Coiling 316L Tubing?

[MeuserReef]

Thanks Bean. Can you see any issues running my chiller barrel inline between my return pump (Mag 12) and my display? Once the barrel is full, it shouldnt pose much of a restriction, should it?

 

[BeanAnimal]

Nope, it should work just fine. The ONLY concern would be slugging the compressor due to the constant supply of warm water over the evaporator. The shorter coil should help that though

 

[t-bone2]

heres a good vid for diy spiral tubing he is doing it to smaller tube but its the same principle http://www.youtube.com/watch?v=YfG6kyifq30&feature=related

 

[MeuserReef]

<a href=showthread.php?s=&postid=12846113#post12846113 target=_blank>Originally posted</a> by BeanAnimal
The ONLY concern would be slugging the compressor due to the constant supply of warm water over the evaporator. The shorter coil should help that though

Bean, would you mind elaborating on this? Is this a concern during compressor startup or during general run time? Im not sure I understand why I would risk slugging the compressor.

My current coil only has around 12" or so of the refrigerant line in contact with the water. I have about 80% of my MAG 12 return feeding the chiller barrel, which then dumps back into the sump. Based on my Evaporation temp/pressure and my superheat, I know that I have an undersized evap coil, hince the upgrade. I figure that my new coil will have close to 60".

I was also thinking that I would split my return line in to two return lines, one feeding the chiller barrel and the other going directly to the display. I could then place a ball valve on the input to the chiller barrel (and the other I suppose), allowing me to regulate the MAX heat load sent across the coil.

 

[Keyoke]

I'd be REAL careful with 316L, as it is *NOT* rated as saltwater safe. The only reason I know this is because I researched the CRAP out of metals trying to find one that I would not have to worry about corroding with continuous saltwater contact.

Go check out the marine corrosion engineering forms at http://www.eng-tips.com/threadminder.cfm?pid=307&page=6 and double check to see.

316L alloy is comprised of Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S. It's the copper component I was worried about corroding and killing everything in the tank.

 

[MeuserReef]

Thanks Keyoke, I appreciate the concern and the info, however there are reefers here on RC that have had 316L in use for various periods of time without any adverse effects (one over 10 years).


BTW, of the elements you listed, copper (Cu) is not on the list

 

[BeanAnimal]

<a href=showthread.php?s=&postid=12846510#post12846510 target=_blank>Originally posted</a> by MeuserReef
Bean, would you mind elaborating on this? Is this a concern during compressor startup or during general run time? Im not sure I understand why I would risk slugging the compressor.

My current coil only has around 12" or so of the refrigerant line in contact with the water. I have about 80% of my MAG 12 return feeding the chiller barrel, which then dumps back into the sump. Based on my Evaporation temp/pressure and my superheat, I know that I have an undersized evap coil, hince the upgrade. I figure that my new coil will have close to 60".

Suck the cold too fast from the refrigerant line and it will turn it from gas back to liquid and slug the compressor. The TXV will and a proper charge will certainly help.

So think about it this way. Take the same chiller tube and run it with a mag5 vs a mag12. The same amount of refrigerant flows through both setups (forget about the TXV for the moment). The water leaving the chiller tube is colder for the mag5 tube setup because there is more contact time per volume of water per time. The COLDER the water, the closer the water temperature is to the evaporator temperature, the less heat transfer there is. The refrigerant at the END of the evaporator is more likely to still be in a gaseous state. Now take the MAG12 setup. The water moves very fast and therefore warmer water is ALWAYS in contact with the evaporator. If the charge or TXV limits are on the border line, then you are more apt to cause a slug.

That said, if the system is charged under the normal operating conditions then it will likely be ok. Also, as I mentioned, the shorter evaporator coil will certainly help.

Both units will run at the same overal carnot efficiency.

Then again I could also be 100% full of it

 

[BeanAnimal]

<a href=showthread.php?s=&postid=12847020#post12847020 target=_blank>Originally posted</a> by Keyoke
I'd be REAL careful with 316L, as it is *NOT* rated as saltwater safe. The only reason I know this is because I researched the CRAP out of metals trying to find one that I would not have to worry about corroding with continuous saltwater contact.

I think you may have your grades mistaken. Grade 316L is the MOST COMMONLY used metal for marine applications due to its corrosion resistance and pitting resistance.

316 is one of the MORE corrosion resistant alloys. It is commonly refered to as "marine grade stainless steel".

316 comes in several sub-alloys.

316L - low carbon, has a lower overall tensile strenght but does not suffer from grain boundry corrosion. Theat means it is less reactive and will not cause carbide precipitation when welded.

316H - high carbon, used in high temperature applications where stability at temperature is required.

316Ti - stabilized for VERY high temperature.

316N - higher strenght than standard 316

The only better SS alternative for resistance to chlorides (salts) would be 904L or 2205. Both would be harder to work with and more expensive.

Then of course there are some very exotic alloys, but they are out of the question for DIY work.

 

[MeuserReef]

<a href=showthread.php?s=&postid=12847672#post12847672 target=_blank>Originally posted</a> by BeanAnimal
Suck the cold too fast from the refrigerant line and it will turn it from gas back to liquid and slug the compressor. The TXV will and a proper charge will certainly help.

So think about it this way. Take the same chiller tube and run it with a mag5 vs a mag12. The same amount of refrigerant flows through both setups (forget about the TXV for the moment). The water leaving the chiller tube is colder for the mag5 tube setup because there is more contact time per volume of water per time. The COLDER the water, the closer the water temperature is to the evaporator temperature, the less heat transfer there is. The refrigerant at the END of the evaporator is more likely to still be in a gaseous state. Now take the MAG12 setup. The water moves very fast and therefore warmer water is ALWAYS in contact with the evaporator. If the charge or TXV limits are on the border line, then you are more apt to cause a slug.

That said, if the system is charged under the normal operating conditions then it will likely be ok. Also, as I mentioned, the shorter evaporator coil will certainly help.

Both units will run at the same overal carnot efficiency.

Then again I could also be 100% full of it

Bean,

Thanks for taking the time to explain both my situation and the metal breakdown. Twice now you have mentioned the "shorter coil", however I am increasing the size of the coil. The flow through the chiller barrel will remain roughly the same, however with the increased surface area of the coil, I am expecting a greater Delta-T through the chiller barrel, which should equate to a bit higher working pressures on the system (which I believe to have enough capacity to handle). Hopefully, this will equate to shorter run-times during the cooling cycle.

In simple terms, Im trying to squeeze every BTU of capacity out of my compressor.

 

[BeanAnimal]

I mean shorter coil as comapred to the "coil" and the "loop" styles.

Yes, more coil surface area should provide for shorter run times. However you must still keep in mind that the carnot cycle (minus startup innefficiency) will dictate the efficiency. If the unit is cycling on and off, then it is working

Too much surface area on the coil will allow to much heat to be added to the gas and it will change state, slugging the compressor.

That said, I am NOT the guy to do the math. I have 3 huge HVAC texts here and they make my head hurt. The TXV and proper superheat will certainly help.

 

[MeuserReef]

If I could do it all over again, I would have trained to be a refrigeration engineer. The math is crazy, however walking into a freezer thats -20° when its 100° outside just amazes me.

 

[MeuserReef]

<a href=showthread.php?s=&postid=12847672#post12847672 target=_blank>Originally posted</a> by BeanAnimal
Suck the cold too fast from the refrigerant line and it will turn it from gas back to liquid and slug the compressor.

Isnt this backwards? Cold is never sucked from a hotter object; Its the heat that is sucked from the water into the refrigerant, which causes the refrigerant to exceed its evaporation point, therefore causing it to boil off. Its the latent heat of evaporation that is obtained from the heat in the water, correct?

 

[BeanAnimal]

Yeah... I certainly did not read what I typed. Energy moves from HOT to COLD and of course the warmer the refrigerant, the more apt it is to become a gas I suppose I should get my head outa my butt and figure out if we are talking about the Evaporator or the Condenser!

That would make most of what I said exactly opposite of reality....

Your larger evaporator should allow you to get a better superheat value (more sensible heat).

 

[MeuserReef]

LOL

I continually confused the evaporator and the condenser when learning the basics of refrigeration. None the less, thanks for your help Bean.

 

[BeanAnimal]

Sadly, I know the difference but have no idea where my head is tonight. (I swear I am not drinking beer either). It has been a long week (maybe 10 hours of sleep since Monday) and I still have hours of work to do. (two clients with servers down).

Most people are amazed (to the point of denial) when they find out that the "hot" line coming into the house is the one that makes things cold, and the COLD line is the one that takes the heat out of the house. "Nah, look the cold line has insulation so that the cold gets to the furnace", they say. How can you argue with that