REFLECTOR:Re: NPG+
Alex Balic
reflector@tvbf.org
Mon, 19 Apr 2004 09:46:26 -0500
This is a multi-part message in MIME format.
--Boundary_(ID_BtncD3kPZMY0TNF3jwY+Ig)
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
You should check that John,
Most systems run with several pounds of pressure- past that, the cap will
open and allow the excess coolant to run to the reservoir (boil over
condition) the cap will also open when the system is warming to allow the
expanding coolant to leave. If you want to run hot for better power then you
need a higher pressure cap to prevent boiling. Typically engines will run at
220-230 which is above the 212 that water boils - adding glycol does not
suppress this point. Have you ever seen someone make the mistake of removing
the cap on a warmed up engine- you only make that mistake one time- the
water boils instantly when the pressure is removed and departs the radiator
like a shaken can of beer. Racing engine systems will typically run a few
pounds higher than passenger cars to allow a higher operating temp- going to
100% non aqueous coolant will also allow this since these liquids are
designed to boil at at higher temperature and do not require the higher
pressures inside of the system which is usually limited by the strength of
the radiator and seals at the water pump.
Alex
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf
Of John Dibble
Sent: Monday, April 19, 2004 8:11 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Re: NPG+
Weeeell, almost. Actually, water cooling systems are usually not
pressurized. To be pressurized the coolant temp would need to be above it's
atmospheric boiling point (212-215F). The thermostat controls the temp
below that. The reason you have pressure when you open the cap is because
once the engine is off, the radiator can not cool, but the engine is still
hot and heats the coolant above the boiling point which results in temporary
pressure buildup.
If the cooling system were pressurized and pressure was lost, there would
be a temporary surge (possibly a steam layer) in the boiling rate and then
normal boiling would resume. The only way to stop nucleate boiling is to
coat the jacket surface with oil. In that case the coolant would superheat
(about 20F above the normal boiling point) and boil spontaneously and the
cooling would be about the same.
Thinking about it further, the coolant temp is probably a good estimate of
the CHT, which means that a hotter coolant temp would be beneficial as Bill
pointed out.
John
Chuck Jensen wrote:
John,I think I've got it straight. You're right (which is probably not
a surprise to you), in that boiling does go on in a pressurized H2O cooling
system. Nucleate boiling forms right at the metal surface and when the
bubble moves away from the metal, they immediately collapse. This is a very
effective heat transfer mechanism. If pressure on the system is lost, then
a steam layer will form on the metal, heat transfer will suffer greviously
and it would be a good idea to have a landing site in mind. So, the NPG+
cooled engine probably runs hotter since it won't support nucleate boiling
for good heat transfer. Is that good?Chuck
--Boundary_(ID_BtncD3kPZMY0TNF3jwY+Ig)
Content-type: text/html; charset=US-ASCII
Content-transfer-encoding: 7BIT
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=us-ascii">
<META content="MSHTML 6.00.2800.1400" name=GENERATOR></HEAD>
<BODY style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; BACKGROUND-COLOR: #ffffff"
bgColor=#ffffff>
<DIV><SPAN class=263213314-19042004>You should check that John, </SPAN></DIV>
<DIV><SPAN class=263213314-19042004>Most systems run with several pounds of
pressure- past that, the cap will open and allow the excess coolant to run to
the reservoir (boil over condition) the cap will also open when the system is
warming to allow the expanding coolant to leave. If you want to run hot for
better power then you need a higher pressure cap to prevent boiling.
Typically engines will run at 220-230 which is above the 212 that water boils -
adding glycol does not suppress this point. Have you ever seen someone make the
mistake of removing the cap on a warmed up engine- you only make that mistake
one time- the water boils instantly when the pressure is removed and departs the
radiator like a shaken can of beer. Racing engine systems will typically
run a few pounds higher than passenger cars to allow a higher operating temp-
going to 100% non aqueous coolant will also allow this since these liquids are
designed to boil at at higher temperature and do not require the higher
pressures inside of the system which is usually limited by the strength of the
radiator and seals at the water pump.</SPAN></DIV>
<DIV><SPAN class=263213314-19042004></SPAN> </DIV>
<DIV><SPAN class=263213314-19042004>Alex</SPAN></DIV>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT
face=Tahoma>-----Original Message-----<BR><B>From:</B>
reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]<B>On Behalf Of
</B>John Dibble<BR><B>Sent:</B> Monday, April 19, 2004 8:11 AM<BR><B>To:</B>
reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Re:
NPG+<BR><BR></FONT></DIV>Weeeell, almost. Actually, water cooling
systems are usually not pressurized. To be pressurized the coolant temp
would need to be above it's atmospheric boiling point (212-215F). The
thermostat controls the temp below that. The reason you have pressure
when you open the cap is because once the engine is off, the radiator can not
cool, but the engine is still hot and heats the coolant above the boiling
point which results in temporary pressure buildup. <BR>If the cooling system
were pressurized and pressure was lost, there would be a temporary surge
(possibly a steam layer) in the boiling rate and then normal boiling would
resume. The only way to stop nucleate boiling is to coat the jacket
surface with oil. In that case the coolant would superheat (about 20F
above the normal boiling point) and boil spontaneously and the cooling would
be about the same. <BR>Thinking about it further, the coolant temp is probably
a good estimate of the CHT, which means that a hotter coolant temp would be
beneficial as Bill pointed out.
<P>John
<P>Chuck Jensen wrote:
<BLOCKQUOTE TYPE="CITE"> <SPAN
class=359083212-19042004>John,</SPAN><SPAN
class=359083212-19042004></SPAN><SPAN class=359083212-19042004>I think I've
got it straight. You're right (which is probably not a surprise to
you), in that boiling does go on in a pressurized H2O cooling system.
Nucleate boiling forms right at the metal surface and when the bubble moves
away from the metal, they immediately collapse. This is a very
effective heat transfer mechanism. If pressure on the system is lost,
then a steam layer will form on the metal, heat transfer will suffer
greviously and it would be a good idea to have a landing site in mind.
So, the NPG+ cooled engine probably runs hotter since it won't support
nucleate boiling for good heat transfer. Is that good?</SPAN><SPAN
class=359083212-19042004></SPAN><SPAN
class=359083212-19042004>Chuck</SPAN></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
--Boundary_(ID_BtncD3kPZMY0TNF3jwY+Ig)--