GERYVON wrote:



 C:\Mes Documents\Stewart Components - Advanced Cooling System Basics.htm

Paul, is this documentation of any value for your website?
Yvon Cournoyer.

http://www.stewartcomponents.com/html/tech_support/techtip5.asp

This is interesting but it flies in the face of what is happening in 
the auto industry in some regards. We shall find out shortly about
the flow through thicker rads. It is also not intuitive as aero drag
in a pipe is proportional to the length of the pipe.

***********************************************************************************
    Tech Tip #5 - Radiators & External Plumbing

    Radiators
    Thicker radiators do have slightly more airflow resistance than thinner radiators but the
difference is minimal. A 4" radiator
    has only approximately 10% more airflow resistance than a 2" radiator.

    In past years, hot rodders and racers would sometimes install a thicker radiator and actually
notice decreased cooling. They
    erroneously came to the conclusion that the air could not flow adequately through the thick
radiator, and therefore became
    fully heat-saturated before exiting the rear of the radiator core. The actual explanation for
the decreased cooling was not the
    air flow, but the coolant flow. The older radiators used the narrow tube design with larger
cross section. Coolant must flow
    through a radiator tube at a velocity adequate to create turbulence.

    The turbulence allows the water in the center of the tube to be forced against the outside of
the tube, which allows for better
    thermal transfer between the coolant and the tube surface. The coolant velocity actually
decreases, and subsequently its ability
    to create the required turbulence, in direct relation to the increase in thickness. If the
thickness of the core is doubled, the
    coolant velocity is halved. Modern radiators, using wide tubes and less cross section area,
require less velocity to achieve
    optimum thermal transfer. The older radiators benefited from baffling inside the tanks and
forcing the coolant through a
    serpentine configuration. This increased velocity and thus the required turbulence was restored.

    Radiators with a higher number of fins will cool better than a comparable radiator with less
fins, assuming it is clean.
    However, a higher fin count is very difficult to keep clean. Determining the best compromise
depends on the actual conditions
    of operation.

    Double pass radiators require 16x more pressure to flow the same volume of coolant through them,
as compared to a single pass
    radiator. Triple pass radiators require 64x more pressure to maintain the same volume.
Automotive water pumps are a
    centrifugal design, not positive displacement, so with a double pass radiator, the pressure is
doubled and flow is reduced by
    approximately 33%. Modern radiator designs, using wide/thin cross sections tubes, seldom benefit
from multiple pass
    configurations. The decrease in flow caused by multiple passes offsets any benefits of a
high-flow water pump.

    Cross flow radiators are superior to upright radiators because the radiator cap is positioned on
the low pressure (suction) side
    of the system. This prevents the pressure created by a high-flow water pump from forcing coolant
past the radiator cap at high
    RPM. As mentioned in the radiator cap section, an upright radiator should be equipped with
radiator cap with the highest
    pressure rating recommended by the manufacturer. The system will still force coolant past the
cap at sustained high RPM. 

**************************************************************************************

Paul Lamar
 
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