Yes, they are stored as text. Of course we can also store them as a flow property, but it might be too "dangerous" that then these properties are used for modeling without reasoning checks.
Of course, you can anytime also add the flow properties for some flows that you are using by yourself. This is all possible in openLCA. As I wrote before, they need to be taken with care. That's why we think that if users really need them, like in some EPDs, they can read the property from the flow description field or from ecoQuery and include it in calculations or modeling efforts as needed.
Here an example from 1 single flow:
price: 0 EUR2005
chromium content: 0.0000344 dimensionless
copper content: 0.00027 dimensionless
heating value, gross: 14.5 MJ
arsenic content: 0.00000248 dimensionless
zinc content: 0.000666 dimensionless
silver content: 0.00000929 dimensionless
phosphorus content: 0.0172 dimensionless
lead content: 0.0000323 dimensionless
beryllium content: 0.00000016 dimensionless
carbon content, non-fossil: 0.353 dimensionless
titanium content: 0.000124 dimensionless
antimony content: 0.00000292 dimensionless
hydrogen content: 0.0492 dimensionless
nitrogen content: 0.044 dimensionless
nickel content: 0.0000131 dimensionless
cadmium content: 0.00000132 dimensionless
carbon content, fossil: 0.00929 dimensionless
sodium content: 0.00271 dimensionless
selenium content: 0.00000281 dimensionless
water in wet mass: 0.75 kg
dry mass: 0.25 kg
wet mass: 1 kg
tin content: 0.0000197 dimensionless
manganese content: 0.00036 dimensionless
scandium content: 0.00000426 dimensionless
potassium content: 0.00347 dimensionless
silicon content: 0.00284 dimensionless
mercury content: 0.000000291 dimensionless
oxygen content: 0.439 dimensionless
water content: 3 dimensionless
heating value, net: 1.72 MJ
magnesium content: 0.00343 dimensionless
cobalt content: 0.00000665 dimensionless
boron content: 0.000024 dimensionless
aluminium content: 0.000026 dimensionless
vanadium content: 0.0000234 dimensionless
molybdenum content: 0.00000663 dimensionless
strontium content: 0.000277 dimensionless
sulfur content: 0.0034 dimensionless
tungsten content: 0.00000139 dimensionless
thallium content: 0.000000202 dimensionless
barium content: 0.000303 dimensionless
calcium content: 0.0432 dimensionless
iron content: 0.0274 dimensionless
Storing all this in the flow properties would make the modeling experience less good. Whenever you want to select the unit of your exchange in the process, you would get many units for plenty of different properties that are not used at all in most of the cases.
But we could think about adding the carbon content and lower heating value as a flow property, since they are used the most in modeling. As I said, one can also quickly add them yourself to the respective flow if wanted.