Modeling the Ultrasonic Atomization Process of Milk and Powder Production Using Spray Drying Method

The beneficial use of ultrasonic systems has been proven in many applications. Among them, ultrasonic atomization is widely used in various industries, including food and coating industries. Ultrasonic vibrations of liquids can produce fine droplets called atomized fluid. During the fluid atomization process, droplet size and distribution can be precisely controlled so that the droplets become very small and high-level particle distribution is achieved which can be easily evaporated. This method is widely used in various industries, including food industry (for the production of driedpowder products) and coating industry. The key factor that affects droplet size is the frequency and amplitude of the ultrasonic vibrations and the properties of the fluid, including the fluid viscosity and surface tension.

Based on a review of literature, it is clear that the modeling of the ultrasonic method for spray dryers and the production of milk powder has not been done so far. In the present work, first, the research background is reviewed and then, using the relationships provided for the ultrasonic atomization of different fluids in the reviewed articles, the effect of ultrasonic vibrations on the atomization and evaporation of milk as a food and the powder production was studied using spray drying process. Then the effects of various oscillation parameters such as frequency, amplitude and also the temperature of the fluid, which affects its viscosity, density and surface tension, on the rate of atomization of the fluid was investigated. In the present work, we first examine the fluid whose range of properties is true in relations. One of the most widely used liquids in the food industry is milk. By examining the viscosity, surface tension and density of the milk and obtaining the dimensionless numbers We, In and Oh, it is determined that the provided relations can also be used for milk. After calculating the diameter of the evaporated particles of milk due to ultrasonic vibrations as well as the evaporation rate, the independent variables of the research can be changed. First, in the constant physical properties of a fluid, we change the frequency and amplitude of ultrasonic oscillations and studied their effect on the produced particle diameter and evaporation rate. In the next step, with the constant frequency and amplitude of ultrasonic oscillations, the effect of changes in fluid properties (temperature change) on the produced particle diameter and evaporation rate was investigated. In the next stepthe effect of frequency and amplitude of ultrasonic fluctuations as well as changes in fluid properties (temperature change) on the powder diameter produced and the time required for the drying process was investigated. The analysis of all data obtained from the above steps was performed using Mathlab software.

The main and summary results obtained from the present study are as follows:As the amplitude of the vibrations and the temperature of the milk increased, the drying time required for the evaporation of droplets decreased, but the powder diameter and the evaporation rate increased.As the frequency of vibrations increased, the drying time required for the evaporation of droplets increased, but the powder diameter and the evaporation rate decreased.The results showed that quadrupling the amplitude of the vibrations reduces the time required for the droplets to dry by 14.4% and increases the evaporation rate by 62.6%. At a constant temperature of the gas dryer and the milk, changing the frequency from 10 to 40 kHzresults in 21.4% increase in the time required for the droplets to dry. Also, with increasing the temperature of the milk from 15 to 30°C, at a constant frequency and amplitude of vibrations, the time required for drying the droplets decreases by 12.4% and the diameter of the particles produced increases by 11.3%.

In this research, the process of ultrasonic assisted evaporation of whole milk and drying and production of milk powder has been modeled mathematically and thermodynamically. The calculation code was written using Mathlab software and after making sure that the solution conditions are in the desired range of equations, the results were presented. In the present work, the effect of the frequency and amplitude of ultrasonic vibrations as well as the initial temperature of milk on the diameter of the evaporated particles, the evaporation rate, the diameter of the powder produced and the time required for the evaporated droplets to dry by ultrasonic method was investigated.