ACCURATE FLOWMETER FOR $10




Barrow Alaska Blowing Soap Bubbles

The full story at the end of this page.


SOAP BUBBLE FLOWMETERS



There are a lot of types of flowmeters available to measure air flow. If you need to measure airflow in the range of .2 to 2 liters per minute, the cheapest and most accurate device is a soap bubble flowmeter. It is simply a tube with constant diameter with a couple of lines to indicate a known volume. For a positive flow system, air is introduced below the surface of a soap bubble solution (Mr. Bubble works great) and the bubble moves up the flowmeter. You time the leading edge of the bubble from one line to another.

The math is simple. If the volume is .1 liter and the time is 5 seconds the flow is calculated as: 60 seconds per minute / 5 seconds per transition = 12 transitions in a minute. .1 liter per transition x 12 transitions = 1.2 liters per minute. If 5% accuracy is acceptable stop here. If you want higher accuracy and the gas you are monitoring is dry, divide the answer by 1.03 to account for the addition of water vapor to the flowing stream at room temperature.

Your accuracy will be determined by the accuracy of your volumetric measurement setting the lines and your timing accuracy. For an approximately one liter per minute the full volume should be somewhere between .1 liter and 3/4 a liter.

POSITIVE PRESSURE FLOWMETERS



To calibrate the flow from a regulator or critical orifice exhaust system you need a positive pressure flowmeter. To make one you need the following materials. A basting bulb and syringe, a constant diameter cylinder, a inlet port, some soap bubble solution, and some epoxy putty from the plumbing department at Lowes.



Remove the cap from the bottle and dispose of the contents in an appropriate manner. Then take the baster apart and slide the baster bulb on the bottle as shown.Cut the bottom off the bottle.

Mix up some epoxy and seal the bulb on the bottle. While it is still soft, stick in the port. I have used a 1/4 inch barbed to 1/8 inch npt pipe fitting. Don't worry about clogging the port at this point. After this semi hardens add more epoxy to build up a secure seal and solid connection.

After it hardens sneak into the kitchen and add some water to the flowmeter until the water is in the constant diameter area. Mark the line.

Now sneak out the spouses measuring cup and measure 1/2 a liter of water. If you have postal scales, you can weigh the cup and then the water and cup. I just used the cup measurement.

Add the water to the flowmeter and mark the new level. When the bubble goes from the bottom to the top, 1/2 liter had flowed. Pretty neat huh. Put the measuring cup back where you found it.

Find a drill bit that fits into your port fitting and drill out the epoxy making sure that you do not drill all the way through the bottle.

Pour your soap bubble liquid into the flowmeter to the red line. Note that it is below the port. Make sure that you wet the walls of the flowmeter with bubble stuff. Now when you hook a tube to the port air will flow though above the level of the liquid, but when you squeeze the bulb, the level rises and a bubble forms. You measure the time for the bubble film to go between the bottom and top lines, do the math and you have your measurement.

Have fun with your bubble meter and if I get inspired I will show you what to do with a live chicken, and egg beater, and a pair of panty hose.





Now for the rest of the story. Somewhere about 1990, I was in Alaska on business. When ever I go somewhere, I try to get in a little Monkey business. Having been in the Antarctic in the 60's, I wanted to count coup on the Arctic. A flight to Barrow was just the thing. I took a bottle of soap bubbles, my plastic flute, and of course my 9mm 14 shot semi automatic. I arrived in the Will Rodgers-Wally Post airport and after checking into the "hotel" looked around the town. That took about 8 minutes. At about 10 PM I headed out on the ice flow carrying my plastic flute, hoping to see a Beluga Whale . After a 1/4 mile hike to the edge of the ice, I found a nice spot and sat down to watch for whales playing my flute. Then the first sign of trouble began.

There were whales all around, maybe they enjoyed the flute, maybe not, but they cut and ran when four native Americans came up in their noisy snowmobiles dragging a sled. They accused me of scaring the whales, and one had the audacity to note my considerable bulk. "Hell, you are so fat, I should harpoon you" he threatened. I laughed and pulled out the gun and said with a smile, "And I ought to shoot your stupid %*%#". They jumped on their iron steeds and zoomed away and I watched the sun go around the horizon, never setting.

Later that morning, I was on the edge of the ice next to the town blowing soap bubbles. The joke was that I was trying to see if they would freeze as a balloon. It really attracted a bunch of kids who had never seen soap bubbles before. After a little while, I gave the bubble stuff to one of the dads who was watching. That was the second event that soon brought the Deputy Sheriff a knocking at my door..

He introduced himself and asked me to dinner...how could I refuse...besides I had never eaten at the Arctic Circle Mexican Restaurant...and I really had no other plans. It is still there.At the restaurant, I relaxed. He was a big burly man about 50 years old and had his young blond good looking French Canadian wife with him. He came right out with it. "You have really stirred up this place in your last 36 hours".

"How so" , I asked innocently.

"First you run off the whales, then you threaten some of the locals, and there are rumors that you were dealing drugs. What are you here for, we do not get many tourists."

I explained that I was here for 2 days to be in the Arctic, I did not run the whales off, the snowmobiles did, and I only responded to a threat of being harpooned, telling my side of the story. He laughed so hard I though he would cry.

"Ok, what about the kids at the beach?"

I explained the soap bubbles and his wife started laughing too. The evening was starting to become fun. He explained that one important element of the local culture is for the men to kill a whale and have a big feast. This year their luck was not good....no whale....and their wives were teasing them.

To make matters worse, they tried for a whale several days before and forgot to load the shotgun shell in the harpoon so it just bounced off. They were getting frantic as their manhood was at stake.

He insisted on picking up the tab and gave me a ride to the airport the next day. I am not sure if it was a kindness or he just wanted to be sure that I left town. That is why this project starts with a picture of soap bubbles.

Happy bubbling

Tom




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