Apparatus for the sensing of refrigerant temperatures and the control of refrigerant loading

A new device is provided for sensing refrigerant tempertatures in refrigerator systems, and for the control of refrigerant loading in a plurality of refrigerator evaporator circuit coils connected in parallel. Such evaporator coils are supplied with refrigerant through a termostatically controlled flow control valve, which is controlled by a sensor to ensure a predetermined amount of superheat. The usual minimum superheat is aobut 5.5.degree. C. (10.degree. F.) and to reduce this value the refrigerant is passed through the devide in which it is rendered thoroughly turbulent and mixed, the device intercepting the entire refrigerant flow just before the sensing of the superheat, thus ensuring that the temperature is accurately measured. In one aspect of the invention the device consists of a series of three chambers connected together by two similar sets of holes, the first and third chambers being similar so that it is completely reversible. In another aspect of the invention the part of the device wall intended to receive the sensor is provided with a groove into which the sensor fits snugly to increase the heat exchange contact between them. Grooves of different sizes can be provided in the same device. The heat conductive contact can be increased further by sandwiching a layer of pasty heat conductive material between the sensor and the groove wall that fills the space between them.

FIELD OF THE INVENTION 
This invention is concerned with apparatus for the sensing of refrigerant 
temperatures in refrigerator systems and particularly with apparatus for 
the control of refrigerant loading in refrigerator evaporators. 
REVIEW OF THE PRIOR ART 
The standard refrigeration compressor-operated system consists of a closed 
circuit in which cool low-pressure refrigerant vapor from a suction line 
enters a compressor which compresses it to a hot high pressure vapor, this 
hot vapor then flowing through a discharge line to a condenser coil or 
coils where it is cooled below its condensing temperature and becomes 
liquid. The liquid flows from the condenser through a return line into a 
liquid receiver, and from the receiver through a liquid line to an 
indicator and filter/drier, from whence it passes to a thermostatically 
controlled expansion valve which maintains at an optimum value the flow of 
the liquid refrigerant into an evaporator coil or coils, in which it 
evaporates with consequent temperature drop and cooling of the coils and 
their environment; the resultant vapor passes through the suction line 
back to the compressor to complete the circuit. 
It is essential to control the expansion valve (usually called the TX 
valve) so as to prevent any liquid refrigerant from reaching the 
compressor, which would damage it, and this valve control usually consists 
of a remote temperature sensing fluid-containing cylindrical bulb 
connected by a metal capillary tube to a charged diaphragm capsule in the 
valve. The capsule responds to changes in temperature of the sensor bulb 
to regulate the flow through the valve. Equivalent electrical sensors have 
also been developed. The sensor bulb or its equivalent normally is clamped 
tightly to the suction line at the exit from an outlet manifold into which 
the evaporator coil or group of coils discharge, so as to sense the 
temperature of the vapor at this point. The temperature characteristic of 
a vaporizing body of liquid is very standard in that its temperature will 
remain relatively constant at about the respective vaporizing (saturation) 
temperature as long as there is some liquid present to vaporize, and then 
will rise relatively rapidly when all the liquid is gone. To ensure that 
no liquid escapes from the evaporator the sensor is set for an operating 
temperature sufficiently higher than the saturation temperature, and the 
difference between these two temperatures is known as the superheat. As an 
example, a quite usual range of values for the saturation temperature of 
such a system is about -7.degree. C. to about 4.5.degree. C. (20.degree. 
F. to 40.degree. F.), while a quite usual value for the superheat is about 
5.5.degree. C. (10.degree. F.), so that the range of control temperatures 
for such systems will be -1.degree. C. to 10.degree. C. (30.degree. F. to 
50.degree. F.). 
In theory it should be possible to use a much lower superheat value, say 
1.degree. C. (2.degree. F.), but in prior art practice it was found that 
this was not sufficient to ensure the complete absence of liquid 
refrigerant from the evaporator manifold outlet and the higher value was 
therefore almost universally used. As the superheat value varies around 
the predetermined amount the TX valve opens and closes, and in theory 
should be operable to maintain it quite accurately at that value, but in 
practice there is a time lag between the sensing of the temperature by the 
sensor and the operation of the TX valve, which also usually cannot 
respond fast enough, resulting in a fluctuating superheat value 
necessitating the higher amount, thereby reducing the efficiency of the 
system. There has therefore been a continuing need for a temperature 
sensor for such systems which can more accurately determine the 
temperature of the refrigerant vapor in the suction line and thus improve 
the efficiency. 
In commercial refrigerators, most evaporators consist of a large number, 
often as many as fifty, separate "circuit coils" connected in parallel so 
as to obtain sufficient cooling capacity without the individual coils 
being of too great length with consequent high pressure drop. These 
circuit coils are arranged in sets, each set having its own expansion 
valve and a common distributor interposed between the valve and the coils 
of the set, the purpose of the distributor being to divide the flow as 
equally as possible between individual small diameter feed pipes of equal 
length leading from the distributor to the respective circuit coil pipe 
inlets. All of the circuit coil pipe outlets are connected to a common 
outlet manifold or stand-pipe. Despite the care that is taken to try to 
make the valve and the distributor feed equal amounts of liquid 
refrigerant to the circuit coils, and to make all of the circuit coils as 
equal in length and flow characteristic as possible, it is in practice 
always found that liquid refrigerant vaporizes in some of the coils at a 
different rate than in the others, due to variables such as differences in 
the flow of air over the different coils, and small differences in the 
pressure drop through each coil. The consequence is that the circuit coil 
or coils which absorb the least amount of ambient heat allow the liquid 
refrigerant to flow further along it or them before vaporizing, so that it 
is this coil or coils that control the TX valve and close it down, 
starving the remainder of the coils of liquid refrigerant and excessively 
superheating the refrigerant vapor in the starved coils, and thereby 
reducing the cooling capacity of the system. This reduction can be as much 
as from about 25 to 35% of the total capacity. 
This unequal loading of the evaporator circuit coils can usually be 
observed by visual inspection of the coils once the system has been in 
operation of a short time, when the starved circuit coils are less frost 
coated toward the outlet end than the others. This unequal loading is 
often mistakenly attributed to unequal distribution of the refrigerant 
liquid among the coils. 
There is disclosed and claimed my prior application No. 07/404,380, filed 8 
Sept. 1989, the disclosure of which is incorporated herein by this 
reference, apparatus for the sensing of the temperature of refrigerant 
exiting from a refrigeration system evaporator coil outlet and for the 
control in accordance with the sensed temperature of a controllable 
evaporator valve feeding liquid refrigerant to the evaporator coil inlet 
the apparatus comprising: 
a turbulating and mixing device having an inlet and an outlet for 
refrigerant and having therein a refrigerant flow path having at least 
part of a wall thereof of heat conductive material for sensing the device 
interior temperature through the wall part; 
turbulence and mixing producing means in the flow path intercepting the 
entire refrigerant flow and creating turbulence and mixing of the 
refrigerant with changes in the direction of the entire refrigerant flow 
to ensure turbulence and mixing of all liquid and vapor refrigerant phases 
present and contact of only mixed phases with the wall part; and 
the apparatus being adapted to have in heat conductive contact with the 
wall part temperature sensing means for sensing the device interior 
temperature and for controlling the evaporator valve in accordance with 
the sensed temperature. 
There is also disclosed and claimed in that prior application apparatus for 
use in a refrigeration system comprising: 
a refrigerant compressor; 
a condenser coil receiving refrigerant from the compressor to cool it; 
a common, thermostatically controlled refrigerant flow control valve 
receiving the cooled refrigerant from the condenser coil; 
an evaporator coil comprising a plurality of circuit coils connected in 
parallel with one another so that all are supplied with refrigerant from 
the common control valve; 
a common member having an inlet and an outlet receiving the refrigerant 
exiting from all of the circuit coils; and 
conduit means connecting the compressor, condenser coil, common control 
valve, evaporator coil, common member inlet, common member outlet and the 
compressor in a closed loop in the order stated; 
a superheat temperature sensor detecting the temperature of the refrigerant 
at the common member outlet and operatively connected to the control valve 
for control thereof; 
the apparatus comprising the said turbulating and mixing device in the said 
loop at the common member outlet and turbulating and mixing the 
refrigerant flows from the circuit coils to average the temperatures of 
the flows, the temperature sensing means sensing the device interior 
temperature. 
DEFINITION OF THE INVENTION 
It is therefore a principal object of the present invention to provide a 
new apparatus for the sensing of refrigerant temperatures in refrigerator 
systems, and in particular a new apparatus by which the temperature of the 
refrigerant exiting from an evaporator coil is sensed more efficiently by 
the temperature sensor controlling the TX valve for more precise superheat 
control. 
In accordance with the present invention there is provided apparatus for 
the sensing of the temperature of refrigerant exiting from a refrigeration 
system evaporator coil outlet and for the control in accordance with the 
temperature sensed by a sensing means of a controllable evaporator valve 
feeding liquid refrigerant to the evaporator coil inlet, the apparatus 
comprising 
a turbulating and mixing device having an inlet and an outlet for 
refrigerant and having therein a refrigerant flow path having at least 
part of a wall thereof of heat conductive material for sensing the 
enclosure device interior temperature through the wall part; 
the said wall part having a grooved portion in which the sensing means can 
be disposed in heat exchange contact with the wall part, corresponding in 
cross-section to the cross-section of the sensing means to increase the 
heat conductive contact of the sensing means with grooved portion; 
and turbulence and mixing producing means in the flow path intercepting the 
entire refrigerant flow and creating turbulence and mixing of the 
refrigerant with changes in the direction of the entire refrigerant flow 
to ensure turbulence and mixing of all liquid and vapor refrigerant phases 
present and contact of only mixed phases with at least the grooved portion 
of the wall part. 
Also in accordance with the invention there is provided apparatus for the 
sensing of the temperature of refrigerant exiting from a refrigeration 
system evaporator coil outlet and for the control in accordance with the 
temperature sensed by a sensing means of a controllable evaporator valve 
feeding liquid refrigerant to the evaporator coil inlet, the apparatus 
comprising: 
a turbulating and mixing device having an inlet and an outlet for 
refrigerant and having therein a refrigerant flow path having at least 
part of a wall thereof of heat conductive material for sensing the 
enclosure device interior temperature through the wall part; 
the device comprising a first tubular member having at least approximately 
midway along its interior a transverse barrier dividing the interior into 
a first chamber connected to the inlet and a second chamber connected to 
the outlet and against which the refrigerant flow impinges to produce 
resultant turbulence in the first chamber; 
a second tubular member surrounding the first tubular member to form an 
annular second chamber between them; 
a first set of bores provided in the wall of the first passage and 
directing the refrigerant flow into the second chamber against the inner 
wall of the second tubular member, and; 
a second set of bores provided in the wall of the third chamber directing 
the refrigerant flow from the second chamber into the third chamber.

The same or similar parts are given the same reference in all the figures 
of the drawing, wherever that is possible. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a typical refrigeration system to which the 
apparatus of the invention can be applied comprises a refrigerant 
compressor 10 having a suction inlet 12 and a high pressure outlet 14, the 
compressor feeding the hot compressed refrigerant fluid via conduit 15 to 
a condenser coil 16 having an inlet 18 and an outlet 20. Cooled 
refrigerant from the coil 16 passes via conduit 21 to a liquid accumulator 
22, and thence via conduit 24 through a filter/drier 26, a liquid 
indicator 28 and a common thermostatically controlled refrigerant flow 
control TX valve 30 into a distributor 32, from which it flows into two 
parallel-connected circuit coils 34a and 34b of an evaporator coil. For 
convenience in illustration only two circuit coils are shown, but in 
practice there can be as many as fifty in a single large evaporator coil, 
each circuit coil being connected by a respective inlet pipe 36a and 36b 
to the common distributor 32. As described above in practice care is taken 
to make all of the circuit coils 34a, 34b, etc., and all of the pipes 361, 
36b, etc., of the same length and as equal as possible, so that the 
refrigerant will be distributed as equally as possible among them. 
Each circuit coil has an inlet 38a, 38b respectively and an outlet 40a and 
40b respectively, the latter all being connected to a common header pipe 
42 (sometimes also called a stand-pipe or manifold), the single outlet 44 
of which is connected to inlet 46 of a turbulator and mixing device 48 of 
the invention. A superheat temperature sensing bulb 50 by which the TX 
valve 30 is controlled is tightly clamped to the exterior of the device 48 
by a clamp 51 to be in good heat exchange with its interior through the 
device wall and is connected by a capillary tube 52 to the valve 30. The 
outlet 54 of the device 48 is connected by conduit 56 to the pump inlet 12 
to complete the system circuit. The usual fans 58 and 60 are provided to 
circulate ambient air over the coils 16 and 34a, 34b respectively. The 
numerous other circuit elements, controls and indicating devices that such 
a system normally includes do not constitute part of this invention and 
therefore do not need to be illustrated. The direction of flow of the 
refrigerant is indicated by the broken arrows. 
Referring now also to FIG. 2, this particular device 48 is made of metal, 
preferably a high conductivity metal such as copper or brass, and consists 
of a first inner cylindrical pipe 62, provided at least approximately at 
its middle along its length with a transversely-extending circular disc 64 
comprising an end barrier extending over its entire cross-sectional area 
and dividing the interior of the pipe into two separate independent 
cylindrical chambers 66 and 68, called for convenience in terminology the 
first and third chambers. In this embodiment the disc is retained in 
position by its entrapment between two radially inwardly extending 
circular ridges 70 produced by a die-forming operation in the pipe; it may 
be noted that the joint between the disc and the inner wall of the pipe 
does not need to be absolutely gas tight. A second outer cylindrical pipe 
72 having a central portion of larger diameter than its two end portions 
surrounds the first inner pipe 62 coaxial therewith and is sealed to the 
pipe at both ends, thereby forming an annular cross-section second chamber 
74 between the two pipes. The inner pipe is held securely within the outer 
pipe between two radially inwardly extending circular ridges 76 die-formed 
in the outer pipe, and the ends of the outer pipe are reduced in diameter 
to the size required for the system in which it is inserted, one end 
constituting the inlet 46 while the other end constitutes the outlet 54. 
The fast flowing refrigerant fluid entering the pipe 62 impinges strongly 
against the transverse barrier 64 and immediately becomes extremely 
turbulent within the first chamber 66. The inner pipe has a first set of a 
plurality of holes 78 distributed uniformly along the part of its length 
within the first chamber 66, and also distributed uniformly around its 
periphery, which holes direct the turbulent refrigerant vapor in the 
chamber 66, together with any liquid entrained therein, forcibly into the 
chamber 74 against the inner wall of the outer pipe 72. The inner pipe has 
another set of a plurality of holes 80 similarly uniformly distributed 
along the part of its length within the second chamber 68 and around its 
periphery, which holes direct the highly turbulent vapor in the chamber 74 
back into the third chamber 68 and out of the outlet 54, the abrupt change 
of direction of the vapor required for its passage through the second set 
of holes 80 considerably increasing its turbulence in the chamber 74. The 
pipes 62 and 72, the barrier 64, and the bores 78 and 80 therefore provide 
within the interior of the device a direction-changing flow path between 
the inlet and the outlet that produces a thorough turbulating and mixing 
action on the refrigerant. The combination of the tortuous path formed by 
the successive chambers 66, 74, and 68, the abrupt changes in direction of 
the fast-flowing fluid, the turbulence in the inner pipe chamber 66 
because of the impingement of the fluid against the closed end, and the 
turbulence in the annular chamber 74 between the two pipes because of the 
said impingement against the outer pipe inner wall, and its subsequent 
change of direction to exit through the holes 80, all ensuring that the 
entire refrigerant flow in the flow path, whether in the liquid or vapor 
phase, is all thoroughly mixed and rendered turbulent, and particularly 
without any possibility of the relatively high velocity vapor phase being 
able to flow through the device separately from the liquid phase. 
Moreover, the vigorous impingement of the high velocity fluid against the 
outer pipe inner wall ensures that any relatively stagnant barrier layer 
of refrigerant, or of the lubricating oil that is always entrained 
therein, is thoroughly disrupted and removed from the inner wall, so that 
it cannot prevent the efficient transfer of heat from the refrigerant 
through the wall to the sensor bulb 50. The bulb is therefore sensing only 
the temperature of a completely turbulent mixed and temperature averaged 
refrigerant flow as received from the outlet of the header pipe 42, and in 
addition is much more sensitive to changes in the refrigerant temperature 
and more accurately measures the device interior temperature which 
corresponds to the averaged refrigerant temperature. This turbulating and 
mixing function of the device 48 is effective in this manner whatever the 
evaporator coil structure employed in the system. 
Unexpectedly I have found that a device as specifically described, 
employing three successive chambers with two abrupt changes of direction 
through respective sets of holes, is more efficient in providing for 
accurate measurement of the temperature of the fluid refrigerant than my 
prior embodiment, as described and illustrated in FIG. 2 of my above 
identified prior application, which employs two successive chambers with 
only a single abrupt change of direction through a single set of holes. 
Another substantial commercial advantage of this embodiment is that it is 
symmetrical end for end and completely reversible, so that it is 
immaterial which end is employed as the inlet and which is employed as the 
outlet; the installer is therefore able to install it in the line 56 
without having to consider the direction of refrigerant flow through the 
device. It was found with the prior art devices that there was a small but 
noticeable decrease in performance if it had been installed reversed, but 
this cannot happen with the devices of the present invention. 
Another improvement in performance is obtained in apparatus in accordance 
with this invention by providing the outer pipe 72 with a longitudinal 
exterior groove 82 of cross-section corresponding to that of the sensor 
bulb 50, so that there is maximum practical heat-exchange surface contact 
between the bulb and the pipe 72, and thus between the interior of the 
chamber 74 and the bulb. In practice sensor bulbs as used in refrigeration 
systems are almost universally of cylindrical shape and circular 
cross-section, and accordingly the groove 82 is made of semi-circular 
cross-section of size such that the bulb will fit snugly within the groove 
and be held firmly in place by the band clamp 51. It is also found in 
commercial practice that sensors are usually either of diameter 12.8 mm 
(0.5 in) or 9.5 mm (0.375 in), and accordingly the tube 72 is provided 
with two circumferentically spaced grooves 82 and 84 of these two 
different diameters, so that the installer can chose the one appropriate 
for the size of bulb to be used. More than two spaced grooves can be 
provided if more than two sizes are involved. The formation of the groove 
or grooves, usually by a die-forming operation, will result in a small 
decrease in the cross-section area of the annular passage 74, and this can 
readily be compensated, if required, by a small increase in diameter of 
the central portion of the pipe 72. Neither the pipe 72 nor the bulb 50 
are likely in practice to be manufactured to close tolerances, and to 
ensure even better heat exchange contact between them the wall of the 
selected groove may be pre-coated with a layer 86 of heat-conductive 
paste, which is squeezed between them as the bulb is pressed into the 
groove by the band clamp 51 and fills any air space that might otherwise 
be left between them. 
In prior practice the circular cross-section bulb has usually been clamped 
to the exterior of the circular cross-section pipe with their axes 
parallel, and at best there is only a line contact between them where 
their peripheries touch one another. In practice the situation is often 
much worse in that, if the installer does not mount the bulb carefully it 
may be somewhat skewed relative to the pipe, with the axes no longer 
parallel, whereupon the area of contact is correspondingly reduced. This 
can very easily happen since it has been usual to attach the bulb by means 
of two longitudinally-spaced band clamps, and it is comparatively easy 
during the installation of the second clamp for the bulb to become skewed; 
and even a small amount of skew causes a considerable reduction in contact 
area. With a device of this aspect of the invention all that is required 
is for the installer to select which of the grooves is closest in size to 
the bulb while able to receive it, apply a bead or layer of the heat 
conductive paste material to the wall of the groove, place the bulb in 
position in the groove and clamp it firmly in place using only a single 
clamp, whereupon accurate positioning and alignment is immediately 
assured. 
The grooves 82 and 84 can be made of cross-sections that are more than 
semi-circular to increase the contact area, but the bulbs must then be 
slid endwise into the groove, which may be difficult in some 
installations; such re-entrant grooves are more difficult to manufacture 
than the open-mouth semicircular grooves illustrated. 
The devices of the invention have the advantages both to the installer, and 
to the owners of the apparatus in which they are installed, that they not 
only produce an improvement in performance of the system by permitting a 
substantial reduction in the superheat, but they provide a pre-established 
preferred and easier installation location for the sensor bulb that both 
ensures the improved performance will be obtained and also simplifies the 
installation procedure. Thus, in practice once the decision has been made 
to install a device of the invention, which is easily done with new 
equipment, and which for retrofitting to old equipment involves the 
relatively simple procedure of cutting a section from the pipe to permit 
its insertion therein, the hitherto sometimes difficult questions of 
proper location and correct installation of the sensor bulb are also 
readily and positively determined. 
The provision of a groove in the suction pipe of a system for reception of 
the sensor can with advantage be applied to the existing systems by 
providing a special grooved section of pipe that is installed at each coil 
outlet, or as close thereto as possible. As with the other embodiments, 
such a device may be provided with two or more circumferentially disposed 
grooves of different sizes to accommodate different sizes of sensor. 
Moreover, it is now practical and feasible to provide a layer of heat 
conductive pasty material in the groove between the pipe wall and the 
sensor. Such a grooved pipe increases the effectiveness of the sensor, as 
well as its ease of installation, and will permit a reduced amount of 
superheat, although not as much as by the other turbulating and mixing 
devices of the invention. 
When the device is used with a system as specifically described, namely 
with multiple circuit coils, then in addition to turbulating and mixing 
the fluid flow in each evaporator circuit coil it also performs a multiple 
mixing function, whereby the fluid flows from all of the circuit coils are 
thoroughly mixed together, so that all of their separate temperatures are 
averaged, and it is this average circuit coil temperature that is detected 
by the bulb 50. Moreover, this very thorough turbulence and mixing ensures 
that if one or more of the circuit coils is not evaporating all of its 
supply of refrigerant, then the small quantities of liquid reaching the 
mixing device are immediately atomized and consequently easily vaporized 
by heat from the superheated vapor from the remaining coils. The supply of 
refrigerant to the starved coil or coils can therefore be increased until 
the superheated vapor they produce is not able to vaporize the liquid 
refrigerant from the underloaded coil or coils. 
The diameters of the pipes 62 and 72 are such that the flow capacities of 
the resultant flow passages are about that of the remainder of the suction 
tube 56, while the number and size of the apertures 78 and 80 are such 
that about the same flow capacity is achieved. These flow capacities can 
vary between about 0.5 and 1.5 times the usual flow capacity of the 
suction tube; it may be preferred to reduce the flow capacity of the 
apertures 78 somewhat below that of the apertures 80 and that of the 
suction tube in order to obtain sufficiently forceful impingement of the 
fluid against the outer tube inner wall. 
In one specific embodiment intended for use in a system of about 2-3 h.p. 
the outer pipe 72 is about 23 cm (9 ins.) long and 3.5 cm. (1.375 ins.) 
maximum outside diameter; the inner pipe 62 is about 17 cm (6.75 ins.) 
long and 2.2 cm (0.875 in.) inside diameter and is provided with the two 
sets of uniformly spaced holes, each of which is 3.1 mm (0.125 in.) in 
diameter. Each set consists of six circumferentically-spaced rows, each of 
seven holes, for a total of forty two holes for each set. 
In another specific embodiment intended for use in a system of about 10-15 
h.p. the outer pipe 72 is about 23 cm (9 ins.) long and 6.35 cm. (2.5 
ins.) maximum outside diameter; the inner pipe 62 is about 17 cm (6.75 
ins.) long and 4.4 cm (1.75 in.) inside diameter and is provided with the 
two sets of uniformly spaced holes, each of which is 6.3 mm (0.25 in.) in 
diameter. Each set consists of five circumferentically-spaced rows, each 
of six holes, for a total of thirty holes for each set. 
In practice if the system is of power from about 40 h.p. and up it is usual 
to split the coils into two sets and to provide each with a separate TX 
valve controlled from its respective sensor. Except therefore for special 
installations it is unlikely that a device with an inner pipe 62 of more 
than 7.8 cm (3.125 ins) O.D. will be required. It is found in practice 
that the pressure drop through the devices of the invention is 
sufficiently low, usually less than about 1 p.s.i., that it does not 
produce any appreciable loss of efficiency, and any loss for this reason 
is amply compensated by the overall considerably improved efficiencies 
that usually are obtained The drop is sufficiently small that it is 
difficult, if not impossible, to detect with the pressure gauges that are 
used in standard refrigeration service practice 
Despite the lengthy period of time for which these problems have existed it 
does not appear to have been understood how to provide turbulator means 
and/or mixing means that will sufficiently improve the temperature 
detection and control of the TX valve, and also in multiple coil systems 
to average the temperatures of the refrigerant flows from the large number 
of individual circuit coils for the same purpose. Thus, the current 
commercial literature in the industry of which I am aware seems to assume 
that all that can be done is to make the lengths of the circuit coils as 
equal as possible, to discharge all of the circuit coils into a common 
header pipe, and to clamp the sensor bulb to the outside of the outlet 
pipe from the header pipe, when the temperature will be measured as 
accurately as possible and the flows will be mixed to the maximum 
obtainable extent. 
I believe that this mistaken assumption may have resulted from a lack of 
adequate appreciation of the flow conditions of the refrigerant fluid in 
the evaporator coils and the outlet pipe or manifold. The refrigerant 
enters the coils as a low volume liquid and is evaporated in the confined 
spaces thereof to a high volume vapor, with the result that the exit speed 
of the vapor is relatively high, to the extent that in the absence of the 
highly positive turbulating and/or mixing apparatus of the invention, 
involving the entire fluid flow or flows, the flows in the coils remain 
laminar and any liquid particles remain entrained without mixing, while 
there is little or no opportunity for the flows from the different coils 
to mix and average. Consequently there is little opportunity for any small 
quantities of liquid refrigerant to be evaporated before the temperature 
must be sensed by the bulb 50. It is essential for the turbulating and 
mixing to be carried out across the entire cross-section of the flow path, 
since any gaps will allow the corresponding portion or portions of the 
high velocity fluid passing through them to remain laminar with liquid 
particles entrained and defeat the purpose of the device. The situation 
would not be made much better in the prior art apparatus by placing the 
sensor bulb 50 further along the suction pipe 56, since the flows will 
still remain relatively laminar along the pipe, and any additional 
distance of the bulb from the evaporator outlet and from the TX valve 
introduces additional difficulty because of the increased time delay for 
operation of the TX valve. 
As evidence of this current lack of appreciation of the problem there is 
and has been considerable discussion of the best physical arrangement for 
the coils to ensure that they are equally loaded, and it has been 
considered important in prior refrigeration systems to locate the sensor 
bulb 50 appropriately on the circumference of the suction pipe in order to 
sense the superheat temperature as accurately as possible and operate with 
minimum superheat. The manufacturers of TX valves in their installation 
manuals stress the importance of proper location of the sensor bulb, but 
do not give a definitive location for it. They advise that preferably the 
bulb should be fastened to a horizontal portion of the suction line, and 
clamped at different places around its circumference depending on the 
diameter, but the location is finally chosen by the installer depending 
upon what appears to be suitable and/or practicable for that installation, 
often with poor results. The theoretically ideal location is at 6 o'clock 
on the circumference of a horizontal suction pipe, where it should be able 
to sense most accurately any small quantity of liquid refrigerant passing 
in the pipe, and would therefore permit the smallest amount of superheat. 
In practice this has not been a satisfactory location because of the 
presence of lubricant oil in the refrigerant, which flows along the bottom 
of the pipe and would thermally insulate the sensor bulb from the 
refrigerant fluid. The usual location for the bulb has therefore been at 
four or eight o'clock on the pipe circumference. It is found that with the 
thorough turbulence and mixing provided by the devices of the invention 
the location of the sensor bulb around the circumference of the device is 
no longer critical, and it can be placed at the most convenient location 
from the point of view of installation and subsequent access for service. 
It will also be seen that the sensor need not be located directly on the 
wall of the mixing device enclosure, which is however overwhelmingly the 
preferred location, especially with the ease and certainty of installation 
provided by the grooved wall, but should be located as close as possible 
to the device outlet. In addition it is now found unnecessary to locate 
the sensor bulb on a horizontal portion of the suction line, and the 
attitude of the device has no effect upon its performance. 
The effectiveness of a device of the invention can readily be seen by 
visual inspection of the evaporator coil before and after its 
installation. Before installation it is usually found that the frost 
deposition on the different circuit coils is non-uniform with some of them 
completely frosted up to the outlet, while others are not frosted for a 
substantial distance back from the outlet, showing that the latter are 
starved of refrigerant and are working much below their maximum cooling 
capacity. Also the evaporator common outlet member is only partially 
frosted. With the device installed all of the circuit coils become more or 
less equally frosted, as well as the entire length of the suction 
manifold, indicating that all of the circuit coils are now operating at 
their full designed capacity. It is now found possible safely to reduce 
the amount of superheat from the prior value of about 5.5.degree. C. 
(10.degree. F.) to as low as 2.degree. C. (4.degree. F.). In some 
installations the resultant improvement in cooling capacity of the system 
can reach as much as 25-35%, indicating that the system previously was 
operating at only 74-80% of the available capacity. 
As a specific example, in an installation employing compressors totaling 
200 h.p. and eight forced air evaporator coils the system prior to the 
installation of the devices of the invention took 3 hours, 10 minutes to 
cool the room temperature from 13.degree. C. (55.degree. F.) to 
-19.degree. C. (-2.degree. F.). With the devices installed the time taken 
was reduced to 2 hours, 10 minutes, an improvement of 29% in efficiency or 
equivalent to increasing the output of the compressors to about 258 h.p. 
An important advantage that has been found to follow from use of the 
invention, demonstrating its unexpected nature, is the flexibility that is 
obtained upon installation in not having to closely match the size of the 
TX valve to the evaporator coil capacity without the valve losing control 
of the refrigerant flow. The capacity of a TX valve is determined both by 
the size of its flow aperture and the head pressure across the aperture, 
and it has been important in prior art installations for this match to be 
as close as possible. For example, one manufacturer provides 21 different 
sizes of valve to cover the range 0.5-180 tons, those in the range 0.5-3 
tons being rated in 0.5 ton increments, with progressively increasing 
intervals up to the maximum. If the valve is too large then with the high 
superheat values employed the valve hunts, overfeeding and underfeeding 
the evaporator with resultant poor efficiency and danger of liquid 
reaching the compressor because of the over-large flow capacity of the 
valve while open. On the other hand, with the valve and coil sizes closely 
matched it becomes necessary to maintain the head pressure above a minimum 
value, since otherwise the valve flow capacity becomes too low. This 
penalizes the system in winter when the air cooled condensers are very 
efficient and could operate with lower head pressure; instead it is 
necessary to maintain it artifically high by various techniques that are 
available. This means that the power required to compress the refrigerant 
must also be maintained at a corresponding high uneconomical value. 
This loss of control is easily observed in practice. For example, if the 
evaporator fan stops for some reason, perhaps a broken fuse, or the flow 
of product being cooled is interrupted, the load on the coil drops 
suddenly, faster than can be controlled by the valve, and liquid floods 
the compressor, which then becomes covered with frost when it should be 
frost-free. The liquid refrigerant washes out the lubricant, and can cause 
valve breakage and damage. Again, if the automatic coil defrost system is 
not operating satisfactorily and the coils become coated with ice the load 
on each coil drops and control can be lost; this of course is easily 
detected by visual inspection of the coils. 
Upon installation of a device or devices of the invention it is found that 
this close match of load capacities is no longer necessary and an oversize 
valve can be employed successfully. In a specific example, in a system 
with a 1.5 ton evaporator the original 2 ton rated valve was replaced with 
an 8 ton rated valve; adequate control was maintained with the superheat 
value fluctuating about 0.5.degree.-1.degree. C. (1.degree.-2.degree. F.). 
Thus with a larger orifice TX valve it is no longer necessary to keep the 
head pressure at an artificially high value to maintain adequate 
refrigerant flow through the valve, and instead it could be allowed to 
drop to a lower level and still maintain proper superheat control with 
maximum evaporator capacity. This not only maximizes the efficiency of the 
system but also provides the possibility of reducing the number of 
different sizes of valves required for a full range of installation sizes. 
In commercial refrigeration practice circular cross-section pipes are 
universally used, and pipes of such cross-section are illustrated for the 
device shown in FIGS. 1-3. However, the devices of the invention can also 
be made using pipes of other cross-sections, such as the square 
cross-section illustrated by FIG. 4. 
FIGS. 5 through 8 illustrate the invention applied to the other forms of 
device described and claimed in my above-identified prior application. As 
described above, if the sensor bulb 50 is not mounted directly on the wall 
that is impinged by the turbulent fluid, then it should be installed as 
close as possible to the device outlet 54 where the maximum mixing has 
occurred. In the embodiment of FIG. 5 the external tube 72 is provided 
with an integral elongated neck portion 72a constituting the outlet 54 on 
which the bulb is fastened. In this embodiment the interior of the inner 
pipe 62 is completely filled with metallic wool 85 as a mixing medium. 
FIG. 6 shows an embodiment in which the refrigerant flow path is provided 
by conduits forming two T-shaped junctions 88 and 90 connected by U-shaped 
connectors 92a and 92b; the connectors may be of smaller internal 
cross-section diameter to produce an increase in flow velocity of the 
refrigerant. The junction 88 divides the refrigerant flow from the common 
header 42 into two separate approximately equal sub-streams which are 
rendered turbulent by their impact against the transverse wall of the T 
cross-bar, the two streams moving separately at high velocity in the 
connectors 92a and 92b and being re-combined with a "head-on" collision in 
the cross-bar of the junction 90 back into a single stream. This collision 
of the two turbulent sub-streams produces even more turbulent mixing 
thereof, so that effective mixing and turbulence takes place before the 
refrigerant is delivered to the leg 94 of the second T-shaped junction, in 
the groove 82 or 84 of which the bulb 50 is installed. Although in this 
embodiment the refrigerant flow is divided into only two separate streams, 
in other embodiments it may be divided into more than two, all of which 
are simultaneously or sequentially recombined. 
FIG. 7 shows a further embodiment wherein the device consists of a 
container 96 having an inlet 98 for unturbulated, unmixed refrigerant and 
an outlet 100 for turbulent mixed refrigerant, the inlet and outlet being 
spaced from another along the length of the container, and both being 
disposed radially with respect to the longitudinal axis of the container, 
so that abrupt changes in direction of the fluid flow path are produced. 
The interior of the container is filled with a porous turbulating and 
mixing medium 85 through which all of the refrigerant must pass in moving 
from the inlet to the outlet. The movement of the refrigerant fluid 
through the myriad of random interconnected channels in the medium 85 
ensures the necessary thorough turbulence and/or mixing thereof. A 
suitable medium is for example metallic wools, foams or screens, or other 
suitable metallic media, particularly of stainless steel or aluminum, 
packed sufficiently densely to achieve the desired amount of turbulence 
and mixing without too great a pressure drop. Other media such as 
open-celled porous plastic and ceramic foams can also be used. Sensor bulb 
50 is firmly clamped into the selected groove 82 or 84 in the heat 
conductive container inner wall, as close as possible to the outlet 100. 
In an example the container 96 was 10 cm (4 ins) in diameter and 25 cm (10 
ins) long and was packed with stainless steel wool. Advantageously the 
body of wool is surrounded by at least a single layer of wire mesh to 
ensure that pieces of the wool cannot break off and enter the system. 
FIG. 8 shows an embodiment in which the device comprises a straight length 
of pipe 72 the whole interior of which is filled with closely wound wire 
mesh 104, so that again the entire refrigerant flow is intercepted, 
rendered sufficiently turbulent and mixed to the necessary extent. Because 
in this embodiment the abrupt changes of direction in the flow path take 
place within the interstices of the wire mesh, the device preferably is 
made much longer so as to provide a longer path than with the previously 
described turbulating and mixing devices, the sensor bulb 50 being 
installed, as with the other embodiments, in the selected groove 82 or 84 
as close as possible to the outlet end 54. As an example of the additional 
length required a device fitted in a system with a compressor of 10 h.p. 
capacity employed a pipe 72 of 4.0 cm (1.6 in) outside diameter, enclosing 
a tightly spirally rolled stainless steel mesh; the pipe was 45 cm (18 in) 
long, as compared with the length of 20-25 cm (8-10 in) required for the 
device of FIG. 2. However, it may also be noted that in another specific 
example a device was produced employing a straight enclosure between the 
inlet and the outlet consisting of a piece of pipe 25 cm (10 in) long and 
4 cm (1.6 in) outside diameter. A piece of permanent aluminum filter 
material made of woven aluminum strands, as used in air conditioning 
filters, measuring about 25 cm by 15 cm (10 in by 6 in) and 6 mm (0.25 
ins) thick, was rolled tightly into a cylinder and inserted endwise into 
the pipe. The device was employed in a system of about 10 h.p. capacity 
with the sensor bulb fastened to the suction line immediately downstream 
of the device. Despite its relatively short length it still resulted in an 
increase of approximately 20% in the cooling capacity of the coil. 
Combinations of these different devices can also be employed, as disclosed 
in more detail in my above identified prior application.