微波單模共振腔於液體食品加熱之應用

Abstract

微波加熱單模共振腔的發展雖有一段時間，但目前的研究中較少提到如何設計出一個高能量集中，並可針對液體做連續性加熱的微波單模共振腔，因此這樣的加熱系統仍是一個值得努力、研究的方向。 本研究針對如何設計出用於液體連續式加熱的微波加熱系統提出了一套有效的設計步驟。此微波加熱系統主要由TE10 矩形波導管傳播波源為2.45GHz的電磁波進入圓柱形共振腔，並在圓柱形共振腔中產生TM010的共振模態，在此模態下能量集中在共振腔中心處，能量集中的特性可用來對液體做連續加熱。由於阻抗匹配會隨著介電材料的加入而有所改變，本研究發現改變加熱水管的管徑可以輕易的調整阻抗匹配，我們使用商業軟體COMSOL Multiphysics作為模擬的輔助工具以求出在圓柱形共振腔內電場能量的分佈以及S參數，由S參數可知能量被介電材料吸收與反射的情形。利用反應曲面法得出在不同的介電材料下，其最適的加熱管徑範圍並以實際實驗加以驗證。 由研究結果可知，我們設計的微波單模共振腔加熱系統在匹配良好的情況下可使2%氯化鈉溶液達到90%以上的加熱效率；10%葡萄糖溶液達到80%以上的加熱效率，的確達到高效率，高能量集中的目的。而本研究所提供的方法，可使後人針對其他各種不同共振模態進行研究，更可以測試不同液體與共振腔如何達到最佳的匹配。

Although microwave single-mode resonant cavities for the purpose of heating have been developed for a long time, however, there are few researches concentrated on engineering design procedure to development a resonant cavity for heating of liquid food continuously with acceptable efficiency. In this study an effective procedure for design of a continuous microwave heating system for liquid food was developed. The major component of the system was a TM010 mode cylindrical resonant cavity which being excited by a rectangular TE10 waveguide with 2.45GHz electromagnetic wave. Liquid flew through and microwave heated in tubing centered in the cavity. Impendence match that might vary with dielectric properties of the heated fluid was the most difficult task for the design. In this study we found that the impendence of the cavity could be easily varied by changing the diameter of the liquid tubing. We used commercial software COMSOL Multiphysics as a design tool to simulate electrical energy filed in the cavity and calculate scattering parameter (S-parameter) as an index for power transmission efficiency and response surface method to obtain the optimum diameter of tubing for model food with various dielectric properties. The designing procedure was validated with experimental works. Our results point out under good impendence match, the heating efficiency can reach 90% and 80% for 2% NaCl solution and 10% glucose solution respectively and the designing procedure developed in this study provides an effective method for design of single-mode microwave heater at any resonant modes.