Experiment on Fire Box - Lab Report Example

Name Course Date Table of Contents Table of Contents 2 Aims 3 Apparatus 3 Methodology 3 What was measured and accuracy 4 Data obtained, explanation & analysis of data 4 Personal observations 6 Explanation & analysis of data 7 Evaluation of the experiment 7 Conclusion 8 Experiment on fire box Aims The aim of the experiment was to study the stages of fire development inside an enclosure in relation a real fire situation. This was accomplished by burning a Polymethyl methacrylate (PMMA) in a fire box in the laboratory. Apparatus The fire box The apparatus were arranged in a fire box as shown in the figure below. Figure 1 shows the measurement of the firebox The firebox was made of Monolux 500 insulating material whose thickness was 25mm. 12 thermocouples were placed in the firebox in a regular pattern and PMMA were near the centre as shown. The sizes of cross section of PMMA used were 100 x 100mm and 200 x 200mm. The temperatures were recorded every two seconds with the help of squirrel data logger. The change in mass was also recorded at an interval of 30 seconds. Methodology PMMA was mixed with petroleum gel before pouring on the fuel and placing them on a metal plate. The plate placed 130mm away from the opening and connected to the balance to measured the change in mass. Thermocouples were also placed evenly inside the compartment and connected to squirrel data logger to record the temperature. Finally, the fuel was ignited using a torch and left to burn till the fire went off by itself. What was measured and accuracy The temperature in the firebox was measured through the use of 12 thermocouples that was places at regular ponts inside the firebox. Thermocouples had an accuracy of 0.10C. Inconel was install in the firebox to record the data and to measure the accuracy. Data obtained, explanation & analysis of data Figure 2: Graph 01 Temperature of the thermocouples From the graph it can be seen that the temperature varies at different parts of the firebox. The temperature recorded by the thermocouples 1, 2, 5, 6, 9, 10 are lower since they are located at a point lower than level of the fuel bed as shown in the figure 1 above. There temperatures ranged between 0 and 3500C. Thermocouples 1, 5, and 9 show the lowest temperatures, with thermocouple 1 being the lowest of the three. Thermocouple 1 was located far from the fuel bed. Thermocouple 5 was placed below the fuel bed where cool air (drawn by the plume rising towards the ceiling due to buoyancy) flows (Barham, 2006). Temperature spikes seen in thermocouple 5 at an end of the developing stage were due to flame impingement. Thermocouples 3, 4, 7, 8, 11, and 12 show the highest temperature as they were located in the region by the generated thermal smoky layer. Thermocouple 8 show the highest temperature as it was located directly above the fuel bed and also at the region where thermal smoky layer are generated. The temperature spikes may be due to the direct impingement by the flame. The mass flow of the compartment resulted in rise in temperature for thermocouple 12. Thermocouple 9 also has low temperature as it is located near the ventilated opening where cool air flow into the firebox. The highest temperature reached is 3200C. Figure 3: Graph 02 Temperature of the thermocouples The temperatures range in this experiment was between 0 and 5500C. Thermocouples 1, 5, and 9 show the lowest temperatures, with thermocouple 5 being the lowest of the three. Thermocouple 5 was directly placed below the fuel bed where cool air flows. Thermocouples 1 and 9 were located at far ends from the fuel bed. Thermocouple 1 was the second lowest as it was located at a far end from the fuel bed. Thermocouple 9 was located near the ventilated opening where cool air flow into the firebox. The highest temperature was 8000C. Personal observations Time line and personal observation from the experiment Incipient stage Time (s) Time (s) Observation made 100 mm PMMA 200 mm PMMA 0 - 5 0 - 5 The fire was ignited on PMMA 50 10 Smoke started being produced from the fuel. 100 - 200 50 - 100 The fire started to grow and it started cracking sound as the colour change to orange. Growth stage Time (s) Time (s) Observation made 100 mm PMMA 200 mm PMMA 250 - 700 200 - 700 The length of the flame and smoke increased, and most parts of the fuel bed was covered by the flame Fully developed stage Time (s) Time (s) Observation made 100 mm PMMA 200 mm PMMA 700 – 1400 700 - 1400 The smoke was seen to be floating and covered the ceiling, the fuel bed was covered with flame and the smoke moved out of the door. Decay stage Time (s) Time (s) Observation made 100 mm PMMA 200 mm PMMA 1450 - 1700 1450 - 1700 The fire began to reduce in size and the smoke produced started to decrease 1750 1750 The flame went off, and the all the fuel was consumed Explanation & analysis of data Mass loss rate and Heat release Rate in different stages of fire Figure 4 For 100x100 mm PMMA a rapid mass loss rate was recorded between 800 and 1500 seconds. For 200x200 mm PMMA a rapid mass loss rate was recorded between 600 and 1500 seconds. Ignition stage This is the initial stages of development as shown in figure 2 and 3. Figure four show mass loos rate for the two PMMA. The mass loss rate increased with time. The rate was low at the beginning since fire took time to penetrate through the thick skin of PMMA. Developing stage The mass loss rate at this stage started to increase. Fully growth stage This stage showed fairly constant mass loss rate. High heat release rate was also recorded at this stage. Decay stage From 1500 to 1700 seconds it showed the highest rate of heat loss rate. The mass loss rate also slowed down as the mass near zero. Evaluation of the experiment The four stage of development of fire, which include ignition, growth stage, fully developed stage and decay has been noticed. At a fully developed stage, the upper and the lower layers are visible from the temperature time graph. The temperature at the upper portion of the enclosure was uniform. This may have been contributed by the small space available in the firebox. The temperature is expected to vary over the entire space in complex or large buildings. In enclosures with ventilation controlled fires, where highest temperature is observed near the supply of air (Drysdale, 2011; Nag, 2008). Time for thermal penetration, tp on the wall is calculated as follows The thickness of the firebox = 25mm Heat transfer coefficient is calculated as follows. 672K Conclusion Three stages for fire develop development has been shown in the experiment. The amount of heat released in the experiment was too small to enable flashover that usually occurs between the developing stage and fully developed stage. The upper layer requires a temperature of 6000C for flashover to occur. References Barham R., (2006). Fire Engineering and Emergency Planning: Research and applications, Routledge Bergman, T. L., & Incropera, F. P. (2011). Fundamentals of heat and mass transfer. Hoboken, NJ: Wiley. Bjorn Karlsson, James Quintiere, (1999). Environmental & Energy Engineering, CRC Press Drysdale, D. (2011). An introduction to fire dynamics. Chichester, West Sussex: Wiley. Enclosure Fire Dynamics Nag, P. K. (2008). Engineering thermodynamics. New Delhi: Tata McGraw-Hill. Read More