Degradation Of Thermal Properties Research Articles

Synthesis of long-chain aliphatic poly(β-thioester)s via thiol-Michael polyaddition and their applications in noble metal recovery and information encryption

Long-chain aliphatic polyesters are recognized as the most promising polyethylene mimics in that these materials show comparative physicochemical properties to polyolefins and own the unique merits of degradability and/or recyclability. Nevertheless, the application scenarios of these polymers are rather limited owing to the lack of functional groups. Herein, sulfur atoms are incorporated into the microstructures of long-chain aliphatic polyesters to decipher the variations of physicochemical properties upon replacing specific methylene units by thioether moieties and simultaneously impart polyethylene-like materials with functionalities. First of all, high molecular weight polyesters P1-P4 and poly(β-thioester)s P5-P8 were obtained via condensation polymerization and thiol-Michael polyaddition, respectively. As for phase transition behaviors, poly(β-thioester)s show inferior crystallization/melting temperatures and the corresponding enthalpy changes than their polyester counterparts, and a loosely packed crystalline structure should be responsible for such thermal property degradation. It is reasonable that replacing specific methylene units of long-chain aliphatic polyesters by sulfur atoms, the much bulkier functional entities, will definitely cause great disturbance to the regular arrangement of polymer chains. The rapid hydrolytic degradation of poly(β-thioester)s in acidic and alkaline media can be ascribed to the easy penetration of water molecules into their incompact amorphous/crystalline regions. In the meantime, these poly(β-thioester)s exhibit great prospects in noble metal recovery and information encryption (optical anticounterfeiting). For instance, poly(β-thioester) P5 is an excellent adsorbent to abstract gold ions from water due to its outstanding metal coordination capability. Moreover, poly(β-thioester) P5 emits bright blue photoluminescence in concentrated solution and solid state upon UV irradiation as a result of the clustering-triggered through space electron delocalization and rigidified polymer chain conformation.

Experimental investigation on the performance of MXene/C-dot hybrid nanofluid-based photovoltaic/thermal system: An Energy, Exergy, and Enviro-Economic analysis

Nanofluids (NFs) with exceptional heat transfer properties are increasingly being adopted in solar collectors as heat transfer fluid (HTF). Hybrid photovoltaic thermal systems are becoming more popular because they increase overall efficiency by producing both high- and low-grade electricity. This research focuses on the application of thermally efficient NFs for enhancing the thermal and electrical output of a photovoltaic/thermal (PV/T) system. Indoor experimental investigation was conducted on the PV/T system to find the thermally efficient HTF. Carbon quantum dot (C-dot), MXene and MXene/C-dot hybrid NFs were selected for experimentation. Thermo-economic factors (thermal conductivity, volumetric heat capacity, thermal property degradation rate, and cost) were used to optimise the NFs' concentration. Optimized C-dot, MXene, and hybrid NFs were used for experimentation in the PV/T system. Energy, exergy, and enviro-economic analysis was conducted on the PV/T system with each HTFs. The results show that the thermal efficiency of PV/T was enhanced by 5.39, 3.87, and 9.45 % with C-dot, MXene and hybrid NFs, respectively. Hottel-Whillier-Bliss (HWB) analysis was performed on the collector from the generated experimental data. The analysis states that at zero heat loss conditions, the thermal efficiency of the PV/T was enhanced by 5.4 % with the hybrid NF. The maximum CO2 emission from PV/T with C-dot, MXene, and hybrid NFs, were calculated to be around 2.024, 1.979, and 1.931 kgCO2/day, respectively. Emission cost reduction analysis states that the hybrid NF achieved the highest reduction of 0.02 $/day which was a considerable decrement of 13.5 % over the water-based PV/T system.

Experimental study of the thermal performance of a PCM in heat sinks

Phase change materials (PCMs) can be great solutions as heat sink for energy storage in microgravity conditions. To guarantee the reliability of the systems, the thermal behavior of the PCMs and their degradation should be understood. Two different configurations of heat sink devices, a cylindrical and a finned hollow parallelepiped based on phase change material (PCM), were investigated. The hydrated salt sodium phosphate dibasic dodecahydrate (Na2HPO4·12H2O) was used as the PCM material, in three different volumes. Were also investigated the effect of copper sponges in the effective thermal conductivity, and the thermal property degradation in the finned heat sink by the sequential heat cycles. The PCM was replaced in each experiment and two power supply heat flux levels were studied. In the second heat sink configuration, consisting of finned heat sink hollow block provided with internal fins, the PCM was not replaced, to observe its property degradation. Power supplied in finned devices varied from 75W to 100W. Experimental results showed a reduction of approximately 50% in the maximum temperature of the heat sink when the copper sponge is inserted. Gaps in hydrated salt decrease the thermal conductance of the heat sink. The PCM thermo-physical properties degradation is negligible for a few numbers of continuous heating cycles. In the case of finned block device, it was observed a variation of 6% in latent heat storage at the first cycles when the same test was realized several times. Contact area loss increased up 15% at the end of the experiments.

A Review of Thermal Property Enhancements of Low-Temperature Nano-Enhanced Phase Change Materials.

Phase change materials (PCMs) are of increasing interest due to their ability to absorb and store large amounts of thermal energy, with minimal temperature variations. In the phase-change process, these large amounts of thermal energy can be stored with a minimal change in temperature during both the solid/liquid and liquid/vapor phase transitions. As a result, these PCMs are experiencing increased use in applications such as solar energy heating or storage, building insulation, electronic cooling, food storage, and waste heat recovery. Low temperature, nano-enhanced phase change materials (NEPCM) are of particular interest, due to the recent increase in applications related to the shipment of cellular based materials and vaccines, both of which require precise temperature control for sustained periods of time. Information such as PCM and nanoparticle type, the effective goals, and manipulation of PCM thermal properties are assembled from the literature, evaluated, and discussed in detail, to provide an overview of NEPCMs and provide guidance for additional study. Current studies of NEPCMs are limited in scope, with the primary focus of a majority of recent investigations directed at increasing the thermal conductivity and reducing the charging and discharging times. Only a limited number of investigations have examined the issues related to increasing the latent heat to improve the thermal capacity or enhancing the stability to prevent sedimentation of the nanoparticles. In addition, this review examines several other important thermophysical parameters, including the thermal conductivity, phase transition temperature, rheological affects, and the chemical stability of NEPCMs. This is accomplished largely through comparing of the thermophysical properties of the base PCMs and their nano-enhanced counter parts and then evaluating the relative effectiveness of the various types of NEPCMs. Although there are exceptions, for a majority of conventional heat transfer fluids the thermal conductivity of the base PCM generally increases, and the latent heat decreases as the mass fraction of the nanoparticles increases, whereas trends in phase change temperature are often dependent upon the properties of the individual components. A number of recommendations for further study are made, including a better understanding of the stability of NEPCMs such that sedimentation is limited and thus capable of withstanding long-term thermal cycles without significant degradation of thermal properties, along with the identification of those factors that have the greatest overall impact and which PCM combinations might result in the most significant increases in latent heat.

슬라이스 가속 시험법에 따른 건축용 단열재의 성능 분석

Thermal property degradation of building insulation materials were analyzed by accelerated laboratory methods defined in ISO 11561 to verify thermal resistance change experimentally. Selected samples varied within one to three days from production date. Primary tests were executed for more than 3,000 hrs for XPS (Extruded PolyStyrene) and Rigid poly urethane, respectively. Secondary tests were carried out for approximately 1,500 hrs for special and first grade of XPS. Measured values of thermal resistance were analyzed to estimate the thermal resistance values of 25 year-time-lapse and to compare with 25 year-average value. It was observed that thermal property of special grade XPS was estimated to decrease after 25 years by 37 to 41% from the initial value. Grade 1 XPS showed relatively better results as of 21 to 27%. In addition, Rigid poly urethane 40K revealed property degradation pattern of 21 to 27% from the production stage.

Newly developed thermoplastic polyolefin encapsulant–A potential candidate for crystalline silicon photovoltaic modules encapsulation

Thermoplastic polyolefin (TPO) is a newly developed non-crosslinking material for photovoltaic (PV) module lamination as an alternative to ethylene–vinyl-acetate (EVA) encapsulant. This article assesses its applicability as an encapsulant material. We report the results of various characterization tests for discoloration, optical, and thermal properties degradation before and after the UV accelerated test. To evaluate its weathering stability, the UV-365 acceleration test has been conducted on the glass to glass TPO laminate, with EVA as a benchmark. In 50 days of weatherability tests, the transmittance of EVA significantly reduced while TPO remained almost unchanged. The discoloration of TPO is around nine times slower than that of EVA. The analytical tools like Raman spectroscopy, fluorescent imaging, and spectra have been used to assess the degradation behavior, which indicates a clear difference between EVA and TPO based encapsulant. Thermal properties (glass and melt transitions) of TPO and EVA have been studied through heat-cool-heat cycle testing by differential scanning calorimeter (DSC). This test confirmed that TPO thermal properties remain almost unchanged, whereas EVA shows significant changes after 50 days of UV exposure. In the thermogravimetry analysis (TGA) results, we found that TPO is stable till a significantly higher temperature than EVA. Additionally, the 180° peel adhesion test suggests that TPO has a higher adhesion strength than EVA. This work will help in understanding the applicability of newly developed non-crosslinking TPO as a potential replacement for EVA for the PV modules.

A non-calorimetric approach for investigating the moisture-induced ageing of a pyrotechnic delay material using spectroscopies

The degradation of thermal properties due to ageing such as burning rate and exothermic heat release are unsolved issues faced during a long-term storage of the pyrotechnic substances. Accordingly, we employed various non-calorimetric methods to investigate the thermal performance of pyrotechnic delay, which is exposed to various moisture-rich conditions at extended durations. The chemical and physical changes in the compositions of a pyrotechnic delay comprised of metal fuel (Zr-Ni alloy) and oxidants (KClO4, BaCrO4) are analysed for four different relative humidity levels using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and laser-induced breakdown spectroscopy. The calculations using the NASA Chemical Equilibrium with Applications (CEA) software indicated that the heat of reaction for the components stored under the moisture-rich conditions is reduced by more than 50%. Unlike the conventional calorimetric analysis, the present non-calorimetric approach provided the compositional changes as well as the cause and effect of the relevant ageing process of pyrotechnic delay.

Damage characteristics and thermo-physical properties changes of limestone and sandstone during thermal treatment from −30 °C to 1000 °C

A series of experiments were carried out to measure the damage characteristics of two common sedimentary rocks of limestone and sandstone at temperatures ranging from −30 °C to 1000 °C The apparent thermal conductivity, thermal diffusivity and specific heat capacity were investigated respectively. Then, several discrepancy reasons for the damage characteristics and thermo-physical properties of limestone and sandstone were probed. The results show that water migration and phase transition are two core factors for the frost damage and thermal behaviors improvement during the cooling process(20 °C → −30 °C).The heating process (20 °C → 1000 °C) was divided into three stages of 20 °C → 200 °C, 200 °C → 600 °Cand 600 °C → 1000 °C. The first stage was closely related to pore-water evaporation, and the next two stages were attributed to the thermal reactions of mineral partials. The mineral decomposition tended to be intensified and resulted in the interior damage or even the accelerated degradation of thermal properties until at a threshold temperature of 600 °C. In essential, the structural features and the sensitivity of mineral composition to temperature were two mainly influential factors on the damage effects and heat conduct of the sedimentary rocks during variations in environmental temperature.

Evolution of transiently melt damaged tungsten under ITER-relevant divertor plasma heat loading

A high-repetition-rate ELM simulation system was used at both the Pilot-PSI and Magnum-PSI linear plasma devices to investigate the nature of W damage under multiple shallow melt events and the subsequent surface evolution under ITER relevant plasma fluence and high ELM number. First, repetitive shallow melting of two W monoblocks separated by a 0.5mm gap was obtained by combined pulsed/steady-state hydrogen plasma loading at normal incidence in the Pilot-PSI device. Surface modifications including melting, cracking and strong net-reshaping of the surface are obtained. During the second step, the pre-damaged W sample was exposed to a high flux plasma regime in the Magnum-PSI device with a grazing angle of 35°. SEM analysis indicates no measurable change to the surface state after the exposure in Magnum-PSI. An increase in transient-induced temperature rise of 40% is however observed, indicating a degradation of thermal properties over time.

Fatigue lifetime of repaired high heat flux components for ITER divertor

Thermal fatigue behaviour of repaired monoblocks was assessed from High Heat Flux (HHF) tests up to 20 MW m −2 on 11 components. Among these components, 8 monoblocks were repaired (2 CFC and 6 tungsten). These components were manufactured by two EU industries: ANSALDO Ricerche and PLANSEE. Non destructive examination was performed on SATIR thermography test bed before and after HHF tests. SATIR results show that repaired monoblocks have a good thermal exhaust capability before HHF tests. For all monoblocks, no degradation of thermal properties was noticed during cycles at 10 MW m −2. After hundreds of cycles at 20 MW m −2, two W repaired monoblock melted. Post-HHF SATIR examination revealed a degradation of thermal properties which is systematic for W melted monoblocks and non-systematic for W repaired ones. For CFC repaired monoblocks, no damage was observed up to 20 MW m −2. For the first ITER divertor set, specifications for the pre-qualification are that CFC (Resp. W) components have to sustain in steady state 1000 cycles at 10 MW m −2 (Resp. 3 MW m −2) followed by 1000 cycles at 20 MW m −2 (Resp. 5 MW m −2). For the first ITER divertor set, the repair process is validated for CFC and W monoblocks.

Evolution of microstructures and thermal properties with heat treatment for absorbing, emitting and scattering fibrous medium

The microstructure changes of a fibrous insulation for thermal protection system were examined before and after thermal exposures at different temperatures between 1000 °C and 1400 °C. The consequent thermal properties, i.e., thermal conductivity, extinction coefficient, albedo of scattering, and linear coefficient of phase function at different stages were measured by using a developed experimental device and data processing method. The effects of microstructure changes on the thermal properties degradation were discussed. It was found that the devitrification of mullite and the microstructure changes induced by heat treatment had a significant influence upon the thermal properties, and higher temperature treatment yielded a strong increase in thermal conductivity of fibrous insulation. The results also indicated that the relative contribution of conductive and radiative heat transfer would be re-regulated after high temperature thermal annealing.

Effect of isotropic interlayers on the mechanical and thermal properties of carbon/carbon composites

Multilayer which consists of isotropic (ISO) interlayer and rough laminar (RL) and single RL structure carbon/carbon (C/C) composites have been prepared by isothermal chemical vapor infiltration at 5 and 1 kPa. Mechanical and thermal properties of both composites have also been studied. Experimental results indicate that ISO interlayer between fiber and matrix plays an important role on fracture behavior and strength of the composites. Comparing with single RL structure composites, the strength decrease of composites with ISO interlayers is about 28–40%. ISO interlayer is the main source of fracture due to its low density and micropores between crystallites. The low thermal conductivity of ISO interlayers also results in the thermal property degradation of obtained C/C composites. By reducing infiltration pressure, the ISO interlayers are substituted by compact RL matrix which improves the general properties of C/C composites.

The effect of thermal property degradation on wear of WC-CO inserts in dry cutting

This paper investigates the relationship between wear and the conditions of heat removal at the tip of the tool. In this work we team numerical simulations to SEM imagery in order to map the thermal conductivity within the tool zone of action of a coated carbide (WC-CO) tool. The results indicate that depending on the temperature rise, the tool tip might undergo a severe drop in thermal conduction. This drop may locally restrict the ability of the tool material to dissipate the applied thermal load. This may nucleate thermally congested clusters within the tool tip where the material completely loses the ability to transport heat. The constriction of thermal transport renders an energetically active zone where the thermal energy available may be used to activate wear through different mechanisms. It is also found that the immediate layer under the surface of the tool tip is important to enhance the ability of the tool material to dissipate the thermal loads. The results highlight the importance of enhancing the efficiency of heat removal within the tool active zone in order to improve wear resistance.

Thermal transport property prediction of a CMC laminate from base materials properties and manufacturing porosities

This paper reviews two publications of the authors. The first relates to the classification of manufacturing porosity of a ceramic matrix composite material DRL-XT and the second to the quantification of thermal property degradation, due to porosity, at the level of the fibre tow and matrix regions. The paper then shows how these degraded thermal properties can be used in macro unit cell finite element analyses to quantify the effect of manufacturing porosity on bulk composite thermal properties. The dominant porosity type is matrix cracking, which is responsible for a 25% reduction of in-plane bulk thermal conductivity. Key to the success of the approach is an accurate knowledge of thermal properties of the constituent materials. However, in their absence, it is shown how property bounds may be used coupled with: semi-inverse finite element unit cell modelling and experimental values of bulk composite thermal properties.

Testing of Tungsten and Tantalum Limiters at the TEXTOR Tokamak: Material Performance and Deuterium Retention

Tungsten and tantalum were examined in the TEXTOR tokamak as test limiters in order to compare their performance under plasma operation and to recognise fuel recycling on endothermic (W) and exothermic (Ta) hydrogen absorbers. Differences have been noticed in the distribution and microstructure of co-deposits, in the fuel inventory in the bulk of metals and, in the deuterium release mechanism (ratio of molecules to atoms). As a result of poor thermal conductivity, the surface temperature of Ta during the power deposition was higher than that of W and it increased shot-by-shot because of the degradation of thermal properties due to surface modification. Results on thermal response, fuel recycling and inventory show that, as a candidate material for plasma facing components, tungsten is superior to tantalum.

Thermomechanical fatigue damage/failure mechanisms in SCS-6/Timetal 21S [formula omitted] composite

The thermomechanical fatigue (TMF) deformation, damage and life behaviors of SCS-6/Timetal 21S [ 0 90 ] s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650°C. An advanced TMF test technique was used to mechanically quantify damage progression. The technique incorporated explicit measurements of the macroscopic (i) isothermal static moduli at the temperature extremes of the TMF cycle, and (ii) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue-life results indicated trends analogous to those established for similar unidirectional [0] reinforced titanium-matrix composite systems. High-stress IP and mid- to low-stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive [0] fiber cracking with sparse matrix damage. No surface-initiated matrix cracks were present. Comparable OP TMF conditions initiated environment-enhanced surface cracking and matrix cracking initiated at [90] fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and [90] F/M interfaces tended to converge and coalesce at the [0] fibers.