[dcicero]

Thank you for the additional reference. I’ve read through it and found it very helpful.

I’m struggling to reconcile the Calculation of LMTD in the Appendix A with Section 5. In Section 5 the LMTD calculation requires:

A = heat exchange surface area, m2
LMTD = log mean temperature difference, K
Q = heat duty, W
U = overall heat transfer coefficient, W/m2/K
hfg = design value of the latent heat of vaporization, J/kg
m = design value of the steam mass flow rate, kg/s
x = design value of the steam quality

In Appendix A, th same calculation requires:

A = heat exchange area, m2
hfg = latent heat of vaporization at design backpressure, J/kg
m = design steam mass flow rate, kg/s
Q = ACC heat load, W
U = overall heat transfer coefficient, W/m2-K
x = design steam quality

And then, in the example calculation…

A = heat exchange surface area (total air side), m2 = 1,150,643
hfg = latent heat of vaporization, kJ/kg = 2,390.3
m = design steam mass flow, kg/s = 234.6
Q = heat load, kW = 560,856.3
U = heat transfer coefficient, W/m2-°C = 34.49
x = exhaust steam quality, .932
LMTD = log mean temperature difference, °C = 14.13

I suspect this is a unit conversion problem, but I can’t seem to get the given equations and given values to calculate the answer of 14.13. I’ve highlighted the different units used in these calculations.

Has anyone else seen this difference between the same calculations in different parts of this document? Any ideas about how I might resolve this?

Dan

[dcicero]

Thank you very much for the reply, Desmond. I’ve downloaded the paper. It’s 165 pages long, so it’s going to take me some time to work through it in detail, so I appreciate your summary.

On casual inspection, I found, “Figure 1 which shows the variation in turbine exhaust pressure vs. ambient temperature for a range of wind speeds.” The author makes the point that at “ambient temperatures above 100°F, the difference between no wind or low wind and high winds (above 20 mph) can be 1.5 to 2.inches Hga with a correspondingly significant effect on turbine output.”

That’s just one example of variables over which the operator has no control (ambient temperature and wind speed) that greatly impact the efficiency of the ACC.

And I think your impression is correct, based on my reading to date, that there is no magic gauge showing efficiency per se. I think that’s true of water-cooled condensers too. A lot of people watch backpressure, cleanliness factor and TTD, but none of those values, alone, give a complete picture of what’s happening in the condenser. A little detective work is always necessary to diagnose a performance issue (or, in some cases, to determine if a performance issue actually exists).

Dan

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