How to cool down Mineral Oil

[Anon_Miner]

TL;DR Summary

Hi kind strangers
I'm asking for different ways to cool down 250 litres of mineral oil in a system.

Hello friendly people of PF

So I have a tank with about 250 litres of mineral oil in it. and computer servers are immersed in it. the oil keeps the servers cool but get's hot in return.

What different (economic) ways are there to cool the oil down? The best way I could think of was Oil-water heat exchanger but i don't know what to do with the produced hot water as I have no use for it.

Further Info: there are 10 servers in the pool. Each server consumes 2100 W. The working temperature for servers is within 10-65 °C.

so can you think of any other ways to optimize cooling down the oil?
or what to do with the hot water produced?

Thanks guys

 

[BvU]

You have to find a place to dump your waste heat. Just like with any airconditioning system: it's got to go somewhere. If you live near the ocean or a river: into the water. Else into the air.

Did your servers come with oil cooling ?

 

[AZFIREBALL]

Drop the hot water through a cooling tower and recycle it.

 

[russ_watters]

Cool problem [pun coincidental]

What different (economic) ways are there to cool the oil down? The best way I could think of was Oil-water heat exchanger but i don't know what to do with the produced hot water as I have no use for it.

Further Info: there are 10 servers in the pool. Each server consumes 2100 W. The working temperature for servers is within 10-65 °C.

You need a cooling tower or dry cooler if you don't have access to a large heat sink (a pool or lake?).

You can make a dry cooler with a car radiator.

 

[Anon_Miner]

You have to find a place to dump your waste heat. Just like with any airconditioning system: it's got to go somewhere. If you live near the ocean or a river: into the water. Else into the air.

Did your servers come with oil cooling ?

Thanks for your reply

No they didn't come with oil cooling, I used immersion cooling by myself.
Unfortunately I don't live near ocean or river and have to use tap water.

Do you have any suggestions on how to dissipate the heat into the air?

 

[Anon_Miner]

Cool problem [pun coincidental]

You need a cooling tower or dry cooler if you don't have access to a large heat sink (a pool or lake?).

You can make a dry cooler with a car radiator.

Drop the hot water through a cooling tower and recycle it.

Thank you guys for taking the time

Yes I was thinking about using a car radiator since they are smaller and I don't have a lot of space. Hence the cooling tower seems not viable.

 

[russ_watters]

Yes I was thinking about using a car radiator since they are smaller and I don't have a lot of space. Hence the cooling tower seems not viable.

I've seen people make cooling towers with PVC pipe and a showerhead, but probably not for 2100W and it's more cumbersome.

 

[Anon_Miner]

I've seen people make cooling towers with PVC pipe and a showerhead, but probably not for 2100W and it's more cumbersome.

Yea I think it's the best solution. but do you know any way (other than Oil-water heat exchanger) to cool down the oil?

 

[russ_watters]

Yea I think it's the best solution. but do you know any way (other than Oil-water heat exchanger) to cool down the oil?

You could use tap water, but that would get expensive/wasteful.

The radiator/dry cooler is probably easiest, but the PVC cooling tower would be more effective (cooler water) and could be fun. You just might need to bank several together. Also, the PVC cooling tower might be able to be done without a fan.

 

[Anon_Miner]

You could use tap water, but that would get expensive/wasteful.

The radiator/dry cooler is probably easiest, but the PVC cooling tower would be more effective (cooler water) and could be fun. You just might need to bank several together. Also, the PVC cooling tower might be able to be done without a fan.

I really appreciate you taking the time

Do you have any blueprints for said cooling tower or any sources I can refer to?

 

[Baluncore]

@Anon_Miner
Mineral transformer oil = 1-Methyl-naphthalene, is circulated through an electrical transformer and external radiator by a thermal siphon. You can use a similar technique.

https://owlcation.com/stem/Cooling-of-transformers

A circulation pump can be used to move the oil if the radiator placement is not suitable for the thermal circulation. A fan can be used to increase the flow of cooling air through a smaller radiator.

 

[Lnewqban]

Another option, which effectiveness depends on the typical dry and humid bulb temperatures of your environment during summer times:

https://en.wikipedia.org/wiki/Evaporative_cooler

 

[russ_watters]

I really appreciate you taking the time

Do you have any blueprints for said cooling tower or any sources I can refer to?

You're welcome!

https://www.overclockers.com/forums/showthread.php/321055-Building-your-First-evaporative-cooling-tower!

A couple of notes:
-Works better in cooler/ drier climates.
-Will humidify the room it is in.
-Taller is better. Or shorter, with a small fan.
-Higher flow through the tower means more cooling (in watts), but warmer water. So you are probably better off with more of them at lower flow (a misting nozzle instead of a shower head). Taking a stab at their effectiveness; 4 at 1 l/m and 10C delta-T.

 

[anorlunda]

transformer

There's a good clue. Your application is very similar to cooling an oil filled transformer. This search shows numerous cooling methods found to be practical. You might even find a used transformer cooling system in a junkyard, and skip designing your own. Design can be fun, but we must recognize the risk of failed designs.

 

[russ_watters]

Another option, which effectiveness depends on the typical dry and humid bulb temperatures of your environment during summer times:

https://en.wikipedia.org/wiki/Evaporative_cooler

Cooling tower = evaporative cooler

 

[berkeman]

Yea I think it's the best solution.

Can you say what the climate is like where you live? How many stories is the building where you have this server farm, and do you have access to the roof? If you aren't going to mount this radiator and fan on the roof, where are you going to dump all of that hot air?

 

[berkeman]

Also, you might look at re-purposing the exterior fan and housing of a heat pump -- it's a nice compact weatherproof unit that you could use to pull air through your radiator...

 

[Anon_Miner]

Can you say what the climate is like where you live? How many stories is the building where you have this server farm, and do you have access to the roof? If you aren't going to mount this radiator and fan on the roof, where are you going to dump all of that hot air?

thanks for your reply

The weather is dry and can reach up to 40°C during summer. The building is 4 story and access to the roof is possible but it's not necessary since the hot air will be dumped into open air (through the yard).

 

[Vanadium 50]

You are trying to dump 21 kW of power. That's a lot. I'd be surprised if you can get that practically with things like evaporative cooling or repurposed heat pumps.

 

[russ_watters]

You are trying to dump 21 kW of power. That's a lot. I'd be surprised if you can get that practically with things like evaporative cooling or repurposed heat pumps.

2.1, not 21...

 

[Bystander]

You are trying to dump 21 kW of power. That's a lot. I'd be surprised if you can get that practically with things like evaporative cooling or repurposed heat pumps.

2.1, not 21...

Ten times two equals twenty in my universe.

 

[russ_watters]

2.1, not 21...

Ten times two equals twenty in my universe.

Dang, sorry guys. I even read it a second time before replying and still misread. Somehow I read this as a home project and couldn't get off that track.

Yep, I agree it's too big for a home built solution. A commercial grade dry-cooler or cooling tower is required.

 

[berkeman]

@russ_watters -- How do you convert from 21kW to the "ton" or "seer" ratings of heat pumps? Is there a way to show the OP just how big the cooler would have to be?

 

[Bystander]

even read it a second time before replying and still misread.

Been there, done that, got the t-shirt(s), worn 'em out, washed the car,...

21kW to the "ton"

"Ton" is order of one horse.(?)

 

[Baluncore]

A ton of air conditioning is a nominal 12,000 Btu/h. It is defined as the rate of heat transfer that results in the freezing or melting of 907 kg (1 short ton = 2,000 lb); of pure ice at 0°C in 24 hours.
12,000 Btu/h. = 12.660672 MJ/hr = 200 Btu/min = 3.517 kW

 

[berkeman]

12,000 Btu/h. = 12.660672 MJ/hr = 200 Btu/min = 3.517 kW

So 21kW is about 7 ton? A 10 ton commercial heat pump is only a few thousand dollars (not including installation)...

https://hvacdirect.com/daikin-10-ton-12-6-ieer-light-commercial-heat-pump-packaged-unit-dch120xxx3vxxx.html

 

[russ_watters]

@russ_watters -- How do you convert from 21kW to the "ton" or "seer" ratings of heat pumps? Is there a way to show the OP just how big the cooler would have to be?

Nice save, thanks.

3.41 BTU per watt, 12,000 btu per ton = 6 Tons. For an air conditioner, that's as big as residential units get. For a dry cooler it depends on the exact weather and coolant temperature limits, but you are probably looking at something of about this size:

 

[Dullard]

Can't help but wonder:
The servers were apparently designed to be air-cooled. Why not build a ducted box and use filtered forced-air cooling? You can discharge the hot air outside, and probably won't need to cool the incoming air (with high enough air flow).

 

[Anon_Miner]

Can't help but wonder:
The servers were apparently designed to be air-cooled. Why not build a ducted box and use filtered forced-air cooling? You can discharge the hot air outside, and probably won't need to cool the incoming air (with high enough air flow).

Yes, they are designed to be air-cooled. They've got very high speed fans to cool them.
But the downside to mentioned fans, They are very loud and make a lot of noise even just for one server. Now imagine 10 of them working simultaneously! It's deafening.

That was the reason I converted to oil cooling. I removed the fans and submerged them in Mineral oil to reduce the noise drastically. Although it came at a high expense but that was the only way I saw to "mute" the servers.

If you have any advice on how to reduce the noise drastically without submerging them; I would really appreciate it if you shared. (for the future server farms).

Thanks!

 

[Dullard]

I'm dating myself, but:

In the good old days, large computer installations were often installed on a false floor with a single large blower / AC pressurizing the under-floor space. Ducts were directed from that space up into the individual enclosures - the pressure difference caused the cool air to flow through the equipment.

You could build a version of that, and use a single large blower (located outside) instead of using the local fans. It's important to get the air where you need it - I'd thoroughly test with a single server before I did anything at scale. You may need to do some 'micro-ducting.'

 

[Anon_Miner]

I'm dating myself, but:

In the good old days, large computer installations were often installed on a false floor with a single large blower / AC pressurizing the under-floor space. Ducts were directed from that space up into the individual enclosures - the pressure difference caused the cool air to flow through the equipment.

You could build a version of that, and use a single large blower (located outside) instead of using the local fans. It's important to get the air where you need it - I'd thoroughly test with a single server before I did anything at scale. You may need to do some 'micro-ducting.'

I did something similar. I created a "tunnel" using tarp; at one end I put a commercial Evaporative cooler (15000 m3/h blowing power) and at the other end I placed the servers with their fans removed. the problem was that the servers' boards are really dense and don't have that much space between them. so the air didn't cool them all properly and some of the boards reached critical temperature.

in case you're wondering i also put the servers really close to each other and tightened as much as possible to reduce the amount of wasted air in the tunnel. kinda tried to force the air to go through the servers by not providing it much space to get out of the tunnel, other than through the servers!

I don't know maybe I did something wrong but that didn't work out for me. the length of the "wind tunnel" was 1.5 meters and had a diameter of 1.5 meters.

edit: I uploaded a picture of how dense the boards are.

 

[jrmichler]

Here's how I would tackle this problem. I'm assuming a submerged oil system, with the heat transferred to air.

1) Heat generated = 21 kW X 3412 = 72,000 BTUH (sorry about the units, but that's what I'm accustomed to).
2) Maximum temperature of oil = 65 C = 149 deg F. This is the temperature that the oil is allowed to reach on a hot (40 C) day.
3) Temperature difference between oil in and oil out: 10 deg F. This is an assumed number, you can adjust it later.
4) Oil flow rate = 72,000 BTUH / 10 deg F delta T / 7.67 lbs/gallon = 39 GPM.
5) Temperature difference between air in and air out of heat exchanger: 10 deg F. This is an assumed number, you can adjust it later.
5) Minimum air flow rate = 72,000 BTUH / 10 deg F delta T / 0.018 BTU/ft^3-deg F / 60 min/hr = 6700 CFM.
6) Decision time. You can transfer heat from oil to air by a spray system in a cooling tower, or by an oil to air heat exchanger. So evaluate both alternatives until one is clearly better.

6a) Cooling tower: My Chemical Engineers Handbook by Perry and Chilton has some good information on cooling towers. Be careful, they assume water to air which includes evaporative cooling. Also, an oil to air cooling tower will collect dirt, so you will need a good filter system. The flow rates calculated above are minimums for the assumed temperature differences. The cooling tower will need to be large enough to exchange that amount of heat without blowing an oil mist over the entire neighborhood.

6b) Heat exchanger. The above assumptions call for a heat exchanger designed for mineral oil at a flow rate of 39 GPM, 149 deg F oil in, 139 deg F oil out, 104 deg F (40 C) air in, 114 deg F air out, and 6700 CFM air flow. This could be about four automobile radiators in a square with a 36 inch panel fan on top. A 36" panel fan with a 1/2 hp motor running 870 RPM would move the required air with little noise. Aerovent is only one of many companies that make these fans: https://www.aerovent.com/wp-content...RF-BPRV-DDP-DDPRC-DDPRF-DDPRV-Catalog-168.pdf. Consider also an engineered systems such as shown by @russ_watters in Post #27.

7) This is where you start to iterate. Try a larger temperature difference on the oil to reduce oil flow rate, a larger temperature difference on air to reduce air flow rate. Either or both of those changes will affect the size of the cooling tower or heat exchanger.

(MTA) 8) The above makes assumptions about the size of the heat exchanger or size of cooling tower. If the heat exchanger is larger, you can get less temperature difference between the oil and the outside air, which would allow you to use smaller air and/or oil flow rates. Lots of iteration to get a complete solution, or take the "easy" way and use several automobile radiators, then blank them off one at a time until you find the minimum that gets the job done.

 

[Tom.G]

I'm not sure if this is repetitive, too many ideas presented above.

A minor variation to what @jrmichler suggested is put those radiators (with the oil circulating in them) in the cold pool at the bottom of the cooling towers.

At the cost of higher operating expense but smaller cooling towers, put a heat pump/air conditioner between the oil and the cooling towers. The higher water temp in the towers will increase their efficiency.

p.s. (Mentors, feel free to delete if this post is repetitive)

 

[jrmichler]

too many ideas presented above

Or possibly not enough ideas. There are many ways to solve the problem of getting rid of excess heat. Choosing the best way to solve a particular problem requires taking into account a number of factors. The amount of heat in kW, the outside air temperature, space available, allowable noise, up front cost, operating cost, reliability, durability, appearance all need to be considered.

Some of these are calculated, others are estimated or are a matter of opinion. All need to be considered.

A key point is that the OP wants to get rid of 72,000 BTUH. That's a lot of heat. It's too much heat to get rid of by adding a few computer cooling fans to blow the heat around the room. For comparison, my house needs 13,000 BTUH to maintain 72 deg F (22 C) inside when it's -20 deg F (-29 C)outside.

 

[Baluncore]

The optimum solution will be dependent on the building that houses the servers, the external climate, and the availability of water. I am surprised there is no use for the heat.

It is not surprising there have been so many suggestions. The OP has not given a clue as to the system's environment.