Cooling water temperature rise

[edison123]

What is the normal temperature rise (Outlet water temp - inlet water temp)in air-to-water cooled machines ? I had always assumed it to be 2-3 deg C. But in one generator, it is around 6 deg C. Flow rate & pressure are normal as per name plate. Does this mean the coolers have insufficient capacity ?


* Basically, I would like a full-time job on part-time basis *

 

[itsmoked]

If you have a higher rise across the generator then it has nothing to do with the chiller. It means the generator is wasting more heat for some reason.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[edison123]

Thx itsmoked. But it is a OEM designed cooler. So, they should know their generator losses and should design their coolers accordingly.

I am still keen to know what is the normal temp difference between outlet & inlet water. Any field experience or standards would help.


* Basically, I would like a full-time job on part-time basis *

 

[aolalde]

Hi Edison123.

The temperature rise will depend on the amount of heat losses and the water flow. For water,
1cal/1gr = 1°C rise
The guideline figures I have are:
AT 80 F incoming cooling water provide 0.85 GPM per each 1 kW loss for around 4.5° C water temperature rise.
The recommended water flow ratio increases or reduces with water temperature, 0.68 GPM for 70F; 1.15 GPM for 95F. However the water temperature rise is not constant if those ratios are followed.

 

[quark]

Generally, heat transfer devices are designed for a dT of 5⁰C for optimizatin of the HX size. Though, the rule varies from case to case, it is a good approximation.

 

[motorspert]

for some reason all the coolers I have been involved wioth were designed for 6C, so seems ok.
flow (l/s)= 0.24 x losses (kW)/water rise

 

[edison123]

Thank you all for the posts. I take it that 6 deg C rise is normal.


* Basically, I would like a full-time job on part-time basis *

 

[IRstuff]

Our design winds up at about 6º to 10º rise. There is some trade-offs between the lowering the operational temperature of unit versus the outlet temperature and amount of water/pumping infrastructure to maintain a substantially lower outlet temperature.

In your example, the difference between designing for a 3º versus a 6º delta is essentially doubling the coolant flow. Therefore, while the unit might operate at a lower temperature, the pumping system is working twice as hard.

Different designers might well pick different design points, based on their unit's capabilities and liabilities.

TTFN

 

[waross]

Hi edison123
If the temperature rise is higher than similar transformers in your plant you may have more losses or a flow restriction.
This may also be an indication of circulating currents, harmonics, or a flux problem (possibly caused by harmonics).
If you circulation is temperature controlled you may have a bad sensor. You may also have thermometer errors.
Or, everything may be normal.
respectfully