Help on Calculations

[bammatt]

hi
I have a pool (8ft x 16ft x 6ft ) which is filled with water @ 80 deg c. A pump will pump the water out once every 2 hours to another output. The water temperature at the output is 60 deg c.
i am trying to cool the water at the pool from 80 deg c to about 60- 50 deg c by attaching a helical coil at the pump area. A water supply (30 deg c )from nearby cooling tower will be connected to the coil to cool the pool water.


What are the ways to calculate the diameter, length and the number of coils turn to cool the pool? How much flow rate do i need to run the water in the coil?

[Bigfreeze]

hi
I have a pool (8ft x 16ft x 6ft ) which is filled with water @ 80 deg c. A pump will pump the water out once every 2 hours to another output. The water temperature at the output is 60 deg c.
i am trying to cool the water at the pool from 80 deg c to about 60- 50 deg c by attaching a helical coil at the pump area. A water supply (30 deg c )from nearby cooling tower will be connected to the coil to cool the pool water.


What are the ways to calculate the diameter, length and the number of coils turn to cool the pool? How much flow rate do i need to run the water in the coil?

Wouldn't it be easier to use a heat exchanger? Your rate of flow will depend on the cooling capacity of the cooling tower, the dt you are aiming for and how quickly the pool recharges heat

[bammatt]

if i insist on using the copper coil to cool the pool,how do i calculate the length, diameter and no. coil turn required? Please someone help me on this.
The pool will have a continuous supply of hot water from a hot water tank.

[Bigfreeze]

if i insist on using the copper coil to cool the pool,how do i calculate the length, diameter and no. coil turn required? Please someone help me on this.
The pool will have a continuous supply of hot water from a hot water tank.

As I mentioned you will need to know the cooling capacity of the cooling tower. You will also need to know which coil you are using. Different coils have different heat transfer abilities, so you would have to consult the spec sheet of a particular type of coil to find this information. By having both of these informations you will then know what length of coil would be required.

[mad fridgie]

so you want to keep the pool at 60C? to be used as when required.
You have a constant flow of hot water entering the pool at 80C.
You have cooling water at 30C.
Your copper coils are they in the pool? or are you talking about a tube in tube?

[NoNickName]

Why don't you just keep the pool in motion. It will cool sponstaneously. Or pump it across a dry cooler?

[frank]

80C - 60C ???

I hope that this is not a Swimming Pool

[Bigfreeze]

so you want to keep the pool at 60C? to be used as when required.
You have a constant flow of hot water entering the pool at 80C.
You have cooling water at 30C.
Your copper coils are they in the pool? or are you talking about a tube in tube?

Was thinking the same thing after my last post. The whole setup is crazy. Pool being fed constant hot water from a tank on one end and cooling it with a cooling tower down the other

[bammatt]

The hot water source are used to clean surface of steel coils. It is then drain to the pool. So the water will have chemicals and oils in it. A pump will pump the water from the pool to the another end which contains treatment tank and filters. Those treatment tank require the water to be at 40 deg c. The pool is located near a cooling tower. So i am trying to find a cheaper way to cool the temp of the pool with the water from cooling tower. Thanks for all the reply then.

[chemi-cool]

How about making a fountain?]
A pump that will throw the hot water up into the air, temperature difference between the air and the hot water will cool them. you can control the pump speed with frequency converter to achieve the right temp.

[NoNickName]

I think it's the best and most economical way too. Just increase the convection between water and air.
Nice human made fog in winter time though.

[MikeHolm]

Depends if the chemicals also get aerated and, depending on what they are, it might be a big VOC mess.

[bammatt]

So does anyone know how to work the calculations out?

[mad fridgie]

so you want the pool at 40C?

[mad fridgie]

So does anyone know how to work the calculations out?

Yes, but what do you want to work out.
Best you doing a drawing, as it would seem that you are not explaining yourself in way that we can understand.
We need to know flow rates, tempertaures, what velocities you are looking at.

[Rerseldergo]

love this forum

[bammatt]

Hi attached is a poor drwaing summary.
Thanks

[mad fridgie]

Hi attached is a poor drwaing summary.
Thanks

OK better, what is the flow of hot water L/s?
This has to marry up wth your cooling tower flow
An energy balance

[bammatt]

the flow of hot water entering the pool to be 1.5L/s.

[mad fridgie]

the flow of hot water entering the pool to be 1.5L/s.

1.5 * 4.2 *30 = 189 Kw.
So you want to but the coil in the pool, so the pool needs to be kept at 50C
So heat transfer has to be based upon 50C on hot side and 30C on the cold side.
Flow into the pool, is not going to give any turbulence within the pool.
heat transfer will be poor.
can you add an air agitor into the bottom of the pool.( a piece of pipe with small holes to make bubbles that cause the water to agitate)

[mad fridgie]

It would be cheaper to cool the 80C water directly before it enters the pool.

[MikeHolm]

Can you break into the line prior to the pool. I would look at a titanium/stainless shell and tube HX similar to Pahlen type swimming pool HX. It would have a pretty low pressure loss on the shell side and it would mean that you could use the pond as a partial settling pond (if you want to get rid of any sediment).

I suspect that the entering pipe would need to be 50mm dia. for the required flow rate (depending on the distance traveled/pressure loss, of course) and an HX for 200kw is an off the shelf item.

[mad fridgie]

You could use the type of heat exchanger shown, but use it as a falling film heat exchanger, directly to your 80C water.
Lets explain
flow is counter flow
water from the cooling tower run in the pipe feed in the bottom, exits the top.
You make a sparge pipe/sparge open tank (pipe cut in half), the same shape as the heat exchanger. The 80C enters the spargeand is didtributed evenenly over the circumeraence of the heat exchanger and the hot water flows on both the inner and outer diameter.
The heat exchanger is mounted over the pool, for the cooled water to drain.
Any shyte gets caught on the heat exchanger, just wash it of with a power hose. Cheap and expandable if you do not get it right first time

[desA]

The problem is trivial.

Place a pump, filter, heat-exchanger set outside the pool. Draw the 80'C water through the HE, with the 30'C cooling water running counterflow.

Place the dirty fluid inside the tubes (if S&T), or select appropriate PHE materials to suit.

Things you need to state to your suppliers:
1. Hot water : in 80'C, out 50'C, flowrate;
2. Cold water : in 30'C, flowrate.
Problem will balance for the unknowns.

[Gary]

Run the hot water through the tower and into the pool.

Or run the hot water through a coil in the bottom of the tower, then into the pool, making it an evaporative cooler.

[mad fridgie]

How is the 80C water being transported from the heat source, is it being pumped through a pipe, then you have many options.
is it flow ing through a pipe under its own steam (excuse the pun) gravity feed, or is falling down a slip way (open) also gravity?

[MikeHolm]

Lots of good ideas here but from an ecological point of view and ease of cleaning the detritus, allowing it to settle in the pond means it can be vacuumed up easily or the oils to be separated a little more easily (assuming you intend to do that). Kinda looks like a bit like a sewage settling pond to me.

[bammatt]

heat source is falling down a slip way (open) also gravity.
it just flows out from the hot water spray section to the drain which leads to the pool.

I appreciate the help from everyone for all the ideas but at the moment i am limited to the pool area.

[mad fridgie]

heat source is falling down a slip way (open) also gravity.
it just flows out from the hot water spray section to the drain which leads to the pool.

I appreciate the help from everyone for all the ideas but at the moment i am limited to the pool area.

Place you cooling tower water pipework on the slip way.

[Gary]

Place your cooling tower water pipework on the slip way.

And make it counterflow.

[bammatt]

if i insist on using a helical coil, how much length and diameter of the coils required to cool the temperature amount down by 20-30 degree C.

WHat are the calculation be like?

[mad fridgie]

if i insist on using a helical coil, how much length and diameter of the coils required to cool the temperature amount down by 20-30 degree C.

WHat are the calculation be like?

Right you want to install a coil in your pool.
You are not cooling the pool down, you are maintaining a temp in the pool.
Your cooling tower flow rate is 3.3L/s, you want an internal pipe velocity of around 2m/s, there you pipe size.
Your mean water cooling temp is 37C so avergaed TD is 13K(C)
You are around 100watt/m2/C or 1.3kw/m2 (static water in tank)
So you need 145M2 of external pipe surface area.
Up to you

[bammatt]

hi Mad fridgie, how did you come up with the calculations, can you sent me the calculations in excel sheets.

[mad fridgie]

hi Mad fridgie, how did you come up with the calculations, can you sent me the calculations in excel sheets.

You have your heat load
80C-50C= 30C
30* 1.5(l/s) * 4.2
=189kw
Cooling tower water
189/4.2/3.3= 14(ish)
so average water temp in heat exchanger
14/2=7C
30+7
=37C
so average diff equals 50C-37C= 13C
100 watts/m2 * 13
=1300w/m or 1.3kw/m2
189kw/1,3
=145m2 of area required.
A shyte load of pipe. this is why no one is recommending this method.

[bammatt]

You have your heat load
80C-50C= 30C
30* 1.5(l/s) * 4.2
=189kw
Cooling tower water
189/4.2/3.3= 14(ish)
so average water temp in heat exchanger
14/2=7C
30+7
=37C
so average diff equals 50C-37C= 13C
100 watts/m2 * 13
=1300w/m or 1.3kw/m2
189kw/1,3
=145m2 of area required.
A shyte load of pipe. this is why no one is recommending this method.

HI mad fridge

Do you mind tell me how you select the "heat transfer coeefficent value of 100W/m2.K" based on what condition?

[mad fridgie]

HI mad fridge

Do you mind tell me how you select the "heat transfer coeefficent value of 100W/m2.K" based on what condition?

I would like say I spent much time calculating this for you, I did not, but back in my history, it had been calculated for "static water" to be around 30btu/ft2/f, in my head thats approx 100w/m2/C.

[bammatt]

Since a big sum of surface area is required, would it make a difference if i use plate heat exchanger instead of helical coil?

[mad fridgie]

Since a big sum of surface area is required, would it make a difference if i use plate heat exchanger instead of helical coil?

As soon as you flow, your heat transfer is going to improve.
But this is external of the pool,
That being the case, but a small tank on the exit to the slip way, pump through any type of heat exchanger (all methods suggested) It will not be a big heat exchanger with 80C and 30C water entering temperatures,

[bammatt]

if i were to use an shell and tube. How am i supposed to determine the size required? Please let me know any reference available.

[NoNickName]

Download any s&t calculation software, e.g. from www.onda-it.com or any other manufacturer.

[mad fridgie]

AS NNN suggest down load selection software, or just give data to a H/E supplier, shift the risk

[MilosBog]

No need to write anything here is the link.http://www.engineeringtoolbox.com/sw...ing-d_878.html
Follow also the rest links and that would be all. Change a heat capacity of water to the mixture that you have. These formulas are based on heating but temperature difference can be negative so you will have also the cooling