Got it now. Sorry, but the idea of a darkroom that is not part of the house and connected to the house plumbing never even occurred to me, so neither did the need for such a thing. Good luck with it, I see now!
Originally Posted by David Brown
With the aquarium heaters, you can often pull off the adjustment knob and reposition it. I did this to see if I could get C-41 temps - though you're not going that high. My only thought is they are not "fast." I'd get a few (depending on the size of your container). I bought some cheap ones at Walmart.
For the hot-plate idea, if the unit is in a place you won't accidentally knock over or touch, you can dial it in at the flow-rate you want. It would take some time, but you'd not have to worry about the temp getting out of hand. Of course, I'm assuming an adjustable hot-plate, not one that is all-or-nothing temperature-wise. If your coils never touched chemicals, you might even make some soup while your washing prints.
Here's a thought. Install an electric heat tape/cable with thermostat (length as needed) to the incoming water line, and cover the line with pipe insulation if necessary. Or wrap the line with heat tape (not sure how electrical power is supplied though).
IIRC most heat tapes are set to kick on around 40*F, if the water temp in the pipe is 50*, the heat tapes will never kick on. Nice thought though!
Shoot more film.
There are eight ways to put a slide into a projector tray. Seven of them are wrong.
I'd say it would sort of work, if you size things right. If you know 1) the required flow rate for wash water, and 2) the temperature rise needed, you should be able to estimate how much wattage you need on the heaters.
Working out a set of numbers, I'd say that a single 300W heating element would be able to raise your water temperature about 15 degrees F (from ~ 50 deg to 65 deg) with a flow rate of about 500 ml per minute (0.14 US gallon per minute, or alternately, 1 gallon every 7 minutes).
While the heater is running full out (300 watts), it doesn't really matter what the temp of your "reverse-chiller" is; all of that 300 W is getting dumped into your system, and the only thing that removes it is the wash water. (Your water bath will eventually rise to the temperature it needs in order for the wash water flow to extract the 300 W equivalent.)
ps. I didn't verify my calcs, so it would be smart to verify with a real test. Based on the numbers I got, 300W should heat a half-liter (500ml) by 15 deg F in about a minute. (Let me be more clear - it would not only be smart to verify, but you would have to be nuts to not do so.)
pps. If you want to calc it yourself, use the old rule that a BTU raises the temp of 1 lb water by 1 deg F. In more modern times, a BTU is equivalent to about 1,055 joules, where a joule is equivalent to 1 watt for 1 second. So you can get your BTU by any combination of watts x seconds; 1 watt for 1,055 seconds, or 1,055 watts for 1 second, or 300 watts for 3.5 seconds.
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Your simple answer is yes, it will work exactly as effectively to warm water as to cool water. Its performance will depend heavily on getting some motion in the bucket otherwise you will have lots of warm water with pockets of cold surrounding the coils and only convection to move things along. You want your heat exchanger pipe to be as long, narrow and as thin-walled as possible, and to be made of copper.
Heat transfer at a point is symmetric with respect to the sign of temperature difference, all that matters is the thermal resistance sigma (kelvins per watt, K/W) and the temperature difference (dT) between the warm and cold water. The power flow rate is just P = dT / sigma, is in watts, and from that number you can compute the temperature rise of your water using its specific heat (4.2 J/g-K). The thermal resistance of your pipe you need to calculate from its wall thickness and surface area.
An aquarium heater is much too low in power (40W?) to be of value here, you will want a powerful submersible heater like those from an electric kettle. By the time you add a temperature controller though, you've basically built a water heater and I'd rather buy one than make one. At 1L/minute and equilibrium, a 40W heater gives you a temperature rise of only half a degree! Sure you could preheat a large quantity of well-insulated water, but this means you're very limited in the amount of washing you can do because you will rapidly cool down your tub of warm water.
I don't know if you have a Jobo, but I've seen them modified by putting a coil of copper tubing in the bottom bath and you run tap water through the tubing to get process-temperature fresh wash water on demand. A Jobo heater can be as much as 1kW (at least, my CPP2 has a 1kW element, the CPE is probably smaller), and with many litres of water in there, you can get a lot of warm wash-water out of it without perturbing the bath temperature too badly. With this approach, you can have basically unlimited wash water with no additional heater.
Last edited by polyglot; 01-04-2014 at 06:50 AM. Click to view previous post history.
Originally Posted by Mr Bill
OK, now. This is getting interesting.
Originally Posted by polyglot
Mr. Bill: I am using a Versalab which specifies a range of .3 to 2.0 GPM, with .3 to .6 GPM as "should be satisfactory". I only need (want) 10 degrees, but that still probably leaves 300 watts a bit short.
Poly: I don't have a Jobo, but the idea you propose using the Jobo with a coil of copper is more or less what I'm talking about: a 50 foot coil of 3/8" copper tubing immersed in a heated water bath. I still have my old Phototherm immersion heater from my color days (back in the 1970s), but it is only 500 watts.
I may experiment with this down the line. For now, though, I suppose I might leave well enough alone. Ilford's data sheets on their papers states that anything above 5C/41F will wash both RC and FB papers. If I have the washer full of water at room temp, about 66-68 degrees these days, then the wash temp will start there and gradually decrease as the flow goes through the washer. Really, that should be fine. I've never really monitored it (wash water temperature IN in washer) but that's probably the next step.
Interesting discussion. Thanks everybody.
When we bought this house, it had 3 full baths and a powder room (still does, duh). Four chairs, no waiting. Since I am used to a dedicated darkroom, (and there is certainly room) and not working in a bath, I suggested gutting one of the baths and refitting it as the darkroom. My wife looked at me, well, you know ...
Originally Posted by Roger Cole
Anyway, we have a detached garage/shop building that the prior owner had built to work on his cars - his hobby. In the large attic space above the shop, he had built a gym, and had partially finished out the space. I completed what he started and it is 12x18, fully insulated, heated and cooled, etc. But, no native plumbing. I ran a cold water line, and actually plumbed for a water heater, but then decided against installing one based on prior experience. It isn't needed in the darkroom in this climate except rarely, and so sits unused most of the time. It's just not good for them in the long run. Yes, one can turn them off and drain them, but then starting them up when they are needed is a job in itself, and it got to be a cost/benefit decision, admittedly subjective on my part.
The same wife referenced above has told me to just get over it and install a heater, but what does she know?
That's a good point. On the other hand, you don't need tight temperature control on wash water, especially with a low flow rate into a larger tank/tray, so I dunno. If I didn't have a submersible pump for circulation, I'd just try it and see how it works.
Originally Posted by polyglot
I don't think it's necessary to figure the efficiency of the heat transfer because the water bath will eventually reach whatever equilibrium temperature it needs to do the job.
That was also my initial thought until I looked them up. Then I found that 300 watt heaters are pretty readily available.
Originally Posted by polyglot
300W is a start and probably good enough to get a nice store of water up to temp while processing film/paper, but not enough in the steady state. 0.3GPM is 1.15L/min at 300W is only 4C of temp rise. Good enough to wash film, but not really enough power for FB washing.
Doing a hypo clear step will obviously reduce the quantity of warm water you need.
Or a proper heater - it sounds like you have permission from Management for that