Temperature Decay Profile Research Articles

Flame extension length and temperature profile beneath ceiling induced by endwall-attached fire inside compartment with lateral openings

This study experimentally investigated the fire characteristics of endwall-attached fire within the long-narrow compartment, including the flame extension and temperature profile. Experiments were conducted in a reduced scaled compartment featuring multiple lateral openings. Results show that the previous models of flame extension length and temperature rise in the literatures, whether for sidewall fires in tunnels or central fires in compartments with lateral openings, cannot predict the experimental data in this study. A new correlation is proposed for the flame extension length based on non-dimensional heat release rate. The longitudinal temperature profile generated by endwall-attached fires in compartment can be classified into three distinct regions related to the position of the lateral opening: temperature rapid decrease region, temperature slow decrease region, and backflow region at the end of the compartment. A model for the maximum temperature rise and a piecewise equation based on single exponential function for temperature decay profile are proposed, and these equations effectively correlate the experimental data. The findings of this study can deepen the understanding of fire dynamics within similar building structures and have value for the fire hazard assessment.

Experimental study on the temperature distribution of impingement flow in a double slope roof generated by jet fire

The double slope roof is a commonly used building structure due to its adequate drainage and stable structural features. The thermal impinging on the double slope roof generated by the jet fire caused many casualties and property damage, whose thermal hazard has not been quantified in literatures. The temperature distribution at different source-ridge heights (H), heat release rates (HRR), and roof angle (θ) was measured in the experiment, with a total of 125 sets of experimental conditions. Results show that the ceiling maximum temperature rise increases with the roof angle decreases. A maximum temperature rise prediction model was established based on the analysis of the free plume length beneath the roof, which considering the effect of θ. Moreover, the model's accuracy was validated by comparing previous experimental data. The mean deviation between the proposed model and the experimental results is less than 5.7 %. The rate of temperature decay beneath the ridge decreased as the θ decreased. When the H is smaller, and the HRR is larger, the influence of the θ on the temperature decay profile is more significant. A new correlation has been proposed to correlate the temperature decay profile of a double slope roof with different θ by introducing flame extension length to modify the characteristic radius b. The model prediction agreed well with the experimental data, with a maximum error of around 20 %. New findings are helpful in guiding the building fire prevention and detection design.

Experimental study of temperature profile in underground corridor of various widths induced by fire in an adjacent compartment

Corridor-compartment fire, i.e., fire plume ejected through the door of the compartment and spread along the adjacent corridor, is a fundamental scientific problem in underground space, which is very important for the evacuation and firefighting. Nevertheless, the relevant studies are still very limited for quantifying the temperature evolutions inside the compartment as well as the corridor ceiling flow induced by corridor-compartment fire scenarios for various compartment door sizes and corridor widths. In the present study, a reduced-scale corridor-compartment experimental model was established, with four opening (door) sizes and eight corridor widths considered. The fuel burning mass loss rate (or instantaneous HRR) and the temperature profile inside the compartment and corridor were measured and analyzed. Results show that: (1) A non-dimensional correlation of the upper-part temperature rise inside the compartment could be found for various opening sizes and corridor widths in over-ventilated and under-ventilated condition, respectively. (2) The temperatures of the ceiling flow at the corner between corridor wall and corridor ceiling increases slowly before over-ventilated and then increases significantly after reaching under-ventilated condition with fire growth, it decreases significantly with the corridor width increasing, due to the change of ventilation condition. A non-dimensional model which considering the effect of corridor width for different opening sizes is proposed for the temperature decay profile of ceiling flow at the corner between corridor wall and corridor ceiling. This model could predict the temperature in underground corridor of various widths induced by a fire in an adjacent compartment, and then analyze and assess the fire thermal hazard on the compartment and corridor.

Performance of ceiling jet induced by dual unequal strong plumes in a naturally ventilated tunnel

• Thermal property of two unequal flames in a naturally ventilated tunnel is studied. • Temperatures induced by the small plume decay faster than that of the large plume. • A new model for maximum ceiling temperature of two unequal plumes is proposed. • Correlations for ceiling temperature decay profiles of dual plumes are developed. The catastrophic tunnel fire accidents are usually accompanied with multi-source burning. Ceiling gas temperature in tunnel is an important parameter in monitoring the daily operation process and unexpected combustion process. Previous studies are mainly focused on single fire or multiple equal fires in tunnel, while multiple unequal fires burning is common in real tunnel fires. Till now, the law of asymmetrical temperature distribution of multi-source below a ceiling is unknown. This paper aims to experimentally study the thermal performance of two unequal fire sources of propane in a naturally ventilated tunnel. A total of 90 experimental tests were conducted. The side lengths of two burners are fixed at 10 cm and 15 cm. The heat release rate (HRR) of each burner are changed with the HRRs ratio of 1–6. And the spacing between two sources along the longitudinal centerline of tunnel varied from 0–45 cm. Analysis shows that there is only one peak temperature with small spacings, while two peak temperatures appear with large spacings. Then the impingement point position and the maximum ceiling gas temperature of each burner are illustrated. The force analysis is adopted to explain the variation of impingement point position. A parameter α is innovatively introduced to characterize the promoting effect of spacing on maximum temperature at small spacings. Then a new normalized HRR is proposed to establish a unified model for the unequal maximum temperature rises below the ceiling of both sources, which indicates that the maximum temperature rise increases with the normalized HRR and then it maintains at 754 K. By introducing the plume radius, models for asymmetrical temperature decay profiles on both sides of two plumes below the ceiling are proposed, which shows that the temperature in the upstream of the small burner decays faster than that in the downstream of the large burner. The proposed models for maximum temperature and temperature decay profiles can be used to predict the ceiling gas temperatures of two unequal fires in tunnel.

Experimental study on temperature profile in long-narrow compartment fire with multiple lateral openings

The openings of a compartment under fire condition are very important to exhaust the hot smoke. However, the related impacts on the indoor environment are still not clear so far to guide future designs. Experiments were then conducted using a model long-narrow compartment with multiple lateral openings. The temperature inside the compartment and the temperature profile underneath the ceiling were investigated and compared with the predict ions of those previous models. Experimental results show that the lateral opening conditions mainly affect the temperature near the fire source, and this effect does not follow a single pattern with the change of the number of lateral openings. Keeping the openings near the fire source closed and symmetrically opening the openings away from the fire source can expand the fire hazard, while asymmetrically opening the openings on the side of the fire source can effectively reduce the temperature caused by the fire. The classic models for predicting the maximum temperature rise based on the confined space with open ends underestimate the experimental data in this work. An empirical model considering various fire sizes was developed to predict the temperature decay profile underneath the ceiling. The critical dimensionless distance and the attenuation index of the attenuation zone are both related to the convective heat release rate, showing power and linear functions, respectively. These findings and results can provide reference for the fire risk assessment of a long-narrow compartment with multiple lateral openings.

Heat diffusion imaging: In-plane thermal conductivity measurement of thin films in a broad temperature range.

This work combines the principles of the heat spreader method and the imaging capability of the thermoreflectance measurements to measure the in-plane thermal conductivity of thin films without the requirement of film suspension or multiple thermometer deposition. We refer to this hybrid technique as heat diffusion imaging. The thermoreflectance imaging system provides a temperature distribution map across the film surface. The in-plane thermal conductivity can be extracted from the temperature decay profile. By coupling the system with a cryostat, we were able to conduct measurements from 40 K to 400 K. Silicon thin film samples with and without periodic holes were measured and compared with in-plane time-domain thermoreflectance measurements and literature data as validation for heat diffusion imaging.

Temperature profile of thermal flow underneath an inclined ceiling induced by a wall-attached fire

The present study for the first time investigates the temperature profile of thermal flows underneath an inclined ceiling induced by a wall-attached fire plume. This kind of thermal flow configuration could happen practically when a fire occurs near the wall of a building with inclined roof, however, has not been quantified in the past. Experiments were conducted in this study employing a square burner attached to the wall as the fire source. The fire plumes rise up along the wall and impinged upon an inclined ceiling. The temperature profiles in the direction normal to the intersection line of the wall and the ceiling were measured for various fire source heat release rates, source-ceiling heights and ceiling inclination angles. Results showed that the inclination angle of the ceiling has no considerable effect on the maximum temperature rise (above ambient) underneath the ceiling in the fire plume impingement zone. However, for the outer-impingement zone, the temperature rise at a given distance from the impingement zone increased with the increasing of the ceiling inclination angle. The effect of the ceiling inclination angle on the temperature decay profile is more significant for smaller source-ceiling height and larger heat release rate. When the ceiling inclination angles were positive, the temperature rise becomes close to each other with the increasing of the distance from the fire plume impingement zone. While as the ceiling inclination angles were negative, the temperature rise decreased sharply along the ceiling and become much smaller than that of the positive inclination angle. A correlation was proposed for the maximum temperature rise underneath the ceiling based on the continuity in the fire plume impingement zone. And the temperature decay profiles for various ceiling inclination angles were described well by a formula proposed to include the effect of the inclined ceiling.

Temperature profile and flame extension length of a ceiling impinging round jet fire in an inclined tunnel

Ceiling jet fire may popularly occur due to gas fuel leakage caused by corrosion of the pipeline in underground galleries or other accidental factors, and usually inflict major heat hazards and related risks. So the characteristics of a ceiling impinging flow induced by a jet fire in an inclined tunnel are valuable to be investigated. Therefore, the temperature profile and flame extension length along an inclined tunnel ceiling in upward and downward directions under different initial fuel momentums and tunnel inclination angles are obtained and analysed. The results show that the flame extension length in both directions along the ceiling can be correlated with flame free height, inclination angles and height between the fire source and ceiling accounting for the non-symmetrical distribution of un-burnt fuel after impingement. Furthermore, the temperature profile of the ceiling jet is obviously affected by the source initial momentum comparing to the flames with negligible initial momentum. New correlations for predicting the temperature decay profiles are proposed considering the source Froude number and inclination angles. The results of this paper would be valuable for modelling of a ceiling jet fire in inclined tunnel or providing significant guidance/raw data for protection and risk assessment of such fire scenarios.

Experimental study on horizontal gas temperature distribution of two propane diffusion flames impinging on an unconfined ceiling

Ceiling gas temperature is one of the most important factors for heat detection and alarm once an undesirable fire along with releasing hot and toxic smoke is erupted in a building. The impinging flame characterized by the unburnt fuel burning along the ceiling has received much attention in recent years as it poses a greater threat to the ceiling structure, devices and trapped people than the non-impinging flame. Many studies have been focused on the ceiling gas temperature induced by a single flame, while little effort has been put with respect to the multiple flames. The interaction between multiple flames might lead to flames tilt to each other and even merge together with small spacings, resulting in different ceiling gas temperature distribution from the single flame. The aim of this experimental work is to investigate the ceiling gas temperature decay profile induced by two impinging flames. Propane was used as the fuel. The heat release rate (HRR), burner edge spacing and ceiling height above the fuel were overall changed. The ceiling gas temperatures along the direction of changing spacing were measured to determine the impingement point position and temperature decay profile. The results showed that the impingement point position is dependent on the HRR and the spacing as well as the ceiling height, while the maximum gas temperature is weakly affected by the spacing. The established correlation reveals that the maximum excess temperature increases first and then maintains unchanged with increasing the HRR normalized by the ceiling height. The plume radius proposed for the single impinging flame is not enough to characterize the ceiling gas temperature of two impinging flames. A new correlation for temperature decay profile induced by two impinging flames is therefore proposed and validated using the experimental results.

Temperature profile beneath an inclined ceiling induced by plume impingement of gas fuel jet flame

Temperature profile of thermal impingement flow beneath sloped ceiling induced by non-isotropic gaseous fuel jet flame has not been studied before and therefore no data are available in the literatures. Experiments were carried out in this work to measure the temperature distribution in both upward and downward directions beneath the inclined ceiling induced by gaseous fuel jet flame. Different inclination angles, various heat release rates and diverse source-plate heights were considered. Results show that the influence of inclination angle has opposite impacts on the temperature rise for upward flow and downward flow respectively and burner dimension has little effect on the temperature attenuation characteristics while the inclined direction is perpendicular to long side of fire source. The experimental data were compared with correlations predicted by predecessors’ researches and it was observed that the experiment data of upward were consistent with the former correlations while an apparent discrepancy can be found along the downward direction. The influence of buoyancy component force parallel to inclined ceiling was discussed and simply reflected by the cosine value of inclination angle. New relatively uniform correlations were proposed to predict the temperature decay profiles by combing the effects of heat release rates, inclination angles and source-ceiling heights.

The effect of liner design and materials selection on prosthesis interface heat dissipation.

Thermal discomfort often affects prosthesis wearers and could be addressed by increasing liner thermal conductivity. This note explores a liner made from thermally conductive silicone and two additional alternative liner designs. Thermally conductive silicone was used to create a conductive liner and a hybrid liner. Additionally, one with open elements was made. These were compared with a plain silicone liner and a no liner scenario. Scaled down liner prototypes were used due to the high-cost of the thermally conductive silicone. Temperature decay profiles were collected by attaching thermistors to a heated liner phantom and used to evaluate scenarios. No scenario performed much better than the plain silicone liner. Implementation of passive solutions may be easier, but alternative liner materials are unlikely to affect dissipation enough to address thermal discomfort. Based on this work, future research efforts may be better spent developing active thermal discomfort solutions. Clinical relevance Thermal discomfort can increase the probability of skin damage, reduce prosthesis satisfaction and, ultimately, the quality of life. The prosthesis-wearing experience could be improved if thermal discomfort can be addressed by technological improvements.

Experimental study on ceiling temperature profile of sidewall fires at reduced pressure in an aircraft cargo compartment

Knowledge about the coupling effects of reduced pressure and sidewall restriction on ceiling temperature profile is crucial for the fire detection system of an aircraft cargo compartment. N-heptane fire tests at three places (floor center, flush with one sidewall, compartment corner) were conducted in a full scale simulated aircraft cargo compartment at 100kPa, 90kPa, 80kPa and 70kPa, since the pressure within an actual aircraft cargo compartment ranges from 100kPa at the sea level to 70kPa at the cruising altitude. Results show that due to the sidewall restriction and reduced pressure, less air entrainment into the flame results in higher maximum ceiling temperature. While ceiling temperature decay profile attenuates faster at reduced pressure and is little affected by sidewall restriction. A uniform correlation of maximum ceiling temperature considering reduced pressure and sidewall restriction is obtained by the introduction of air entrainment ratio Cα and modified mirror model coefficient. The classical correlations of Alpert, Heskestad and Delichatsios for the ceiling temperature decay profile are modified similarly to be extended to sidewall fires at reduced pressure and compared with results showing more accurate predicted results by Heskestad and Delichatsios’ method.

Quantitative Schlieren Measurement of Explosively‐Driven Shock Wave Density, Temperature, and Pressure Profiles

AbstractShock waves produced from the detonation of laboratory‐scale explosive charges are characterized using high‐speed, quantitative schlieren imaging. This imaging allows the refractive index gradient field to be measured and converted to a density field using an Abel deconvolution. The density field is used in conjunction with simultaneous piezoelectric pressure measurements to determine the shock wave temperature decay profile. Alternatively, the shock wave pressure decay profile can be estimated by assuming the shape of the temperature decay. Results are presented for two explosive sources. The results demonstrate the ability to measure both temperature and pressure decay profiles optically for spherical shock waves that have detached from the driving explosion product gases.

Experiment investigation on the influence of low pressure on ceiling temperature profile in aircraft cargo compartment fires

The objective of the present study is to evaluate the low pressure effects on ceiling temperature profile in aircraft cargo compartment fires, which will affect the activation of fire detectors. A Series of fire tests were carried out in a full scale simulated aircraft cargo compartment at four atmospheric pressures (100 kPa, 90 kPa, 80 kPa and 70 kPa) corresponding to the pressure within an actual aircraft cargo compartment from the sea level to the cruising altitude (about 10,000 m). Results show that the maximum ceiling temperature increases and the ceiling temperature decays faster as ambient pressure reduces. The air entrainment ratio Cα is proposed in the correlation to predict the maximum ceiling temperature based on previous plume theory, considering the low pressure effect and entrainment coefficient. Meanwhile, modified by the air entrainment ratio Cα, the previous classic correlations established by Alpert, Heskestad and Delichatsios for the ceiling temperature decay profile are further extended to low pressure conditions. The results based on Heskestad and Delichatsios method are more accurate than that of Alpert method in the experiments. All these findings would provide theoretical basis for the design of fire detection system in the aircraft cargo compartment.

Flame extension length and temperature profile in thermal impinging flow of buoyant round jet upon a horizontal plate

This paper investigates the flame extension length and temperature profile in a thermal impinging flow, induced by a buoyant turbulent round jet impingement upon a horizontal plate, focusing on the scenarios that flame heights are comparable to or larger than plate-source height. Results show that the measured flame extension lengths in this work with a wider range [(Hf−H)/D from 0 to 14.5] can be still well approached by the You and Faeth's correlation obtained from limited data range [(Hf−H)/D from 0 to 5.8]. New correlations to predict the flame extension length are also developed based on physically the unburnt fuel (at impingement) estimation with cylindrical- or ellipse flame shape hypothesis. The change of maximum temperature at the impingement zone along with plate-source height is found to be well described by a three-regime law. A new correlation is proposed, with modified characteristic plume radius, to collapse the horizontal temperature decay profile with Hf/H up to 4.13.

Optically measured explosive impulse

An experimental technique is investigated to optically measure the explosive impulse produced by laboratory-scale spherical charges detonated in air. Explosive impulse has historically been calculated from temporal pressure measurements obtained via piezoelectric transducers. The presented technique instead combines schlieren flow visualization and high-speed digital imaging to optically measure explosive impulse. Prior to an explosive event, schlieren system calibration is performed using known light-ray refractions and resulting digital image intensities. Explosive charges are detonated in the test section of a schlieren system and imaged by a high-speed digital camera in pseudo-streak mode. Spatiotemporal schlieren intensity maps are converted using an Abel deconvolution, Rankine-Hugoniot jump equations, ideal gas law, triangular temperature decay profile, and Schardin’s standard photometric technique to yield spatiotemporal pressure maps. Temporal integration of individual pixel pressure profiles over the positive pressure duration of the shock wave yields the explosive impulse generated for a given radial standoff. Calculated explosive impulses are shown to exhibit good agreement between optically derived values and pencil gage pressure transducers.

Modelling transport phenomena and epitaxial behaviours of cluster–surface collisions viamolecular dynamics simulations

This paper studies the transport phenomena of disordered systems in the thermalrelaxation process by cluster impact on a solid surface. Constant-temperaturemolecular dynamics simulations were applied for nanoscale modelling. The surfacewetting and epitaxial behaviours of deposited clusters with various flow and internalkinetic energy were investigated. This revealed that the internal temperature ofclusters enhanced the lateral activity of atoms, while normal incident energy wasrelated to atomic implantation. By exchanging momentum and energy from thesystem to a heat sink with constant temperature, the collision system reachedthermal equilibrium after a long enough simulation time. The temperature decayprofiles of the system were presented as an exponential-type function, which isdependent on the efficiency of the cooling model and the heat conductivity of thematerial. Finally, the nanostructure growth mechanism by cluster deposition wasstudied. It showed that both epitaxial film and voids were constructed by thecluster–island and island–island collision mechanism, which was dependent on the incidentenergy of the cluster and the surface temperature. As a dynamic behaviour of ananostructure with a non-zero momentum of its mass centre, the rocking phenomenonwas presented as an important characteristic of thin films by cluster deposition.