Test your temperature!!!

[djklmnop]

Last night, my developing room temperature was at 77 degrees. I cooled all the water down to 75F for developing, so I figured all is dandy. After I had poured the developer out of my Jobo once it was through developing. I gathered a sudden urge to measure what the outcome temperature was. Turns out, it ended up at 76.4F !!!

Water temperature consistancy is great, just be sure to test actual temperature too! The humidity and heat bumped it up 1.4 degrees which can effect highlights by a whole stop!!!

Just a friendly reminder - Don't test just the water. Be sure to test the actual water in the tank!!!

Andy

 

[kenh]

I have seen this effect too. I don't know what causes it. I have even seen a rise in temperature when the room is exactly the same temperature as the developer. I don't know what causes it. But I know that I am not the only one who has seen this effect.

 

[glbeas]

Did you temper the tank in the water before putting the developer in? The heat of the tank material plus the temp of the water bath will average out somewhat higher dependant on the actual thermal load of the whole system. I usually try to get some equilibrium before running the process.

 

[djklmnop]

As the Jobo rotates, it touches the water which is set at 75F. I would imagine it's because of the hot weather which will allow the tank to create a humid environment within in the tank. I do know that on colder days, I would have to set my temperature to around 75.7F or 75.9F to get a perfect 75F in the tank. I just didn't realize how tremendous the effect would be for a hot day. My Tmax negatives ended up with a lot more contrast than I really needed/wanted.

 

[Snapper]

Simple thermodynamics - any chemical reaction will either generate or absorb energy (exothermic or endothermic reactions), which may account for the temperature change. Whether the reaction between developer and film would be enough to raise the temperature significantly in a tank, I couldn't say.

 

[L Gebhardt]

I would also think that friction might acount for some rise. I guess as it gets warmer we need to watch this more - thanks for the reminder.

 

[gainer]

I believe you fellows have discovered a law of physics. Mechanical energy can be converted to heat energy. Trouble is, someone else beat you to it.

Excuse the ribbing. I couldn't resist.

The continouos motion of a rotating tank agitates the developer as it should. It also imparts energy to the developer. Because you have the tank in a constant temperature bath at the desired temperature, the energy has no place to go. There must be a temperature differential for it to flow out of the liquid in the tank to the liquid outside the tank. The temperature difference will necessarily be such as to reach equilibrium. Nature will see to it that there is a higher temperature in the tank so that the energy of motion can flow out. If it stays in, the temperature gets higher until it can get out.

 

[gainer]

P.S. If you want to find out if the temperature rise is due to mechanical energy transfer or chemical reaction, run a simulated development with distilled water.
Don't forget that the film you put in the tank has a temperature and must come to equilibrium with the liquid temperature.