U.S. patent application number 11/720347 was filed with the patent office on 2008-06-05 for warewash machine havaing controlled drop size and/or weber number and related design process.
This patent application is currently assigned to PREMARK FEG L.L.C.. Invention is credited to Harald Disch, James E. Doherty, Kui-Chiu Kwok, Charles E. Warner.
Application Number | 20080128004 11/720347 |
Document ID | / |
Family ID | 36190475 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080128004 |
Kind Code |
A1 |
Doherty; James E. ; et
al. |
June 5, 2008 |
Warewash Machine Havaing Controlled Drop Size And/Or Weber Number
And Related Design Process
Abstract
A design process for a conveyor-type warewash machine involves
consideration of Weber number for flow from nozzles within at least
one zone of the machine. Warewash machines having one or more zones
with flows within certain Weber number limits or ranges are also
described.
Inventors: |
Doherty; James E.; (Gurnee,
IL) ; Warner; Charles E.; (Troy, OH) ; Kwok;
Kui-Chiu; (Gurnee, IL) ; Disch; Harald;
(Elzach, DE) |
Correspondence
Address: |
THOMPSON HINE LLP;Intellectual Property Group
P.O Box 8801
DAYTON
OH
45401-8801
US
|
Assignee: |
PREMARK FEG L.L.C.
Wilmington
DE
|
Family ID: |
36190475 |
Appl. No.: |
11/720347 |
Filed: |
December 5, 2005 |
PCT Filed: |
December 5, 2005 |
PCT NO: |
PCT/US05/44011 |
371 Date: |
May 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60634966 |
Dec 10, 2004 |
|
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|
Current U.S.
Class: |
134/61 |
Current CPC
Class: |
A47L 15/24 20130101 |
Class at
Publication: |
134/61 |
International
Class: |
A47L 15/24 20060101
A47L015/24 |
Claims
1. A warewash machine, comprising: a housing having a ware inlet
toward one and a ware outlet toward an opposite end, a plurality of
warewash zones within the housing between the ware inlet and the
ware outlet, including at least a wash zone, a post wash zone and a
final rinse zone, the post wash zone is between the wash zone and
the final rinse zone; a ware conveyance path extending through the
housing from the ware inlet to the ware outlet; a first one of the
warewash zones includes a plurality of nozzles located to direct
liquid onto wares passing through the first warewash zone, liquid
temperature in the first warewash zone is greater than 65.degree.
C., and at least 85% of flow output by the nozzles in the first
warewash zone consists of drops that have a Weber number that is in
the range of about 800 to 1200.
2. The warewash machine of claim 1 wherein a second one of the
warewash zones includes a plurality of nozzles located to direct
liquid onto wares passing through the second warewash zone, liquid
temperature in the second warewash zone is less than 65.degree. C.,
and at least 85% of flow output by the nozzles in the second
warewash zone consists of drops that have a Weber number that is
less than about 1200.
3. The warewash machine of claim 2 wherein the first warewash zone
is the post wash zone and the second warewash zone is the final
rinse zone, post wash liquid temperature in the post wash zone is
between about 65-85.degree. C., the wash zone includes a plurality
of nozzles located to direct wash liquid onto wares passing through
the wash zone.
4. The warewash machine of claim 3 wherein operating pressure of
nozzles in the post wash zone is between about 0.4 and 0.8 bar, and
the nozzles of the post wash zone output a range defined drop size
of about 0.75 to 2.80 mm.
5. The warewash machine of claim 4 wherein operating pressure of
nozzles in the post wash zone is between about 0.6 and 0.8 bar, and
the nozzles of the post wash zone output a range defined drop size
of about 0.75 to 2.00 mm.
6. The warewash machine of claim 5 wherein operating pressure of
the nozzles in the post wash zone is about 0.7 bar and the nozzles
of the post wash zone output a range defined drop size of about
1.00 to 1.75 mm.
7. The warewash machine of claim 4 wherein operating pressure of
nozzles in the wash zone is between about 0.3 bar and 0.5 bar, and
the nozzles of the wash zone output a range defined drop size of
about 1.50 to 4.00 mm.
8. The warewash machine of claim 7 wherein nozzles in the final
rinse zone output a range defined drop size of about 0.10 to 0.40
mm.
9. The warewash machine of claim 3 wherein wash liquid temperature
in the wash zone is less than 65.degree. C., at least 85% of flow
output by nozzles in the wash zone consists of drops that have a
Weber number that is less than about 1200.
10. The warewash machine of claim 3 wherein at least 95% of flow
output by the nozzles in the post wash zone consists of drops that
have a Weber number in the range of about 800 to about 1200, and at
least 95% of flow output by the nozzles in the final rinse zone
consists of drops that have a Weber number that is less than about
1200.
11. The warewash machine of claim 3 wherein wash liquid temperature
in the wash zone is at least 65.degree. C., at least 85% of flow
output by nozzles in the wash zone consists of drops that have a
Weber number in the range of about 800 to 1200.
12. The warewash machine of claim 1 wherein the first warewash zone
is the final rinse zone, final rinse liquid temperature in the
final rinse zone is at least 70.degree. C., the wash zone includes
a plurality of nozzles for directing wash liquid onto wares and the
post wash zone includes a plurality of nozzles for directing post
wash liquid onto wares.
13. The warewash machine of claim 12 wherein post wash liquid
temperature in the post wash zone is at least 65.degree. C., at
least 85% of flow output by the nozzles in the post wash zone
consists of drops that have a Weber number in the range of about
800 to about 1200.
14. The warewash machine of claim 13 wherein wash liquid
temperature in the wash zone is at least 65.degree. C., at least
85% of flow output by the nozzles in the wash zone consists of
drops that have a Weber number in the range of about 800 to about
1200.
15. The warewash machine of claim 13 wherein wash liquid
temperature in the wash zone is less than 65.degree. C., at least
85% of flow output by the nozzles in the wash zone consists of
drops that have a Weber number less than about 1200.
16. The warewash machine of claim 12 wherein final rinse liquid
temperature in the final rinse zone is at least 75.degree. C.
17. The warewash machine of claim 12 wherein operating pressure of
nozzles in the final rinse zone is between about 0.4 and 0.8 bar,
and the nozzles of the final rinse zone output a range defined drop
size of about 0.75 to 2.80 mm.
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. (canceled)
Description
TECHNICAL FIELD
[0001] The present application relates generally to machines used
to wash kitchen wares such as dishes, glasses, utensils and pots
and pans, and more particularly to a warewash machine that makes
effective use of nozzle pressure and/or drop size to achieve
desired Weber number criteria for various warewash zones and/or
during various portions of the warewash cycle.
BACKGROUND
[0002] It is known to provide varying types of warewash machines.
Two of the most common types of commercial machines are the single
rack-type box unit and the conveyor-type unit. The former may
include a single chamber into which a rack of soiled ware can be
placed. Within the chamber, the entire cleaning process, typically
including washing, rinsing and drying is performed on the rack.
Multiple racks must be washed sequentially, with each rack being
completely cleaned before the next can be operated upon. A
conveyor-type machine, on the other hand, includes a conveyor for
carrying individual items or entire racks of ware through multiple
stations within the machine housing. A different operation may be
carried out at each station, such as washing, rinsing, or drying.
Thus, multiple items or racks of ware can be placed on the conveyor
and moved continuously through the machine so that, for example,
while one item or rack is being rinsed, a preceding item or rack
can be dried. One difficulty encountered in the construction of
such machines, regardless of type, is balancing effective washing,
rinsing and sanitizing with the goal of limiting the amount of
energy, liquid, detergents, rinse agents and sanitizers used for
such washing and rinsing, while at the same time taking into
account throughput of the machine.
[0003] To the knowledge of applicants, there is no history of
managing drop size in warewash machines. The classic debates have
been over high pressure vs. low pressure liquid flows and which
produces cleaner dishes. There is also a general awareness that
liquid flow rates in the rinse section (or rinse process step)
should be as low as possible to conserve energy, water and other
consumables, particularly when the rinse section or process uses
especially hot water. There are also general concerns about total
liquid flow and total time ware is wet and the usual practice is to
add more nozzles to achieve this result; nozzle sizes chosen are
usually something practical so the number of nozzles is not
excessive for a given desired total flow rate. In all cases the
drop size found in a particular machine at a particular location is
what ever it turns out to be. It is well known that drop size
distributions from a typical nozzle, such as a fanjet nozzle, are
very broad indeed. Design concerns typically focus on "coverage" or
the distribution of water from place to place within the
machine.
SUMMARY
[0004] In one aspect, a method of constructing a conveyor-type
warewash machine including a housing having a ware inlet toward one
and a ware outlet toward an opposite end, a plurality of warewash
zones within the housing between the ware inlet and the ware
outlet, including at least a wash zone, a post wash zone and a
final rinse zone, the post wash zone is between the wash zone and
the final rinse zone, the method comprising the steps of: for a
given zone, selecting a maximum Weber number; selecting a nozzle
construction and operating pressure for the given zone such that
flow from the selected nozzle construction at the selected
operating pressure produces drops in accordance with the selected
maximum Weber number; positioning and orienting a plurality of
nozzles having the selected nozzle construction such that flow from
the plurality of nozzles produces desired coverage for the given
zone.
[0005] In another aspect, a warewash machine includes a housing
having a ware inlet toward one and a ware outlet toward an opposite
end. A plurality of warewash zones are within the housing between
the ware inlet and the ware outlet, including at least a wash zone,
a post wash zone and a final rinse zone. The post wash zone is
between the wash zone and the final rinse zone. A ware conveyance
path extends through the housing from the ware inlet to the ware
outlet. The wash zone includes a plurality of nozzles located to
direct wash liquid onto wares passing through the wash zone. Wash
liquid temperature in the wash zone is less than 65.degree. C., and
at least 85% of flow output by nozzles in the wash zone consists of
drops that have a Weber number that is less than about 1200. The
post wash zone includes a plurality of nozzles located to direct
post wash liquid onto wares passing through the post wash zone.
Post wash liquid temperature in the post wash zone is between about
65-85.degree. C., and at least 85% of flow output by the nozzles in
the post wash zone consists of drops that have a Weber number in
the range of about 800 to about 1200. The final rinse zone includes
a plurality of nozzles located to direct final rinse liquid onto
wares passing through the final rinse zone. Final rinse liquid
temperature in the final rinse zone is less than 65.degree. C., and
at least 85% of flow output by the nozzles in the final rinse zone
consists of drops that have a Weber number that is less than about
1200.
[0006] In yet another aspect, a warewash machine includes a housing
having a ware inlet toward one and a ware outlet toward an opposite
end. A plurality of warewash zones are located within the housing
between the ware inlet and the ware outlet, including at least a
wash zone, a post wash zone and a final rinse zone. The post wash
zone is between the wash zone and the final rinse zone. A ware
conveyance path extends through the housing from the ware inlet to
the ware outlet. The wash zone includes a plurality of nozzles
located to direct wash liquid onto wares passing through the wash
zone. The post wash zone includes a plurality of nozzles located to
direct post wash liquid onto wares passing through the post wash
zone. The final rinse zone includes a plurality of nozzles located
to direct final rinse liquid onto wares passing through the final
rinse zone. Final rinse liquid temperature in the final rinse zone
is at least 65.degree. C., and at least 85% of flow output by the
nozzles in the post wash zone consists of drops that have a Weber
number in the range of about 800 to about 1200.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a perspective view of one embodiment of a
conveyor-type unit;
[0008] FIG. 2 is a side elevation of the unit of FIG. 1;
[0009] FIG. 3 is a graph of plate temperature vs. evaporation;
[0010] FIG. 4 is a graph of drop velocity vs. pressure;
[0011] FIG. 5 depicts drop deformation upon impact with a flat
surface of a ware;
[0012] FIG. 6 is a graph showing drop size vs. pressure for three
different Weber numbers;
[0013] FIG. 7 a graph of evaporation heat loss vs. temperature for
certain drop sizes;
[0014] FIG. 7a is a graph showing drop size vs. temperature to
achieve 90% heat transfer to wares;
[0015] FIG. 8 is a graph of ware temperature vs. distance through
an exemplary conveyor machine;
[0016] FIGS. 9-11 depict one embodiment of a rinse arm; and
[0017] FIGS. 12-13 illustrate one embodiment of an undercounter
warewash box-type unit.
DETAILED DESCRIPTION
[0018] Referring to FIGS. 1 and 2, a conveyor-type unit 10 includes
a housing 12 with a conveyor 14 extending therethrough. The
conveyor 14 may be formed by spaced apart belts or a dog-type
system as described in U.S. Pat. No. 6,559,607. Other types of
conveyor systems could also be used, including conveyors pre-formed
with structures for receiving and supporting individual wares.
Whatever the construction of the conveyor, the region generally
above the conveyor represents a ware receiving area within the
housing 12.
[0019] The unit 10 includes an entry side 16 and an exit side 18. A
wash section 20 within the housing includes one or more wash arms
22 for directing wash liquid or other wash media onto wares
traveling along the conveyor 14. The wash liquid may be
recirculated by a suitable pump through a wash liquid tank 24
located beneath the wash section to receive the wash liquid as it
falls from the wares. The tank 24 may typically include an overflow
drain as well as a manual or automatic drain mechanism to enable
draining of the entire tank 24. In the illustrated embodiment the
wash arms 22 are located beneath the conveyor 14 to direct wash
liquid upward onto the wares. Other locations for the wash arms 22
are possible, including toward the top of the housing and on the
sides of the housing. A rinse section 26 located downstream of the
wash section 20 includes rinse arms 28 that direct rinse liquid
onto wares traveling along the conveyor 14. In the illustrated
embodiment, an upper rinse arm directs rinse liquid downward onto
the wares and a lower rinse arm directs rinse liquid upward onto
the wares. Other locations for the rinse arms are possible, such as
toward the sides of the housing. One or more pre-wash sections may
precede the wash section 20, each such section including its own
respective nozzles for directing liquid onto wares. Further, the
rinse section 26 could implement the "final rinse" operation and
one or more additional sections, sometimes referred to as post-wash
or pre-rinse sections, could be located between the wash section 20
and the rinse section 26. Thus, in a conveyor type machine it is
common to have different sections of the machine for carrying out
different actions with respect to the wares traveling through the
machine.
[0020] Applicants' research efforts indicate that in warewash
machines direct management of liquid drop size within the machine
can yield highly thermally efficient machines capable of effective
cleaning of wares. To understand how this is so requires
consideration of the fundamental functions that are active in the
machine. The primary warewash functions are (i) wetting ware, (ii)
removing soil, (iii) heating (this includes sanitizing) ware, (iv)
removal of wash residue or rinsing ware and (v) drying ware. The
manner in which the last three functions are accomplished has a
significant impact on thermal efficiency.
[0021] There is an optimum drop size for heating ware with hot
water. This size generally depends on the velocity of the drop
which itself depends on pressure at the orifice where the water jet
that forms the drop emerges. FIG. 4 attached shows the general
relationship between drop velocity and driving pressure for
practical nozzles used in warewash machines.
[0022] When drops at low velocities and low Weber numbers (the
Weber number is, for a drop, the ratio of the inertial energy to
the surface tension energy), impact a surface they expand into disk
shaped areas. Weber number (We) can be expressed as:
We=(.rho.v.sup.2l)/.sigma.
Where:
[0023] l=characteristic length [0024] v=velocity [0025]
.sigma.=surface tension [0026] .rho.=density
[0027] An example showing drop deformation at impact is shown in
FIG. 5, which is for a 1.5 mm drop impacting at 1 m/sec; with times
given in milliseconds.
[0028] The final diameter of the wetted area is dependent on
surface tension so that in the extreme of the high surface tension
case a small drop will immediately contract into a hemispherical
dome and not expand across the surface but bounce from it. In the
practical warewash case, the final disk size is typically 2.5 to 4
times the original drop diameter. The rate at which the impacting
drop expands into the disk depends on the impact velocity. If the
velocity is low enough then the expanding disk can keep ahead of
the impacting drop. If the velocity is high then water in the
impacting drop will splatter or bounce and not maintain contact
with the surface, which it must if heat in the drop is to be
transferred to the ware. Typically the transition between high and
low case is at Weber numbers around 1000 or more generally in the
range of 800 to 1200.
[0029] Hot water drops transfer heat to the ware by: a) forced
convection as the water in the drop spreads across the surface and
b) conduction as the thin expanded layer of drop water transfers
heat to the surface. The expanding water disk transfers heat
because water is flowing over the ware surface as the disk expands.
A fully expanded drop transfers heat by conduction because there is
no movement. Drop size unto itself is important. For Weber numbers
less than 1000 (typically drop sizes less than 5 mm and velocities
less that 4 m/sec) the film thickness of expanded drops on surfaces
is greater for larger drops than it is for smaller drops since the
drop expansion ratio is independent of drop size. This means that
conduction heat transfer is less effective for larger drops. The
time needed to transfer the heat energy of the drop becomes much
longer than the residence time of the drop on (inclined) ware. The
resultant effect can be envisioned by considering the extreme of a
drop as large as the ware; not much of the water ever reaches very
close to the ware surface as the very large drop impacts the ware.
Said another way it is better that the water interacts with the
ware as many more smaller drops than fewer larger drops. The
threshold between large and small drops is dependent on nozzle
pressure and is shown in FIG. 6. FIG. 6 shows that the maximum
allowable drop size decreases as the nozzle pressure increases.
This result is due to the fact that flow velocity increases with
pressure for a fixed nozzle size. The upper limit in drop size
exists because when the Weber number is too high, the surface
tension energy is too low to hold the drop together in a desired,
single volume. Drops may break up while passing through the air,
and any drops that make it to the ware surface in one piece will
break apart and rebound from the ware surface, rendering much of
the drop ineffective to transfer heat to the ware. While the Weber
number for the larger drops is low, at some point the drops become
too large, as the drops will be too thick when spread on the ware
surface to effectively transfer heat by conduction, and much of the
water of the drop will leave the ware before the desired amount of
heat transfer has taken place. As a general rule, and again
referencing FIG. 6 and the Weber number equal to 1000 curve, for a
nozzle operating with a pressure that is 0.5 bar or higher, a drop
of 2 mm or larger diameter will have a drop velocity and Weber
number far too large for the drops to be effective in a warewash
machine. If drop diameter is above 2 mm, film thickness becomes
excessively high and the number of times a plate is impacted by
drops becomes too low for effective heat transfer from the water
drops to the ware. As suggested by Weber number theory, pressures
below 0.5 bar are more suitable for a drop of 2 mm in size.
[0030] It does not take much water to remove wash residue from ware
or in other words rinse it. Approximately 1 mL of water residue
remains on a typical 200 mm diameter plate after wash. In a
warewash machine this residue is removed by dilution or flowing the
residue water off by mixing fresh water with it. Experiments
indicate that it may only take 5 to 10 mL to rinse the residue from
the plate. There is no requirement that water drops have any
significant impact velocity as rinsing occurs by a simple flow over
the surface. Drops just have to impact the surface to do their job.
This is fortunate since the small amounts of water needed are best
achieved with misting nozzles producing drop sizes of 0.1 mm and
lower.
[0031] Hot water drops lose energy because of water evaporating
from the drops. For a given flow rate, a flow made up of small
drops has a significantly higher surface area than if it were made
up of large drops. The effect of drop size on evaporative heat loss
is shown in FIG. 7, and in FIG. 7a is converted to a drop size
above which 90% or more of the initial water temperature is
retained in the drop as it strikes the ware. In many cases the very
large drop sizes required to achieve low evaporation energy loss
water temperatures above 75.degree. C. are not practical except for
higher nozzle flow rates. In those cases where nozzle flow rate is
restricted for some reason, then it is prudent to use the largest
drop diameter permitted according to desired Weber number, with the
narrowest drop size distribution possible.
[0032] There are two general types of warewash machines: those
which must have a final high temperature fresh water rinse and
those only requiring a final fresh water rinse of lower
temperature. Two basic design criteria for either machine are (i)
to establish drop size in accordance with a specified/desired Weber
number limit and/or (ii) to establish drop size in accordance with
specified/desired evaporation limit. Of the two design criteria,
applicants have determined that the controlling criteria should be
the Weber number criteria. With this determination in mind,
applicants have identified a number of general design principles as
follows: (1) a desirable Weber number for drops in any of a wash
zone, post wash zone or final rinse zone of a warewash machine is
generally less than a Weber number of about 1000; (2) given
limitations in ability to narrowly control drop size in any nozzle
flow, a desirable Weber number upper limit (or maximum Weber
number) for drops in any of a wash zone, post wash zone or final
rinse zone of a warewash machine is about 1200; (3) where achieving
flows at a selected Weber number of 1000 is desired, a desirable
lower Weber number limit for drops in any of a wash zone, post wash
zone or final rinse zone of a warewash machine is about 800; (4)
when wash liquid, post wash liquid or final rinse liquid
temperature is less than about 65.degree. C., drops in the flow
should generally be of any size below that specified by the Weber
number limit, so long as desired ware coverage is satisfied; (5)
when wash liquid, post wash liquid or final rinse liquid
temperature is less than about 65.degree. C. and the level of flow
needed in the warewash zone is particularly low, drops in the flow
should generally be below that specified by the Weber number limit
and as small as practical while obtaining desired coverage and
avoiding a predominance of water drops so small that they cannot be
properly directed onto the ware; (6) when wash liquid, post wash
liquid or final rinse liquid temperature is above 65.degree. C.,
evaporation size criteria should be taken into account, meaning
that the drop size should be established at or above that set by
the evaporation criteria (e.g., the 90% line of FIG. 7a); and (7)
if there is a conflict between the size set by the evaporation
criteria and that set by Weber number criteria (e.g., temperature
above 65.degree. C. and evaporation criteria suggests a size larger
than the maximum limit permitted under the Weber number criteria),
then the Weber number criteria should control and drop size should
be set as close as possible to the maximum specified by the Weber
number limit so as to reduce the affect of evaporation as much as
possible without abandoning the Weber number design criteria.
[0033] From the above discussion it should be evident that to
achieve the desired results, drop size distributions must be
managed along with the mean drop size. Conventional fan nozzles
used in warewash machines are notorious for very broad drop size
distributions; very large and very small drops can be found in the
same flow. There are nozzles, which can produce a fan shaped flow,
at least on the average, with very uniform drop size. One example
is reflected in fluidic oscillator type nozzles, which can be sized
to output fluid streams that result in drop sizes the majority of
which are within a fairly narrow size range.
[0034] Referring now to the exemplary rinse arm 28 shown in FIG. 9,
the arm includes a plurality of fluidic oscillator nozzles 30
positioned thereon for outputting respective streams of rinse
liquid. The fluidic oscillator nozzle 30 and arm 28 may include
connecting structure such that, when connected to the arm, the
fluidic oscillator nozzle outputs a desired oscillating fluid
stream pattern relative to the ware receiving area. The connecting
structure can allow the fluidic oscillator nozzle 30 to be
connected to the arm 28 in either one of two, pre-selected
orientations with the fluidic oscillator nozzle providing the same
desired oscillating stream pattern in each of the orientations.
[0035] A fluidic oscillator nozzle is generally any nozzle that
outputs an oscillating stream of fluid, meaning that the direction
of the output stream of fluid varies in an oscillatory manner. In
the case of liquids, the stream of liquid typically breaks up into
a series of drops of the liquid being output, or may be output as
drops in the first place. The resulting fan-shape 32 covered by the
sweep of the output stream of each nozzle is best seen in FIGS. 10
and 11, with the output stream 34 at a given moment in time
reflected in FIG. 5. Arrows A1-A5 reflect the instantaneous
direction of different points or drops (P1-P5) of the stream output
by the port at respectively different times, A1 representing
instantaneous direction for point or drop P1 of the stream output
at an earliest point in time, A2 representing instantaneous
direction for point or drop P2 output at a later time and so on.
The illustrated arm 28 includes five nozzles 30, but the number
could vary considerably. In one example the lower rinse arm 28
includes six nozzles 30 and the upper rinse arm includes five
nozzles. The illustrated rinse arm has an axis that extends
substantially perpendicular to the direction of the conveyor, but
it is recognized that variations on this orientation are possible.
As used herein the terminology "drop" is intended to refer to a
distinct volume of liquid output by a nozzle, regardless of whether
the volume is generally spherical or is distorted from spherical so
as to take on some other uniform or non-uniform shape. In the case
of a drop that is not spherical, its drop size will be considered
as the diameter such volume would take on if the drop was in fact
spherical.
[0036] The wash arms 22 could also include fluidic oscillator
nozzles or other variable stream orientation nozzles positioned
therein to direct wash fluid onto the wares. It is generally
contemplated that the wash arm nozzles would be constructed to
produce a higher flow rate than the rinse arm nozzles, but
variations are possible, including the use of identical nozzles for
both rinse and wash.
[0037] By way of example, the following tables (I, II and III) set
forth drop sizes for each zone in relation to temperature of the
liquid delivered in that zone. The Weber number criteria utilized
is based upon a Weber number range of 800 to 1200, as per FIG.
6.
TABLE-US-00001 TABLE I Wash Zone Max DROP SIZE TEMPERATURE
(diameter) Pressure range 45-65.degree. C. 1.50-4.00 mm 0.3 to 0.5
bar 45-65.degree. C. 0.80-2.30 mm 0.5 to 01.0 bar 65-75.degree. C.
2.50-4.00 mm 0.3 bar 65-75.degree. C. 1.80-2.80 mm 0.4 bar
65-75.degree. C. 1.50-2.70 mm 0.5 bar 65-75.degree. C. 1.25-2.0 mm
0.6 bar 65-75.degree. C. 1.00-1.75 mm 0.7 bar 65-75.degree. C.
0.75-1.50 mm Above .07 bar
TABLE-US-00002 TABLE II Post Wash Zone TEMPERATURE Max DROP SIZE
Pressure range 55-65.degree. C. 1.50-4.00 mm 0.3-0.5 bar
55-65.degree. C. 0.80-2.30 mm 0.5 to 01.0 bar 65-85.degree. C.
2.50-4.00 mm 0.3 bar 65-85.degree. C. 1.80-2.80 mm 0.4 bar
65-85.degree. C. 1.50-2.70 mm 0.5 bar 65-85.degree. C. 1.25-2.00 mm
0.6 bar 65-85.degree. C. 1.00-1.75 mm 0.7 bar 65-85.degree. C.
0.75-1.50 mm Above .07 bar
TABLE-US-00003 TABLE III Final Rinse Zone TEMPERATURE Max DROP SIZE
Pressure range 45-65.degree. C. 1.50-4.00 mm 0.3 to 0.5 bar
45-65.degree. C. 0.80-2.30 mm 0.5 to 01.0 bar 65-85.degree. C.
2.50-4.00 mm 0.3 bar 65-85.degree. C. 1.80-2.80 mm 0.4 bar
65-85.degree. C. 1.50-2.70 mm 0.5 bar 65-85.degree. C. 1.25-2.00 mm
0.6 bar 65-85.degree. C. 1.00-1.75 mm 0.7 bar 65-85.degree. C.
0.75-1.50 mm Above .07 bar
[0038] Drop size in the foregoing exemplary tables reflects average
maximum drop size, with the expectation that at least 50% of drops
delivered in the zone will be in the specified drop size range. As
used herein the term "range defined drop size" when referenced to a
corresponding range shall mean that at least 50% of drops are of a
size within that range. As used herein the term "distribution
established drop size" when referenced to a specific drop size
shall mean that at least 50% of drops are of a size that departs
from the specific drop size by no more than 50%. Tables IV and V
below provide examples of two theoretically optimized embodiments,
one including a low temperature final rinse (with particularly
small drop size in the final rinse) and the other including a high
temperature final rinse.
TABLE-US-00004 TABLE IV Low Temp Final Rinse Machine WASH POST WASH
FINAL RINSE Pressure 0.3 bar Pressure 0.7 bar Pressure 0.5 bar
45-55.degree. C./ 75-85.degree. C./ 45-55.degree. C./ 1.50-4.00 mm
1.00-1.75 mm 0.10-0.40 mm
TABLE-US-00005 TABLE V High Temp Final Rinse Machine WASH POST WASH
FINAL RINSE Pressure 0.3 bar Pressure 0.5 bar Pressure 0.7 bar
65-75.degree. C./ 60-70.degree. C./ 75-85.degree. C./ 2.50-4.00 mm
1.50-2.70 mm 1.00-1.75 mm
Other variations and combinations based upon the principles
outlined above. As pressure changes, drop size changes can be made
in accordance with tables I, II and III.
[0039] One basic design process for any given zone of a warewash
machine is to select a desired maximum Weber number (e.g., 1200)
and to select the nozzle size/type that will be used. Operating
pressure and number and positioning of nozzles is then established
to achieve desired drop size and desired coverage. Where
temperature in the zone is less than 65.degree. C. pressure can be
selected such that at least 85%, or more preferably 95%, of flow
from the nozzles consists of drops having a Weber number less than
the selected maximum Weber number. Where temperature in the zone is
greater than 65.degree. C., in order to account for evaporation
criteria, pressure can be selected such that at least 85%, or more
preferably 95%, of flow from the nozzles consists of drops having a
Weber number in a range close to the maximum Weber number (e.g.,
800 to 1200 for a maximum Weber number of 1200).
[0040] Another basic design process would be to select a desired
maximum Weber number (e.g., 1200) and to select an operating
pressure for that zone. The nozzle size/type is then selected, and
nozzle position established, to achieve desired drop size and
desired coverage. Again, where temperature in the zone is less than
65.degree. C. the nozzles can be selected such that at least 85%,
or more preferably 95%, of flow from the nozzles consists of drops
having a Weber number less than the selected maximum Weber number.
Where temperature in the zone is greater than 65.degree. C., in
order to account for evaporation criteria, the nozzles can be
selected such that at least 85%, or more preferably 95%, of flow
from the nozzles consists of drops having a Weber number in a range
close to the maximum Weber number (e.g., 800 to 1200 for a maximum
Weber number of 1200).
[0041] Use of fluidic oscillator nozzles to achieve specific drop
sizes as determined by Weber number theory and design process in
undercounter and other box units is also contemplated. For example,
referring to FIGS. 12 and 13, an exemplary undercounter unit is
shown and includes a washing/rinsing chamber 100 that is defined by
a cabinet, housing usually formed of stainless steel panels and
components, and including a top wall 110, side walls 120 and rear
wall 140, and a front facing door 150, hinged at its lower end, as
indicated at 160. The chamber 100 is vented to ambient pressure
through labyrinth seals (not shown) near the top wall. The cabinet
is supported upon legs 170 which provide the clearance for the
underside of the machine to permit cleaning beneath it as may be
required by various local sanitation codes. At the bottom of the
chamber, as part of the sloping bottom wall 200 of the cabinet, is
a relatively small sump 220 that may have a removable strainer
cover 230.
[0042] Above the bottom wall, rails 240 provide support for
standard ware racks 250, loaded with ware to be washed and
sanitized, which are loaded and unloaded through the front door.
The rack 250 may be a rolling rack intended to remain with the unit
or may be a mobile rack intended to be removed entirely when the
wares are removed. A coaxial fitting 270 is supported on the lower
wall 200, centrally of the chamber, and this fitting in turn
provides support for a lower wash arm 300 and lower rinse arm 320,
each being rotational as is common. An upper wash arm 340 and upper
rinse spray heads or nozzles 360 are supported from the top wall of
the chamber. In order to best achieve Weber number theory design
process requirements, the wash arms 300 and 340 may include
suitable fluidic oscillator nozzles 302 (or other variable stream
orientation nozzles) incorporated therein. Likewise rinse arm 320
may include suitable fluidic oscillator nozzles 322 (or other
variable stream orientation nozzles), and the spray heads 360 may
include suitable fluidic oscillator nozzles (or other variable
stream orientation nozzles).
[0043] It is to be clearly understood that the above description is
intended by way of illustration and example only and is not
intended to be taken by way of limitation. While the use of fluidic
oscillator nozzles is described as the primary mechanism for
achieving desired drop sizes, it is recognized that other nozzle
types could be utilized to achieve such purpose. Other changes and
modifications could be made.
* * * * *