Very nice work.
I'm a little confused
I tried these configurations:
SOLID PP CORE
DISTANCED PP CORE
ALUMINUM CORE
Which is the Solid PP core and which is distanced????
SOLID PP DUAL CORE
ALUMINUM DUAL CORE
The distanced PP core was a total looser, did not even reached a 40% efficiency
How are you measuring efficiency?
Assuming no condensation and equal air mass flows, I've decided that
efficiency is
1-((stale Tout-Fresh Tin)/(inside temp - outside temp)).
For a cross flow exchanger, if the thermal conductivity of the barrier
is infinite, you can take out the metal and let the air mix. That
says the best you can do is 50% efficiency with the internal temperature
midway between inside and outside temperatures.
As a practical matter, you probably can do a little better
than 50% because there is a thermal gradient across
the core. Stated a different way, I think that a barrier
with less than perfect conductivity does increase the
efficiency by allowing a thermal gradient.
Solid PP and aluminum core have equal efficiency, reached 98% with low flow (PC fans with no relevant pressure...)
98% sounds unreasonable for any decent air flow. I'm too sleepy to
do the math, but I'd expect a series dual core cross flow exchanger
to be something like 75% efficient.
If you imagine a series of many cross flow exchangers, the limiting
case becomes a counter-flow exchanger. At any point along the length
the incoming and outgoing air is at the same temperature, but
that temperature varies along the length. Theoretical maximum
efficiency can approach 100%.
Dual core rates quite the same, but allows much more air to pass trough.
The last dual core photo was a combination of PP and aluminum cores, same results (but that was quite obvious..)
I'm confused by that paragraph.
Two equal cores in series should have twice the resistance
to air flow. If e is the efficiency of one core, I'd expect
n cores in series to be something like 1-(1-e)^n...but it's
too early in the morning to try to prove that.
What am I missing?
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