|
|
Leon kindly provide the webpage for the Davies EWP of recent discussion
(Thanks, Leon). I
just took a look a the tech data on the EWP that Todd is going to test out
for aircraft application. The data looks impressive. Taking one of the
charts it shows that at 5500 rpm for a typical? 6 cyl water pump engine
that 6000 watts of power are consumed by the mechanical water pump. From
the data, it appears that the Davies EWP can do the same cooling job for
approx 105 watts of energy (7.5 amps x 14 volts = 105 Watts). 6000 watts =
approx 8.5 HP or say a net gain of 6000-105 = 5895 Watts = 7.9 HP. So for
say a 160HP engine installation that would be a useful HP gain of approx 5
% - not too bad.
Now my first knee jerk reaction was "No Way" based on some previous round
house discussions about electrical water pumps for the reasons cited below.
However, it appears that my initial reaction may be based on an incorrect
assumption about the amount of energy needed for adequate coolant flow Vs
that consumed by the typical mechanical water pump.
I recall that on another list that one figure that was derived for HP
required to drive a mechanical water pump at 6000 rpm was on the order of
8HP, which appears to correlate rather well with the figures shown on the
tech data chart from Davies website. On that list, this was viewed as
fairly convincing "proof" that an electric water pump would be impractical
based on the "required" 6000 watts at 14 volts. This would require 6000/14
= 428 amps! Hey! thats engine cranking power. Clearly not feasible for an
aircraft application. End of Story! Well, as they say "Not So Quick!".
It appears that the crucial difference is that the assumption was made that
6000 watts constituted the power required to drive the coolant at those rpms
to assure adequate cooling. What the Davies charts seem to imply is that
most of that energy is wasted by a mechanical pump (at that engine rpm) and
is simply unnecessary
friction and head pressure losses. Certainly thought provoking and clearly
worth looking into.
I also examined the data log chart on use of the EWP pump with the typical
six cylinder engine but am not certain I am interperting it correctly. This
is the last chart under the Technical Data Menu of their web site. If I am
reading it correctly, it appears that the engine is started and the coolant
temp starts to climb. While based on the current drain, the EWP appears to
be running, there does not appear to be any coolant flow trace shown until
after approx ___ minutes. Then the electric current appears to increase to
____ amps and coolant flow appears to start. Then the coolant temp gradient
appears to start to level off (presumably because the pump is now flowing
coolant) and remains steady unitl end of chart.
There are a couple of coolant flow spikes which may imply the pump is
cycling On and Off based on need. In any case, without any indication of
engine power or RPM its hard for me to tell what the chart truly means.
The best I can come up with it that what ever the power level the engine is
operating at, the pump appears to move sufficient coolant to stabilize the
system temperature within 15 minutes. But of course there is a BIG
difference in heat rejection needed if at idle, vs mid power level vs WOT.
I know, I know - my skepticism is still showing through and I'm not even
from Missouri {:>). But, I am convinced that previous discussions about the
viability of the EWP may have been based on flawed assumptions and the topic
deserves another look.
So, Todd, based on this technical data, it appears that I may have been off
in
left field on my comments about the practicality of the electric water pump
for aircraft application. However, I will truly be convinced when we get
your data. Looking forward to your results.
Ed Anderson
Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com
|
|