[AT] Wind Chill And Such

[Gene Dotson]

WIND CHILL
      The effect relating to bare skin and removal of heat above what would 
normally occur, by removing                             the normal boundary 
layer, or blanket layer next to the body. This is hastened by rapid air 
movement on the body.

VENTURI EFFECT
    The characreristic of low pressure air to hold less heat than higher 
pressure air.  Air passing the throttle plate and especially the carburetor 
venturi increases in velocity and decreases in pressure. This causes a much 
lower temperature downstream, causing moisture in the low pressure air to 
condense and, when conditions prevail, to freeze, as low temperature and low 
pressure air is not capable of of suspending as much water vapor as at 
higher temperature and pressure

 COMPRESSIVE HEATING AND COOLING.
    As compared to ambient air, when air is compressed the temperature rises 
and when the pressure is lowered the temperature lowers. Each molecule 
contains a specific amount of heat and when they are crowded together, the 
heat is concentrated, This is why your air compressor is hot while it is 
running and your gloves freeze to the air grinder when used heavily.

EVAPORATIVE COOLING.
    When water is exposed to air that is below the saturation point, the 
water partially evaporates, giving up heat to the atmosphere thereby 
lowering the temperature allowing the remaining water to freeze as frost, 
even at 38 degrees.

COLD SOAKING
    As applies to machinery, is when the entire assembly has reached near 
the same low temperature as the surrounding atmosphere. The time interval 
can vary widely, depending on air movement and protective measures, such as 
a closed barn or covered with a blanket. The actual time can be a few hours 
or even days. This will actually be a paraballic curve where fastest cooling 
is when the temperatures differences are greatest  and actually never quite 
reaching the actual ambient temperature though will come close.

RELATIVE HUMIDITY
    This is the percentage of water vapor in suspension as compared to the 
amount of totally saturated air at that particular temperature. RH is 
calculated by using identical thermometers. One is dry and records the 
actual temperature of the air, and the other has a mediam saturated with and 
suspended in water. The EVAPORATIVE COOLING causes the wet bulb to read 
lower temperature and by using an index table comparing the temperatures to 
arrive at the relative humidity expressed in percentage saturation at that 
temperature. Higher moisture air will have a lower temperature spread in 
this exercise.

Note
    All of these descriptions are my own feeble effort to try to clear up 
some of this discussion, and may contain errors or vague descriptions and 
are worth whatever you want to make of them.

                    Gene