US20080128004A1

US20080128004A1 - Warewash Machine Havaing Controlled Drop Size And/Or Weber Number And Related Design Process

Info

Publication number: US20080128004A1
Application number: US11/720,347
Authority: US
Inventors: James E. Doherty; Charles E. Warner; Kui-Chiu Kwok; Harald Disch
Original assignee: Premark FEG LLC
Current assignee: Premark FEG LLC
Priority date: 2004-12-10
Filing date: 2005-12-05
Publication date: 2008-06-05
Also published as: MX2007006888A; AU2005314191B2; AU2005314191A1; NZ556401A; CN100562282C; BRPI0518941A2; CN101068496A; CA2588289A1; EP1819262A1; EP1819262B1; WO2006062927A1

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.

Description

TECHNICAL FIELD

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

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.
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

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.
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° 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° 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° 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.
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° 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

FIG. 1 is a perspective view of one embodiment of a conveyor-type unit;

FIG. 2 is a side elevation of the unit of FIG. 1;

FIG. 3 is a graph of plate temperature vs. evaporation;

FIG. 4 is a graph of drop velocity vs. pressure;

FIG. 5 depicts drop deformation upon impact with a flat surface of a ware;

FIG. 6 is a graph showing drop size vs. pressure for three different Weber numbers;

FIG. 7 a graph of evaporation heat loss vs. temperature for certain drop sizes;

FIG. 7 a is a graph showing drop size vs. temperature to achieve 90% heat transfer to wares;

FIG. 8 is a graph of ware temperature vs. distance through an exemplary conveyor machine;

FIGS. 9-11 depict one embodiment of a rinse arm; and

FIGS. 12-13 illustrate one embodiment of an undercounter warewash box-type unit.

DETAILED DESCRIPTION

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.
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.
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.
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.
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=(ρv ² l)/σ

Where:

l=characteristic length
v=velocity
σ=surface tension
ρ=density

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.
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.
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.
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.
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. 7 a 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° 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.
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° 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° 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° 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. 7 a); 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° 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.
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.
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.
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.
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.
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 I

Wash Zone

	Max DROP SIZE
TEMPERATURE	(diameter)	Pressure range

45-65° C.	1.50-4.00 mm	0.3 to 0.5 bar
45-65° C.	0.80-2.30 mm	0.5 to 01.0 bar
65-75° C.	2.50-4.00 mm	0.3 bar
65-75° C.	1.80-2.80 mm	0.4 bar
65-75° C.	1.50-2.70 mm	0.5 bar
65-75° C.	1.25-2.0 mm	0.6 bar
65-75° C.	1.00-1.75 mm	0.7 bar
65-75° C.	0.75-1.50 mm	Above .07 bar

TABLE II

Post Wash Zone

TEMPERATURE	Max DROP SIZE	Pressure range

55-65° C.	1.50-4.00 mm	0.3-0.5 bar
55-65° C.	0.80-2.30 mm	0.5 to 01.0 bar
65-85° C.	2.50-4.00 mm	0.3 bar
65-85° C.	1.80-2.80 mm	0.4 bar
65-85° C.	1.50-2.70 mm	0.5 bar
65-85° C.	1.25-2.00 mm	0.6 bar
65-85° C.	1.00-1.75 mm	0.7 bar
65-85° C.	0.75-1.50 mm	Above .07 bar

TABLE III

Final Rinse Zone

TEMPERATURE	Max DROP SIZE	Pressure range

45-65° C.	1.50-4.00 mm	0.3 to 0.5 bar
45-65° C.	0.80-2.30 mm	0.5 to 01.0 bar
65-85° C.	2.50-4.00 mm	0.3 bar
65-85° C.	1.80-2.80 mm	0.4 bar
65-85° C.	1.50-2.70 mm	0.5 bar
65-85° C.	1.25-2.00 mm	0.6 bar
65-85° C.	1.00-1.75 mm	0.7 bar
65-85° C.	0.75-1.50 mm	Above .07 bar

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 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° C./	75-85° C./	45-55° C./
1.50-4.00 mm	1.00-1.75 mm	0.10-0.40 mm

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° C./ 60-70° C./ 75-85° 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.
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° 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° 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).
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° 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° 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).
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.
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).
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.

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° 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° 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° 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° 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° 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° 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° 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° 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° 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° 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)