Temperature drop in Jobo Tank

[benjiboy]

Have you tried the experiment with a scrap film in the tank, because the surface area of the film can have an effect on the temperature drop, and if you're doing a dummy run all the factors should be the same.

[Rudeofus]

Have you tried the experiment with a scrap film in the tank, because the surface area of the film can have an effect on the temperature drop, and if you're doing a dummy run all the factors should be the same.

The fact that I ran my experiment with an open lid will distort the results a whole lot more than whether there is film inside the tank or not - and frankly I don't see any reason why surface area inside the tank should affect the temperature profile at all.

A lot of folks here posted comments about rotary processing, but this is a completely different animal as the quantity of soup is much lower. Of course such a setup will have a much more pronounced temperature drop over time, that's why good rotary processors have a water bath. My experiment provided good evidence that inversion tank processing maintains the temperature inside the tank quite well.

Personally I don't think that putting an inversion tank in some uncontrolled water bath is such a good idea: the temperature drop in that water bath will be much worse than the temperature drop in the tank itself without the water bath.

[Diapositivo]

Personally I don't think that putting an inversion tank in some uncontrolled water bath is such a good idea: the temperature drop in that water bath will be much worse than the temperature drop in the tank itself without the water bath.

I might be wrong (never been a champion in Physics) but if you fill a plastic basin with warm water (warmer than needed so that a certain heat is used to warm the container itself) shouldn't the higher thermal mass of the water surrounding the tank require a larger "contact" with the room air in order to be chilled, than the air itself?

In more understandable terms:
If the tank is surrounded by air, air and tank will exchange heat, air will get warmer, tank will get cooler. This exchange is influenced by several factors (surface, temperature difference, "wind") and by the "thermal mass" of both air and tank.

If the tank is immersed in water, and water is contained in the plastic basin, and the plastic basin is immersed in air the heat exchange will take place between the basin and air, and between the water surface and air.
But considering that the plastic basin, and water, have a considerably higher "thermal mass" than air, you will need "much more air" to cool down the higher thermal mass. That's why I expect the plastic basin with warm water to cool down more slowly than the tank when exposed to air.

In a word: you can use water as a accumulator of temperature that will discharge more slowly than air, when in contact with air. It will also "insulate" the tank from the cooler ambient air, a bit of a "thermal mass overcoat" for the tank.

(Not that I am sure of this. I am just reasoning).

Fabrizio

[Photo Engineer]

You have forgotten evaporative cooling. The larger the surface area of the hot container (bath) and / or the lower the humidity, the faster the hot bath will cool down! Another law of physics. Sorry.

Without constant renewal of heat, you are bound to cool off.

Kodak suggests starting a degree warm and finishing a degree low so that over the development time, you get an average "good" temperature. So, start and 101, and end at 99 in 3' 15" for C41.

PE

PE

[Rollei fan]

Thanks for comments. I will redo the experiment with the water bath filled as full as it can be filled.
I have had inconsistent results with C41, with the same films developed in different runs needing different filtrations when enlarging. Some runs have been OK, but none have been as good as the negatives I get from a commercial lab. Those have better contrast and higher density than any film I developed myself and I can use the same filtration for each and every film (of the same type) when enlarging. The film base color is always lighter in the negatives I have developed myself than that of those developed in a commercial lab.