Radiation Blockage Research Articles

Powering the Future Green Buildings: Multifunctional Ultraviolet-Shielding Transparent Wood.

Indoor UV damage is a serious problem that is often ignored. Common glasses cannot filter UV rays well and have fragility and environmental issues. UV-shielding transparent wood (TW) holds promise, yet striking the right balance between blocking UV rays and allowing sufficient visible-light transmission poses a challenge. The pronounced capillary force, fueled by persistent moisture and extractives in wood, alongside the existence of multiphase interfaces, collectively hinder the uniform penetration of polymers and the effective dispersion of nanomaterials within the wood skeleton. Here, we incorporate high-pressure supercritical CO2 fluid-assisted impregnation (HSCFI) into fabricating UV-shielding TW. The supercritical CO2 pretreatment efficiently eliminates moisture and refines wood structure by extracting polar substances, resulting in a prominent 52.4% increase in average water permeability. Subsequently, this HSCFI method facilitates the infiltration of methyl methacrylate (MMA) monomer and Ce-ZnO nanorods (NRDs) into the refined anhydrous wood, leveraging the excellent solvency of supercritical CO2 for MMA. The impregnation rate of PMMA undergoes a substantial increase from 34.5 to 59.1%. With the robust UV-blocking capability of Ce-ZnO NRDs, thanks to dual-valence Ce doping widening the ZnO energy gap via the Burstein-Moss effect and their unique photoactive microstructure featuring a solid prism with a sharp hexahedral pyramidal tip, along with intrinsic physical scattering/reflection actions, Ce-ZnO NRDs@TW achieves an impressive 99.6% UVA radiation blockage (the highest for TW) and maintains high visible-light transmission (83.2%). Furthermore, Ce-ZnO NRDs@TW presents favorable energy-saving, sound absorption, and antifungal abilities, making it a promising candidate for future green buildings.

Experimental research on radiation blockage of the fuel vapor and flame in pool fires

Pool fires are the most prevalent accidents in the process industry. Revealing the physical mechanism of pool fire has both fundamental and practical applications in process safety and risk analysis. This paper intends to study the radiation blockage phenomenon caused by fuel vapor and flame in pool fires. Combustion and evaporation (non-combustion) experiments under different external radiative heat fluxes have been conducted to differentiate the radiation blockage of the fuel vapor and the flame. Four different sooting fuels including methanol, ethanol, n-heptane and toluene were used in the experiments. The radiation blockage of fuel vapor was determined through evaporation experiments. The radiation blockage of flame and the total radiation blockage of pool fires were investigated by burning experiments. Based on the assumptions of radiation gray for flame radiation and external radiation, the effective radiation blockage was determined. It is found that the effective radiation blockage coefficient of the fuel vapor increases with fuel mass flux first, and then gradually approaches a constant value because the radiation absorption capacity of the fuel vapor tends to saturate with the increase of fuel mass flux. The correlations between the fuel vapor radiation blockage coefficient and fuel mass flux are established based on theoretical analysis and experimental data. Moreover, the flame blockage coefficient decreases with external radiation for methanol, ethanol and n-heptane because the fire expands, causing enhanced radiative heat feedback from the flame. For the heavily sooting fuel, toluene, the flame radiation blockage almost remains constant with external radiation due to high soot concentrations.

Thermal performance of cavities in 3DPC building façades

In the quest for sufficient and comfortable housing in South Africa, attention to building orientation and thermal transmittance principles has significantly improved thermal performance in local houses. Thermal simulation and monitoring of houses in the Joe Slovo Phase Three development in Cape Town confirms improved performance by solar radiation blockage and shading. This paper simulates the thermal performance of a housing unit in this development. The house was instrumented with thermocouples, and monitored from March to December 2013 by Sustainable Energy Africa in collaboration with the National Department of Human Settlements. Sustainable Energy Africa reported significant improvement when compared to a nearby traditional Reconstruction and Development Programme house that had been monitored during the same period. With the benefit of the monitored thermal data, complete drawings, and specification details of the Joe Slovo Phase Three unit, the current research modelled and calibrated a simulation model in DesignBuilder. DesignBuilder was selected given its accreditation status for Green Star Rating of buildings in South Africa. An additional motivation for investigating this unit was the availability of recorded weather data from the nearby Cape Town International Airport, captured in the DesignBuilder climate data base for 2013, which was assumed relevant in lieu of complete weather station data measured at the location of the housing unit. The study aimed to simulate the monitored temperatures in the house with acceptable agreement, and to investigate further potential improvement in occupant thermal comfort by alternative 3D-printed concrete walling developed by the authors. Systematic finite element analysis (FEA) iteratively solved cavity radiation and convection in wall cavities to calibrate thermal transmittance parameters for DesignBuilder. The FEA results acceptably simulated temperatures monitored in this physical wall experiment. The calibrated DesignBuilder model simulated the indoor temperatures of the monitored house with acceptable agreement, and predicted significant improvement in occupant thermal comfort if the walls were 3D-printed with a particular cross-sectional design.

PROPERTY ENHANCEMENT OF PIGMENT PRINTED POLYESTER FABRIC USING PLASMA TECHNOLOGY

Today, the customer is the king of the market and polyester fabric is in high demand as it is more economical and has many good properties when compared with other textile material. Polyester is claiming more than 75percent of the estimated 60 million metric tons of fibres consumed in man-made textiles in the apparel industry over natural fibres. Naseerali (2013) In this study the researcher has made an attempt to improve the absorbency of polyester fabric as well as to reduce its static charge. Air plasma technology was used to treat the surface of 100% polyester fabric at different time durations of 15, 30, 45, 60, 90, 120 minutes. The control and the surface modified fabrics were then printed with water- based pigments which are eco-friendly and without water based pigments which are commercially used. As most of the pigment printed samples get peeled off so it was plasma treated and then printed to evaluate the durability of the pigment prints. The UPF (ultra-violet protection factor) value of all the control and the modified sample were then evaluated to determine the ultraviolet radiation blockage or transmittance by fabrics intended to be used for UV protection. It was further found that better UPF value of the modified non water- based pigment at 90 minutes when compared to water based pigment samples and untreated samples. The fastness properties like rub and color fastness were observed with standard methods. In the rub fastness tests it was observed that the plasma treated with water based pigments for 30 minutes gave better dry rub fastness and it concludes that plasma treatment more than 30 minutes is not required because it gives a better results at 30 minutes. In the color fastness properties the water- based and non-water based pigment printing gave a better result at all-time durations than the control sample, so in concern of energy usage, treatment can be given for less time duration to have better quality products.

TiO2 nano-coated thin film PV glazing with superior thermal resistance, self-cleaning, electricity generation and adaptive optical control

Abstract A unique nano-coated photovoltaic (PV) glazing technology with superior multifunctional features, thermally resistive PV glazing (TRPVG), is introduced, and for three different configurations of TRPVG (TRPVG-Air12, TRPVG-Ar12, TRPVG-Ar16), UVC/UVA absorption, noise reduction, thermal insulation, electricity generation, visible light and solar radiation control are evaluated through an extensive experimental methodology. Energy production and acoustic tests are conducted in a simulation house, whereas the rest of the experiments are carried out under real operating conditions. The results reveal that each sample is capable of blocking 100% of incoming UVC and UVA light. Visible light control of TRPVG-Ar12 (Glass 1) is found to be 94.4%, whereas it is 88.9% for TRPVG-Air12 (Glass 2) and 93.6% for TRPVG-Ar16 (Glass 3). Solar radiation blockage of Glasses 1–3 is found to be 93.5%, 90.9% and 94.8%, respectively. Average temperature difference between front and rear glazing is determined to be 21.3°C, 19.9°C and 21.7°C for Glasses 1, 2 and 3, respectively. A total of 25 independent acoustic tests are performed for Glass 3, and the sample is observed to reduce 33% of outdoor noise in dBA. Solar simulator tests reveal that Glass 3 can generate 102.6 W of electricity per square metre of PV module area.

Experimental study on the diffusion burning and radiative heat delivery of two adjacent heptane pool fires

This paper investigated the effect of separation distance on the flame appearance and radiation heat flux of medium-scale pool fires dominated by radiation. A series of experiments were conducted on two adjacent heptane pool fires with diameters of 20 cm, 40 cm and 60 cm at separation distances ranging from 0 to 60 cm. According to experimental results, flame height and flame inclination angle increase monotonously with the increase of pool diameter. As separation distance increases, flame height increases first and decreases gradually for 3 different sized pool fires. However, the variation law of flame inclination angle with separation distance varies with pool diameter. The normalized flame height (Hf/D) is found to increase exponentially with the dimensionless heat release rate (Q*) with an exponent of 0.71. The radiative heat flux at the center of the pool surface peaks at the critical separation distance of flame merging, which results from increased flame emissivity and view factor. Based on thermal analysis, a model to predict the radiative heat flux on the fuel surface is developed. The predicted radiative heat fluxes quantitatively match the experimental results but with 20% overvalued, due to the neglection of radiation blockage effect of cool fuel vapors zone and soot. The blockage effect is more pronounced for the merging pool fires with a diameter of 60 cm.

Evaluating Orientation Effects on the Fire Reaction Properties of Flax-Polypropylene Composites.

In this work, the fire reaction properties of flax-polypropylene (PP) composites were investigated at multiple sample angles both experimentally and numerically under two different heat flux conditions (35 and 50 kW/m2) in the cone calorimeter environment. An innovative testing setup which can accommodate a wide range of angles between 0° and 90° for the sample angle frame was developed to perform cone calorimeter tests at different sample angles. An advanced numerical predictive model based on the finite volume method was developed using the fire dynamics simulator (FDS) to quantify the dependency of ignition and combustion properties with sample angles. The numerical model was validated against experimental data from the cone calorimeter tests. The experimental and numerical analyses were conducted to quantify the effects of sample orientation on the different fire reaction properties i.e., ignition time, ignition temperature, burn time, heat release rate (HRR), critical heat flux, etc. The numerical method was utilised to analyse the mechanisms controlling the effect of heat convection and radiation blockage on the heating process. The study establishes that the sample orientation (with respect to the heat flux normal) has a significant influence on the fire reaction properties of natural fibre composites.

Invisibility Utilizing Huygens’ Metasurface Based on Mantle Cloak and Scattering Suppression Phenomen

This communication presents the design of a Huygens' metasurface (HMS) coating aiming to achieve strongly enhanced invisibility. An analytical formulation for obtaining the required electric surface admittance and magnetic surface impedance is presented. The proposed unit cell consists of a pair of split-rin resonators in the top layer and a metal capacitor in the bottom layer of the same substrate. The geometries are properly designed to provide the required electric surface admittance and magnetic surface impedance for maximum scattering reduction at the operational frequency of 4 GHz. The designed HMS is optimized to realize the required electric surface admittance and magnetic surface impedance for remarkable cloaking purposes. Scattering-cross section (SCS) of uncloaked and cloaked conducting cylinders is obtained with CST Microwave Studio simulation which matches the analytical results. The results show robust scattering reduction with considerable bandwidth for the covered cylinder by the HMS. Furthermore, the obtained results with HMS are compared with the results presented in the literature for cloaking with ordinary metasurface. This comparison emphasizes a much better cloaking performance of the HMS. Considerable cloaking obtained in this communication can be applied for invisibility purposes, sensing applications, antenna isolation, radiation blockage reduction in antennas, etc.

Effects of shade location and protection from direct solar radiation on the behavior of Holstein cows.

Two trials (E1 and E2) were performed to assess the behavior of eight Holstein dairy cows with 367 ± 58kg of body weight and 10.52 ± 0.08kg of milk yield. A 4 × 4 Latin square design (four periods of lactation and four levels of solar blockage) with four paddocks was used. Each paddock contained a wood shading structure covered with a cloth that blocked 30% (T1), 50% (T2), 70% (T3), or 100% (T4) of direct solar radiation. In the first trial (E1) each shade structure was located approximately 40m from the feeder and water troughs; in the second trial (E2), the distance was reduced to 5m. Air temperature (TA, °C), relative humidity (RH, %), wind speed (U, ms-1), black globe temperature (TG, K), mean radiant temperature (TMR, K), radiant heat load (RHL, Wm-2), and local shortwave radiation (RS, Wm-2) were recorded at 15-min intervals from 08:00 to 17:00h. Four behavioral activities were recorded: grazing, eating at the feed trough, ruminating, and idling. For each of these activities, animal posture (lying or upright) and location (under shade or exposed to sunlight) were recorded. The meteorological conditions showed similar variations from 8:00 to 17:00h between the two trials. However, the air temperatures in E1 were lower (± 2°C) than those in E2. In a PCA analysis, the first and the second principal components explained 56.87% and 21.85%, respectively, of the total variation in the behavioral variables. Under the E1 conditions, the animals did not seek shade, whereas in E2, the dairy cows spent 35 ± 5% of their time lying and idling in the shade. At a solar radiation blockage of 100%, cows were in the shade more than 60% of the time due to the intensity of solar radiation, which was 722.19 ± 14.59Wm-2 at 11:45. In a PCA analysis, the first and the second principal components explained 65.18 and 22.3%, respectively, and 87.48% together, of the total variation in the original variables. Consequently, it was possible to develop a shade index (IST) based on the first two components. In E1, animals spent very little time in the shade, spending only 0.15% of total time under the shade, irrespective of blockage. However, E2 cows used shade, reaching almost 80% of time under the shade, at midday, when the blockage was 100%.

Flame spread characteristics and a multi-cylinder radiation model for diesel tray fires against a sidewall

A series of experiments were conducted to study the flame spread and radiation characteristics for diesel tray fires against a sidewall. The tray width and the height of the sidewall were varied. The flame spread appearances and rate, subsurface flow and transverse fuel surface temperature were analyzed. Results showed that the sidewall has a great influence on the flame spread behavior due to its restriction on air entrainment. The flame distribution was uneven along the length of the tray, and the front propagating flame inclines to the tray outboard side edge (i.e. the tray's long side that is not attaching to the sidewall) for more oxygen, then more heat transferred from the flame through tray wall to the fuel results in uneven surface temperature profiles. The main flame being one short distance away from the flame spread front is against the sidewall. When the ratio of the sidewall height to the tray width, H/W, is less than 1, both the flame spread rate and subsurface flow increase with the increasing H/W, due to enhanced heat transfer. For H/W > 1, both of these parameters decrease with the increasing H/W, indicating a strong restriction of air entrainment by the sidewall. To estimate the flame radiation to the fuel surface during propagation, a multi-cylinder radiation model was proposed. By dividing the whole flame into several cylindrical sub-flames, the radiation blockage and sidewall effects are considered in the model. The comparison of calculated and measured radiation heat fluxes shows that the proposed model is reliable with a maximum error of 20%. These findings will provide scientific supports to fire monitoring and contribute to estimating radiative heat flux of spreading flame.

Radiation Blockage Reduction in Antennas Using Radio-Frequency Cloaks [Antenna Applications Corner

This article presents an experimental demonstration of antenna blockage reduction based on the concept of radio-frequency (RF) cloaking. The proposed cloaking configuration is validated by studying the antenna characteristics in the presence of obstacles that are covered with and without the cloaking surface. The known concept of thin cloaks used for reducing the scattering width is extended in this article to mitigate the blockage in antennas. An attempt is made to improve the degraded radiation characteristics of the antenna due to the presence of metal obstacles loaded in front of the aperture. This is accomplished by covering the obstacles with a cloaking surface made up of a periodic arrangement of interconnected patches and microstrip lines. The optimizations are carried out for various scenarios by varying the thickness of the substrate and the length of the interconnecting microstrip line to achieve an optimum cloaking performance. It is demonstrated through measurements that the RF cloaking could be achieved between the frequencies 3 and 3.3 GHz. At 3.2 GHz, the gain of the horn antenna in free space is measured to be 17.2 dBi, and the gain of the horn antenna with uncloaked obstacles at the aperture is 3.73 dBi. The same configuration with cloaked obstacles exhibits a gain of 12.13 dBi.

Heat transfer blockage effect of small-scale PMMA flame under exterior heat radiation

In this work, experiments of small-scale vertical and horizontal PMMA flames were performed under exterior heat radiation, in order to investigate the heat transfer blockage effect based on energy balance of steady state. It is found that for both sample orientations, the mass loss rate of PMMA increased linearly with increasing exterior heat radiation, and the flame height depends linearly on mass loss rate to the power 2/3. Calculated and measured mass loss data indicate that the heat transfer blockage fraction is independent of the exterior heat radiation for both sample orientations. For vertical PMMA flame, the radiation blockage fraction increases with vertical height. For horizontal PMMA flame, the radiation blockage fraction is the highest at the sample center. For both horizontal and vertical samples, the mean radiation blockage fraction increases with exterior heat radiation and gradually reaches an equilibrium value. The convective heating to the sample surface is enhanced by hot gas flow for vertical PMMA flame, while it is weakened for horizontal PMMA flame.

The Janus face of iron on anoxic worlds: iron oxides are both protective and destructive to life on the early Earth and present-day Mars.

The surface of the early Earth was probably subjected to a higher flux of ultraviolet (UV) radiation than today. UV radiation is known to severely damage DNA and other key molecules of life. Using a liquid culture and a rock analogue system, we investigated the interplay of protective and deleterious effects of iron oxides under UV radiation on the viability of the model organism, Bacillus subtilis. In the presence of hydrogen peroxide, there exists a fine balance between iron oxide's protective effects against this radiation and its deleterious effects caused by Photo-Fenton reactions. The maximum damage was caused by a concentration of hematite of ∼1 mg/mL. Concentrations above this confer increasing protection by physical blockage of the UV radiation, concentrations below this cause less effective UV radiation blockage, but also a correspondingly less effective Photo-Fenton reaction, providing an overall advantage. These results show that on anoxic worlds, surface habitability under a high UV flux leaves life precariously poised between the beneficial and deleterious effects of iron oxides. These results have relevance to the Archean Earth, but also the habitability of the Martian surface, where high levels of UV radiation in combination with iron oxides and hydrogen peroxide can be found.

Dispersion engineering of metasurfaces for dual-frequency quasi-three-dimensional cloaking of microwave radiators.

In this work, the design methodology and experimental investigation of compact and lightweight dispersive coatings, comprised by multiple layers of anisotropic metasurfaces, which are capable of cloaking radiators at multiple frequencies are presented. To determine the required surface electromagnetic properties for each layer, an analytical model is developed for predicting the scattering from a cylinder surrounded by multiple layers of anisotropic metasurfaces subject to plane-wave illumination at a general oblique incidence angle. Particularly, two different metasurface coating solutions with different dispersive properties are designed to provide more than 10 dB scattering width suppression at two pre-selected frequencies within a field-of-view (FOV) of ± 20° off normal incidence. Both coating designs implemented using metasurfaces are fabricated and measured, experimentally demonstrating the simultaneous suppression of mutual coupling and quasi-three-dimensional radiation blockage at the two pre-selected frequency ranges. At the same time, the functionality of the coated monopole is still well-maintained. The performance comparison further sheds light on how the optimal performance can be obtained by properly exploiting the dispersion of each metasurface layer of the coating. In addition, the cloaking effect is retained even when the distance between the radiators is significantly reduced. The concept and general design methodology presented here can be extended for applications that would benefit from cloaking multi-spectral terahertz as well as optical antennas.

Restoring Intrinsic Properties of Electromagnetic Radiators Using Ultralightweight Integrated Metasurface Cloaks

The concept of invisibility has garnered long‐standing interest throughout human history but has only been realized experimentally within the past decade, albeit over a limited bandwidth. While the physical wave phenomenon of a reduced scattering signature has been demonstrated with different cloaking methods such as transformation optics and scattering cancellation, such technology has yet to be incorporated into any practical real‐world devices. Through the use of quasi‐2D functional metasurfaces, the long‐standing issue of simultaneous mutual coupling and radiation blockage is addressed that occurs when two or more electromagnetic radiators are placed in close proximity to one another. The proposed compact and ultralightweight metasurfaces, comprising arrays of subwavelength electric and magnetic resonators with tailored dispersive properties, are capable of fully restoring the intrinsic properties of real‐world electromagnetic radiators when placed in a multiradiator environment. This work introduces a general design approach to bridge the gap between the theory and practice for cloaks, which is applicable to microwave, terahertz, and optical radiators, as well as acoustic and thermal sources. Moreover, this technology provides an unprecedented opportunity for enabling high‐density deployment of radiating systems with low interference and undistorted signal wave fronts.

Effects of sample orientation on pyrolysis and piloted ignition of wood

In this work, the pyrolysis and piloted ignition behavior of thermally thick paulownia wood brick for different orientations has been experimentally investigated, by using the conical heater. Three typical orientations were adopted, that is, upward, downward, and vertical cases with the incident heat flux ranging from 12 to 39 kW/m2. A numerical approach was used to test the effect of heat convection and radiation blockage on pyrolysis. The ignition time was observed to be strongly dependent on orientation. In detail, the shortest ignition time turns to be for downward orientation, but longest ignition time for vertical orientation. Total mass loss at ignition is weakly dependent on orientation. Meanwhile, critical mass flux increases with external heat flux rising and varies somewhat with orientation.

Measurement and Monte Carlo simulation for energy‐ and intensity‐modulated electron radiotherapy delivered by a computer‐controlled electron multileaf collimator

The dosimetric advantage of modulated electron radiotherapy (MERT) has been explored by many investigators and is considered to be an advanced radiation therapy technique in the utilization of electrons. A computer‐controlled electron multileaf collimator (MLC) prototype, newly designed to be added onto a Varian linac to deliver MERT, was investigated both experimentally and by Monte Carlo simulations. Four different electron energies, 6, 9, 12, and 15 MeV, were employed for this investigation. To ensure that this device was capable of delivering the electron beams properly, measurements were performed to examine the electron MLC (eMLC) leaf leakage and to determine the appropriate jaw positioning for an eMLC‐shaped field in order to eliminate a secondary radiation peak that could otherwise appear outside of an intended radiation field in the case of inappropriate jaw positioning due to insufficient radiation blockage from the jaws. Phase space data were obtained by Monte Carlo (MC) simulation and recorded at the plane just above the jaws for each of the energies (6, 9, 12, and 15 MeV). As an input source, phase space data were used in MC dose calculations for various sizes of the eMLC shaped field (10×10 cm2, 3.4×3.4 cm2, and 2×2 cm2) with respect to a water phantom at source‐to‐surface distance (SSD)=94cm, while the jaws, eMLC leaves, and some accessories associated with the eMLC assembly as well were modeled as modifiers in the calculations. The calculated results were then compared with measurements from a water scanning system. The results showed that jaw settings with 5 mm margins beyond the field shaped by the eMLC were appropriate to eliminate the secondary radiation peak while not widening the beam penumbra; the eMLC leaf leakage measurements ranged from 0.3% to 1.8% for different energies based on in‐phantom measurements, which should be quite acceptable for MERT. Comparisons between MC dose calculations and measurements showed agreement within 1%/1mm based on percentage depth doses (PDDs) and off‐axis dose profiles for a range of field sizes for each of the electron energies. Our current work has demonstrated that the eMLC and other relevant components in the linac were correctly modeled and simulated via our in‐house MC codes, and the eMLC is capable of accurately delivering electron beams for various eMLC‐shaped field sizes with appropriate jaw settings. In the next stage, patient‐specific verification with a full MERT plan should be performed.PACS number: 87.55.ne

Leaf temperatures in glasshouses and open‐top chambers

Climate manipulation experiments are of key importance in identifying possible responses of plant communities and ecosystems to climate change. Experiments for warming the air under sunlit conditions are carried out in (partial) enclosures. These inevitably alter the energy balance inside, potentially altering tissue temperatures which affect metabolism and growth. Using an empirically validated energy balance model, we investigate effects of two widely used warming methods, climate-controlled glasshouses and passively warmed open-top chambers (OTCs), on leaf temperatures. The model applies standard energy balance formulas, supplemented with data on optical properties of glasshouse materials and wind conditions inside OTCs. Results show that the different radiation environment inside glasshouses did not produce large leaf temperature deviations compared with outside. Poor glasshouse design with significant radiation blockage by the structure or with insufficient ventilation did affect tissue temperatures more significantly. The drastic wind speed reduction inside OTCs approximately doubled the actual (canopy) warming compared with earlier reported increases in air temperature provided by this technique - an effect that was inflated if the plants' stomates closed. These results demonstrate that leaf temperatures were higher than previously considered in OTCs but not in climate-controlled glasshouses.

Radiation blockage in small scale PMMA combustion

Fuel vapors, soot and products of combustion near a burning fuel surface often block much of the radiative heat feedback to the fuel surface of a burning object. The blockage phenomenon was clearly observed in experiments of small 9.5 cm diameter PMMA pool fires subjected to external radiation burning in ambient atmospheres of different oxygen concentrations. The measurements are explained by a one-dimensional model of a diffusion flame, which focuses on the radiant absorption and emission of the soot–gas mixture of the flame. An approximate Band Model was developed and inserted into Radcal to compute gas absorption and emission from MMA vapor, CO 2 and H 2O. The Radcal results are included in the one-dimensional diffusion flame model to provide a greater understanding of the radiation blockage and burning rates in various ambient atmospheres and externally imposed radiant heat fluxes. A comparison between experimental data and model prediction shows a good agreement.

Thermally Induced Stresses in Glazing Systems

A thorough examination has been performed of the thermally induced stresses on a window in an enclosure-fire environment. Analytical and numerical methods establish the importance of bridling stress (due to axial elongation) and flexing stress (due to normal deformation). Most previous studies omitted the consideration of flexing stresses. Maximum stresses, being the sum of bridling and flexing stresses on the side, have been calculated for varying aspect ratios of a rectangular window and for varying ratios of shaded width to the window sides. For uniform width and heating (e.g., represented, by constant high temperature in the heated region and ambient temperature in the shaded region), the maximum stresses are bridling and equal to those of an infinite strip shaded on two sides when the shaded width is less than 40% of the short side. For nonuniform shading (e.g., due to radiation blockage) or nonuniform heating, flexing stresses contribute to the total stress by an increase up to 50%. These new results have been applied in predicting the magnitude of stresses and the location of the first crack in well-controlled experiments and measurements. These results are important because they extend and delineate the limitations of currently used relations for determining thermally induced stresses and times of first cracking in windows.