Microwave drying is an energy-efficient drying method. The output power of most commercial microwave ovens is controlled in an intermittent fashion, where the amount of microwave energy is determined by the ratio of "ON cycles" to "OFF cycles." To provide a more efficient and continuous power control for the magnetron, a microcontroller-based, feedback power control system was developed. The system was based on a phase-control principle to achieve smooth power variations depending on a feedback temperature signal of processed products. Two temperature sensors, a thermocouple and an infrared sensor, were used to measure the temperature. A fiber-optic thermometer was used for calibration and evaluation of the system performance during microwave drying. With the IR sensor, the mean standard deviation and maximum error in temperature measurement of controlled water samples were +/-0.34ºC and +/-1.5ºC, respectively. This result demonstrated the accuracy of the IR sensor in the system control. Under the IR sensor-controlled system, carrot cubes (Daucus carota L.) lost 85.37% of their water content and resulted in better color quality than the conventional microwave-hot air convective drying without a temperature feedback control.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.82278 |
| Date | January 2004 |
| Creators | Li, Zhenfeng, 1968 Oct. 9- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Bioresource Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002227409, proquestno: AAIMR12489, Theses scanned by UMI/ProQuest. |
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