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lana
25-10-2006, 07:21 AM
Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40C 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 40C water to 15C then this cooled water enters the second chiller.
Any comment will be appreciated.

Cheers.:)

NoNickName
25-10-2006, 08:31 AM
What is the expected leaving water temperature?

taz24
25-10-2006, 10:58 AM
Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40C 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 40C water to 15C 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
25-10-2006, 12:05 PM
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
25-10-2006, 05:16 PM
Why you think an entering temperature of 40C 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
25-10-2006, 05:39 PM
Why you think an entering temperature of 40C 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
26-10-2006, 06:20 AM
Thank you all.
The required water temp. is 5 or 7C 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 70C 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:mad: .
Here I will use plate heat exchangers both for evaporators and the middle HX.

Cheers.:)

NoNickName
26-10-2006, 08:48 AM
40 to 5? What is the application, just for curiosity.

taz24
26-10-2006, 08:51 PM
Thank you all.
The required water temp. is 5 or 7C 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 70C 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:mad: .
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
27-10-2006, 07:09 AM
Hi there,

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

Thanks:)

taz24
28-10-2006, 12:46 PM
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
30-10-2006, 02:14 AM
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
30-10-2006, 05:10 AM
Hi TXiceman (Ken),


Thank you.
What I am going to do is :

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

Regards :)

TXiceman
31-10-2006, 02:02 AM
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
02-11-2006, 01:26 PM
Thank you TXIceman. Most helpful.
Cheers

nevgee
22-06-2007, 12:42 AM
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
22-06-2007, 12:28 PM
Hi everybody,

I am asked to design a water chiller to cool water with temp. of 40C 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 40C water to 15C 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 40C to 5C. that means using finned-tube heat exchanger in which the tube side is the hot water of 40C 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
22-06-2007, 02:01 PM
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 40C to 5C. that means using finned-tube heat exchanger in which the tube side is the hot water of 40C 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 10C to 12C and this makes the water outlet temperature form the finned-tube heat exchanger of 15C to 17C. therefore, this cold water will complete its cycle to go to a chiller of Tev of 2C to discharge chilled water of 5 or 7C as u need. This is Just an idea

cheers

lana
22-06-2007, 03:27 PM
Thanks everybody,

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

Cheers

nevgee
23-06-2007, 01:13 AM
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
23-06-2007, 01:19 AM
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 (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=144) 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?