Experiment on Quantitative Analysis of Plastic Polymers Using Cone Calorimetry - Coursework Example

Title: Experiment on Quantitative analysis of plastic polymers using cone calorimetry. Date the Experiment was performed: Name: Partner’s Name: Purpose/Objective. The purpose of this experiment was to asses fire safety in plastics usually used in electronic applications, by examining fire risk scenarios when changes occur from internal ignition to an external one. This as a scenario that has drawn great interests to meet environmental regulations in non-flame retarded polymers. This experimental report has the objective of explaining why quantitative analysis using cone calorimeter remains elusive and to understand how materials fails or passes specific Heat release ratings (Morgan and Bundy 258). Cone calorimeter Cone calorimeter test has remained for along time a useful research tool in quantitative flammability analysis of materials and also used by engineers to assess fire safety. Cone calorimetry experiment is a valuable bench-scale test that simulates real-world fire conditions. The cone calorimeter applies quantitative flammability analysis of materials in research by evaluating parameters like ignition time, heat release rate, mass loss rate, and total heat release. The heat release rate is interpreted further through analysis of peak, average, and peak time (Figure 3). If the cone calorimeter is properly configured, it can also be used to quantify and measure output of smoke and CO/CO2 release rates (Morgan and Bundy 258). Hypothesis The hypothesis of this experiment is build on experimental data and seeks to establish heat release rate test through understanding of how certain materials pass small/bench-scale fire risk tests. It has been noticed that several published works on polymer rating do not give a widely accepted discussion of how UL-94 V-rating of materials may be understood better in calorimetry. This report will elaborate more on the correlation between heat release rate and UL-94 V ratings and further open dialogue on this subject. In addition, the report will try to improve on the uses of cone calorimeter in development of new products for specific fire risk scenarios in more realistic scenarios (Morgan and Bundy 258). Cone calorimeter test Calculations of heat release were based on the principle of oxygen consumption. This principle states that complete combustion range in most fuels is 13.1 (plus-minus 5%) kJ of energy per every gramme of oxygen consumed in the process. The samples used in this experiment conformed to be within this range, although the effects of other factors like additives were not ascertained. The diameters specimen’s sizes were 10 Plus-minus 0.1 cm and 1.6 or 3.2 (Plus-minus 0.1) mm in thickness. The tests were carried out under a conditioned environment of 50 (Plus-minus 5%) relative humidity and temperatures within 23 – 26 degrees centigrade for a period of 48 hours. The specimens were placed in a round aluminium foil pan with 5mm at the top of sample. All collected data in this experiment (Table I) show a standard combined uncertainty of (Plus–Minus 10%) approximately (Rangwala 401-414). Theoretical background Early experiments for testing material ignition were based on exposure of small specimen to furnace fire with assumption that it had uniform temperature. Setchkin furnace was a widely used process that had been developed in late 1940s. However, the procedure could not be applied in comparison experiments of samples with different sizes or study of composite materials. More recently, ignitability set up has evolved by adopting apparatuses designed with heating source primarily from 1 radiant heat, 2. Convective heat, 3. Later direct flame ignition (Parker and Babrauskas 31-43). NBS endeavored to develop an economically viable instrument for commercial laboratory testing to avoid existing difficulties and shortcomings. This led to development of conical heater that gave rise to modern day cone calorimeter. Cone calorimeter emerged as a new-generation instrument specially designed to measure heat release measurements. The instrument has a uniform and well partitioned irradiance source for taking measures of radiant ignition on materials (Parker and Babrauskas 31-43). Experimental set up This section describes the process of laboratory experimental test carried out in the institution’s fire science laboratory. In the experiment, a total of 4 tests were undertaken on plastic polymers 5 cm width by 20cm height. The samples were combusted uniformly across the base of the cone calorimeter (Diagram 1). A digital SLR camera was used to record videos of the front view during sample combustions. The cone calorimeter test measured the quantities of heat release and mass loss rates to provide necessary data for calculation of time-averaged mass transfer number for each test (Rangwala 401-414). The ignition mode used a small aluminium tray of 5cm by 0.5 cm by 0.5 cm measurements that were placed at the bottom of each of the samples which were wrapped in a thin of fiber insulation soaked with n-Heptane. The main reason was to ensure even flame along the entire base for each test sample. To ensure vertically burning, the samples were insulated at the back and the sides with a ¼ in (0.64mm) thick fiberboard Kaowool which insulated the samples to isolate combustion of the front faces only. The samples burned completely and were self-extinguished when the fuel was exhausted (Rangwala 401-414). Diagram 1 is the schematic display of experimental set-up. (Source: Hostikka Experiments and modeling on vertical flame spread). Results and discussion During the experiment, the heat release rate and rate of mass loss for sample plastic polymers were measured to determine effects to upward spread of the flame. Initial ignition depicted an even spread of flame vertically along the sample. In the preceding process, the samples burned above ignition temperature and the rate of flame spread increased upwards rapidly. On reaching the pyrolysis zone at the top of the sample, heat release rate decayed quickly from the peak. Figure 3 displays the experiments heat release rates of the 4 sample tests performed (Rangwala 401-414). The experiment displayed a good repeatability mode of combustion in the tested series since the curves for heat release rates are similar. The vertical growth rates for the flame height in the tests were approximately 0.86 cm/s and 0.94 cm/s. Table 1 gives a summary of the 4 test results. The mass loss data collected and the samples properties were used to determine the mass transfer number for each test using equation (figure 2) the experiment achieved an average mass transfer number of 1.77 in all the 4 tests. These results were simulated to a real-world flame spread phenomena, acquired from videos of three large-scale flame heights (Wolfram and Steinhaus BRE Centre for fire safety engineering: Laboratory Experiments). Fig 2 is the equation for determining the mass transfer number. Table 1 shows results of cone calorimeter experiment. Sample Heat Flux Time to ignition [#] [kW/m2] [s] 1 14.1 - 2 14.35 481 3 16.7 274 4 18.6 330 (Source Wolfram and Steinhaus BRE Centre for fire safety engineering: Laboratory Experiments) Fig 3. Is the graphical representation of HRR [kW/m2] Vs time [s] (Source: Hostikka Experiments and modeling on vertical flame spread). Notes. [kW/m2] – refers to heat release rate for small samples [kW] – refers to heat release rate for large items Previous research experiments show that UL-94-rated materials at V-1 do better in external ignition fire scenarios thus can easily be flamed by small size candle flame compared to those with less V-1 ignition rates. However, this assumption is debatable since not all polymer materials behave in similar ways during full-scale fire tests. Therefore UL-94-rated plastic polymers are effective at providing fire safety at local ignition scenarios. However, there safety level on exposure to aggressive external fire risk scenario is not clear (Morgan and Bundy 258). Conclusion This experimental analysis noticed that the cone calorimeter model satisfied the following properties, 1.Steady state heat release rate, 2. Heat release curve displayed a parabolic growth curve and is always time dependent, 3. Spread of fire was by means of igniting materials and should be a function of critical heat flux for ignition, and 4. Fire growth was based purely on the materials thermophysical properties. Therefore this experiment clearly applies cone calorimeter method to determine mass transfer number of materials for fire hazard rankings. In addition the model successfully predicts vertical flame spread rates for various polymers (Quintiere Fundamentals of Fire Phenomena). Sources of error Any inaccuracies in this experiment can be attributed to spurious mass loss data fluctuations during combustion process. Existence of discrepancy in flame heights from predicted values is because the model accounts only for vertically driven transfer of heat without consideration of radiation that actually increases as fire expands in size. However the experimental results display a clear agreement with large-scale experimental flame height figures by simulating the mass transfer numbers of the small-scale tests (Rangwala 401-414). Works cited Hostikka, Simo, Johan Mangs, and Olavi Keski-Rakonen. VTT Building and Transport: Experiments and modeling on vertical flame spread. Espoo, Finland, 2005. Morgan, B Alexander, and Mathew Bundy. Fire mater: Cone calorimeter analysis of UL-94 V-rated plastics. Wiley Interscience 31(2007):257-283. Parker, J William, and Vytensis Babrauskas. Fire and Materials: Ignitability Measurements with the cone calorimeter 11 (1987):31-43. Available at http://www.fire.nist.gov/bfrlpubs/fire87/PDF/f87009.pdf (Accessed on August 22, 2009). Quintiere, JG. Fundamentals of Fire Phenomena. John Wiley, Chichester, 2006. Available at http://www.fire.nist.gov/bfrlpubs/fire07/PDF/f07039.pdf (Accessed on August 22, 2009). Rangwala, AS, Buckley S, and Torero JL. Combustion and Flame: Analysis of the constant B-number assumption while modeling flame spread. 152.3 (2008): 401–414. Wolfram, Jahn, and Steinhaus Thomas. BRE Centre for fire safety Engineering: Laboratory Experiments. University of Edinburgh, n.d. Available at http://www.see.ed.ac.uk/FIRESEAT/DFT_PDF/06_Lab.pdf (Accessed on August 22, 2009). Read More