Enhanced control of a microwave heating system

Abstract

A method for controlling a microwave heating system is provided. The method may be used with a system having a liquid-filled microwave heating chamber and includes measuring the value of one or more microwave system parameters. Suitable parameters can include, for example, net microwave power discharged, the temperature of the liquid in the microwave chamber, the flow rate of liquid through the microwave chamber, and the speed of the conveyance system disposed within the microwave chamber. The measured value of the selected parameter is then compared to a target value for that parameter in order to determine a difference. Based on the difference, one or more actions can be taken in order to start, stop, or alter the operation of the microwave heating system.

1 . A microwave heating system for pasteurizing or sterilizing a plurality of articles, said system comprising:
 a thermalization zone for thermalizing said articles to a substantially uniform temperature, wherein said thermalization zone comprises a thermalization chamber and a plurality of fluid jet locations for discharging pressurized jets of liquid toward said articles in said thermalization chamber;   a microwave heating zone located downstream of said thermalization zone for heating the thermalized articles using microwave energy, wherein said microwave heating zone comprises a microwave heating chamber, a convey line, and at least two microwave launchers for discharging microwave energy into said microwave heating chamber, wherein said convey line is configured to transport said articles through said microwave heating chamber in a convey direction, wherein said microwave launchers are axially spaced from one another in said convey direction, and wherein at least a portion of each of said microwave launchers extends in a direction perpendicular to said convey direction;   a quench zone located downstream of said microwave heating zone for cooling said articles, wherein said quench zone comprises a quench chamber; and   a plurality of individual carriers for securing and holding said articles as said articles pass through said thermalization chamber, said microwave heating chamber, and said quench chamber.   
     
     
         2 . The system of  claim 1 , wherein at least a portion of each of said microwave launchers extends into the interior of said microwave heating chamber. 
     
     
         3 . The system of  claim 1 , wherein no portion of any of said microwave launchers extends into the interior of said microwave heating chamber. 
     
     
         4 . The system of  claim 1 , wherein each of said microwave launchers defines an open internal microwave pathway configured to propagate said microwave energy through the microwave launcher. 
     
     
         5 . The system of  claim 1 , wherein each of said microwave launchers defines at least one launch opening through which said microwave energy is discharged into said microwave heating chamber. 
     
     
         6 . The system of  claim 1 , further comprising at least two additional microwave launchers disposed on the opposite side of said microwave heating chamber as said microwave launchers, wherein said additional microwave launchers are axially spaced from one another in said convey direction, and wherein at least a portion of each of said additional microwave launchers extends in a direction perpendicular to said convey direction. 
     
     
         7 . The system of  claim 1 , wherein said microwave energy discharged into said microwave chamber has a predominate wavelength (λ), wherein the minimum dimension of the portion of each of said microwave launchers discharging said microwave energy into said microwave chamber is not more than 0.625λ. 
     
     
         8 . The system of  claim 1 , wherein each of said thermalization chamber, said microwave heating chamber, and said quench chamber are configured to be filled with a liquid medium. 
     
     
         9 . The system of  claim 8 , further comprising a holding zone located between said microwave heating zone and said quench zone, wherein said holding zone comprises a liquid-filled holding chamber for maintaining the temperature of said articles in said carriers at or above a minimum temperature. 
     
     
         10 . The system of  claim 8 , wherein said thermalization zone is configured to adjust the temperature of said articles to a substantially uniform temperature so that at least 85 percent of said articles have a temperature within 5° C. of each other prior to the introduction of said articles into said microwave heating chamber, wherein said quench zone is configured to cool the heated articles by at least about 30° C., wherein said microwave heating zone is configured to heat said articles by at least about 25° C. in a time period in the range of from about 60 seconds to about 10 minutes, wherein said system is configured to pasteurize or sterilize said articles at a rate of at least 15 packages per minute per convey line. 
     
     
         11 . A method for pasteurizing or sterilizing a plurality of articles in a microwave heating system, said method comprising:
 (a) securing a plurality of articles in one or more individual carriers;   (b) thermalizing said articles in said carriers in a thermalization chamber to provide a plurality of thermalized articles having a substantially uniform temperature;   (c) during at least a portion of said thermalizing, discharging a plurality of pressurized liquid jets toward said articles from multiple locations within said thermalization chamber;   (d) passing said articles in said carriers along a convey line in a convey direction through a microwave heating chamber; and   (e) during at least a portion of said passing, directing microwave energy into said microwave heating chamber with at least two microwave launchers to thereby heat said articles with at least a portion of said microwave energy,   wherein said microwave launchers are axially spaced apart from one another in said convey direction, and wherein at least a portion of each of said microwave launchers extends in a direction perpendicular to said convey direction.   
     
     
         12 . The method of  claim 11 , wherein at least a portion of each of said microwave launchers extends into the interior of said microwave heating chamber. 
     
     
         13 . The method of  claim 11 , further comprising propagating microwave energy through an open internal microwave pathway defined within each of said microwave launchers. 
     
     
         14 . The method of  claim 11 , wherein each of said microwave launchers defines at least one launch opening through which said microwave energy is discharged into said microwave heating chamber. 
     
     
         15 . The method of  claim 11 , further comprising at least two additional microwave launchers located on the opposite side of said microwave heating chamber, wherein said additional microwave launchers are axially spaced from one another in said convey direction, and wherein at least a portion of each of said additional microwave launchers extends in a direction perpendicular to said convey direction. 
     
     
         16 . The method of  claim 11 , wherein said articles are submerged in a liquid medium during at least a portion of said discharging of said liquid jets into said thermalization chamber, and during said passing of said carriers through said microwave heating chamber. 
     
     
         17 . The method of  claim 11 , wherein each of said liquid jets discharged into said thermalization chamber has a Reynolds number of at least 4500. 
     
     
         18 . The method of  claim 11 , wherein at least about 85 percent of the thermalized articles have a temperature within about 5° C. of one another, wherein said articles are heated by at least about 25° C. in a time period in the range of from 60 seconds to 10 minutes in said microwave heating chamber, further comprising, subsequent to step (e) cooling said articles in said carrier to a lower temperature in a quench chamber, wherein said cooling is sufficient to reduce the temperature of said articles in said carriers by at least about 30° C. to a temperature of not more than about 70° C., wherein said articles are submerged in a liquid medium during said cooling, and wherein said articles are pasteurized or sterilized at a rate of at least 15 packages per minute. 
     
     
         19 . A microwave heating system for pasteurizing or sterilizing a plurality of articles, said system comprising:
 a microwave heating chamber configured to receive said articles;   at least one convey line for transporting said articles through said microwave heating chamber in a convey direction;   at least one microwave generator for generating microwave energy having a wavelength (λ); and   two or more axially spaced microwave launchers configured to propagate at least a portion of said microwave energy into said microwave heating chamber, wherein each of said microwave launchers defines n laterally spaced launch openings for discharging microwave energy into said microwave heating chamber, and wherein each of said launch openings has at least one dimension that is not more than about 0.625λ.   
     
     
         20 . The system of  claim 19 , wherein said microwave launchers are same-side launchers and wherein said system comprises at least four and not more than twenty microwave launchers. 
     
     
         21 . The system of  claim 19 , wherein n is at least three. 
     
     
         22 . The system of  claim 19 , wherein at least a portion of said launch openings are at least partially covered with a microwave-transparent window that defines at least a portion of a side wall of said microwave heating chamber. 
     
     
         23 . The system of  claim 19 , wherein said microwave heating chamber is at least partially filled with a liquid medium and further comprising a plurality of individual carriers for securing and holding said articles as said articles pass through said microwave heating chamber. 
     
     
         24 . The system of  claim 23 , further comprising a thermalization chamber, a holding chamber, and a quench chamber, wherein said thermalization chamber is located upstream of said microwave heating chamber and is configured to adjust the temperature of said articles to a substantially uniform temperature so that at least 85 percent of the articles exiting the thermalization chamber have a temperature within 5° C. of one another, wherein said quench chamber is located downstream of said microwave heating chamber and is configured for cooling the heated articles by at least about 30° C., wherein said holding chamber is located between said microwave heating chamber and said quench chamber for maintaining the temperature of said articles at or above a minimum temperature for a time period in the range of from about 2 minutes to about 10 minutes, wherein each of said thermalization chamber, said holding chamber, and said quench chamber are configured to be at least partially filled with said liquid medium, wherein at least one of said thermalization chamber and said microwave heating chamber comprise a plurality of fluid jet agitators configured for discharging pressurized jets of liquid toward said articles, wherein said microwave heating chamber is configured to heat said articles by at least about 25° C. in a period of time in the range of from about 60 seconds to about 10 minutes, wherein n is at least three and each of said launch openings has at least one dimension that is less than about 0.5λ, wherein said system is configured to pasteurize or sterilize said articles at a rate of at least 15 packages per minute. 
     
     
         25 . A method for pasteurizing or sterilizing a plurality of articles in a microwave heating system, said method comprising:
 (a) passing said plurality of articles along at least one convey line through a microwave heating chamber in a convey direction;   (b) during at least a portion of said passing, discharging microwave energy into said microwave heating chamber with at least three microwave launchers, wherein said microwave launchers are axially spaced from one another in said convey direction, wherein each of said microwave launchers comprises at least two launch openings for directing microwave energy toward said articles moving along said convey line, wherein said launch openings are laterally spaced from one another in a direction perpendicular to said convey direction; and   (c) heating said articles with at least a portion of said microwave energy discharged into said microwave heating chamber.   
     
     
         26 . The method of  claim 25 , wherein said discharging is carried out with at least four and not more than twenty axially-spaced microwave launchers, and wherein each microwave launcher includes at least three laterally-spaced launch openings. 
     
     
         27 . The method of  claim 25 , further comprising generating microwave energy with at least three microwave generators, wherein at least a portion of said microwave energy is discharged from each of said microwave launchers. 
     
     
         28 . The method of  claim 25 , wherein said microwave heating chamber is at least partially filled with a liquid medium, and wherein said articles are secured in a plurality of individual carriers prior to said passing, wherein said articles are passed along said convey line in said carriers during said passing, and wherein said heating comprises heating said articles in said carriers. 
     
     
         29 . The method of  claim 25 , wherein each launch opening has a width (w) and a depth (d), wherein the width of each of said launch openings is greater than its depth, and wherein d is not more than about 0.625λ. 
     
     
         30 . The method of  claim 25 , wherein during said heating said articles are heated in said microwave heating chamber by at least about 25° C. in a time period in the range of from 60 seconds to 10 minutes, further comprising prior to said passing, thermalizing said articles through a thermalization chamber upstream of said microwave heating chamber to provide a plurality of thermalized articles having a substantially uniform temperature so that at least 85 percent of said articles exiting said thermalization chamber have a temperature within about 5° C. of one another, further comprising, subsequent to said heating, maintaining the temperature of the articles at or above a minimum temperature for a time period in the range of from about 2 minutes to about 16 minutes in a holding chamber, and subsequent to passing said articles through said holding chamber, cooling said articles in a quench chamber downstream of said holding chamber by at least about 30° C., wherein said articles are submerged in a liquid medium during at least a portion of said thermalizing, said heating, said maintaining, and said cooling, and wherein said articles are pasteurized or sterilized at a rate of at least 15 packages per minute per convey line.