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It is desirable to get a rated load or some agreed-upon load
on the turbine which will be the same for each successive check and read the
load, air leakage, inlet water temperature, outlet water temperature and the
absolute pressure in the condenser, and convert the absolute pressure into the
corresponding saturated steam temperature; also, calculate the temperature rise,
initial temperature difference and terminal difference.
The terminal difference is the difference between the steam
temperature and the outlet water temperature; the temperature rise is the
increase in the CW temperature. The initial temperature difference is the
difference between the inlet water temperature and the steam temperature (or the
saturation temperature corresponding to the absolute pressure).
If this data is recorded periodically and checked, any
deviation will give the operator the best indication of what has been happening
to his condenser.
During a period of high air leakage, when air blankets tube
surfaces, the absolute pressure, air leakage, steam temperature and terminal
difference will rise and again upon correcting the leakage, will return to
normal. Also, during a period of dirty condenser tubes, the absolute pressure,
steam temperature and terminal difference increases and after cleaning will
return to normal. This holds true with non-condenser type heat exchanger.
Other factors:
Other factors, which would affect the condenser trend, are
the change in water inlet temperatures and change in loads. These changes do not
affect the condenser performance although they change most of the condenser
temperature values and do change the condenser backpressure. As a guide to
condenser performance the terminal difference gives the operator the alarm and
should be watched carefully.
Data taken at a different lad may be compared to that at the
desired load by the following device. Load to the condenser, either in terms of
BTU per hour or kw load plotted against rise and initial temperature difference.
“Rise” will be a straight line from zero at no load to maximum rise at full
load. Disregarding the effects of air leakage and vacuum pump capacity and some
of these matters in the very low load range, the initial temperature difference
will also be a straight line.
Operators should watch pump discharge pressures and pump
horsepower for clues as to tube sheets plugged by rubbish accumulation. These
indications can also be obtained from delta P of CW across the condenser.
Poor heat transfer due to tube fouling will affect vacuum
performance at all loads but will be most noticeable at high loads.
Circulating water pump data to approximate water flow, which
with rise in circulating water temperature gives another approximation of heat
load.
The condenser performance is evaluated, expressed as
percentage:
% = U actual >< 100
U designed
U actual can be calculated as: U = Q/A∆Tlmtd
U actual = actual heat transfer rate, btu/hr/sq ft/deg F Lmtd
Q = duty, Btu/hr
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Introduction |
Combined heat transfer process |
Heat transfer in cooling tower |
Variables affecting performance of CT heat transfer |
Heat transfer within
cooling system (heat exchanger) |
Types of heat exchanger |
Basic design
procedure and theory |
Designing a test heat exchanger |
Log Mean Temperature
difference | L.M.T.D. Correction factors |
Overall heat transfer coefficient |
Elaborated method for calculating U values |
Effect of scale formation |
Condensation of steam |
Condenser, where the hot fluid temperature varies |
Significance of pressure |
Significance of flow rate |
Methods of checking steam
condenser performance |
Common conversion factors
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