Experimental and Theoretical Analysis of the Impinging Stream Drying

The experiments of one-stage semi-circular and two-stage semi-circular impinging stream drying as well as the vertical and semi-circular combined impinging stream drying were carried out. The velocity distribution and the mean residence time of particles, and the influence of various factors on drying characteristics were studied. A mathematical model of granular material drying in a semi-circular impinging stream dryer was proposed, in which the flow characteristics as well as the heat and mass transfer mechanisms were considered. Reasonable numerical methods were used to solve the equations. Under various conditions, the calculated results agree well with the experimental data. The unsteady-state drying dynamic equation, as well as the variations of drying rate and moisture content versus time were obtained. The results indicate that constant drying rate period does not exist in a semi-circular impinging stream dryer. Appropriate semi-circular stage number and curvature radius, flow-rate ratio, air velocity, and higher inlet air temperature should be used for enhancing the drying process.

Experimental Investigation on Flow and Drying Characteristics of Impinging Stream Drying

Based on the experimental investigation of one-stage semi-circular impinging stream drying, the experiments with the two-stage semi-circular, as well as the vertical and semi-circular combined impinging stream drying were conducted. The variations of system pressure drop, the mean residence time of particles with the mass flow-rate ratio and air velocity etc, were determined. The influences of inlet air temperature, mass flow-rate ratio, initial moisture content of particles and air velocity etc. on drying characteristics were also studied. The results indicate that the vertical and semi-circular combined impinging stream drying can make full use of the advantages of both the vertical and semi-circular impinging stream drying. Reasonable mass flow-rate ratio, air velocity, and higher inlet air temperature should be used for less energy consumption and cost during drying process.

Innovative superheated steam impingement blanching(SSIB)enhances drying rate and quality attributes of line pepper

Blanching is an essential step before processing of agricultural products as it can inactivate enzymes that cause undesirable changes.In current work the effects of superheated steam impingement blanching(SSIB)time and temperature on drying characteristics and red pigments content of line pepper were investigated.Results showed that after a 3-min SSIB pretreatment at 110℃ the pepper epidermis covered with wax coat was damaged.In addition,the drying time was extensively decreased and the loss of red pigments of dried products was reduced.Results showed that the whole drying process took place in the falling rate period,which indicated that diffusion was the dominant physical mechanism governing moisture movement in the samples.Therefore,the second Fick’s law of diffusion was used to determine the effective moisture diffusivity(Deff)of line pepper,which increased from 1.193×10^-10 to 3.128×10^-10 m^2/s with increasing of the drying temperature and air velocity.The drying activation energy(Ea)of pretreated samples was 34.31 kJ/mol,which decreased by 3% compared with the non-pretreatment group.The findings of this work indicate that SSIB is very promising pretreatment technique as it not only enhances drying process but also improves bioactive substance preservation of red pepper.