Water Chiller

[lana]

Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40°C which flows constantly with low flow rate.
I think that with one chiller this would be a problem because of high entering temp.
I want to use two chillers with one heat exchanger in between, i.e. cold water from the first chiller goes into a plate heat exchanger then cools the 40°C water to 15°C then this cooled water enters the second chiller.
Any comment will be appreciated.

Cheers.

[NoNickName]

What is the expected leaving water temperature?

[taz24]

Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40°C which flows constantly with low flow rate.
I think that with one chiller this would be a problem because of high entering temp.
I want to use two chillers with one heat exchanger in between, i.e. cold water from the first chiller goes into a plate heat exchanger then cools the 40°C water to 15°C then this cooled water enters the second chiller.
Any comment will be appreciated.

Cheers.

Flow rate, voluum of water and end temp are all critical to working out the size you need.
They way you explain would work, taking the temp down in stages. one system correctly sized would do it alsoit literaly is horses for courses.

Cheers taz.

[vijay_study]

Hi Lana,

If your assuming that 40deg C is Dry bulb temperature. If you can get 30 to 32 deg C of wet bulb temperature then it would be a better option to go for a cooling tower rather than a chiller !

Regards

Vijay Kumar
HVAC Engineer

[Peter_1]

Why you think an entering temperature of 40°C with a chiller in a counterflow setup will give problems?
The only thing the warm entering water will do is raise the SH, not necessarily the evaporating pressure.
NoNickName is the best person to judge this.

[NoNickName]

Why you think an entering temperature of 40°C with a chiller in a counterflow setup will give problems?
The only thing the warm entering water will do is raise the SH, not necessarily the evaporating pressure.
NoNickName is the best person to judge this.

I would say to use MOP TXV (or even better: EXV) to limit the SH and numerous baffles in the s&t evaporator.
Nothing is said, though, about the required leaving water temperature.

[lana]

Thank you all.
The required water temp. is 5 or 7°C and the flow rate is 2 lit/min.
There is no way that a cooling tower could be used because of ambient conditions.
I have an experience with an air cooler which was supposed to cool 70°C steam. There the suction pressure went up (also the SH) and basically there was no way that the TEV could be adjusted to get the required capacity .
Here I will use plate heat exchangers both for evaporators and the middle HX.

Cheers.

[NoNickName]

40° to 5°? What is the application, just for curiosity.

[taz24]

Thank you all.
The required water temp. is 5 or 7°C and the flow rate is 2 lit/min.
There is no way that a cooling tower could be used because of ambient conditions.
I have an experience with an air cooler which was supposed to cool 70°C steam. There the suction pressure went up (also the SH) and basically there was no way that the TEV could be adjusted to get the required capacity .
Here I will use plate heat exchangers both for evaporators and the middle HX.

Cheers.

Are you using the water to add to flour to mix bread by chance.

Cheers taz.

[lana]

Hi there,

The cold water is used to cool some kind of high temp. gas in the chamber jacket.

Thanks

[taz24]

Hi there,

The cold water is used to cool some kind of high temp. gas in the chamber jacket.

Thanks

In that case, why not cool the gas directly with the primary circuit. Cut out the middle man
It would be more efficient to cool the gas directly with the primary system.

Cheers taz.

[TXiceman]

You can design a unit for 40 dC inlet, but you need to careefully watch the compresssor inlet temperature and it's limits. You can use a run-around loopto temper the water temp entering the chiller. Or use a secondary process loop and a primary chiller loop with a mixing tank to temper the return to the chiler.

Personally, I'd go with the two pump and mixing tank approach to keep it in a standard chiller.

Ken

[lana]

Hi TXiceman (Ken),


Thank you.
What I am going to do is :

Use first chiller to cool 40°C to 15°C by using a Plate heat exchanger therefore 40°C water will not enter the chiller evaporator.
Then the second chiller will cool the 15°C water to 7°C.
Because of very low flow rate I don't think that water tank is necessary.

Regards

[TXiceman]

You will need some sort of expansion tank for the closed loop system. I like to keep the loop closed or sealed under a low pressure nitrogen pad to keep out contaminents. You will need some inhibitors in the water to control corrision and letting it breath as in an open loop will deplete the inhibitors sooner.

The expansion tank can be either a simple sealed tank or a bladder tank.

You can do it in one loop system with a hot/cold divided mixing tank and separate pumps for the process flow and for the chiller flow. By using the mixing taank, you can keep the hot water off the chiller.

Ken

[lana]

Thank you TXIceman. Most helpful.
Cheers

[nevgee]

Lana.

You may already have this contact,
SWEP They make plate exchangers just as Alfa Laval etc. I'm not allowed to post the URL here because I'm still a rookie! But you'll know how to do a search ...i'm sure?

They will let you have selection software for plate exchangers. Which I have used for many years ..much better than the old fashioned shell and tube.

[mohamed khamis]

Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40°C which flows constantly with low flow rate.
I think that with one chiller this would be a problem because of high entering temp.
I want to use two chillers with one heat exchanger in between, i.e. cold water from the first chiller goes into a plate heat exchanger then cools the 40°C water to 15°C then this cooled water enters the second chiller.
Any comment will be appreciated.

Cheers.

Hi Lana

Just an idea and i did not make any calculation for it. what about you using Package unit with DX coil with a certain capacity with all return air and then using the cooled air from this Package to cool the water from 40°C to 5°C. that means using finned-tube heat exchanger in which the tube side is the hot water of 40°C and the cold side is the supplied air from the package unit over the finned-tube. By this u strike, avoid abnormal raising in chiller suction temperature and energy saving of using all return air. I wish this idea is reseaonble for being used in ur project

Cheers

[mohamed khamis]

Hi Lana

Just an idea and i did not make any calculation for it. what about you using Package unit with DX coil with a certain capacity with all return air and then using the cooled air from this Package to cool the water from 40°C to 5°C. that means using finned-tube heat exchanger in which the tube side is the hot water of 40°C and the cold side is the supplied air from the package unit over the finned-tube. By this u strike, avoid abnormal raising in chiller suction temperature and energy saving of using all return air. I wish this idea is reseaonble for being used in ur project

Cheers

oh sorry i discover a mistake in the idea. It should be divided into stage, the first one as a formentioned by using package unit and the second stage by using chiller. Because of the minimum supply temperature will be exited from package unit may be around 10°C to 12°C and this makes the water outlet temperature form the finned-tube heat exchanger of 15°C to 17°C. therefore, this cold water will complete its cycle to go to a chiller of Tev of 2°C to discharge chilled water of 5 or 7°C as u need. This is Just an idea

cheers

[lana]

Thanks everybody,

I have proposed the two chiller units which has been proved but there is no contract for the job yet.
Everything takes ages to complete.

Cheers

[nevgee]

That's the way of contracting .... loads of design and probabilities ...then the wait for the order .....and then more waiting and then more re arranging and so it goes on. Why do we do this?

[nevgee]

TXICEMAN.

I like to keep the loop closed or sealed under a low pressure nitrogen pad to keep out contaminents. You will need some inhibitors in the water to Control corrision and letting it breath as in an open loop will deplete the inhibitors sooner.


If you blanket with nitrogen then surely there will be no need for the inhibitor as there will be no oxidation occuring?