Sensitivity analysis of temperature in heated soft tissues with respect to time delays

Axisymmetric tissue region heated by an external heat flux is considered. The mathematical model is based on the dual-phase lag equation supplemented by appropriate boundary and initial conditions. This equation, in relation to the Pennes’ equation, has two additional parameters, namely the relaxation time and the thermalization time. The aim of this research is to estimate the temperature changes due to changes of these parameters. To achieve this, sensitivity analysis methods are used. The basic problem and additional ones related to the sensitivity functions are solved using the implicit scheme of the finite difference method. The performed computations show that the temperature changes caused by changes in the relaxation and thermalization times are larger for higher values of the external heat flux and shorter times of its action.

In-depth temperature and smoke production of charring wood under a constant external heat flux

The combustion characteristics of charring wood have been studied experimentally in a well-ventilated environment of a smoke chamber. A numerical simulation has also been performed for a limited case, with the Fire Dynamics Simulator, to estimate the burning environment. A horizontally placed specimen (ponderosa pine) with a moisture content of 0% or 20% is exposed to a radiant flux (25 kW/m2), with or without flaming ignition. Simultaneous measurements of the specimen’s in-depth temperature and the mass loss determine the charring front (rate) at 300 °C and the gasification rate, respectively. These condensed-phase conditions relate directly to real-time variations of gas-phase quantities: the specific optical density of smoke and the concentrations of toxic gases measured by a Fourier transform infrared gas analyzer. In-depth temperature trends are similar whether the flame exists, whereas the smoke and toxicants’ concentrations are substantially different. After the charring front moves through the specimen, the oxidative pyrolysis continues under the irradiation at high temperatures (up to ∼550 °C). Carbon monoxide and acrolein are produced continuously throughout the test, and the results indicate strong correlations. Although char formation of wood is favorable for fire safety, consequent incomplete combustion produces smoke and toxicants.

Effects of External Heat Flux and Exhaust Flow Rate on CO and Soot Yields of Acrylic in a Cone Calorimeter

The effects of changes in irradiance level (external heat flux), exhaust flow rate, and hood height on CO and soot yield were examined using a cone calorimeter. Black acrylic, having similar constituents as polymethyl methacrylate, was used as a combustible, and external heat fluxes ranging from 15 to 65 kW/m2 were considered. Both auto and spark ignitions were applied as ignition methods. The difference in auto and spark ignition methods had no effect on CO and soot yields, or on the mass loss rate (MLR), heat release rate (HRR), and effective heat of combustion (EHC), which are global parameters of fire. As the external heat flux increased, the mean MLR and HRR linearly increased while the EHC remained constant. When the external heat flux increased, the mean mass flow rates of CO and CO2 had a directly proportional relationship with the mean MLR. Consequently, CO and CO2 yields remained constant regardless of the external heat flux. In contrast, the mean mass flow rate and mean MLR of soot were linearly proportional as opposed to directly proportional, and the soot yield thus increased linearly with external heat flux. Variations in the exhaust flow rate and hood height, which can alter the velocity and temperature fields in post-flame and plume regions, had almost no impact on CO and soot yields, as well as on MLR and HRR. The results of this study are expected to provide improved insight into conventional approaches on the recognition of CO and soot yields as unique properties of each combustible.

Initiation Parameters of Granulated Synthetic Polymers

Polymeric materials, which are currently very often used in various industries, are often transported and stored in the form of granules before processing. This method has several advantages, but in most studies the test samples are modified to different shapes and dimensions. This paper is therefore focused on the initiation of selected granular plastics. Samples of five polymeric materials were exposed to an external heat flux from 20 kW.m−2 to 40 kW.m−2. A spark initiator was used to ignite the released gaseous products of thermal decomposition of the polymer sample. FTP (flow-time product) method was applied to the obtained parameter - time to ignition, from which other initiation parameters were determined. The critical heat flux was determined in the range of 5.0 kW.m−2 - 11.8 kW.m−2. Despite the relatively small thickness (4 mm), the samples behaved as thermally thick. During the measurement, thin surface layer melted, and the rest of the polymer remained in its original granulated form. Ignition temperatures were calculated according to the Stefan-Boltzmann’s law between 273 °C - 402 °C.

The Evaluation of Torrefied Wood Using a Cone Calorimeter

This study focuses on the energy potential and combustion process of torrefied wood. Samples were prepared through the torrefaction of five types of wood: Ash, beech, oak, pine and spruce. These were heated for 2 h at a temperature of 300 °C under a nitrogen atmosphere. Torrefied wood was prepared from wood samples with dimensions of 100 × 100 × 20 mm3. These dimensions have enabled investigation of torrefied wood combustion in compact form. The effect of the external heat flux on the combustion of the samples was measured using a cone calorimeter. The observed parameters, include initiation times, heat release rate and combustion efficiency. The results show that increasing the external heat flux decreases the evenness of combustion of torrefied wood. At the same time, it increases the combustion efficiency, which reached an average value of approximately 72% at 20 kW m−2, 81% at 30 kW m−2 and 90% at 40 kW m−2. The calculated values of critical heat flux of the individual samples ranged from 4.67 kW m−2 to 15.2 kW m−2, the thermal response parameter ranged from 134 kW s0.5 m−2 to 297 kW s0.5 m−2 and calculated ignition temperature ranged from 277 °C to 452 °C. Obtained results are useful both for energy production field and for fire safety risk assessment of stored torrefied wood.

An Experimental Study of Vertical Fire Spread through Openings in Compartments

In this study, a real scale fire experiment was conducted to analyze the characteristics of the flame that is ejected from an opening. The experiment was conducted by setting mattresses and wood cribs in compartments sized 2.4 (L) × 3.6 (W) × 2.4 (H) m and using heptane as an ignition source, and changes in external heat flux and temperature were measured during the experiment. In the experiment, openings of two sizes: small [2.2 (L) × 1.0 × 1.0 (H) m] and large [2.2 (L) × 2.0 × 2.0 (H) m], were used. The results showed that the maximum decrease of 40.7 kW/㎡ and 31.7 kW/㎡ was measured in small and large openings, respectively, at the distance of 0.5 m from the top of the opening. As a test result, securing the separation distance of the upper and lower openings can greatly affect the prevention of vertical spread of the flame, and if sufficient separation distance is not secured, it is considered that an additional fire diffusion prevention method is necessary.

Smoke Hazard Assessment of Cypress Wood Coated with Boron/Silicon Sol Compounds

In this study, boron/silicon sol compounds were applied to wood for construction and durable materials, and fire risks were investigated in terms of smoke performance index (SPI), smoke growth index (SGI), and smoke intensity (SI). The compound was synthesized by reacting tetraethoxyorthosilicate with boric acid and boronic acid derivatives. Smoke characteristics were investigated using a cone calorimeter (ISO 5660-1) equipment for cypress wood. The fire intensity fixed the external heat flux at 50 kW/m². The smoke performance index measured after the combustion reaction increased between 13.4% and 126.7% compared with cypress wood. The fire risk due to the smoke performance index decreased in the order of cypress, phenylboronic acid/silicon sol (PBA/Si), (2-methylpropyl) boronic acid/silicon sol (IBBA/Si), boric acid/silicon sol (BA/Si). The smoke growth index decreased between 12.0% and 57.5% compared to the base specimen. The risk of fire caused by the smoke growth index decreased in the order of cypress, PBA/Si, IBBA/Si, BA/Si. The fire risk due to smoke intensity decreased between 3.2% and 57.8%, and in the order of cypress, PBA/Si, IBBA/Si, BA/Si. CO_peak concentrations ranged between 85 and 93 ppm, and decreased between 37% and 43% compared to the base specimen. A comprehensive assessment of the fire risk on smoke hazards decreased in the order of cypress, PBA/Si, IBBA/Si, BA/Si.