Thermal Losses Research Articles

Integrated optical–thermal modelling and techno-economic evaluation of a ‘bladed’ solar-thermal receiver

The receiver in a concentrating solar thermal system is a costly component, and its contribution to system-level techno-economics must be carefully evaluated. This study examined the strategy of adding ‘blades’ to conventional tubular receivers, in the form of additional tube-banks perpendicular to the primary aperture surface, to improve light trapping and reduce size. An integrated optical–thermal model was used, incorporating geometrical configuration, flow path design and aiming strategy, and optical and thermal performance assessed followed by an economic analysis of its dynamic annual performance. A 65MW˙th polar heliostat field and molten nitrate salt working fluid were assumed, and design iterations conducted to maximise overall optical–thermal receiver efficiency. The final design achieved a 30% reduction in optical and thermal losses, equivalent to 2.5% increased efficiency. Even though the final design can sustain higher peak flux, its size could not be reduced without incurring excessive spillage loss. Meanwhile, the added blades did not increase the intercepted radiation. As a result, in the techno-economic evaluation, the approximately doubled tube mass increased the receiver cost by 16%–25%, and only 1–3USD/MWh˙e savings were achieved in the levelised cost of electricity (LCOE). The LCOE of bladed receivers was evaluated for the first time in this study, confirming that bladed receivers in their current form are not promising. However, the study provides insight into the benefits of the related ‘STAR’ concept, where vertical blades are added to cylindrical receivers, which increase the receiver aperture while decreasing the tube cost per aperture area.

Performance enhancement of CsPbI3-xBrx perovskite solar cells via graded bandgap and affinity engineering

All inorganic cesium lead-based perovskite solar cells (PSCs) have gained attention as alternative absorbing materials owing to their exceptional thermal stability. However, these devices are suffer from transmission and thermalization losses. Therefore, a novel grading approach is used in CsPbI3-x Brx perovskite solar cell to reduce the transmission and thermalization losses by enhancing the cell’s ability to capture a broad spectrum of light wavelengths and suitably accommodate the material’s energy bandgap. In this work, the performance of CsPbI3-xBrx perovskite solar cell with graded bandgap (Eg) and affinity has been explored and analyzed using the simulation SCAPS-1D tool. Different compositions (x) are varied to adjust the bandgap of CsPbI3-xBrx with different grading profiles such as linear, parabolic and beta grading. The graded structure enhances the absorption wavelength range and carrier lifetime. However, it also leads to the redistribution of the electrical field within the device, promoting more effective charge separation and collection. By utilizing this approach, the impact of absorber thickness variations from (50 nm to 700 nm) is also studied and analyzed with respect to grading profiles. Initially, 16.75% power conversion efficiency (PCE) is obtained by calibrating the experimental CsPbI3-xBrx graded solar cell. Then, performance is further improved by adjusting the bandgap with grading profiles, optimizing ETLs/HTLs and achieving optimum PV parameters: short-circuit current density (JSC) of 20.50 mA cm−2, open-circuit voltage (VOC) of 1.35 V, fill factor (FF) of 84.15% and PCE of 23.11%. The findings of the reported study would significantly provide a path for the development of graded PSC.

Flower-like Ni-Al/LDH synergistic polyaniline anchored to the carbon sphere surface to improve the fire performance of waterborne epoxy coatings

In this study, phytic acid -doped polyaniline (PPA) was loaded on the surface of carbon spheres, resulting in a classical C-N-P flame retardant system, that has a beneficial function for the formation of residual carbon. Subsequently, using this phosphorus-nitride carbon sphere (CS/PPA) as a carrier, flower-like Ni-Al-layered double hydroxide (Ni-Al/LDH) were uniformly grown on its surface, thus obtaining a novel nano-fire retardant with a graded structure to heighten the fire-resistant properties of aqueous epoxy resin. Importantly, the intervention of Ni-Al/LDH nanosheets not only imparts a gas-phase fire retardant function to the coating, but also the presence of Ni and Al bimetals can effectively catalyze the formation of more residual carbon in the combustion process. The highest residual carbon (30.7 %) in thermal weight loss experiments of the CS/PPA@Ni-Al/LDH/EP composite coating confirmed this view. Tests on the thermal insulation behavior of coatings illustrated that the backside temperature (168.8 °C) for CS/PPA@Ni-Al/LDH/EP was significantly smaller than that of other coatings, and that this optimum thermal shielding is inextricably linked to the high residual carbon and the residual metal oxides. Furthermore, the CS/PPA@Ni-Al/LDH/EP specimen shown the greatest expansion height (25.1 mm), expansion ratio (19.61) as well as the smallest smoke density rating (39.1 %), proving that its expansion property and smoke suppression were effectively improved. Moreover, the microstructure for the expanded carbon layer demonstrated that the CS/PPA@Ni-Al/LDH filled EP possessed a more complete and dense residual carbon after burning. Moreover, the high degree of graphitization of the residual carbon for CS/PPA@Ni-Al/LDH/EP determined its high thermal stability. The lowest cracked gas phase products and CO release of the CS/PPA@Ni-Al/LDH/EP composite coating during TG-IR testing confirmed its lowest fire toxicity. The development of such a composite flame retardant with a graded structure could help to advance the progress of waterborne intumescent fire coatings.

Impact resistance of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers

In this study, the low velocity impact resistance of pure and modified epoxy adhesives for single lap joints between aluminum and carbon epoxy composites was investigated. Epoxy resin was used as the adhesive, and pure epoxy resin was modified by adding graphene-doped nylon 6.6 nanofibers (1%, 3% and 5% by weight) and pure nylon 6.6 nanofibers produced by electrospinning. These nanofibers are reinforced to aluminum-composite single lap joints as a second interface according to ASTM D1002-10 standard. Thus, single lap joints were prepared using 5 different adhesives. To create the impact effect, some joints were subjected to impact at a low velocity (1.04 m/s). Then, all impacted and non-impacted samples were subjected to single lap shear testing at room temperature and constant load to determine the impact resistance. While the non-impact lap shear strength of the pure epoxy adhesive samples was 6.81 MPa, the non-impact shear strength of the samples using pure nanofiber reinforced epoxy adhesive increased by 71.3% to 11.67 MPa compared to the pure epoxy adhesive. When comparing the post-impact failure loads, it was determined that the addition of graphene increases the impact resistance. Furthermore, adhesive surfaces were examined by scanning electron microscopy (SEM) for damage analysis after the tensile tests and toughening mechanisms such as bridging, adhesive crack formation, nanofibers breakage was determined in epoxy adhesives reinforced nanofiber with graphene in different proportions by weight. In addition, the glass transition temperature, melting temperature, thermal decomposition temperature and mass loss of epoxy resin, and graphene doped/undoped N6.6 nanofiber-reinforced epoxy adhesives were analyzed by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) and it was determined that the addition of 3% GNP to N6.6 nanofiber reinforcement increased the thermal stability by 12.4%, the addition of 1% GNP to N6.6 nanofiber reinforcement increased the thermal resistance (glass transition temperature) by 34.9% compared pure epoxy.

Itinerant ferromagnetism and room temperature giant magnetocaloric effect in (Mn0.6Fe0.4) (Ni0.5Co0.5) Si shape memory alloy

In this article, the feasibility of obtaining a magneto-structural coupling over a wide working temperature range of about 127 K (from 206.5 K to 333.5 K) with negligible thermal hysteresis in combination with the structural, microstructural, magnetic, and magnetocaloric properties of a 50 % Co-doped (at the Ni site) polycrystalline (Mn0.6Fe0.4) (Ni0.5Co0.5) Si (MFNCS-0.5) magnetic shape memory alloy (MSMA) has been thoroughly investigated. Along with leaf-like microstructure, at room temperature, the system shows a mixed phase of TiNiSi type low-temperature high-magnetic (ferromagnetic) orthorhombic martensite and Ni2In type high-temperature low-magnetic (paramagnetic) hexagonal austenite, with the dominance of the second one. To estimate the magnetocaloric effect (MCE) across the phase transition, the isothermal magnetic measurement technique has been employed. The merging of heating and cooling iso-field thermo-magnetization (M-T) curves, the presence of negligible thermal hysteresis in the MH curves, universal magnetic entropy curves, a proposed phenomenological model (across the Curie temperature), and the positive slopes of the Arrott plot (Banerjee criterion) show that the first-order structural and magnetic transition are coupled along with a second-order ferromagnetic to paramagnetic (FM → PM) phase transition (SOPT). By extrapolating the Arrott plot to the H/M = 0 axis the spontaneous magnetization value very close to 0 K, Ms(0), is found to be 71.92 emu/g (∼1.83 µB/f.u.). The linear dependency of MS2T on T2 below SOPT and the RWR (Rhodes–Wolhfarth ratio) = 4.29 > 1 indicate the long-range itinerant ferromagnetism in this alloy. A giant magnetic entropy change (ΔSm) of 25.77 J kg−1 K−1 and a refrigerant capacity (RC) of 472.83 J kg−1 are obtained at 6 T field. This observed magnetic refrigerant's key characteristics, including a giant magnetocaloric effect (MCE) near room temperature (RT), negligible thermal hysteresis loss, a wide operating temperature range of 127 K, and the use of cost-effective, non-toxic constituent elements, make it a suitable and very promising member for applications in solid-state refrigeration technology near RT.

Reliability issues of GaN HEMT: Current status and challenges

With the development of power electronic devices, there is an increasing demand for energy-saving, emission reduction, and environmental protection. Thus, higher energy conversion efficiency of power electronic devices is required. While traditional Si-based power electronic devices have the disadvantage of low energy utilization efficiency and high thermal losses, GaN-based HEMT has significant advantages, making it a frontier and hotspot in global semiconductor research. However, the failure mechanisms that affect the reliability of GaN HEMTs are not completely comprehended. Many reliability issues affect devices performance, among which electrical reliability and thermal reliability are widely studied concerns. Electrical reliability issues contain inverse piezoelectric effect, hot electron effect, trapping effect, and mental instability. Thermal reliability issues contain self-heating effects, which are caused by the materials unsatisfying thermal conductivity, and improper structure design. This paper is focused on the current research results of the GaN HEMTs electrical reliability and thermal reliability. The first part of this paper gives a review of GaN HEMT reliability issues at their current status, and the second part outlines the challenges of GaN HEMTs in future development. This review will help researchers to better understand factors that affect GaN HEMTs reliability and help with their device design for further research.

Preparation and performance of silicone-modified 3D printing photosensitive materials

Abstract Herein, the performance of silicone-modified 3D printing photosensitive resin was examined. Bisphenol-A epoxy acrylate (EA) was used as the substrate and isophorone diisocyanate, hydroxy-silicone oil, and hydroxyethyl acrylate were used as the raw materials. A silicone intermediate was synthesized to modify the substrate to prepare the 3D printing photosensitive material. The as-synthesized materials were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. The tensile fracture morphology was also analyzed. The effects of the addition of silicone intermediates on the mechanical properties, thermal stability, and shrinkage of the prepared 3D printing photosensitive resins were investigated. The results showed that an organosilicone group was successfully introduced into the side chain of EA. When the ratio of n(silicone):n(EA) is 0.3:1, the material has a high impact strength of 19.4 kJ·m−2, which is 32.8% higher than that of the pure resin; in addition, the elongation at break is 8.65% (compared to 6.56% of the pure resin). The maximum thermal weight loss temperature is 430.33°C, which is 6°C higher than that of the pure resin.

A fast multipole boundary element method for acoustics in viscothermal fluids

Standard numerical models in acoustics rely on the isentropic Helmholtz equation. Its derivation assumes adiabatic and reversible, i.e., dissipation-free, wave propagation. Sound waves in fluids are, however, subject to viscous and thermal losses. These losses originate from viscous friction and heat conduction, leading to the formation of acoustic boundary layers. Considering these effects becomes significant in setups with acoustic cavities of similar dimension as the boundary layers. Recently, boundary element methods (BEM) accounting for the viscothermal dissipation have been proposed. These methods limit the discretization to the surface of the fluid domain and require significantly fewer degrees of freedom than comparable finite element models. However, the BEM coefficient matrices are fully populated, resulting in high computational costs and storage requirements. This study develops a new BEM formulation for acoustics in viscothermal fluids that uses the fast multipole method - a low-rank approximation technique based on a hierarchical subdivision of the computational domain - to alleviate this shortcoming. It is shown that the fast viscothermal BEM improves the algorithmic complexity over the conventional formulation, reducing both the memory requirements and solution time. The results indicate good scalability of the method making it feasible for larger applications such as acoustic metamaterials.

Research on thermal performance and pressure loss of a new perforated-folded baffle solar air collector

In order to further improve the heat collection performance of solar air heaters and reduce internal pressure. This study establishes a collector with perforated baffle based on baffled collector. The model was simulated using CFD software. Fit and analyze the efficiency of the collector with the hole-opened rate (the ratio of the opening area to the baffle area). The results show that compared with non-perforated baffle collectors, perforated baffle collectors have lower pressure loss, higher collection efficiency, lower heat dissipation coefficient of about 37.58%, and higher heat transfer coefficient of about 10.51%. When the hole height is 30 mm, the hole diameter is 80 mm, and the hole-opened rate is 0.24, the coupling between heat collection efficiency and pressure loss is the best, which is 64.11% and 4.32 Pa, respectively. The heat collection efficiency decreases with the increase of porosity, and the fitting degree R 2 = 0.98. The deviation of fitting curve (between turbulence intensity and hole-opened rate) is less than 10%. Nusselt number increases gradually with the increase of Reynolds number. Fitting correlation between Nusselt number and Reynolds number, and fitting degree is 0.9985. Perforated-folded baffle collector provides theoretical basis for improving the solar thermal utilization rate.

Field-test performance of an ice-melting probe in a terrestrial analogue environment

Melting probes are a proven tool for the exploration of thick ice layers and clean sampling of subglacial water on Earth. Their compact size and ease of operation also make them a key technology for the future exploration of icy moons in our Solar System, most prominently Europa and Enceladus. For both mission planning and hardware engineering, metrics such as efficiency and expected performance in terms of achievable speed, power requirements, and necessary heating power have to be known.Theoretical studies aim at describing thermal losses on the one hand, while laboratory experiments and field tests allow an empirical investigation of the true performance on the other hand. To investigate the practical value of a performance model for the operational performance in extraterrestrial environments, we first contrast measured data from terrestrial field tests on temperate and polythermal glaciers with results from basic heat loss models and a melt trajectory model. For this purpose, we propose conventions for the determination of two different efficiencies that can be applied to both measured data and models. One definition of efficiency is related to the melting head only, while the other definition considers the melting probe as a whole. We also present methods to combine several sources of heat loss for probes with a circular cross-section, and to translate the geometry of probes with a non-circular cross-section to analyse them in the same way. The models were selected in a way that minimizes the need to make assumptions about unknown parameters of the probe or the ice environment.The results indicate that currently used models do not yet reliably reproduce the performance of a probe under realistic conditions. Melting velocities and efficiencies are constantly overestimated by 15 to 50% in the models, but qualitatively agree with the field test data. Hence, losses are observed, that are not yet covered and quantified by the available loss models. We find that the deviation increases with decreasing ice temperature. We suspect that this mismatch is mainly due to the too restrictive idealization of the probe model and the fact that the probe was not operated in an efficiency-optimized manner during the field tests. With respect to space mission engineering, we find that performance and efficiency models must be used with caution in unknown ice environments, as various ice parameters have a significant effect on the melting process. Some of these are difficult to estimate from afar.

Theoretical study of a double-slope solar still with solar air heater condenser

Despite their limited water production and efficiency, double-slope solar stills are an appropriate solution for water scarcity in hot arid regions. Numerous studies have focused on enhancing the effectiveness of double-slope solar stills. In this context, this study introduces a double-slope solar with a solar air heater condenser (DSSS-SAHC). The back cover of a conventional double-slope solar still was replaced by a glass air heater in order to recover the still’s thermal losses in heating air. The transient performance of the DSSS-SAHC was investigated numerically under real weather conditions and compared to the performance of a conventional double-slope solar still (CDSSS) with the same aspects. The impact of various weather and operation factors on the DSSS-SAHC performance was investigated at air flows of 0.01 and 0.1 kg/s to account for both natural and forced air circulation, respectively. The results revealed an increase of about 15% and 6% in the thermal efficiency of the DSSS-SAHC over that of the CDSSS, respectively, at air flows of 0.1 and 0.01 kg/s despite the DSSS-SAHC distillate was insignificantly greater than that of the CDSSS at both air flows. In addition, the water distillate of the DSSS-SAHC increased as the solar irradiance increased, the ambient wind and ambient temperature had contrary effects on the efficiency, and the initial saline water level had a negligible impact on the overall performance

Thermochemical storage networks for integration of renewable energy sources through seasonal load shifting

Thermochemical networks are a rather new subject in research and support our goal to lower winter electricity demand and foster the integration of renewable energy sources. This paper takes a first step towards a performance analysis of thermochemical networks and a comparison to a classical district heating network for a virtually defined network of 1.3 km length, assuming a space heating load of 204.7 MWh represented by 33 residential buildings. The performance comparison is done for winter operation when space heating demand is present. The simulation results clearly revealed that for the classical district heating system, thermal and pressure losses lead to a significant increase in the loads, further increasing the electricity demand for the heat pump and the circulation pump. Conversely, for the thermochemical network, no compressor is needed to extract the heat from the boreholes and the circulation of the sorbent solution was found to be minute, leading to a negligible electricity demand for space heating supply. This resulted in a very high electric COP as well as a high exergy efficiency compared to a classical district heating system. Further, the volumetric energy storage density was compared, recording a 2 to 22.3 times higher value for the thermochemical network.

Impact of different CRPS phenotypes and diagnostic criteria on quantitative sensory testing outcomes: systematic review and meta-analysis.

This review and meta-analysis evaluated the impact of diagnostic criteria and clinical phenotypes on quantitative sensory testing (QST) outcomes in patients with complex regional pain syndrome (CRPS). Eight databases were searched based on a previously published protocol. Forty studies comparing QST outcomes between CRPS-I vs II, warm vs cold CRPS, upper vs lower limb CRPS, males vs females, or using Budapest vs older IASP criteria were included. Studies investigating QST differences between CRPS-I vs II (n = 4), between males vs females (n = 2), and between upper and lower limb CRPS (n = 2) showed no significant differences. Four studies compared QST outcomes in warm vs cold CRPS, showing heat hyperalgesia in warm CRPS, with thermal and mechanical sensory loss in cold CRPS. Although CRPS diagnosed using the Budapest criteria (24 studies) vs 1994 IASP criteria (13 studies) showed similar sensory profiles, there was significant heterogeneity and low quality of evidence in the latter. Based on the findings of this review, classifying CRPS according to presence or absence of nerve lesion into CRPS-I and II, location (upper or lower limb) or according to sex might not be clinically relevant as all appear to have comparable sensory profiles that might suggest similar underlying mechanisms. In contrast, warm vs cold phenotypes exhibited clear differences in their associated QST sensory profiles. To the extent that differences in underlying mechanisms might lead to differential treatment responsiveness, it appears unlikely that CRPS-I vs II, CRPS location, or patient sex would prove useful in guiding clinical management.

Optimization of PCM Properties for Thermal Energy Storage in Solar Parabolic Trough Systems: A Review

Abstract: Solar Parabolic Trough Systems (PTS) are highly efficient solar thermal technologies for converting concentrated solar radiation into thermal energy. However, their intermittent energy production, primarily due to variations in solar availability, underscores the necessity for effective thermal energy storage (TES) solutions. Phase Change Materials (PCMs) have emerged as a promising means to store and release thermal energy efficiently. This study focuses on the critical task of optimizing PCM properties to enhance thermal energy storage within Solar Parabolic Trough Systems. The selection and fine-tuning of PCM properties are paramount to achieving superior TES performance. Parameters under scrutiny include the melting temperature, latent heat of fusion, thermal conductivity, and cost-effectiveness. Each of these factors plays a pivotal role in the overall efficiency and economic viability of PCM-based TES systems integrated with PTS. Through a thorough review of existing research and recent advancements in the field, this study sheds light on the profound impact of tailored PCM properties. It demonstrates how optimizing these properties can lead to substantial improvements in energy storage capacity, system efficiency, and overall cost-effectiveness. Such optimizations are crucial not only for enhancing the competitiveness of solar thermal technology but also for promoting sustainable energy utilization. The investigation presented herein underscores the significance of PCM property optimization as a strategic pathway toward advancing solar thermal technology. By maximizing energy storage capacity, minimizing thermal losses, and optimizing cost factors, we can unlock the full potential of PTS, making them more reliable and accessible for meeting the world's growing energy demands. This research serves as a valuable resource for engineers, researchers, and stakeholders working towards the integration of PCM-based TES with solar thermal systems. Ultimately, it contributes to the realization of a cleaner, more sustainable energy future, addressing the urgent need to reduce greenhouse gas emissions and our reliance on non-renewable energy sources

Evaluation of thermal loss of Chinese solar greenhouse cover under all operating conditions

The solar greenhouses in China are composed of gables on the east and west sides, north walls, and north and south roofs. The south roof is the main heat dissipation surface of the greenhouse. To quantitatively and comprehensively analyse the heat transfer characteristics and heat loss pathways of the south roof of a solar greenhouse, based on the actual usage of the greenhouse, the heat transfer of the south roof is classified into two working conditions: heat transfer of the transparent covering material (TCM) and heat transfer of the composite thermal insulation coating (CTIC). A theoretical heat transfer model of the covering layer of the solar greenhouse under all working conditions is constructed by applying the heat transfer theory. The model was tested using field test data from two areas different regions in China: Beijing and Lhasa. The results show good agreement between the simulated and measured values, the relative errors between simulated and measured values were 18.54% and 8.17%, respectively, with root mean square errors of 1.69 and 1.92. The model can comprehensively and accurately reflect the comprehensive heat transfer coefficient and heat loss changes of the south roof of the solar greenhouse. It can be used to analyze the proportion of heat loss caused by radiation, convection, and water vapor condensation. The analysis shows that condensation heat loss cannot be ignored during the winter night period. Measures such as covering the roof with plastic film and controlled irrigation can help reduce condensation heat loss.

SUMOylation Modulates Reactive Oxygen Species (ROS) Levels and Acts as a Protective Mechanism in the Type 2 Model of Diabetic Peripheral Neuropathy.

Diabetic peripheral neuropathy (DPN) is the prevalent type of peripheral neuropathy; it primarily impacts extremity nerves. Its multifaceted nature makes the molecular mechanisms of diabetic neuropathy intricate and incompletely elucidated. Several types of post-translational modifications (PTMs) have been implicated in the development and progression of DPN, including phosphorylation, glycation, acetylation and SUMOylation. SUMOylation involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target proteins, and it plays a role in various cellular processes, including protein localization, stability, and function. While the specific relationship between high blood glucose and SUMOylation is not extensively studied, recent evidence implies its involvement in the development of DPN in type 1 diabetes. In this study, we investigated the impact of SUMOylation on the onset and progression of DPN in a type 2 diabetes model using genetically modified mutant mice lacking SUMOylation, specifically in peripheral sensory neurons (SNS-Ubc9-/-). Behavioural measurement for evoked pain, morphological analyses of nerve fibre loss in the epidermis, measurement of reactive oxygen species (ROS) levels, and antioxidant molecules were analysed over several months in SUMOylation-deficient and control mice. Our longitudinal analysis at 30 weeks post-high-fat diet revealed that SNS-Ubc9-/- mice exhibited earlier and more pronounced thermal and mechanical sensation loss and accelerated intraepidermal nerve fibre loss compared to control mice. Mechanistically, these changes are associated with increased levels of ROS both in sensory neuronal soma and in peripheral axonal nerve endings in SNS-Ubc9-/- mice. In addition, we observed compromised detoxifying potential, impaired respiratory chain complexes, and reduced levels of protective lipids in sensory neurons upon deletion of SUMOylation in diabetic mice. Importantly, we also identified mitochondrial malate dehydrogenase (MDH2) as a SUMOylation target, the activity of which is negatively regulated by SUMOylation. Our results indicate that SUMOylation is an essential neuroprotective mechanism in sensory neurons in type 2 diabetes, the deletion of which causes oxidative stress and an impaired respiratory chain, resulting in energy depletion and subsequent damage to sensory neurons.

Thermal performances of a bioclimatic building in hot and dry tropical climate

This paper is concerned with the thermal comfort of a double-walls seven stories bioclimatic building built with local construction materials. First of all, we use a numerical code to investigate the construction materials thermal inertia effects on the optimization of the building envelop. Second, the outer and inner surface temperatures are determined utilizing the TRNSYS code. A system of trap is then design to evacuate during nighttimes, the stored daily heat. The conditioned air thermal load differences between the double and simple walls are also investigated. Similarly, the linear thermal loss coefficients and the thermal bridge losses are computed utilizing respectively the ‘Heat’ software and the Degree Day method. The results show a difference of 6 to 7 oC between the outer and the inner maxima surface temperatures. The computation of the conditioned air thermal load indicates a net energy gain of the order of 5.8 % in the office spaces and 12.1% in the bedrooms, respectively for the double and simple walls. The double-walls thermal bridge losses amount to 16.46 % of the total building losses and 20.77 % for the 20 cm thick simple wall. The building envelop optimisation process continues with the study of the effects of the addition of a garden roof on the thermal comfort.

Solution by the self-adjoint operator method for a model of a co/counter-current moving bed heat exchanger with heat losses

A solution by the self-adjoint operator method (SAO) (still not widely used in engineering) is presented for a lumped parameter model (LM) of a co/counter-current, indirect heated, diluted, tubular, vertical moving bed heat exchanger (MBHE), with heat loss to surroundings. The self-adjoint formulation of the problem and several mathematical techniques enabled the development of an ingenious methodology capable of solving the difficult problem of establishing the character of the eigenvalues of the MBHE operator - only partially known to date - for co/counter flow.For co-current flow, it is demonstrated that the self-adjoint solution corresponds to a solution from the literature - obtained by the Laplace transform - but with the character of the roots not yet established. Therefore, the work aims to, through analysis, study the character of the eigenvalues of the MBHE operator to generalize results from the literature, allowing the use of the solution in a comprehensive parametric range, as well as for different flow arrangements, discussed within the scope of case studies. From the analysis of the eigenvalue equation, five thermal behaviors of the MBHE could be identified. The model was also solved numerically, and the results show excellent agreement in both calculation methods. The obtained analytical solution reveals a possible inconsistency in a literature solution of the analogous heat transfer problem in a triple tube heat exchanger (the) with thermal losses at the outer surface. The study generalizes previous results and allows its extension, by analogy, to the solution for the TTHE with thermal losses at the outer surface.

Laboratory evaluation of different bio-oil recycled aged asphalts: Conventional performances and microscopic characteristics

The performance of diverse types of bio-oils varies greatly from each other, which makes it arduous to apply different bio-oils directly in engineering practice. This study is based on physical and microscopic properties, studying different types of bio-oil recycled asphalt and analyzing their differences. Five bio-oils (castor oil, straw oil, soybean oil, gutter oil, and vegetable oil) were used to regenerate asphalts after short-term and long-term aging to prepare recycled asphalts. The physical performances of recycled asphalts with different bio-oils were assessed, including penetration, softening point, and ductility tests. In addition, scanning electron microscopy was utilized to investigate the microscopic morphologies of recycled asphalts. Simultaneous thermogravimetry and differential scanning calorimetry were applied to determine the thermal stabilities of recycled asphalts. Finally, Gel permeation chromatography was employed to analyze the asphalt's relative molecular masses. The results revealed that vegetable and gutter oil have apparent adverse effects on temperature sensitivity and high-temperature performance of aged asphalt. In contrast, they have positive effects on low-temperature performance. All five bio-oils can repair cracks on the surface of aged asphalt. However, the surface wrinkles of vegetable oil-recycled asphalt and castor oil-recycled asphalt are relatively less and have an outstanding recycling effect. The slight thermal weight loss of recycled asphalts corresponding to castor oil, straw oil, and soybean oil at high temperatures positively impacted the high-temperature stability of aged asphalt. The castor oil and soybean oil recycled asphalts have significantly larger relative molecular masses and have advantages in high-temperature performance. This paper reveals the impact of different bio-oils on asphalt regeneration, which contributes a theoretical basis for promoting the practical implementation of bio-oil in road projects, with obvious economic and social benefits.

Aging Mechanism and Lifetime Prediction of Glass Fiber Reinforced Liquid Crystal Polymer Composite under Thermal and Oxidative Conditions

AbstractDevelopment of fifth‐generation technology leads to a growing demand for materials with exceptional thermal property, mechanical strength, and low dielectric loss. However, ensuring the broad application of such materials by comprehensively investigating their aging mechanisms and service lifetimes remains a challenge. In this work, we have developed a glass fiber (GF) reinforced liquid crystal polymer composite (GF/LCP) and conducted a thorough exploration of its aging mechanism, behavior, and service lifetime under thermal and oxidative conditions. On the basis of the general Arrhenius model, the composite maintains a high level of functionality for a remarkable 18 years at 150 °C and 1.5 years at 200 °C. Despite the extremely high thermal resistance of GF/LCP composite, the LCP matrix exhibits localized brittle fracture, and the main chains still undergo gradual degradation to generate phenolic groups, which ultimately leads to severe pulverization and mass loss. However, a high degree of connection maintenance between GF and LCP components is still reserved. This work provides a valuable reference for the reliable application of 5G materials under thermal and oxidative conditions.