Impinging jet drying

Materials like plywood or chip board require long residence times to dry. Impinging jets may be used initially to remove surface moisture internal moisture removal can be achieved in a tunnel dryer with modest parallel flow of drying medium. 

Continuous conveyor, through-circulation, or impinging jet-fluidized bed dryers (sometimes called jet-zone dryers) are often used in the wood processing (e.g., wafer board) and food processing (e.g., potato chips, etc.) industries. In the jet-zone process, hot air jets impinge on a thin layer of wet chips, which are conveyed mechanically the high-velocity jets pseudo-fluidize the material to accomplish uniform drying. Wood chips, for example, may be dried in a rotary or a conveyor dryer. 

Figure 9.11 Scanning electron micrographs of slow drying (stagnant air) versus fast drying (impinging jet of air) coatings of cellulose acetate in mixed acetone-water solvent...

Li, Y. K., Mujumdar, A. S., and Douglas, W. J. M. 1978. Coupled heat and mass transfer under a laminar impinging jet. In Proceedings of the First International Symposium on Drying, Ed. A. S. Mumudar, pp. 175-184. Montreal, Quebec, Canada McGill University. 

Bond et al. [103] discuss the drying of paper by impinging jets of superheated steam. Svensson [105] discusses applications in the drying of wood pulp while Amoux et al. [106] consider the use of superheated steam in the drying of softwood biomass. 

Mujumdar, A.S., Huang, P.G., and Douglas, W.J.M., Prediction of heat transfer under a plan turbulent impinging jet including effects of cross-flow and wall motion. In Drying 82, Mujumdar, A.S. (Ed.), Hemisphere, New York, 1982, pp. 91-98. 

For the design of some specific dryers, for example, impinging jet, spray, and flash dryers, computational (such as computational fluid dynamics known as CFD) analysis of the complex gas-particle two-phase flow with inter-gas-particle heat and mass transfer can help understand the effects of dryer geometries to the drying process and make better design decisions. 

Here we focus oti the impacts onto films with 5 <2 since this condition is often satisfied in most practical spray applications. Similarly to droplet impingement on dry targets, diverse outcomes may occur deposition and coalescence, bounce, formation of a crater, corraia splash or uprising of a central jet. Most studies reported in the Uterature consider corona splash and focus on three issues (1) characterization of crown morphology, (2) establishment of threshold criteria for disintegration and (3) characterization of secondary atomization. 

Bond J-F. Drying paper by impinging jets of superheated steam Drying rates and thermodynamic cycles. Ph.D. thesis, McGill University, Montreal, 1991. 

Keywords Nanocapsules, nanospheres, polymer nanoparticles, confined impinging jets mixer, vortex mixer, flash nanoprecipitation, solvent displacement, freeze-drying, lyoprotectants,... 

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