Fire vortex from an alcohol substrate.





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Introduction

Despite the fact that the anatomy of the vortex is not a major fixation of physics, many questions of vortex behavior continue to interest designers of ships and aircraft. It also interests those who construct hydroelectric power stations and foresters concerned with fire prevention. Vortices in the wake of ships and aircraft represent wasted fuel; their presence requires considerable expenditure of energy. Vortices become a serious menace during forest fires because they are capable of picking up large flaming timbers and dropping them elsewhere to start new fires. According to Vincent J. Schaefer of the Atmospheric Sciences Research Center of the State University of New York, fire vortices are of prime concern to foresters who assume to burn over an area in order to clean it up before planting it with new trees. Even when care is taken to protect the surrounding area by lanes cleared of all combustible debris; a vortex can develop during the burn and spread the fire.

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Purpose

To determine what conditions influence the formation of vortices and what factors determine their intensity and rotation.

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Apparatus

  1. One piece of sheet metal ( 72 CM x 45 CM ) with a hole cut on center (15 CM x 15 CM)
  2. One piece of plexy glass big enough to cover the hole cut into the sheet metal.
  3. One roll of heavy duty aluminum foil to make various pieces in our apparatus, which include: chimney (chimney with holes) covering for the top of the cylinder
  4. Ethanol alcohol
  5. Petri dish
  6. Bunsen burner
  7. Ring stands
  8. Tongs
  9. Matches
  10. Ruler
  11. Scissors
  12. Safety glasses
  13. Cotton swabs
  14. Tape

Diagrams of our apparatus.

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Methods

WARNING: It is strongly advised that safety goggles are worn during all experiments.

Experiment #1: gap in cylinder apparatus vs. number of turns in vortex.

(See observation #1 for Bunsen burner and observation #2 for alcohol flame.)

  1. Adjust gap in cylinder to 1 cm.
  2. Place ring stands around Bunsen burner to support the cylinder
  3. Place aluminum over ring stands to block updraft.
  4. Light Bunsen burner
  5. Place cylinder apparatus over burner
  6. Have some one time ten seconds as at least two people count the number of twists in the flame during the ten second time span.
  7. Record the number
  8. Repeat steps two through 7 again and average the data.
  9. Repeat steps 1 through 8 with gaps set at 1.5, 2.0, 2.5, 3.0 CM

Experiment #2: chimney height from base vs. number of turns in vortex.

(See observation #3 for Bunsen burner and observation #4 for alcohol flame.)

  1. Set your gap at optimal results (we found 1cm was optimal)
  2. Construct a chimney 20 cm high and 6cm across
  3. Construct a base for the chimney and fit the chimney into it, place this on top of the cylinder.
  4. Light the Bunsen and place cylinder and chimney on the ring stands
  5. Have two people count the amount of twists in the flame in a ten second span
  6. Record data
  7. Repeat steps 5 and 6 and average data.
  8. Repeat steps 2 through 7 with chimney heights at 18, 16, 14, 12, and 10 CM


Experiment #3: height of hole from base of chimney vs. number of turns in vortex.

(See observation #5 for Bunsen burner and observation #6 for alcohol flame.)

  1. Set your gap at optimal results (we found 1cm was optimal)
  2. Construct a chimney 20 cm high and 6cm across with holes at 2.0, 3.0, 7.0 11.0, 15.0, 19.0 cm from base of chimney.
  3. Cover all holes except for 2.0
  4. Light Bunsen burner
  5. Place apparatus on the ring stands
  6. Have two people count the twists in the flame in a ten second time span
  7. Record data
  8. Repeat steps 3 through 7 and average data
  9. Repeat steps 3 through 8 except with holes open at 3.0, 7.0, 11.0, 15.0, 19.0


Experiment #4: squared area at the top of cylinder vs. number of turns in vortex.

(See observation #7 for Bunsen burner and observation #8 for alcohol flame.)

  1. Set your gap at optimal results (we found 1cm was optimal)
  2. Take a piece of aluminum and cut a hole 4 cm2
  3. Put this in place of the chimney
  4. Light the Bunsen burner
  5. Place the apparatus on the ring stands
  6. Have two people count the twists in the flame in the ten second period
  7. Record the data
  8. Repeat steps 6 and 7 and average data
  9. Repeat steps 2 through 8 with holes sizes set at 9, 16, 25, 36 cm2


Vortex Characteristics In Alcohol Flame

Repeat steps above with an alcohol flame. To create the alcohol flame, saturate a cotton swab with ethanol alcohol, put it in a petri dish and light it.

Failures And Successes Of Apparatus

Our first attempt at an apparatus was the use of sheet metal. This failed because it was not pliable enough to form a cylinder. Next was the use of aluminum foil to form a cylinder. This did not work because we could produce an accurate gap. So after the failure of the aluminum foil we decided the sheet metal was a good idea but we needed to make it more pliable. To solve that problem we used the same metal but applied heat through the use of a torch to make it more flexible. Then we cut a hole in the center of the metal and applied a piece of plexy glass to the hole. Then we drilled three holes on each end of the sheet metal, so when shaped into a cylinder they were parallel, then with nuts and bolts we fastened the holes together making it very easy to adjust the gap in the cylinder. The gap was only able to open to 4 CM because of the size of the bolt, but he apparatus was a success. Between making the apparatus and testing it through trial and error the making of the cylinder took us roughly three months. At times this project was very frustrating but very rewarding in the end.

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Observations

Observation #1

See Method Experiment #1

Observation #2

See Method Experiment #1

Observation #3

See Method Experiment #2

Observation #4

See Method Experiment #2

Observation #5

See Method Experiment #3

Observation #6

See Method Experiment #3

Observation #7

See Method Experiment #4

Observation #8

See Method Experiment #4


CLICK HERE TO VIEW A SHORT VIDEO CLIP OF A FIRE VORTEX PRODUCED DURING OUR EXPERIMENT.

CLICK HERE FOR PHOTOGRAPHS OF OUR RESULTS

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Analysis

In experiment #1(involving the adjusting of the gap)We found a negative correlation, which is as the gap became smaller the intensity of the flame increased. The intensity decreased with an increase in gap size. The Bernoulli effect could cause this; similar to when you pinch a hose the water leaving exerts more force.

In experiment #2 (involving the chimney height on the apparatus) we found that as the higher the chimney went, the more intense the flame was, this was a positive correlation. But when we used an alcohol flame it became a negative correlation.

Next we experimented with cutting different size squares at the ceiling part of the apparatus, we found as the hole size increased so did the intensity of the vortex.

In our next experiment we cut holes at different heights from the base of the chimney. We found that as the holes were cut at higher heights we noticed a stronger vortex.

We found that when we switched to the alcohol flame that the flame became more intense with all the experiments, but in experiments # 2 and 3 the correlation of the graph was negative with the alcohol and a positive with a Bunsen burner.

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Applications

Right to this day one of the best ways in Canada to quickly control a forest fire is the use of aircraft. There is no doubt that, when compared to other methods of controlling forest fires, aircraft are expensive to buy and operate, but when used effectively, they are fully capable of saving the equal of an entire season's operating cost in a single mission by stopping one potentially disastrous fire. One of the biggest problems in a forest fire is when the vortex becomes so intense that it can actually lift flaming timber and toss it elsewhere, starting a new fire. According to our data, a simple cut/gap in a formation of trees could be the difference between disaster and a quickly controlled and extinguished forest fire. This cut could be similar to our apparatus, in that we leave an opening or a “gap” to let air rush in, this gap would be cut at approximately 165 degrees to the fire. This according to our data will make the vortex less intense because the air isn’t being forced through a small opening between the trees. This will slow the fire down and make it more accessible to fire fighters and floatplanes.

On the other hand, for foresters who want to clear a plot of land, burning is a very low cost technique. There have been many cases were these fires have gotten out of hand because of lack of proper technique or because of a sudden shift in wind. According to our data, once again a simple cut/gap could be the solution. By making the cut before the fire, foresters and farmers, could control the fire. When a cut is made this alters the direction of spin in a vortex and the direction that it moves. So when the cuts are made on an angle of approximately 165 degrees to the fire, they create channels for the wind, which manipulates the direction that the wind hits the fire and controls the fire.

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Conclusion

According to our data as the gap in the cylinder is decreased the vortex in the flame increases in strength. When we adjusted the height of the chimney on top of the cylinder we noticed with the bunsen burner as the chimney went higher the flame grew in intensity, but with the alcohol flame when the chimney was short in height the flame grew more intense. When we adjusted the position of holes that we cut into the chimney we found, as the holes were placed higher, the vortex characteristics of the bunsen burner flame became more intense. However when we used the alcohol flame the lowest hole from the base of chimney produced the most intense vortex.

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Acknowledgements

We would like to thank our biology teacher Mr. De La Lis for his guidance and patience, without his assistance none of this would be possible. Also we would like to thank Mr. Frasier and Mr. Hillis for providing the materials needed and the help building the apparatus, also for lending us the digital camera. Also we would like to thank Mr. Church for kindly giving us disks to save our work on.

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Credit for the background design goes to 'T. Becker'. More free backgrounds from this source can be found at http://fireflii.8m.com/graphics/index.html.