REFLECTOR: High Oil Temps

[Brian Michalk]

After looking up some racing forums, it appears as though the parallel 
configuration is more efficient, all things being equal.

On 06/23/2013 05:42 PM, Brian Michalk wrote:
> Today I had a very good test flight.
>
> I've been battling high CHT and oil temps, and made the decision to 
> increase my prop pitch for todays flight to bring down RPM's. That 
> made a marked difference in CHT temps, and I could fly without 
> redlining the CHT's.
>
> Now, I still have high oil temps.  My oil cooler arrangement is two 
> oil coolers in the nose in parallel.  The secondary cooler has a 
> radiator fan attached with a flapper valve that doubles for ground 
> operations and cabin heat.  Needless to say, the fan doesn't do a very 
> good job, and I think is the source of my high oil temps.
> For this thought game, assume two identical oil coolers with equal oil 
> flow in parallel.  This means that each cooler gets 50% of the oil.  
> Now, assume no cooling air flows through one of the coolers. The 
> result is that half the oil is cooled, and the other half gets 
> returned at the same temperature it began.  The result is that I get 
> 50% of the cooling that's available.
>
> What I've done in the meantime is I've capped off my second cooler. I 
> have not flown with this configuration, and will do so this coming 
> weekend.  I really do think this will get me within the temperature 
> ranges to get around to some serious flight testing.
>
> Now, the real question:
> Given two identical coolers that flow equal parts oil, and also have 
> equal amounts of airflow, is it better to plumb them in series or in 
> parallel for maximum heat rejection?  It seems to me that parallel is 
> like having more frontal cooler area, while in series would be like 
> having a thicker cooler, with the larger frontal area being the more 
> efficient design.
>
> Does anyone have any info on this?
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