Recirculate water or not?

norcalfrank

I am building a 4' tank that will have a separate scavenge tank. I plan on heating only the scavenge side, which will be about 25-30 gallons of water. Main tank will hold about 250-275 gallons of water. Do you guys think I need to have a way to circulate the water out of the heated part of the tank into the main tank to help heat or at least warm up the main tank, or just heat the the scavenge side and spray that water on the top? If I do that, will the water on the top be warm enough for long enough to hydrate the film correctly? Thanks guys.

smedlin

I think you need to heat the main part of your tank.

DeviousDips

I think alot of professional bought tanks are made this way and you just recirculation to heat it up. I personally like a heating element in the main side that I can turn off when I need to

norcalfrank

I read lots of bad things about elements in the main tank, so I won't be doing that. I could put a gate valve in and recirculate if it was necessary, but don't want to do it if I dont have to. Just one more tank penetration to leak or give problems.

PagesHydroDipping

@norcalfrank i had my tank made by a guy the i put two 4500 watt heating elements in main tank and then i have elements in the scavenge tank as well. They are hooked to different switches.

PagesHydroDipping

Been 2 years no problems yet

MidOhioHydrographics

If you can turn off the elements in the main tank well before dipping and
Not ever hit them with a part, should be fine. The bubbles would be bad coming up under the film.

I have elements only in my scavenge side. I plumbed a small spa circulation pump between the drains and it keeps the whole thing warm.

norcalfrank

MidOhioHydrographics said:

If you can turn off the elements in the main tank well before dipping and
Not ever hit them with a part, should be fine. The bubbles would be bad coming up under the film.

I have elements only in my scavenge side. I plumbed a small spa circulation pump between the drains and it keeps the whole thing warm.

So do you think that just spraying water over the top will not be enough? Sounds like I need to recirculate to at least get the main part of the tank somewhat warm.

PagesHydroDipping

@norcalfrank you just need to be able to get water surface to 90°.

MidOhioHydrographics

You’ll be fine. Most people can wait a bit for the tank to get right. We may have to start dipping hundreds of parts as soon as the doors open in the morning. I just prefer it to be ready always and consistent.

norcalfrank

Okay, thanks guys!

WileECoyote

The temp of the water "on the top" is actually unknown. And will likely be different every time you use your tank. The whole point of getting better equipment is to REDUCE variability... You are proposing going the opposite way. Yes you need to recirculate, or don't bother building the tank. If you go with what @MidOhioHydrographics suggested (a small spa circulation pump) you can do it constantly. But if you can wait a half hour to an hour to start working, you will be fine just heating the scavenge side. Insulate well, and make the divider stainless (for heat transfer).

K2Concepts

Your heat transfer exchange will be much better in the scavenge side because it is a smaller volume of area...so the efficiency is much higher...if you don't care how much it costs to heat up your tank? Then stick the elements in the main body...

norcalfrank

K2Concepts said:

Your heat transfer exchange will be much better in the scavenge side because it is a smaller volume of area...so the efficiency is much higher...if you don't care how much it costs to heat up your tank? Then stick the elements in the main body...

This is what I was thinking. But wasn't sure if the loss of heat on the air side, and the cooler water on the water side would make the surface temp bleed off too fast before you could dip. I guess I could put in a path for circulation and use it if I needed it. Just didn't want any more penetrations in the main body of the tank than I actually needed.

As far as doing circulation in this tank, I would just put a pipe off the pump discharge going directly into the tank, and ball valves to direct the water to either the body of the main tank, or the spray bar. Then if needed, I could quickly circulate 25-30 gallons ( about 10% of my tank volume) very quickly, or even bleed off some pressure to the spray bar if the pressure is too great for what is needed.

schidro

Would it not be cost effective to keep the whole tank at temperature versus trying to keep part of it right? If you insulate the tank and put a top or cover the top with that foam insulation board from Lowe's or Home Depot it shouldn't have much fluctuation. 

norcalfrank

schidro said:

Would it not be cost effective to keep the whole tank at temperature versus trying to keep part of it right? If you insulate the tank and put a top or cover the top with that foam insulation board from Lowe's or Home Depot it shouldn't have much fluctuation. 

It might be if I were dipping everyday, but I'm not.

MidOhioHydrographics

Honestly I would leave the tank off, then they day before I were going to dip? Go turn it on and let it get up to temp. This is what we do during shutdowns and long weekends. Leave everything off, then I'll go in the day before and turn everything back on to heat up.

WileECoyote

We have our tank in the garage. No heat in the winter, and it was 10 degrees F for a two week stretch. We used an insulated milk tank and 1-1/2" rigid foam insulation on top. We wrapped the pipe in a blanket. We lost 3 degrees every day. We left the heaters on, and the heat transferred through the stainless divider pretty well (no circulation). It took us about 15 minutes to stabilize the tank once we started circulating. Keep in mind, this is nearly PERFECT insulation, you guys adding foam to the outside would have to get under the tank and seal REALLY well, or spray urethane foam all over it.

Insulation goes a long way toward saving you money.

smedlin

I guess that really only counts if your dipping every day?

more for the "full timers"?

I'll go days at a time without even turning my tank on.

WileECoyote

It will certainly help the pros, but only losing 3degrees a day you can do the math. If you didn't dip for a week, you are still only down 21 degrees, in a garage that is below freezing. For the guys in areas of the country that are at 40 and 50 degrees right now, you are probably losing a degree a day. But an uninsulated tank you would lose 40 degrees in less than a day. 

Simple fact is that electricity costs around $.10 a kw/hr no matter where you are at. 2 4500 watt heaters take 9kw an hour and heating up 40 degrees likely takes us an hour (this varies by the amount of water, and again, the insulation and temp Delta) how long does it take you to reach $100 worth of insulation when every time you dip you burn just under a buck? @smedlin you must be going on 2 years by now. If you dip once a week you would have completed your ROI by now.

smedlin

@WileECoyote , It sure seems like 2 years. But my first dip in my shop was April 2017.

The usage really varies. There have been several weeks in a row I never turned the tank on. And then there are times when it's on every day for several weeks.

And your logic may be off. Keep in mind that the majority of the year down here (on the Gulf Coast), most of the time the outside temp is at or greater than the tank temp.

I remember back in August, when the tank hadn't been on for about a week. I turned it on and the water temp was in the low 80's.

But I do see your point. I turned it on Wed, and it took a LONG time for it to heat up. Next time I drain it, maybe I'll look into wrapping it.

how do y'all hold that insulation on the tank? Strap it?

WileECoyote

Well, ours is a double stainless wall with insulation in between. It was an old refrigerated milk tank that we cut the top off, so the hard work was already done. I might suggest some rigid foam adhesive in a few spots, and then wrap the corners with some foil tape. I would suggest the foil backed to begin with, as the activator would just eat the stuff that isn't protected. If you had access to 2component urethane spray foam, I would just blast it with that.

DeviousDips

@smediln. I used the 3m adhesive spray glue to put my insulation up. Then I used the foil tape to tape every seam

schidro

Never thought about the spray foam. I used 1" foam from Lowe's. If you can catch a sheet that's been broke they mark it way down. Save a buck where you can. I had my tank built but the mechanical engineer that welded it thought he knew what I needed more than what I wanted I guess. I built an additional 1" box frame around it.