Craig,

Here's my understanding:

On a local level, an increase in temperature results in a decrease in relative
humidity.  On the global level, the moisture content is constant.  Some
assumptions include the ability of the oven to maintain the conditions, a
fixed pressure, and moisture penetration within the board.  Calculations
require use of vapor pressure tables (one source, CRC Handbook).

Based on your conditions, I calculate a local relative humidity of 5.1%

Hope this helps,

Glenn

Ref:
1)  http://www.usatoday.com/weather/whumcalc.htm
2)  CRC Handbook of Chemistry and Physics
3)  Accelerated Testing Handbook, Peck and Trapp

Craig Hillman <[log in to unmask]> Wrote:
|
| An environmental question:
|
|         I have a board operating in a 30C, 70%RH environment. The board
| is operating at 85C. How do I determine the humidity level at the
| board?
|
|         1. Is the moisture concentration and the RH lower than ambient
| because of evaporation?
|         2. Is the moisture concentration the same and the RH lower because
| of a higher temperature (and thus higher solubility limit)?
|         3. Is the moisture concentration and the RH higher than ambient
| because the higher temperature results in a higher solubility limit?
|
| Thanks in advance,
| Craig

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