| |
 |
 |
 |
| |
| Tony's Tips |
ARTICLE DATE: 08/01/2006 |
| Aftercooler Condensation - A different way to look at air |
|
|
|
 |
|
 |
|
|
The air around us contains vast amounts
of moisture. It's always there and the amount averages (leaving out the
extremes of the world) from about 30% to 75% measured in relative humidity.
Of course, if you are like me, the term "relative humidity" kinda relates
to how uncomfortable I feel in the middle of a hot day and is not much use
in the practical life of diesel engines. Or, you might just say "Relative
to What?" What I like is this term "Absolute humidity," which is a measure
of the amount of moisture in the air; OR the weight of water vapor per unit
volume of air.
What we all need to really understand is how much water is actually in the
air around us. I'll try to explain it this way, at least this is the way
it makes some sense to me.
A typical modern turbocharged diesel producing 300 HP will consume about
1500 CFM of air at this HP output level. Ambient air at 80 F can hold about
35 grams of water per cubic meter of volume at 100% saturation (got that
from a chart from a lecture at UC a while back)... On a typical nasty late
80 degree F afternoon when the humidity is at 70%, that would work out to
about 2 1/4 lbs of water vapor being consumed by the engine per minute running
at 300 HP output (check my calcs to be sure I didn't screw up). Now, let's
take that "captive air" that's being fed from the turbo through the seawater
cooled aftercooler. When the hot air touches the relatively cool tubes/fins
, you have a perfect medium for a percentage of that air to cool sufficiently
to reach its dew point and condense on the tubes/fins and form water droplets
which can (and do) fall to bottom of the aftercooler housing (don't forget,
for air to condense, you MUST have a surface for it to attach to). But also
realize, even if it didn't condense, the engine is still eating this water
without harm (the water is in the air anyway), but under the right conditions,
the water droplets form in the aftercooler and sits there until the conditions
are right for it to go back into a vapor form and get fed to the engine
again, and again. This process is a continual one and at times, the aftercooler
on a Cummins 6CTA 8.3 may have about 3-5 ounces of "loose" water" in it,
and then, that water will just "go away."
During the course of our business we service about 2-3 aftercoolers per
month, and many of these servicings happen the morning after the customer
worked the entire previous day, came into the harbor late w/ the sun going
down, he had just come off "plane" and idled to his slip for 5-10 minutes
before shutting down.. Next morning he removes the cooler and brings it
to me. This seems to be the case when we can find a few ounces of water
in the coolers (tip it over and it spills out). I've had to show many customers
that this is NOT salt water (a leak) but "condensation"......I just taste
it in front of them and offer the same.........Usually, no takers...
Anyway, the water in the aftercooler is sometimes there, and sometimes not
. But it's always in the air and it doesn't hurt the engine. As far as a
"drain hole" (ala Volvo)?? May have some value and I've wondered about a
small leak/weep hole in the right spot on a Cummins aftercooler many times.
It's not the water going into the engine that bothers me, it's the water
sitting in the aftercooler causing unnecessary corrosion. But of course,
that's a another topic for the couch engineers that designed an aftercooler
with many preventable design flaws that can lead to less than a long term
life, especially with less than a prescribed sensible and applicable maintenance
schedule in the O&M manual furnished w/ these engines......................................................Tony |
|
|
|
