Posted tagged ‘fluid dynamics’

Day 441

November 20, 2012

You know you’re getting deep into the semester in Brewhouse Calculations when it takes you a solid hour just to review last week’s class. Finished with review, we moved on to some basic fluid mechanics. Liquids and semi-solids are moved all around the brewery in pipes, so an understanding of flow rates and turbulence would seem to be fairly important.

First, we learned that (in the metric world), a force of one newton pressing on one square metre equals a pressure of one pascal. That’s not much pressure, by the way–typical barometric pressure on a nice day is about 101,325 pascals (or about 101.3 kilopascals).

(Isaac Newton, by the way, was an English mathemetician who undoubtedly put many newtons of pressure on the seat of his chair when he sat down despite the fact that he was only one Newton. Blaise Pascal was a French mathemetician, which just goes to show that if you want something named after you, become a mathemetician. But I digress…)

We reviewed the various types of pressure gauges, then moved on to flow meters–the instruments that measure how fast fluid is moving through a pipe.

Due to friction with the pipe walls, fluid near the walls always moves slowest, while fluid in the middle of the pipe always moves fastest. If there is a gradual gradient between the two extremes and little in the way of eddying and break-up, then the flow is said to be smooth or “laminar”. If there is a lot of eddying and mixing of the liquid, the flow is turbulent. This is represented by something called a “Reynolds number”, and the formula for calcualting it is

Re = pud/µ

where

  • Re = the Reynolds number: less than 2100 is laminar, more than 4000 is turbulent, somewhere in between is transitional
  • p =  density of fluid (kg/m3)
  • u = velocity of the liquid (metres per second)
  • d = diameter of the pipe (metres)
  • µ = fluid dynamnic viscosity (kg per metre-second)

If you want to determine the minimum diameter pipe you need to ensure laminar flow, or conversely, the maximum diameter needed for turbulent flow, you can rearrange this formula:

d = (Re µ) / (p u)

For instance, if you want to move some wort that has a density of 1034 kg/m3 and a dynamic viscosity of 5 x 10-3 kg/ms, and your pump is going to move the wort at 5 m/s, then to ensure laminar flow (a Reynolds number of 2100):

d = (2100 x 5 x 103) / (5 x 1034) = 0.002 m = 2 millimetres

So to ensure laminar flow, your pipe can be no smaller than 2 mm in diameter. Since most pipes carrying wort are much larger than 2 mm, it seems you won’t have any trouble maintaining a laminar flow with this particular wort.

In History of Beer, it was more student presentations, including a history of glassware, brewing in Ontario, and the Aztec production and use of pulque, an intoxicating spirit made from the agave plant.

Instructor Bill White also covered brewing in North America in the 20th century (although at times I felt like it was Bill’s history of Labbatt’s in the 20th century.)

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Day 147

February 3, 2012

In Microbiology Lab, we created fresh growth medium in a petri dish, perfect for culturing the evil bacteria and wild yeast hanging around your brewery.

The actual weighing and mixing of the solution took just a few minutes. “Great,” I thought smugly. “We’ll be out of here early.”

Hah.

The next step was to sterilize the solution in the autoclave. Using the autoclave turned out to be a two-hour bottle-neck.

Result: an hour after the lab was supposed to end, we finally poured a bit of the sterilized solution into a petri dish, let it sit for five minutes to solidify, then put the petri dish in the fridge, just as Doug Pengelly came through the door for three hours of Packaging.

So we returned to our lab stools to learn about fluid dynamics, specifically how liquid in your brewery operates inside a pipe. Here’s the thing: as liquid flows through a pipe, the liquid closest to the pipe wall slows down a bit due to the drag against the pipe wall. However, the further away from the wall you get, the less friction and therefore the faster the liquid moves until you get to the very centre of the pipe, where the liquid moves the fastest. This difference in velocity from the pipe wall to the centre of the pipe can cause turbulence as the layers of liquid moving at different velocities interact with each other.

However, there are various factors that affect this. If the liquid is moving very slowly, there won’t be much friction with the pipe, therefore less difference in velocities throughout the pipe and less turbulence. If the liquid is thicker (more viscous), it will cause more friction and more turbulence. If the pipe has a large diameter, proportionally less of the liquid will be in contact with the pipe walls, meaning less overall friction, and therefore less turbulence.

Now, less turbulence would seem to be a good thing, but as Doug pointed out, there are times in the brewery when mixing the liquid up via turbulence is a good thing: cleaning the pipes, oxygenating the beer on the way to the fermenting tank, carbonating the beer, and removing heat in the heat exchanger. And of course, conversely, anytime you are transferring carbonated beer, you want as little turbulence as possible so that it doesn’t foam up.

We also looked at moving liquids around the brewery, especially when that involves moving from one level to another. That brought us to–

Pumps.

Nooooooooooooooo! I ran from the room. (Perhaps in spirit if not in body.)

Finally, after 6 straight hours sitting on a lab stool, it was time to go home. Oh wait, not tonight. It was actually time to trade in jeans and a sweater for a jacket and tie, since I was participating in the inaugural “Caps, Corks & Forks” dinner, a beer versus wine competition. Culinary students created and presented six fabulous courses, then wine and brewmaster students paired a wine and a beer with each course. The 80 diners then voted (with either a cap or a cork) on which one paired better with the food of each course.

It was a close competition: after five courses, the score was Wine 3, Beer 2.

For the final course–dessert–I presented the beer we had chosen to be paired with cinnamon pumpkin fritters: Great Lakes Brewery Winter Ale, a spiced honey ale. Winner!

Final score: Beer 3, Wine 3.

Ah, but as a tiebreaker, the organizer counted the total of all votes cast, and wine was declared the winner.

Dang!


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