基于介质湿度控制的苹果片红外漂烫传热模拟与试验.

Infrared blanching is a new pretreatment method for fruits and vegetables apple slices drying. However, the influence of the air medium properties on the infrared blanching is not clear, which is not conducive to developing the infrared blanching technology. In order to reveal the mechanism of the heat and mass transfer of infrared blanching pretreatment of apple slices and that effects on the drying process, the air medium humidity control technology was used in infrared blanching of apple slices in this paper. Numerical simulation was used to analyze the law of heat and mass transfer during infrared blanching of apple slices under different air relative humidity. The convection heat and mass transfer between air and material was obtained by Newton’s law of cooling, and the radiation heat transfer between infrared radiation source and material was solved by Stefan-Boltzmann’s law. According to Fick’s diffusion law and Fourier’s heat conduction law, the moisture diffusion and heat transfer in apple slice were calculated. The effect of infrared blanching under medium humidity control on drying efficiency and the color of products were studied by combining blanching and drying experiments. The results showed that the heat and mass transfer of infrared blanching for apple slices could be described by the mathematical model, which based on the heat transfer of infrared radiation and air convection, and considering moisture evaporation and vapor condensation. The model fitted well with the apple slice moisture and temperature data with average relative errors of 0.54% and 0.39%, respectively. The heat and mass transfer during infrared blanching involved the interaction of infrared radiation source, air medium and apple slice. At constant 120℃ of infrared heating temperature, the relative humidity of medium had effect on the heat and mass transfer during infrared blanching, drying rate after blanching, and product quality. Under the condition of low humidity (1% relative humidity), the water vapor partial pressure of the air medium was lower than that of the material surface. The moisture in material was transferred from the surface of the material to the air medium via diffusion, and the heat consumption of water evaporation accounted for 40% of the total absorbed heat of material, resulted in slow heating rate of material. At the constant temperature, the higher relative humidity, the more water vapor content in the equal amount of dry air. Increasing the relative humidity of the medium to 50% could effectively restrain the water evaporation of the apple slice that could greatly improve the heating rate of material at the initial stage of blanching. In 50% relative humidity, The center temperature of the material increased to 86.8℃ after blanching for 120 s. The drying rate and color quality of the apple chips could be improved by infrared blanching under high air relative humidity. Compared with 1% relative humidity, the pre-drying time of the apple slice was shortened by 8.3% under 50%IRB, and color difference and browning index of apple slice were reduced by 55.6% and 37.4%, respectively. The results provided a new idea for the development of infrared blanching pretreatment technology of fruits and vegetables to achieve high quality and efficient drying. [ABSTRACT FROM AUTHOR]