U.S. patent number 3,556,204 [Application Number 04/827,837] was granted by the patent office on 1971-01-19 for air cooled surface condenser.
This patent grant is currently assigned to Perfex Corporation. Invention is credited to Manfred F. Dehne.
United States Patent |
3,556,204 |
|
January 19, 1971 |
AIR COOLED SURFACE CONDENSER
Abstract
An air-cooled surface condenser has a supply of cooling air
which is varied in accordance with the temperature of the
condensate to thereby diminish the possibilities of freezeup at
below normal ambient temperatures. The condenser has at least two
downflow tubes and one reflux tube with the tubes so arranged that
the cooling air travels first over the reflux tube and then
sequentially over the first and second downflow tubes, and with the
tubes being of such dimensions that condensate is formed in the
reflux tube. With this arrangement the air supply can be varied in
response to drop in condensate temperature at the first downflow
tube and thus assure that the air, before reaching those portions
of the first downflow tube where condensate has formed, has a
temperature which has been elevated by the latent heat of
condensation within the reflux tube.
Inventors: |
Manfred F. Dehne (Mequon,
WI) |
Assignee: |
Perfex Corporation (Milwaukee,
WI)
|
Family
ID: |
25250298 |
Appl.
No.: |
04/827,837 |
Filed: |
May 26, 1969 |
Current U.S.
Class: |
165/299; 165/113;
165/111 |
Current CPC
Class: |
F28B
1/06 (20130101); F28B 2001/065 (20130101) |
Current International
Class: |
F28B
1/00 (20060101); F28B 1/06 (20060101); B60h
001/00 () |
Field of
Search: |
;165/39,41,176,121,122,111--114,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Charles Sukalo
Attorney, Agent or Firm: John W. Michael Gerrit D. Foster
Bayard H. Michael Paul R. Puerner Joseph A. Gemignani Andrew O.
Riteris Spencer B. Michael
Claims
1. An air cooled surface condenser of the type in which the cooling
airflow is varied in response to temperature changes in the
condenser tubes in order to render the condenser operable at below
maximum cooling air temperatures, the condenser having: first and
second downflow tube means communicating at their top ends with a
source of vapor and communicating at their bottom ends with a
condensate collecting chamber; reflux tube means communicating at
the bottom end thereof with said collecting chamber and said first
and second downflow tube means and communicating at its top end
with an exit passage from the condenser; airflow generating means
operable to provide a cooling airflow across said two downflow tube
means and said reflux tube means; said tube means being so
positioned relative to each other and with respect to the direction
of airflow that the cooling air initially impinges on said reflux
tube means, thereafter impinges on said first downflow tube means
and subsequently impinges on said second downflow tube means; and
temperature change sensing means positioned to sense temperature
changes within the condenser and operably connected to said flow
generating means to cause said generating means to vary said
airflow in response to such
2. A condenser according to claim 1 wherein: said first and second
downflow tube means and said reflux tube means are so dimensioned
as to cause condensation to be completed within said reflux tube
means as well as within said first downflow tube means at
relatively low cooling air temperatures; said temperature change
sensing means positioned to sense temperature changes in the
condensate of said first downflow tube means; and wherein said flow
generating means diminishes said cooling airflow in response to a
decrease in said first downflow tube means condensate temperature
below a
3. A condenser according to claim 2 wherein said first and second
downflow tube means and said reflux tube means are generally of
equal length and extend generally parallel to each other between a
top header and a bottom header of the condenser and being arranged
at an angle to the horizontal, with said top header having an inlet
chamber and an exit chamber and with said inlet chamber including
means for communication with said source of vapor and with said two
downflow tube means, and with said exit chamber being provided with
exit port means to permit escape of the noncondensables from the
condenser; and with said bottom header being provided with said
condensate collecting chamber which is in communication
4. A condenser according to claim 3 wherein said reflux tube means
has a plurality of reflux tubes which are aligned in succession
with respect to said cooling airflow, and wherein the number of
reflux tubes equals the sum of the tubes contained in said first
and second downflow tube means.
5. A condenser according to claim 4 wherein a separate condensate
collecting means is provided at the exit of said first downflow
tube means, said separate collecting means intercepting the
condensate of said first downflow tube means; wherein, said
temperature change sensing means is positioned to sense the
condensate temperature in said separate
6. A condenser according to claim 1 wherein said temperature change
sensing means is operative to control said airflow generating means
such that the level of complete condensation in said reflux tube
means overlaps the level of complete condensation in said first
downflow tube means so that the temperature of the cooling air
impinging on said first downflow tube means below said complete
condensation level will have been raised by passage over the
portion of said reflux tube means below said complete condensation
level of said reflux tube.
Description
BACKGROUND OF INVENTION
The field of invention may be defined as the art of air-cooled
surface condensers in which the air supply is varied in accordance
with condensate temperature for the purpose of avoiding
freezeup.
A great number of condensers are intended for outdoor installation
and depend upon the outdoor air for a coolant. Freezeup of the
condenser is a generally recognized problem and a variety of design
features have been suggested as possible solutions to this problem
of freezeup.
A number of prior art designs have suggested the variance in either
the fin dimensions or tube diameter between those tubes which are
first impinged by the coolant air and those which are subsequently
impinged by the air after its temperature has been elevated because
of the initial pass. These suggestions have been successful to some
degree; however, the variance in tube design from row to row is
considered a disadvantage from a manufacturing and cost
standpoint.
SUMMARY OF INVENTION
The concept underlying the present invention is considered to be
control of the cooling airflow in response to condensate
temperature so that latent heat of condensation in one or more of
the reflux tubes (which, because of their steam-condensate
counterflow, are less susceptible of freezeup than a downflow tube)
elevates the temperature of the cooling air before it passes over
those sections of subsequent downflow tubes in which complete
condensation occurs at low temperatures.
In order to so utilize the latent heat, the condenser embodying the
present invention includes at least two downflow tubes which are
located on the downstream side of one or more reflux tubes with
respect to airflow over the tubes. Further, the airflow is
controlled in response to condensate temperature changes in the
first downflow tube (i.e. the first with respect to the airflow) to
assure that the air which impinges those sections of the downflow
tubes in which full or complete condensation has taken place has
first passed over sections of the reflux tube in which full or
complete condensation has taken place.
Other objects and advantages will be pointed out in, or be apparent
from, the specification and claims, as will obvious modifications
of the embodiment shown in the drawing.
DESCRIPTION OF THE DRAWING
The drawing is a cross-sectional view of a condenser section taken
in the plane of airflow, and the levels at which condensation has
been completed in the tubes at various airflow temperatures are
shown by the dotted lines.
DESCRIPTION OF PREFERRED EMBODIMENT
The illustrated condenser has top and bottom headers 10 and 12,
respectively, which are connected by rows (one row only being
shown) of four finned condenser tubes of the usual design. The top
header is divided into an inlet chamber 14 which is connected to a
source of steam or vapor and an exit chamber 16 which is provided
with appropriate exit ports for the noncondensable gases. The
bottom header has only one chamber 18 which provides communication
between all of the condenser tubes and which serves to collect and
drain the condensate.
The condenser may be classified as a mixed flow condenser in that
it incorporates two downflow tubes 20 and 22 and two reflux tubes
24 and 26. A variable speed or variable volume blower 30 is
positioned to provide cooling airflow in a path generally
transverse to the tubes 20, 22, 24 and 26. The blower is connected
to a temperature sensing device 32 which senses the condensate
temperature which may accumulate in a small cup 34 below tube 20
or, if may be located inside the bottom end of tube 20. Temperature
sensing device 32 can be of conventional design, e.g. a
thermocouple arrangement and for that reason has not been shown in
detail. Since in operation of the condenser the downflow tubes do
at times differ in their functions, it is best to classify them in
accordance with their position in the airflow path and to thus
refer to tube 20 as the first downflow tube and to tube 22 as the
second downflow tube. On the other hand, one or more reflux tubes
can be used in proper operation of the condenser and, thus, such a
classification will not be made in respect to the reflux tubes.
The significance of the present invention can best be appreciated
by comparing the operating characteristics of the condenser as the
cooling air temperature is lowered from a maximum design
temperature to those extremely low temperatures at which condensate
solidification might normally pose a problem. In operation, steam
passes through downflow tubes 20 and 22, changes direction in
chamber 18, and proceeds upwardly through tubes 24 and 26. The four
tubes of the condenser are of such design that at maximum air
temperature, maximum vapor temperature, and maximum load (measured
by the pounds of material which can be removed by condensation)
condensation will take place in all tubes and will have been
completed at levels a and b in tubes 24 and 26. The difference in
the levels a and b is, of course, caused by the fact that both
tubes receive steam at the same temperature and that tube 26 is
cooled by air at a higher temperature than tube 24.
The condensate in tubes 24 and 26 will flow downwardly and counter
to the steam flow out of chamber 18 and the noncondensable gases
will be conveyed out through the outlet of exit chamber 16. At all
temperatures some condensation will take place in all tubes. As the
cooling air temperature decreases from the maximum design
temperature to a lower temperature, the location of complete
condensation falls to levels c and d in tubes 24 and 26. With
further decrease in cooling air temperature a point is reached
where complete condensation will start to take place in the first
downflow tube 20 while some condensation continues to take place in
both of the reflux tubes as complete condensation will not be
occurring in the second downflow tube 22. The reason for this
phenomenon is that at each tube the airstream temperature gradient
is different. Steam entering reflux tubes 24 and 26 is at the same
temperature, which, when disregarding heat losses in chamber 18 and
pressure differences between tubes 20 and 22, may be assumed for
purposes of this illustration to be at the temperature of the steam
leaving tubes 20 and 22. However, despite the identical initial
steam temperature, the increase in air temperature caused by the
condensation in tube 24 will result in a significantly smaller
steam-air gradient at the bottom portion of tube 26 and, thus, at
low air temperatures will cause full condensation at level f which
is above level e of tube 24.
The air flow reaching the first downflow tube may be divided into a
"cold" section, which has passed over those sections of the reflux
tubes which are above levels f and e and a "warm" section, which is
that air which has passed over the reflux tube sections between
their inlets and levels f and e. As the air reaches the first
downflow tube 20, the upper or "cold" section will have been only
slightly heated by tubes 24 and 26, but the lower or "warm" section
will have benefited from the latent heat of condensation which has
been transferred from the portions of tubes 24 and 26 which are
below levels f and e. Thus, the steam-air temperature gradient at
that portion of the first downflow tube which is impinged by the
"cold" airflow will be sufficient to cause complete condensation at
level g in tube 20. However, the latent heat of condensation of the
steam in the first downflow tube which is transferred to the "warm"
portion of the air flow at that tube, plus the heat which has
already accumulated because of passage over tubes 24 and 26 will
sufficiently decrease the steam-air gradient at the second downflow
tube to prevent full condensation in that tube.
Subcooling takes place below level g in tube 20 and the temperature
sensing device 32 must reduce the airflow to prevent the condensate
being subcooled to the freezing point at the bottom of tube 20. If
not, ice will form in the lower portion of the tube 20, i.e. below
level g.
This invention proposes to solve this problem of freezeup due to
subcooling by controlling the flow of air, and thus the amount of
heat transfer, such that the complete condensation level in the
reflux tubes overlaps the complete condensation level in the
downflow tubes; as illustrated so that level f (or f and e ) is
higher than level g. With that arrangement, the "warm" portion of
the airflow which impinges on the lower portion of the first
downflow tube prevents subcooling to a degree which would otherwise
cause freezing of the condensate in the tube section below level g.
The prevention of full or complete condensation in the second
downflow tube is, of course, essential since that tube must supply
steam to the reflux tubes to permit condensation therein and, thus,
the transfer of latent heat to the flowing air at the lower
sections of the reflux tubes.
With a decrease in the cooling air temperature the full
condensation levels e and f in tubes 24 and 26 will drop whereas
the level g of the first downflow tube 20 will rise. If the point
is reached where the levels e and f in tubes 24 and 26 a below the
level g in tube 20, a portion of the condensate within tube 20 will
be subjected to the "cold" portion of the airflow which will
increase the subcooling of the condensate. This can result in
solidification of the condensate at the bottom of tube 20.
Specifically, in order to avoid the exposure of tube 20 below level
g to the "cold" portion of the airflow, probe 32 is designed to
sense the temperature of the condensate as it leaves tube 20 and to
cause the blower to decrease the airflow at times when the
condensate temperature drops sufficiently low to indicate that
level g is approaching level f. A decrease in airflow, either by
decrease in blower speed or volume of air intake, will in turn
cause an increase in the air temperature at tubes 24 and 26 and
thereby raise the full condensation levels in the reflux tubes and
correspondingly lower the full condensation level in tube 20. Thus,
the sequential arrangement of the tubes and the control of the fan
in response to the downflow tube condensate temperature permits the
system to be maintained in a balance which maintains a sufficiently
wide "warm" air path to cover at least that portion of the first
downflow tube in which condensation has been completed. Temperature
sensing device 32 by responding to change in temperature of the
condensate at the bottom of tube 20 automatically keeps the system
in balance upon changes in air temperature or upon changes in vapor
temperature or load.
In analyzing the above, it should be noted that the freezeup
problems which are encountered in the downflow tubes result from
the fact that condensate flow is in the same direction as the steam
or vapor flow. The condensate flow in the reflux tubes is in the
opposite direction of the steam or vapor flow. For this reason the
freezeup problems, in absence of a maintenance of the
aforementioned balance, will normally be first encountered at the
bottom of the first downflow tube and not in the reflux tubes,
despite the fact that the air which impinges upon the reflux tubes
is at a lower temperature than that which impinges upon the first
downflow tube.
* * * * *