Heat Release Measurements Research Articles

Thermal Decomposition of a Melt-Castable High Explosive: Isoconversional Analysis of TNAZ

The thermal decomposition kinetics of the high explosive 1,3,3-trinitroazetidine (TNAZ) have been measured by nonisothermal differential scanning calorimetry (DSC). Samples of TNAZ in open pans and pierced pans undergo mainly melting (ΔHfus = 27 ± 3 kJ mol-1) and vaporization (ΔHvap = 74 ± 10 kJ mol-1) during heating. However, when confined in sealed high-pressure crucibles, exothermic thermal decomposition is observed. The activation energy for thermal decomposition has been determined as a function of the extent of reaction by isoconversional analysis. The initial value of 184 kJ mol-1 at the start of the reaction decreases to 38 kJ mol-1 near the end of the reaction. The rates clearly exhibit acceleratory behavior that is ascribed to autocatalysis. The measured heat release of thermal decomposition (Q = 640 ± 150 kJ mol-1) is independent of the heating rate and the sample mass. These results are consistent with proposed mechanisms of TNAZ decomposition in which the initial step is preferential loss of the nitramine NO2 group over loss of a gem-dinitroalkyl NO2 group.

Low-Temperature Acoustic and Thermal Properties of Plastically Deformed, High-Purity Polycrystalline Aluminum

The low-temperature internal friction Q -1 , thermal conductivity K, specific heat cp and heat release of plastically deformed, high-purity aluminum polycrystals have been investigated and have been compared with measurements on an amorphous SiO 2 specimen. Plastic deformation has a pronounced effect on both internal friction Q -1 and thermal conductivity K in the superconducting state. The magnitude of the internal friction Q -1 can be increased over two orders by plastic deformation over that observed on an annealed sample, and approaches a value approximately equal to that of the amorphous SiO 2 specimen. The lattice thermal conductivity K of the deformed specimens also has a magnitude which is of the same order as that of amorphous SiO 2 , it is, however, nearly independent of the amount of deformation. No glass-like anomalies could be observed in the specific heat cp and heat release measurements. The specific heat c p approaches a T 3 -relationship at the lowest temperatures investigated, and heat release experiments clearly show no long-time energy relaxation effects. Thus, it must be concluded that the defects introduced into deformed aluminum cannot be described with the tunneling model which had been proposed to describe the low temperature elastic and thermal properties of amorphous solids and which is based on the assumption of a constant spectral density of tunneling states. The phonon scattering mechanism observed in the deformed aluminum is tentatively related to the interaction of phonons with geometrical kinks in dislocations.

Numerical model of upward flame spread on practical wall materials

The focus of this paper is the development of a thermal, finite difference numerical model to describe one-dimensional upward flame spread on practical wall materials. Practical materials include composite materials and those that char, in addition to clean burning, homogeneous materials. A set of equations used in the model is developed and the methods for obtaining necessary “fire properties” are discussed. Some of the particular features of the model include the use of a correlation for flame heat feedback and the use of an experimentally measured mass loss rate to incorporate the burning characteristics of practical materials. A comparison of the numerical predictions with the experimental results for flame heights and temperatures are shown for Douglas fir particle board. The model correctly predicts trends but underpredicts the flame heights and pyrolysis height in the cases tested. Two additional cases are shown for materials for which experimentally measured heat release rate data are used in place of the mass loss rate data. The flame and pyrolysis height predictions are in much better agreement for these cases. Further efforts to obtain material property data that is appropriate for flame spread modeling is indicated by this work.

Heat release measurements for non‐flaming barrier fabrics using thermopile and oxygen consumption techniques

Two standard methods of measuring the heat release have been used for barrier fabrics comprising flame-retardant cellulosic fibres and selected reactive intumescent components. These methods are based on the principles of (i) direct measurement of the convective and radiant heat liberated using a mass loss calorimeter fitted with thermopiles, and (ii) oxygen consumption using a cone calorimeter. The results obtained from these two methods are different, which is contrary to work published by other researchers. The barrier fabrics used for the present study do not undergo flaming combustion; instead they char immediately and then oxidize slowly when subjected to heat fluxes in the range 25-75 kW m -2 . Furthermore, heat release rate (HRR) measurements from thermopile sensors are only slightly dependent on the presence, absence or type of intumescent present, unlike oxygen consumption HRR measurements and, indeed, earlier values determined using the Ohio State University apparatus. Cone calorimetry determines the reduced HRR values associated with the burning behaviour of these char-promoting samples, whereas with thermopiles embedded above the heater, the sensors will be influenced by radiative heat from the charred fabric samples. The latter will be less affected by the intumescent character as results suggest, because thermopile responses are determined by the black body radiative characteristics of the chars. These initial studies, therefore, have demonstrated that heat release rate measurements for very effective char-forming samples using either technique require careful interpretation because of the non-convective flame burning character of char combustion. In subsequent experiments, shielding of thermopiles from direct radiation is recommended.

Heat release measurements for non‐flaming barrier fabrics using thermopile and oxygen consumption techniques

Heat release measurements for non‐flaming barrier fabrics using thermopile and oxygen consumption techniques

The Measurement of Heat Release from Oxygen Consumption in Sooty Fires

The Measurement of Heat Release from Oxygen Consumption in Sooty Fires

The Measurement of Heat Release from Oxygen Consumption in Sooty Fires

This paper is a further contribution to the development of practi cal relationships based on oxygen consumption calorimetry to calculate the rate of heat release (RHR) in fires. The measurement of the RHR based on oxygen consumption was promoted in the 1980s. Previous workers introduced and as sessed the significance of adequate correction factors to take into account in completeness of combustion as reflected by carbon monoxide release. This paper focuses on materials releasing large amounts of soot in combustion. Classical oxygen consumption relationships are reviewed to derive adequate calculation procedures integrating the soot contribution. An analysis 1Author to whom correspondence should be addressed. E-mail: sylvain.brohez@fpms. ac.be of the significance of the suggested soot correction factor is discussed through theoretical considerations as well as from results of lab-scale experiments.

On the Experimental Determination of Combustion Process Driving in an Unstable Combustor

This paper investigates the accuracy of the typical experimental practices that estimate the unsteady pressure in the flame region of an unstable combustor from pressure measurements along the combustor walls. This measurement, along with that of the unsteady heat release, is often used to determine information about the flame's driving characteristics. These wall pressure measurements are only meaningful, however, if the unsteady pressure is nearly one-dimensional in the combustor; that is, if the transverse gradient of the pressure in the flame region is small. This paper presents computational results of the interior acoustic field in a combuslor undergoing longitudinal oscillations in order to quantify the difference between the acoustic pressures at the wall (where they are typically measured) and the flame. These results show that the duct pressure at the flame and the wall typically differ in magnitude by five to twenty five percent, and in phase by ten to twenty degrees. It is concluded from these results that wall pressure measurements provide qualitative information about the fluctuating pressure at the flame and can, in some cases, be used in conjunction with heat release measurements to characterize the flame driving.

Influence of delay times and response times on heat release measurements

This paper presents results from the analysis of the calibration results from the 1997 single burning item (SBI) test round-robin. The influence of the method of determining delay times and response times for the parameters involved in the heat release rate (HRR) calculation, on the overall result of the HRR and the FIre Growth RAte (FIGRA) index is shown. A procedure to determine response times and delay times based on the analysis is proposed. Examples of how to find delay times and response times, and how time shifting the measured data according to these times influences the test results, are shown in detail. Finally a mathematical approach to analyse the influence of response times is given. Calculations are performed to show how the response time influences the result when heat output is changed in steps and how this can lead to incorrect measured data. Guidance on acceptable response times is given. Copyright © 2000 John Wiley & Sons, Ltd.

Active control of combustion instabilities on a rijke tube using neural networks

The active control of combustion instabilities with feedback is a promising new tool. In this paper, we first describe a Rijke tube that presents, for some operating conditions, instabilities with pressure levels up to 145 dB/Hz. To control these instabilities, we have developed an internal model control scheme for nonlinear systems that uses two artificial neural networks. The first one, the internal model (IM), approximates the system forward dynamic. The second one, the controller, calculates the control input. The controller's parameters are updated adaptively in real time. The IM was first trained to reproduce the burner response (given by the pressure or heat-release measurements) to open loop excitation. It was then used in the control loop to predict the response of the burner to the control action. The adaptive control algorithm used this prediction to update the controller's parameters. The developed controller is able to attenuate the instabilities in real time for fixed or variable operating conditions: pressure level attenuation down to −40 dB/Hz has been obtained.

Basic Study on Backdraft. Mass Loss Rate of Wood Combustion on the Low Oxygen Concentration Condition.

In this study, we measured pyrolysis and combustion characteristics of wood with a view to make clear premix and ignition mechanism of backdraft. Cone calorimeter was used to measure heat release rate(HRR)curves and mass loss rate(MLR)curves for 18 mm thick Lauan woods at an incident heat flux of 50 kW/m2. Lauan has two peaks in the HRR and MLR curve. First sharp peak comes soon after ignition and a second peak appears near the end of the flaming combustion period. We also measured MLR curves and oxygen concentration curves for 18 mm thick Lauan woods in constant temperature, low oxygen concentration furnace. In low oxygen condition, MLR was de-creased because heat feedback from flame was decreased. In order to explain the second peak observed in the HRR and MLR curve, a simple calculation was carried out by considering wood and char properties and wood pyrolysis rate. It was found that the second peak is the result of a rapid rise in the bulk temperature of the remaining wood. The second peak is primarily dependent on the un-exposed face conditions.

Heat release measurements for non-flaming barrier fabrics using thermopile and oxygen consumption techniques

Heat release measurements for non-flaming barrier fabrics using thermopile and oxygen consumption techniques

Measurement of equivalence ratio fluctuation and its effect on heat release during unstable combustion

This paper presents the first quantitative measurements of equivalence ratio fluctuations during unstable combustion in a lean premixed model dump combustor operating on natural gas with a nominal heat release rate of 75 kW. Equivalence ratio was measured using an infrared absorption probe based on the absorption by methane of the 3.39 μm output of a He−Ne laser. In order to make quantitative equivalence ratio measurements it was necessary to independently measure the absorption coefficient over a wide range of temperatures (293–683 K) and pressures (up to 600 kPa). Using simultaneous equivalence ratio, pressure, and chemiluminescence-based heat release measurements, it was demonstrated that new insights could be obtained regarding the role of equivalence ratio fluctuations during unstable combustion. For example, the measurements indicate that the observed heat release can be primarily attributed to the measured equivalence ratio fluctuations, and they show that the equivalence ratio fluctuations exhibit significantly higher harmonics, whereas the heat release and pressure fluctuations occur predominately at the fundamental frequency of the instability.

Liver Freezing Response of the Freeze-Tolerant Wood Frog, Rana sylvatica, in the Presence and Absence of Glucose. I. Experimental Measurements

In this study, two methods are used to assess the equilibrium and dynamic cell volumes in Rana sylvatica liver tissue during freezing in the presence and absence of a cryoprotectant (glucose). The first is a “two-step” low-temperature microscopy (equilibrium and dynamic) freezing method and the second is a differential scanning calorimeter (DSC) technique. These two techniques were used to study (i) the in vitro architecture of R. sylvatica frog liver tissue and to measure its characteristic Krogh cylinder dimensions; (ii) the “equilibrium” (infinitely slow) cooling behavior and the osmotically inactive cell volume (Vb) of R. sylvatica liver cells; and (iii) the dynamic water transport response of R. sylvatica liver cells in the presence and absence of the CPA (glucose) at a cooling rate of 5°C/min. Stereological analysis of the slam frozen (>1000°C/min) micrographs led to the determination that 74% of the liver tissue in control frogs was cellular versus 26% that was extracellular (vascular or interstitial). Mapping the stereological measurements onto a standard Krogh cylinder geometry (Model 1) yielded distance between adjacent sinusoid centers, ΔX = 64 μm; original sinusoid (vascular) radius, rvo = 18.4 μm; and length of the Krogh cylinder, L = 0.71 μm (based on an isolated frog hepatocyte cell diameter of 16 μm). A significant observation was that ∼24% of the frog hepatocyte cells are not in direct contact with the vasculature. To account for the cell–cell contact in the frog liver architecture a modified Krogh cylinder geometry (Model 2) was constructed. In this model (Model 2) a second radius, r2 = 28.7 μm, was defined (in addition to the original sinusoid radius, rvo = 18.4 μm, defined above) as the radius of the membrane between the adjacent cells (directly adjacent to vascular spaces) and embedded cells (removed from vascular spaces). By plotting the two-step equilibrium cooling results on a Boyle–van't Hoff plot, the osmotically inactive cell volume, Vb was obtained as 0.4 · Vo (where Vo is the isotonic cell volume). The two-step dynamic micrographs and the heat release measurements from the DSC were used to obtain water transport data during freezing. The DSC technique confirmed that R. sylvatica cells in control liver tissue do not dehydrate completely when cooled at 5°C/min but do so when cooled at 2°C/min.

The kinetics of indium/amorphous-selenium multilayer thin film reactions

The reaction kinetics in vapor-deposited indium/amorphous-selenium (a-Se) multilayer thin films were studied using differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). A number of reactions were observed upon heating with characteristic temperatures which were found to be independent of the multilayer modulation wavelength. The initial interface reaction between In and a-Se is the formation of an In2Se phase. Kinetic analyses of the In2Se formation process combined with TEM observations indicated that interface reaction is characterized by the two-dimensional growth of pre-existing In2Se regions formed during deposition to impingement in the plane of the original In/a-Se interface. The change of the density of In2Se grains with temperature was analyzed in terms of the derived kinetic parameters, which is consistent with TEM observations and the heat release measurements.

Prediction of the effect of injection parameters on NOx emission and burning quality in the direct injection diesel engine using a modified multizone model

Combustion process in a quiescent chamber diesel engine is modelled using a multizone model. This model divides the cylinder charge into two zones, namely the unburnt zone (surrounding air) and the burnt zone (fuel spray with entrained air). The burnt zone is subdivided into 16 concentric sprays, instead of only eight sprays as in previous work, each one with its own temperature and composition. Liquid fuel, fuel vapour, air and products of combustion are assumed to be present in each zone. Real gas relations are used to calculate the properties of the mixture while products of combustion are assumed to be in chemical equilibrium at local temperature. The extended Zeldovich mechanism is used to predict the NO x formation. The cylinder pressure, temperature, heat release rate, NO x rate and concentration are calculated. For different injection pressures, injection advance angles and different fuel orifice hole diameters, the results show that the model can predict the measured cylinder pressure with high accuracy but it predicts the measured heat release rate and NO x emission rate with moderate accuracy. In addition, the effect of injection parameters on the NO x emission and engine power is predicted and it has been shown that NO x emission can be reduced without noticeable loss of engine power. This can be done by appropriate choice of injection pressure, injection advance angle and fuel nozzle hole diameters.

98/00990 Kinetic parameters of oxidation of coals by heat-release measurement and their relevance to self-heating tests: Jones, J. C. et al. Fuel, 1998, 77, (1/2), 19–22

98/00990 Kinetic parameters of oxidation of coals by heat-release measurement and their relevance to self-heating tests: Jones, J. C. et al. Fuel, 1998, 77, (1/2), 19–22

Measurement of Water Transport during Freezing in Cell Suspensions Using a Differential Scanning Calorimeter

A new technique using a differential scanning calorimeter (DSC) was developed to obtain dynamic and quantitative water transport data in cell suspensions during freezing. The model system investigated was a nonattached spherical lymphocyte (Epstein–Barr virus transformed, EBVT) human cell line. Data from the technique show that the initial heat release of a prenucleated sample containing osmotically active cells in media isgreaterthan the final heat release of an identical sample of osmotically inactive or lysed cells in media. The total integrated magnitude of this difference, Δqdsc, was found to be proportional to the cytocrit and hence also to the supercooled water volume in the sample. Further, the normalized fractional integrated heat release difference as a function of temperature, Δq(T)dsc/Δqdsc, was shown to correlate with the amount of supercooled cellular water which had exosmosed from the cell as a function of subzero temperature at constant cooling rates of 5, 10, and 20°C/min. Several important limitations of the technique are (1) that it requires a priori knowledge of geometric parameters such as the surface area, initial volume, and osmotically inactive cell volume and (2) that the technique alone cannot determine whether the heat released from supercooled cellular water is due to dehydration or intracellular ice formation. Cryomicroscopy was used to address these limitations. The initial cell volume and surface area were obtained directly whereas a Boyle–van't Hoff (BVH) plot was constructed to obtain the osmotically inactive cell volumeVb. Curve fitting the BVH data assuming linear osmometric behavior yieldedVb= 0.258V0; however, nonlinearity in the data suggests that the EBVT lymphocyte cells are not “ideal osmometers” at low subzero temperatures and created some uncertainty in the actual value ofVb. Cryomicroscopy further confirmed that dehydration was the predominant biophysical response of the cells over the range of cooling rates investigated. One notable exception occurred at a rate of 20°C/min where evidence for intracellular ice formation due to a DSC measured heat release between −30 and −34°C correlated with a higher end volume but no darkening of the cells during cryomicroscopy. For the cooling rate tested (5°C/min) the cryomicroscopy data correlated statistically very well with the DSC water transport data. A model of water transport was fit to the DSC water transport data and the average (5, 10, and 20°C/min) biophysical parameters for the EBVT lymphocytes were found to beLpg= 0.10 μm/min-atm,ELp= 15.5 kcal/mol. Finally, the decrease in heat release from osmotically active cells measured by the DSC during repetitive freezing and thawing was found to correlate strongly with the viability of the cells measured during identical freeze/thaw protocols with cryomicroscopy. This shows the additional ability of the technique to assess freeze/thaw injury. In summary, this DSC technique is a promising new approach for measuring water transport in cellular systems during freezing.

Doorway Calorimetry for Heat Release Rate Measurement in Building Fires

Heat release rates obtained with conventional room calorimeters are not always readily applicable to the study of realistic fires, since the local environment in a conventional room calorimeter can be vastly different to that in a normal building enclosure. The doorway room calorimeter studied in this work was developed to overcome this difficulty and measure the heal release rate without disturbing the conditions in the burn room. Heat release rate is obtained from the use of the oxygen consumption method and the analysis of the measured velocity, temperature and oxygen concentration profiles across the burn room door. The technique was used in a series of building fire experiments involving various types of fuel loads under naturally ventilated combustion conditions. The measured heat release rates were compared with that based on fuel mass loss measurement. The results supported the feasibility of the technique and demonstrated its potential application in the studies of naturally ventilated fire growth and smoke spread in buildings.

Combustibility Parameters for Enclosure Lining Materials Obtained During Surface Flame Spread Using a Reduced Scale Ignition and Flame Spread Technique

A reduced scale ignition and flame spread technique, RIFT, was implemented in the cone calorimeter system to obtain thermocombustibility properties of enclosure lining materials during flame spread over the sample surface. Previously, a thermal model of ignition and opposed flow flame spread was used to analyze flame spread data obtained using RIFT. Here, a framework is discussed for deducing critical material combustibility parameters from the measured heat release and mass loss rates as the spreading flame proceeds to the point of flame extinction. The nature of the data and analytical framework allows users to deduce spreading flame flux from the heat release rate (HRR) and mass loss rate (MLR) data relatively economically and directly. The anomalies highlighted by comparing flame spread data in the RIFT system compared to data from the BS 476 Part 7 apparatus indicates that the RIFT system is well-suited for developing and refining models describing ignition, flame spread, and mass burning.