Dynamic simulation of a plate pasteurizer unit: Mathematical modeling and experimental validation

Study of heat transfer coefficients and temperature distribution in a continuous flow pasteurizer with helical tubes using model fluids in laminar flow

Modeling of continuous pasteurization is useful for predicting time-temperature history of the product and lethality. The use of helical tubes in the heat exchangers and holding tube can simplify modeling in laminar flow due to the narrowing of the residence time distribution. To present this approach, three model fluids (water, 80% glycerol/water and 1% carboxymethylcellulose) were processed in 25 conditions in a pilot scale unit and the overall heat transfer coefficients of the heater, cooler and holding tube were correlated with Reynolds and Prandtl numbers. For heater and cooler, 3–7 parameters were needed for a fair adjustment, while in the holding tube an average value was obtained. Using these correlations, a simple unidimensional model was simulated to predict the time-temperature history and lethality distribution. Simulation examples for processing at 90 °C provided the F-value contribution of each step showing that this model can be useful for process analysis and design.

Designing process and operational effect of modified septic tank for the pre-treatment of rural domestic sewage

Structure and performance of a newly designed four-chamber septic tank were investigated in current study. A three-layer orifice plate was fitted in the first compartment in an upward direction, and a baffle was arranged in the second compartment of the septic tank. The filter placed in the third and fourth compartment was used to collect water for field irrigation or connect subsequent devices for further processing. Flow field distribution in the first chamber was numerically simulated by Fluent software, and simulation results were verified by residence time distribution tracer experiment. The improved treatment effects of the modified septic tank with optimal parameters of 20 mm (diameter), 60 mm (gap) and 180 mm (distance) were validated by simulation experiments. High removal rates of chemical and biological oxygen demand reflected the effectiveness of modified septic tanks.