I spoke too soon!
Mike
-----Original Message-----
From: Ron Soave <redlotus@spacey.net>
To: Peter Samaroo <mrbugeye@hotmail.com>; autox@earthlink.net
<autox@earthlink.net>
Cc: spridgets@autox.team.net <spridgets@autox.team.net>
Date: Tuesday, December 08, 1998 1:57 PM
Subject: Re: Radiator Stuff
>
>> On a left top entry right bottom exit radiator.
>> Downflow would have faster travel over the top and down the right side
>> while the left bottom would not see much flow. The hotter water would
>> flow faster through the downflow resulting in less cooling time.
>> Cross flow would be much more even with the water spending more time in
>> the radiator resulting in better cooling.
>
>Run away now if math bothers you in the least. It isn't that simple.
>True, less "hot" flow would provide a greater temperature difference
>between inlet and outlet, but from a system standpoint, you'd be in
>trouble. Remember, the coolant is the "hot" flow in the radiator, but it
>is also the "cold" flow, or sink, in the engine. You want as great a
>flowrate of coolant as you can get . The heat transfer is directly
>proportional to the mass flow of the working fluid (at a given temperature
>difference) - more flow, more heat transfer. The heat transferred to the
>coolant (or Ethylene Glycol Water mix, EGW), Q, is equal to the (EGW
>massflow) * (specific heat of EGW) * (temp difference of EGW), with the CP
>of EGW (in btu/lb-degF units) in a 50-50 mix is .0005T + .7498, with T in
>deg F. Less EGW flow = less heat removal from your engine. Think about it
>- if your water pump now supplied 1/10th it's normal flow, is that a good
>thing?
>
>For the radiator, what thermal control systems guys try to design for is a
>radiator sized for an effectiveness near 1. The hot side effectiveness of
>your radiator is defined as:
>
>(T_hotin - T_hotout)/(T_hotin - T_coldin). {cold side effectiveness is
>T_coldin - T_coldout in the numerator}.
>
>Therefore the best you can get is an effectiveness of 1 when T_hotout =
>T_coldin. This will occur when you've got lots of cold flow (air, in the
>radiator's case) and only a little hot flow. However, you've just cooked
>your engine. Regarding heat exchanger design, for a single-pass unit,
>cross flow vs. downflow is a push. The heat transfer will be driven by the
>fin design and density as well as the tube design. This is more nasty
>stuff that is well documented in Kays and London's "Compact Heat Exchanger
>Design" (it is the Vizard book of heat exchanger design), and is dependent
>upon fin material, pitch, density, etc. Not worth getting into.
>
>Everyone asleep yet? Sorry.
>
>
>
>Tcold cold DT COLD/DT MAX
>
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