Non-linear evaporation

[Iceni]

 

Can you please explain non-linear evaporation to me. I have not studied physics and it was a very long time ago that I learned chemistry and maths at school. So please explain it to someone with no prior knowledge of physics.

 

A small glass tube is filled with the liquid methyl benzoate. The radius along the glass tube appears constant. The glass tube is housed in a plastic case with metal backing, and fixed to a radiator. When turned on the radiator has hot water flowing through it so as to warm up a room in winter. The idea is that the extent of evaporation in the glass tube shows the heat consumption and so used to apportion heating costs to individual users. The hot water feeding the radiator comes from a communal central heating system. Unlike a conventional meter the hot water flowing through the radiator is not measured.

 

Below is a photo of the glass tube, or search for Minotherm II

https://www.google.de/search?q=Minotherm%2BII&client=ubuntu&hs=N6v&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiMqKKm85zgAhWCjCwKHfKkDh8Q_AUIDigB&biw=1859&bih=942#imgrc=hzA_s3oxM_XwRM:

 

It is said that evaporation is non-linear, and differs depending on the liquid level in the glass tube.

Q1. What is here meant by non-linear?

Q2. What role does the height of the liquid play in the evaporation rate?

 

 

On the left of the glass tube is a normal millimetre ruler, 7mm above zero, below zero 0-60mm, placed there for comparison.

 

To measure the amount of methyl benzoate that has evaporated in a year, they used a scale that has a unique layout ( the “unique scale”). This is the scale on the right of the glass tube. This unique scale has 7 units above 0, marked by 901, 903, 905 and 907. These equate to 7mm.

 

Below 0 the unique scale diverges from a normal millimetre ruler. The spacing is different and for every 10 units down the glass tube, the bands become increasingly narrower. After 30, each 10 units (30-40, 40-50, 50-60, 60-70, 70-80) are shown by only 5 dashes which seem to be due to limited place for marking. Still, the bands continue to be increasingly narrower from 30 to 80. The unique scale runs up to 80 units whereas the millimetre ruler runs up to 60 mm.

 

The effect of the unique scale is that lower down the glass tube, a smaller amount of liquid evaporated will reach the next dash / the next unit / the next consumed unit used for calculating heating costs.

 

Q3. Is the unique scale an adjustment to neutralize non-linear evaporation?

 

Phrased differently - When the same amount of heat flows through the radiator, leading to units of methyl benzoate in the glass tube being evaporated (the consumed units), is the unique scale used to counter non-linear evaporation? Is it used to neutralize possible influence from the height of the liquid in the glass tube (be it at 4, 34 or 44) in the evaporation?

 

Q4. If not, what is the use of such unique scale?

 

I am grateful for your clarifications. Thank you in advance.