Flame Heat Research Articles

调修温度对6005A铝合金焊接接头组织及性能的影响

调修温度对6005A铝合金焊接接头组织及性能的影响

Pengaruh Kuat Arus Dan Besar Sudut Kampuh Terhadap Kekuatan Impact Dan Nilai Kekerasan Plat Baja Karbon Rendah Dengan Menggunakan Las SMAW

Abstract: Welding is welding that utilizes flame heat in electric arcs to melt electrodes and workpieces. SMAW welding is widely used because of its relatively easy to use, cost-friendly and maximum quality results. In conducting welding has several factors that will affect the quality of the welding results such as a welder, welding current and metal distance and welding seam angle. This study aims to determine whether there is an influence of current variations and magnitude of the seam angle to the value of the impact strength and the hardness value of the SMAW welding results. This study uses a pre-experimental method with a one-shot case model. The results of this study indicate the highest impact strength values of current variations in the 80 Ampere specimen at the angle of seam V 60o in the amount of 0.0799 J / mm2 and in the 80 Ampere specimen in the angle of the 80o V in the seam angle of 0.0942 J / mm2. Then for the highest impact strength value variation of seam angle V group of seam angle specimen V 80o current 80 Amperes is equal to 0.0942 J / mm2 and specimen angle of seam V 80o current 100 Ampere 0.0824 J / mm2. The highest hardness value is obtained with a variation of the current specimen group of 100 Ampere in the angle of seam V 60o that is equal to 187.1 HVN and in the specimen group 100 Ampere with the angle of contact V 80o that is equal to 204.4 HVN. Then the highest hardness value variation angle seam V specimen V 80o with current 80 Amperes is equal to 191.63 HVN and specimen angle of seam V 80o with 100 amperes current that is equal to 204.4 HVN. KeyWords : SMAW, Welding current, V groove, Impact Strength, Hardness

Experimental determination of the evolution of the incident heat flux received by a combustible during a cone calorimeter test: Influence of the flame irradiance

The decomposition kinetic of polymeric materials in a cone calorimeter strongly depends on the irradiance level imposed at the sample’s surface. Indeed, even if the irradiance level is supposed to be kept constant during cone calorimeter test, the amount of heat flux which is emitted by the flame can greatly increase the total heat flux received by the material. Analytical treatment on recently obtained results of an acrylonitrile-butadiene-styrene’s mass loss rate with controlled atmosphere cone calorimeter has shown that the differences observed between well-ventilated and inert environments can be attributed to the impact of the flame. This observation has brought the necessity to determine the impact of the flaming process on the material thermal decomposition. To do so, series of experiments have been devised, based on the insertion of a heat fluxmeter within the matrix of an acrylonitrile butadiene styrene material, during cone calorimeter tests in order to measure the flame heat flux as a function of the decomposition and the combustion processes.

Effects of carbon dioxide addition to fuel on flame radiation fraction in propane diffusion flames

The flame radiation fraction of the turbulent jet diffusion flame of propane and carbon dioxide mixed gas was studied under the ambient temperature of 300 K and the pressure of 1 bar. The diameters of the nozzle were 2, 3, and 4 mm. Different flow rates of propane and carbon dioxide were controlled to obtain different concentration ratios. The results showed that for a given heat release rate, the flame heat radiation fraction decreases with increasing the concentration of carbon dioxide in the gas mixture. Theories of soot formation and laminar flame speed were used to explain the evolution of the radiation fraction under different volume fractions of carbon dioxide. A correlation model about the relationship among the radiation fraction, heat release rate, and fuel equivalent ratio was proposed.

High Frequency Characteristics of the Near Wake and Vortex Past a Triangular Cylinder

Abstract The flow past a triangular cylinder is one of the fundamental flows and widely utilized in flame stabilization and heat transfer. In this study, the near wake and vortex characteristics of the flow past an equilateral triangular cylinder are experimentally measured by a high frequency particle image velocimetry (PIV) system at 3 kHz. The triangular cylinder is installed in a wind tunnel with Reynolds numbers ranging from 10,700 to 17,700. The Reynolds-averaged and phase-averaged methods are utilized to analyze the flow field. Based on the flow fields, the length of the vortex formation region is about 1.5 times of the length of the equilateral triangle side. The residence time of a vortex in the vortex formation region is equal to a vortex shedding period. The stream wise velocity of the vortex core center downstream the vortex formation is about 0.8 times of the freestream velocity, which is slightly larger than the value about 0.7 for the flow past a circular cylinder at the same Reynolds number. The maximum tangential velocity at the periphery of the vortex core maybe occurs slightly in advance of the vortex reaching the boundary of the vortex formation region. The normalized lengths of the recirculation zone of the triangular cylinder keep nearly unchanged and are about 1.55 to 1.9 times of those of the circular cylinder at the same Reynolds number. The normalized normal wise instead of stream wise turbulence intensity has stronger effects on the distribution of the normalized turbulent kinetic energy.

Influence of U-shaped structure on upward flame spread and heat transfer behaviors of PMMA used in building thermal engineering

Both experimental and theoretical study on upward flame spread and heat transfer behaviors of PMMA (polymethyl methacrylate) under different U-shaped structure factors (Π) was conducted. The main results are as follows. The progress of pyrolysis front is used to determine flame spread rate since the flame front is more fluctuating than pyrolysis front. The flame spread rate is stable for 30 cm-length PMMA in this work. For Π<1, the flame spread rate increases as Π rises. For Π≥1, the flame spread rate tends to be stable. Based on heat transfer analysis, two models are established to predict flame spread rates with different Π for laminar and turbulent flame, respectively. Compared with experimental results, the prediction error is lower than 9%, within acceptable range of engineering. The prediction accuracy of the present model is better than that of previous model. In addition, theoretical correlation between the flame height and pyrolysis length is xf=1.639xp. Predicted flame heights are basically consistent with experimental results when Π = 0.4 or Π = 1.6. This work is beneficial for safety evaluation and optimization design of building thermal engineering using PMMA.

Neural Network Flame Closure for a Turbulent Combustor with Unsteady Pressure

In this paper, neural network (NN)-based models are generated to replace flamelet tables for subgrid modeling in large-eddy simulations of a single-injector liquid-propellant rocket engine. In the most accurate case, separate NNs for each of the flame variables are designed and tested by comparing the NN output values with the corresponding values in the table. The gas constant, internal flame energy, and flame heat capacity ratio are estimated with 0.0506, 0.0852, and 0.0778% error, respectively. Flame temperature, thermal conductivity, and coefficient of heat capacity ratio are estimated with 0.63, 0.68, and 0.86% error, respectively. The progress variable reaction rate is also estimated with 3.59% error. The errors are calculated based on mean square error over all points in the table. The developed NNs are successfully implemented within the computational fluid dynamics (CFD) simulation, replacing the flamelet table entirely. The NN-based CFD is validated through comparison of its results with the table-based CFD.

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.

Heat Transfer Characteristic for Premixed Flame Jet from Swirl Chamber

The objective of this research is to study flame structure and heat transfer characteristics for the premixed flame jet from the swirling chamber. In this study, LPG and air was utilized as gas fuel and oxidizer for a premixed flame. The equivalence ratios () of LPG and air were considered at 0.8, 1.0, and 1.2 under a Reynolds number Re = 4,000. The swirl flame was generated by double tangential inlets in cylindrical chamber. The diameter of chamber was fixed at D = 20 mm and the hydraulic diameter of the inlet was Dh = 5 mm. In this study, the effect of chamber geometry on flame structure was investigated by varying the chamber from H = 2.2Dh to 7.0Dh. The structures and temperature of the free flame jet was recorded with camera and measured with a thermocouple. The heat transfer rate of impinging flame jet was also measured at distance from chamber outlet to flame impingement surface varying from L = 4Dh to 10Dh. The results show that the maximum of flame temperature occurs at =1.2. Impinging flame jet for case of chamber height at H = 4.6Dh and impingement distance at L = 4Dh give the highest heat transfer for all equivalence ratios due to the reaction zone of combustion reached to approach near the heat transfer surface.

Experimental characterization and modeling of boundary conditions and flame spread dynamics observed in the UL-94V test

Abstract To characterize the UL-94 vertical burning test (UL-94 V), temperature, oxygen content, and heat flux of the burner flame were measured using an R-type thermocouple, oxygen analyzer, and water-cooled Schmidt–Boelter gage, respectively. To account for sample geometry, mock samples from Kaowool PM insulation board were used during the burner measurements. Temperature and heat flux measurements were used to express the heat flux of the burner as a linear, piecewise function of burner flame temperature and a constant convective heat transfer coefficient. UL-94 V tests were conducted using 0.27 cm thick poly(methyl methacrylate) (PMMA) samples with and without insulated sides to investigate edge effects. All UL-94 V tests were recorded on video using a 900-nm narrow-band filter to focus on emissions from soot for tracking flame length over time. In some of these tests, a heat flux gage was embedded into the sample to measure PMMA flame heat flux to verify a previously developed laminar wall flame heat feedback submodel. PMMA flame heat fluxes of insulated samples confirmed the wall flame submodel, while non-insulated samples had significantly greater heat fluxes; the flame submodel was scaled accordingly. The burner and wall flame heat flux submodels were combined with an independently developed pyrolysis model of PMMA to conduct two-dimensional, time-resolved simulations of the UL-94 V test. Burner flame oxygen content was measured to be about 5 vol% and was found to enhance PMMA decomposition. Inclusion of the oxygen effect was essential to predict ignition. The simulation predicted flame length and spread on insulated UL-94 V samples reasonably well, validating the submodels. However, the simulation underpredicted flame length on the non-insulated samples; discrepancies were attributed to burning and spread on the edges which were not modeled explicitly. The developed model can be applied to non-charring polymeric solids with no to moderate amount of dripping. Its applicability for charring and intumescent materials will be explored in the future.

Effect of Pulsating Flame Jet on Flow and Heat Transfer Characteristics

This research aims to study the effect of pulsating frequency on flame structure and heat transfer characteristics of premixed flame from a pipe nozzle. The LPG and air were used as gas fuel and oxidizer. The equivalence ratios ( ) were evaluated at 0.8, 1.0, and 1.2 under a constant Reynolds number Re = 500. The effect of nozzle-to-impingement surface distance ratio was investigated at H = 2D to 10D, here D is the nozzle diameter at 12 mm. The frequency of pulsating (f) was varied from f = 0 to 10 Hz using a solenoid valve. The flame structures of free flame jet and the impinging flame jet were recorded with a digital camera. The average heat flux on impingement surface was measured with water cooling plate and evaluated from the heat balance of the cooling water. The results show that the pulsating of flame jet become having gap on flame and the mushroom appear at the end of flame. The size of mushroom structure becomes larger when increasing the frequency. While the non-pulsating jet did not appear in this structure. Pulsating flame jet can increase the overall average heat flux on the impingement surface up to about 12% for case of = 1.2 and H = 2D and f = 10 Hz. when compared to case of f = 0 Hz.

Combustion of Lean Methane–air Flames in Mesoscale Reactor with Opposite Gas Flows

ABSTRACT In this work, we study a countercurrent premixed rich-lean coaxial reactor to realize an overall lean combustion of hydrocarbon fuels. Flame topology and stability of the axially symmetric reaction fronts of methane-air mixtures are investigated both numerically and experimentally. These studies show that depending on the equivalence ratio of the mixture fed into the inner tube, playing the role of supporting a pilot burner, there can occur two or three-layered stable flame structures. It is demonstrated that flames can be stabilized over a wide range of mixture compositions and flow rates. In particular, it is possible to stabilize methane-air flames with the overall equivalence ratio below the lean flammability limit for this mixture due to the existence of the weak supporting flame and combined effect of the flame stretch and heat recirculation realized in the examined configuration. The diverse unsteady combustion modes, including flame oscillations and flame periodic extinction and ignition, are also found. The prospects of further investigations are discussed.

Flammability testing of wool/cellulosic and wool/synthetic fiber blends: Vertical flame spread and heat release results

Wool is a natural fiber with lower heat release/flammability than some synthetic fabrics, but it has not been well studied for its heat release when other fibers such as cotton, linen, and nylon are present in the woven fabric. In this article, the heat release and vertical flame spread of six commercially available natural color fabrics is reported. This includes 100% wool, 80% wool/20% nylon, 70% wool/30% linen, 45% wool/55% cotton, and 40% wool/38% cotton/12% nylon/10% metallic thread fabric. Heat release was measured through cone calorimetry (ASTM E1354) as a function of the sample mounting method, through microscale combustion calorimetry (ASTM D7309), and flame spread was measured by ASTM D6413. The type of insulated backing used greatly affected the cone calorimeter results, and fabric types did show some effects in vertical flame spread and microscale combustion calorimeter testing.

Influence of Equation-of-States on Supercritical CO2 Combustion Mixtures

Abstract Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia, and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability of various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict–Webb–Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.

Study on the Flammability Limits of Lithium-Ion Battery Vent Gas under Different Initial Conditions.

In this paper, the flammability limit of the battery thermal runaway vent gas (BVG) is studied numerically by using the CHEMKIN 2.0 code. The research content mainly includes the change of flammability limit with the state of charge, initial temperature, and initial pressure. The chemical reaction kinetics at the flammability limit is also analyzed. The results show that the flammability limit obtained by numerical simulation is in good agreement with that calculated by Le Chatelier’s mixing rule. The lean and rich limits increase with the increase of the initial pressure, and the increasing trend gradually slows down. As for the change of initial temperature, higher the temperature is, wider the limits are. In addition, according to the simulation results, the fitting formula of the flammability limit changing with the initial conditions is given. Furthermore, in order to reveal the important elementary reactions controlling the flammability limit, the sensitivity analysis with respect to the flame speed and heat release rate analysis of the elementary reactions are carried out at the flammability limit. Finally, the effect of CO2 and H2 content on the flammability limit of BVG is discussed.

Deep learning-based super-resolution images for synchronous measurement of temperature and deformation at elevated temperature

Measuring temperature and deformation at elevated temperature has recently been a major concern for the engineering tests and the quality improvement of captured images is critical to it. Here, we propose a simple, high-precision and easy-to-implement technique combing the image capturing and processing methods to obtain the high-resolution images as well as the corresponding temperature and deformation fields. The super-resolution convolutional neural network (SRCNN) algorithm is used for the super-resolution reconstruction, while the deformation field is calculated by the DIC method and the temperature field is synchronous obtained by the improved two-color method. Flame heating experiment of the SiC material validated the applicability and the improvement of the proposed method, showing the improvement in image quality (with PSNR increased 16.7 %) and calculation accuracy of temperature and deformation (with error decreased 3.57 %). Meanwhile, the phenomenon of "feature point drift" is pointed out and the error of deformation measurement for high-resolution and low-resolution is analyzed. Furthermore, the sub-pixel edge detection can be achieved by the combination of the proposed method and the edge detection method, which shows a potential value in detecting of surface defects or cracks.

Experimental investigation into the influence of ignition location on flame spread and heat release rates of polyurethane foam slabs

SummaryThis study presents the results from a set of 11 large‐scale open fire tests performed on flexible polyurethane foam slabs/mattresses. The purpose of the study was to investigate the influence of the ignition location on the fire behaviour of the foam slabs and to generate data on a highly characterised material that could be used for modelling work in the future. A method for obtaining spatially resolved flame spread data for this type of material was presented using a gridded array of 5 × 10 thermocouples placed on the underside the foam slab and from this, flame spread was examined using three different approaches. The heat release rate (HRR) results showed clear shapes forming that were dependent on the ignition location, with two distinct behaviours being observed between the various different ignition locations, this was also observed in the calculated flame spread rate (FSR) data. Results within an individual test, showed the calculated range of FSRs over the geometry of the slab varied between approximately 1 and 8 mm/s depending on the ignition location. The average FSR values between tests varied between 3 and 7 mm/s and the maximum and minimum values were calculated to be approximately 11 and 2 mm/s respectively.

Facile preparation of an effective intumescent flame-retardant coating for cotton fabric

In the present study, phytic acid was used as an environmentally sustainable phosphorus-containing flame retardant (FR) to improve the flammability of cotton fabrics. The facile preparation approach is adequate for offering an intumescent FR system for cotton, as phytic acid and triethanolamine could serve as the acid source and blowing agent, respectively, and a cellulose substrate may function as the carbon source. The flame retardancy, thermal stability, heat and smoke generation and mechanical performance of cotton fabrics were evaluated. The cotton fabrics coated with 70 g/l phytic acid at pH 5 had a weight gain of 15.1% and self-extinguished by way of an intumescent charring mechanism in the vertical burning test, and the textile structures of the burned portion were well preserved. The intumescent FR coating also greatly reduced the heat and smoke generation ability of cotton and enhanced its thermal stability at high temperature, but it suffered from poor washing resistance. The present intumescent FR system based on phytic acid is an eco-friendly and sustainable production approach compared with synthetically engineered chemicals.

Mechanisms of flame spread and burnout in large enclosure fires

Knowledge of the first principles defining fire behaviour in large enclosures remains limited despite their common use in modern tall buildings. The evolution of a fire in large enclosures can be defined by the relationship between the flame front and burnout velocities (VS/VBO). This relationship can be classified into three distinct fire spread modes being Mode 1 (VS/VBO → ∞), Mode 2 (VS/VBO > 1), and Mode 3 (VS/VBO ≈ 1). The mechanisms governing flame spread and burnout are investigated using four full-scale enclosure fire experiments with high porosity wood cribs with similar enclosure geometries. Flame and burnout front positions and velocities are estimated using video data. Velocities are affected by the heat feedback from the enclosure and smoke layer to the fuel. The spread velocity shows two regimes, a minimum external heat flux above which there is surface spread (q˙s,min″) and a heat flux that defines the onset of very rapid flame spread (q˙rs,crit″). A phenomenological model is developed to help identify the underlying mechanisms controlling the transition between the different spread modes. Both the model and data show that for wood cribs, the dependence of the burnout front velocity to the external radiation is weak, whereas the dependence of the flame spread velocity to the external and flame heat flux is strong. A transition from Mode 3 (VS/VBO ≈ 1) to Mode 2 (VS/VBO > 1) occurs with increasing external heat fluxes above q˙s,min″. The transition to Mode 1 (VS/VBO → ∞) is further defined once q˙rs,crit″ is attained due to a sudden increase in the flame heat flux by changing the ventilation condition, or by significant increases in the external heat flux from the enclosure.

Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

SUMMARYFire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.