Multi-pass Microwave Heating for Uniform Pasteurization
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Solution Overview
Problem
Current microwave heating systems face challenges in achieving consistent, uniform, and rapid heating of packaged foodstuffs and other items, particularly in commercial-scale applications, due to issues with hot and cold spots and limited operational flexibility, which affects microbial lethality and overall quality.
Innovation Solution
A microwave heating system and process that involves multiple passes of articles through a microwave heating chamber with strategically positioned microwave launchers and a convey line control system, allowing articles to be exposed to microwave energy multiple times, along with the use of a microwave distribution system with circulators and dummy loads to manage energy distribution, ensuring uniform heating and operational flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If articles are heated in a single pass through a microwave heating chamber, then the heating process is rapid, but the heating uniformity is poor with hot and cold spots
Solution Approach 1:
The system implements multi-pass periodic heating where articles are transported through the microwave heating chamber multiple times in alternating directions. Each pass exposes different portions of the articles to microwave energy, and the periodic reversal of conveyance direction ensures that hot and cold spots are redistributed and eliminated, achieving uniform heating while maintaining rapid processing speed
Solution Approach 2:
The convey line control system pre-plans the multi-pass heating path and timing before articles enter the heating chamber. By predeterminedly arranging the sequence of passes and direction changes, the system ensures optimal exposure of all article surfaces to microwave energy, preventing hot and cold spots before they can develop
2Manufacturing precision
If multiple microwave launchers are used to improve heating uniformity, then heating consistency improves, but system complexity increases
Solution Approach 1:
A single microwave launcher is designed to perform multiple functions by directing microwave energy at articles from different angles during multiple passes. The launcher serves as both a heating source for forward-pass articles and a heating source for reverse-pass articles, eliminating the need for separate launchers for each direction while maintaining heating consistency
Solution Approach 2:
The system makes the heating process dynamic by reversing the conveyance direction of articles rather than adding static additional launchers. The microwave launcher remains stationary while the articles dynamically change direction, allowing the same launcher to effectively heat different portions of articles during different passes without increasing system complexity
3Manufacturing precision
If articles are moved back and forth multiple times through the heating chamber, then heating uniformity improves, but processing time increases
Solution Approach 1:
The multi-pass heating process is implemented as a continuous operation without stopping the convey line. Articles are continuously moved through the heating chamber, reversed direction, and moved back through the same chamber, maintaining continuous microwave energy application throughout the entire multi-pass process. This eliminates idle time between passes and keeps the heating action continuous and useful
Solution Approach 2:
The system adds the time dimension to the heating process by implementing multiple passes, but compensates by using the spatial dimension of the existing chamber twice. Rather than extending the chamber length to accommodate multiple heating zones, the articles traverse the same spatial path multiple times in alternating directions, efficiently using the existing spatial resources to achieve uniform heating without proportionally increasing processing time
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables consistent and rapid heating of articles, minimizing hot and cold spots, and achieving target temperatures for pasteurization or sterilization, while maintaining system efficiency and operational flexibility, thereby ensuring high-quality processed products.
Implementation Method 1
Microwave radiation is a known mechanism for delivering energy to an object. The ability of microwave energy to penetrate and heat an object in a rapid and effective manner has proven advantageous in many chemical and industrial processes.
Implementation Method 2
Because of its ability to quickly and thoroughly heat an article, microwave energy has been employed in heating processes wherein the rapid achievement of a prescribed minimum temperature is desired
Data Source
AI summary
Processes and systems for pasteurizing and sterilizing a plurality of articles in a microwave heating system are provided. In certain aspects, groups of articles may be passed by a microwave launcher in a first convey direction and a second, opposite convey direction, so that each group of articles passes the microwave launcher more than once. Processes and systems described herein are also configured to uniformly heat spaced apart groups of articles without disrupting the operation of the microwave generator or distribution system.