Hi all, I'm looking at material selection for an ammonia and salt water heat exchanger application. The working temperatures are relatively ambient with a low approach (temperature difference is less than 10 degrees C), and the pressures don't go above 13 bar (188 psi). I was thinking, therefore, that plastics might be an alternative except for their low thermal conductivity (anyone know of some newer plastics manufacturers that are ramping up production of improved heat exchangers?). I was also looking at aluminum, but I don’t know how it performs relative to steels. Steels are probably not as ideal as titanium because of their general higher susceptibility to corrosion effects, however, I'm not familiar with all steels relative to titanium and a cost per performance analysis might be in order. Copper alloys or aluminum-copper alloys seem to be out because of coppers reactivity with ammonia. However, I don’t want to rule out any ideas, these are just my initial thoughts. Again, cost relative to titanium is the biggest issue at this point since titanium is otherwise somewhat ideal. Any help would be greatly appreciated!
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Low-cost heat exchanger 2
- Thread starter ddot
- Start date
ddot,
Low cost is a pretty relative term. However for your combination of materials, I would strongly consider a titanium plate and frame exchanger for the following reasons:
1. Titanium is the preferred material in contact with salt water.
2. PHE's have a high heat transfer coefficient compared to other types of exchangers (but they don't use fouling factors either).
3. PHE's are normally capable of close approach temperatures. The flow rates of the two fluids should be more-or-less ballanced, however for best performance.
Regards,
speco (
Low cost is a pretty relative term. However for your combination of materials, I would strongly consider a titanium plate and frame exchanger for the following reasons:
1. Titanium is the preferred material in contact with salt water.
2. PHE's have a high heat transfer coefficient compared to other types of exchangers (but they don't use fouling factors either).
3. PHE's are normally capable of close approach temperatures. The flow rates of the two fluids should be more-or-less ballanced, however for best performance.
Regards,
speco (
EdStainless
Materials
You will get closer approach temps in PHE than S&T.
Ti is the traditional material for these. Not hte only choice, but PHE builders have not been agressive about using high performance stainless alloys.
S&T will be larger and heavier, but you have more material choices. You could use superferritic stainless tubes, which offer excellent corrosion resistance and are a lot less expensive than Ti.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
Ti is the traditional material for these. Not hte only choice, but PHE builders have not been agressive about using high performance stainless alloys.
S&T will be larger and heavier, but you have more material choices. You could use superferritic stainless tubes, which offer excellent corrosion resistance and are a lot less expensive than Ti.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
- Thread starter
- #5
Thanks very much for the input! PHE's do seem to be the way to go. However, I do still wonder about materials options. One of the problems with titanium is the long wait on availability. Contacing a firm or two I found a long wait list over a year for titanium PHE's due to the large quantity that I require. Does anyone have any experience with seawater and plastic S&T or PHE's? I would really like to consider a cheaper alternative to titanium (with better availability).
The issue then would be lifetime and increased surface area requirements. If the cost savings are significant, though, I would definitely consider plastic PHE's.
ddot
The issue then would be lifetime and increased surface area requirements. If the cost savings are significant, though, I would definitely consider plastic PHE's.
ddot
- Thread starter
- #6
Thanks Panduru for suggesting this idea of cladding. I don't really know that titanium cladding could work for PHE's due to their thickness (for titanium, plate thickness is probably below 2mm thick for my application).
Has anyone heard of titanium cladding on steel at these thicknesses?
Has anyone heard of titanium cladding on steel at these thicknesses?
@ddot:
You actually mean due their thinness !![[bigsmile]](/data/assets/smilies/bigsmile.gif "[bigsmile] [bigsmile]")
When you think Titanium-clad-Steel, it is the Steel that matters for thickness, not the cladding material. You'll have to adopt base material of suitable thickness, with a thin Ti cladding.
Btw, I was not thinking PHE in particular when I posted my point. It is interesting to note that both speco and EdStainless seem to recommend PHE over ST in your case.
You actually mean due their thinness !
When you think Titanium-clad-Steel, it is the Steel that matters for thickness, not the cladding material. You'll have to adopt base material of suitable thickness, with a thin Ti cladding.
Btw, I was not thinking PHE in particular when I posted my point. It is interesting to note that both speco and EdStainless seem to recommend PHE over ST in your case.
You might want to explore the possibility of glass lined Heat Exchanegrs. They use silicon carbide tubes and the shell is lined with glass. They can be used up to 200 deg C and offer excellent Heat Transfer coefficient. The recommended manufatures are De-Dietrich, Estrella etc.
Asif Raza
Asif Raza
- Thread starter
- #10
Thank you all for the suggestions. I hadn't explored glass-lined heat exchangers, though if they are not used in plate applications, I doubt they would fit in the area I have allocated. Definitely will look into that though. I hear that graphite PHEs are pretty pricy, so I'd have to check that out. We'll see. If anyone has any other suggetions, let me know!
ddot
ddot
What about using a secondary cooling fluid on your exchangers, say cooling water. Then you have two types of exchangers. Ammonia and cooling water then cooling water and salt water. You could isolate your need for titanium to one larger exchanger and make the rest of them out of carbon steel shell and tubes.
Just a thought.
Just a thought.
- Thread starter
- #12
Thanks very much for the fluid change suggestion, but the setup doesn't allow me to change the fluids that I'm using. It would be nice, though. I've been playing with the idea of using a composite material like the titanium-cladding that panduru mentioned. However, I don't know who I would contact for that kind of manufacturing if it is even possible.
dott
dott
MedicineEng
Industrial
Just a remark with graphite HE. They are quite nice and compact, but be sure the temperatures that you are working with will not go below the freezing point of the sea water or the boiling point of the ammonia. Graphite HEs are quite fragile when the fluid changes physical state. I know this because I recently had a graphite HE that it was broken due to water freezing inside it. And the only repair is a full replacement of the interior module.
ddot,
I am not aware of any manufacturers of plate heat exchangers who make any kind of titanium clad plates. The normal thickness for ti plates is around .4 to .5 mm. There is an industry standard, but don't have the actual thickness handy.
In your intitial posting you said that you were looking for an inexpensive heat exchanger. While titanium is not cheap, the glass-lined exchangers with silicon carbide tubes are REALLY expensive. I believe that you find that the graphite phe is also way up there in price.
I would suggest concentrating on finding a phe manufacturer who can provide this exchanger. There are many out there to choose from. Some of the lesser-known names (example: Sondex in Louisville, KY) might be worth checking out.
Regards,
speco (
I am not aware of any manufacturers of plate heat exchangers who make any kind of titanium clad plates. The normal thickness for ti plates is around .4 to .5 mm. There is an industry standard, but don't have the actual thickness handy.
In your intitial posting you said that you were looking for an inexpensive heat exchanger. While titanium is not cheap, the glass-lined exchangers with silicon carbide tubes are REALLY expensive. I believe that you find that the graphite phe is also way up there in price.
I would suggest concentrating on finding a phe manufacturer who can provide this exchanger. There are many out there to choose from. Some of the lesser-known names (example: Sondex in Louisville, KY) might be worth checking out.
Regards,
speco (
- Thread starter
- #15
Thanks for the advice on the graphite PHEs and on the lack of titanium clad plate manufacturers. It appears that you are both correct unless I am missing something. A number of sources have cited graphite HE as more expensive than even titanium while I have yet to find a website for titanium clad plate manufacturers or an HE manufacturer with these plates as part of their production.
At this point, I'm contacting a number of manufacturers (probably the hardest thing to do is getting someone on the phone who knows what they are talking about).
Thanks for the Sondex name, I'll check them out.
ddot
At this point, I'm contacting a number of manufacturers (probably the hardest thing to do is getting someone on the phone who knows what they are talking about).
Thanks for the Sondex name, I'll check them out.
ddot
Check out FAFCO.COM and contact a fella there by the name Freeman Ford, he's the best bet for info relative to it,
they are currently in prototype semi-commercial production of a seawater cooling system using PE bundles submerged in a seawater bath for hot (90 degrees C) process water cooling in a steel mill.
they are currently in prototype semi-commercial production of a seawater cooling system using PE bundles submerged in a seawater bath for hot (90 degrees C) process water cooling in a steel mill.
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1
- #17
As a cheaper option you may also give a try to polyethylene material for the heat exchanger. Due to the low thermal conductivity of the plastic material you will need more tube bundles but the PE material is relatively cheaper option for the HE. We have use these kind of heat exchangers with salt water as the heat transfer medium. This is particular good also due to their low reactivity and resistance against corrosion. As long as you dont have any space limitations, you can end up with relatively low cost heat exchanger using PE tubes.
How big are these heat exchangers?
There are lots of tube in tube manufacturers who build "vent space" between dissimilar tube materials for just this type of application, in some case "vent space" becomes a fill of its own, like an alcohol solution....The S & T manufacturers would go either sacraficial containment or titanium tube, and if you are dealing with multiple high capacity units, the cost effectiveness can get pretty good...
Won't beat a P & F for compactness though they are all pre-designed based on equivalent passages, largely; and you are looking at a sizeable volumetric change on the condensing side.
There are lots of tube in tube manufacturers who build "vent space" between dissimilar tube materials for just this type of application, in some case "vent space" becomes a fill of its own, like an alcohol solution....The S & T manufacturers would go either sacraficial containment or titanium tube, and if you are dealing with multiple high capacity units, the cost effectiveness can get pretty good...
Won't beat a P & F for compactness though they are all pre-designed based on equivalent passages, largely; and you are looking at a sizeable volumetric change on the condensing side.
- Thread starter
- #19
Thank you for new suggestions!
Thermcool,
I actually did hear about HDPE (high-density PE) as an option for tube heat exchangers. I'm actually very interested in hearing about your PE tube application. Do you have any problems with bio-fouling or shortened lifecycles? I read about PE used as downhole heat exchangers for geothermal applications (similarly mineral rich liquids at low temps/pressures) and would really like to dig deeper in that direction since cost savings may be substantial.
As I said, however, size is still a limitation to some degree. A substantial cost savings in material, though, could warrant the increased area. Please let me know more!
Sterl,
These heat exchangers have a pretty big duty. Other than the manufacturer that I've already established for the current titanium PHE's, most manufacturers I've contacted have said they aren't prepared to meet the duty that I'm looking at based on the standardized PHE's they have available. What I'm looking for, really, is something modular rather than one large heat exchanger. Of course, the bigger each module the better.
I really do need to limit the floor area required (it can go larger than titanium PHE but I don't know about switching to S&T). I'm really curious to know what the size difference is in thermcools application though. It would be great to cut cost on this project.
Again, thanks much for you valuable input!
ddot
Thermcool,
I actually did hear about HDPE (high-density PE) as an option for tube heat exchangers. I'm actually very interested in hearing about your PE tube application. Do you have any problems with bio-fouling or shortened lifecycles? I read about PE used as downhole heat exchangers for geothermal applications (similarly mineral rich liquids at low temps/pressures) and would really like to dig deeper in that direction since cost savings may be substantial.
As I said, however, size is still a limitation to some degree. A substantial cost savings in material, though, could warrant the increased area. Please let me know more!
Sterl,
These heat exchangers have a pretty big duty. Other than the manufacturer that I've already established for the current titanium PHE's, most manufacturers I've contacted have said they aren't prepared to meet the duty that I'm looking at based on the standardized PHE's they have available. What I'm looking for, really, is something modular rather than one large heat exchanger. Of course, the bigger each module the better.
I really do need to limit the floor area required (it can go larger than titanium PHE but I don't know about switching to S&T). I'm really curious to know what the size difference is in thermcools application though. It would be great to cut cost on this project.
Again, thanks much for you valuable input!
ddot
We had use these heat exchanger without any substantial problems. Actually, with stagnant flow or very low flow rates for highly saturated salt mixture sometime deposition of the salt takes place in these tubes but it is very easy to clear the pipes by periodic increasing the flow. As i said such a deposition only occured when the flow was stangnant for longer time period like more than a week or so. PE tubes are relatively smooth and does not pose any of the issues as faced by the metal heat exchanger with bulk saturated fluid. we had use very small diameter PE tubes for sampling solar pond salinity trends as well as extraction of the heat from the ponds. Also, we have use these kind of heat exchanger for aquaculature using solar ponds.
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