[Chrysler300] Was Short lesson in thermodam - Now Radiator Flow

[Bill Huff <czbill@xxxxxxxxxx>]

Here is a learned thesis on the cooling system 
and radiator flow.  Short story -  slow flow, higher temps.

There are diagrams on the site if anyone is interested.

Bill Huff

http://www.stewartcomponents.com/tech_tips/Tech_Tips_6.htm

Stewart Components Tech Tips
   Cooling System Basics for Spark Ignition Engines
SuperFlow Advanced Engine Technology Conference, December 7, 1992

Common Misconceptions
Coolant temperatures are not an accurate 
indicator of metal temperatures. The coolant's 
maximum temperature is it's pressure corrected 
vapor point. The metal can be several hundred 
degrees hotter than the adjacent coolant.
Temperatures of critical areas must be determined 
by checking the metal at a controlled distance 
from the combustion chamber surface. This 
eliminates discrepancies caused by the variances in metal thicknesses.
Higher coolant flow will ALWAYS result in higher 
heat transfer. Coolant cannot absorb heat after 
it reaches it's pressure corrected vapor point. 
Furthermore, coolant absorbs heat at a 
progressively slower rate as it approaches this point.


Energy Loss

Spark ignition engines loose almost 33% of their 
energy input through the cooling system.
Energy loss is very simple to calculate on the 
dyno or the vehicle. All you need is the inlet 
coolant temperature, outlet coolant temperature, 
coolant flow and the specific heat of the coolant.
Following is a typical engine:

Inlet temperature = 180 F
Outlet temperature = 190 F
Coolant flow = 100 GPM
Specific heat of coolant = 1.0
1 HP = 5.2769885 GPM 1 F
{ (Outlet-Inlet)CS} / 5.2769885 = HP loss
{(190-180) 100*1.0} / 5.2769885 = 189.5 H
Basic Functions of the Cooling System

Peak temperature in the combustion chamber is in 
excess of 5000 F. Aluminum melts at 1220 F, Iron 
at 1990-2300 F. Therefore, the obvious primary 
function of the cooling system is the prevention of component damage.
However, spark ignition (SI) engines experience 
pre-ignition and subsequent detonation at 
temperatures much lower than those resulting in component failure.
Poor cooling system performance results in 
component damage in SI engines but, this damage 
is a result of pre-ignition/detonation. Not the temperature alone.
This secondary function of controlling 
pre-ignition/detonation is actually the most important in the SI engine.


Engines

On traditional flow configurations the block is 
pressurized by the water pump and functions as a 
manifold. The head gasket distributes the coolant 
through it's orifices. Block pressure must be 
consistent from front to rear to insure uniform 
coolant distribution. Low pressure will results 
in less flow around the rear cylinders.
Reverse flow systems pressurize the cylinder 
heads and bleed off through the block. Coolant 
gains only 1-2 F as it goes through the block. 
Reverse flow decreases the temperature of the 
coolant through the cylinder heads by this 
amount. The fact that steam rises complicates 
reverse flow systems and generally makes the 1-2 
F reduction in coolant temperature insignificant at best.
The flow through each orifice in the head gasket 
can be determined by measuring the pressure drop 
across each orifice while coolant is being forced through the engine.
Coolant flow has a direct relationship to area 
and an exponential relationship to pressure. 
Meaning that when you double the area of an 
orifice and maintain pressure the flow doubles, 
but when you double the pressure and maintain 
area the flow is only increased by 1.414 (the square root of 2).
Strategic Flow systems take advantage of the 
knowledge gained through flow mapping. 100% of 
the coolant flow crosses the critical exhaust 
seat area first and is then distributed according 
to need to the other areas of the engine. Coolant 
is taken from the highest point thus eliminating 
the pitfalls of reverse flow systems.







Radiators

The most important criteria for any radiator is 
it's surface area. The thickness of the core is 
increased only after the surface area is 
maximized. Adding thickness to a radiator does 
not increase it's efficiency the same extent as 
surface area, but in no case will additional 
thickness alone decrease the efficiency.
The radiator becomes less efficient as the 
coolant outlet temperature approaches ambient. 
Therefore, a low flow rate keeps the coolant in 
the radiator longer. The longer the coolant stays 
in the radiator the lower the efficiency of the radiator.
Non-laminar or turbulent coolant flow must be 
maintained within the radiator core.
When baffles are inserted in the tanks to force 
the water to go through the radiator twice, the 
water spends the same amount of time in the 
radiator but must go twice the distance. Thus doubling the sped of the water.
Crossflow radiators with a fill cap always have 
the cap on the outlet side. Upright radiators 
have the cap in the inlet side and thus subject 
the filler cap to the pressure drop of the 
radiator's core in addition to the system 
pressure. This can lower the effective pressure 
of a 22 PSI cap to as low as 10 PSI.
Thermostat housing restrictors were useful when 
upright radiators were used with 7 lb. caps. The 
restrictor slowed the flow and kept the pressure 
in the radiator down. This prevented the cap from 
expelling water and causing the car to overheat. 
Most people wrongly assumed the car ran hot and 
expelled water. The cars actually expelled water and ran hot.
Hoses
Large diameter hoses with large radius bends 
should be used. Never use braided hoses, they 
will always result in higher metal temperatures.






Pressure

Higher system pressures raise the vapor point of 
the coolant and subsequently it's ability to 
absorb heat. A system pressure of 12-17 PSI 
results from the expansion of the coolant and 
trapped air going from ambient temperature to operating temperature.
The system achieves this pressure only when the 
system is filled cold. When a warm system is 
opened and resealed this pressure is not 
obtainable because the coolant and trapped air 
are already expanded when the system is sealed.
A Schrader valve installed in the system will 
allow the system to be charged by an air hose. 
This allows an already warm system to achieve 
operating pressure and minimizes the effect of trapped air in a cold system.
The fill cap must be the highest point of the 
system. Surge tanks must be used if the top of 
the radiator is not the highest point.
Trapped air seeks the highest point. A new system always has trapped air.
Always fill the surge tank completely, when the 
system reaches operating temperature it will 
expel any excess water out the overflow.
Placing a fill cap in the top radiator hose 
subjects the cap to the pressure drop of the top 
hose and the radiator core in addition to the 
system pressure. This can lower the effective 
pressure of a 22 PSI cap to as low as 2 PSI.
The vapor point of water increases under pressure as follows:

10 PSIG = 239° F
20 PSIG = 259° F
30 PSIG = 273° F
40 PSIG = 286° F
50 PSIG = 297° F
60 PSIG = 307° F
70 PSIG = 316° F
Always use the highest pressure cap available. It 
merely serves as safety valve that has no 
function when the system is operating properly.

Coolant

1 BTU is the amount of energy required to raise 1 
pound of water 1°F. Of all common liquids water 
requires the most energy to accomplish this. 
Therefore water has a specific heat of 1°. An 
Ethylene Glycol/water mix has a specific heat of 
.5, meaning it requires only .5 BTUs to raise the 
temperature of 1 pound Ethylene Glycol/water mix 
1° F. Propylene Glycol has a specific heat of only .3.
On a typical engine with a coolant flow rate of 
100 GPM and an energy loss through the cooling 
system of 189.5 HP, water would need to gain only 
10° F, Ethylene Glycol/water mix would gain 20° 
F, and Propylene Glycol would gain 33.3° F.
This equation is complicated by the difference in 
a vapor point of the 3 coolants. Ethylene Glycol 
and Propylene Glycol have higher vapor points and 
thus can absorb heat at higher temperatures. 
However, even with it's lower vapor point, water 
still carries more heat per unit than the others.
Grill Opening

Radiators have approximately one third open area. 
The remainder is taken up by the fins and tubes. 
The maximum functional grill opening equals the open area of the radiator.
Radiator open area can be calculated by 
subtracting the area taken up by tubes and fins from the total.
Grill open area can be calculated by subtracting 
the area taken up by decorative grill work and the wire mesh from the total.
The angle of the grill opening complicates the 
issue because a sloping opening passes less air than a vertical opening.
Blocking off a sloping grill opening affects the 
aerodynamic balance much greater than blocking a 
vertical opening. The entire grill opening should 
be vertical if at all possible.
Pumps

Proper bench testing of accessories is the only 
proper method of development. The accessories 
affect so many functions of the engine that 
testing them on a running engine on the dyno is a total waste of effort.
The coolant pump is a great example of an 
accessory that must be tested and developed off 
the engine. To bench test the coolant pump you 
must know pressure drops at a given flow for all 
the components of the cooling system.
Following is a typical Winston Cup engine at 100 GPM:

Lower radiator hose = 1.5 PSI
Block and cylinder head - each (at 50 GPM) = 8.5
Outlet manifolding = 1.25
Top radiator hose = 2.25
Radiator = 1.5
Total = 15.00 PSI
In addition to having the proper flow restriction 
as expressed in GPM @ PSI the cooling system 
pressure and temperature must be known. All these 
conditions are duplicated for the bench test.

Energy losses due to driving the coolant pump can 
only be calculated when all conditions are 
duplicated and torque and RPM measured. Amp draw 
of the drive motor is not an accurate measure of 
the energy required to drive the pump. Torque 
must be measured with a load cell and horsepower calculated from there.

Most pumps are biased to the inlet side. Most 
even spaced cylinder heads (IE, IE, IE, IE) are biased to the exhaust end.

There are three basic impeller designs: 
universal, clockwise, and counter clockwise. The 
directional specific impellers are more efficient 
that the universal impellers. The performance of 
all designs are very similar when installed in the same housing.

Metal temperatures always increase when you slow the water pump down.

Next Tip - Competitors Comparison

  



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