Not all science/engineering is warp drives and robotics. Some of it’s not even as sexy as electronics. I’m talking about some of the low-level, apparently boring stuff like metallurgy, acoustics, heat flow, and fluid dynamics. These are all those invisible things that seem to magically flow forth from the lab in the back into the products in the front. There’s no glamor, no product launch, no telling the kids how it has impacted their lives. But some of it shows up in odd places.
Today I’m going to talk a little about ICEEs. Here in the states, an ICEE is a cold treat that’s basically flavored slush. It comes under many different brands, from Slurpee to Slushee to God-only-knowsee. It comes in a variety of flavors like cherry or raspberry as well as a few branded soda flavors including my favorite Coca-Cola. They’re great on a summer’s day, and I’ve probably suffered some kind of permanent damage from the cumulative effect of all the brain-freeze moments I’ve had from sucking these down too fast.
But they are also the source of the saddest sound in the world: that moment when it will no longer rise up the straw. We’ve all heard it, that gurgling gasping sound, the very death rattle of joy. You can stir it. You can shake it. You can move the straw. But all this buys you is another two or three slurps before you hit again. You’re like that desperate doctor trying to shock the dying patient’s heart back to life, all to no avail.
What causes this? I don’t mean the particular acoustics of the sound. I mean, why can’t I keep sucking on that straw until the very last ounce of ICEE is in my mouth, freezing my brain? It’s not like it’s always the last twenty percent that remains inaccessible. Sometimes I get down to the final few sucks before losing this joy, while other times my happiness dies at birth with the cup over half full.
I figure it’s a combination of factors: the overall temperature of the mix, the ratio of ice to fluid, the viscosity of the fluid portion, the width of the straw, the atmospheric pressure, the height of the remaining stack vs. the length of the straw, and so on and so on. These factors together define a region in some multi-dimensional vector-space. Inside the region we are filled with that childhood joy, while outside we are left to the barren wasteland, cast out of our ICEE paradise.
But how is that boundary condition defined? This is where I return to that unglamorous science. Somewhere out there, I’ll bet some fluid dynamics scientist has done the research to answer this. I think of him as Dr. Jablowski. I doubt his PhD dissertation was titled “On the End of ICEE Joy”, but he did the same kind of research on the fluid dynamics of phase-transition liquids in suction pumps. He probably had in mind some kind of industrial coolant application, but there’s always the possibility that he was inspired by some disappointment in the cafeteria’s drink line.
The shame of it is, as back lab as such research would have been and with as much information out there as there is, I will probably never find that dissertation. What’s worse is that even my relatively high level of mathematic and scientific literacy will not be up to the challenge of the multi-variable differential equations necessary to understand his conclusions. I will probably never shakes hands with Dr. Jablowski, or whatever his/her name is.
But I still appreciate that he has done the work. It probably influenced the design of the ICEE machine. His work probably keeps that slurry stirred at just the right temperature for optimum conditions. He may have advised them on the proper shape for the dispensing nozzle to maintain the surface tension around the flowing column.
So now, when I hear that saddest sound in the world, I acknowledge the work of this unheralded researcher. My friends and I now call this transition from joyful slurree to anguished gasps the Jablowski Limit.
I just hope he doesn’t mind that we made him Polish.
So long as you pronounce his name “Yablovski”, he’ll probably be ok with it.
Heh… yes, I probably should pronounce it that way. Alas, I think so far, I was giving a proper American butchering.
“Heat transfer and pressure drop in ice-water slurries”
Wow, that’s pretty close to being spot-on. I bow to your google-fu.
Of particular interest, they highlighted a factor I did not consider, namely the size of the ice particles in their ice-water slurry.
In their industrial application, many of their ice crystals were over 1mm in diameter, and they had a non-linear pressure drop-off at between 2% and 4% ice solution, though other tests suggested that smaller particles (i.e. 1mm) could maintain the higher pressure at concentrations of as much as 11%- 30%.
Which begs the question, how large are the ice crystals in an ICEE? When I look at a fresh ICEE, I don’t see any features as course as 1mm, so I suspect that the particles are much more fine than that.
However, when I look later at the dregs, i.e. past my “Jablowski” limit, I do see much courser textures. This leads me to wonder if the thing that pushes my ICEE too far is that over time, the ice particles coalesce to become large enough that their friction factor is too great, making it a mechanical issue rather than a matter of percentages or temperature.