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'[OT]: Wind Chill Question'
2001\10\03@102619 by Roman Black

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Hi all, one of my motorcycle associates has
modified his fuel injection system by placing
the air temperature sensor in his airscoop,
not the airbox.

I'm worried that since it is now in a very
high-flow air tube the sensor will read lower
temperature (error) because of wind chill,
compared to the more "stable" air position
where it was mounted before.

He argues that wind-chill will not occur
because the wind can't chill lower than the
actual air temperature, so the temperature
remains an accurate reading.

Any thoughts?? :o)
-Roman

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2001\10\03@114641 by Douglas Butler

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He is correct with two assumptions:

1) The sensor must be dry, else evaporation will affect the reading.

2) The sensor self heating must be negligable.  Reading any sensor
dissipates power in the sensor causing it to heat itself.  In still air
the self heating effect will be larger than in moving air.  The OEM may
be compensating for that self heating and moving the sensor may cause
over compensation.

I think in this application there is no problem.

Sherpa Doug

> {Original Message removed}

2001\10\03@114650 by t F. Touchton

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Wind chill only occurs when some form of evaporation takes place.  If the
sensor is dry, the only thing that wind can do is reduce any self heating.

Scott



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Hi all, one of my motorcycle associates has
modified his fuel injection system by placing
the air temperature sensor in his airscoop,
not the airbox.

I'm worried that since it is now in a very
high-flow air tube the sensor will read lower
temperature (error) because of wind chill,
compared to the more "stable" air position
where it was mounted before.

He argues that wind-chill will not occur
because the wind can't chill lower than the
actual air temperature, so the temperature
remains an accurate reading.

Any thoughts?? :o)
-Roman

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2001\10\03@121053 by John Pfaff

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Go back to thermodynamics class.  Remember that pressure is inversely
proportional to velocity, an PV=nRT, and all those silly equations.  In
my opinion, it will read lower.

jp

Roman Black wrote:
{Quote hidden}

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2001\10\03@123529 by Jim

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> He argues that wind-chill will not occur

It won't.

Not unless the sensor is self-heating or 'sweats' ...

Jim



{Original Message removed}

2001\10\03@123540 by John Ferrell

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I will vote with your friend on this one.
Consider:
The measured temperature in the airbox is really more accurate because it is
what is going to be ingested. Also, is the differential really significant?

Wind chill is really a nontechnical (read "inaccurate") expression of rate
of cooling rather than a temperature measurement.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



{Original Message removed}

2001\10\03@123544 by Ian Rozowsky

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Hi Roman

Gut feel tells me that if

a) The sensor is not self heating and
b) There is no evaporative cooling (ie: the sensor does not perspire)

there should be no wind chill effect. Or am I missing a point?

Ian Rozowsky
Engineering Manager
Centurion Systems
P.O. Box 506
Cramerview 2060
South Africa
Tel   : +27-11-462-4499
Fax   : +27-11-704-3412
e-mail: @spam@rozKILLspamspamcentsys.co.za
web: http://www.centsys.co.za

{Original Message removed}

2001\10\03@130227 by robertf

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If it's fuction is to switch
cold running mixture vs.
warmed up/normal mode) then
there might be an little
offset.  If it's used to
determine the gas/air ratio
mixture, it may richen it a
bit, the ecu will think there
is denser air so it increases
the fuel pulse-maybe the O2
sensor( if it has one) will
bring it back. thermistor
value depend a little on self
warming.

regards,

Robert
{Original Message removed}

2001\10\03@133859 by Roman Black

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Is this entirely correct? Doesn't wind chill
increase the heat energy lost from the device
in question? So if the device is hotter than
the wind the greater the heat lost with greater
wind speeds? I wasn't considering evaporation,
more so the measurement of the temperature of
the air itself.

So the general concensus is that the velocity
of the air is unimportant, and that the sensor
will stabilise at the average air temperature,
regardless of the air velocity?
-Roman



Scott F. Touchton wrote:
{Quote hidden}

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2001\10\03@143957 by Douglas Butler

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If there is significant pressure drop I guess there would be a
corresponding temperature change.  I am used to working with water so I
am not used to compressibility.

Sherpa Doug

> {Original Message removed}

2001\10\03@144457 by mike

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On Wed, 3 Oct 2001 23:46:37 +1000, you wrote:

>Hi all, one of my motorcycle associates has
>modified his fuel injection system by placing
>the air temperature sensor in his airscoop,
>not the airbox.
>
>I'm worried that since it is now in a very
>high-flow air tube the sensor will read lower
>temperature (error) because of wind chill,
>compared to the more "stable" air position
>where it was mounted before.
>
>He argues that wind-chill will not occur
>because the wind can't chill lower than the
>actual air temperature, so the temperature
>remains an accurate reading.
>
>Any thoughts?? :o)
>-Roman
As long as the air and sensor are dry, flow rate shouldn't make a
difference. If however there is moisture on the sensor, it will read
lower, but with high airflow, the moisture probably won't stay there
for long!

The reading could well be affected if rain, snow  etc. can reach it.
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2001\10\03@144500 by Douglas Butler

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Velocity relates to how fast the sensor comes to thermal equilibrium,
not at what temperature that equilibrium is (excluding self heating
effects).

Sherpa Doug

> {Original Message removed}

2001\10\03@144506 by Spehro Pefhany

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At 10:00 AM 10/3/01 -0500, you wrote:
>> He argues that wind-chill will not occur
>
>It won't.
>
>Not unless the sensor is self-heating or 'sweats' ...

I guess you will also get a small amount of heating from the
viscous behavior of the air. I'd have to pull out the fluid dynamics
texts to figure out just how much.

Best regards,
Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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