Heat Flux Gauges Research Articles

Mars Entry, Descent, and Landing Instrumentation 2 Trajectory, Aerodynamics, and Atmosphere Reconstruction

On February 18th, 2021, the Mars 2020 entry system successfully delivered the Perseverance rover to the surface of Mars at Jezero Crater. The entry capsule carried a set of instrumentation installed on the heat shield and backshell, named the “Mars Entry, Descent, and Landing Instrumentation 2.” The instruments include pressure transducers, thermocouples, heat flux gauges, and radiometers to measure the aerodynamic and aerothermodynamic performance of the entry vehicle. This paper describes the trajectory and atmosphere reconstruction results based on the pressure sensor measurements. The process uses a Kalman filter approach to estimate the freestream atmospheric properties from the pressure measurements combined with a model of the pressure distribution of the heatshield and other sensor inputs, including an inertial measurement unit and other on-board navigation sensors, and several external atmospheric observations. The results indicate that the upper altitude density was up to 150% higher than nominal, which is consistent with the observed early entry guidance start time. The density below 40 km was within 12% of the preflight predictions. The reconstructed axial force coefficient was approximately 2% lower than the preflight prediction across the flight range.

Characterizing Flow Instabilities During Transient Events in the Turbine Rim Seal Cavity

Abstract Gas turbine engine design requires considerations not only for long-term steady operation but also for critical transient events. Aircraft engines undergo significant stress during takeoff and landing, while power generation turbines must be flexible for hot restarts as renewable energy sources come online and offline. During these transient cycles, engines sustain wear and degradation that can lead to a reduction in the lifespan of their components and more frequent, costly maintenance. Cooling flows are often used to mitigate these effects, but can lead to complex and problematic flow interactions. This study uses high-frequency response pressure probes and heat flux gauges in the rim seal cavity of a one-stage research turbine to characterize the properties of large-scale flow structures during transient operation. A continuous-duration turbine testing facility provides the ability to assess the importance of these transients by first reaching steady-state operation before imposing transient behaviors. Although previous studies have conducted similar measurements for steady purge flows and wheel speeds, varying these parameters to simulate transient effects revealed several unique phenomena not identifiable with discrete steady measurements. The measurement approach connects the varied transient parameter to the behavior of the flow structures to enable a better understanding of the type of instability observed and the root cause of its formation. In particular, a relationship between instability cell formation and rim sealing effectiveness was identified using experimental data and was supported through computational simulations.

Theoretical and Experimental Analysis of Flight-to-Ground Scaling for Axisymmetric and Planar Bodies

This paper proposes a methodology to scale the stagnation point plasma conditions of an axially symmetric body to a two-dimensional planar body. The method is required to correlate material samples tested under thermochemical loads combined with aeromechanical loads in order to relate the measurements to actual flight scenarios. The equations governing the boundary-layer and heat transfer equations are introduced and analyzed using the commonly known local heat transfer simulation concept. This technique is then adapted to the given constraints and results in a two-step flight-to-ground scaling approach. Flight conditions are first transformed to axisymmetric ground testing equivalents before being scaled to planar bodies. Thereby, the mass-specific enthalpy, total pressure, and Stanton number stay constant; and the velocity gradient doubles when scaling from axisymmetric to planar. Formulations for the velocity gradient are analyzed for both the sub- and supersonic cases. The results are compared between a theoretical approach and plasma wind-tunnel tests. Three heat flux gauges were tested at two conditions. The planar sensors were evaluated with two independent methods, and the results were scaled to a comparable condition. The results compare very well with the theoretically calculated values. The axisymmetric to planar conversion theory detailed in this paper is therefore considered experimentally verified.

Indirect inverse flux mapping of a concentrated solar source using infrared imaging.

With the growing interest in high-flux solar sources, a need exists for simple, accurate, and inexpensive strategies to characterize their output radiative flux. In this paper, the irradiation output from a 10 kWe xenon lamp solar simulator is characterized by an inverse mapping technique that uses a custom radiometer and infrared camera, validated by a direct characterization method (heat flux gauge). The heat flux distribution is determined in a vacuum chamber using an easily obtainable graphite target and an inverse heat transfer model. The solar simulator produces peak fluxes in the range of 1.5-4.5 MW/m2 as measured directly by a heat flux gauge, and its output can be controlled using a variable power supply. Spectral measurements indicate that minor variations in the simulator's output with respect to its current supply occur in the spectral range of 450-800nm. The radiometer presented in this work allows for characterizing solar irradiation under practical conditions (e.g., inside a solar reactor) and thus accounts for deviations due to additional components, such as viewport effects. Additionally, it provides an inexpensive and efficient means of monitoring any deterioration in the performance of solar sources over time without the need for complex recalibration.

Magnetohydrodynamic Experiments of Total Heat Flux Mitigation for Superorbital Earth Reentry

A set of experiments was conducted with the aim of evaluating total heat flux mitigation using magnetohydrodynamic flow control over ionized shock layers surrounding planetary entry vehicles. The University of Queensland’s X2 expansion tube was used to generate a flow condition representative of a Mars return trajectory. Spherical permanent magnets were fitted into a scaled test model based on NASA’s Stardust capsule. Thermocouples located at the stagnation point and shoulder of the test model, as well as thin-film heat transfer gauges located in the aft section, measured total heat flux for both magnetic and nonmagnetic experiments. High-speed imaging of the shock layer showed a significant increase in shock standoff when using the magnet, and polynomial fits were derived, describing standoff distance along the model’s forebody. Despite significant noise affecting the heat flux gauges signals for the magnetic experiments, a simple methodology allowed to compare heat flux during the useful test time. It was found that the applied magnetic field significantly reduces total heat flux at the stagnation point and shoulder of the test model, although heat flux to the aft section was found to significantly increase. Reasonable agreement with the numerical predictions was found for the aft section of the test model, but discrepancies were observed at the other locations.

Development of thin film heat flux sensor based on transparent conductive oxide thermopile with antireflective coating

PurposeThe measurement of heat flux is of importance to the development of aerospace engine as basic physical quantities in extreme environment. Heat radiation is one of the basic forms of heat transfer phenomenon. The structure optimizing can improve the performance and infrared absorptivity of the thin film sensor.Design/methodology/approachThis paper designed one kind of thin film heat flux sensor (HFS) with antireflective coating based on transparent conductive oxide thermopile. The introduced membrane structure is so thin that it has little impact on sensor performance. Fabrication of thin film sensors were fabricated by physical vapor deposition (PVD) process.FindingsThe steady-state and dynamic response characteristics of the HFS were investigated by calibration platform. The experimental results shown that the absorptivity of the membrane structure (for1070nm) improved compared with that before optimization. The sensitivity of heat flux gauge was 48.56 µV/ (kW/m2) and its frequency response was determined to be about 1980 Hz.Originality/valueThe thin film HFS uses thermopile based on Indium Tin Oxid and In2O3. The antireflective coating is introduced to hot endpoint of HFS to improve sensitivity on laser thermal source. The infrared optical properties of membrane layer structure were investigated. The steady-state and the transient response characteristics of the heat flux sensor were also investigated.

Optical alignment and radiative flux characterization of a multi-source high-flux solar simulator

High-flux solar simulators are research-grade sources of artificial radiation mimicking optical characteristics of concentrating solar systems. They allow for experimental evaluation of high-temperature solar thermal devices and materials under controlled and reproducible conditions. In this study, we demonstrate the application of close-range photogrammetry in tandem with radiometry to optically align radiation modules of a multi-source high-flux solar simulator and to characterize its radiative output. The photogrammetric setup consists of photogrammetry targets, a digital camera and photogrammetry software. The radiometric measurements are conducted using mobile Lambertian targets, a heat flux gauge, and a complementary metal-oxide semi-conductor camera equipped with neutral density filters. An iterative procedure for adjusting lamp positions allows obtaining optical configurations of radiative modules meeting experimental requirements of high and ultra-high temperature solar thermal and thermochemical research. Close-range photogrammetry is demonstrated to be a convenient and effective method to obtain the as-built geometric configuration of the solar simulator setup. We report characteristics of an example radiative module configuration for a subset of six radiation modules. The peak and mean radiative fluxes over a 60-mm diameter flat target located in the focal plane are 3080kWm−2 and 1135kWm−2, respectively. The mean aiming error, defined as the average distance between theoretical and actual aiming points in the focal plane, is reduced from 37.20mm to 4.50mm for the pre- and post-alignment configurations, respectively.

High-Sensitive Thin Film Heat Flux Gauge With ITO/In2O3 Thermopile on Nickel Alloys for Turbine Blade Applications

Heat flux is key parameter for evaluating the heat dissipation of turbine blade. The accurate measurement of heat flux is vital for the optimizing cooling system and fabrication of turbine blade. The thin film heat flux gauge is usually fabricated on insulated substrate and located away from the measured area of turbine blade. As a result, the changes of heat flux on the surface of turbine blade cannot be reflected quickly and accurately. This paper innovatively designs membrane structure of thin film heat flux gauge on nickel alloys. The sensor is fabricated on the surface of the nickel alloys by thin-film depositing technology to realize in-situ surface heat flux measurement, and ITO/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thermopile is used to replace precious thermopile to improve sensitivity. The results show that the sensitivity and response frequency of the sensor respectively are measured to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$61.93~\mu \text{V}$ </tex-math></inline-formula> /(kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and over 14400Hz respectively, which can measure heat flux of 236.4kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$888^\circ \text{C}$ </tex-math></inline-formula> . Besides, the thin film heat flux gauge is fabricated on the surface of turbine blade to verify functional feasibility with same preparation process of that on nickel alloys, and can obtain reproducible results. This work suggest that the thin film sensor based on ITO/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thermopile has great potential in applications used as optimizing cooling system of components in aeronautics and astronautics.

Flame attachment and downstream heating effect of inclined line fires

Experiments were conducted to quantify downstream heating from inclined fires generated by a 25 cm wide, 5 cm deep gaseous line burner. A variety of orientation angles (θ) and fire heat-release rates (HRR) were employed simulating, at reduced scale, the dynamics of two-dimensional (2-D) inclined flame spread as found in wildland or building fires. The total heat flux q˙f″(x) to a nearly-adiabatic surface ahead of the burner was measured by a water-cooled total heat flux gage at different downstream locations (x). It was found that, with an increase in fire HRR or θ, q˙f″(x) increases. The same is true for both the flame projection length on the inclined surface (Lf,p) and the flame attachment length (La). The location of flame attachment divides a flame into an attachment region (0≤x≤La) and a liftoff region (La<x≤Lf,p). A scaling analysis was performed to correlate the modified non-dimensional heat flux q˙f*(x) and the normalized downstream distance x/La in these two regions as a piecewise power-law function. Lf,p is scaled by a non-dimensional HRR, Q˙θ*=Q˙/(ρ∞cpT∞(gcosθ)1/2D3/2L), together with the angle between a flame and an inclined surface (α). La is well represented by two derived non-dimensional quantities, L/Lf,0 and Lf,p/Lf,0 (Lf,0 is free flame height), based on the analysis of the balance between the buoyancy force of a flame (upward) and the inertial force due to air entrainment (horizontal). The quantitative comparison with previous flame spread tests over inclined PMMA samples demonstrates the effectiveness of the proposed correlations in predicting downstream heating of 2-D flame spread over inclined terrains.

Development of coated heat flux gauges for fast responding measurements

Thermal systems often exhibit transient behaviors that have important implications for the operation of the system and can be difficult to predict. For these reasons, experimental testing is often required to ensure system durability requirements are achieved. One important parameter governing the survivability of components in hot, high-stress environments is the heat flux into the part that dictates the temperature distribution for the component. However, sensors required to experimentally characterize heat fluxes in extreme environments must also be resilient. This study presents the development of coated heat transfer gauges capable of robust, high-frequency measurements in turbine research facilities. The addition of a protective coating increases the durability of the gauge, but inherent of that coating is the attenuation of high-frequency temperature penetrations. As a result, this study first outlines the use of analytical solutions to define a gauge design for a specific frequency range and heat transfer, ensuring that subsurface signals can be rectified to surface conditions through inverse methods. Then, the fabrication of polyimide substrate sensors with a parylene-F coating is described. Micro surface heaters added to the custom sensors were used to determine important geometric and thermal properties necessary to calculate accurate surface heat flux. Ultimately, this work shows increased sensor robustness in a turbine test bed and experimentally validates that the frequency response of the fabricated sensors meet the design intent.

Unsteady phenomena at the combustor-turbine interface

The combustor-turbine interface in a gas turbine is characterised by complex, highly unsteady flows. In a combined experimental and large eddy simulation (LES) study including realistic combustor geometry, the standard model of secondary flows in the nozzle guide vanes (NGV) is found to be oversimplified. A swirl core is created in the combustion chamber which convects into the first vane passages. Four main consequences of this are identified: variation in vane loading; unsteady heat transfer on vane surfaces; unsteadiness at the leading edge horseshoe vortex, and variation in the position of the passage vortex. These phenomena occur at relatively low frequencies, from 50–300 Hz. It seems likely that these unsteady phenomena result in non-optimal film cooling, and that by reducing unsteadiness designs with greater cooling efficiency could be achieved. Measurements were performed in a high speed test facility modelling a large industrial gas turbine with can combustors, including nozzle guide vanes and combustion chambers. Vane surfaces and endwalls of a nozzle guide vane were instrumented with 384 high speed thin film heat flux gauges, to measure unsteady heat transfer. The high resolution of measurements was such to allow direct visualisation in time of large scale turbulent structures over the endwalls and vane surfaces. A matching LES simulation was carried out in a domain matching experimental conditions including upstream swirl generators and transition duct. Data reduction allowed time-varying LES data to be recorded for several cycles of the unsteady phenomena observed. The combination of LES and experimental data allows physical explanation and visualisation of flow events.

Application of 3-omega method for thin-film heat flux gauge calibration

Double-sided thin-film resistance temperature detector (RTD) heat flux gauges (HFGs) are commonly used to characterize heat transfer rates in high-heat flux environments with complex flow features. These gauges comprise two thin-film RTDs on opposing sides of a dielectric. To deduce accurate heat flux, the RTDs must be properly calibrated and the material properties of the dielectric must be characterized. This study presents a complete gauge characterization method for sensors of this type by applying standard calibration procedures with specially-designed RTDs capable of utilizing the 3-omega method. The 3-omega method quantifies the thermal conductivity and thermal product of a material by measuring the response of a specially designed heater/thermometer deposited on the substrate. This study shows the 3-omega method enables RTD calibrations and thermal property determination over a range of temperatures for individual gauges, reducing the uncertainty in calculated heat flux. Although the method is quite general, this study utilized platinum RTDs with a polyimide dielectric, which is common in turbomachinery applications. The thermal properties obtained through this method agree with previous characterization efforts; however, discrete characterization of seven gauges shows that gauge-to-gauge variation in the dielectric could influence measured heat flux by as much as 30%. This study also builds the framework to characterize the thermal conductivity of the adhesive layer beneath the gauge which is necessary to mount the sensors to the test article. Although often uncharacterized, the adhesive thermal conductivity has a significant impact on matching experimental measurements to simulations. Additionally, this study found that if the thermal conductivity of the dielectric is constant (an assumption that holds for the present study), an in-situ RTD calibration can be performed. In-situ RTD calibration and traditional method RTD calibration agreed to within 0.1%. Overall, this work has practical implications in obtaining high quality measurements from HFGs of this type.

PHANTOM COOLING EFFECTS ON ROTOR BLADE SURFACE HEAT FLUX IN A TRANSONIC FULL SCALE 1+1/2 STAGE ROTATING TURBINE

Abstract An experimental and numerical investigation of phantom cooling effects on cooled and uncooled rotating high pressure turbine blades in a full scale 1+1/2 stage turbine test is carried out. Objectives set to capture, separate, and quantify the effects of upstream vane film-cooling and leakage flows on the downstream rotor blade surface heat flux. Multiple series of tests were carried out in the Air Force Research Laboratory, Turbine Research Facility, at Wright-Patterson Air Force Base, Ohio. A non-proprietary research turbine test article is uniquely instrumented with high frequency double-sided thin film heat flux gauges custom made at AFRL. High bandwidth, time resolved surface heat flux is measured on multiple film-cooled and non-film-cooled HPT rotor blades downstream of both film-cooled and non-film-cooled vane sectors. Upstream wake passing and heat flux is characterized on both rotor pressure and suction side surfaces, along with quantifying rotor phantom cooling effects from non-uniform 1st stage vane film cooling and leakage flows. Fast response heat flux measurements quantify how rotor phantom cooling impacts the blade pressure side greatest; increasing along the pressure side towards the trailing edge. It is discovered upstream vane film-cooling alone can account for 50% of the rotor blade cooling effect, and even outweigh the rotor blade film cooling effect far from the blade showerhead holes. Added unsteady numerical simulation demonstrates how variations in inlet total temperature and incidence angle can also contribute to circumferentially non-uniform rotor heat flux.

Fast-Response transient heat flux measurements in a plasma wind tunnel

A fast response heat transfer gauge has been developed to measure the radial distribution and the fluctuations of heat flux in a supersonic arcjet plasma wind tunnel. The heat flux gauge consists of 3.2 mm diameter coaxial surface junction thermocouple which was positioned behind a thin layer of PTFE and mounted in a ESA standard 50 mm diameter flat faced copper probe head. A non-dimensional impulse response for the heat flux gauge was identified using pulsed optical power deposition from a laser. The impulse response was used in combination with reference measurements from a calorimeter at a single location to determine the distribution and fluctuations in heat flux. Eight traverses of the PWK4 jet at the University of Stuttgart confirmed a symmetric Gaussian-like heat flux distribution with a centreline heat flux consistent to within ±6%. These distributions were measured in less than one second, representing a significant gain in productivity when compared to calorimeter-based heat flux measurements where probes must be held stationary at a number of locations in order to resolve spatial distributions. At this particular PWK4 operating condition, which had a flow stagnation enthalpy of approximately 15 MJkg−1, heat flux fluctuations of up to ± 140 kWm-2 (corresponding to a relative variation of 15% of the centreline heat flux) were identified near the vicinity of the nozzle centreline for frequencies from 4 Hz to 1 kHz.

Design and Testing of a Rig to Investigate Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

Abstract The change in compressor blade-tip clearance across the flight cycle depends on the expansion of the rotor, which in turn depends on the temperature and stress in the disks. The radial distribution of temperature is directly coupled to the buoyancy-driven flow and heat transfer in the rotating disk cavities. This paper describes a new test rig specifically designed to investigate this conjugate phenomenon. The rig test section includes four rotating disks enclosing three cavities. Two disks in the central cavity are instrumented with thermocouples to provide the radial distribution of temperature; the two outer cavities are thermally insulated to create appropriate boundary conditions for the heat transfer analysis. An axial throughflow of air is supplied between a stationary shaft and the bore of the disks. The temperature of the throughflow air is measured by thermocouples in rakes upstream and downstream of the central cavity. For a cold throughflow, the outer shroud of the central cavity is heated. Two independently controlled radiant heaters allow differential shroud temperatures for the upstream and downstream disks, as found in aero-engine compressors. Alternatively, the throughflow can be heated above the shroud temperature to simulate the transient conditions during engine operation where stratified flow can occur inside the cavity. The rig is designed to operate in conditions where both convective and radiative heat transfer dominate; all internal surfaces of the cavity are painted matt black to allow the accurate calculation of the radiant heat transfer. Separate attachments can be fitted to the cobs of both central disks; the attachments reduce the axial gap between the cobs—reducing the gap to zero creates a closed cavity, which can occur in some compressor designs. Other instrumentation includes heat-flux gages on the shroud and high-frequency pressure transducers embedded into the disk diaphragm to capture unsteady flow structures. Attention has been given to experimental uncertainty, including the computation of the thermal-disturbance errors, caused by thermocouples embedded in the rotating disks; a Bayesian statistical model is used to reduce the effect of uncertainties in temperature measurements on the calculation of the Nusselt number. The effect of relevant nondimensional parameters on the radial distribution of the disk and throughflow temperatures has been shown for some typical cases.

The influence of spatial arrangement of endpoints on output characteristics of ITO/In2O3 heat flux gauge

Thermopile is a common test structure, in which the distribution of hot and cold endpoints has a high impact on its performance especially for applications in thin-film heat flux gauge. In this work, the influence of spatial distribution of endpoints is investigated on the output characteristics of the thin film heat flux gauge based on ITO/In2O3 thermopile. Three different structures of the heat flux gauges, which are horizontal, vertical and stepped, are designed and fabricated via sputtering according to different spatial arrangement of endpoints. The results show that the heat flux gauges based on vertical distributed structures have higher sensitivities than the gauges based on the other two structures on a convection heat source calibration platform. The output sensitivities of the gauges based on stepped distributed structure is the highest on laser radiation calibration platform, which reach 74.9 μV/(kW/m2). The thin-film heat flux gauge based on horizontal distribution structure has the best dynamic characteristic on a laser heat source calibration system. The operating temperature of the gauge is close to 800 °C, and the dynamic frequency reaches 5.2 kHz.

Calibration of thermopile heat flux gauges using a physically-based equation

A thermopile, in which a number of thermocouple junctions are arranged on either side of a thin layer of insulation, is commonly used to determine the heat flux for steady-state measurements. Gauges using this method are available commercially and a new, generic calibration method is described here. For this purpose, an equation based on physical properties has been derived to determine the theoretical relationship between the measured voltage output of the gauge and the heat flux through it. An experimental rig has been built and used to calibrate gauges under steady-state conditions for heat fluxes between 0.5 and 8 kW/m2. The gauge temperature was controlled between 30 and 110 °C, and voltage-flux correlation – based on the theoretical relationship – was determined using maximum likelihood estimation (MLE). For tests with constant gauge temperature, there was a linear relationship between the voltage and heat flux; owing to the temperature dependency of the Seebeck constants of the thermoelectric materials, the voltage increased with increasing gauge temperature. In all cases, there was very good agreement between the measured and correlated values, and the overall uncertainty of the correlation was estimated to be less than 5% of the measured heat flux.

Numerical modelling of thin film gauge for short duration thermal measurement

Abstract The numerical study of direct heat conduction through thin film heat flux gauge is carried out to see how closely it resembles with short duration experimental thermal data. The thermal data obtained from transient impulse facilities at Von Karman Institute, Belgium (case1) and Oxford University (case2) is taken from literature as a reference for validation purpose. The numerically simulated temperature data is compared with experimental data. A good agreement is observed. Further, heat flux is recovered from temperature data using the cubic spline technique for comparative study. The peak deviation from experimental heat flux data for case 1 and 2 is found to be 6% and 7.2% respectively. All these deviations are in the acceptable range of 8%. This deviation is also accounted by the fact that direct heat condition modelling is used instead of numerical modelling of impulse facilities. Thus, direct heat conduction modelling is acceptable approach to predict the transient thermal data with admissible errors.

Laminated Ag and Ag/CNT nanocomposite films as sensing element for efficient thin film temperature sensors

Thin film sensor (TFS) is one of the most promising candidates for instantaneous temperature measurements owing to their extremely small response time (~milliseconds) aided with fair accuracy. Since they are capable of making quick and precise temperature measurements, they can be also used as heat flux gauges to measure surface heat fluxes in dynamic environments like high speed aerospace applications, gas turbine blades etc. Usual TFS are made by depositing a thin metallic film over insulating substrate. In this work we developed an Ag-Carbon nanotube (CNT) nanocomposite film as the sensing element of a TFS and compare it with pure Ag TFS, both having Macor as substrate. Static calibration established a better temperature coefficient of resistance (TCR) value i.e. better sensitivity, for the nanocomposite TFS. X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX) studies are done to probe behind the increase in sensitivity of the nanocomposite TFS compared to its conventional metallic counterpart.

Experimental analysis and modeling of Buoyancy-driven flame spread on cast poly(methyl methacrylate) in corner configuration

A new experimental setup was developed to study turbulent, buoyancy-driven flame spread on a corner wall. Two 146 × 50 × 0.58 cm panels of cast black poly(methyl methacrylate) (PMMA), whose pyrolysis properties were fully characterized in a separate study, were ignited using a triangular propane burner. The corner wall assembly was placed into a well-ventilated enclosure and heat release rate (HRR) and flame heat flux to the corner wall were measured in 7 repeated experiments. The HRR measurement was designed to achieve a fast response time (13 s) and was correlated with the flame heat flux, which was obtained using water-cooled heat flux gauges positioned in 28 locations distributed over the PMMA surface. Simultaneously, a monochromatic, 900 nm, video of the spreading flame was recorded and analyzed to determine the evolution of soot radiation intensity and flame geometry. Using collected data, an empirical model relating spatially resolved heat feedback from the flame to the solid fuel surface and HRR was developed and integrated with a detailed pyrolysis model. Simulations were conducted in an uncoupled and coupled mode. The uncoupled simulations, where the flame heat feedback was effectively prescribed to match the experimental measurements, revealed the importance of the knowledge of the split between the convective and radiative portions of the flame heat flux. The coupled simulations, where the flame heat feedback was computed from the simulated HRR, revealed that the coupling amplifies even relatively small uncertainties in the model parameters to produce large errors in the HRR predictions.