Energy Transfer and Thermodynamics - Article Example

Energy Transfer and Thermodynamics Contents Abstract 3 Introduction 4 Methods and Materials 5 Results and Discussion 7 Conclusions and Recommendations 11 References 12 Abstract This paper elaborates on the an experiment conducted with the Cone Calorimeter on three materials, namely blue carpet samples, green carpet samples and underlay samples. This experiment is done in order to determine the values of wide array parameters that help understand and compare their properties to assess the fire behaviour of each of these samples. The results are obtained and the values are analyzed in order to arrive at a conclusion that will aid researchers who are interested in information regarding the properties of these samples as well as to provide data input for mathematical models that are developed for the purpose of predicting fire development. It starts with a small introduction that examines the aim, objectives and background of the experiment, followed by an explanation of the methodology and equipment used, the results of the experiment with a discussion and a conclusion. Introduction Aims The main aim of this experiment is to determine the fire behaviour of certain materials. Objectives The main objectives include: To gather information and parameters associated with combustion To determine the properties of fire including cumulative heat release, the rate of heat release per unit area, time to ignition, effective heat combustion, effective heat combustion, total mass loss, mass loss rate and smoke obstruction. To assess the fire hazard of materials involved. Background The first law of thermodynamics states that everything exists in some form of energy. This implies that energy can neither be created nor destroyed. On the contrary it can only be transformed into various forms. It can change from one form to different forms, but the sum of all forms of it cannot change (Bradford, 2009). This first law of thermodynamics is applied in combustion. Combustion is a sequence of exothermal chemical reactions between a fuel and an oxidant which is accompanied by the production of heat or light or both heat and light. Bradford (2009) defines combustion as, “a process involving rapid oxidation at elevated temperatures, accompanied by the evolution of heated gaseous products of combustion and the emission of visible and invisible radiation.” Zhou (2008) gives a very simple definition of combustion. He defines combustion as, “the burning of a fuel and oxidant to produce heat and/or work.” Fire is a chemical reaction in which a carbon based material mixes with oxygen and is heated to a point when flammable vapours are produced. When these vapours come into contact with something that is hot enough to cause vapour ignition, it results in a fire. Fire is a chemical reaction known as oxidation. The fire triangle or combustion indicates and illustrates the rule that in order for a fire to ignite and burn, it requires three important elements namely heat, fuel and oxygen. A fire naturally occurs when these elements are combined in the right mixture. There is a fourth element in the triangle which is the sustaining chemical reaction. Combustion is the chemical reaction that feeds the fire more heat and allows it to sustain. It is important to understand the above concepts of combustion, fire and the law of thermodynamics in order to assess the fire behaviour of materials in this experiment. Methods and Materials/ Equipment The equipment that will be used in this experiment to assess the fire behaviour of materials is the Cone Calorimeter. Cone Calorimeter is one of the most common methods that is used to determine material fire properties. The name cone calorimeter was derived from the truncated conical shaped heater that was used by Dr. Vytenis Babrauskas, to irradiate the test specimen with fluxes upto 100 kW/m2 in a bench scale oxygen depletion calorimeter. This was developed by Dr. Babrauskas and his associates in NIST. The Cone Calorimeter is considered to be the most significant bench scale instrument in the filed of fire testing as it is a key to measure vital real fire properties of the material being tested under an array of preset conditions. These measurements and results can be directly used by a number of researchers. The measurements can also be used as data for input into co-relation of mathematical models that are developed for the purpose of predicting fire development (Fire Testing Technology Limited). Cone calorimeter data is often used to predict combustion product levels (Lattimer, 1999). The Cone Calorimeter is designed to measure many important properties that help in characterizing the fire behaviour of materials. These properties include ignitability, heat release rate, total heat released, effective heat of combustion, specific extinction area, soot yield, mass loss rate and the evolution of CO and CO2 and other combustion products (Janoff, Royals and Gunaji, 1995). The Cone Calorimeter determines the rate of heat release and the effective heat of combustion. Many cone calorimeters are also used to determine carbon monoxide and carbon dioxide yields although this is not considered to be the standard test procedure (Brown, 1999). Out of the many parameters that are measured through the Cone Calorimeter, the Heat Release Rate is the most vital measurement that is required to assess the fire hazard of materials and products as it calculates fire size, rate of fire growth and accordingly the release of associated smoke or toxic gases. ISO 5660-1 in Brown (1999) defines the Cone Calorimeter as one of the most widely used methods used to test the rate of heat release. The method used in this experiment is the oxygen consumption method. A horizontal 100cm2 square specimen is exposed to a radiant heat flux of 10 to 100 kW/m2 with a spark ignition system. The effluent is drawn through a duct. This duct is fitted with sensors that that determine the temperature, gas flow rate and oxygen concentration. These data help determine the rate of heat that is released. The basic principle or technique of measurement is based on the empirical observation that the amount and rate of heat released by burning materials is directly proportional to the quantity of oxygen used in the process of combustion. Measurement of the precise quantity and concentrations of oxygen in the duct and the volumetric flow of air gives the rate of oxygen consumption. This measurement can consequently be used to determine the heat release rates. The samples used in this experiment included blue carpet samples, green carpet samples and underlay samples. Most of the leading fire research groups use the Cone Calorimeter to draw prime data on properties of materials and to obtain input data for predicting the fire behaviour of materials as well as finished products. Results and Discussion The results of the experiment with blue carpet samples are as follows. Parameters measured First Blue Carpet Second Blue Carpet Third Blue Carpet Fourth Blue Carpet Sample of Mass 21.96g 17.63g 24.9g 27.6g Surface Area 100cm2 100cm2 100cm2 100cm2 Thickness 8mm 8mm 8mm 8mm Heat Flux of the Experiment 25 kW/m2 35 kW/m2 45 kW/m2 55 kW/m2 Time of Test 481 seconds 378 seconds 715 seconds 458 seconds Total Heat Evolved 45.5 MJ/ m2 34.9 MJ/ m2 39.4 MJ/ m2 38.8 MJ/ m2 Total amount of Oxygen consumed 31.8g 24.7g 27.5g 27.4g Smoke Released 651 m2 / m2 474 m2 / m2 449.4 m2 / m2 736.3 m2 / m2 Mass lost during the experiment 12.1 g 13.2 g 12.4 g 13.2 g Specific mass loss rate 2.79 g/ m2 s 5.09 g/ m2 s 1.82 g/ m2 s 3 g/ m2 s Average heat release rate 108.79kW/m2 103.45kW/m2 57.32kW/m2 87.95 kW/m2 Effective heat of combustion 38.66 MJ/ Kg 20.88 MJ/ Kg 31.41 MJ/ Kg 28.83 MJ/ Kg Mass loss rate 0.028 g / sec 0.051 g / sec 0.018 g / sec 0.030 g / sec Specific extinction area 494.81 m2 / kg 204.47 m2 / kg 180.12 m2 / kg 506.11 m2 / kg Carbon monoxide yield 0.0194 kg/kg 0.0149 kg/kg 0.0126 kg/kg 0.0170 kg/kg Carbon dioxide yield 2.04 kg/kg 1.21 kg/kg 1.68 kg/kg 1.65 kg/kg A heat flux of 25 kW/m2 was observed for a blue carpet sample weighing 21.6g with a surface area of 100cm2 and a thickness of 8mm. The above results indicate that the rate of heat released is decreased as the heat flux is increased with the lowest value being recorded at 45 kW/m2. However the heat flux used did not have a direct effect on oxygen consumption. The total oxygen consumed remained comparable irrespective of the heat flux used. High levels of average specific mass loss were observed in this experiment. The main reason for this could be the small sample weight used in the experiment. However this mass loss was not related to the rate of heat flux. The carbon monoxide and carbon dioxide yield was low for 35 kW/m2 and 45 kW/m2 when compared to 55 kW/m2 and 35 kW/m2 , although at 35 kW/m2 . In the experiment with 35 kW/m2 and 45 kW/m2 all the average values for heat release rate, mass loss rate and specific extinction area were smaller. Schartel et al. (2005), point out that the low 45 kW/m2 heat release that was recorded was due to increased time. Hence it can be seen from the above results that while heat flux has a direct effect on rate of heat released; it does not influence or change the levels of oxygen consumption or loss of mass. The following are the results of the experiment with Green carpet samples. Parameters measured First Green Carpet Second Green Carpet Third Green Carpet Fourth Green Carpet Sample of Mass 13.68g 12.95g 12.65g 12.17g Surface Area 100cm2 100cm2 100cm2 100cm2 Thickness 5.5 mm 5.5 mm 5.5 mm 5.5 mm Heat Flux of the Experiment 25 kW/m2 35 kW/m2 45 kW/m2 50 kW/m2 Time of Test 495 seconds 281 seconds 265 seconds 460 seconds Total Heat Evolved 25.9 MJ/ m2 - 309.7 MJ/ m2 28.2 MJ/ m2 Total amount of Oxygen consumed 18.6g - -1174.7g 20g Smoke Released 393.9 m2 / m2 - 486.2 m2 / m2 517.9 m2 / m2 Mass lost during the experiment 9 g - 8.1 g 9.6 g Specific mass loss rate 2.45 g/ m2 s - 3.25 g/ m2 s 2.11 g/ m2 s Average heat release rate 57.53 kW/m2 - 1237.36 kW/m2 62.3 kW/m2 Effective heat of combustion 23.10 MJ/ Kg - 380.66 MJ/ Kg 29.21 MJ/ Kg Mass loss rate 0.025 g / sec - 0.033 g / sec 0.021 g / sec Specific extinction area 131.71 m2 / kg - 549.70 m2 / kg 423.16 m2 / kg Carbon monoxide yield 0.0140 kg/kg - 0.0239 kg/kg 0.0239 kg/kg Carbon dioxide yield 1.52 kg/kg - 1.90 kg/kg 1.68 kg/kg In this experiment with green carpet sample as the material, only 25 kW/m2 and 50 kW/m2 flux could be compared. This is because at 35 kW/m2 no results could be obtained in the experiment and at 45 kW/m2 flux most of the results were flawed and incorrect, for example the total amount of oxygen consumed at 25 kW/m2 and 50 kW/m2 were 18.6g and 20g respectively, but at 45 kW/m2 it was -1174.7 g and 35 kW/m2 failed to record values. Similarly, the average heat release rate at 25 kW/m2 and 50 kW/m2 57.53 kW/m2 and 62.3 kW/m2 respectively, while at 45 kW/m2 the average heat release rate was observed to be 1237.36. Not only were there vast differences between the values at 25 kW/m2 and 50 kW/m2 and 45 kW/m2 , it was also mostly erroneous at the flux value. Almost all of the values including, total heat evolved, mass lost, amount of oxygen consumed and amount of smoke released during the experiment were high at 50 kW/m2 when compared to the values observed at 25 kW/m2 . The primary exception here was specific mass loss which continued to remain average. The specific extinction rate observed in this experiment at 50 kW/m2 was approximately four times the value observed at 25 kW/m2 . Other values such as average effective heat of combustion, heat release rate and carbon dioxide and carbon monoxide yield were high at 50 kW/m2 when compared to 25 kW/m2 . Mass loss rate however seemed to be less at 50 kW/m2 when compared to 25 kW/m2 . The following results were observed of the experiment with Underlay samples. Parameters measured First Underlay Sample Second Underlay Sample Third Underlay Sample Fourth Underlay Sample Sample of Mass 10.46g 11.68g 12.12g 16.05g Surface Area 100cm2 100cm2 100cm2 100cm2 Thickness 10 mm 10 mm 10 mm 10 mm Heat Flux of the Experiment 45 kW/m2 25 kW/m2 35 kW/m2 55 kW/m2 Time of Test 139 seconds 225 seconds 303 seconds 240 seconds Total Heat Evolved 16.2 MJ/ m2 16.3 MJ/ m2 18.3 MJ/ m2 23.6 MJ/ m2 Total amount of Oxygen consumed 12 g 11.9 g 13.4g 17.4g Smoke Released 416.6 m2 / m2 291 m2 / m2 305.7 m2 / m2 553.6 m2 / m2 Mass lost during the experiment 12 g 12.4 g 9.3 g 58.4 g Specific mass loss rate 8.63 g/ m2 s 6.85 g/ m2 s 3.15 g/ m2 s 21.93 g/ m2 s Average heat release rate 118.71kW/m2 74.94kW/m2 61.44kW/m2 99.55 kW/m2 Effective heat of combustion 13.66 MJ/ Kg 10.69 MJ/ Kg 19.49 MJ/ Kg 4.48 MJ/ Kg Mass loss rate 0.086 g / sec 0.069 g / sec 0.031 g / sec 0.219 g / sec Specific extinction area 338.71 m2 / kg 154.9 m2 / kg 221.93 m2 / kg 102.46 m2 / kg Carbon monoxide yield 0.0291 kg/kg 0.0125 kg/kg 0.0269 kg/kg 0.0093 kg/kg Carbon dioxide yield 1.04 kg/kg 0.79 kg/kg 1.40 kg/kg 0.33 kg/kg Consistent and reliable values were recorded only at 35 kW/m2 flux as the values of other fluxes were reduced to zero with the increase of time. For 25 kW/m2 all values were reduced to zero in 5 minutes, for 45 kW/m2 all values were reduced to zero in 4 minutes and for 55 kW/m2 all values were reduced to zero in 6 minutes. In this experiment with Underlay samples, the total mass lost, smoke released and specific mass loss rate were all proportional to the heat fluxes used. Another aspect that was proportional to the heat flux was the specific heat release rate. The total heat evolved at 55 kW/m2 was slightly higher than when compared to other fluxes. It was valued at 23.6 MJ/ m2 . The mass lost and average specific mass loss rates were found to be higher at 55 kW/m2 when compared to other fluxes of the same value. Another aspect observed in this experiment with the Underlay samples is that at 55 kW/m2 the effective heat of combustion was low when compared to other flux values. The carbon monoxide and carbon dioxide yields from ignition to ignition plus were stable at 35 kW/m2 at all time intervals. Conclusion and Recommendations Due to the differences in sample sizes and time for the three different materials used, it may prove to be difficult to compare the properties and parameters of all the three materials. However, it can clearly be noted that the total consumption of oxygen, total heat evolved and smoke released were the highest for the blue carpet samples. The heat release rate and effective heat of combustion were also seen to be the highest for blue carpet. Two other parameters that recorded the highest values with specific reference to blue carpet samples included specific extinction area and carbon dioxide and carbon monoxide yields. The lowest mass loss was recorded in the green carpet samples. The underlay samples recorded highest average specific mass loss rate and highest mass loss rate during the experiment. The above conclusions and analysis of the results of all three samples will aid the researchers who are interested in obtaining data and information on blue, green and underlay samples and their fire behaviour. The results obtained from the above experiments will also aid in providing the data input for mathematical models that are aimed at predicting fire development. It is recommended that an experiment with similar sample sizes and time periods should be used for these materials in order to obtain accurate value on their parameters and consequently compare their properties in order to assess their fire behaviour. References Bradford, T E (2009). The First Law of Thermodynamics. Energy Transfer and Thermodynamics. Bradford, T E (2009). Thermodynamic Revision: Combustion. Energy Transfer and Thermodynamics. Brown, R (1999). Handbook of Polymer Testing: Physical Methods. CRC Press, 1999. p 680, 681. Fire Testing Technology Limited. Cone Calorimeters. Instrument Fact Sheet. Fire Testing Technology Website. Retrieved August 20, 2009. http://www.fire-testing.com/html/instruments/cone.pdf Janoff D D and Royals, W T and Gunaji M V (1995). Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres. ASTM International, 1995. p 153. Lattimer, B Y(1999). Adaptation of Cone Calorimeter (ASTM E1354) Data for Use in Performance-Based Fire Protection Analysis. ASTMs Role in Performance-Based Fire Codes and Standards, ASTM STP 1377. American Society for Testing and Materials. Schartel B, Bartholmai M and Knoll, U (2005). Some Comments on the Use of Cone Calorimeter Data. Polymer Degradation and Stability 2005; 88: 540-547 Zhou, C (2008). Combustion. Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment).Retrieved August 20, 2009. http://www.eoearth.org/article/Combustion Read More