3 ms·

CO2 is super weird. In a CO2 tank it's actually two-phase, CO2 gas and liquid in a steady state equilibrium that is exclusively a function of the temperature. S

CO2 is super weird. In a CO2 tank it's actually two-phase, CO2 gas and liquid in a steady state equilibrium that is exclusively a function of the temperature. Since the outlet was connected to the HPLC pump inlet, if the temperature between the tank and the pump head was exactly equal, when the pump piston draws liquid in it every so slightly reduces the pressure, which results in the liquid CO2 boiling inside the pump head producing bubbles that make metering the flow rate impossible. So the cavitation in this case is indeed temperature driven (albeit indirectly) but it's really just a side effect of the pump type. A syringe pump style system just is well, a syringe, so the problem goes away.

fuzzfactor 7y ago
Excellent use of the HPLC pump, we used to order them by the pallet. Here's the phase diagram: https://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-temperature_phase_diagram.svg https://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-t... I'm no engineer, but I like to work with engineers that are good at not just established "engines" but imaginary ones too. I always thought any engineer should be able to understand this well-established graph just by looking at it, regardless of whether they had any ChE background. Engineers already exposed to material phase behavior sometimes still take a little while, but there's not much there, it's a pretty straightforward graph. Studying it alone should bring understanding, not of the full implications of the dynamic physico-chemical properties of course, just the states of matter that exist under the conditions indicated by the data. Some engineers can never get this, I don't get that. While I would prefer an engineer with an appreciation for what it takes to turn the imagination of some PhDs into apparatus capable of creating drawings like this, using commercially available components when possible, based primarily on drawings like this. I'm no capitalist without other people's money (I personally owned two of the automated positive-displacement high-pressure [syringe] pumps), but a good capitalist to work with would have enough imagination for an intuitive understanding of the leverage used to assemble advanced equipment into money-making machines, when the majority of operators must accept the high-dollar components as unrecoverable costs.
- neltnerb 7y ago
  I sort of agree, but I think you're too harsh. Having taught phase diagrams to freshmen, very smart freshmen, as with everything else it comes down to familiarity and practice. I tend not to look down on people for not knowing stuff they're not familiar with, I'm sure they could all get it with someone who can actually guide them through it. But I do appreciate a simple, inexpensive design of course. But they're so hard for people to make if they don't understand the deep details of everything in the system, and once the knowledge is split between two brains then it's a lot harder to spot inconsistencies. But I also can hardly blame people for throwing in the towel on deeply researching the sheer vastness of the McMaster, Swagelok, and Digikey catalogs. Much less ASTM standards or the ASM handbook. I work on building a lot of surprisingly easy things like electromagnets and battery charging circuits and low noise filters and precision temperature controllers and such like that in-house because it's shocking how bad and expensive stuff made commercially usually is. Just yesterday I was replacing a flow sensor in a water pump to water cool a vibrating scanning magnetometer my office mate designed. It's a fun line of work. I also do stuff on the side as a consultant along these lines to scratch the "let's make something people can use in industry" itch (http://neltnerlabs.com/ http://neltnerlabs.com/). But my biggest pipe dream for the past 9 years has been using AI tools to close the loop around synthesis and testing and predicting properties for heterogeneous catalysts. Equipment is a key part of that dream, sadly Google was uninterested (no ads?) and I've only ever found a handful of companies working on it all of which don't quite seem to get just how big a deal it is almost certain to be. At least the national labs are catching on.
  - Gibbon1 7y ago
    > but I think you're too harsh. What I found when I took thermo which is where you learn this stuff. Nothing really prepares you for the basic concepts before hand. So it's a steep hill to climb. I think some students get through it via rote memorization. Which means they don't actually understand it. I had to retake the first semester because I got a C-. Which was likely for the best. I also think that thermo is somehow very deeply connected to how the universe actually works. And the next step down is a doozy. So it's difficult to explain it in terms of something familiar.

fuzzfactor 7y ago

Excellent use of the HPLC pump, we used to order them by the pallet. Here's the phase diagram: https://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-temperature_phase_diagram.svg https://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-t... I'm no engineer, but I like to work with engineers that are good at not just established "engines" but imaginary ones too. I always thought any engineer should be able to understand this well-established graph just by looking at it, regardless of whether they had any ChE background. Engineers already exposed to material phase behavior sometimes still take a little while, but there's not much there, it's a pretty straightforward graph. Studying it alone should bring understanding, not of the full implications of the dynamic physico-chemical properties of course, just the states of matter that exist under the conditions indicated by the data. Some engineers can never get this, I don't get that. While I would prefer an engineer with an appreciation for what it takes to turn the imagination of some PhDs into apparatus capable of creating drawings like this, using commercially available components when possible, based primarily on drawings like this. I'm no capitalist without other people's money (I personally owned two of the automated positive-displacement high-pressure [syringe] pumps), but a good capitalist to work with would have enough imagination for an intuitive understanding of the leverage used to assemble advanced equipment into money-making machines, when the majority of operators must accept the high-dollar components as unrecoverable costs.

neltnerb 7y ago
I sort of agree, but I think you're too harsh. Having taught phase diagrams to freshmen, very smart freshmen, as with everything else it comes down to familiarity and practice. I tend not to look down on people for not knowing stuff they're not familiar with, I'm sure they could all get it with someone who can actually guide them through it. But I do appreciate a simple, inexpensive design of course. But they're so hard for people to make if they don't understand the deep details of everything in the system, and once the knowledge is split between two brains then it's a lot harder to spot inconsistencies. But I also can hardly blame people for throwing in the towel on deeply researching the sheer vastness of the McMaster, Swagelok, and Digikey catalogs. Much less ASTM standards or the ASM handbook. I work on building a lot of surprisingly easy things like electromagnets and battery charging circuits and low noise filters and precision temperature controllers and such like that in-house because it's shocking how bad and expensive stuff made commercially usually is. Just yesterday I was replacing a flow sensor in a water pump to water cool a vibrating scanning magnetometer my office mate designed. It's a fun line of work. I also do stuff on the side as a consultant along these lines to scratch the "let's make something people can use in industry" itch (http://neltnerlabs.com/ http://neltnerlabs.com/). But my biggest pipe dream for the past 9 years has been using AI tools to close the loop around synthesis and testing and predicting properties for heterogeneous catalysts. Equipment is a key part of that dream, sadly Google was uninterested (no ads?) and I've only ever found a handful of companies working on it all of which don't quite seem to get just how big a deal it is almost certain to be. At least the national labs are catching on.
- Gibbon1 7y ago
  > but I think you're too harsh. What I found when I took thermo which is where you learn this stuff. Nothing really prepares you for the basic concepts before hand. So it's a steep hill to climb. I think some students get through it via rote memorization. Which means they don't actually understand it. I had to retake the first semester because I got a C-. Which was likely for the best. I also think that thermo is somehow very deeply connected to how the universe actually works. And the next step down is a doozy. So it's difficult to explain it in terms of something familiar.