Study On Hot Air Drying Characteristics Of Carrot Slices

Hot air drying of carrot can not only prolong its storage time but also increase its added value.Therefore,it is of great significance to further optimize the drying process of carrot by solving the problems of poor drying quality,long drying time and high energy consumption of traditional hot air drying technology of carrot slices.In order to improve the above problems,hot air drying testing device was built and the single-factor experimental method was used to study the drying process of carrot slices.Hot air drying testing device has three system forms: open,semi-open and closed.At the same time,the drying chamber can realize various air supply modes,such as down-supply and up-return above the same side,up-supply and down-return above the same side,and mid-supply and mid-return.The orifice plate air supply is used in the drying room,and the air distribution was simulated and analyzed by software.It was found that the 6 mm orifice air supply plate can make the air distribution more uniform in the drying room.The drying technology of carrot slices was studied.Firstly,the effects of different temperature,wind speed and relative humidity on the drying characteristics of carrot slices were analyzed.Then the drying characteristics of carrot slices were compared and analyzed under the conditions of temperature-raising and humidity-lowering,temperature and humidity reduction,and constant temperature and humidity.Drying time,energy consumption,rehydration,color and shape were used as evaluation indexes to compare and analyze the drying of carrot slices under the different test conditions above.It is found that the temperature has the greatest influence on the drying quality.If the drying temperature is too high,the drying time can be significantly reduced,but the carrot slices are coking,the deformation is severe,and the rehydration is poor.If the drying temperature is too low,the drying time will be prolonged and the color of the carrot will be yellow.The wind speed has the greatest influence on the accelerated drying stage and the first deceleration drying stage.The larger the wind speed,the larger the drying rate of the two stages.The effect on the drying rate of the second deceleration drying stage is not very large,and the drying rate is basically the same at different wind speeds.Increasing the relative humidity in the drying chamber during the preheating phase can quickly preheat the material to a higher temperature,thereby balancing the moisture loss rate inside and outside the carrot slices,preventing the surface of the carrot slices from drying quickly to form a hard skin.Lowering the relative humidity in subsequent stages can increase the drying rate.Under the condition of temperature-raising and humidity-lowering,the dry product has the best rehydration and the best drying quality.Temperature-raising and humidity-lowering is the best drying method.The linear fit of the experimental data shows that the Page model is more in line with the hot air drying process of carrot slices,and the experimental data is in good agreement with the simulated data.The effective diffusion coefficient is calculated based on the Fick’s law equation.It is found that the higher the temperature,the higher the wind speed and the lower the relative humidity,the larger the effective diffusion coefficient.The research results of this paper have important guiding significance for the engineering practice of hot air drying of carrot slices.