 |
Description  |
|
|
CROSS-REFERENCE TO RELATED APPLICATION
Putman U.S. patent application Ser. No. 383,425, filed July 27, 1973, is a
related application in that it discloses and claims the basic invention
upon which this invention is considered to be an improvement.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the art of refrigerant expansion valves.
2. Description of the Prior Art
One commonly used automatic expansion valve for controlling the flow of
refrigerant between a condenser and an evaporator is called a constant
pressure refrigerant expansion valve and is designed to attempt to keep a
constant absolute pressure in the evaporator during operation of the
system. This valve is typically operated by a preset spring force and a
force derived from the feedback of the pressure from the evaporator. The
valve is arranged so that with the valve set and feeding refrigerant at a
given pressure, a small increase in the evaporator pressure will act to
move the valve toward a closing direction, thereby restricting the
refrigerant flow and limiting the evaporator pressure. When the evaporator
pressure drops below the valve setting because of a decrease in load, the
valve moves in an opening position to increase the refrigerant flow in an
effort to raise the evaporator pressure to the particular balanced valve
setting. In a number of applications of the valve, including some room air
conditioners, the valve is provided with a bypass in the form of a small
slot or drilled hole in the valve seat or valve pin to prevent complete
valve close-off when the compressor shuts down. This is to permit
refrigerant to continue to flow at a reduced rate until high and low side
pressures are equalized.
While the bypass type valve provides for the equalization after several
minutes, it is believed that the bypass itself contributes to a problem
which occurs when an air conditioner is operated without any forced air
flow over the evaporator and condenser. In such an arrangement using a
constant pressure bypass type valve, and starting with the system
pressures equalized, but with the fans not operating, the valve remains
closed and gives a bypass feed only. If this occurs in a system using an
expansion valve which also includes a relief valve, and with, say, R-22
refrigerant, the relief valve will open at say a 600-700 p.s.i.
differential so that refrigerant can then flow to the compressor and load
it sufficiently that the current and temperature overload means will be
operated to shut the compressor down. However if the expansion valve does
not include the relief value, the condenser pressure can build up to a
valve of up to 200 p.s.i. over what would be desirable before the current
and temperature overload of the compressor operates. It is believed that
if the bypass in the expansion valve were omitted, it is likely that the
high pressure problem would be avoided. However this would not permit
equalization of the system after shutdown.
The valve according to the invention is considered to be preferable in that
no bypass arrangement is needed for equalization, and under a fan failure
condition the valve functions in a manner which does not create any
problems for the air conditioning system itself.
Of the prior art patents of which applicant is aware, U.S. Pat. No.
1,786,110 is considered to be the closest in the field of refrigerant
expansion valves, but differs substantially in that it in effect includes
two valves, one of which functions as an on-off valve, while the other
functions like a capillary tube; neither of which corresponds to the
operation of the valve of applicants' invention.
Flow control devices for controlling the flow of lubricant to hydrostatic
bearings and similar in structure to the valve arrangements embodying this
invention are disclosed in U.S. Pat. No. 3,110,527. However these devices
are incorporated in a system where an increase in differential pressure
between a source pressure and the load pressure is taught to result in a
restriction of the flow which would be directly the opposite of the result
of the operation of the refrigerant expansion valve of this invention.
SUMMARY OF THE INVENTION
In accordance with this invention, the refrigerant expansion valve includes
a valve body having a disc-shaped deflectable member supported at its
periphery from the valve body and separating the interior of the valve
body into an upstream space and a downstream space, the disc-shaped
deflectable member being provided with a generally centered aperture, the
valve body also having structure therein spaced relatively closely to that
part of the deflectable members defining the aperture so that the
structure defines, with the aperture defining part, an annular refrigerant
expansion orifice therebetween, the upstream space in the valve body
confining the liquid refrigerant in its passage through the valve and
thereby subjecting the upstream face of the member to the pressure of the
liquid refrigerant, and with the downstream space in the valve confining
the expanded vaporous refrigerant in its passage and thereby subjecting
the downstream face to the pressure of the expanded vaporous refrigerant,
so that the deflection of the deflectable member and correspondingly the
change in the effective opening of the orifice is in accordance with
changes in the differential pressure of the liquid and expanded vaporous
refrigerant.
As is noted in the companion Putman patent application, it is emphasized
that the differential pressure across the expansion valve is used to
control the refrigerant flow area of the valve so that the quantity of
flow is a function of the difference between the supply (condenser) and
outlet (evaporator) pressures, rather than simply being a function of the
pressure in the evaporator as is the case with the constant pressure
refrigerant expansion valves.
DRAWING DESCRIPTION
FIG. 1 is a schematic representation of an air conditioning system in which
the invention may be incorporated;
FIG. 2 is a sectional view of the expansion valve according to the
invention and corresponds to a view taken along the line II--II of FIG. 3;
FIG. 3 is a plan view of one form of the valve;
FIG. 4 is a sectional view corresponding to one taken along the line IV--IV
of FIG. 2;
FIG. 5 is an enlarged fragmentary view illustrating the general
relationship between the part of the disc including the aperture and the
facing nozzle-shaped structure;
FIG. 6 is a schematic representation of a refrigerant expansion valve of
the type having an apertured disc-shaped deflectable member for reference
in connection with selecting specific values in accordance with a design
example;
FIG. 7 is a graphical representation illustrating the general relationship
between pressure drop and valve openings for a typical air conditioner for
purposes of explaining the design example; and
FIG. 8 is a graphical representation of pressure drop versus valve opening
for the design example for a specific room air conditioner.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The same general principles in the design of the valve forms disclosed in
the companion noted patent application, and the form of valve of this
invention are applicable, and accordingly reference should be had to the
noted patent application for the fullest understanding of these general
principles.
In FIG. 1, the schematically illustrated refrigerant system includes a
compressor 10, condenser 12, evaporator 14, the connecting refrigerant
lines between these components, an expansion device 16 in the line between
the condenser and evaporator, and a fan-motor assembly 18 for supplying
separate flows of air over the condenser and evaporator as is conventional
in air conditioning systems.
An example of a currently preferred form that the valve according to the
present invention may take is shown in FIGS. 2-5. The hollow valve body 36
is provided with an inlet 22 adapted to be connected to a refrigerant
system condenser, and one or more outlets 24 and 24a adapted to be
connected to a refrigerant system evaporator. The hollow interior of the
valve body contains a flexible disc-shaped member 38 supported at its
periphery by the valve body 36 and having a generally centered aperture
40. The structure 42 which is supported from the valve body base and which
with the member 38 defines the expansion orifice 44 has an upper chamfered
end 43 which is similar in shape to a nozzle structure and accordingly is
so termed the nozzle structure 42. The annular expansion orifice 44 is
defined between the upper rim of the nozzle structure 42 and the bottom
rim of the aperture 40. With this arrangement the space 46 on the upper
side of the disc 38 is subject to the liquid refrigerant supply pressure
from the condenser, while the lower space 48 below the disc is subject to
the expanded vaporous refrigerant pressure. As will be apparent
hereinafter, the aperture 40 is large enough relative to the annular
expansion orifice 44 that the expansion takes place in the passage of the
refrigerant through the orifice 44.
As noted in the companion patent application, it is believed that the
arrangement of the valve as shown in FIG. 2, in which the entire opposite
faces of the disc 38 are subject to the different pressures, is
advantageous in that this is believed to reduce the likelihood of flow
induced vibrations requiring dampening of the flexible member. The theory
is that a pumping type action would arise from vibration of the disc and
this would be self-dampening. Also, since the differential pressure ie
effective over virtually the total disc area, it is believed that the
valve can likely be operated at higher force levels with less uncertainty
(on a percentage basis) about the area the pressure differential acts
upon. Additionally, any potential problem from deformation of the lower
part of the valve body is reduced since it is acted upon by the outlet
pressure, which is substantially lower than the supply pressure. Finally,
it will be appreciated that since the entire lower space 48 contains
expanded refrigerant, multiple outlets from the space can be accommodated
more easily than where the upper end of the nozzle structure 42
constitutes the inlet to the outlet passage from the valve. The use of
multiple outlets from the lower space 48 can be advantageous where the
valve is to be used for multiple evaporator circuit applications.
In the arrangement described, the upper face of the disc is subject to the
liquid refrigerant supply pressure, while the lower face of the disc is
subject to the pressure of the expanded vaporous refrigerant. Based upon
the total area of the faces of the disc subject to the pressure producing
the forces causing deflection, slight differences in the diameter of the
aperture 40, and the diameter of the upper end of the nozzle structure 42
are of little significance with respect to the forces applied to cause
deflection of the disc. With the arrangement described, the change in
differential pressure across the expansion orifice (which corresponds
substantially with the changes in the differential pressure between the
condenser and evaporator) results in changes in the deflection of the disc
and accordingly results in changes in the effective opening of the
expansion orifice 44.
In the operation of the valve described, under a high load condition for an
air conditioning system the pressure differential between the condenser
and evaporator is greater than when the system is operating under rated
conditions, or under a low load condition. Under the high load condition,
the greater differential pressure causes greater deflection of the disc,
and accordingly results in an effective expansion orifice which is smaller
than at the other conditions. The converse is of course also true in that
the effective opening of the orifice is greater when the load is less, due
to the lesser differential pressure.
In designing a valve to carry out the invention, the designer starts with
knowledge of the desired pressure drop across the valve for, say, two of
three conditions such as high load, rated load, and low load, and then can
determine the required valve openings for two of the three conditions.
That is, the valve is designed so that its characteristic is such that it
passes through two selected points on a plot of differential pressures
versus valve openings. The way in which a valve such as that illustrated
in FIG. 2 is designed and calculated is described in the following.
The basic parts of the described expansion valve are the deflectable disc
38 and the expansion orifice 44 as are shown schematically in FIG. 6. The
concept of using this valve as a refrigerant control device is based on
the pressure and flow rate characteristics of a selected air conditioner
system. The notations below are defined for the purpose of the
calculations which follow, and which are intended to explain an example of
the underlying theory and design procedure for a particular valve.
P.sub.1 = psi, inlet pressure
P.sub.2 = psi, outlet pressure
.DELTA.P = P.sub.1 - P.sub.2 = psi, pressure drop across the valve
x = in., orifice opening
x.sub.o = in., value of x when .DELTA.P = 0
d = in., disc diameter of faces of disc subject to pressure (selected as
1.0")
A = in..sup.2, effective orifice area
K = lb/in., disc stiffness
t = in., disc thickness
n = in., nozzle diameter (selected as 0.110")
r = in., disc aperture radius (selected as 0.0475")
Q = f.sup.3 /sec, discharge flow rate
C.sub.d = discharge coefficient
.rho. = slug/ft.sup.3, fluid density
f = lb, force on the disc
W = lb, total applied load
y = x.sub.o - x = in., vertical deflection
E = psi, modulus of elasticity
Subscripts h and l denote the high and low load conditions, respectively.
The force acting on the disc body can be expressed by f = (.pi./4) d.sup.2
.DELTA. P. Also, the force can be expressed in terms of disc stiffness and
deflection, i.e., f = Ky = K(x.sub.o - x). Hence, (.pi./4) d.sup.2 .DELTA.
P = K(x.sub.o - x)
or
.DELTA.P = (4/.pi.) (K/d.sup.2) (x.sub.o - x) = m(x.sub.o - x) (1)
where
m = (4/.pi.) (K/d.sup.2)
From Equation (1) it may be seen that the valve opening is related to the
pressure drop across the valve. This relationship is also graphically
illustrated by the straight line valve characteristic line 66 in FIG. 7.
Line 68 of FIG. 7 illustrates a typical shape of a curve of values of
pressure drop versus valve opening that can be obtained by adjusting the
valve opening of a manually adjustable expansion valve of an air
conditioner operated under a high load condition while measuring the
corresponding pressure drop. Line 70 of FIG. 7 illustrates a typical shape
of a curve for operation under a low load condition.
The valve designer has control over the slope and the x intercept of the
valve characteristic. Therefore, as illustrated in FIG. 7, it is
theoretically possible to design the valve to satisfy any high load and
low load pressure drop requirements (i.e., by operation at points H and L)
so long as these requirements are consistent with other constraints of the
valve design.
Although the above discussion has been based upon meeting specified high
load and low load operating points, by design the valve can as well meet
specified high load and rated load, or low load and rated load points.
Since there are only two independent design parameters, the slope and the
intercept, the design cannot generally meet independently specified high
load, rated load, and low load operating pressure drops. However, from a
practical point of view it is not necessary to meet three independent
conditions.
The following paragraphs give a numerical example of how to design a valve
to meet high and low load conditions for a specific room air conditioner
charged with R-22 refrigerant and having a nominal 15,000 BTU per hour
rating. The values set forth in the table below are those measured and
calculated from the operation of such an air conditioner provided with a
conventional automatic expansion valve.
______________________________________
Low Load
Rating High Load
Conditions
Conditions
Conditions
______________________________________
Pressure Drop P (psi)
142 253 322
Flow Rate (lb/hr)
203 209 244
Density before Valve
(Slug/ft.sup.3)
2.225 2.190 2.145
Flow Rate (cfs)
7.90 .times. 10.sup.-.sup.4
8.24 .times. 10.sup.-.sup.4
9.05 .times. 10.sup.-.sup.4
______________________________________
From the standard orifice equation, the effective expansion orifice area A
is found for high and low load conditions, as follows:
##EQU1##
where C.sub.d = 0.611 is obtained from FIG. 85 of the reference book of
H. Rouse entitled "Elementary Mechanics of Fluids," published by John
Wiley and Sons, 1960.
The nozzle diameter is selected to be 0.110 in. to get reasonable values of
x for high and low load conditions.
x.sub.h = (A.sub.h /.pi. .sub.n), x = (A/90 .sub.n)
Then, x.sub.h = 0.00298 in., and x.sub.1 = 0.00397 in.
The ratio of the area of disc aperture .pi.r.sup.2 and the area of
effective orifice (.pi.nx.sub.l) at low load conditions is 5.16. This area
ratio is large enough so that the annular opening is the principal
restriction and controls the expansion.
By plotting the high and low load operating points in a .DELTA.P versus x
plane as shown in FIG. 8, a calculated or a graphical determination can be
made of the x.sub.o intercept and -m the slope, these determinations being
x.sub.o = 0.0048 in. and -m = - 1.82 .times. 10.sup.5 lb./in.sup.3, from
line 72.
Then the required beam stiffness is calculated based on a disc diameter of
d = 1.00 in.
K = (.pi.d.sup.2 /4) (m) = (.pi./4)(1.0).sup.2 .times. 1.82 .times.
10.sup.5 = 1.423 .times. 10.sup.5 lb/in
Next, it is required to determine the disc thickness which will realize
this stiffness. The relationship between the deflection and load for such
a disc is given in the text by R. J. Roark. Formulas for Stress and Strain
and takes the form:
Y = (W/ Et.sup.3) C (4)
where
E = 30 .times. 10.sup.6
W is the total load uniformly distributed.
C in in..sup.2 is a constant which depends upon the outside diameter, the
hole diameter and Poisson's ratio which is taken to be 0.270. For an
outside diameter of 1.0 in. and a hole diameter of 0.095 in., the value of
C is 0.245.
The stiffness is w/y so that the disc thickness can be expressed as
follows:
##EQU2##
Experimental operation of the disc type valve of this invention shows that
it, along with the beam-type valves of the companion patent application,
compares favorably with the conventional automatic expansion valve in
performing the throttling function at low, rated and high load conditions.
Since it does not respond to evaporator pressure increases alone, and is
open during off periods of compressor operation, it does not impose a
limitation of waiting to restart the compressor until equalization of
pressures occurs through a bleed port. Fan motor failures are avoided as a
problem with this type of valve without any requirement of a pressure
relief device. Finally, the simplicity of the construction, and the
limited number of parts, should be apparent from the foregoing description
.
* * * * *
|
|
 |
|
 |
Description |
|
