Design and manufacturing of an inductive liquid food heat treatment-filling system

Abstract

In this study, an inductive heat treatment-filling system for milk pasteurization was designed and constructed. To identify the design parameters of the system, basic computational fluid dynamics (CFD) and lethality (reduction of a target pathogen during heating or thermal destruction of microorganisms) analyses were carried out simultaneously. In this context, the temperature–time combination of heated milk related to pipe design was taken into consideration. Induction calculations were made to provide the necessary heating for the selected flow rate and pipe construction material and diameter. Required frequency, power, and optimum coil design for the system were identified and validated. In the study, analyses were made for three different temperatures (90, 120, 150°C) with different designs (straight pipe, flow breaker blades on the surface, central shaft) to define the required pipe length to obtain milk temperature (85°C). Pipe dimensions were evaluated by CFD design and the shortest pipe length was 540 mm for the pipe having surface modification at 150°C. However, for simplicity and applicability, a straight pipe at 90°C constant surface temperature was selected for prototyping. From lethality calculations, 80°C outlet temperature for 2700 mm pipe length was found to be sufficient and these parameters were considered for calculating induction parameters such as coil design and induction power. Experimental validation showed that heat balance was achieved compared to CFD calculations for the given system in steady condition; however, 130 s is required for reaching steady condition and this gap can be considered as come-up time. Although heat provided by induction was sufficient to heat milk to the desired temperature at the given pipe length, time was needed to heat the pipe to 90°C with 25°C milk passing inside at 1 L/s capacity.