The Cone Calorimeter Experiment - Essay Example

THE CONE CALORIMETER EXPERIMENT The Cone Calorimeter Experiment Fire testing plays a pivotal role in the development of new superior materials as well as enabling fire research engineers study the different effects of fire on materials used for building and construction. The cone calorimeter is one of the most important equipment for performing fire test on the bench. The equipment is used for measuring and testing the heat release rate of a given sample. The instrument has been adapted by the international standard organization (ISO) and other standardizations bodies. It is important to study and understand the fire performance of different PVC materials as they are constituent of the electrical wiring system which may result to the start of a fire. This paper presents the introduction to cone calorimeter test, the experimental procedure for conducting the experiment, the test results obtained and finally the results obtained are evaluated and a conclusions is drawn based on the results. Table of content THE CONE CALORIMETER EXPERIMENT 1 The Cone Calorimeter Experiment 2 Abstract 2 Table of content 2 Introduction 4 Background information 4 Method of measurement 6 Aim and Objectives 7 Materials and methods 8 Materials used: 8 Equipment used: 8 Material preparation 8 Experimentation procedure 9 Calibrations 9 Performing the measurement 10 Results 11 The Heat Release Rate 12 Fire performance index 12 The smoke parameter (SP) and carbon monoxide yield 13 Conclusion 15 References 16 Introduction The name cone calorimeter was coined from the shape of truncated conical heater that was developed by Dr. Vytenis Babrauskas who used the equipment to irradiate a test specimen of size 100 mm by 100mm. most of the laboratory contain the FTT cone calorimeter as it is compact and easy to use. Background information Some of the most important parts of the cone calorimeter equipment that helps in the measurement are Exhaust system: It comprises of the hood, gas sampling ring probe and an exhaust fan which are manufactured from stainless steel. The flow can be controlled and the equipment also allows for orifice flow measurement. Sampling of the gas: the gas sampling system comprises of a refrigerated cold trap, a pump, drying columns and flow regulators. Oxygen analysis: The equipment has a paramagnetic oxygen analyzer Smoke Obstruction: This is measured using a laser system using photodiodes with the main reference being photodiodes. Conical heater: This is wound in the form of a conical or truncated connect and it can be used in the horizontal and vertical orientation. Heat flux meter: This meter is used for setting the irradiance level at the surface of the specimen Calibration burner: This equipment is used to calibrate the rate of heat release. Data acquisitions: Several measurement techniques are employed to study fire characteristics Specimen holders: Most of the specimens used are 100mm length, 100mm width and 50mm thick. The specimen can be put in the horizontal or the vertical orientation. Software: User friendly software is used to help the researcher operate the calorimeter. Split shutter mechanism: This system is used to protect the sample area before conducting the test. It ensures that the initial mass measurement is constant. The operator is given extra time before starting the test. The shutter system also prevents premature ignition of highly ignitable materials The cone calorimeter equipment is as shown below.. The structural and interior parts of the cone calorimeter are as shown in the diagram below; Diagram 2 showing the main parts of a cone calorimeter (Source: Johan, A. 2002. Cone Calorimeter –A Tool for Measuring Heat Release Rate. Finland: Abo Akademi process chemistry center. [Online]. Available at http://www.tut.fi/units/me/ener/IFRF/FinSweFlameDays09/4B/LindholmPaper.pdf . Accessed august 20, 2009. ) The cone calorimeter equipment is used for measuring the following fire parameters; The ignition time The smoke release rate The critical ignition flux The effective heat of combustion The mass loss rate The materials rate of release of toxic substance, this toxic gas that is considered is carbon dioxide. The rate of heat release Method of measurement The principle method of measurement The oxygen consumption principle is used in the formulation of empirical observation in a cone calorimeter test. The underlying principle used stipulates that the heat released is directly proportional to the oxygen consumed. Measurement of the oxygen concentration at the exhaust duct and the volumetric flow rate of air give data that is used in the computation of the rate of oxygen consumption. The heat released in a cone calorimeter is given by; Where; The rate of heat release expressed as The orifice plate coefficient given by This is the pressure drop across the orifice plate This is the mole fraction of oxygen contained in the exhaust gases This value represents the gas temperature at the orifice plate The calorimeter main specifications are; The electrical power is 230 volts AC, 30 amps and the frequency is 50 Hz. The type of air used is oxygen free nitrogen. Water is supplied at 250Kpa The exhaust extraction is done 250 to 500 I/S Aim and Objectives The main objectives for conducting this experiment are to determine the rate of heat release, the total heat release rate and other fire related parameters. The specific objectives for this analysis are; To set up the experiment on a cone calorimeter Obtain results from the test Analyze the results and determine the rate of heat release from four PVC specimens. Materials and methods Materials used: The main materials used for these experiments were; Polyvinyl chloride: Polyethylene PVC Sheath and insulated material Polyethylene and insulated material Equipment used: The dual cone calorimeter plus other accessories The test pieces were shaped as provided by the ISO 5660. Material preparation The specifications of the cables used for the experimentation were as outlined in the table below; Cable specimen Section of cable in mm2 Diameter of cable in mm Area of cable exposed to the fire mm2 Mass in grams Polyvinyl chloride as sheath material and polyethylene in cable 4×35+1×16 30.00 94.2 333.1 Both sheath and cable made of PVC 3×35+1×16 28.30 77.3 320.1 Polyvinyl chloride as sheath material and polyethylene in cable 4×2.5 12.00 169.6 166.80 Both sheath and cable made of PVC 4×2.5 12.00 169.6 171.10 (Sample results obtained from Zhongjun, S. 2002. Experiment Study on Fire Performance of PVC Sheath Electrical Cables Exposed to High-level Heat Flux. Department of Fire Protection Engineering. Hebei, China: Chinese People’s Armed Police Academy). Experimentation procedure Calibrations 1) The smoke measurement system, the gas analyzer for analyzing carbon dioxide, oxygen and carbon monoxide were turned on ready for use 2) The system for measuring the smoke was then calibrated to initialize it to zero. This was done by blocking the laser beam to archive the lowest range and unblocking the laser beam to archive the full range 3) The gas analyzer was calibrated using the nitrogen for zero level to be archived 4) The orifice plate coefficient or the C-factor was calibrated using the methane burner 5) The temperature of the cone was set to produce the wanted heat flux at the surface of the sample; this was done by putting a water cooled heat flux gauge 25mm below the cone and adjusting the cone temperature till the required heat flux level was archived. Performing the measurement 1) The PVC sheaths were machined to 100mm length by 100mm width and a thickness of 50 mm. They were wrapped in aluminum specimen foil so that the top part of the foil was exposed to the radiation from the conical heater. 2) All the other sides were shielded from radiative heat. 3) Before the spark igniter was placed in position, the baseline data was collected for 60 seconds. 4) Experimental data was measured from the baseline. Results The results from the cone calorimeter test were as shown in the table below; Specimen Time of ignition(TTI) (seconds) Mean Heat Release Rate (HRR) Peak HRR Mean MLR Peak MLR Specific extinguish area SEA CO/Kg/kg PFI/(m2.s.kW) Polyvinyl chloride as sheath material and polyethylene in cable 7 128.50 239.89 0.066 0.132 790.79 0.0669 0.0292 Both sheath and cable made of PVC 8 109.80 183.55 0.063 0.148 745.01 0.0724 0.0536 Polyvinyl chloride as sheath material and polyethylene in cable 6 93.11 187.45 0.091 0.221 808.57 0.0570 0.0320 Both sheath and cable made of PVC 8 69.99 98.72 0.097 0.244 770.35 0.0546 0.0810 The Heat Release Rate This is one of the most important flammability parameters used for evaluating the fire hazard caused by different materials. The HRR curve with respect to time for this experiment is shown in the graph below Diagram showing the Heat Release Rate (Sample results obtained from Zhongjun, S. 2002. Experiment Study on Fire Performance of PVC Sheath Electrical Cables Exposed to High-level Heat Flux. Department of Fire Protection Engineering. Hebei, China: Chinese People’s Armed Police Academy). Fire performance index This index is defined by the proportion of the time of ignition TTI and the peak HRR. It is related to the FPI of the material and the flashover time. The flash over increases when the FPI reduces. The graphical comparison of the FPI for there four materials under consideration is shown in the diagram below X Polyvinyl chloride as sheath material and polyethylene in cable Y Both sheath and cable made of PVC X1 Polyvinyl chloride as sheath material and polyethylene in cable Y1 Both sheath and cable made of PVC The smoke parameter (SP) and carbon monoxide yield The smoke parameter is given by: SEA×HRR Where: SEA is the specific extinguish area HRR is the heat release rate When the smoke parameter value is high, the hazard caused by smoke is high. The variation in the smoke parameter (SP) is as shown in the graph below Graph showing the smoke parameter variation against time (Sample results obtained from Zhongjun, S. 2002. Experiment Study on Fire Performance of PVC Sheath Electrical Cables Exposed to High-level Heat Flux. Department of Fire Protection Engineering. Hebei, China: Chinese People’s Armed Police Academy). The carbon monoxide production value versus time for the four specimens is as shown in the graph below Graph showing the carbon monoxide production variation against time (Sample results obtained from Zhongjun, S. 2002. Experiment Study on Fire Performance of PVC Sheath Electrical Cables Exposed to High-level Heat Flux. Department of Fire Protection Engineering. Hebei, China: Chinese People’s Armed Police Academy). Conclusion It was found out that different materials had different time of ignition; they also had different fire performance index (FPI) and different heat release rate (HRR). It was also found out that Polyvinyl chloride as sheath material and polyethylene in cable had the highest HRR, FPI and SP value among the four materials. This means that it has the highest risk of causing a fire. From the HRR curves it was also found out that the HRR value of the both sheath and cable made of PVC increased rapidly meaning that the flame will spread more. References Grayson, J. P.Van Hees, A.M.Green. 2001. Assessing the fire performances of electric Cable (FIPEC). Fire and materials. Maijia, H.; Robinson, J. 1998. The Impact of the Type of Insulation on Overall Cable Fire Retardancy. Fire Retardants. Wang, Q.; Zhang, J, Zhang, F. 2003. The Principle and Application of the Cone Calorimeter. The modern science instrument. Zhang Jun, J. 2005. Polymer Combustion and Fire Retardant Technology. Beijing: Chemical Industry Press. Zhongjun, S. 2002. Experiment Study on Fire Performance of PVC Sheath Electrical Cables Exposed to High-level Heat Flux. Department of Fire Protection Engineering. Hebei, China: Chinese People’s Armed Police Academy Johan, A. 2002. Cone Calorimeter –A Tool for Measuring Heat Release Rate. Finland: Abo Akademi process chemistry center. [Online]. Available at http://www.tut.fi/units/me/ener/IFRF/FinSweFlameDays09/4B/LindholmPaper.pdf . Accessed august 20, 2009. Read More