Effect of holding tube configuration and curvature ratio on the residence time distribution of multiple particles in helical tube flow

The flow of solid-liquid mixtures in helical tubes of different configurations was investigated. The effects of curvature ratio of the helical tube (ratio of tube diameter to coil diameter), flow rate, carrier fluid viscosity, and particle concentration on the residence time and residence time distribution (RTD) of particles were determined. Curvature ratio and flow rate were found to be the most important factors affecting the RTD of particles. Interactions between particles were found to be important, as the residence time of slower-moving acrylic particles decreased while that of faster-moving polystyrene particles increased slightly upon mixing the two types of particles.; Single-phase flow in a helical tube was simulated using CFD software. The effect of different processing parameters on the degree of mixing and axial and radial pressure drops were determined. Axial velocity profile became flatter with increasing Dean number. Correlations were developed to calculate axial and radial pressure drops, and also the ratio of maximum to average fluid velocities. Experimental investigation of the degree of mixing in different configurations was performed by flow visualization. A higher degree of mixing was attained when the tube with a larger curvature ratio was used, which was in agreement with the simulation results.; In addition, a computer program was developed to simulate the heating of a particle in the holding tube. The effect of h_fp on microbial and nutrient destruction was studied. An increase in h_fp reduced the time of heating required to reach a target lethality. However, the highest nutrient retention was obtained with the most conservative h_fp. Nutrient losses were found to be more pronounced for larger particles. It was found that even if the process were designed using the most conservative h_fp, product quality would still be acceptable for particles of small sizes. Nevertheless, ensuring a narrow RTD in the holding tube can minimize over-processing of the already sterilized particles.