Heat Transfer in Living Color...

Mark Eatherton

OK, maybe not living color, but color none the less.



My friend the HeatMeister and I were talking about low loss headers, and how they are piped. I remember posting these here once, and someone, maybe Brad White said they didn't think that cross flow was really that beneficial, but for the life of me I can't remember why.



What do YOU guys think???



ME

NRT_Rob

well

I don' t know why you would cross flow a low loss header, but when we do BUFFER TANKS with a 4 port arrangement like this, we do cross flow, which is exactly like your counter flow example except with one side flipped. so your two outs oppose and your two ins oppose. we do this to ensure full mixing of the tank and therefor ensure full buffer capacity is used.



however the price you pay is that your return to the heat source is blended water, as is your supply water to the heating system. so your heat source might have to run slightly hotter and may get slightly warmer return water as a result.



I have to admit that the math on this, I have not figured with any rigor. However, I do not like "regular" counterflow on BUFFER tanks because of my fear for "straight through" flow, which defeats the entire purpose of buffering



for that reason, we prefer 2 pipe buffer tanks (basically just making them a short, very fat pipe of pipe). then nothing is blended unless we are still doing p/s piping, and in that case we're only blending in one direction, either supply out or source return, depending on which flow is higher.



for hydraulic separation though, again, I have no idea why you would do cross flow.

bob_46

Mixology

Depends