Spray drying technology has long attracted the attention of researchers as an effective method for increasing the shelf life an‎d maintaining the nutritional value of milk, one of the most widely consumed food worldwide. In this context, achieving uniformity of particle size, energy efficiency, an‎d quality characteristics of powdered milk is of particular importance. The use of ultrasound waves improves uniformity an‎d efficiency in the spraying process. The horn, as a key component in the ultrasonic wave generation system, is responsible for transmitting an‎d amplifying the amplitude of vibrations produced by the transducer, an‎d its optimal design has a direct impact on the overall performance of the system. In this study, first, the design an‎d performance eva‎luation of a stepped ultrasonic horn were addressed with the aim of achieving optimal conditions for transmitting vibration power at the desired frequency an‎d amplitude. Compared to previous studies, this design is considered as an applied innovation in the field of powdered milk production that can provide a more optimal path for future processes. The design process was carried out with an analytical approach in MATLAB software an‎d, for more accurate validation an‎d analysis, it was numerically eva‎luated using the finite element method in ABAQUS software an‎d finally the designed horn was manufactured. Then, the performance of the designed ultrasonic nozzle at inlet air temperatures of 90 an‎d 110 degrees Celsius was compared with the performance of the pneumatic nozzle in the U07 industrial spray dryer. The experiments were conducted using a completely ran‎domized factorial design with 4 treatments an‎d 2 replications. In order to eva‎luate the quality of milk powder produced with both types of atomizers, physicochemical parameters including powder bulk density, total dissolved solids, solubility, final moisture content an‎d particle size distribution were measured an‎d eva‎luated. The results showed that the ultrasonic nozzle with an operating frequency of 46 kHz an‎d made of 7075 aluminum had a better performance in improving the physical an‎d qualitative properties of milk powder compared to the pneumatic nozzle. Under the test conditions, the final moisture content of the samples obtained from the ultrasonic nozzle at 90 an‎d 110 degrees Celsius was recorded as 6.5% an‎d 5%, respectively, which showed a greater reduction compared to the pneumatic nozzle, although this difference was not statistically significant. In contrast, the total dissolved solids content was significantly higher in the ultrasonic nozzle (12.05% at 90 degrees Celsius an‎d 14.15% at 110 degrees Celsius), indicating improved mass transfer an‎d reduced particle aggregation during the drying process. The results of the analysis of variance also showed that the effect of nozzle type on the bulk density of the powder was significant, but temperature an‎d its interaction with nozzle type did not have a significant effect. The solubility an‎d particle diameter were also significantly affected by nozzle type an‎d temperature, but their interaction was not significant. The ultrasonic nozzle produced particles with smaller size an‎d more uniform structure due to more uniform atomization an‎d more precise control of dro‎plets. Analysis of mechanical stresses applied to the ultrasonic horn also showed that the maximum stress was concentrated in the cylindrical region with a larger diameter an‎d decreased in the region with a smaller diameter, which resulted in increased structural stability in the atomization process. Overall, the ultrasonic nozzle showed better performance in uniform particle size distribution, improved final milk powder quality, an‎d increased spray drying process efficiency.

مرتضي صادقي

اميرحسين گلي

علي قاسمي , ميلاد فتحي