> I spoke too soon!
It really isn't that bad in person. It doesn't translate well to e-mail.
Heat exchanger design is actually pretty cookbook, nothing as hard as
turbomachinery analysis or two-phase refrigerant flow in an evaporator
(other stuff I get paid to do). Now, no flames or I show you the calculus
used to determine a good cam grind (seat of the pants beats calculus any
day, actually)!
> -----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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