Psychrometry WTF? #1 - Dry-bulb temperature

OK - we have the "terrifying" psychrometric chart in all of its' glory.

Put it out of mind right now ! (click on it for a gory detail reminder if you must)

I have promised to explain

Psychrometry wtf-without-fear series
and make it crystal clear.

I am going to do this by playing with some simple ideas about household objects.  These may also help you remember things.

We start off with the humble thermometer - these are not frightening - mothers and doctors stick them in the mouths (and elsewhere) of babies and sick people so they cannot be all that bad.

So here is a thermometer :  

As it gets hotter the red liquid expands and moves up into a vacuum from the "bulb" or reserve at the bottom.  

So the longer the red marker the hotter it is.

The bulb is important !

Generally if you stick your finger in your mouth so its wet, and then stick it in the air (no picture :) it will feel colder than if you stick it in the air while it is dry.  However, if it is raining or foggy (very humid) it does not feel colder.

So how it feels depends on how wet it is.

Normal temperatures are taken with a "dry bulb" -
i.e. stick your finger in the air (not in your mouth).

I asked a friend of mine to demonstrate - but he said he gets fed up with them - so here is someone clearly chosen entirely at random doing it for you.

So even politicians know that summer is warm and winter is cold. 

My argument is that if a politician can understand this issue you can.

All you need to know about the dry-bulb temperature and a psychrometic chart is that it gets hotter from left to right !

You can imagine the thermometer being laid on its side so the red line rises from left to right.

In this diagram you will see vertical green lines drawn from the bottom where they are marked with the dry-bulb temperature (how hot it is - rising left to right )

Click to Enlarge