Heat transfer in a combination microwave–jet impingement oven

Characterization of a combination oven prototype: Effects of microwave exposure and enhanced convection to local temperature rise in a moist substrate

“…The fluid pattern resulting from the impact, even for the sample's side regions, may contribute to the treatment, specially when multiple jets are interacting. The thermal evolution of food substrates subject to combined MW/JI treatment was first reported by Geedipalli et al [9], but they used a multiple, less controlled impingement system, and it was limited to surface and average sample temperatures, therefore the relative merit of the two driving forces at stake was not emphasized.…”

“…[6], or in assistance of traditional processes [7]. In the field of food treatment, different systems have been tried, and have been found nowadays in the consumer market to alleviate problems, such as the use of barriers, succeptors, intermittent rotation and alternative internal tray [8,9]. But due to their limited response in process performance, MW treatments are being more often proposed in combination with other heat transfer mechanisms, as with sole bulk convection: some authors focused on changes in quality parameters and in mechanical properties of different food substrates undergoing combined convective and MW drying [10][11][12][13], some others proposed to combine convection as a method to control MW power and heating [14,15] while some more [3,16,17] focused on theoretical and modeling approaches.…”

“…But due to their limited response in process performance, MW treatments are being more often proposed in combination with other heat transfer mechanisms, as with sole bulk convection: some authors focused on changes in quality parameters and in mechanical properties of different food substrates undergoing combined convective and MW drying [10][11][12][13], some others proposed to combine convection as a method to control MW power and heating [14,15] while some more [3,16,17] focused on theoretical and modeling approaches. Sole localized convection was then explored [8,9,18], while sole infrared [19,20], infrared and bulk convection [21], and a combination of radiant and localized forced convection [22,23] were implemented as well. It is then seen that bulk convection can help increase surface temperature (then reducing surface moisture), but not as effectively as infrared heat, due to its inefficient surface heat flux.…”

Combined microwaves and convection heating: A conjugate approach

“…7) holds the favorable features of both mechanisms: the substrate is treated faster that with sole MW, but on the leading edge a moisture excess still exist. In accord with Geedipalli et al (2008), who explored the combination of MW with local enhanced forced convection (jet impingement), this is due to thermal mechanism dominance at the given process duration: therefore the mechanism intensities (T p and v p for convection, and Q 0 for MW) must be adjusted for a more uniform treatment. Then, the convective behavior (heat flux) is inverted at the trailing edge, with respect to Case I (Fig.…”

“…Moreover, forced air convection can be profitably supplemented inducing a desired superficial finish (Geedipalli et al, 2008), but the transfer phenomena must be coupled and intertwined, due to the coexistence of heating mechanisms, the evaporation of the free water from and within the substrate and the related diffusion of water vapor, the macroscopic transport and elimination of such vapor from the same substrate.…”