Note: Descriptions are shown in the official language in which they were submitted.
:~3~8~8
FIELD OF l~ INVENq~ION
The present inven~ion relates to improvements
in vapour compression cycle refrigeration systems, and
especially those utilizing hot gas by-pass systems for varying
the re~rigeration capacity of the system.
BAC~GR~UND OF THE I~ENTION
In a simple cycle ~ie single stage) vapour
compression cycle refrigeration system, the refrigerant
ideally enters the evaporator as a mixture of saturated liquid
and saturated vapour. Full utiliæati~n of the heat transfer
surfaces in the evaporator circuits re~uires the presence of
liquid refrigerant in or on all parts of the tubes that make
up the various circuits o~ the evaporator. In the evaporator
the liquid refrigerant changes, under relatively constant
pressures, into a vapour and absorbs heat from the zone
serviced by the evapor~tor. The refrigerant then leaves the
evaporator preferably as a saturated vapour, or as a slightly
superheated vapour.
The refrigerant next anters the compressor, where it
is isentropically compressed to the condensers operating
pressure. The refrigerant flows from the compressor and
through the condenser under fairly constant pressure
conditions, and dissipates heat to the atmosphare.
Finally the refrigerant leaves the condenser as a
liquid and flows through t~e expansion valve and back to the
3~
3 8
evaporator, with part of the refrigerant flashing into vapour
as the line pressure drops across the expansion valve.
Such a simplistic system only operates efficiently
and safely within a narrow range of ambient heat loads. Since
normal seasonal a~d even diurnal variations in ambient
conditions impose loads outside of the range that can be
handled by simplistic systems such as that described
hereinabove, steps are usually taken in the design of modern
refrigeration eq~ipment so as to provide for a broader range
of operating conditions.
These steps typically include the use of
thermostatic expa~sion valves in combination with capillary
tubes, flat valves and automatic expansion valves. Even so
such equipment is capable of dealing only with those
variations in heat load that are imposed by a ~airly modest
range of ambient operatlng conditions.
Even with such addition~, however, ambient load
conditions can still exceed dasign li~itations, and further
precaution~ have been found to be necessary. It is important,
20 for example, that no substantial amount of liquid refrigerant
be carried out of the evaporator with the vapour that is
returned to the compressor. This problem does arise, however,
when the refrigerativn equipment is operated at ambient heat
: loads below the lower limits of the de~igned heat transfer
capacity ~or that e~uipment. In such cir~umstances the amount
: o~ ambient heat available ~t a given flow rate of re~rigerant
; through the evaporator is insufficient to vapouri~e
sub~tantially all of the liquid pre~ent in the evaporator.
3 ~
The liquid re~rigerant that does exit the evaporator must be
trapped before it reaches ~he campressor, or serious loss of
compressor lubrication is likely to result. In-line liqui~
traps ranging ~rom simple l'U~ tu~eæ, or ~w~n neck~, up to
S ~omplex suc~ion gas/llquid heat exchangar and ~uction pots are
used ~or this purpo~e, wlth th~ choice o~ apparatus dependin~
on the anticipated operating loads.
As has alr~ady been mentioned, the full utilization
oP the ~eat ~ran~er s~rfaces in all evapora~or circuits
requir~s the presen~e of liquid refrigerant in or on all parts
o~ the tubes that ma~e up the heat transfer suraces i~ tl~e
various evaporator circuits. Under very low load conditions
~he need to maintain suffi~i~nt liquid refrigerant in the
evaporator, and the proportionatsly ~mall amount af hea~ taken
up by that re~rigerant relative to th~ design capacity o~ the
sy~tem, may result in too large an amount of liquid
re~rigerant leaving the evaporator and exceeding the capacity
of thæ a~ove-mentioned traps. ~e consequences Gf returning
; li~uid r~rigerant to ~he c~mpre3~0r nas a~so already been
~ 2~ mentioned~
O~her approaches a~e therefor use~ in t~nde~ with
those mention~d hereinabove. In small sy~t~ms ~he compressor
is merely shu~ dbwn when the cooling thermosta~ setting ~s
~en satisfie~. In lar~e systems that ~ptiQn i~ not as
readily availa~le, beause of the wear that at~end~ ~ha onJof~
cyaling of the lar~e compres~o~æ us~d in these sys~e~s.
~3~3~
~ çcordingly, in large systems employing centrifugal
compressors the capacity may be varied to match a change in
ambient loading by: 1~ varying the speed at which the
compressor is driven; 2) adjusting vanes at the inlet to the
impellers; 3) th~ottling the suction gas; or, ~ varying the
condenser pressure. Methods 1 and 2 require feedback controls
with their attendant increased capital and maintenance C05tS.
Attempting to control the capacity by either throttling the
suction gas or varying the condenser pressure results in
reduced system efficiency.
In large systems u~ing the more common reciprocatin~
compressors (and in which the lu~rication problems are much
more serious than with centrifugal compressors), capacity
control can be accomplished through several means which are
used in combination with one ~nother. The most common
approach is to unload the co~pressor through a series of
unloading sta~es until a final unloading stage, wh~reupon a
controlled reErigerant bypass of the condenser and the
expansion valve is employed to reroute hot-gas to the
20 evaporator, by directing gas from the compressor discharge
into the low pressure side of the system, at a point either up
or downstream of the e.vaporator. This approach is known to
seriously reduce system efficiency since even though the
reduc2d condenser pressures whiçh normally accompany a reduced
25 system load result ln a saving in compressor power, it may
interfere with the flow of liquid re~rigerant through the
expansion device and cause unsatisEactQry operation oE the
system. This i8 ~ecau~e the expansion valve meters less
refrigerant to the evaporator when the system is operated at
reduced condenser pressures. In a typical installation
equipped with such a hot-gas bypass system, the discharge
bypass valve will attempt to compensate for the substantial
reduction in suction pressure when the compressor is in its
final unloading stage and maintain a given predetermined (ie
design~ pressure. With the reduced demand for refrigerant and
less volume o~ liquid throughput, the expanding liquid has
less velocity in the evaporator~ It has now been found that
this allows the hot gas, that has entered the auxilliary side
connector upstream of the evaporator and has been mergad into
the refrigerant flow leaving the expansion valve and entering
the dis~ributorf to push the expanding liquid refrigerant away
from some of the distributor tubes. This in turn causes an
uneven distribution of vapour and liquid within the various
evaporator circuits. The desuperheating that then taXes place
within the evaporator not only renders some circuits inactive
for cooling purposes, but actually results in localized
heating of the ambient environment over certain portions of
the evaporators heat exchange surface.
One example of the type of installatioll where these
problems are particularly acute is in ship-board
airconditioning syste~s. These l'mobilei' systems must have a
design capacity which will deal with large ranges of sensi~le
heat variation, particularly in the case of ocean-going
vessels which often txaver~e both tropical and high latitudes.
; 5
.
~31l~38
31~RY OF T~ I~r~IO
The pres~nt inverltion rela~es to a metho~, ar
~ppara~us and a sul~-assembly for enhanoing the operating rang~
of vapour compre~ on ~ycle ~efrigeration systems.
According~y, there i~ provided a method of operating
a vapour c:omp~e~slon cycle re~rig~ration sys tem comE~rising an
evaporator, co~pressor, con~lens6~r a~ expansion valve, and
~url~her including compressor unloading means in combination
wit~ hot-gas b~pas3 rQeans op~rable during the ~inal compr~r
wlloading stage ~or compen~ating for imbalances b2tween the
e~apc)rator's and the compre~sor's respeo~iYe cooling
capacities under low-load operating conditiQns ~ w~erein the
meth~d comprises the step o meter~ ng a ~low o:e ho~as
through ~aid by-pas$ means while the compressor is still
~ub~tantially loaded, wherel3y re6ulting vapour injeCtion into
the di~'crib~tor increases th~3 re~ri~e~an~ velocity through the
~aporator to thereby a~sis~ in ~aturning ~il tQ ~he
c:ompressor .
In addl~ion to iTnproving oi~ ~sturn, ~his method has
tne Purther adv~ntag~3 of helpiny to ~3nsure more e~ual
di~tribution o~ the hot ga~ to each circuit o~ a mul~i-
~ ircuited evaporator. Morec~Yer this lnethod al~3o help~; to
increa~e the amoun~ o~ e~EIporator sur~ace that is ac~iv~, an~
th~r~by ~ids in air de~umidif ic~tion ev*n ~hile the system i5
operatirlg under low-~oading ct~r~dition~. Pr~ra1~ly the hot-
is metered throug~ the by-pass means in accordance with
the above method, while the con~presso~ is ~t~ 11 fully lo~ded~
:
~-~s~
Additionally, there is provided a method for
combining at least two discrete flows of a refrigerant in
substantially dissimilar thermodynamic states in a vapour
compression cycle r~frigeration system, including the step of
imparting substantial turbulent mixing of the at least two
flows to produce a generally thermodynamically uniform
admixture thereof.
In one aspect, ~he method i5 intended for use in a
gas/liquid refrigerant mixing stage of a vapour compression
cycle refrigeratlon system, and comprises the steps of
imparting a substantial helical motion to a first flow of
fluid xefrigerant in one thermodynamic state, and mer~ing tha
first flow with a second flow of fluid refrigerant in a
dissimilar thermodynamic state. q'he helical m~tion of the
first flow results in sub~tantial turbulent mixing of the
first and second flows upon merging thereof, to produce a
generally thermodynamically uniform admixture. In practice
; these refrigerant flows may be discrete coaxial flows at the
point of mixing. Accordingly the present invention includes a
method substantially as set forth hereinabove, comprising the
steps of impartin~ a substantial helical motion to the fixst,
axial flow of fluid refrigerant, and merging it with the
second, coaxial flow.
Preferably the first/ axial flow of fluid
re~rigerant has a substantial gaseous component, and the
second, aoaxial flow o~ ~luid refrigerant has a substantial
liquid co~ponent.
3 ~
The method of the present invent.ion finds
application in the so-called hot-gas condenser by-pass systems
ment.ioned hereinabove. In one such embodiment the first axial
flow comprises a hot-gas condenser bypass flow betwe~n high
and low pressure sides of the vapour compression cycle
refrigeration system, which flow is directed through an outer
annular channel in a multicircuited evaporator distributor.
The second coaxial flow comprises an expanding liquid flow
exiting from a thermo~tatic expansion valve located upstream
of the distributor, whi~h second flow is dirscted through a
cylindrical channel located centrally witnin the outer annular
channel of the distri~utor. In accord~nce ~ith this
embodiment of the invention, the first flow is passed through
flow redixecting means arranged within the annular channel.
The first flow is thereby imparted with a sub~tantial helical
motion, and eXit~ the annular channel and merge~ with the
~econd flow as the two flows exit their respective cnannels
into the distribution manifold of the distributor.
Substantial turbulen~ mixing of the two flows takes place and
results in the formation of a subs~antially thermodynamicalIy
uniform mixture thereof.
Preferably the flow redir~cting means imparts a
helical ~otion to the first flow that is substantially normal
to the outl~ts of the ~istributor.
Also prefer~bly, the helical motion of the ~irst
flow comprises a plurality of coaxial helical paths.
The pres~nt invention also relate6 to an apparatus
comprising in-line re~rigerant flow redirecting means having a
3~
plurality of vanes adapted ko be di~posad in the path of a
generally linear refri~erant flow in a vapour compression
cycle refrigeration ~ystem. The ~low redirsctin~ means is
pre~erably a static de~ic~, operable in situ to r~irect the
linear.flow into a non-linear ~low, where~y down~tream
thermodynamic uniformity of ~he ~low is incr~a~ed.
As with ~he ~o~e ~escribed method, the a~paratus of
the present invention has applicatio~ where two flows of
~efrigerant are to b~ commingle~. ~n this a~pect o~ the
pre~ent inve~tion the flow redirecting mean~ is di~po~ed in
the path o~ a ~ir~t generally linear ~low in a first
th~rmodynamie state, at a location generally upstrea~ o~ a
point at which a second gene~ally linear flow of refrigerant
in a second t~ermo~ynamic state, is introduced ~hereto. trhe
~5 ~low redirecting means is operable in si~u ~o ~edlrect the
irst linea~ ~low into a non~ ear ~low, ~o thereby pro~ucs
turbulent ad~ixin~ o~ ~he first and second flows ~t the po}nt
wher~ the two ~lows ar~ brought ~o~eth~r.
Pre~erably tha vanes are arr~nged so as to impart a
s~betantially helical, ~ie non-linear) ~l~w to the first flow.
In a pr~ferred em~odiment of the present invention
the f3OW redirecting msans comp~ises ~ di~c adapt~d to be
arra~ge~ w~th ~ha plane of said disc n~r~al to ~he dirsc~ion
: o~ tha ~irst ~low. A plurality o~ radi~lly ~xtending slots in
: 25 the disc de~ine r~spective sur~ace portion~ o~ the di~c
betwe~n adjacen~ pairs o~ the ~lots and an edge o~ the disc.
~ch s~ch sur~ace porti~n has a ~oot end attachad to t~
balanc~ of the disc at an an~e adjacent that ro~t ~nd and
~ 3 ~
relative to the plane o~ the disc so as to provide vanes
adapted to i~part substantially helical, non-linear flow to
the first flow.
In one aspect of ~he pre6ent invention it is
contemplated that the disc incl~de resilient root portions,
and that the vanes are resiliently biased at said angle, in a
first position, and are deflectable into a plurality of other
positions on flexion of the root portion caused by the flow of
refrigerant past the disc. ~his has the advantage of
maintaining a more constant helical flow velocity, by creating
what i6 in effect a variable venturi between respective
leading and tralling edgea of adjacent pairs of vanes.
Where the first and second flows are coaxial, the
flow redirecting means is preferably adapted to accommodate
said second flow through an aperture i~ the center o said
disc. In one embodiment of this aspect of the present
invention, the aperture is adapted to receive a tube for
conducting the second flow thereth~ough.
In accordance with yet another aspect of the present
invention, there is provided a refrigeration sub-assembly
~ including a multicircuited evaporator distributor adapted to
: be arranged in a refrigerant flow ~nd flow redirecting means
positioned upstream of the distributor. The flow redirecting
means is adapted to introduce a non-linear flow of refrigerant
into the distributor to improve the uniformity of di~tribution
of refrigerant exiting through the outlet of the distri~utor.
In one e~bodiment this aspect of the in~ention includes a side
connector for receiving a first flow of hot gas condenser
1~
,
~ 3 ~
~ypass refrigerant and entraining within the first flow a
second, coaxial flow of refrigerant from an expansion valve
located upstream of the side connector. In this embodiment
the flow redirecting means is disposed intermediate the
distributor and the side connector, and is o]perable
therebetween to produce a non-linear flow of the hot gas
condenser bypass rerigerant around the seco:nd coaxial ~low.
~he flow redirecting means in the sub assembly
preferably comprises a plurality of vanes adapted to be
disposed in the path of the first flow of said hot gas
condenser bypass refrigerant. The vanes are preferably
arranged so as to impart a substantially helical, non-linear
flow to said first flow~ As with the above described
apparatus, the f low redirecting means preferably comprises a
: 15 disc adapted to be arranged with the plane of the disc normal
to the direction of flow of the firs~ flow. The disc has a
plurality of radially extending slots defining respective
~urface portions of the disc between adjacent pairs of the
slots and ~n edge of the disc~ Each such surface portion has
a root end attached to the ~alance of the disc, and each
surface portion is angled adjacent the root end and relative
to ~ne plane of the disc so a6 to provide vanes adapted to
impart substantial helical, (ie non-linear), motion to the
fir~ flow.
; 25 As before the disc is preferably adapted to
accommodate the seaond flow through an aperture in the center
of the disc. That aperture is, in one embodiment, adapted to
receive a side connector tube for conducting the second flow.
3 ~
In any case, a pre~erred su~-a~sembly of the present
invention i6 adapted to produc~e a helical flow which is
substantially n~rmal to the outlets of -the distri}~u~or, and in
particular a heliaal flow which compri~es ~ plurality of
5 coaxial helical paths is espec~ally pre~erred. In one
embodiment, tne helical flow compr.ises seven such helic~l
paths .
~l~eA~ D DE~ lOlR OE~ F~15D ~l~I~NT
1~ Intxc~ducti~2n ~;:o thç ~awings
Figure 1 o~ the drawlngs appended h~re~o is a
schema'cic cross-section throu~h a vapour compression cycle
r~rigeratlon ~yst~m.
Fi~re 2 o~` ~he drawing~ is ~ explode~l p~rspective
15 ~riew o~ a subas~e~bly including means ror impartin~ helica:L
ms:~tion to a f irst axial f low ln R hot-~a~ ~pass sy~tem .
F t gure 3 shows ~n alterna~ive em:~odiment o~ the
hellc~l motion i~parting me~ns depict~d in Flqure 2.
Re~erring now tc~ Ure 1 of the ~Iraw.ing~;, ther~ is
shown in partial cro6s-æ~c~ion, a ~chematic: repre~n~ation of
a v~pour compress~on refri~eratiorl system which i~ equipped
wi~h ~ hot-ga~ bypas~ line, 1, connec:~ed at one end thereof
la, to the high pr~isure side o~ the ~ystem, between the
Gcsmpressc~r 2~ and ltne cc~ndenser 3. In keeping with known
prac~ics~, the connection o end la to the hi~h pre~:sure side
o~ tne sy~tem is p~a:Eera~ly as close to the compres~;or as
pos~;ibleO ~e hot-gi3~; lbypass line i~3 aonnected at itæ oth~r
~ 3~3~
end, lb, to the low pressure side oE the system, through a
side connector to a thermostatic expansion valve/ distributor
sub-assembly, 4. A metering valve 5, including an external
pressure equalizing line 6 arranged between valve 5 and the
vapour collection manifold 7 of evaporator ~, is connected
intermedlate the two ends~ la and lb, of byE~ass line 1,
preferably as close to end la as possible, in keeping with
known practice in the art. Valve 5 is operable, to control
the flow of hot-gas that bypasses condenser 3 in response to
pressure drops across the system.
Subassembly 4 includes a thermostatic expansion
valve 9 and a side connector/distributor subassembly 12.
Expansion valve 9 is connected downstream of the condenser 3
and is adapted to receive and meter refrigerant flowing from
condenser 3 to evaporator 8. Subassembly 4 is connected in
known manner to the vapour collection ~ani~old 7, througn an
equalizer line 10 and through a temperature sensing
element/bulb subassembly 11.
Referring now to Figure 2 of the drawin~s, there is
shown an exploded, partially cut-away perspective view of side
connector/distributor sub-assembly 12, which is shown in
cross-section in Figure 1, and which is connected to receive
hot-gas metered through valve 5. In operation, the hot-gas
flow, indicated by arrow ~ in Figure 2, exits tube end lb, and
enters an annular chamber 13 whase only exits are per~orations
~ 14 ~ormed in the septum plate 15 that is located at one end o~
:~ chamber 13, downstream of tube lb. The hot-gas leaves the
chamber 13 through the per~orations 14 and enters an outer
~3~3~
.
annular channel 16. Disc 17 is adapted to be arranged with
the plane of the disc normal to the direction Qf the axial
flow of the hot-gas w.ithin ~he outer annular channel 16. A
plurality oE radially extending slots 21 in the disc 17 define
respective surface portions of the diæc between adjacent
pairs of the slots and an edge 22 of the disc. E~ch slot 21
is generally "~" shaped, having a first/ radially extending
portion and a second portion extending substantially normal to
the first and generally parallel to the outer edge 23 of the
disc. Each such surface portion has a root end attached to
the balance of the disc. The surface portions are angled
adjacent their respective root ends and relative to the plane
of the disc so as to form vanes 18 adapted to impart a
~ubstantially helical flow pattern to the first flow~ Di~c 18
is located within passage 16 in in-line refrigerant flow-
diracting relation in the pa~h of the g~.nerally linear hot-gas
~eXrigerant flow exiting from the septum plate 15. ~he disc
redir~cts the linear flow o~ hot-gas refrigerant into a
helical (ie non-linear) flow pattern. The disc i5 formed to
receive tube 1g through a hole in the center o~ the disc.
~ he flow of saturated liquidJvapour re~rigerant,
indicated by Arrow B, exits the thermostatic expansion valve
9, enters tube 19 at the base thereof, and travels coaxially
relative to the flow of hot-gas in outer annular channel 16,
upwardly int~ t~e interior of the distributor body 20. In the
distributor ~ody 20 the generally linear flow ~'B" mixes with
the helical fl~w of the hot-gas as the two flows exit tube 19
and chamber 16, respectively. Th~ ~ixing of the two flows in
14
~3~3~
their respec~ive, di~ferent thermodynamic states, due to the
helical flow pattern imparted to the f irst f low o~ hot-gas by
disc 17, improves ~he uni~or~ity o~ the admixtur~. Thi5 in
turn helps to reduce the risk of locali2atio~ of unevap~rated
refrigerant within the various evapQrator circuits and tha
various pro~lems that ensue under such undesirable conditions.
Moreover, ~he ~aten~ heat o~ the hot-gas is w~ll distributed
and this helps to avoid li~uîd re~rigerant ~eing returned to
the compr~s~or.
Figure 3 of the drawing~ illuetra~es ~n al~ernakiv~
embodimQnt of the disc 17 shown in Figure 2. D.i~c 24 in
Figure 3 c~mprises a disc in which adjac~nt pairs o~ sl~ts
extend radially inwardly ~rom th~ outer edge 26 of ~he disc
24, and defina batween them, surface portions eaah havinq a
root end at~ach~d to the ~alance of the disc. These sur~ace
p~tions are angled ~d~acent their respecti~e root cnds and
relative to the plan~ of the disc so as to form vanes 27
a~apted to impart a s~bst~ntially helical flow pattern to ~he
~irs~ f~ow. In ~his em~ nt a p~rtion o~ ~he outer edCJe of
eacll surface portion, indicated at referenc~ numeral 28, i.
rem~ved to i~cr~a~e ~he æiz~ of the passag~ ~ormed betwe~n
respectiYe le~ding and trailing adge~ o~ adjacent vanes 270
In accordance ~i~h one c~ntempla~ed arrange~ent o~ the present
invention ~he dis~ 17 and 24 are used in a tandem mutually
~pacQd-apar~ arrang~ment w.i~hin t~e ohannel 16, pre~erably
; ~ith di~c l~ po~itioned ups~ream in the re~rig~rant ~low,
relative to disa ~4,
