5. (30 points) A vortex cooler is a real device that, on first glance, seems like it would be impossible.
The device doesn't require any work input, but it can take in a stream of gas, and separate it into a hot
outlet and a cold outlet. See the image below from www.vortec.com. For this problem, consider a
vortex tube that operates on air, which you should treat as an ideal gas with constant specific heats.
Air enters the tube at 1,000 kPa and 300 K. The hot exit temperature is 325 K and the cold exit
temperature is 250 K. The device is adiabatic, and has no moving parts (so there is no work).
a. (25 points) Assuming both exits have the same pressure and the process is reversible (best-
case scenario), what is the maximum exit pressure? Hint: you will need to use the 1$^{st}$ law, 2$^{nd}$
law, and mass conservation law.
b. (5 points) When introducing the concept of reversibility, I originally said that it was
impossible to \"unmix\" hot and cold gases, but this device does exactly that. How is it
possible for this device to \"unmix\" gases without violating the 2$^{nd}$ law?