systematic study is conducted to develop a suitable methodology. First, various finite element model analyses are carried out to formulate suitable relations between the measurements and elastic modulus. Subsequently, experiments are conducted to validate the procedure to estimate coating moduli. The results are compared with more accurate measurements obtained from post-deposition characterization technique under low temperature thermal cycles. The comparison suggests that the moduli estimated using the proposed procedure are in good agreements with those obtained from the post-deposition technique. Further, the nonlinear response of coatings are evaluated from the estimated moduli during deposition and cool down, which offer additional information on the characteristics of thermal spray coatings.