Optimization of pulsed microwave heating

Abstract

A simulation model was used to optimize pulsed microwave heating of precooked mashed potato cylinders of 82.7% moisture content. The experimental variables were: (1) sample radius: 2.4, 2.8 and 3.2 cm (or 1.5, 1.75 and 2.0 times the penetration depth of microwave radiation), (2) temperature rise during microwave power-on constraint (Δ T on): 20 and 15 °C, (3) temperature drop during microwave power-off constraint (Δ T d): 5 and 3 °C lower than Δ T on, (4) total processing time (<1000 s) and (5) average sample temperature (60 °C). The evaluation showed that the 2.4–2.8-cm radius samples were heated uniformly and efficiently. The Δ T on constraint is very critical for optimum pulsed microwave heating; Δ T on = 20 °C was a better choice than Δ T on = 15 °C. Δ T d constraint affects the total processing time for a large sample more significantly than for a small sample. The total processing time depends on Δ T on, Δ T d, and sample radius. In the case of 2.4-cm radius samples (1.5 times the penetration depth) with Δ T on(Δ T d) = 20(3) °C constraint, the pulsed microwave energy can heat the mashed potato sample to an average temperature of 60 °C in 336 s. This was the most efficient process among all evaluated conditions with respect to total processing time.