Quote:
Originally Posted by 911monty
Wow. I like the KISS principle. Real world example, a centrifugal pump or compressor works by taking a fluid and increasing it's velocity (impeller) then routing to a volute (fancy name for wide part of the pipe) which decreases velocity and increases pressure. P&V inverse relationship. As far as temperature is concerned expanding gasses cool. The wrap otherwise is a good idea.
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I admit that I had not thought of an exhaust expansion like a volute but I really do not think that they are equal. Lets try to think this through though. The flow dynamics of an exhaust system and centrifugal pump are not the same. Exhaust systems are pulsatile, centrifugal pumps rely on constant flow, and these two phenomenon do not behave the same. Even if exhaust were a constant flow, the geometry between the two are markedly different - small diameter increase over relatively short distance versus marked expansion over relatively longer distances. Look at the role that A/R plays in turbocharger applications - reducing the length of the volute substantially decreases the effectiveness in the design's ability to build top end pressure. Since this is a straight line, the R would be approaching infinity which means that little number divided by really big number is a teeny tiny number. Where there may be a marginal increase in pressure at the expansion joint, the reduced resistance of the pipe to follow it would more than make up for it.
Here is another real world example (I'm a surgeon who sees a fair bit of trauma so bear with me here) - someone comes into the ER bleeding to death. I have a choice - an IV catheter (the part that goes in the vein) that is smaller than the tubing that goes back to the bag, or an IV catheter that is larger than the tubing that goes back to the bag. If you are correct, the larger IV catheter would not flow as well since there is an increase in relative diameter in the system. Trust me when I say that this is not the case. That catheter (called a Cordis) saves peoples lives by replacing blood faster than most injuries can lose it.
Shorter and fatter is the way to go when flow matters. Just ask Ron Jeremy. That is, until you disrupt gas scavenging (complete disruption of laminar flow), and then you've gone too fat.
I know I sound like a smart ass, I am just having fun with this though. Your statements are valid. I wish I had a setup to test it truthfully. I always learn the most when I'm dead ass wrong.