Enhancement of continuous flow cooling using hydrophobic surface treatment

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.

Experimental Investigation and Control of a Hot-Air Tunnel with Improved Performance and Energy Saving

The paper is focused on the identification, control design, and experimental verification of a two-input two-output hot-air laboratory apparatus representing a small-scale version of appliances widely used in the industry. A decentralized multivariable controller design is proposed, satisfying control-loop decoupling and measurable disturbance rejection. The proposed inverted or equivalent noninverted decoupling controllers serve for the rejection of cross-interactions in controlled loops, whereas open-loop antidisturbance members satisfy the absolute invariance to the disturbances. Explicit controller-structure design formulae are derived, and their equivalence to other decoupling schemes is proven. Three tuning rules are used to set primary controller parameters, which are further discretized. All the control responses are simulated in the Matlab/Simulink environment. In the experimental part, two data-acquisition, communication, and control interfaces are set up. Namely, a programmable logic controller and a computer equipped with the peripheral component interconnect card commonly used in industrial practice are implemented. A simple supervisory control and data acquisition human-machine interface via the Control Web environment is developed. The laboratory experiments prove better temperature control performance measured by integral criteria by 35.3%, less energy consumption by up to 6%, and control effort of mechanical actuator parts by up to 17.1% for our method compared to the coupled or disturbance-ignoring design in practice. It was also observed that the use of a programmable logic controller gives better performance measures for both temperature and air-flow control.