Kyung Ryu

An optimum design study of the yarn-channel shape of the air-interlacing nozzle by analysis of fluid flow

The air-interlacing process provides assurance in the downstream performance in weaving and knitting without changing the properties of the synthetic yarn. The air-interlacing nozzle is an important component for improving the performance in the air-interlacing process. The airflow inside the air-interlacing nozzle is investigated to design an optimum yarn-channel shape of the nozzle. The width and height of the yarn-channel and inlet pressure are the design variables of the air-interlacing nozzle. The design variables are evaluated by the vorticity. The design of experiments (DOE) approach is utilized to study the influence of the nozzle configuration. Minitab is used as a practical and effective tool in optimizing the nozzle geometry to improve performance. Computational simulations of the impinging airflow inside the nozzle are undertaken using ANSYS CFX. The airflow characteristics such as the vorticity, shock wave, and velocity distributions were discussed. Various cross-sectional shapes of the yarn-channel are investigated with the same inlet pressure. The cross-sectional shape of Shape 6 which has high vorticity is observed to find optimal configurations for the nozzle of the air-interlacing process. The design variables of the nozzle are the width and the height of the yarn-channel and the inlet pressure. The reason for the evaluation of the performance of the nozzle is the maximization of the vorticity. The response surface method (RSM) is applied for the shape optimization. The vorticity cannot increase at the high inlet pressure due to the shock wave. The air-interlacing nozzle, with optimum configurations, is verified numerically and experimentally.

Growth and predictive model of Bacillus cereus on blanched spinach with or without seasoning at various temperatures

The growth of Bacillus cereus on blanched spinach with or without seasoning at various temperatures (15, 20, 25, 30, and 35°C) was investigated. The number of B. cereus on blanched spinach stored at 35°C was significantly increased and resulted in maximum populations (7.8 log CFU/g) after 10 h. However, the growth rate of B. cereus on blanched spinach with seasoning stored at 35oC was lower than on blanched spinach without seasoning. The growth rate (GR) of B. cereus on blanched spinach stored at 15°C was lower than the other temperatures. The lag time (LT) of B. cereus on blanched spinach with seasoning was longer than blanched spinach without seasoning. Primary growth models of B. cereus on blanched spinach fit well to a modified Gompertz model (blanched spinach R2 =0.98; blanched spinach with seasoning R2 =0.96). These results might be used for developing safe storage guidelines for cooked vegetable at various temperatures.

Predictive model for growth of Staphylococcus aureus in blanched spinach with seasoning

The safe storage time of blanched spinach with seasoning was determined using a predictive model of Staphylococcus aureus as a function of storage temperatures (5, 15, 20, 25, 30, 35°C). Storage of blanched spinach with seasoning at 5 and 15°C did not show any appreciable increase in the viable populations of S. aureus. At 20, 25, 30, and 35°C, a progressive increase in the viable populations of S. aureus was observed and increased more rapidly at 30 and 35dgC. A primary model (Gompertz model) was used to determine the determination coefficient (R2) values of lag time (LT) and specific growth rate (SGR). R2 values were not detected (ND) (5°C), 0.9777 (15°C), 0.9980 (20°C), 0.9949 (25°C), 0.9940 (30°C), and 0.9959 (35°C). A quadratic polynomial model equation could be proposed as a secondary model and was applied for lag time and SGR from primary modeling graphed as a function of storage temperature. The compatibility of the model was confirmed by calculating R2, mean square error (MSE), bias factor (Af), and accuracy factor (Bf) values as static parameters. For LT and SGR, R2 values were 0.9718 and 0.9789; MSE. 3.25 and 0.00; Af. 1.19 and 1.12; Bf, 1.05 and 1.02, respectively. These results indicate that the predictive model for S. aureus on blanched spinach with seasoning has a high statistical compatibility. Predicting S. aureus growth under different temperature storage conditions yielded safe storage times of blanched spinach with seasoning of 10, 10, 8, and 6 h for storage temperatures of 20, 25, 30, and 35°C, respectively.

Microbial Hazard Analysis of Manufacturing Processes for Starch Noodle

The purpose of this study was to identify control points through microbiological hazard analysis in the manufacturing processes of starch noodles. Samples were collected from the ingredients, manufacturing pro- cesses, equipment and environment. Microbiological hazard assessments were performed using aerobic plate counts (APC), Enterobacteriaceae (EB), E. coli and five pathogens including B. cereus, E. coli O157:H7, L. monocytogenes, Salmonella spp., and S. aureus. The APC levels in raw materials were from 2.12 to 3.83 log CFU/g. The contamina- tion levels after kneading were 4.31 log CFU/g for APCs and 2.88 log CFU/g for EB counts. APCs decreased to 1.63 log CFU/g and EB were not detected after gelatinization, but their levels slightly increased upon cooling, cutting, ripening, freezing, thawing, and separating. The reuse of cooling and coating water would be a critical source of microbial increase after cooling. After drying, APCs and EB counts decreased to 5.05 log CFU/g and 2.74 log CFU/ g, respectively, and the levels were maintained to final products. These results suggest that the cooling process is a critical control point for microbiological safety, and the cooling water should be treated and controlled to prevent cross contamination by pre-requisite program.

Evaluation of Food Safety Performance and Food Storage Condition in Restaurants against Climate Change

This study was conducted to investigate the current status of hygiene performance and food preparation/storage condition in restaurants during the summer season in order to evaluate the sanitary management systems in restaurants against climate change. Total 30 restaurants located in Gyeonggi participated in a survey in which they were asked current hygiene performance, food preparation/storage condition, and purchasing practices for 5 food ingredients. As results, regarding the performance degree of respondents on food hygiene management, the average scores of 9 questions were well over 4 points. However, only 6.83% of the respondents claimed that they use sanitizers (chlorine) to disinfect food ingredients. About food storage condition, a high proportion of respondents said that they store food materials in plastic bags or airtight containers following pretreatment and use refrigerator for the storage of pretreated food materials. However, 5.55% and 14.85% of respondents answered that they store pretreated food materials in the kitchen or inside of dining room, respectively. Respondents (21.50%) answered that they store pretreated food materials for more than 6 hours before cooking. Therefore, food materials need to be disinfected properly with sanitizer to remove microbial contamination and stored at refrigerator using closed bags or containers before cooking in order to prevent foodborne disease in restaurants especially during summer season.

Assessment of Microbiological Quality of Outsourced School Meals

The purpose of this study was to provide a basic resource for establishment of hygienic management stand- ards for meal delivery from the central kitchen to schools. Flow diagrams for delivery of food were analyzed, and time-temperature conditions of the food and environment were measured. Four different foods samples in- cluding Mexican salad, radish salad, stir-fried pork and vegetables, and stir-fried chicken and vegetables were collected after production and before service. Microbiological analysis was performed for aerobic plate counts (APC), Enterobacteriaceae, coliforms, E. coli, Salmonella spp., S. aureus, B. cereus, C. perfringens, and L. monocytogenes. After completion of production of cooked foods 2∼3 hours were taken for the cooked foods to reach the temperature danger zone. Food temperatures at the meal service did not meet the recommended temperatures (10/57 o C) for conventional school food service systems. The highest APC counts were observed in radish salad (5.70 log CFU/g), followed by Mexican salad (5.18 log CFU/g). Enterobacteriaceae and coli- form counts were within acceptable levels of those recommended by the UK Public Health Laboratory Service. No E. coli or pathogens were found. These results provide useful information for determination of microbiological hazards in school food service systems, and suggest that time-temperature control during deliv- ery is necessary for the safety of cooked foods.

Improving airflow loss through the yarn-loading slit of the air-interlacing nozzle using TRIZ

The air-interlacing nozzle has a yarn channel, an air inlet and a yarn-loading slit. The previously investigated optimum air-interlacing nozzle was analyzed to improve the airflow loss through the slit by reducing the width of the slit and by applying TRIZ tool. TRIZ, the theory of inventive problem solving, was applied to find a solution for the airflow loss through the yarn-loading slit. The airflow inside the air-interlacing nozzle was computed using ANSYS CFX software. The computational results of the air-interlacing nozzle were evaluated by the vorticity, velocity and the airflow loss. The vorticity was increased and the airflow loss was improved slightly when the width of the slit was reduced. The yarn-loading slit is for the yarn loading into the yarn channel before the air-interlacing process. The technical contradiction of the air-interlacing nozzle was that reducing the width of the yarn-loading slit makes it difficult to load the yarn into the yarn channel. Principles 10 and 31 of TRIZ were obtained through the contradiction matrix and were applied to the nozzle. The computational results showed that the vorticity and velocity were increased and the airflow loss through the slit was improved. The air-interlacing nozzle after applying principles of TRIZ showed better results when compared numerically and experimentally with other existing nozzles.

Influences of the air inlet and yarn-loading slit on the performance of an air-twist nozzle

An air-twist nozzle has an air inlet and yarn channel with a yarn-loading slit. The nozzle was investigated by changing the width and length of the air inlet and by modifying the yarn-loading slit using computational fluid dynamics. The airflow vorticity, mass flow rate, and velocities of the air-twist nozzle were evaluated to analyze the influences of the air inlet and yarn-loading slit. The velocity and vorticity were high when the width and length of the air inlet were 0.2 and 0.1 mm, while the diameter and length of the yarn channel were fixed at 1 and 3.5 mm, respectively. The air inlet was divided into two and three small rectangular air inlet holes to increase the velocity and vorticity. The velocity and vorticity were high but not uniform at the yarn channel. Dividing the air inlet increased the velocity but disturbed the air-twisting process; therefore, the air inlet without dividing was selected for further computations. The influence of the yarn-loading slit on the air-twist nozzle flowfield was observed to improve the performance of the nozzle by changing and removing the slit. The velocity, vorticity, and mass flow rate were improved significantly when the yarn-loading slit was removed. The air-twist nozzle with the removed yarn-loading slit was fabricated as a prototype for testing. The air-twist nozzle was compared with the existing air-twist nozzles under identical conditions. The test results showed that the developed air-twist nozzle with removed yarn-loading slit had better performance than the existing nozzles.

Optimum design of the injection nozzle system of a three-drive jigger dyeing machine

A jigger dyeing machine is used to dye fabric across the width, which enables the fabric to be passed back and forth in a perfect dyeing bath. A three-drive jigger dyeing machine contains an injection nozzle system. The flowfield inside the injection nozzle system was computed using ANSYS CFX software and was evaluated by mass flow rate, velocity, and pressure. The injection nozzle system was observed by installing two different division plates and by changing the diameter and distance of the outlet holes to improve dyeing efficiency. The division plates have slits and holes help to distribute the dye liquid evenly over all the holes. The standard deviations of the mass flow rate of the division plates with slits and holes were 0.000551 and 0.000368, respectively. The effects of distance and diameter of the outlet holes were analyzed and evaluated by mass flow rate and standard deviation. The developed injection nozzle system of the jigger machine has more uniform mass flow rate. A diameter of 5 mm for the outlet holes and a distance of 50 mm between them were selected to manufacture a prototype. The prototype of the injection nozzle system of the three-drive jigger machine was manufactured and tested. The test results were compared with the computational results from the developed three-drive jigger dyeing machine, the original three-drive jigger dyeing machine, and a classic jigger dyeing machine.

Predictive modeling for the growth of Listeria monocytogenes and Salmonella Typhimurium on fresh-cut cabbage at various temperatures

The growth of Listeria monocytogenes and Salmonella Typhimurium on fresh-cut cabbage at between 15 and 35°C before and after treatment with water washing, chlorine dipping, and chlorine dipping followed by water washing were investigated. It is apparent that these pathogens could grow faster at higher temperature. Chlorine treatments reduced L. monocytogenes and S. Typhimurium on cabbage by 1.04–1.15 log CFU/g and 1.35–1.51 log CFU/g, respectively. Gompertz model and polynomial equation were used to describe the behaviors of L. monocytogenes and S. Typhimurium on cabbage before and after treatment with water washing, chlorine dipping, and chlorine dipping followed by water washing as a function of temperature. The lag times of L. monocytogenes and S. Typhimurium were the longest when treated with chlorine dipping followed by water washing at 15°C. The growth rates of L. monocytogenes and S. Typhimurium were the lowest when treated with water washing at 15°C, indicating that the growth of pathogen was more affected by storage temperature than chlorine treatment. Validation was also performed to evaluate the reliability of developed predictive models. The Bf values of the growth rate and lag time for L. monocytogenes and S. Typhimurium ranged from 0.90 to 1.25, indicating that they were mostly in the acceptable level, whereas Af values ranged from 1.07 to 1.80, showing that they were over-predicted.