"Wayne Whitney" wrote in message
. ..
Hello,

I'm interested in comparing two designs of water-water heat exchanger,
where one side is pressurized and one is not (gravity flow). The
pressurized flow rate will be 50-75% of the unpressurized flow rate.

Design #1: Unpressurized flow through 2" copper pipe, pressurized flow
through 1/2" copper pipe wound helically around the 2" copper pipe. I
guess the helical 1/2" coil should be soldered to the 2" pipe for
improved heat transfer?

Design #2: Unpressurized flow through 1.5" copper pipe, which is
sleeved in a 2" copper pipe. The space between the pipes is
pressurized; water enters one end and exits at the other through the
creative use of reducing tee connectors.

So which design is better? If Design #1 used 1.5" pipe instead of 2"
pipe, and Design #2 used a helical baffle between the two pipes to
direct the flow, I think there is no question that Design #2 is
better. But absent those changes, does Design #1 win? By alot?

Thanks, Wayne

Maybe I am missing something, How do you get the pressurized side to go
slower than the non pressured side?

Not knowing more about the delta t it is impossible to guess which would
work. Discounting efficiency completely.