Convective Heat Release Rate Research Articles

A Numerical Study on the Estimation of Heat Release Rate Based on the Flow Field through the Doorway

The present study has been conducted to examine the possibility of estimation of heat release rate using opening flow in the real structure fire. As a preliminary study to quantify the heat release rate based on the flow field through the opening, a series of CFD calculation for the ISO-9705 room has been performed and compared with experiments. Prior to the full numerical simulation, the grid independence test was performed to optimize the mesh size, and then the doorway flow calculated by the CFD analysis is compared with the PIV and bi-directional probe measurement. The chemical and convective heat release rate was obtained by integration of individual cell value through the doorway and the chemical heat release rate by the CFD model was well matched with the nominal heat release rate within 8 %. The convective heat release rate through the doorway shows reasonable agreement with the nominal heat release rate having maximum discrepancy of 20 % with considering the heat loss effect. In this matter, this work improves our understanding of heat release rate measurement in real structure fire.

Transient Ceiling Jet Temperature and Velocity Profiles in the Presence of an Upper Layer: Comparison with Predictions by LAVENT and JET Computer Fire Models

Results of a scaled experimental study are compared with the predictions produced by the LAVENT and JET computer fire models. As in most large-scale fire testing, characterization of heat release rate (HRR) and accuracy of its measurement creates a lot of uncertainty for validation of these codes. Sensitivity of LAVENT results to the assumed radiative loss of 35% is examined by varying the total HRR which corresponds to varying the convective HRR. Comparisons show that LAVENT uses the wall-jet theory at its core for prediction of the ceiling jet flow and thus does not capture the ceiling jet profile well and overpredicts the upper layer temperature during the development of the layer. The velocity is generally overpredicted since the retardation of the jet momentum by the upper layer does not seem to be modeled accurately. JET has a better user interface and slightly different parameters, but does not provide ceiling jet profiles. The major difference between JET and LAVENT include the ceiling jet temperature and velocity algorithms, the fusible link algorithms, and the use of a variable radiative fraction as a function of fire size and type.

Assessment of Commodity Classification for Sprinkler Protection Using Representative Fuels

In order to assess the classification of commodities for sprinkler protection, fire suppression tests were conducted using representative fuels. The measured heat release rates and applied water fluxes are used to calculate the critical delivered flux (CDF) and develop a suppression correlation for each tested commodity. The heat release rate (HRR) measurements together with the CDF calculations show that the CDF can be obtained within an uncertainty of ±3 mm/min. The CDF values are then combined with the measured convective HRR to project the critical sprinkler discharge flux (SDF) – the minimum water flux above which the fire will be controlled. Comparison of SDF values and full-scale sprinkler test results shows that the SDF is a reasonable choice for ranking commodities. Examination of the calculated CDF values using the suppression correlations suggests that the ranking remains the same for various fuel array heights. Furthermore, the responses to suppression by the exposed plastics are very different from those of the cartoned fuels, indicating that these two types of commodities require different treatment.

Comparison of flammability measurements in vertical and horizontal exhaust duct in the ASTM E‐2058 fire propagation apparatus

AbstractThe ASTM E‐2058 fire propagation apparatus (FPA) is capable of measuring time to ignition, chemical and convective heat release rates, mass loss rate, smoke generation rate, generation rates of CO, CO2 and O2 consumption rate, effective (chemical) heat of combustion and vertical fire propagation of materials. The original design of the FPA incorporated a vertical exhaust system with the measurement section finishing about 3.5 m from the floor. The exhaust measuring duct of the new FPA is horizontally oriented to enable its use in a wider range of laboratory environments. In this paper, the functionality of the new FPA was compared with the original FPA. The measurements and results indicate that the performance of the new FPA is equivalent to the original FPA. Copyright © 2003 John Wiley & Sons, Ltd.

Effects Of Flue Spaces On The Initial In-rack Plume Flow

This paper describes the effects of the vertical flue space (gap) on the convective Heat Release Rate (HRR) and the in-rack plume flow in rack storage fires. Four large-scale tests with Standard Class II commodity, which consists of double triwall corrugated board cartons, were carried out with vertical flue spaces of 75 mm, 150 mm, 225 mm and 300 mm. Measurements of convective HRR per height of the rack storage, in-rack flame height, centreline excess gas temperature, centreline gas velocity and in-rack temperature profiles are presented. The objective of the study was to compare the results of the four full-scale rack storage tests to the results of the 1:3 model-scale tests and one large-scale test carried out in an earlier study

Plume flow in high rack storages

A theoretical and experimental study of rack storage fires is presented. Free-burn tests with multiple-wall corrugated paper cartons were carried out in reduced scale and in large scale. The in-rack flame height, excess centreline gas temperature and gas velocity were plotted using axi-symmetric quasi-steady state power law correlations. The correlations include overall convective heat release rate, vertical flue width, height above the floor and height of virtual origin. The correlations obtained can be used to predict activation times of in-rack sprinklers and they can be incorporated into engineering models designed to predict flame spread and fire growth in storage geometries. The study shows that it is possible to reproduce flow conditions and flame heights in different scales which is of practical importance since all large scale testing with high rack storages is very expensive.

In-Rack Fire Plumes

A theoretical and experimental study of in-rack fire plumes in a combustible rack storage is presented. The commodity used in the experiments consisted of multiple-wall corrugated paper cartons equally separated in a steel rack, two cartons wide, two cartons deep and four cartons high. Free-bum tests were carried out mostly in reduced scale with verification in full scale. The centreline in-rack gas temperatures and velocities were measured at four elevations inside the rack storage and the heat release rate was measured above the rack storage with a hood system. In-rack temperatures and velocities are plotted using theoretically obtained quasi-steady correlations assuming a point source of buoyancy at floor level and entrainment only in the vertical flues. The theoretical correlations include convective heat release rate, vertical flue width and height above the floor. Temperatures for both reduced scale and full scale correlate reasonably well with the theoretically obtained relationships which have the same functional form as convective plume flow above a linear fire source (line plume). In order to obtain similar correspondance for the velocity in the two scales it was necessary to use Froude number scaling with storage height as length scale. The storage arrangement is found to be important for the initial flame spread and fire growth rate. The reduced scale study shows that the initial fire growth rate decreases with increasing vertical gaps (flues) and that the vertical and lateral flame spread rate increase when the lateral flue height increases. For the initial in-rack fire growth rate, the convective heat release rate was found to be better described by an exponential function rather than a power-law dependence on time to the third power.

熱伝達率と発熱速度及び区画規模との関係 : 小規模区画における火災初期の対流熱伝達 その2

熱伝達率と発熱速度及び区画規模との関係 : 小規模区画における火災初期の対流熱伝達 その2

Thermal sensitivity limits of residential sprinklers

The effect of thermal sensitivity parameters on room tenability and heat release rate at first sprinkler actuation was investigated for sprinklers installed at a 3·66 m spacing in a living-room fire scenario. The thermal response was modeled using the response time index (RTI), the conduction factor (C) and the sprinkler actuation temperature. Actuation times of a bulb and a solder type of residential sprinkler were obtained in a living-room fire test in which there was no water discharge from the sprinklers. The bulb and solder models were installed at three different locations within the enclosure to verify the predictive capabilities of the response model. The living-room scenario was the same as that used to develop approval criteria for residential sprinklers in the USA. Gas velocities and temperatures in the vicinity of the sprinklers were obtained during the fire test. The sprinkler actuation times were predicted from the experimentally obtained ceiling flows. The predictions were in excellent agreement with the observed actuation times. Measurements of the gas temperature at the 1·5 m level in the room center and mass loss of a burning chair, the primary combustible in the living-room fire scenario, were also obtained as a function of time. These measurements, in conjunction with predicted actuation times for varying values of RTI and C, allowed the effect of RTI and C on room tenability and heat release rate at the time of sprinkler actuation to be predicted for a sprinkler installed at a 3·66 m spacing. The results indicate that sprinklers of the ‘fast response’ type will actuate in the living-room scenario while gas temperatures at the 1·5 m level are near ambient and before the convective heat release rate of the burning chair in the living-room fire exceeds 130 kW.

Fire behavior of polymethylmethacrylate

A comprehensive study on the flammability, flame spread, and flame extinction behaviors of polymethylmethacrylate slabs and cylinders is presented. These behaviors have been quantified simultaneously for the first time in the Factory Mutual Research Corporation's 50 kW-Scale Flammability Apparatus. All experimental data show good agreement with the literature. A new technique has been developed to calculate pyrolysis height and flame spread rate from chemical and convective heat release rates. The calculated flame spread rate conveniently provides more information than obtained from the conventional methods. Flame spread behavior is found to be accelerating for upward spread and nonaccelerating for downward spread. Flame spread rate increases with increase in the oxygen mass fraction. Surface regression rates for upward and downward flame spread are negligible compared to the flame spread rates. Flame height is proportional to the pyrolysis height to the 2 3 power; ratio of flame height to pyrolysis height is proportional to the Froude number to the 2 3 power, and the flame height is proportional to the 2 3 power of the chemical heat release rate, in agreement with the literature. The study suggests that it is possible to use conventional flammability apparatus to simultaneously determine flame spread rate, heat release rate, and generation rates of material vapors and chemical compounds. It is our hope that this study will generate further research interest and standardized test apparatus and procedures will be developed.

Volume expansion pressures and global heat transfer in compartment fires

Volume expansion pressures generated by fire must be considered in designing smoke control systems. These pressures depend primarily on the heat deposition rate by the fire in the gas phase as well as enthalpy and mass exchanges with the surroundings through openings in the enclosure. This paper describes systematic experiments with fires in enclosures, vented through apertures near the floor which exchanged insignificant enthalpy flux with the outside. The heat deposition rate, expressed as a fraction of the total convective heat release rate in freeburn, γ c , was determined as a function of time in t-square fires (in which the heat release rate increases with the square of time) based on measurements of volume expansion pressures in the enclosures. Full scale experiments using several different fire growth rates were augmented with extensive experiments in one-quarter scale models, following verification of the scaling method. The major experimental phase simulated fires in rooms with floor areas of 10 m×10 m, 15 m×15 m and 15 m×29 m and ceiling heights of 2.4, 3.7, 4.9 and 10 m, using both methane (clean burning) and propylene (very smokey) burners. Heat deposition fractions were found to correlate well according to γ c =fn( t 2c * ), where t 2c * is a nondimensional time proportional to t/(t gc 2/5 H 4/5 ) for a fixed environment ( t being the time from ignition, t gc the growth time to a fixed freeburn convective heat release rate, and H the ceiling height above the fire source). Values of γ c were near unity at small t 2c * , decreasing to approximately 0.2 at the highest values of t 2c * investigated.

Predicting the Suppression Capability of Quick Response Sprinklers in a Light Hazard Scenario: PART 1: Fire Growth and Required Delivered Density (RDD) Measurements

Fire growth and Required Delivered Density measurements were obtained for a vinyl-cov ered reclining chair as part of a program to evaluate the Actual Delivered Density (ADD)/Required Delivered Density (RDD) approach to suppression prediction for quick response sprinklers in a light hazard scenario. In two tests, chemical and convective heat release rates of the burning chair were obtained from a fire products collector, while the radiative heat release rate was measured using a heat flux gauge.The average maximum chemical heat release rate was 1.5 MW (85,000 Btu/min) with the convective fraction being 56%. The average growth time of the fire, assuming a second power growth curve (t2), was 100 s. The RDD of the chair was determined by measuring the effect of water application on the convective heat release rate of the chair. Nominal application densities of 2.4, 3.7, 6.1 and 8.6 mm/min (0.06, 0.09, 0.15, and 0.21 gpm/ft2) were applied over a convective heat release rate range of 100 to 450 kW (5700 to 25,...

The Transient Ceiling Flows Of Growing Rack Storage Fires

Transient ceiling flows induced by growing rack storage fire were investigated in the period where the convective heat release rates produced by these fires had a power-law dependence on time to the third power. Empirical correlations for the ,maximum excess gas temperature, maximum gas velocity, temperature profile depth, and velocity profile depth of the transient ceiling flow were established in terms of a normalized convective heat release rate of the fire and a normalized radial distance from the fire axis.

Predicting the Suppression Capability of Quick Response Sprinklers in a Light Hazard Scenario: PART 2: Actual Delivered Density (ADD) Measurements and Full-Scale Fire Tests

An apparatus to determine the Actual Delivered Density (ADD) of quick response and resi dential sprinklers under light hazard conditions was constructed and calibrated. The plume of a burning chair at different stages of fire development was simulated by the apparatus using five convective heat release rates: 110, 160, 250, 300 and 390 kW (6300, 9100, 14,200, 17,100, and 22,200 Btu/min). The ADD as a function of the convective heat release rate was determined for a residential sprinkler at ceiling heights ranging from 2.4 m to 4.6 m (8 ft to 15 ft). ADDs were obtained for single and multiple sprinklers installed using a 3.6 m x 3.6 m (12 ft x 12 ft ) spacing. The ADD of a 12.7 mm (1/2 in.) orifice, quick response sprinkler was determined for a single sprinkler directly over the ADD appa ratus at a ceiling height of 3 m (10 ft). Previously reported Required Delivered Density (RDD) measurements for the reclining chair allowed suppression predictions to be made. Seven full-scale fire tests were conducted to ...

Fire Induced Flow Under A Sloped Ceiling

A series of fire tests was conducted under a smooth ceiling to investigate the ceiling gas flow as affected by ceiling slope, convective heat release rate of the fire and clearance between the fuel top surface and the ceiling. Besides a horizontal ceiling reference, three ceiling slopes were investigated: lo0, 20' and 30'. Pool fires were used as f i r e sources. Two pool diameters, two different fuels (heptane and methanol) and three ceiling clearances were used. In each test, measurements were made of ceiling gas temperatures, ceiling gas velocities, and fuel mass loss. Empirical correlations for the near-maximum gas velocity and excess temperature of the ceiling flow along the steepest run were established in terms of ceiling slope, radius from the point of intersection of the ceiling with the pool centerline, and characteristics of the undeflected plume at the ceiling level. The ceiling slope had a more pronounced effect on velocity variation along the steepest run than on temperature variation. In the upward direction, the rate of velocity decrease with radius was reduced significantly as the ceiling slope increased. In the downward direction, at a certain distance from the pool centerline, the flow separated from the ceiling and turned upward. The larger the ceiling slope, the sooner the turning occurred. Furthermore, the rate a t which gas temperature approached ambient i n the downward direction increased with ceiling slope, while the temperature decrease in the upward direction was not much affected by change of ceiling slope.

Transient Plume Influence in Measurement of Convective Heat Release Rates of Fast-Growing Fires Using a Large-Scale Fire Products Collector

A theory for strongly buoyant transient plumes was used to determine whether the convective heat flow measured by a large-scale Fire Products Collector (FPC) could approximate the instantaneous convective heat release rate generated by fast-growing fires. The theory was confirmed by the plume data of rack storage fires obtained in this study. The theory provides a scheme for deriving the convective heat release rate generated at the fire source from the convective heat flow measured by the FPC.

Heat release rates from samples of polymethlmethacrylate and polystyrene burning in normal air

AbstractResults are presented for mass generation rates of major combustion products (CO2, CO, total hydrocarbons and smoke particulates) and heat release rates from samples of polymethylmethacrylate and polystyrene burning in normal air under varying magnitudes of externally applied radiant heat flux. In the experiments mass generation rates of products and convective heat release rates are measured and, from heat and mass balance, actual and radiative rate of heat release, as well as heat that is not released due to incompleteness of combustion, are calculated. From the data, 99% of the rate of the theoretical heat release for complete combustion can be accounted for. In some cases the experimentally derived heat release rate was less than half that predicted from mass loss rate (assuming complete combustion). This ‘combustion efficiency’ decreased strongly with increasing externally applied radiant flux, and was always much lower for polystrene than for polymethylmethacrylate. At the ‘deal’ condition, defined as a condition where heat losses have been compensated and where the mass burning rate of polystyrene is 1.44 times the rate for polymethylmethacrylate, polystyrene generates 6.60 times more CO, 7.83 times more smoke particulates, and the radiative rate of heat release is 1.75 times more than that of polymethylmethacrylate.

Air velocity, temperature, and radiant-heatmeasurements within and around a large free-burning fire

Operation Euroka was a 210,000 m 2 (50 acres) free-burning mass fire experiment carried out in Queensland, Australia. At the peak of the fire, 42 min after ignition, the maximum average induced horizontal wind velocity at the edge of the fire was 4.2 m/sec. The fire was of relatively low intensity, with a peak convective heat-release rate of 2.0×10 10 W and a peak radiant energy-release rate of 4×10 9 W. The ratio of the radius of the projection of the conical portion of the convection plume ontothe surface to the radius of the fire bed was only 0.18, compared with the value of 0.4 reported for the more-intense Flambeau fires. Consequently, this ratio may be a function of the fire intensity. If this is so, then, for a fire of a given size, the induced influw wind velocity is a stronger function than the cube root of the heat-release rate.