Test Chamber Research Articles

Experimental investigation of impact of fire size on heat transfer and flame behavior of initial stage unsteady pool fires inside a cubical enclosure

The ventilation equipment for enclosed spaces or office rooms is specified according National Building Code of India published by the Bureau of Indian Standards. Natural ventilation peri-odically together with mechanical ventilation is recommended to remove pollutants. The need to study fire and smoke behavior inside a completely closed room with air intake and exhaust vents becomes important in case of low or no mechanical ventilation service. An experimental study on unsteady heptane pool fires of different sizes in their initial stages was conducted in a cubical fire test chamber of 27 m3 inside dimensions. The compartment was naturally ventilated with a typical configuration of a vertical intake on a side wall and an exhaust vent at the ceiling leading into a duct. Three circular pans of diameters 0.34, 0.47 and 0.61 m were employed to generate the fire with n-heptane as fuel on a bed of water. Temperatures, wall heat fluxes and mass loss rate were measured. The flame was visualized using a video camera through a tempered view glass. The total heat transfer to the ceiling and wall increased with the increase in fire size as the flames became taller in the initial stages (3-4 minutes) with sig-nificant increase in case of 500 kW fire. The smoke layer was observed at about mid height (1.5 m) above floor. The leaning behavior of flames was seen due to naturally induced air inflow. The wall heat flux of about 50 kW/m2 obtained indicate hazardous environment for further flame spread. A fourfold increase in mass loss rate was observed with just 2.5 times increase in fire size inside the ceiling vented compartment.

Development of a dry-type double floor with high vibration isolation for improvement of floor impact sound insulation performance on CLT buildings

To improve the floor impact sound insulation performance of cross laminated timber (CLT) buildings, a box-type test chamber made of CLT was constructed, and the countermeasure using a dry-type double floor was investigated. Several specimens with different area density and bending stiffness of double flooring structure were prepared, and the materials of flooring and elastic floor posts were adjusted so that the natural frequency of each specimen was about 14 Hz when the specimen was considered as a single-degree-of-freedom system. The dry-type double flooring structure affected the response at the natural frequencies not only of the slab but of walls. When installing the dry-type double flooring structure, the influence of acoustic radiation from the ceiling surface was relatively high at lower frequencies, while at higher frequencies, the influence from the walls was relatively high. The installation of the dry-type double flooring structure resulted in an improvement in floor impact sound insulation performance.

Material point method simulations of displacement pile and CPT penetration in sand considering the effects of grain breakage

Full displacement installation dramatically alters the stress and strain fields applying around piles and Cone Penetrometer (CPT) probes at sand sites. Calibration chamber tests have indicated that severe particle crushing occurs near to the pile or cone tips and a distinct shear zone may develop that leaves crushed sand adhering to the pile or cone shaft. It is therefore important to investigate how particle breakage affects the stress and deformation fields developed as this process occurs. In this study, installation by monotonic jacking of conically tipped model piles or CPT probes into silica sand is simulated by material point method (MPM) analyses. A thermodynamically consistent model which considers competing grain crushing and dilation is employed to model the sand behavior, while an MPM approach is adopted to cater for the large deformations involved in the penetration process. Particle crushing is predicted beneath the pile tip and around the pile shaft. The numerical results are compared to directly related instrumented pile calibration chamber tests. The numerical results show that the computed stress and displacement fields match key aspects of the experimental results well, especially in reproducing the volumetric compression observed experimentally. The results confirm that combining MPM with suitably sophisticated constitutive models creates new capabilities for analyzing large-deformation problems.

Hydrogen sensor with a thick catalyst layer anchored on soda-lime glass

Hydrogen is a green energy source with zero pollutant emissions and increasing demand. Hydrogen sensors are required due to the flammable nature of hydrogen in air. Current catalytic combustion hydrogen sensors based on membrane platforms strike a balance between sensitivity and mechanical strength. A thick catalyst layer allows enhanced sensor sensitivity, producing an acceptable sensor signal change. A hydrogen sensor with a thick catalyst layer is introduced on soda-lime glass, which has low thermal conductivity and prefabricated catalyst anchoring channels. The hydrogen sensor is composed of a 44 Ω platinum sensing electrode and a 100 Ω gold microheater, both of which are coated with a thin layer of alumina. The sensing electrode is buried in the catalyst anchoring channels with a 10 μm depth and 78 μm width using a hydrogen combustible catalyst. The response for 1 % H2 in air is 9.43 % in a test chamber at 80 °C with a response time of 48 s and recovery time of 75 s. The calculated temperature increment due to catalytic combustion is 84 °C. A hydrogen sensor with a thick catalyst layer on soda-lime glass shows enhanced heat generation, resulting in an improved thermoresistive response, and consistent mechanical support.

Graphite Nanoplatelets Nanostructured Films as Multifunctional Protective Layer in Kevlar/Nomex Sandwich Composites

In the aerospace sector, structural and non-structural composite components are usually subjected to a wide range of environmental conditions. Among all, moisture can seriously damage these materials’ performance, reducing their mechanical, thermal, electrical, and physical properties as well as their service time. Lightweight protective barrier coatings capable of reducing the diffusion of gases and/or liquids in a material can improve the material’s resistance in humid environments. In this work, nanolamellar nanocomposites characterized by a high in-plane orientation of nanoplatelets have been employed as protective coatings for Kevlar sandwich panels, reproducing the construction of a nacelle engine. The effectiveness of the protection against water uptake of nanocomposites reinforced with graphite nanoplatelets (GNPs) at high filler contents (70, 80 and 90 wt%) has been investigated using moisture uptake and Ground-Air-Ground (GAG) tests in an environmental chamber. GNP coatings effectively work as barrier by generating highly tortuous paths for molecule diffusion. Results showed a dependence of the absorption on the coating composition and inner structure. Films @70 wt% GNPs showed the best protection against moisture uptake by delaying the phenomenon and reducing the absorption by −80% after 3 days and −35% after 41 days.

Influence of Chemical Composition and Degree of Fragmentation of Millet Grain on Confused Flour Beetle (Tribolium confusum Duv.) Infestation

Owing to its wealth of nutritional values and low cultivation requirements, millet can become a key crop in global food systems. Thus, the Food and Agriculture Organization (FAO) declared that 2023 is the International Year of Millet. The introduction of this cereal and its products into universal food circulation calls for a multidimensional approach, which would also consider threats posed by pests during the storage of cereal kernels. The aim of this study was to evaluate the development of the confused flour beetle (Tribolium confusum Duv.) on common millet (Panicum miliaceum L.) and products obtained from this cereal, and to analyze the factors which influence its development (chemical composition of kernels, degree of their fragmentation). The study was conducted under laboratory conditions in an environmental test chamber (temperature 30 °C, humidity 70%, light—complete darkness). Millet grains of the Jagna cultivar and its products were weighed at 20 g, placed in vinidur dishes, and 10 beetles were then placed on the prepared material. The experiment demonstrated that the millet grain and food products obtained from this grain (millet flour, flakes, groats) could be a suitable habitat for the development of the confused flour beetle. The key regulator for the development of this pest insect is the degree of fragmentation of the infested material. The millet grain and millet products (except millet flour) are characterized by less numerous developments of beetle progeny than wheat products, which could be another advantage of millet in an integrated international system of grain storage. Chemical analysis also showed a significant correlation between the abundance of offspring generation and the content of crude fat (especially linoleic acid—C 18:2). Knowledge of the resistance or susceptibility of millet to storage pests may be useful in implementing integrated principles of protection of stored products against pests.

Flow Confinement Effects on sUAS Rotor Noise

The goal of this paper is to investigate the effects of flow confinement on the noise generated by a small unmanned aerial system rotor measured and simulated in a partially closed test room. More specifically, the influence of the flow recirculation in the test room and the consequent blade turbulence interaction on both the tonal unsteady loading noise and the broadband laminar separation noise components are scrutinized. The study also aims at improving our prediction capabilities of drone rotor noise, and deepening our fundamental knowledge of rotor aeroacoustics in transitional boundary layer regimes. Numerical simulations are conducted by means of a scale-resolving wall-modelled lattice Boltzmann solver to calculate the unsteady flow and the noise generated by the same reference configuration used in our previous works, which consists in a rotor operated at a chord-based Reynolds number of about 70000 at 75% of the tip radius, both in hover and axial flow conditions. Results for a rotor in pristine flow conditions are compared to results obtained by simulating the rotor in a confined environment that reproduces the A-Tunnel test chamber of Delft University of Technology. One one hand, our study reveals that previously observed discrepancies between measured and predicted noise spectra in hover conditions are not due to the influence of the flow confinement on the laminar separation mechanisms, as hypothesized in our previous study, rather to a lack of numerical resolution. On the other hand, the new results reveal that, in hover conditions, the dominant effect of the flow recirculation is to increase the unsteady loading tonal noise components, whereas, in axial flow conditions, no significant effect due to the test environment is observed. Some of our conclusive observations are supported by results obtained using a source identification technique herein presented for the first time.

The reliability of models for converting formaldehyde emissions from wood-based materials to different environmental conditions

The monitoring of the formaldehyde emission potential of wood-based materials by means of test chamber investigations has been established by national and international standards and has made an important contribution to significantly reducing the formaldehyde concentrations indoors. The procedures used are mostly methodologically different, so that the results cannot be directly compared. The first empirical models for converting formaldehyde steady-state concentrations as a function of temperature, air humidity, air change rate and loading were derived in the 1970s. However, the development of lower-emitting materials made it necessary to modify and adapt these models. Formaldehyde emissions from wood-based materials are complex from both a reaction-kinetic and dynamic perspective. There is an exponential dependence of the steady-state concentration on temperature and humidity and an inverse proportionality to the air change rate. The mathematical analysis requires multiple non-linear regression tools. A large data set with reliable results obtained under different conditions is available from previous investigations. With a total of 128 measurement data, there was very good agreement between theory and experiment for a wide range of chamber settings from a statistical point of view. However, the model is not suitable for predicting the emission behavior of individual products. Some uncertainty also exists due to the allowed tolerance limits of the chamber parameters. Since the formaldehyde emission rate depends on the air change rate, a simple linear conversion of steady-state chamber concentrations into room air concentrations for indoor exposure assessments is not possible even at constant temperature and humidity.

Development of a deployable mechanism for a conical optical baffle for a small satellite

Baffles in optical systems on a satellite, such as imaging payloads and star trackers, involve structures with large empty volumes that take up significant payload volume. Limiting the volume of optical systems is essential, considering the demand for small satellite platforms and rideshare launch missions. A baffle structure with empty volume can be configured to stow in a packed configuration during launch and deploy to its operational configuration once the satellite is in orbit. An analytical model for deployable conical baffles is developed to trade off various design parameters. A simple and reliable deployment mechanism with large torsion springs is designed and developed for an optical baffle. A prototype baffle is developed with representative materials, and functional testing is carried out. The deployment tests were carried out to measure the shocks and deployment accuracy. The baffle in its stowed configuration performed satisfactorily and indicated no damages when subjected to vibration testing. Further, the deployment mechanism performed adequately at a low temperature of -40°C and at 0.062 mPa during the cold functional test in a thermovac chamber. The baffle is a precursor to the flight model, which will be launched as a part of a hyperspectral imager, CyanoSat of CSIRO.

Dual-band photoluminescence mechanism of magnetic doped two-dimensional (PEA)2PbBr4 single crystals

Mn2+ doping effectively realizes white light emission in three-dimensional lead halide perovskite nanocrystals. Meanwhile, research on Mn-doped two-dimensional layered perovskite single crystal is limited. We report centimeter-scale Mn-doped PEA2PbBr4 (C6H5CH2CH2NH3+ and PEA+) single crystals prepared by a slow evaporation method. Mn2+ dopants mainly act as substitutional doping and exhibit paramagnetic properties in the crystal at low doping density, while interstitial doping of Mn2+ prevails and induces antiferromagnetic characteristics at high doping density. Mn:PEA2PbBr4 single crystals exhibit dual-band chromacity-tunable blue-orange photoluminescence originating from excitons and Mn2+ emission. The negative temperature quenching effect is achieved by Mn-doping defects for the temperature-dependent exciton photoluminescence. Upon testing in the low-pressure vacuum chamber, the Mn2+ peak of the single crystal shows a dramatic shift from 610 to 690 nm. These results indicate that Mn:PEA2PbBr4 single crystal can serve as a potential and promising luminescent device material that achieves color tunable properties by regulating the systematic changes in the intensity ratio of exciton emission and Mn2+ emission, which will be very helpful for exploring the application of perovskite in magneto-optical devices in the future.

Wind tunnel testing of a Formula Student vehicle for checking CFD simulation trends

The aerodynamic performance analysis of Formula Student racecars has been mostly done by teams with CFD tools, for time and cost savings, that often lack proper validation. To address this, the FST Lisboa team performed a detailed wind tunnel (WT) test campaign, using a one-third scale model, under different configurations, including variable ride heights, bullhorn appendix, and rear wing flap settings, also replicated in CFD. The simulations used RANS with the SST k-omega turbulence model, with a 13.7 million polyhedral mesh for the test chamber region domain. Both experimental and numerical errors were estimated from the instrumentation and mesh convergence analysis, respectively. Comparisons were made between WT and CFD both in terms of local flow, using tufts for flow visualization, and global flow, using lift, drag, and pitching moment coefficients. Overall, the numerical streamlines agreed very well with the orientations of the tufts in experiments, but some discrepancies were found in regions of cross-flow and high-frequency unsteadiness, mainly caused by limitations of the visualization technique. The gamma transition model in CFD was abandoned as it could not replicate the WT observations. In terms of aerodynamic coefficients, a strong correlation was found between WT and CFD. The parametric studies revealed that the simulations captured the experimental sensitivity to each car setting parameter studied but the uncertainties did not enable a full quantitative evaluation of the aerodynamic performance. The drag reduction system significantly impacted the aerodynamic balance of the racecar, while the current bullhorn design proved to be ineffective. The ride height increase led to higher downforce, mostly due to the higher pitch angle of the vehicle, with negligible variation of the aerodynamic balance. This work validated the team CFD studies, building confidence in that trends estimated in numerical parametric studies are likely to be translated to the real prototype performance.

Kinetic simulation of ion thruster plume neutralization in a vacuum chamber

The electrical environment of a ground vacuum testing chamber creates facility effects for gridded ion thrusters. For example, it is well known that the plume from the thruster generates current paths that are very different from what occurs in space, and the neutralization of this plume is also different. For reasons such as this, it is important to clarify how the experimental testing environment affects plasma flows, but understanding this effect solely through ground experiments is difficult. To that end, this study utilizes particle-in-cell and direct simulation Monte Carlo methods to simulate xenon beam ions and electrons emitted from a neutralizer. First, we compare simulations conducted within the chamber to those conducted in space, demonstrating that grounded chamber walls increase the electric potential and electron temperature. Next, we investigate the impact of the neutralizer’s position and the background pressure on the plume in the vacuum chamber. We find that as the neutralizer position moves closer to the location of maximum potential, more electrons are extracted, resulting in increased neutralization of the plume. We also observe that high background pressure generates slow charge-exchange ions, creating ion sheaths on the side walls that alter ion current paths. Finally, we discuss how the potential at the thruster and neutralizer exits affects the plume. The relative potential of the neutralizer to the vacuum chamber wall is observed to significantly influence the behavior of the electrons, thereby altering the degree of plume neutralization. These findings are shown to be consistent with experimental results in the literature and demonstrate the promise of high-performance simulation.

Experimental development and evaluation of a fiber bragg grating-based outside air temperature sensor for aircraft applications

This study presents the development and rigorous evaluation of a Fiber Bragg Grating (FBG)-based Outside Air Temperature (OAT) sensor designed for aircraft applications. Employing a Design of Experiments (DoE) approach, the research optimized the sensor's performance for reliability, accuracy, and durability in aviation environments. Experimental assessment covered detailed installation of the FBG sensor on an aircraft, considering influential parameters such as outside dimensions and varying temperature. The OAT sensor's design focused on robustness and precision for accurate real-time temperature recording, vital for operational efficiency and safety. Extensive statistical analysis assessed the sensor's performance under differing conditions, providing valuable insights into operational capabilities and overall efficacy. Thermo-climatic chamber tests simulated extreme environmental conditions to validate the sensor's durability and function under potential aircraft operational scenarios. This research enhances understanding of FBG-based OAT sensors for aircraft applications, demonstrating their superior robustness and performance capabilities, thereby contributing to aviation safety, operational efficiency, and data precision.© 2017 Elsevier Inc. All rights reserved.

Optimization of electrical resistivity survey utilizing modified harmony search algorithm to predict anomalous zone ahead of tunnel faces

Predicting anomalies ahead of a tunnel face is essential to ensure construction safety and efficiency during tunneling. This study proposes an optimization system to estimate the characteristics of anomalies ahead of a tunnel face. The developed system can estimate the location, the thickness and the electrical resistivity of the anomaly using inverse analysis based on the modified harmony search algorithm with resistivity measurement. To verify the efficacy of the developed system, laboratory chamber tests were conducted by simulating ground formations with faults. The experimental results indicated that the developed system had substantial prediction performance with a short data analysis time. Notably, the location of an anomaly was relatively well predicted compared to the other properties, which is crucial information that can prevent potential risks. Therefore, the system could predict anomaly characteristics and enable the appropriate management of potential risks.

Multi-disciplinary optimization of hybrid composite radomes for enhanced performance

The focus of this research is to develop a specialized multidisciplinary design optimization framework for composite sandwich-structured radomes. Radomes play a crucial role in safeguarding antenna systems from challenging environmental conditions. However, they can adversely impact the electromagnetic performance of the antenna. Unlike traditional approaches that separately address electromagnetic performance and mechanical responses, our framework considers both aspects concurrently, resulting in a more efficient process. The main objectives of the optimization are to enhance electromagnetic performance while also accounting for deformations, material integrity, and structural stability. To evaluate the electromagnetic performance, a 3-dimensional numerical simulation is employed to analyze parameters such as electromagnetic transmission loss, bore sight error, and side lobe characteristics. The model's accuracy is verified through experimental testing in an anechoic chamber, utilizing a hybrid sandwich structure. The results indicate minimal attenuation, with an average loss of only 1.5 % in the transmission of antenna signals, using the proposed radome thickness. Furthermore, the configuration of the material provides structural stability, ensuring a factor of safety of 2.5 while satisfying operational constraints. Hence, the proposed multidisciplinary optimization model represents an efficient and feasible approach to radome design. This advancement in the field equips engineers and researchers with a valuable tool to develop dependable and effective radome systems.

Effect of Graphene Nanoplatelets on Flexural Behavior of Glass Fiber Reinforced Polymer Composites Subjected to Different Temperatures

Glass Fiber Reinforced Polymer (GFRP) Composite are increasing rapidly in Aerospace Industry, Civil and Wind energy sectors, where they can frequently be exposed to different temperature conditions. As the constituent polymer matrix is highly affected by temperature, extreme temperature conditions are critical for GFRP composite structural design. Researchers have recently found nanofillers such as graphene and carbon nanotubes with excellent multifunctional mechanical properties. Graphene Nanoplatelets (GnP) consist of several layers of graphene. GnP is considering an attractive nanofillers as it has improved polymer matrix properties. In this study, the weight percentage of GnP added in GnP-GFRP laminate is 0.25% and 0.5%.GFRP and GnP-GFRP laminates are fabricated by using the hand lay-up method, and the specimens are subjected to a three-point bending test in a thermal chamber with varying the temperature, i.e., 30°C, 50°C, 75°C, and 100°C. This paper investigates the effect of graphene nanoplatelets on the flexural behavior of glass fiber-reinforced polymer composites subjected to different temperatures. Flexural strength and modulus are evaluated, and the appropriate conclusions are determined. GFRP with 0.25% GnP shows higher strength than the neat and 0.5% GnP-GFRP. Here, it has also been shown that flexural strength and modulus decrease significantly with increasing temperature.

Fabrication of Superhydrophobic Coatings by Using Spraying and Analysis of Their Anti-Icing Properties

Ice accumulation on glass insulators is likely to cause faults such as flashover, tripping and power failure, which interfere with the normal operation of the power grid. Accordingly, superhydrophobic coatings with great anti-icing potential have received much attention. In this study, three superhydrophobic coatings (PTFE, Al2O3 and SiO2) were successfully prepared on glass surfaces by using one-step spraying. The microscopic morphology, wettability, anti-icing and anti-glaze icing properties of the superhydrophobic coatings were comparatively analyzed. The results indicated that the PTFE coating had a densely distributed rough structure, showing a contact angle of 165.5° and a sliding angle of 3.1°. The water droplets on the surface could rebound five times. Compared with the Al2O3 and SiO2 coatings, the anti-icing performance of the PTFE coating was significantly improved. The freezing time was far more than 16 times that of glass (4898.7 s), and the ice adhesion strength was 9 times lower than that of glass (27.5 kPa). The glaze icing test in the artificial climate chamber showed that the icing weight of the PTFE coating was 1.38 g, which was about 32% lower than that of the glass. In addition, the icing/melting and abrasion cycles destroyed the low-surface-energy substances and nanostructures on the surface, leading to the degradation of the anti-icing durability of the PTFE coatings. However, the PTFE coating still maintained excellent hydrophobicity and anti-icing properties after UV irradiation for up to 624 h. The superhydrophobic coatings prepared in this work have promising development prospects and offer experimental guidance for the application of anti-icing coatings on glass insulators.

Вплив шорсткості поверхні камери енергетичної установки на низькочас-тотні автоколивання холодного робочого газу

Dynamic processes in the combustion chamber have a significant effect on the characteristics of the working processes of solid-propellant rocket engines (LPREs). Pressure jumps and a sharp increase in the local temperature of the combustion products in non-stationary engine operation modes can lead to overrating values of operating parameters and a failure of the LPRE combustion chamber structure. The dynamic processes in the LPRE combustion chamber develop in a complex interconnection of a large number of physical and chemical processes that occur in the gas-dynamic part of the working space of the engine chamber and often lead to self-oscillating modes of engine operation. This is evidenced by numerous data on LPRE fire tests. This paper presents the results of a numerical study of the effect of the LPRE chamber inner surface roughness on LPRE operating parameter low-frequency self-oscillations. The study was made using up-to-date computer simulation means and analysis. Low-frequency (up to 1,000 Hz) oscillations in an LPRE combustion chamber were studied for a power plant test chamber in cold operation with the use of two different approaches to numerical modeling of the dynamics of in-chamber processes: the development and study of a 3D model of the dynamic system of combustion chamber structure – combustion products using the finite element method and the development and study of an axisymmetric 2D model of engine chamber gas flow using the finite volume method. The study revealed a self-oscillatory flow regime caused by combustion product vorticity and acoustic feedback due to vortices colliding with the chamber components or the LPRE nozzle. It was shown that accounting for the wall roughness increased gas vorticity in the gas–solid dynamic interaction zone and the chamber gas oscillation amplitude (on the average, by a factor of 2.5 at a maximum wall roughness height of 56 ?m). The calculated gas flow pattern in the vorticity zones of the chamber and the low-frequency gas pressure oscillation parameters are in qualitative agreement with the experimental ones.

Reliability Evaluation of Environmental Test Chambers Based on Bayesian Network

Reliability Evaluation of Environmental Test Chambers Based on Bayesian Network

Social play exclusion model in adolescent rats: Monitoring locomotor and emotional behavior associated with social play and examining c-Fos expression in the brain

The exclusion of social play within an adolescent group interferes with learning and the acquisition of essential social behavior during development and can cause modulations in the social brain areas. However, despite the importance of social play in adolescence, an in-depth explanation of its physiological mechanisms is limited because of the lack of experimental animal models that embody social play exclusion in human society. To determine the mechanism of social play in adolescence, we identified differences in emotional behavior and brain activity in animal models of social play exclusion that mimicked human society. Emotional changes in the social play exclusion and non-exclusion groups were examined by tracking social play-related social interaction behavior, social play-related space preference, social play-related locomotor behavior, and anxiety-like behavior using a behavioral data analysis program. Differences in brain activity among groups were identified using immunohistochemical staining. During the social play exclusion model, the rats preferred the partition zone to the other areas in the test chamber. The exclusion group preferred the partition and the center zone over the non-exclusion group. When comparing before and after the social play exclusion, the exclusion group showed a decrease in mobility and an increase in anxiety-like behavior compared to the non-exclusion group. We found that c-Fos expression in the dentate gyrus (DG) of the exclusion group was lower than that in the non-exclusion group, whereas c-Fos expression in the lateral habenula (LHb) of the exclusion group was higher than that in the non-exclusion group. Taken together, in adolescence, exclusion from social play with peers can increase anxiety-like behavior in the exclusion group and change the neuronal activity of the DG and LHb, suggesting that exclusion from social play is linked to modifications in the DG and LHb, which are regions associated with mood regulation.