Joe,

You are right about hot air holding more moisture and therefore dropping
the relative humidity.  The easiest method for converting the RH at one
temperature to another is to use a Psychrometric Chart.  I have one in
Perry's Chemical Engineers Handbook but you should be able to find one
on the internet.

The example you gave converts as follows (My chart is in English units)
40%RH at 73F (23F) is approx 0.006 lb water/lb dry air
at 194C (90F), 0.006 lb-H20/lb converts to approx 1.5%RH

For reference air at 5%RH at 90C hits the saturation line at about 25C
which means air at temperatures below that doesn't have to be
dehumidified before heating.

Unfortunately there is is no easy equation for the conversion.  If you
need more information let me know.

Steve Pence
714-672-9944

Unit Design, Inc.
576 Explorer Street
Brea, CA 92821
http://www.unitdesign.com/

Macko, Joe @ IEC wrote:

>Technets,
>
>Commonly, Moisture Sensitive Devices (MSD) are baked out at either 125 C or
>90 C in a convection air oven to remove moisture.  J-STD-033A requires the
>humidity to be < or equal to 5% at 90 C.  Would someone point me to an
>explanation of how to adjust the humidity content of the air at 125 C or 90
>C when say the incoming air is at a humidity level of 40% and 23 C.  If I
>remember correctly, warmer air can hold more moisture.  Is a dehumidifier
>required in the air inlet to reduce ambient humidity levels to 5%?  Look
>forward to your inputs.
>
>thanks
>joe
>
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