| Enhancement of continuous flow cooling of viscous products was examined numerically and experimentally, using computer simulation modeling and studies of surface modified heat exchangers, respectively.;Computer simulation studies were conducted using Multiphysics software system Comsol 5.2, in order to study cooling of applesauce and sweet potato puree. Simulation studies were used to compare the efficiency of cooling under two different flow regimes within the same tube in tube heat exchanger, with the food materials: i) flowing within the inner tube of the heat exchanger and ii) flowing within the annulus. The simulation results indicate that under an identical set of operating conditions, potential improvements in the cooling efficiency resulting from the movement of process material flow from the internal tube into the external annulus could be up to 14% and 23%, for applesauce and sweet potato puree, respectively.;Using the heat exchanger design selected based on results of the simulation studies, a preliminary study was conducted to examine the effects of surface treatment on cooling (97- 57 °C) and thermal mixing via vibration of sweet potato puree, banana puree, and cheese sauce. Cooling performance and temperature uniformity were compared between two identical horizontal stainless steel tube in tube heat exchangers, one untreated and one with the foodcontact surfaces chemically treated with a commercially available hydrophobic solution. A lower average product outlet temperatures ranging from 4 to 6 °C were observed for banana puree and cheese sauce with the treated heat exchanger, compared to the untreated case. However, for sweet potato puree cooling was slightly better (by 2-4 °C) using the untreated heat exchanger, compared to the treated case. Application of vibration at the resonance frequency (20 Hz) of the mixing unit resulted in a more uniform cross sectional temperature distribution, which was observed for sweet potato puree and banana puree. However, application of vibration had no significant influence on cross sectional temperature distribution within cheese sauce.;In continuation of the previous studies, effects of different surface characteristics (wettability, roughness) on the adhesive behavior of sweet potato puree, banana puree, and cheese sauce, and the flow behavior of Carboxymethyl Cellulose (CMC) solution (conc. 1.5%) were examined for potential applications in cooling and mixing. Different engineered foodcontact materials, including untreated and chemically treated stainless steel, polytetrafluoroethylene (PTFE), silicone sheets as well as treated and untreated knitted and woven polyester fabrics, were studied. Adhesive behavior of the tested foods and repellent behavior of the engineered surfaces were examined by comparing the residual product mass, during the standard methods of product depletion and the centrifuge adhesion tests. These tests were performed under two different temperature conditions; at ambient and at cooling processing temperature conditions. Results from the product depletion test showed that the hydrophobic surfaces with smooth characteristics (chemically treated stainless steel samples, PTFE, and treated knitted fabrics) retained the lowest amount of the foods, with the residual amounts of 35-45% at room temperature, and 45-65% at cooling conditions. In order to examine the cooling efficiency under cooling conditions, the temperature difference (DeltaT) between the initial and final highest product temperature was compared between the examined surfaces. The treated and untreated stainless steel, and PTFE surfaces presented the highest DeltaT values, for all the foods tested. For the centrifugal adhesion test, the superhydrophobic knitted fabrics exhibited the best repellent behavior with all the foods tested, reducing the residual product to 0-10% and 20-40% levels, under room and cooling temperature conditions, respectively.;Pressure drop and velocity profile of 1.5% CMC solution, flowing within the annulus of a tubular heat exchanger, were used to compare the effects of the examined surfaces on adhesive and flow behavior, respectively. Highly rough, hydrophobic surfaces (silicone sheets and untreated woven textiles), exhibited the highest pressure drop across the system with a value of 75842.4 Pa. While, the lowest pressure drop, at 48263.3-55158.1 Pa, was observed with the smooth surfaces (chemically treated stainless steel) and with the superhydrophobic samples (treated knitted and woven textile samples). The velocity profile of 1.5% CMC was also examined, using particle tracking velocimetry (PTV) as the testing method. The PTV results for the velocity profile of 1.5% CMC, showed a parabolic velocity profile for all the examined cases, with the fastest flowing particle located close to the center of the annulus flow.;The final study investigated the effects of two different food-contact materials; untreated stainless steel and engineered food-grade PTFE textile on cooling of sweet potato puree, banana puree, and cheese sauce. The PTFE textile was designed based on the surface characteristics observed in the previous studies. Using PTFE for its stability, the engineered surface was fabricated with hydrophobic properties, smooth characteristics, and knitted structure. Cooling experiments for both examined surfaces were conducted under steady state, identical operating conditions, with tested foods flowing within the annulus of a tubular heat exchanger. The outside surface of the inner tube of the heat exchanger was used as the tested food-contact surface, by the application of the knitted PTFE textile. Finally, results for all the tested foods showed a total improvement between 15-25% of cooling efficiency when using the inner tube of the heat exchanger covered with the PTFE textile. |
