Orbital type freezing apparatus and method

A machine for freezing or chilling a liquid continuously to produce a slurry of the liquid and frozen crystals feeds the liquid into a vertically oriented heat transfer tube at its upper end. A refrigerant flow at the outer tube surface evaporates in a vapor/foam stream causing the liquid to freeze at the inner tube surface. A whip rod, preferably one that is free-standing, revolves over the inner surface to dislodge the frozen crystals mechanically and to distribute the liquid. An additive to the liquid such as ethylene glycol (in water) aids the dislodging. In one form, a mechanical flow guide surrounding the outer surface produces a thin, high velocity upward flow of the boiling refrigerant to increase the heat transfer. An orbital drive propels the whip rod. In one form the orbital drive includes a pair of horizontal plates coupled between the whip rod and at least one eccentric crank. In another form, the drive includes a pair of counterweights coupled rigidly to the heat transfer tube that rotate in phase synchronization by independent motors through the dynamic design characteristics of the system.

BACKGROUND OF THE INVENTION 
This invention relates in general to apparatus and methods for evaporating, 
distilling, freezing or chilling liquids, and more specifically, to an 
orbital rod drive for use with a vertical heat transfer tube. 
Making an ice slurry under mechanical agitation is a common practice in a 
wide variety of applications ranging from the manufacture of food products 
such as ice cream and frozen orange juice to the softening of ice on 
highways with salt to facilitate plowing. A particularly important 
application is the manufacture of ice in slurry form to be used as a cold 
storage. Ice slurries are also useful as refrigerants, e.g., to preserve 
seafood catches on a fishing vessel. Freezing and chilling apparatus and 
methods are also used in the manufacture of salts, the concentration of 
various solutions and suspensions, and the purification of water or other 
fluids. 
Cold storage application for air conditioning systems has been urged by the 
utility industry as a way to transfer the power demand for cooling the air 
from daytime to the nighttime and thereby smooth out the overall power 
demand of the entire power distribution system. Freezing of water into ice 
would release its latent heat and hence can be an effective cold storage. 
Unfortunately, ice formed over a heat transfer surface tends to stick to 
the surface and thereby to block the heat transfer property of that 
surface. This has been found to be a major stumbling block for the wide 
use of ice for cold storage. 
Currently, there are two types of cold storage systems on the market using 
ice. One is known as the ice harvester type, where a group of ice making 
machines are installed over an open storage tank. Ice formed periodically 
to a certain thickness is harvested into the tank by a defrosting cycle. 
The other one is known as the ice bank type. It employs a group of low 
cost heat transfer units, usually made of plastic, on which all the ice 
needed for cold storage accumulates continuously during each chilling 
cycle. In either of these two types the effectiveness of transferring the 
heat from the water to the refrigerant during the ice forming process is 
not as efficient as desired, thus increasing equipment cost. 
The concept of making ice in slurry form so that the ice making machine can 
operate continuously without interruption and with some improved heat 
transfer property has been attempted in the industry by companies such as 
the Chicago Bridge and Iron, Inc. and more recently, by the Electric Power 
Research Institute ("EPRI") with their scheme publicized in the name of 
"slippery ice". At the present time the performance of the slippery ice 
cold storage system is still in the evaluation stage. 
The EPRI sponsored research to develop a "slippery ice" system was reported 
in an article entitled "Cool Storage: Saving Money and Energy" published 
in the July/August 1992 issue of the EPRI Journal. In the EPRI scheme, 
calcium magnesium acetate, a substance similar to the chemical used for 
de-icing aircraft, is added to the water. According to EPRI, the use of 
this additive causes ice to form in the liquid pool, away from the heat 
exchanger surface, and results in a slushy type of substance that does not 
cling to metal. The advantages of the "slippery ice" for improving the 
economy were also reported in Sep. 27, 1992 edition of The New York Times 
entitled "Keeping Buildings Cool With Greater Efficiency". In this article 
the use of automobile antifreeze in the water to be frozen was reported to 
be unsatisfactory because it tends to lower the freezing point too much. 
The slippery-ice concept is attractive because it causes an ice slurry to 
flow down a chilling surface under the influence of gravity only, without 
mechanical aid. While slippery ice works, how it works is not known. 
Moreover, this approach has several significant drawbacks. First, only one 
known additive lets ice overcome the initial stickiness barrier to a 
gravity feed of crystals down the chilling surface. This is of particular 
concern where the liquid being processed is a food product; this additive 
cannot be used. Another limitation is that the heat flux, wetting rate and 
additive concentration must be carefully controlled for the slippery ice 
to form. Also, the heat transfer surface must be electropolished. 
One of the present applicants has produced evaporation and distillation 
apparatus and methods which use one or more vertically oriented heat 
transfer tubes (HTT's) mounted in a container and driven in an orbital 
motion. These apparatus are described in U.S. Pat. Nos. 4,230,529; 
4,441,963; 4,618,399; and 4,762,592. The tubes are smoothed surface, 
circular in cross section, open at both ends, and made of a material with 
good heat conductivity properties. A distributor directs a feed liquid to 
the interior of each tube. The orbital motion spreads the liquid into a 
film. Heat transferred radially inward through the wall of the tube 
evaporates a portion of the feed liquid into a vapor stream. 
Many known heat transfer apparatus use a rigid wiper bar that is positively 
driven to rotate within the tube to spread viscous liquids into thin, 
evenly distributed film. However, any rigid, positively driven wiper or 
scraper has drawbacks. First there is a need to introduce and seal a 
rotational drive shaft. Second, because the wiper or scraper is rigid and 
moving over a fixed surface at close spacings, manufacturing and assembly 
become difficult and costly. The surface must be machined to close 
tolerances, as well as the wiper/scraper and its support structures. 
Further, these rigid arrangements are susceptible to, and comparatively 
intolerant of, wear. 
To solve these problems for low viscosity fluids, e.g. 1 to 1,000 c.p., the 
'399 patent describes a whip rod located in the tube which spreads the 
feed liquid into a highly thin and uniform film to reduce its thermal 
resistance and to enhance its evaporation. The whip rod also controls the 
build up of solid residue of evaporation. The '399 patent discloses 
several arrangements for mounting the rod, including lengths of cables, a 
flexible, but non-rotating anchor connected between a base and the lower 
end of the rod, and a double universal joint also connected between the 
lower end of the whip rod and the base. While the whip rod is effective as 
a film distributor, the mounting arrangements have disadvantages. They 
increase the overall material, assembly and operating costs. Also, they 
fail. Material fatigue of flexible cables supporting the whip rods is a 
particular concern. 
While the orbital tube approach has been used for evaporation and 
distillation, heretofore it has not been applied for freezing. One reason 
is that city water freezes to the heat transfer surface of an orbital tube 
evaporator and greatly reduces any performance advantages. 
It is therefore a principal object of this invention to provide an 
apparatus and method for freezing and chilling a process fluid to produce 
a slurry continuously and at greatly enhanced energy efficiencies. 
Another principal object is to provide these results with an apparatus that 
can be readily scaled up in size. 
A further object is to provide a freezer and method of operation that are 
not limited to any one additive and which can freeze and chill a wide 
variety of liquids including seawater and food products. 
Yet another object is to provide the foregoing advantages without requiring 
unfavorable restrictions of operating conditions such as heat flux, 
wetting rate and additive concentration. 
A still further object is to provide a freezer and method of freezing with 
the foregoing advantages that is highly compact. 
Another object is to provide the foregoing advantages while also providing 
favorable capital and operating costs as compared to comparable known 
equipment and methods. 
SUMMARY OF THE INVENTION 
An apparatus for freezing and chilling a liquid feeds the liquid into at 
least one generally vertical, open-ended heat transfer tube at its upper, 
inner surface. In one form an outer tube surrounds each heat transfer tube 
to define a refrigeration chamber. In the preferred form an upward flow of 
a conventional refrigerant over the outer surface of the heat transfer 
tube evaporates at least in part. The resulting outward radial heat flow 
through the heat transfer tube causes a cooling of the liquid on the inner 
tube surface. An additive in the liquid reduces the strength of the 
adherence of the crystals to the heat transfer surface. Suitable additives 
for water are ethylene glycol (automobile antifreeze), propylene glycol, 
seawater, milk, and certain inorganic salts that form anhydrous crystals. 
Suitable additives yield a powdery crystalline structure in the ice, as 
opposed to large, flat, flaky crystal structures. 
A whip rod is located inside each tube. It is preferably free-standing on 
its lower end, supported on a horizontal plate spaced below the tube or 
tubes. The rod is preferably formed of stainless steel, with a circular or 
non-circular cross-section. It flexes to conform to the inner surface when 
whipped. In one form it has a low friction slider secured on its lower end 
and is weighted also near its lower end. 
An orbital drive propels the whip rod or rods to move in an orbital motion. 
In one form the drive propels a shell containing the HTT and structures 
secured to it (a system with mass M). The whip rod is dynamically coupled 
to revolve in response to the orbital motion of the tube or tubes. This 
drive can include a plurality of force carrying members such as cables 
that support the shell from a fixed reference structure via a rigid 
coupling member such as a horizontal mounting plate. The motion is 
generated by at least one, and preferably a pair of counterweights rotated 
by independent motors in phase synchronization. To produce this phase 
synchronization, the distance L from the center of mass M to the center of 
rotation of a counterweight T exceeds .sqroot.2.rho. where .rho. is the 
radius of the orbital gyration of the mass M. 
In another form the HTT or HTT's are stationary, but the whip rod or rods 
orbit within them. In either form, each rod distributes the liquid over 
the inner surface and mechanically dislodges frozen crystals from the 
inner surface. A preferred arrangement for the positive rod drive includes 
a pair of vertically spaced, horizontal plates that hold the rod or rods 
freely in aligned openings in the plates. A set of eccentric cranks drive 
the plates in an orbital motion, which is coupled to the rods via the 
plates. 
The use of these orbital plates is to transmit the orbital motion from an 
orbital drive mechanism to each rod so that in the extreme case all excess 
area on the plate can be eliminated to lighten the mass of the plate and 
to allow the free flow of the fluid into or out from the tubes. 
In some applications the upper orbital plate can also be used to distribute 
the feed via the openings which hold the rods freely with clearance to 
allow the feed to flow through at a predetermined flow rate. In this 
manner the openings used to drive the rods also serve as the feed 
distribution nozzle with the feeds serving as the lubricant of the drive 
mechanism of the rod and the rod as a stirrer to prevent the clogging of 
the nozzle. In this arrangement the plate will be perforated only at the 
openings for driving the rods. 
To increase the heat transfer efficiency at the outer surface of the HTT, a 
generally tubular flow jacket surrounds the HTT with flow openings at its 
upper and lower ends to set up a high speed convection flow of refrigerant 
vapor or vapor/foam over the outer surface. Feed water distribution to 
plural HTT's can include a rotating vane with plural nozzles that varies 
the feed as a function of radius.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an orbital tube freezer/chiller 75 according to the present 
invention. To facilitate the discussion, the invention will be described 
with reference to water as the liquid being processed to form an ice 
slurry 20. A generally vertically oriented, thin-walled, open-ended heat 
transfer tube (HTT) 1 is formed of a material with excellent heat transfer 
characteristics and which is also compatible with the liquid being 
processed and with standard refrigerants. Preferred materials for ice 
slurry operation with a Freon.RTM. refrigerant include copper and steel. 
HTT 1 is inserted concentrically inside an outer tube 2. Annular end walls 
2a at both ends seal tube 2 to HTT 1 to form an annular refrigeration 
chamber 3. 
The assembly of the tubes 1 and 2 is rigidly secured to a horizontally 
extending frame 4 which is in turn attached to the lower ends of cables 5. 
At least three such cables will be used; four are shown. The upper ends of 
the cables 5 attach to a fixed reference structure 6, partially shown. In 
this manner, frame 4 can move freely in an orbital motion 30 in a 
horizontal plane determined by the frame 4 and the cables 5. (There is 
some slight vertical movement as the orbital motion commences or ceases, 
but during steady state operation the frame 4 orbits in substantially one 
plane.) The assembly of tubes 1 and 2 remains in a vertical alignment. 
The orbital motion 30 is produced by the rotation of a pair of 
counterweights 7,7 which are driven to revolve synchronously by a pair of 
motors 8,8. Inside HTT 1 there is a free-standing whip rod 9 which is 
supported at its lower end on a plate 10 attached to the tube assembly by 
a set of rigid members 11,11. In operation, the rotation of counterweights 
7,7 causes the frame 4 and tubes 1 and 2 to orbit (not rotate) in a small 
circle 30. This orbital motion in turn drives the whip rod 9 to revolve 
inside HTT 1. The lower end of the rod 9 slides on the plate 10 along a 
circular path 31. The mechanism of this dynamic coupling and the 
synchronization of the counterweights will be discussed in greater detail 
below. 
The process liquid is introduced to the freezer/chiller 75 as a feed stream 
13 from a feed tube 12 to the upper end of the inside surface la of the 
HTT 1. 
As the freezer/chiller 75 revolves in the orbital motion 30, the whip rod 9 
pushes the feed stream 13 into a downward flowing stream 14 that runs 
principally in front of the rod 9, but with a thin, generally cylindrical 
film 26 of the process liquid remaining on the inner surface la where it 
cools. The stream 14 discharges from the HTT 1 and flows over the plate 10 
as an effluent flow 15 into a tank 19. The effluent stream carries with it 
frozen liquid crystals removed from the surface 1a by the whip rod 9 to 
form the ice slurry 20. 
A conventional refrigeration system 80 includes a compressor and condenser 
16 that delivers a liquified conventional refrigerant via tube 17 to the 
one end (lower end as shown) of the chamber 3 which functions as the 
evaporator of the refrigeration system. The gasified refrigerant returns 
to the compressor/condenser from the opposite end (upper end as shown) of 
chamber 3 via tube 18. The heat of evaporation of the liquefied 
refrigerant is obtained from the HTT 1 by freezing the water inside the 
tube 1. In other words, the latent heat generated by freezing the water 
into ice inside tube 1 is transferred generally radially through the wall 
of tube 1 to its outside surface 1b to supply the latent heat for 
evaporating the liquefied refrigerant into vapor form. Thus, the heat 
transfer property of HTT 1 is essential to the efficiency of the 
freezer/chiller 75 in making ice, or more generally, in 
chilling/thickening the process liquid. 
On the evaporation side of HTT 1, the heat transfer property is improved by 
maintaining a major portion of the outer tube surface 1b in a wetted 
condition. This is accomplished simply and effectively with a rising film 
or rising foam evaporator concept, as illustrated in FIGS. 5-7. A jacket 
tube 35 placed around the HTT 1 partitions chamber 3' into chambers 37 and 
38. (Like parts in the various embodiments have the same reference number, 
but are distinguished by primes.) Holes 36 are formed at the lower end of 
jacket tube 35 and an open space 48 is provided at its upper end so that 
chamber 37 communicates with chamber 38. This construction promotes a 
convection flow between these two chambers when the refrigerant inside 
chamber 37 is warmer than inside chamber 38 due to the heat input from HTT 
or HTT's 1'. 
In particular, when vapors are formed in the refrigerant in contact with 
the HTT 1', they further lower the average density of the liquid column in 
chamber 37 as compared to the average density in chamber 38. This 
accelerates the upward flow rate in chamber 37. In this manner this 
two-phase flow on the HTT 1' sweeps upwardly at a comparatively high 
velocity to improve the heat transfer characteristic of tube 1' by the 
strong shear force of this flow. This decreases the thickness of the 
laminar sub-layer of the liquid film which is the controlling factor of 
the heat transfer rate. 
The dashed circle 2' in FIG. 6 represents the tube of the refrigerant 
chamber 3 in a single tube configuration. The outer tube defines the 
chamber 3 and is the outer housing for the freezer/chiller 75. In the 
multi-tube embodiment of FIG. 5 the outer tube or housing 2' encloses 
multiple HTT's and associated jacket tubes 35. It therefore functions as 
the outer tube 2 in FIG. 1, and as a container or housing for all of the 
HTT-whip rod assemblies. Only a narrow section of the housing tube 2' in a 
multi-tube system is shown in FIG. 5 for clarity. 
The lower portion of FIG. 5 also illustrates a double sheet arrangement to 
provide uniform distribution of the refrigerant to each tube in a multiple 
tube system. In this figure, 40 is the top sheet where the upper end of 
the tubes are secured by welding joints 45 or other standard shop practice 
for such purpose. The upper end of only one adjacent tube assembly is 
shown, but it is representative of all other HTT's 1'. A lower sheet 41 
attaches to the lower end of tube 1 at a joint 46. Sheets 40 and 41 and 
the container wall 2', as well as all of the tubes 1', form the 
refrigerant chamber 3'. An inner partition 42 is placed inside chamber 3' 
in parallel with the bottom tube sheet 41 to form a horizontal chamber 47. 
A narrow gap 43 is provided around each tube to allow the refrigerant to 
flow upwardly from the chamber 47 into the chamber 37 as represented by 
arrow 39. Protrusions 44 may be used to assure the positioning of tube 1' 
to maintain the proper width of the gap 43 and the even distribution of 
the flow of the refrigerant around every tube. An intake 53 of the 
liquefied refrigerant through the tube 17' into the chamber 47, then 
through the passage 37, is gasified enroute upwardly as the flow 39. This 
flow then overflows at the opening 48 into the chamber 38 (upper portion 
of 3'), and is finally evacuated by suction from the top of the container 
via the tube 18'. 
FIG. 7 shows a jacket tube 35' that is not attached to the tube 1' and 
tube/housing 2' assembly and therefore is driven to orbit around HTT 1' in 
a manner similar to the whip rod. 
For an orbital tube freezer, improving the refrigerant side heat transfer 
is more important than in an ordinary freezer because after the heat 
transfer coefficient of the heat transfer tube on the inner, ice side is 
increased by the orbital motion of the whip rod, the heat transfer 
resistance of the HTT 1 or 1' on the refrigerant side becomes the dominant 
factor limiting heat transfer. Experimental test results yielded a heat 
transfer coefficient over 1100 BTU/ft.sup.2, .degree.F., hr. versus 75 
BTU/ft.sup.2, .degree.F., hr. for the traditional plate-type ice 
harvester. 
In making ice slurry, a storage tank 19 is provided to collect the effluent 
15, and to hold the bulk of the slurry product 20. A recirculation pump 21 
propels the product from the tank 19 via the tube 12 to become the feed 
stream 13. 
To facilitate the making of slurry, another principal feature of this 
invention is the use of a small amount of solute, such as conventional 
automobile antifreeze, added to the water stored in the tank 19. A 
solution of about 5% antifreeze is typical. The additive changes the 
crystal structure of the ice that forms on the inner surface 1a. With the 
additive, the ice forms as very fine crystals that have a powdery 
appearance, as opposed to larger crystals which have a visibly flat, flaky 
appearance. The fine, powdery crystals adhere less strongly to the inner 
surface la, and are more readily removed from the surface by the 
mechanical action of the whip rod as it rolls over the ice forming on the 
surface 1a, than the larger, flaky crystals. As the liquid stream 14 flows 
down inside tube 1, it is chilled by the refrigeration system to form ice 
slurry at the lower end of stream 14 which is discharged into the tank 19. 
The system starts with no ice; more ice slurry will be formed as the 
operation progresses until it reaches an ice consistency of between 50% to 
70%, limited mostly by the flow of liquid slurry to the pump suction. 
The nature and amount of the additive depend upon many other engineering 
parameters such as the shape, size and weight of the whip rod; the radius 
and speed of the orbital motion; the heat flux density; the flow rate of 
the feed; the evaporation side heat transfer coefficient, and the surface 
conditions of the HTT 1. Many, but not all substances promote the 
formation of the fine crystals needed for the orbital tube freezer/chiller 
("OTF") 75 to work. Substances known to work include certain brands of 
automotive antifreeze, milk, calcium magnesium acetate, and certain 
inorganic salts such as sodium bicarbonate and those found in seawater. 
Commercially available automobile antifreeze compounds are all ethylene 
glycol based, with approximately 95% ethylene and diethylene glycol 
content. Antifreeze formulations differ in the secondary additives used to 
prevent corrosion, limit oxidation, control foaming, and govern product 
appearance. Ethylene glycol is the primary additive, having the function 
of depressing the freezing point of the automobile radiator fluid. 
Diethylene glycol is an impurity present in the industrial grade of 
ethylene glycol used by antifreeze manufacturers. 
Automobile cooling systems may contain copper, aluminum, cast iron and 
steel. These materials are protected from corrosion by secondary additives 
such as pH buffers (pH 9 works well), as well as by corrosion inhibitors 
(which may be specific for one material). Potassium or sodium hydroxide 
and phosphoric acid work well as pH buffers. Alkali borates and phosphates 
will protect all four materials. Sodium or potassium nitrate will protect 
aluminum. Various organic compounds (such as tolyltriazole) protect 
copper. Silicates and silicate stabilizers are also commonly added. 
Antifreezes that work with the present invention promote formation of very 
fine ice crystals. Additives that do not work promote formation of much 
larger crystals having a noticeably flat appearance. Antifreeze compounds 
may be screened by leaving a test solution overnight in the freezing 
compartment of a household refrigerator. Successful antifreeze 
formulations form into a thick, but stirrable slush. Unsuccessful 
formulations form large flakes of ice and cannot be stirred. Thus far the 
only automobile antifreezes that are not suitable at 5% concentration are 
the ones manufactured by First Brands Corp. under the trade designations 
"Prestone.RTM." and "STP Heavy Duty.RTM." which state that they contain a 
patented anti-corrosive additive. 
With automobile antifreeze, the freezing point depression increases with 
glycol concentration, so the temperature in the slush tank steadily drops 
as ice is formed. It is also possible to run an orbital tube 
freezer/chiller 75 with a constant freezing temperature by using a 
saturated solution of an inorganic salt. When an excess of the salt is 
present, the aqueous phase always contains the same (saturated) 
concentration of salt regardless of the amount of ice that has been 
formed. The freezing point depression (which depends on concentration) and 
hence freezing point are both constant in such cases. These so-called 
eutectic mixtures of salts may be useful when designing lower temperature 
thermal storage systems. For example, a eutectic mixture of sodium 
bicarbonate freezes at 27.degree. F. Not all eutectic mixtures work. 
However, successful salts all formed anhydrous crystals. 
Turning now to the design and operation of the whip rod 9, as the whip rod 
orbits over the surface 1a it pushes the stream 14 in the direction 30. 
This action leaves the thin film 26 behind the rod. Freezing takes place 
both in the turbulent flow stream of 14 and the thin film 26. Both the 
turbulence in the stream 14 and the thin film greatly enhance the heat 
transfer property of the freezing. For this reason, the whip rod 9 not 
only prevents ice from sticking to the tube surface 1a, but also improves 
the efficiency of the overall refrigeration system. 
In operation, the whip rod glides over the thin fluid film 26 by a 
hydrofoil action and thereby minimizes the wear and the friction loss. 
Furthermore, the rod is driven by the motors 8,8 to revolve through the 
dynamic coupling of the orbital motion; it is not driven mechanically like 
a traditional wiper. For this reason, extreme longitudinal stiffness of 
the rod is not needed; it is sufficient merely that the rod be able to 
stand on end. In fact it should be sufficiently flexible for the rod to 
conform with the shape of the tube, which may not be perfectly round or 
straight due to manufacturing tolerances. 
In an orbital type heat transfer device free revolving rods are employed so 
that the centrifugal force of each section of the rods along its entire 
length is responsible for its own prescribed function such as to create 
turbulence in the fluid or to prohibit the deposit of solids upon the heat 
transfer surface. In contrast to positively driven wiper which derives its 
engaging pressure through mechanical means, the orbital driven rod depends 
upon its own mass to produce the desirable function, and in a sense works 
like a whip, and is therefore called the whip rod. 
The dynamic coupling and ice removal efficiency are also functions of rod 
properties such as its weight, and cross-sectional configuration. To yield 
the necessary weight and rigidity for ice removal, steel or stainless 
steel are preferred materials. A four foot (1.22 m) length whip rod 9 is 
preferably circular in cross-section with a diameter of 154 inch (0.94 
cm). In addition to the circular cross-section shown in FIGS. 1, 3 and 
5-8, it is also possible to use non-circular cross-sections such as 
rectangular rod 9* (FIG. 2), triangular 9** (FIG. 2 in phantom), or gear 
shaped 9*** (FIG. 4). The rectangular and triangular shapes work better at 
low additive concentrations than the free-rolling, round rod 9 (FIG. 3). 
The edges produce a chisel action. The gear shape combines features of 
both the circular and angled edge shapes. 
FIG. 5A shows an alternative whip rod design which has been found to be 
more effective with taller units, e.g. those with the aforementioned four 
foot length tubes and rods. A slider 90 of a low friction material is 
secured on the lower end of the rod to facilitate movement of the rod over 
plate 10'. A weight 92 is secured on the rod near its lower end to enhance 
the dynamic coupling to the orbiting tube 1'. 
Because the whip rod is driven to revolve by the orbital motion of the 
tube, system capacity may be increased conveniently by adding more heat 
transfer tubes and rods, driven by the same orbital drive system, 
proportionally enlarged. This scaleability is a major advantage of the OTF 
freezer/chiller 75. 
The use of a wiper and a stirrer in an old fashioned ice cream maker is a 
well known art. Here a strong positively engaged mechanism is employed to 
move the ingredient which usually has a very high viscosity such as 
1,000,000 c.p. or higher. In an orbital type heat transfer device the 
viscosity range of the fluid to be handled are much lower such as less 
than 1,000 c.p. while the throughput of the fluid per tube is usually 
quite significant such as 1 gal/min. 
The use of one or more sets of rotating counterweights to introduce an 
orbital motion in a heat transfer apparatus was discussed in the 
aforementioned U.S. Pat. No. 4,762,592. In essence, in this prior 
arrangement the mass center of the counterweights tends to balance against 
the mass of the main container, as well as all whip rods, in a 180.degree. 
phase angle relationship with respect to a common orbital center. This 
effect is analogous to a hammer thrower leaning backwards to swing the 
hammer, or a male ice skater leaning backwards to swing his partner. For 
orbital drive with two counterweights as shown in FIG. 1 (and again in 
FIG. 8 for a multi-tube system), one straightforward solution would be to 
drive the two (or more) counterweights in synphaseous condition through 
various forms of mechanical coupling such as timing belts, connecting 
rods, gears, or an electrical servo system to make the counterweights 
behave like one single counterweight, with an effective common mass center 
revolving around the center of the main mass in the same horizontal plane. 
In practice it has been found, however, that the two counterweights as 
shown in FIG. 1 or FIG. 8 may synchronize with each other automatically in 
either one of two modes i.e. either a desirable 0.degree. phase angle mode 
or an undesirable 180.degree. phase angle mode, depending upon the 
distribution of the main mass M the container, HTT's, whip rods, and all 
masses rigidly coupled to them such as the frame 4, sheets 40, 41 and 42, 
members 11,11 and plate 10. 
Indeed, all whip rods in the HTT's in the main container 2' shown in FIG. 8 
are driven to revolve near the 180.degree. phase difference with respect 
to the counterweights. By this logic one would think the effect of two 
counterweights upon each other would also follow this tendency to assume a 
180.degree. phase angle between them. In one simple case, with zero 
orbital motion, it is readily shown that two independently driven 
counterweights mounted on the same center axis would stabilize themselves 
at 180.degree. apart, as in the hammer toss example given above. But for 
the present purposes, a zero degree phase difference is desired. 
The mutual synchronization effect between two independently driven 
counterweights mounted symmetrically as shown in FIG. 8 falls in the 
general class of dynamic problems treated theoretically in a 
"Synchronization In Science And Technology" by I. I. Bleckhman with an 
English translation published by ASME Press (1988 edition, p. 78). It can 
be shown that satisfactory orbital drive can be obtained with two 
independently driven counterweights if they are positioned sufficiently 
apart from the center of the main mass M. Otherwise they will assume the 
180.degree. mode to cause the main mass to oscillate in a torsion mode 
instead of the orbital mode. More specifically, in order for the system to 
achieve a synphaseous running mode, it should satisfy the relationship 
EQU L&gt;.sqroot.2.rho. 
where 
L is the distance of the pivot of the counterweights from the system 
center, 
.rho. is the radius of gyration of the main mass M. 
This condition checks very well with experimental results to the extent 
that either mode of synchronization can be maintained even with the power 
input of either one of the two driving motors 8,8 cut off. This condition 
is also quite practical. For instance in the layout of FIG. 8 the value of 
L is almost equal to 2.rho. by simple design rule. 
FIG. 9 shows an alternative approach to orbital tube heat transfer system 
where the tube assembly is stationary while the whip rods 9 are driven in 
an orbital motion. In this figure, an upper orbital rod driving plate 101 
and a lower orbital rod driving plate 102 each extend generally 
horizontally in a parallel spaced relationship. Holes 103 in the upper 
plate 101 engage loosely the upper ends of the rods 9. Holes 104 in the 
lower plate 102 similarly engage the lower ends of the rods. Plates 101 
and 102 are driven into orbital motion by at least one shaft 110 acting 
through brackets 111,111, eccentric cranks 109,109, and crank pins 108,108 
that engage bearings 107,107 secured on the plates. Two additional cranks 
are used in each of the upper and lower plates to duplicate as much as 
possible the translational motion in similar kinds of drives commonly used 
for orbital shakers. Shaft 110 is driven by motor 116 through pulleys 112 
and 114 coupled together by a belt 113. Rotation of the motors 116 rotates 
the shafts 110 which drives the plates 101, 102 and the rods 9 engaged in 
the plates in an orbital motion. Alternatively a single motor 116' (FIG. 
9A) located over the housing 1 rotates a drive shaft 110' that penetrates 
through an end wall of the housing in a rotary bearing 190. A 
counterweight 7a is mounted on the shaft. An eccentric 109' connects the 
drive shaft to a second shaft 108' that extends through one of the HTT's 1 
to another eccentric 109' coupled to a shaft 110a' that rotates in a 
bearing 190 in the other housing end wall. Shaft 110a' also carries a 
counterweight 7a. 
Feed fluid 120 is introduced to the upper plate 101. Since the tubes are 
stationary, the distribution of the liquid evenly over the tubes can be 
accomplished by traditional methods such as a weir type distributor. FIG. 
12 illustrates the use of the upper orbital drive plate 101 to distribute 
the feed through the openings 103 used to drive the upper ends of whip 
rods 9. In this manner the feed serves as the lubricant for rods 9 moving 
inside the opening 103 and the motion of the rod 9 keeps the opening 103 
from being clogged up by any solids which might be carried by the feed 
including the formation of ice. 
The effluent discharge 15 of FIG. 11 escapes downwardly via holes 106 in 
the lower plate 102 located generally below each HTT 1. 
In the FIGS. 1, 5, and 8 embodiments, the process fluid 14 flowing down the 
tube 1 is driven to revolve inside the tube through the orbital dynamic 
coupling even without the rod or rods. Whereas in the FIG. 9 fixed tube 
arrangement, the fluid inside the tube is spread primarily by the 
revolving rod which generates the engaging pressure by its centrifugal 
force while revolving inside the tube. The rod 9 is a whip rod, not a 
wiper rod. It is free-standing on its lower end on plate 10. It is free to 
assume a position vis-a-vis the associated surface 1a pursuant to the 
design and operational factors discussed above. 
By driving the rod with a positive mechanism may appear to be cumbersome, 
but there are significant advantages in driving a rod, including its 
associated mechanisms, which weigh less than 10% of the entire 
freezer/chiller 75. As a result it is possible to avoid using a heavier 
suspension system for much heavier equipment and to eliminate the need for 
couplings with a large flexibility for handling the flow of the 
pressurized refrigerant between the moving heat transfer apparatus and the 
associated stationary equipment. 
This fixed tube/orbiting rod embodiment is particularly well suited to 
applications where the inertial reference frame in which the 
freezer/chiller 75 is mounted moves, as on a sea-going vessel or any 
moving transport. One practical application is the refrigeration of 
seafood caught and stored on a fishing vessel. 
One concern of the FIG. 9 orbital rod embodiment is that it is preferable 
to locate the electric motors 116 on the outside of the housing/tube 2, 
which then necessitates some form of seal between driving plates 101,102 
and the motor. Known rotary seals of a variety of forms can be used. 
However, any such seal is subject to wear and failure, and it introduces 
an added cost. 
An alternative sealing and drive arrangement which does not use rotary 
seals is illustrated in FIG. 10. An outside shell 119 surrounds and 
encloses multiple heat transfer assemblies 1,2 each with an associated 
whip rod 9. A pair of rigid rings 120,120 each act as an orbital rod drive 
plate. Two sets of wires 121 and rod mounting rings 103 interconnected as 
shown in the form of a net transmit the orbital motion from each ring 120 
to the individual whip rods. Each ring 120 is stretched between two sets 
of cables 122,122 and 122*,122*, driven through drive plates 124 and 124* 
with four bellows 123 serving as the seal. A linear oscillatory motion of 
the two sets of drive plates 124,124* is coordinated to produce a 
resultant orbital motion. 
The FIG. 10 drive also lends itself to use with a rotating vane type fluid 
distributing system as shown in FIG. 11. It employs nozzles 134-137 and 
134'-137' mounted on a rotating vane 133 to distribute the fluid evenly 
over the upper end of the HTT's 1. Fluid is introduced into a main conduit 
130 with holes 140 and a thrust bearing 131 upon which the housing 132 of 
the rotating vane is supported. The hollow vane 133 is made of two 
diametrically aligned arms, as illustrated, each carrying several nozzles 
134-137 and 134'-137'. Their orientation pushes the vane to rotate in a 
predetermined direction, like a lawn sprinkler. The orifice of the nozzles 
are adjusted so that for a given pressure drop the flow rate of each spray 
141-144 is in ratio to its radius from the rotation center so that the 
flow received by each tube 1 is generally uniform. Concentric divider 
rings 160-163 are also provided to minimize the cross flow between annular 
tracks of the revolving sprays 141-144. 
Viewed as a process, the present invention involves providing a heat 
transfer tube, orienting it generally vertically, flowing a liquid over 
the inner surface of the heat transfer tube, refrigerating the outer 
surface of the tube, and mechanically removing liquid that freezes to the 
inner surface by orbiting a whip rod over the surface. The process also 
includes adding a chemical agent to the liquid which reduces the strength 
of the bond between the crystals and the inner surface to facilitate the 
mechanical removal. 
In a preferred form, the cooling is by flowing a refrigerant liquid 
upwardly over the outer surface so that it evaporates. It also involves 
producing a high speed convection flow of refrigerant and evaporated vapor 
over the outer surface to enhance the heat transfer coefficient. The 
process is also preferably continuous, with the flow exiting the tube 
being collected and recirculated back to the tube. The process is also 
scaleable, both in size and number of heat transfer tubes as by 
simultaneously feeding liquid to plural heat transfer tubes, collecting 
the effluent from the plural tubes, and recirculating it. The mechanical 
removing includes both 1) driving the tube or tubes in an orbital motion 
with the whip rod or rods driven through a dynamic coupling and 2) driving 
the whip rod or rods by a positive coupling, with the tube or tubes 
stationary. The driving process includes rotating plural counterweights 
rigidly secured to the tube or tubes in phase synchronization with each 
other and placing the counterweights at a distance L from the center of 
mass of the system such that L is greater than .sqroot.2.rho. where .rho. 
is the radius of gyration of the system mass M. In the positively driven 
rod form of the invention, the orbital driving includes producing an 
orbital motion, coupling it mechanically to the rod or rods, and sealing 
the region of the orbital motion producing from the region adjacent the 
heat transfer tube. 
By way of illustration, but not of limitation, a freezer/chiller 75 of the 
type shown in FIGS. 5-8 uses seven HTT's, each four feet (1.2 m) high, 
made of carbon steel with a wall thickness of 0.049 inch (1.24 mm) and an 
outside diameter of 11/2 inch (3.175 cm). The whip rods are each also four 
feet high with a circular, 3/8 inch (0.95 cm) diameter cross-section and 
made of stainless steel. The additive is a 5%-10% solution of automobile 
antifreeze in water fed at a rate of about 1.2 gpm per tube. The orbital 
drive produces a 1/4 inch (0.635 cm) orbital radius (.rho.) at 380 rpm. 
This arrangement has proven to be able to produce ice slurry continuously 
with a heat transfer of more than 800 BTU/sq.ft/hr/.degree.F., about three 
times better than current freezers for slippery ice and about ten times 
better than current plate-type ice harvesters. Even greater efficiencies 
should be attainable using the general orbital tube approach of this 
invention. 
Compared to the new "slippery ice" freezers, there is a decided advantage 
in that only one additive is known to make the slippery ice technique 
work, whereas the present invention can use a wide range of additives, 
including seawater. Another advantage is over a two-fold improvement in 
heat flux--slippery ice starts to stick to the heat transfer surface when 
the heat flux gets too high. Another advantage is a higher freezing point, 
e.g. -1.7.degree. C. versus -2.3.degree. C. for slippery ice, which, 
depending on the ambient temperature, can translate into energy cost 
savings of 2% to 3%. Using higher molecular weight additives in the 
present invention (with corresponding increase in freezing temperature) 
can produce even greater savings. Slippery ice units require highly 
polished surfaces to keep the ice from sticking; the present invention has 
no such requirement. Also, the reduction in equipment size, about 2:1 
orbital tube versus slippery ice and 10:1 versus known plate type ice 
harvesters, produces equipment cost savings, even after accounting for the 
extra cost of an orbital drive. 
There has been described a freezing and chilling apparatus and method that 
produces a chilled and/or frozen slurry continuously, compactly, and with 
many times greater heat transfer efficiency than heretofore available. The 
invention is not restricted to any process liquid or any one additive. The 
equipment and process are readily scaleable. The equipment has no critical 
alignments or wear sensitive components, as with mechanical wiper systems. 
While the invention has been described with respect to an upflow 
evaporation system, it will be understood that many arrangements can be 
used to withdraw heat at the outer surface of the heat transfer tube. A 
wide variety of arrangements can also be used to develop the desired 
orbital motion. An arrangement using spring loaded struts acting in 
combination with one or more coaxial rotating counterweights, for example, 
is described in U.S. Pat. No. 4,762,592. Non-mechanical drives are also 
possible, e.g. magnetic coupling to an orbiting element inside the 
freezer/chiller. Also, while the invention has focussed on the production 
of an ice slurry for cold storage applications, it can be used for any 
application where it is desired to chill or freeze a liquid, as in 
concentration of food products such as fruit juices. These and other 
modifications and variations are intended to fall within the scope of the 
appended claims.