Attenuation Of Thermal Radiation Research Articles

Thermal radiation attenuation performance of fine water spray using twin-fluid nozzles with multiple holes

Thermal radiation attenuation performance of fine water spray using twin-fluid nozzles with multiple holes

Fire Dynamics Simulator Analysis of Smoke Confinement and Radiation Shielding using Water Mist Curtains

This research was conducted to numerically analyze the smoke confinement and radiation shielding characteristics of water mist curtains during the process of plume flow that propagates along the ceiling after its occurrence in fire source. We reviewed the flow field based on the location of the spray, size of water mist droplets, temperature distribution, and soot distribution. The optical density extracted at a height of 1.5 m and the thermal radiation attenuation rate values were comparatively analyzed. In the case of no water-mist operation, the temperature and soot concentration were stable as they formed a layer toward the floor from the ceiling. By contrast, when the water mist curtain was operational, the spray flow obstructed the ceiling jet flow and caused considerable mixing. The results from reviewing the optical density predictions showed that it tended to decrease at a distance sufficiently far downstream of the curtain, but overall the effect was not meaningful compared to the case of no water-mist operation. This was considered to be because a considerable number of fine droplets, as well as soot particles included in the smoke, affected the optical density. Conversely, the attenuation rate of thermal radiation was greatly affected by the average size of the droplets. In the case when the location of the water mist curtain was x<sub>inj</sub> = 6 m, the thermal radiation attenuation rate at the lowermost part changed from 79.0%, 29.7%, and 17.0% as the average spray droplet size increased from 200, 500, and 1,000 <i>μ</i>m., respectively.

An experimental study on the thermal radiation attenuation effect of water mist from flat fan nozzle

The factors which influence the radiation attenuation efficiency of the water mist from flat fan nozzle have been investigated in the study. The characteristic parameters of the water mist were obtained by laser-based diagnostic system for flow field. Both blackbody furnace and gasoline pool fires were used as heat sources in the experiments. The influences of system pressure, the vertical distance from the nozzle, the temperature of the radiation source and the number of the mist layers on the radiation attenuation effectiveness have been systematically studied. The experimental results showed that when the vertical distance down the nozzle increased from 20 cm to 200 cm, the radiation attenuation efficiency increased at first, then remained almost stable for a substantial distance and decreased afterwards, and three vertical zones were identified based on the attenuation characteristics; as the temperature of the blackbody furnace radiation aperture increased from 1000 ℃ to 1300 ℃, the radiation attenuation efficiency had a certain decrease, a linear correlation was found between the mitigation rate and the radiative source temperature under different system pressures. The attenuation effectiveness improved with the increase of both system pressure and the number (thickness) of water mist layer, while the augmentation rate in attenuation slowed as the system pressure and the water mist thickness increased. The findings provide useful insights into the optimization of attenuation performance of water mist and potentially contribute to the protection against thermal radiation in fields like the fluorine chemical industry.

Study on smoke blocking and thermal radiation attenuation by water curtain in tunnel fire

A 1:10 scale model tunnel with a length, height and width of 9 m, 0.6 m and 0.8 m, respectively, was set up in this paper. A water curtain system was installed in the model to investigate the effect of water curtain systems on smoke flow and heat propagation. A reduced-scale experimental and theoretical study was carried out by varying the heat release rate of the fire source, the water curtain pressure, and the number of water curtain rows. A series of tests were carried out for various setups to quantify each mechanism of interaction between the water mist and hot smoke, to propose a method for qualitatively analysing water curtain systems blocking the propagation of heat radiation and the flow of smoke from combustion, and to propose a method for predicting heat fluxes. The study found that the pressure of the water curtain, the number of rows, and the heat release rate of the fire source all had an effect on the smoke blocking effect of the water curtain system. This effect decreased as the heat release rate of the fire source increased and increased significantly with the pressure of the water curtain and the number of rows. The smoke blocking effect was quantified using conservation of momentum by establishing a dimensionless parameter R to represent the ratio of water curtain momentum to smoke momentum, as well as the ratio of heat flux before and after the water curtain to represent the smoke blocking capacity delta of the water curtain. The smoke blockage rate delta ranges between 40 and 75%, and the smoke blockage rate increases as the momentum R increases. Finally, in tunnel fires, a predictive model for the attenuation of heat radiation by water curtains has been developed, providing theoretical support for the quantitative study of the smoke and thermal blockage effects of water curtains, which is beneficial to the protection of human life in confined spaces.

Effect of Installation Conditions of Water Mist Nozzle on Thermal Radiation Attenuation Performance

In this experimental study, the effect of installation conditions of a water mist nozzle on thermal radiation attenuation performance was investigated. Two types of nozzles (Small_nozzle and Large_nozzle) were used. Experiments were conducted under conditions in which the nozzle was installed near the heater and heat flux sensor (Position_NH and Position_NS, respectively), and water mist was discharged from one and two nozzles (Case_ID and Case_SD, respectively). To characterize the water mist spray, the water supply pressure and droplet size were measured, and visualization of the sprayed water mist was performed. The thermal radiation attenuation performance improved with an increase in the water flow rate, and Small_nozzle showed higher thermal radiation attenuation performance than Large_nozzle. Moreover, Case_SD showed lower thermal radiation attenuation performance than Case_ID_Sum (that is, the Sum of Case_ID & Position_NS and Case_ID & Position_NH) and the difference in thermal radiation attenuation performance between Case_SD and Case_ID_Sum at a higher water flow rate was more significant than that at a lower water flow rate. These might be attributed to the wide overlapping area of water mist discharged from two nozzles in Case_SD and at a higher water flow rate, narrowing the overall width of the water mist.

Experimental evaluation of individual effects of water mist spray characteristics on thermal radiation attenuation using twin‐fluid nozzles with full‐cone spray pattern

AbstractIn this study, the effects of water mist spray characteristics on thermal radiation attenuation were experimentally investigated using five types of external and internal mixing twin‐fluid nozzles with a full‐cone spray pattern. To the best of our knowledge, this may be the first attempt to experimentally examine the separate effects of water mist spray characteristics on thermal radiation attenuation. Water and air supply pressures were measured, and their values were 1.3–55.5 and 29.8–316 kPa, respectively. The Sauter mean diameter and volume median diameter of the water mist were measured to be 20–99 μm and 21–108 μm, respectively. The spray angle and width of the water mist were approximately 20° and 110 mm, respectively. The thermal radiation attenuation afforded by the water mist discharged from the twin‐fluid nozzle increased with increasing water and air flow rates and decreasing droplet sizes. Within the experimental range, the thermal radiation attenuation was approximately 6.9%–28.4%. Based on experimental data, the effects of the water flow rate and droplet size on thermal radiation attenuation were examined independently. The dependence of the thermal radiation attenuation on the droplet size was greater than that on the water flow rate.

Investigation on Effects of Water Mist Characteristics According to Axial Position on Thermal Radiation Attenuation Performance

In this study, the effects of water mist characteristics according to the axial position on thermal radiation attenuation performance were experimentally investigated using the single-fluid nozzle. Under the water flow rate conditions of 200∼350 g/min, the thermal radiation attenuation performance was measured at the axial position (i.e., downstream direction of water mist from nozzle exit) of 200∼1000 mm. In addition, during the discharge of water mist, the water supply pressure and droplet size of water mist were measured and the water mist was visualized. As a result, with an increase in the water flow rate, the thermal radiation attenuation performance was improved. Overall, the attenuation rate was measured to be 12.4∼30.1%. In the axial position of 200∼400 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was improved. This may be because the effect of improvement of the thermal radiation attenuation performance by an increase in the spray width is predominant over the effect of reduction in it by an increase in the droplet size. In addition, in the axial position of 400∼1000 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was reduced. This is because the droplet size of water mist increases and spray width is narrowed. Based on this study, it was confirmed that the water mist characteristics according to the axial position and thermal radiation attenuation performance are closely correlated.

Experimental Study on Thermal Radiation Attenuation Using Water Mist of Twin-fluid Atomizer

In this study, the thermal radiation attenuation performance of water mist was investigated using twin-fluid atomizers. The water and air flow rates of Small atomizer were 36~105 g/min and 10~30 L/min, whereas those of Large atomizer were 37~300 g/min and 20~60 L/min, respectively. In the present experimental range, the thermal radiation attenuation of Small atomizer and Large atomizer were 6.1~11.9% and 5.2~14.6%, respectively. With the increase in water and air flow rates, the thermal radiation attenuation increased, and under similar water and air flow rate conditions, Small atomizer showed higher thermal radiation attenuation than Large atomizer. Based on the present experimental data, it was found that the air (gas) discharge area is a potentially important factor in determining the thermal radiation attenuation performance. Additionally, through the analysis of thermal radiation attenuation per unit water flow rate, it was confirmed that the twin-fluid atomizer can result in higher thermal radiation attenuation than the single-fluid atomizer under the same water flow rate condition.

Measurement and calculation technology of temperature compensation of explosion flame based on infrared radiation

In testing explosion flame temperature with radiation thermometry, there is relatively great deviation of empirical value of flame emissivity from flame combustion mechanism. Meanwhile, the distance of measure point from the flame and ambient temperature and humidity also cause attenuation of thermal radiation to different extent, affecting the accuracy of measurement of explosion flame’s temperature. With focuses on foregoing two problems and based on atmospheric radiation theory and the law of optics propagation, a model of radiation path attenuation compensation was deduced in accordance with the functional relation among explosion flame’s radiance, digital output value of thermal imager and explosion flame’s temperature, followed by obtainment of relevant parameters i.e. system responsivity in the model from radiometric calibration of thermal imager; then, the applicability of the gray body hypothesis of TNT explosion flame was confirmed by analyzing the composition of the products of TNT explosion flame. Therefore, a function model of explosion flame’s dynamic average emissivity was deduced concerning onsite atmospheric transmittance, digital output value of thermal imager and explosion flame’s temperature measured by the colorimetric thermometer in accordance with the expression of explosion flame’s radiance; finally, based on the receiver function of thermal imager’s effective radiation, a joint temperature compensation evaluation method, which combines radiation path compensation and dynamic emissivity, was proposed for joint inversion of explosion flame’s temperature at the explosion site and the range of temperature error of inversion was obtained through comparison of measured result with explosion flame’s surface temperature measured by colorimetric thermometer. The test result suggests the error of explosion flame’s temperature measured with the proposed compensation model is reduced to 11.292%−59.077% from previous 55.699%−89.847% before compensation, thus effectively improving the accuracy of measurement of transient flame temperature of explosion at external field and providing a means for accurate infrared thermography-based evaluation of thermal effect in explosion field.

Examination on Effects of Spray Characteristics of Water Mist on Thermal Radiation Attenuation Using Fire Dynamics Simulator

In this study, numerical simulations to investigate the effects of the spray characteristics of water mist on thermal radiation attenuation were performed using fire dynamics simulator (FDS). The droplet size, flow rate, and spray angle of the water mist were 100-300 µm, 1-3 L/min, and 60-180°, respectively. As the droplet size decreased and flow rate increased, the thermal radiation attenuation increased. When the spray angles decreased and increased behind the near nozzle center and behind a certain remote distance from the nozzle center, respectively, the thermal radiation attenuation increased. The peak thermal radiation attenuation increased with decreases in droplet size and spray angle and an increase in flow rate, whereas the average thermal radiation attenuation increased with a decrease in droplet size and increases in flow rate and spray angle. Under the numerical simulation conditions of this study, the peak and average thermal radiation attenuations were significantly altered by the ratios of droplet size and flow rate and by that of flow rate, respectively. However, their variations with the ratio of spray angle were the smallest.

Numerical Study on the Attenuation Effect of Water Mist on Thermal Radiation

A numerical study was conducted to investigate the effects of the spray characteristics of water mist on the attenuation of thermal radiation. The attenuation process of the thermal radiation, generated from a hot surface panel, passing through the water mist was calculated via Fire Dynamics Simulator (FDS), and the effects of the flow rate, droplet mean diameter, and spray injecting angle of the water mist were analyzed. The results indicated that the increase in flowrate and decrease in droplet size led to an increase in the attenuation of thermal radiation. As the thermal radiation passed through the spray droplets, the effect of the spatial distribution of spray droplets was verified by calculating the thermal radiation attenuation at different spray injecting angles. The results indicated that the radiation attenuation increases as the spray angle increases. This implies that a wider distribution of spray droplets, irrespective of the droplet size and flowrate, increases the attenuation effect on thermal radiation.

Observations of Radiation‐Dominated Rapid Cooling of Structures Based on Carbon Nanotubes and Graphene

It is often desirable to cause rapid thermal cycles in isolated systems, and it is convenient to do so by means of radiant heating and cooling. In principle, the rate of heating is arbitrarily increased simply by applying sufficient irradiance. This is not true for cooling, wherein the radiant emittance of a surface is determined by its emissivity and temperature. In an optically thin structure, the cooling rate is determined by the ratio of the material's emissivity to its specific heat, a factor that is expected to be greater in materials with a short characteristic absorption length, such as graphite. Herein, several forms of carbon‐based nanostructures, which have very short thermal radiation attenuation lengths, and are very robust and can withstand the high temperatures required for substantial Planckian thermal radiant emittance, are examined. Rapid cooling times ranging from about 100 μs to 1 ms are observed in structures cooling from a typical high temperature of 1500 K to a low of roughly half that value. Such rapid extreme thermal cycling of isolated materials provides new opportunities, for both research and potentially practical applications.

Full-scale Experimental study on the suppression effect of water sprinkler system on energy saving building fire

In an energy saving building fire, the high temperature and pressure of the indoor smoke or flame break the window glass, and even forms ejecting fire that the flame spills out of the window. It is extremely dangers that the ejecting fire flame to the upper floor might contribute to the unpredicted hazard of the fire in energy saving building with amounts of insulation material. Therefore, the aim of this paper is proposing a method of protecting external windows based on the water sprinkler system. The system can suppress the spread of fire on the facade of the building, and prevent the formation of three-dimensional combustion of the building. This paper design and carried the two groups full-scale experiments to check the suppression effect of water spray system on the glass of the window under the different heat release rate (HRR) and thermal radiation from the fire. The conclusions describe the thermal radiation attenuation characteristics and temperature attenuation characteristics inside and outside the window. Consequently, we find that the sprinkler system can effectively protect the integrity of the glass and control the outdoor temperature within a safe range under the conditions of fire source power of 0.6 MW, 1.5 MW, and 3 MW. After the sprinkler system was turned on, the outdoor heat flux density rapidly decreased from a peak of 197 W/m2 and stabilized at 80 W/m2, which was 59% lower than the peak value. The research provides the deep insight into the temperature suppression phenomenon under the spray, and the protection method of ejecting fire for the external window is helpful to reduce the possibility of flashover in the indoor spray coverage. Due to the large range of heat release rates set in this paper, the experimental results provide a data reference for the fire protection design of future energy saving buildings.

Attenuation of thermal radiation through water mist

This article focuses on the interaction of thermal radiation with water droplets and the creation of water mist for the purpose of evaluating the decrease of heat flux when positioning a water curtain of various parameters between a radiation source and a radiometer. The change of water curtain parameters, affecting the passing through of thermal radiation, was performed using five nozzles with a variable spray characteristics. For the respective nozzles the attenuation of thermal radiation was determined and the thermal radiation transmittance was calculated. Water mist was created using a high‐pressure pump and nozzles with a different size of the orifice. The measurement of droplet size was performed using the time‐shift technique. The Omegalux radiant panel was used as the radiation source and the Hukseflux SBG01 radiometer with a working range of 0–5 kW.m−2 was used as the detector. © 2017 American Institute of Chemical Engineers Process Process Saf Prog 37:18–24, 2018

Radiative shielding effect due to different water sprays used in a real scale application

Thermal radiation attenuation is a well-known positive effect of water sprays applied to firefighting. It was studied here to quantify its real effect on the whole process of fire mitigation. For the demonstration, three different real scale spraying devices were used: a water mist nozzle operating at 85 bars, a sprinkler operating at low pressure (0.3 bars at the nozzle) and a sprinkler operating at a higher pressure (1.3 bars at the nozzle). The radiation attenuation was specifically studied, separately from other actions of the sprays on the fire, using an experimental configuration where water was injected between the radiation source and a detector, but not directly onto the actual fire. Hence, the radiation flux reduction could only be attributed to mixing of water droplets and smoke, not to any reduction in heat release due to water directly cooling the fire area nor to inerting effects occurring simultaneously. The flux was measured using an infrared device combining a Fourier transform infrared spectrometer and a multispectral infrared camera. Two radiative sources were used: a high-temperature blackbody for quantification of the radiation transmission with a calibrated source, and a 200 kW heptane pool fire for an application to a realistic radiation source involved in fires. When using a blackbody source for radiation generation, the radiation attenuation of the incident fluxes was 89% for the high-pressure water mist, 62% for the sprinkler at the higher operating pressure and 20% for the sprinkler at the lower pressure. These differences were easily explained by a sensitivity study conducted coupling the Mie theory for the prediction of droplet radiative properties to the Monte Carlo method for radiative transfer simulation. This showed the sensitivity of the radiation attenuation to droplet size and concentration. When the blackbody source was replaced by a pool fire, the flux reduction was even higher for the low pressure sprinkler, i.e. 45%, while being almost unchanged for the water mist. In the present configuration, where smoke stratification was observed before spray activation, this was mainly attributed to the fact that a mixing of droplets and smoke was produced in the measurement area due to the drag effect. The smoke and spray mixing resulted in a stronger attenuation capacity with the sprinkler device. This increased attenuation was not observed through the transmission data for the water mist, perhaps because of compensating effects related to evaporation and the surrounding temperature, or a smoke flow that was highly penalized by the spray activation.

Experimental and numerical study on attenuation of thermal radiation from large-scale pool fires by water mist curtain

Full-scale experiments and numerical simulations were conducted to study the thermal radiation attenuation from large fires by water mist curtain with low and intermediate pressures. Fire dynamics simulator (version 6) was used for numerical simulations. A novel multi-injector nozzle was designed to generate a homogeneous water mist curtain with low water consumption. Water mist characteristics of one of the injectors were measured by Shadowgraphy technology. A 1 × 1 m diesel pool fire was considered as the fire source. The experimental results show that the water mist curtain has high thermal radiation attenuation efficiency, for example, about 82.7% radiant heat flux could be attenuated by the water mist curtain with 2 MPa working pressure and flow rate of 13.3 L/min. Comparisons with the experimental results show that the calculated radiant heat flux and temperature are slightly underestimated.

Numerical Investigation on the Effectiveness of Water Spray Deluge in Providing Cooling, Smoke Dilution and Radiation Attenuation in Fires

The effectiveness of water spray is influenced by nozzle type, spray momentum and orientation as well as water droplet size. It is also subject to the influence of environment conditions, most notably wind condition in open fires and ventilation in enclosures. The present study is focused on the effect of such external parameters on the effectiveness of water spray systems when used as water curtains to provide cooling and smoke dilution; and create an “escape” corridor for crews on offshore oil and gas production facilities. In such applications, water spray is more frequently referred to as “water deluge”. A related study has also been carried out to investigate the attenuation of thermal radiation by water deluge on an oil tank fire. Overall the present study has led to some useful conclusions and demonstrated the potential of numerical modeling techniques as an effective means to aid the design of water curtains and surface water deluge systems.

Preliminary study on the suppression chemistry of water mists on poly(methyl methacrylate) flames

It is well-known that fire suppression by water mist is mainly based on physical effects such as heat extraction, oxygen displacement and attenuation of thermal radiation. However, the chemical effects of water mist on fire suppression are not yet clearly understood. As polymeric materials have been widely used in modern buildings, investigating the suppression chemistry of water mist on burning polymers is also important. The objective of this paper is to simulate the water sprays for fire extinction by a small-scale apparatus. Combustion products of poly(methyl methacrylate) (PMMA) in the surroundings with and without fine water mist were collected and analysed by gas chromatography (GC) and GC with mass spectrometry. The results showed that there exists a critical flow value of the water mist applied in the confined fire space. Complex products, such as aromatic compounds, were produced due to the interaction of water vapour with the PMMA flame.

SUPPRESSION CHEMISTRY OF WATER MISTS ON DIFFUSIONAL FLAMES

It is well-known that fire suppression by water mist is mainly based on physical effects such as heat extraction through evaporation, oxygen displacement, and attenuation of thermal radiation. However, there might be chemical inhibition effects which are not clearly understood. Chemical kinetics associated with the interaction of water with flames should be studied, but the reaction chemistry depends on the flame to be suppressed. It would be very interesting to investigate the suppression chemistry of water mist on burning different fuels of polymers. Suppression chemistry of water mist on diffusion flames from burning different fuels will be reviewed first. Homogeneous interaction of water with gas fuel in the combustion will then be discussed. Heterogeneous oxidation of carbon in the existence of water will be briefly introduced. The kinetics and mechanisms of selected reactions involving hydrogen (H), carbon monoxide (CO), carbon-based fuels (C), and small hydrocarbons such as methane (CH4) will also be discussed. Those are considered key combustion reactions which can provide useful information for understanding burning polymers. Note that polymeric materials have been widely used in modern buildings. Fire safety associated with burning plastics is a great concern. In such interaction reactions, water is taken as interacting with the flame by converting the oxygen (O) radicals to hydroxyl groups (OH). These products would have direct involvement in the water-gas reaction system by acting as efficient collision partners in the chemical kinetics of the combustion reactions.

DYNAMIC AND RADIATIVE ASPECTS OF FIRE–WATER MIST INTERACTIONS

A two-phase multiclass model is developed to describe the interaction between a compartment fire and a water mist. Turbulent combustion is modeled using the EBU-Ar coupled with the renormalization group k–ϵ turbulence model. A multiphase radiative transfer equation including the contributions of soot particles, combustion products and water droplets is used to model radiation. The model is applied first to a two-dimensional enclosure fire. A parametric study of the influence of water spray flow rate and water droplet diameter on fire mitigation is presented. Gas-phase cooling is found to be the main fire suppression mechanism. The influence of water spray on radiation is studied with special emphasis on the contribution of each radiative phenomenon. Results demonstrated that the attenuation of radiation by the water spray is two-fold: the radiant energy emitted by the flame is reduced and this energy is attenuated by water droplets. The role of droplet scattering in the attenuation of thermal radiation in fire–water mist interactions is clearly demonstrated. For the droplet diameters considered, it is found that there are two distinct regimes: a fire extinction regime and a fire enhanced regime. This finding is consistent with previous experiments. Applied to a three-dimensional fire-sprinkler scenario, the model predictions are in good agreement with experimental data.