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MODELING OF TEMPERATURE PROFILES UNDER CONTINUOUS TUBE‐FLOW MICROWAVE AND STEAM HEATING CONDITIONS
Author(s) -
BAIL A. Le,
KOUTCHMA T.,
RAMASWAMY H.S.
Publication year - 2000
Publication title -
journal of food process engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 45
eISSN - 1745-4530
pISSN - 0145-8876
DOI - 10.1111/j.1745-4530.2000.tb00501.x
Subject(s) - mechanics , laminar flow , materials science , thermodynamics , turbulence , microwave , thermal , flow (mathematics) , physics , quantum mechanics
Mathematical models were developed based on perfectly mixed flow (PMF), piston flow with heat diffusion (PFHD) and laminar flow (LF) approaches to predict liquid temperature history under continuous tube‐flow microwave and steam heating conditions. Two helical glass coils placed inside domestic microwave ovens (one coil in each of the two 700 W capacity ovens) or in a steam cabinet were used for heating and a spiral condenser at the exit was used for cooling. Transient and steady state mean temperatures of the fluid were experimentally measured at the exit and were compared with predictions from the mathematical models for both systems. The residence time, velocity distribution as well as temperature profiles, along the radius and the length of the tubes, were computed using the models. The PFHD and the LF models better described temperature profiles during the initial transient period, while the PMF model shovsed a better agreement with experimental data during steady staie conditions. The occurrence of secondary turbulence in the helical coil (associated with high Dean numbers) was believed to be responsible for reducing the radial temperature gradients and achieving close to “perfectly mixed piston flow” situation. A relatively larger temperature gradient across the radius was observed under microwave heating conditions than under steam heating conditions. The time‐temperature effects were integrated to predict the lethality at selected temperatures and flow rates for both continuous‐flow thermal processing.