PDA

View Full Version : Seeking water chiller advise



rok
23-07-2010, 05:54 AM
Hi all,

this is my first post on this forum, I am a maintenance fitter, not a refrigerations technician and I am seeking some advice on an idea I'm working on.

Basically, it's a heat exchanger that will be used to chill water - I believe this component is called the evaporator.

Initial water temp will be between 5C-10C and I require the water to be 0C or less when it leaves the exchanger.

The basic idea is to have a 2" steel pipe, 3' long, with 3/8" copper pipes for refrigerant running axially along it ... and to have 4 of these 3' sections connected side by side with elbows.

Flow rate will be about 5l/s.

Ambient atmospheric temp is around 0C and humidity is around 80%.

I like some opinion on whether this design will be successful in removing enough heat from the water before it exits the system.

Will it require an excessively large system?

All constructive comments are welcome!

Tesla
23-07-2010, 11:25 AM
Hi rok
Welcome to the forum.
I was once a fitter too... and wondered about stuff like this then I did a fridgie apprenticeship. You need to let us know the application for your heat exchanger (roughly). You are talking about a water cooled heat exchanger in an ambiant of 0°(alt+2,4,8)C, with initial water temp of 5 - 10°C. Also you've given the flo rate of 5l/S
So Q = M x SHC x delta T.
5 x 4.2 x 5 = 105kJ/s or kW. with 100% exchange efficiency we get 50% max, so we are looking for 52 -105kW.
The question is what medium are we to transfer this heat to? If air what would be the heat transfer area and air flo rate?
If I have misunderstood pls put me right, or give us a little more to go on.

norseman
23-07-2010, 12:02 PM
Hi Rok.

Another aspect here is the low temperature you are looking at. To create an outlet temperature around Oc. would involve that your coolings tubes would have to be quite some colder to achive that. The innerside of the tubes will probably freeze up layer on layer of ice pretty soon. May be you will see some nice sausages of ice coming out of the end;).
Not the same, but I have seen a lot of recirculators types containing some liquids which does not freeze before all from -10 to -90c start to build up a form of gel around the evaporator tubes at a much higher temperature than you would expect. This due to the evaporator surface gets colder than the liquid around them. May be a wild flow and pressure can avoid it, but the ones I am used to is tricky by the "undercooled" eva. surface. The only times I have seen a "corrupt" behaviour of water is on some osmotic test instruments which cool ultrapure water down to -10 to -12c without freezing. Just a stir in this water makes a solid ice in a millisecond, wow

toprunner
23-07-2010, 12:16 PM
Hi all,

this is my first post on this forum, I am a maintenance fitter, not a refrigerations technician and I am seeking some advice on an idea I'm working on.

Basically, it's a heat exchanger that will be used to chill water - I believe this component is called the evaporator.

Initial water temp will be between 5C-10C and I require the water to be 0C or less when it leaves the exchanger.

The basic idea is to have a 2" steel pipe, 3' long, with 3/8" copper pipes for refrigerant running axially along it ... and to have 4 of these 3' sections connected side by side with elbows.

Flow rate will be about 5l/s.

Ambient atmospheric temp is around 0C and humidity is around 80%.

I like some opinion on whether this design will be successful in removing enough heat from the water before it exits the system.

Will it require an excessively large system?

All constructive comments are welcome!

You will need 210 kW cooling power to cool down 5 l/s water from 10 to 0 degree. I guess your smallest problem will be the evaporator :cool:

Tycho
23-07-2010, 07:42 PM
Hi all,

this is my first post on this forum, I am a maintenance fitter, not a refrigerations technician and I am seeking some advice on an idea I'm working on.

Basically, it's a heat exchanger that will be used to chill water - I believe this component is called the evaporator.

Initial water temp will be between 5C-10C and I require the water to be 0C or less when it leaves the exchanger.

The basic idea is to have a 2" steel pipe, 3' long, with 3/8" copper pipes for refrigerant running axially along it ... and to have 4 of these 3' sections connected side by side with elbows.

Flow rate will be about 5l/s.

Ambient atmospheric temp is around 0C and humidity is around 80%.

I like some opinion on whether this design will be successful in removing enough heat from the water before it exits the system.

Will it require an excessively large system?

All constructive comments are welcome!

first off, salt or freshwater? ;)

rok
24-07-2010, 08:46 AM
Thanks to all the replies! - I'm finally making some progress!

WOW! - 100kW?!>. ..210kW!?!?! :(
... sound like some serious numbers!

Initial idea was to have 7 3/8" tubes running within the 2" pipe, this would give a lot more cooling surface, but very little room for the water to move through, velocity would increase dramatically at water enters the exchanger.

Our line pressure is 45bar and the MINIMUM flow I am after is 5L/s ... 10 would be better. Fresh water, not salt water.

Heat is to be transferred to air. not sure about area or flow ... whatever it needs to be I guess?! - heat is bad for us, so the cooler the better.

This chiller would be for a snowmaking application ... cooling the water would dramatically increase the output of the snowgun and would increase the ability to make snow at marginal temperatures...
so, let's talk real world mechanics - What would be the size, cost, power consumption of a unit that would be capable of chilling my water :)

Again, thank you to all that replied!

Bones
26-07-2010, 09:25 AM
can you store the chilled water? or were you wanting to use it instantaniously?

this is sounding to be quite expensive...

how many litres of water do you use at a time? how many times during the day do you use it etc?

if you can store it... you might be able to use an old milk vat(s) or the like to chill and store large quantity of water over night or during the day when not 'making snow' pump from chilled water vat 0~1'c to snow maker with high flow pump?

equipement for this would be cheaper as you could allow 12 to 18 hours or what ever to chill 'X' amount of water, rather then chill it 'right now'.

NoNickName
26-07-2010, 09:48 AM
Yes, cooling it down by half the deltaT, it would require half the cooling capacity, with the same water flow. So I would suggest to cool the water in two passes, if you can afford that.

rok
09-08-2010, 07:55 AM
On a good night, we can use around 30 megalitres ... this is beginning to sound VERY expensive! ... back to the drawing board!

Bones
09-08-2010, 10:37 AM
wow... would hate your water bill...

ibraheem
09-08-2010, 10:48 AM
Dear all, I would have preffer to have more deep information regarding the issue gentle man brought up, any way as i am interested in sharing more knowledge and experience,because this forum is very interesting place.

I would like to call our attention to type of refrigerant to be used, it's attributes before other aspect of design, the main task start there, then selection of related items.
best of luck










Yes, cooling it down by half the deltaT, it would require half the cooling capacity, with the same water flow. So I would suggest to cool the water in two passes, if you can afford that.

rok
11-08-2010, 10:15 AM
Hahahaha - in June this year we pumped nearly 200Ml.. in August it was over 300Ml ... our current pumping capacity is 240L/s ... I think our air capacity is about 60,000 M3/h ...although I'm sure it's not impossible, I've come to realise that it would be far too expesive to chill such massive amounts of water ...would be an interesting excercise though! thanks everyone for your input, I'll start working on a different design :)