Estimate cooler performance 1

[hirschaplin]

Hello,

We are regularly buying standard catalogue shell and tube coolers. It is a range of 13 coolers with the smallest one at about 50 kg (DN40 flanges) and the biggest one at about 1000 kg (DN300 flanges).

The problem is that the vendor doesn't share the design/selection software. Hence I am depending on their response to provide accurate cooler performance data to my customer. In the project phase that is fine, because the amount of changes are few and far in between but during the bidding phase it can be a lot of changes required and it sometimes take very long time to get an answer with new calculations from the vendor... simply a pain in the ass as my working flow is spoiled.

Therefore I am curious to learn if there is a way to make a rough cooler performance calculation myself without having to disturb and wait for my supplier until the project is mature enough.

What I have available to do this is the following:
Inlet gas mixture properties
Inlet cooling water properties
Outlet gas temperature
Outlet cooling water temperature

Example specification:
Inlet gas at 1 barg and 118 deg C, 3398 Nm3/h, gas mixture 93% Oxygen, 4% Argon, 3% Nitrogen
Inlet cooling water at 4 barg and 20 deg C
Outlet gas temperature 25 deg C and 30 mbar pressure drop
Outlet cooling water temperature 28 deg C and 1 bar pressure drop

As per vendor calculations this resulted in a water flow of 12193 liter/hour.

To do this, I guess I need to receive some cooler specific performance parameter for each model from the vendor?

I am not looking for a 100% result but I would like to do the calculation myself and say to my customer that the estimated cooling water flow is xxx liter/hour +/- 10% or similar.

Any simple yet efficient ideas?

 

[LittleInch]

Well once you have a few cases you should be able to figure out max heat flow from the HX and also what sort of capacity each size has.

Also which side is which in your example as a 30mbar pressure drop for the gas sounds a bit low.

But second guessing someone else's design is a bit of potential problem/

What data do they provide wrt capacity?

But each case is unique and it won't be easy to have a simple calc unless they give you some parameters to use.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hirschaplin]

These coolers are especially designed for low pressure blowers, hence very low pressure drop. The gas is on tube side and cooling water on shell side.

Well I don't want to guess the parameters. I want to ask them for it! I am just struggling to know what to ask for. Max heat flow and min/max flow for each model is what we need?

What is wrt capacity?

 

[LittleInch]

wrt = with respect to"

So what info do they provide in their catalogue or website?

If they are designed especially for low pressure, low pressure drop system then they will use some parameters such as velocity, delta T, density etc to work out the heat flow required out from the gas. Water flow again will be up to a certain mass rate and with a certain DT to get a heat flow out.

But to be fair there are so many variables here on the tube side (DT, inlet temp, density, gas Cp, mass flowrate, actual velocity etc) that without the design software you can't really start to guess which size of HX you need until you build up a good set of examples. And then only if your new case is similar to the old one will you get any joy. Change things too much and the assumptions don't work.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hirschaplin]

As far as I can see they do not provide any public information that helps to determine the thermal capacity of each model.

Then if I only want to find out the required cooling water amount, is that possible irrespective of which model that is selected? Is it possible to get to the 12193 liter/hour with the data provided above?

 

[LittleInch]

The heat extraverted by the water is approx 113kW.

Heat loss from the gas mix is about the same, but I used oxygen only and approximated some figures.

So they seem to be just doing a heat balance but this looks like a very slow gas speed and the final delta T assuming counter flow is only 8C.

So as long as you want your gas to be a few C (8C) higher than the water exit temp then you're good.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hirschaplin]

Sure normally the gas is between 5 and 10 deg C above the inlet cooling water temperature.

How to calculate and make me good? )

 

[Snickster]

Here is a very good manual on sizing heat exchangers from Yuba an old heat exchanger manufacturer. They were bought out by SPX then an India company so they do not exist anymore so I think the manual is no longer available. It should help you to understand sizing of heat exchangers.

 

[hirschaplin]

That looks like exactly what I need, I will have a more careful look tomorrow. Thank you!

 

[Snickster]

Here is another good reference from Wolverine who although they still exists, they do not manufacture heat exchangers anymore at least I don't see on website. These were good references I found when a yound design engineer so they are very old but still have good info.

 

[pierreick]

Hi,
Consider this excel sheet for your calculations, more important it's the methodology to perform heat balance.
The reason why I suggested you considering buying thermodynamic books.
Good luck
Pierre

 

[hirschaplin]

Hi Pierre, you are the man. Is it possible to get in contact with you in some chat program outside of the forum? Firstly I would like to pay you a symbolic amount of money for all your help. Perhaps through Paypal if you have that? Secondly, I would like to discuss if you are interested to take on some part time work and help me with some of these excel issues against reimbursement.

 

[LittleInch]

hirsc

Your particular HX is, as you say, designed for low pressure drop gas application and is sized accordingly so that the pressure drop is low on the gas side and the cooling capacity is such that the exit gas temp is within 5C of the water inlet temp based on cross flow. It is very difficult to get below 4-5C differential temp so the HX is probably oversized compared to many others where there is a much larger differential between exit temp of the cooled fluid and the inlet temp of the cooling fluid.

At some point in each size range, the effective capacity of the cooling system reaches a maximum, but if you put more gas through it the exit temperature will rise accordingly.

Only the vendor really knows where this inflection point is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

This appears to be a countercurrent shell and tube HX. Open loop cooling water causes fouling on the shellside, higher than expected pressure drop and corrosion problems, all of which lead to HX failure in the future. Finned tubes cannot be used in open loop cooling water applications.
It would be better if you have CW on the tubeside, since this is the more corrosive of the 2 feedstreams. Thermal design wise, this makes sense also.
Most heat transfer textbooks discuss thermal design of shell and tube HX units.