U.S. patent number 3,866,427 [Application Number 05/374,701] was granted by the patent office on 1975-02-18 for refrigeration system.
This patent grant is currently assigned to Allied Chemical Corporation. Invention is credited to James Crawford B. MacKeand, Noel Y. Rothmayer, Clark W. Smith.
United States Patent |
3,866,427 |
Rothmayer , et al. |
February 18, 1975 |
REFRIGERATION SYSTEM
Abstract
Improved means and method for determining the presence of liquid
ammonia refrigerant flowing through a tubular evaporator coil of a
open cycle refrigeration system and for regulating the flow of
refrigerant through the tubular coil involving a vapor-liquid
sensing unit disposed at an intermediate point of the tubular
evaporator in heat transfer contact with refrigerant flowing
through the evaporator, said vapor-liquid sensing unit comprising a
heat conductive element and means for heating said heat conductive
element whereby the temperature of the heat conductive element will
vary as a result of heat abstraction by refrigerant in heat
transfer contact, the variation in temperature dependent on the
proportion of liquid and vapor refrigerant.
Inventors: |
Rothmayer; Noel Y. (Madison,
NJ), MacKeand; James Crawford B. (Convent Station, NJ),
Smith; Clark W. (Bloomingdale, NJ) |
Assignee: |
Allied Chemical Corporation
(New York, NY)
|
Family
ID: |
23477865 |
Appl.
No.: |
05/374,701 |
Filed: |
June 28, 1973 |
Current U.S.
Class: |
62/7; 62/83;
62/225; 236/92B; 62/202; 62/503 |
Current CPC
Class: |
F25B
41/30 (20210101); F25B 40/02 (20130101); F25B
19/00 (20130101) |
Current International
Class: |
F25B
41/06 (20060101); F25B 40/02 (20060101); F25B
40/00 (20060101); F25B 19/00 (20060101); F25b
019/00 () |
Field of
Search: |
;62/7,83,202,225,503,512
;236/92B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: O'Dea; William F.
Assistant Examiner: Ferguson; Peter D.
Attorney, Agent or Firm: Rooney; Gerard P.
Claims
1. An open cycle ammonia refrigeration system comprising:
a. a storage tank for liquid ammonia refrigerant;
b. a tubular evaporator wherein the liquid refrigerant is vaporized
by absorbing heat from the surroundings of the evaporator;
c. a first conduit for conveying the liquid refrigerant from the
storage tank to the evaporator;
d. a second conduit for conveying vaporized refrigerant from the
evaporator to combusting means;
e. means for combusting the vaporized refrigerant;
f. a vapor-liquid sensing unit disposed at an intermediate point
between the tubular evaporator entry and exit in heat transfer
contact with the refrigerant flowing through the evaporator, said
vapor-liquid sensing unit comprising a heat conductive element and
means for heating said heat conductive element whereby the
temperature of the heat conductive element will vary as a result of
heat abstraction by refrigerant in heat transfer contact, the
variation in temperature dependent on the proportion of liquid and
vapor refrigerant; and
g. means for regulating the flow of the refrigerant through the
tubular evaporator actuated by said vapor-liquid sensing unit, said
means
2. A refrigeration system as claimed in claim 1 wherein said
vapor-liquid sensing unit is disposed in the tubular evaporator in
the path of and in
3. A refrigeration system as claimed in claim 1 wherein said
vapor-liquid sensing unit is disposed externally to the tubular
evaporator in indirect
4. A refrigerant system as claimed in claim 1 wherein the means for
heating
5. A refrigerant system as claimed in claim 1 wherein the means for
heating said heat conductive element is a heated member is contact
with said
6. A refrigerant system as claimed in claim 1 wherein a member is
provided a conduct heat from the combustion means to the heat
conductive element.
7. A refrigerant system as claimed in claim 1 wherein the
evaporator is composed of a plurality of tubular coils thru which
the refrigerant flows in parallel coils and a single tubular coil
through which the refrigerant
8. A refrigerant system as claimed in claim 7 wherein the
vapor-liquid sensing unit is disposed near the inlet of the single
tubular coil into
9. A refrigeration system as claimed in claim 1 wherein the means
for regulating the flow of the refrigerant through the evaporator
includes a liquid feed control valve disposed in the first conduit
in communication with said vapor-liquid sensing unit, whereby the
liquid refrigerant is prevented from entering the means for
combusting vaporized refrigerant.
10. A refrigeration system as claimed in claim 1 including a
thermostatic control valve disposed in the first conduit in
communication with a temperature sensing element located in a
refrigerated compartment
11. A method for determining liquid refrigerant in a tubular
evaporator of an open cycle ammonia refrigeration system wherein
liquid amonia refrigerant is vaporized by absorbing heat from the
surroundings of the evaporator, which comprises:
a. disposing a heat conductive element in heat transfer contact
with the refrigerant flowing through the evaporator;
b. heating said heat conductive element whereby the temperature of
the heat conductive element will vary as a result of heat
abstraction by refrigerant in heat transfer contact, the variation
in temperature dependent on the proportion of liquid and vapor
refrigerant; and
c. relating the temperature of the heat conductive element to the
proportion of liquid refrigerant flowing through the evaporator
with the highest temperature indicating refrigerant substantially
all in vapor and a lower temperature indicating liquid refrigerant
in heat transfer contact with the heat conductive element to effect
heat abstraction therefrom to
12. A method as claimed in claim 11 wherein the flow of refrigerant
through the tubular evaporator is regulated, actuated by variation
in temperature
13. A method as claimed in claim 11 wherein the vapor-liquid
sensing unit actuates valve means to regulate the flow of the
refrigerant through the evaporator to obtain 5 to 25 percent liquid
refrigerant at the point of
14. An open cycle refrigeration system comprising:
a. a storage tank for liquid ammonia refrigerant;
b. a tubular evaporator wherein the liquid refrigerant is vaporized
by absorbing heat from the surroundings of the evaporator;
c. a first conduit for conveying a liquid refrigerant from the
storage tank to the evaporator;
d. a second conduit for conveying vaporized refrigerant from the
evaporator to combusting means;
e. means for combusting the vaporized refrigerant;
f. vapor-liquid sensing unit disposed at an intermediate point
between the tubular evaporator entry and exit in heat transfer
contact with the refrigerant flowing through the evaporator such
that the heat transfer surface area of an auxiliary portion of the
tubular evaporator located on the discharge side of said
vapor-liquid sensing unit ranges from about one-fourth to one-third
of the total heat transfer area of the tubular evaporator, said
vapor-liquid sensing unit comprising a heat conductive element and
means for heating said heat conductive element whereby the
temperature of the heat conductive element will vary as a result of
heat abstraction by refrigerant in heat transfer contact, the
variation in temperature dependent on the proportion of liquid and
vapor refrigerant; and
g. interposed in said first conduit, means for regulating the flow
of the refrigerant through the tubular evaporator actuated by said
vapor-liquid sensing unit.
Description
BACKGROUND OF THE INVENTION
This invention relates to a refrigeration system and more
particularly refers to a new and improved means and method for
determining the presence of liquid refrigerant flowing through a
tubular evaporator coil of the refrigeration system and for
regulating the flow of refrigerant through the tubular coil.
Refrigeration systems commonly employ an evaporator in the form of
a tubular coil into which is introduced a liquid refrigerant which
is vaporized by absorbing heat from the surroundings of the
evaporator. Conventional practice is to regulate the flow of
refrigerant through the evaporator in response to the desired
temperature of the compartment being refrigerated.
Effective utilization of the evaporator results when only
sufficient liquid refrigerant is introduced into the tubular coil
with vaporization taking place throughout the length of the coil
and with substantially all vapor with little or no liquid
refrigerant discharging from the tubular coil. Complete
vaporization of the liquid refrigerant in the coil at an
appreciable distance upstream of the terminal discharge point of
the coil is inefficient utilization of that portion of the coil in
which no vaporization occurs. Of greater significance perhaps is
the condition where incomplete vaporization of all the liquid
introduced into the evaporator occurs and a substantial amount of
liquid discharges from the coil. This condition of incomplete
vaporization of liquid refrigerant in the evaporator is
particularly significant in open cycle systems because not only
does the liquid refrigerant discharged from the evaporator
represent a loss of valuable refrigerant in that cooling by
evaporation in the tubular coil did not occur but also the
discharge of substantial quantities of liquid refrigerant places a
heavy disposal burden on the rest of the system, as for example, a
burner as more fully described in U.S. Pat. Nos. 3,685,310 of Aug.
22, 1972 and 3,740,961 of June 26, 1973.
An object of the present invention is to provide a more efficient
refrigeration system by means and methods of determining liquid
refrigerant flowing through the tubular evaporator of the
refrigeration system and regulating the flow of refrigerant
therethrough to prevent discharge from the evaporator of
substantial amounts of liquid refrigerant.
SUMMARY OF THE INVENTION
The refrigeration system of the present invention comprises:
a. a storage tank for liquid refrigerant;
b. a tubular evaporator wherein the liquid refrigerant is vaporized
by absorbing heat from the surroundings of the evaporator;
c. a conduit for conveying liquid refrigerant from the storage tank
to the evaporator;
d. a conduit for conveying vaporized refrigerant from the
evaporator;
e. a vapor-liquid sensing unit disposed at an intermediate point of
the tubular evaporator in heat transfer contact with refrigerant
flowing through the evaporator, said vapor-liquid sensing unit
comprising a heat conductive element and means for heating said
heat conductive element whereby the temperature of the heat
conductive element will vary as a result of heat abstraction by
refrigerant in heat transfer contact, the variation in temperature
dependent on the proportion of liquid and vapor refrigerant;
and
f. means for regulating the flow of refrigerant through the tubular
evaporator, acutated by said vapor-liquid sensing unit.
In a more specific embodiment, the evaporator is composed of a
plurality of tubular coils through which the refrigerant flows in
parallel and the effluent therefrom discharges through another
tubular coil and wherein the vapor-liquid sensing unit is disposed
near the inlet of the tubular coil into which the effluent
discharges.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing,
FIG. 1, diagrammatically illustrates an open cycle ammonia
refrigeration system including a catalytic ammonia burner and
having a vapor-liquid sensing unit to determine liquid refrigerant
flowing through the evaporator and to regulate the flow of liquid
through the evaporator to prevent discharge therefrom of
substantial amounts of liquid refrigerant.
FIG. 2 illustrates a portion of the open cycle ammonia
refrigeration system depicted in FIG. 1 wherein an alternate method
of heating the vapor-liquid sensing unit is shown.
DETAILED DESCRIPTION
Referring to the drawings, liquid refrigerant 1 is contained in
storage tank 2 under autogenous pressure and the liquid is conveyed
by dip pipe 3 and conduit 4 to a coil 5 located inside separator
vessel 6. Although the drawing will be described with specific
reference to ammonia liquid refrigerant, other liquid refrigerants
are known such as SO.sub.2 and fluorinated hydrocarbons. Ammonia,
which has flashed or boiled to vapor in the conduit 4 is
recondensed to liquid in the coil 5, which is immersed or partially
immersed in liquid ammonia contained in the lower part of the
separator vessel 6. The pressure in separator vessel 6 is normally
maintained between 0 psig. and 10 psig. and the liquid ammonia in
the vessel therefore boils at a pressure between -28.degree. F. and
-8.degree. F. The pressure in storage tank 2 will vary dependent
upon the ambient temperature which may range from 0.degree. F. to
about 110.degree. F. and the corresponding pressures in storage
tank 2 will therefore vary from 15.7 pounds per square inch gauge
to 247 pounds per square inch gauge. Separator vessel 6 is
conveniently located at an elevation above storage tank 2, about 10
feet above the level of liquid refrigerant 1 in tank 2. As a
result, the pressure in precooler coil 5 will be slightly lower
than the pressure in storage tank 2 and the pressure inside
precooler coil 5 will vary from about 14.2 psig to 243.5 psig. A
subcooling of the liquid will therefore be produced, and this is
normally between 8.degree. and 137.degree. difference
Fahrenheit.
The liquid ammonia required to provide the pool of liquid 7 in
separator 6 is initially supplied, and maintained as necessary, by
a conduit 8 extending from the ammonia supply conduit 4 through
valve 9, line 11 into the vessel 6. A liquid level sensing element
12 activates valve 9 to permit the flow of ammonia when required
from storage tank 2 through lines 4 and 8, valve 9, line 11 to
vessel 6. As previously mentioned, the pressure in vessel 6 is
maintained between 0 and 10 pounds per square inch gauge which
would correspond to a temperature of the liquid ammonia in the tank
of between -28.degree. F. and -8.degree. F.
Liquid ammonia may contain a minor amount of oil and other foreign
particles. Subcooling the ammonia induces the oil to coalesce with
the foreign particulate matter to form a substance which is more
readily removed by filtration. Liquid ammonia subcooled in
precooler coil 5 together with coalesced foreign particulate
matter, if any, is conveyed from precooler coil 5 by conduit 13 to
filter 14 wherein removal of the foreign material is effected.
Subcooled liquid ammonia flows from filter 14 through line 15 to
thermostatic control valve 16. This valve controls the flow of
ammonia in the conduit 15 in response to the cooling requirements
of the refrigerated compartment surrounding the cooling coils as
sensed by temperature sensing element 17 and temperature controller
18. The ammonia then passes to the liquid feed control valve 21 via
conduit 19 and then through control restriction orifices 22 into
the main cooling coils 23. The ammonia discharges from the
restrictions 22 into the coils 23, 50 percent or more of the system
pressure drop being developed across the restrictions. This ensures
equal distribution to the ammonia flow to the several coils 23
which may, for example, be located at the front, center and rear of
a truck body. Such means of ensuring distribution also provide the
wherewithal to control ammonia distribution, for instance, to
supply a larger flow to a cooling coil section near the rear doors
of a truck, where greater refrigeration requirement might be
expected than elsewhere in the body.
Ammonia from the main cooling coils 23 discharges the manifold 24
to vapor-liquid sensing unit 25. This comprises a heat conductive
element and means for heating the heat conductive element, the
resultant temperature of which is dependent on the rate of heat
transfer therefrom. The heat conductive element may be stainless
steel or aluminum or other heat conductive material which is
non-corrosive and non-reactive to the refrigerant passing
therethrough. A convenient method of heating the heat conductive
element is by an electric resistance element connected by means of
wires 26 to a source of electricity, such as a battery. Other
heating means may be provided, as for example, by heat conduction
in which a metal rod is connected at one end to the heat conductive
element and heated at its other end by a flame or any other
suitable means and heat conducted from the flame to the element. In
some instances, as in trailer trucks, it may be inconvenient to
provide a source of electric power. In this event, as illustrated
in FIG. 2, the burner in which the spent ammonia is burned may be
used as a source of heat and one end of heat conducting rod 40 may
be disposed in the heated portion of the burner and the other end
disposed adjacent the heat conductive element with, of course, heat
being supplied by conduction through the rod. The various parts
should be arranged so as to provide a relatively short distance
between the burner and the vapor-liquid sensing unit. If desired,
the heat rod can be insulated to prevent loss of heat to the
surroundings.
The heat conductive element of the vapor-liquid sensing unit may be
disposed in the tubular evaporator in the path of and in direct
contact with the flowing refrigerant. Alternatively, the
vapor-liquid sensing unit may be disposed externally to the tubular
evaporator in indirect heat transfer contact with refrigerant
flowing through the evaporator. The heat conductive element may be
bonded or clamped to the tubular evaporator which is usually
fabricated of aluminum or stainless steel, both of which are good
heat conductors and heat can be readily absorbed through the walls
of the tube from the heated conductive element.
As illustrative, if only ammonia gas is present in the evaporator
tube at the point of insertion of vapor-liquid sensing unit 25 as
shown in the drawing, due to previous total evaporation of liquid
ammonia in the coils 23, a heat transfer coefficient for the
internally heated element would be of the order of about 10 Btu per
hour per square foot per degree F and at an operating pressure in
manifold 24 and sensing unit 25 of 7.5 pounds per square inch
gauge, the heat conductive element would settle at a temperature of
about 38.degree. F., based on an element surface area of 0.07
square feet and an effective heat load from the internal heater of
36 Btu per hour. On the other hand, in the presence of liquid
ammonia the heat transfer coefficient is of the order of 250 Btu
per hour per square foot per degree F and would produce a final
temperature of the sensing element of -11.degree. F. This wide
temperature swing of the sensing element 25 depends only on the
presence or absence of liquid at the point of insertion in the
manifold 24, and vapor-liquid sensing unit 25 is so arranged as to
cause liquid feed control valve 21 to close off the supply of
liquid to the restrictions 22 and main cooling coils 23 when
liquid-ammonia is detected. Vapor-liquid sensing unit 25 may
actuate liquid feed control valve 21 by any suitable means, as for
example, by hydraulic means, e.g., ammonia in conduit 27 which upon
being heated or cooled actuates a diaphragm in valve 21 to open or
close the valve.
At the time at which liquid is detected by vapor-liquid sensing
unit 25, and the valve and liquid feed control valve 21 is closed,
there may well be a substantial amount of unevaporated liquid
ammonia remaining in the coils 23 and the conduit between valve 21
and control restriction orifices 22. Final coil 28 is therefore
provided in order to make effective use of such liquid as may pass
vapor-liquid sensing unit 25. Although the relative size of coil 28
may vary, good results were obtained when coil 28 had a heat
transfer surface area of about one-fourth to one-third of the total
heat transfer surface area of all the coils 23 and 28. Effective
utilization of coil 28 to substantially complete evaporation of
liquid entering therein is obtained when vapor-liquid sensing unit
25 actuates valve 21 to regulate the flow of refrigerant through
main cooling coils 23 to obtain 5 - 25 percent by weight,
preferably 5 - 15 percent liquid refrigerant at the point of
vapor-liquid sensing unit 25.
Although vaporization of liquid entering final coil 28 will be
substantially complete at the end of coil 28, at times some liquid
refrigerant will discharge with the vapor. Any liquid not
evaporated in coil 28 flows together with vapor through conduit 29
into separator vessel 6, equipped with precooler coil 5, wherein
the liquid is separated from the vapor. Thus, any liquid introduced
through line 29 is used effectively in the precooler, and serves to
reduce the amount required from valve 9. Separator vessel 6 is
located typically with its vapor inlet 29 level with or below coil
28.
The operation of the system therefore results in a well defined
distribution of ammonia, wherein liquid is flowing in the cooling
tubes 23 and 28 and is evaporating on the walls of these cooling
tubes. The point at which the liquid evaporates to dryness is not
fixed but will move towards the end of the coils 28 nearest to the
vessel 6 when valves 16 and 21 permit flow of liquid ammonia, and
away from that point when either of valve 16 or 21 is interrupting
the flow of ammonia. This characteristic of the embodiment
described wherein the valves 16 and 21 are of the on-off type, as
distinguished from the throttling type.
The coils 23 and 28 can be disposed on the ceiling of a
refrigerated vehicle or other compartment. An alternative
embodiment, with particular advantages for smaller refrigerator
trucks, as distinct from trailers or semi-trailers, is obtained by
locating the coils 23 and 28 on the inside of the front bulkhead of
the vehicle, behind a partition which may be detachable for
convenient access to the coils. In such an arrangement the coils 23
should be arranged above the manifold 24 and coil 28, the ammonia
feed and restrictors 22 being at the top of the system and the exit
from coil 28 being at the bottom. In such a layout the entry 31 to
vessel 6 may be located either level with or below coil 28, or the
vessel may be located above the exit of coil 28, in which case
conduit 29 should be so sized as to provide hydraulic lift from
coil 28 to vessel 6 of any given liquid which might flow through to
the end of coil 28.
As an added precaution to prevent sudden surges of ammonia vapor,
there is provided a restrictor 32 which has positive limitations of
flow to the burner at the maximum desired rate of flow and with
little limitation of flow at rates below the desired maximum. To
this end, restrictor 32 is so sized as to have a pressure drop of
about 1-2 pounds per square inch at a flow rate of 40 pounds per
hour of ammonia which is an average rate for truck usage. A
sensitive reducing valve 33 is located upstream of restrictor 32 in
conduit 34 leading from separator vessel 6. Valve 33 is set to a
pressure, typically 2 pounds per square inch gauge, this being the
back pressure developed by the restrictor 32 and such other
components as are in the further flow path of the ammonia vapor
from the separator vessel 6 to the burner 35, when the flow of this
vapor is 40 pounds per hour, on such other value as is chosen to be
the permitted maximum flow. The valve 33 will then exercise no
control over the flow until the flow is very close to the desired
maximum value, typically within 0.8 pounds per hour of the 40
pounds per hour value taken as typical. As the flow tends to exceed
39.2 pounds per hour, valve 33 will tend to close and, by imposing
the back pressure on the vessel 6 and coils 28 and 23 will hold the
maximum ammonia flow to about 40 pounds per hour.
It is also desirable to prevent the use of refrigeration system
while the doors of the refrigerator compartment are open, and for
this purpose a door switch 36 may be provided. This switch will
cause valve 16 to close, thus preventing the flow of ammonia to the
cooling coils, whenever the doors are open, so preventing wasteful
and ineffective use of ammonia. If no ammonia is supplied to burner
35 it will go out. When the compartment to be cooled is down to the
required temperature, the evaporation from coils 23 and 28, and
from vessel 6 may be insufficent to maintain an adequate flame in
burner 35. For this purpose some 2-3 pounds per hour ammonia are
needed and this is supplied from the vapor phase of storage tank 2
through conduit 37 to a pressure reducing valve 38, and thence
through a conduit 39. Conduit 39 is so sized that with a pressure
of about 0.5 - 1 pounds per square inch gauge from valve 38 a
supply of 2-3 pounds per hour of ammonia will be provided to burner
35. As the burner back pressure rises in normal operation, the
valve 38 will close, thus conserving ammonia, by closing the
by-pass flow of vapor off when the flow of vapor from vessel 6 is
insufficient to maintain the flame.
Catalytic ammonia burner is disclosed and described in detail in
U.S. Pat. No. 3,685,310 of Aug. 22, 1972 which is hereby
incorporated by reference.
A refrigeration system substantially as illustrated in the drawing
with coils 23 and coil 28 each three-fourth inch diameter and 48
feet long and with vapor-liquid sensing unit disposed at the inlet
of coil 28 was tested first as a stationary unit and then after
successful operation was disposed in the truck and tested as an
in-transit refrigerating unit under varied conditions of
temperature and refrigeration load. The vapor-liquid sensing unit
effectively detected and maintained the liquid ammonia flowing past
the sensing unit within the range of 5 - 15 percent liquid by
actuating valve 21 which controlled the flow of liquid ammonia
entering coils 23.
* * * * *