Thermal Chamber Research Articles

Numerical and experimental study of a CO[formula omitted] multi-channel radiator used for space application

This article presents a novel multi-channel condenser/radiator designed for mechanically pumped two-phase cooling systems in space. A numerical model coupling two-phase condensation heat transfer with thermal radiation is proposed to design and accurately predict the performance of the radiator, taking into account both single-phase and two-phase heat transfer occurring within the fluid channels. The performance assessment of the radiator is carried out in a thermal vacuum chamber with CO2 circulating through a closed cooling loop. The validation of the numerical model is confirmed by comparing the predicted results with the experimental data obtained. The comparison demonstrates good agreement with the discrepancy of 10% between the predictions and the actual measurements. The numerical method presented here is simpler compared to Computational Fluid Dynamics (CFD), making calculations more accessible, particularly for those without access to CFD tools. Additionally, this paper explores ways to simplify complex thermal radiation issues using surface-to-surface radiation models and the Monte Carlo method to calculate the view factor.

Features of the change in the thermal coefficient of electrical resistance upon heating electrically conductive composites of crystallizable polyolefins with carbon black

Objectives. To investigate electrically conductive polymer composite materials (EPCMs) based on crystallizable polyolefins and electrically conductive carbon black for the production of self-regulating heaters; to study the mechanism of the occurrence of positive and negative temperature coefficients (PTC and NTC) upon heating such composites.Methods. A comprehensive study of the structure and properties of crystallizable EPCMs with electrically conductive technical carbon was carried out. In order to measure the electrical characteristics of the composites, they were compacted into plates to model polymer heaters. Contact electrodes made of an ungreased brass mesh were embedded in their ends. The temperature dependencies of the electrical characteristics of the samples were investigated in a modified thermal chamber of an FWV 633.10 Vicat softening temperature meter. The change in the degree of crystallinity was analyzed by means of differential scanning calorimetry with a NETZSCH DSC 204 F1 Phoenix calorimeter. The dilatometric and rheological characteristics of the samples were studied using an IIRT-AM melt flow index tester.Results. It was determined that the self-regulation ability (an abnormally high positive thermal coefficient of electrical resistance) of selfregulating heaters made of composites of crystallizable polyolefins with electrically conductive technical carbon cannot be explained by the thermal expansion of EPCMs alone. It was shown that in crystallizable polyolefin-based EPCMs, the inversion of the thermal coefficients of electrical resistance (transition from PTC to NTC) is associated with a change in the aggregate state of EPCMs and the beginning of its transition to a viscous-flow state. A mechanism involving a sharp increase in the electrical resistance of self-regulating crystallizable polyolefin-based composite with electrically conductive technical carbon was proposed and substantiated. This mechanism takes into account the additional shear deformation effect produced on the crystalline phase of the EPCM by numerous expanding melt microvolumes formed at the early stages of the melting process with a minimum change in the degree of crystallinity.

The Regulation of Temperature Fluctuations and Energy Consumption in Buildings Using Phase Change Material–Gypsum Boards in Summer

This study examined the thermal performance of Comfortboard23, a commercial gypsum board from Knauf infused with phase change material (PCM). Structural characterization using XRD and SEM confirmed the presence of microencapsulated PCM within the gypsum matrix. The study does not provide a direct comparison between Comfortboard23 and other PCM-integrated gypsum boards on the market. This is a limitation of the research. A comprehensive comparison would involve testing multiple products under identical conditions, and evaluating factors such as thermal performance, cost-effectiveness, durability, and ease of installation. Thermal characterization involved a novel low-scale thermal chamber to measure U-value, thermal conductivity, heat storage capacity, and dynamic thermal response. Results showed incorporating PCM decreased the U-value by 2% compared to standard gypsum boards. Additionally, PCM inclusion increased heat storage capacity by around 45% and improved dynamic thermal characteristics by decreasing thermal stability coefficient from 0.92 to 0.76 and increasing thermal lag from 0.27 to 0.49 h. The 45% increase in heat storage capacity of Comfortboard23 could lead to a 10–20% reduction in heating and cooling energy consumption, improved thermal comfort, and potential HVAC downsizing. Exact benefits depend on climate, building design, and occupancy patterns, necessitating further research in diverse real-world settings. The findings demonstrate Comfortboard23’s potential for enhancing thermal energy storage in buildings, contributing to energy savings, improved thermal comfort, and reduced temperature fluctuations across varying daily temperatures. Overall, the study highlights the promise of Comfortboard23 as an energy-efficient PCM-integrated building material.

Study on Thermal Chamber Expansion of VH-SAGD Process Using CO2-Inducing Effect for Heavy Oil Reservoirs

In heavy oil thermal recovery processes, higher pressure usually leads to low dryness and expansion difficulty for the injected steam in thermal recovery processes, which will result in lower oil recovery and more carbon emissions. This paper proposed a new CO2-inducing method to accelerate the steam chamber expansion, based on a core flooding experiment and numerical simulation. First, the CO2 showed significant viscosity reduction at high pressure in the PVT test. In the core flooding experiment, the CO2 provided strong flow conductivity in porous media for the thermal flooding, as the CO2 pre-injection restrained the steam condensation. Using the CO2-inducing method, CO2 pre-injection before steam built a fast flow channel in a relatively higher permeability layer and reduced the thermal injection pressure by about 1.0~2.4 MPa. As a result, the steam overlap around the injection wells became slower and the gravity drainage process was able to heat and displace the heavy oil above the channel. Furthermore, the CO2 gas trapped at the top reduced heat loss by about 12.4%. The field numerical simulation showed that this new method improved thermal recovery by 7.5% and reduced CO2 emissions by about 18 million kg/unit for the whole process. This method changes the conventional thermal expansion direction by CO2 inducing effect and fundamentally reduces heat loss, which provides significant advantages in low-carbon EOR.

Pore-Scale Mechanism Analysis of Enhanced Oil Recovery by Horizontal Well, Dissolver, Nitrogen, and Steam Combined Flooding in Reducer Systems with Different Viscosities for Heavy Oil Thermal Recovery

Horizontal well, dissolver, nitrogen, and steam (HDNS) combined flooding is mainly applied to shallow and thin heavy oil reservoirs to enhance oil recovery. Due to the lack of pore-scale mechanism studies, it is impossible to clarify the oil displacement mechanism of each slug in the process combination and the influence of their interaction on enhanced oil recovery (EOR). Therefore, in this study, HDNS combined flooding technology was simulated in a two-dimensional visualization microscopic model, and three viscosity reducer systems and multi-cycle combined flooding processes were considered. In combination with an emulsification and viscosity reduction experiment, two-dimensional microscopic multiphase seepage experiments were carried out to compare the dynamic seepage law and microscopic occurrence state of multiphase fluids in different systems. The results showed that the ability of three viscosity reducers to improve viscosity reduction efficiency in HDNS combined flooding was A > B > C, and their contributions to the recovery reached 65%, 41%, and 30%, respectively. In the system where a high viscosity reduction efficiency was shown by the viscosity reducer, the enhancements of both sweeping efficiency and displacement efficiency were primarily influenced by the viscosity reducer flooding. Steam flooding collaborated to improve displacement efficiency. The thermal insulation characteristics of N2 flooding may not provide a gain effect. In the system where a low viscosity reduction efficiency was shown by the viscosity reducer, the steam flooding was more important, contributing to 57% of the sweeping efficiency. Nitrogen was helpful for expanding the sweep area of the subsequent steam and viscosity reducer, and the gain effect of the thermal insulation steam chamber significantly improved the displacement efficiency of the subsequent steam flooding by 25%. The interaction of each slug in HDNS combined flooding resulted in the additive effect of increasing production. In actual production, it is necessary to optimize the process and screen the viscosity reducer according to the actual conditions of the reservoir and the characteristics of different viscosity reducers.

Experimental analysis of a pilot plant in Organic Rankine Cycle configuration with regenerator and thermal energy storage (TES-RORC)

Applying thermal energy storage in a Regenerative Organic Rankine Cycle system is a possible combination of energy storage for renewable and waste energy sources. This research presents an experimental analysis of a regenerative organic Rankine cycle pilot plant, incorporating a thermal energy storage chamber based on a phase change materials to obtain thermal inertia in the system. The primary heat source is the residual heat of combustion gases at a temperature of approximately 320 °C coming from a generating set that operates within a thermal power generation plant. The prototype uses a twin-screw expander modified to work as a turbine. Novec 649 was used as the working fluid which is an organic compound. The experimental evaluation of the regenerative organic Rankine cycle with thermal energy storage has been carried out through energy and exergetic efficiency analysis to verify the operation of the pilot plant. Values of 13.2 % were obtained for the exergetic efficiency and 2.67 % for the global efficiency of the cycle, with a maximum expander work of 11.8 kW. It was demonstrated that the thermal energy storage system provides energy in response to the plant's operating inertia for 17.5 min, sufficient time for the gradual shutdown of the plant equipment, maintaining the working power of the regenerative organic Rankine cycle.

Ultrasonic Analysis for Monitoring Li-Ion Batteries

To seek for increasing accuracy in LIBs monitoring a new trend is to rely on data indicative of material properties whose variations are induced by Li ions intercalation and deintercalation. A wider variety of information can be achieved if data are referred to a specific layer of the battery. Since ultrasounds propagate at different speed according to materials properties and are reflected every time they hit an interface, ultrasonic analysis (UA) has the potential to improve the quality of LIB monitoring providing in operando and through thickness information.In this work NMC-graphite LIBs are cycled and monitored in operando via UA in pulse-echo and through-thickness modes with a temporal resolution of 7 ns (which to the best of our knowledge is the highest ever tested) and a 5 MHz frequency. First, the effect of (i) temperature and (ii) C-rate on the waveform evolution was investigated: (i) a 100% charged battery was kept at rest in a thermal chamber at fixed temperatures varying between 10 and 50°C, the ultrasonic signal was acquired after 30 min at rest; (ii) an initially 100% charged battery underwent two subsequent discharge-charge cycles at constant current with fixed C-rates varying between 0.2 and 2C. Then a series of cycles at 50°C aimed at causing battery degradation was performed while acquiring the ultrasonic signal every 2 min. The efficacy of the degradation protocol was assessed through EIS prior and post cycling the battery. Surprisingly, results show an opposite (but systemic) trend with respect to what is reported in literature, with an increasing time of flight (ToF) for increasing state of charge (SoC). Additionally, it is observed that most of the peaks increase their ToF with the number of cycles. Signal amplitude shows a periodical behavior as well but values vary as degradation has gone on. It is also observed that within a cycle some peaks increase their intensity during charge while others decrease, suggesting that they belong to opposite electrodes.

The main strength material parameters of deformable cement adhesives

The deformable cement adhesives types C2S1 and C2S2 are usually used to glue ceramic slabs onto so-called critical substrates (other than concrete), including under changing weather conditions. The declared strengths of these adhesives attached to substrates can be found in the manufacturer’s standards and declarations. The use of cement adhesives on surfaces other than concrete or in other applications, such as a lightweight heated floor system (LHFS), should meet safety standards. To determine this, basic strength parameters for deformable adhesives, which have not been specified until now, need to be set. For this purpose, many analyses were performed, such as tensile and compressive strength tests, as well as the measurement of displacements in the thermal chamber, using, for example, digital image correlation and extensometric techniques. It was possible to define the main strength parameters of deformable adhesives, such as Young’s modulus (E), Poisson’s ratio (ν) and linear thermal expansion coefficient (α). These multiple measuring techniques were able to authenticate the obtained results, determining the maximum compressive strength of deformable adhesives, as well as longitudinal and transverse deformations. The research material parameters E, ν and α can be used for the calculation of LHFS with a heating coil, as well as for other building partitions or on critical substrates (different from concrete), using some of the many numerical methods available.

Thermal compensation of monolithic distributed fibre optic sensors: From the lab to the field

Distributed fibre optic sensing (DFOS) is gaining popularity as a diagnostic solution for short-term non-destructive testing (NDT) and long-term structural health monitoring (SHM). However, there are still challenges to be overcome, particularly with regard to long-term measurements under real field conditions, taking into account, among other things, temperature changes. These changes affect strain measurements through both thermal expansion and optical effects, and appropriate correction depends on the internal design of the sensor and the installation methods. Therefore, despite the fact that thermal compensation is one of the key prerequisites for correct data interpretation, there are no universal and clear procedures for DFOS. The lack of sufficient guidelines and proven applications is the main motivation for undertaking studies. The scope and novelty of the presented research lies in 1) the theoretical explanation of the thermal performance of monolithic DFOS sensors compared to the layered sensing cables; 2) the analysis and correction of strain data measured with monolithic sensors placed in a thermal chamber; 3) the verification of the laboratory results and the proposed approach in real field conditions: in a concrete footbridge deck and in a steel underground gas pipeline. All presented measurements were performed with high spatial resolution (mm order) Rayleigh-based interrogators under the control of conventional reference spot thermistors. The research demonstrated the linear thermal response of the monolithic sensors and confirmed their usefulness for distinguishing between length- and stress-dependent strains. Finally, the thermal compensation approach was proposed and verified in real operating conditions.

Thermal Variation on 18650 Cylindrical Cells under Different Testing Arrangement

Cylindrical cell, especially with the 18650 format, is widely used for power electronics and electric vehicle. The cell's performance is strongly dictated by the current rate of charge/discharge and the cell temperature. The former is relatively easy to gauge because the value is constant for a certain period. Therefore, the cell performance can be mapped with respect to the current rate. However, the cell temperature varies temporally and dimensionally, making mapping cell performance concerning temperature difficult. This study employs a comprehensive thermal approach, with the aim to evaluate the degree of thermal variation with respect to various testing temperatures and cell arrangements conducted in a thermal chamber. Thermal measurements are measured, such as cell surface temperature at various cell locations. The experimental results provide an insight that different testing arrangements in which the cell is suspended vertically and horizontally do not alter the temperature variation of the cell significantly. Nevertheless, temperature difference up to 3oC is manifested along the cell surface, which happens at 5oC ambient temperature. This analysis highlights that cell temperature on the surface of 18650 cell is highly non-uniform, and the data could be further used to facilitate the cell's cooling system in for cells in this nature.

Using mylar-insulated cryopumping panels to improve vacuum level during warm temperature testing at JSC’s large thermal vacuum facilities

Johnson Space Center’s Space Environment Simulation Lab (SESL) has both Chamber A, the world’s largest purpose-built thermal vacuum chamber capable of creating deep space conditions, and Chamber B, the largest human rated thermal vacuum chamber. A unique design feature of these chambers is the gaseous helium cryopumping panels within the liquid nitrogen shroud. This shroud is used to bring the chamber to cryogenic temperatures while the cryopumping panels trap gasses on its surface area to create a high vacuum environment of 5*10−6 Torr. In preparation for the James Webb Space Telescope (JWST) flight test, a series of functionals required the chamber to run at higher temperatures, and therefore did not need active cooling from the liquid nitrogen shroud. During testing, cryopumping panels were used to mitigate contamination during this main shroud warm-up. One of the cryopumping panels in Chamber A was covered with several layers of aluminized mylar to thermally protect the zone from the warmed shroud. This strategy was effective and became part of operations during JWST testing. Currently, Chamber B has requests for both commercial and NASA space suit tests at both high and low temperatures to validate thermal models. High temperature tests could benefit from reduced heater demand with an insulated shroud while still sustaining the high vacuum environment provided by the cryopumping panels. This paper will quantitatively define the thermal loads on the panels used in previous Chamber A warm up sequences. Additionally, this report will perform thermal analyses to assess the feasibility of adding layers of aluminized mylar to the cryopumping panels of Chamber B.

Evaluation of Thermal Support during Anesthesia Induction on Body Temperature in C57BL/6 and Nude Mice.

Heat supplementation during surgery is a common practice; however, thermal support is not commonly used during anesthesia induction. Mice lose body temperature quickly, and air movement can exacerbate this, potentially putting mice at a thermal deficit before surgery. Whether the method of warming during induction affects overall heat loss during anesthesia is unknown. We hypothesized that the method of heating would affect body temperature (Tb) during anesthesia induction, maintenance, recovery, and once placed back on the rack. Mice (C57BL/6NHsd-6M/6F [C57BL/6]; Hsd:Athymic Nude-Foxn1nu [Nude]; N = 24;12M/12F) were assigned to a treatment in a factorial design: thermal chamber (TC; ambient temperature [Ta] = 28.8°C); heating pad (HP; induction chamber placed on an electric heating pad;Ta = 28.4°C); and control (Ctrl; Ta = 21.6°C). During induction, one mouse at a time was anesthetized with isoflurane over a 3min period and then maintained under anesthesia for 10min on a hot water heating pad (33 °C). Then isoflurane was stopped and time to ambulation was recorded. Tb and activity were tracked in the home cage on the rack before and after anesthesia. During induction, Ctrl mice lost significantly more heat (-2.8 °C) than did TC (+0.2 °C) and HP mice (+0.1 °C) but TC and HP were not different. During anesthesia maintenance, Ctrl mice regained 1 °C, but their Tb was still lower than that of the treated groups. Nude mice consistently had a lower Tb than C57BL/6 mice, regardless of treatment or anesthesia phase. C57BL/6 Ctrl mice took longer to ambulate than either HP or TC mice, but the method of heating did not differentially affect Nude mice. In general, C57BL/6 as compared with Nude and females as compared with males were comparatively more active and had higher Tb during certain times of day, regardless of the heating methods. Overall, our findings support the provision of heat during anesthesia induction, regardless of method, to reduce overall Tb loss during a short anesthesia event.

Optomechanical industrial-level camera modifications forrepeatable thermal image drift

Thermal image drift is observed in prevalent industrial-level cameras because their optomechanical design is not optimised to reduce this phenomenon. In this paper, the effect of temperature on industrial-level cameras is investigated, focusing on the thermal image drift resulting from ambient temperature changes and warming-up process. Standard methods for reducing thermal image drift are reviewed, concentrating on the lack of repeatability aspect of this drift. Repeatable thermal image drift is crucial for applying a compensation model as random thermal deformations in sensors cannot be compensated. Moreover, the possible cause of this issue is explored, and novel optomechanical camera modifications are proposed that maintain the thermal degrees of freedom for the deforming sensor, limiting the lack of repeatability aspect of thermal image drift to a low level. The improvement is verified by conducting experiments using a specialised test stand equipped with an invar frame and thermal chamber. Considering the results from the application of the polynomial compensation model, the standard deviation of the central shifts of image drift is reduced by ×3.99, and the absolute range of image drift is reduced by ×2.53.

A “one‐pot” method for synthesizing zinc tryptophan and its derivatives as highly efficient PVC thermal stabilizer with excellent mechanical properties

AbstractZinc Tryptophan (Trp‐Zn) and zinc N‐(salicylic) tryptophan (SalTrp‐Zn) were synthesized from tryptophan, zinc acetate, and salicylic aldehyde by one‐pot method, respectively. The structure was analyzed by FT‐IR, 1H NMR, and elemental analysis. PVC samples were prepared by stirring method and solvent film process, and then the thermal properties of PVC samples were studied by thermal aging chamber test, Congo red test, electrical conductivity test, and thermogravimetric analysis (TGA). The thermal stability of Trp‐Zn and SalTrp‐Zn stabilized PVC samples was better than calcium and zinc soaps used in industry. The thermal stability time was up to 80 min, and it was a long‐acting thermal stabilizer. After the addition of CaSt2 and Trp‐Zn stabilizer in different proportions, the thermal stability of PVC was obviously improved, and the initial whiteness of the film was improved after the combination of Trp‐Zn/SalTrp‐Zn. In addition, the tensile test verified that the PVC samples stabilized by Trp‐Zn and SalTrp‐Zn had the highest elongation at break. The addition of Trp‐Zn can reduce the elastic modulus of PVC, effectively improve the mechanical properties of PVC, and make the PVC film have better toughness and elasticity. Through DMA and EDS tests, it can be seen that Trp, SalTrp‐Zn had good compatibility with PVC and DOP. The quantum chemical calculation of Trp‐Zn, SalTrp‐Zn and vinyl chloride models was carried out, and the thermal stability mechanism of thermal stabilizer on PVC was analyzed accurately, mainly the absorption mechanism of HCl and the substitution mechanism of unstable chlorine atoms.

Effect of cork powder concentration and service temperature on strength characteristics and failure modes of tubular adhesively bonded joints

The current study investigates the synergistic influence of cork powder and temperature on the strength characteristics of tubular adhesive joints subjected to pure mode-II failure. Two distinct joint configurations, Steel-CPVC and Steel-PVC, were employed in the study. The adhesive matrix consisted of Araldite-LY-556 and hardener AD-22962, with cork powder serving as the filler. Various proportions of cork powder, specifically 0.25 wt%, 0.50 wt%, 0.75 wt%, and 1 wt%, were incorporated into the adhesive mixture. Test samples were prepared for each configuration by using the modified adhesive followed, by a curing step at an elevated temperature. Tensile tests were conducted at four different temperature settings: 25 °C, 50 °C, 75 °C, and 100 °C, by utilizing a universal testing machine (UTM) equipped with a thermal chamber. The results revealed that, in the case of the Steel-CPVC configuration, the failure load characteristics of the joint exhibited an increasing response at lower cork concentration of 0.25 wt%, irrespective of the service temperature. However, was negatively impacted with the further increase in cork concentration. A maximum improvement of 53.48 % in failure load compared to the neat adhesive case at 25 °C was reported. Notably, the influence of cork powder persisted even under elevated temperature conditions, hence suggesting that that the impact of cork filler reinforcement is independent of service temperature. For the Steel-PVC joint layout, an entirely opposite trend was observed were both the increase in concentration of cork filler and service temperature significantly reduced the strength compared to the control case.

Calculation and Design of the Main Equipment for Mobile Space Simulation System

ABSTRACT This article presents the results of the analysis of approaches to designing a mobile vacuum system ‘METAMORPHOSIS’ for simulation of space environment, which could help provide services of testing space objects at the request of the customers at a place and time acceptable to them, which allows saving time and assets in the development of space objects, their elements, including satellites. As a result of the conducted analysis, methodological approaches to the determination of the structure of the vacuum system were undertaken. To avoid unanticipated issues and to validate computer-driven modelling, testing in a space simulation chamber is an important part of the quality-assurance process. Spacecraft and their components must withstand extreme temperatures and pressure to travel outside the Earth’s atmosphere. Space simulation testing involves the use of a thermal vacuum chamber to replicate the conditions experienced in space.

A Novel Temperature Drift Error Estimation Model for Capacitive MEMS Gyros Using Thermal Stress Deformation Analysis.

Because the conventional Temperature Drift Error (TDE) estimation model for Capacitive MEMS Gyros (CMGs) has inadequate Temperature Correlated Quantities (TCQs) and inaccurate parameter identification to improve their bias stability, its novel model based on thermal stress deformation analysis is presented. Firstly, the TDE of the CMG is traced precisely by analyzing its structural deformation under thermal stress, and more key decisive TCQs are explored, including ambient temperature variation ∆T and its square ∆T2, as well its square root ∆T1/2; then, a novel TDE estimation model is established. Secondly, a Radial Basis Function Neural Network (RBFNN) is applied to identify its parameter accurately, which eliminates local optimums of the conventional model based on a Back-Propagation Neural Network (BPNN) to improve bias stability. By analyzing heat conduction between CMGs and the thermal chamber with heat flux analysis, proper temperature control intervals and reasonable temperature control periods are obtained to form a TDE precise test method to avoid time-consuming and expensive experiments. The novel model is implemented with an adequate TCQ and RBFNN, and the Mean Square Deviation (MSD) is introduced to evaluate its performance. Finally, the conventional model and novel model are compared with bias stability. Compared with the conventional model, the novel one improves CMG's bias stability by 15% evenly. It estimates TDE more precisely to decouple Si-based materials' temperature dependence effectively, and CMG's environmental adaptability is enhanced to widen its application under complex conditions.

The effects of temperature on mechanical properties of neat and montmorillonite reinforced epoxy compounds

ABSTRACT The aim of the article was to determine the effect of temperature on the tensile strength of two types of the epoxy compounds: the neat and the montmorillonite reinforced epoxy compounds. These epoxy compounds were made in four variants, which included two epoxy resins based on bisphenol A (unmodified base epoxy resin and modified with polyester resin epoxy resin) as well as two curing agents: triethylenetetramine and polyamide curing agent. The samples were exposed in two types of environment: (i) at 80°C for 1 and 2 months in a thermal chamber and also (ii) in the temperature range from −40°C to 80°C for 1 and 2 months in a thermal shock chamber. The reference samples of epoxy compounds were also compared. After the aging time, the dog-bone samples of epoxy compounds were subjected to the tensile strength tests in accordance with PN-EN ISO 527–2. The compressive strength of reference samples is higher for epoxy compounds containing the triethylenetetramine curing agent (both for epoxy compounds comprising Epidian 5 and Epidian 57 epoxy resin), The values of tensile strength, elongation at break are affected by the ambient and curing temperature, the curing period and the presence of a filler (montmorillonite). The tensile strength of the reference epoxy compounds containing Epidian 5 epoxy resin and the triethylenetetramine curing agent is lower than that of epoxy compounds containing unmodified epoxy resin (Epidian 5) and the polyaminoamide curing agent, while the tensile strength of the epoxy compounds containing modified epoxy resin (Epidian 57) and the triethylenetetramine curing agent is higher than that of the epoxy compounds containing Epidian 57 epoxy resin and the polyaminoamide curing agent. Aging of the epoxy compounds both in the climatic chamber and in the thermal shock chamber in most cases it contributed to an increase in the tensile strength.

Effects of external influencing factors on the microstructure and physico-mechanical characteristics of glass-reinforced polymer composite material based on polyimide binder

The article presents the results of experimental studies of the effects of external influencing factors (natural exposure in climatic zones, such as a temperate climate and a climate with an industrial atmosphere, during accelerated climatic tests in a thermal humidity chamber, during thermal aging, exposure in technical environments) on the microstructure and physical and mechanical characteristics of a glass-reinforced polymer composite material grade VPS-72 based on polyimide binder grade VS-51. The state of the surface of fiberglass samples after exposure was studied for one year.

Effect of Various Hydration Strategies on Work Intensity and Selected Physiological Indices in Young Male Athletes during Prolonged Physical Exercise at High Ambient Temperatures.

Background: In high temperatures, adequate hydration is vital for sustained physical exercise. This study explores the effect of three hydration strategies on physiological indices and work intensity. Methods: The research involved 12 healthy males who engaged in three test series, each separated by a one-week interval. During the trials, participants underwent a 120 min cycling session in a thermal climate chamber (temperature: 31 ± 2 °C, humidity: 60 ± 3%, air movement: <1 m/s). Measurements of rectal temperature (Tre) and heart rate (HR), and assessment of subjective workload perception, and thermal comfort were made both before and during the exercise. The computation of the physical strain index (PSI) relied on Tre and HR values. Three hydration strategies (isotonic drink, water, and no hydration) were administered before, during, and after the exercise. Results: Regardless of the hydration strategy, the participants' mean body mass decreased as a result of the exercise. Statistically significant differences in HR were observed between the no-hydration and water groups (p < 0.036). The mean PSI values significantly varied between hydration strategies, with the no hydration group exhibiting a higher PSI compared to the isotonic drink or water groups (p < 0.001). Conclusions: All hydration strategies contribute to thermoregulatory processes and mitigate the rise in internal body temperature during sustained physical exercise in elevated ambient temperatures.