I’ve
pondered about this issue and I think there may be a number of factors
involved. (Group input is highly desired) We both used large hoses
for our installations. 1.5” to the Y’s and 1” from the
Y’s to the rads. (Actually, one of us used Y’s and the other
T’s). I’m wondering if the large hoses after the Y was too
little flow resistance thereby allowing most of the coolant to pass through one
rad. I notice Tracey uses smaller hoses which may increase flow
resistance to each rad and provide more of a balance. I think someone is
using AN16 fittings which is 1” hose but by the time you get through the
restrictive male coupling, the same factors may apply.
Al
G. may be able to help me with this one… Assuming a perfect
world… what would the outlet temperature difference be between
series rads vs, parallel. My guess is… if we had 215 degrees
coolant entering the parallel rads and we get 180 degrees leaving the rads,
there is a 35 degree drop, or about a 16.3% drop. Series rads would give
a similar % drop divided by 2 for each. 215 – 8% = 199. Then
the second rad sees 199 – 8% = 184 (I rounded off the numbers cuz 1
degree isn’t an issue) By my calculation (which may be out in left
field) the difference is negligible.
In general, you will get better heat
rejection with more flow, and with higher average temperature in the radiator
cores (smaller delta T). Running the rads in parallel is better on both
counts. Connecting in parallel results in a larger flow path and less
pressure drop – less pressure drop results in more flow – more flow
results in a higher average core temp. And using large diameter, low
pressure drop lines is good because the lower the pressure drop, the greater
the flow.
If you had a positive displacement pump
(so the flow wasn’t dependant on pressure drop) the outlet temp would be about
the same in either case, series or parallel, for the same amount of heat rejected.
But with a centrifugal pump, the flow does drop off with higher pressure drop. So
how much better parallel flow is depends on how much of an issue the pressure
drop is.
When connecting in parallel, the same
flow will go to both cores only if the pressure drop (flow resistance) is the
same in both loops. The coolant will take the path of least resistance, so
it will automatically balance the pressure drop, not the flow. With large
enough lines, most of the resistance is generally through the cores, so
identical cores will likely balance well enough so you don’t need to be
concerned.
But since it is unlikely that the air
flow to the two cores is also balanced, getting equal flow isn’t really
the issue, and probably not very important. So if you want to get picky; it
is likely best to make the temp drop (delta T) equal. So the idea is to
measure the outlet temp from each core at operating conditions, and then
orifice the flow to the core with the lowest delta T until the outlet temps are
the same.
It’s not so tough really. Clamp
on a thermocouple to each outlet pipe, cover with insulation. If you have
a hose barb connection, get a brass washer with same o.d. (or just a little
larger) as the connector tube on the core (grind as necessary). File out
the i.d. until the area is maybe 60% of the inlet area of the tube. Place
this on the inlet side tube and slip the hose over and clamp. Measure
delta T’s again – you guessed it – adjust the hole size in
the washer until you get about the same delta T through both cores.
So there you have my take on the
issue. I connected two different rad designs in parallel, so I expect to
have a little balancing to do.
Al