Assessment of heating dynamics in a prototype magnetic induction heat exchanger
Abstract
Magnetic induction (MI) heating has the potential to be used in food processing systems to heat flowing food material. Due to electromagnetic properties, MI heating theoretically has the ability to evenly distribute energy to heat exchanger surfaces in a manner that is more energy efficient and gentler to the processing stream than current steam-boiler systems. The goal of this project was to analyze the processing capabilities of an MI unit composed of a high-frequency power source, an induction coil, and four simple heat exchanger designs for heating uniformity and overall heating efficiency. Tests were first performed to determine the cross-sectional temperature distribution for a 6 and 9-tube bundle in a ∼180 kHz, ∼10 kW prototype induction heater. Heating efficiencies were > 98% when regenerated heat from the cooling coil was considered. Results showed fairly uniform (within 4.7%) heating occurring in the symmetrical centered 6-tube bundle, although thermal images taken during tube bundle testing showed non-uniformities in heating along the heat exchanger. In order to determine longitudinal heating patterns, the MI heat exchanger was simplified to a 1.9 cm diameter stainless steel rod and a 3.5 cm O.D. stainless steel tube. Temperature measurements were taken using a number of methods, including a movable thermocouple used to incrementally measure temperature along the length of the rod, a thermal imaging camera used to take surface temperatures of the tube, and a fouling-labile egg albumen solution used to indicate heating patterns along the rod. Results showed two distinct heating non-uniformities: Coil end effects caused by even coil spacing and proximity effect heating from the use of the very high frequency. Suggested improvements on future systems include reducing the resonance frequency to line frequency in order to increase heating efficiency in the heat exchanger and to decrease proximity heating. Also, coil spacing should be altered in order to achieve the desired heat gradient across the heat exchanger.
Degree
M.S.
Advisors
Martin, Purdue University.
Subject Area
Food Science
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