• Korean Journal of Food Science and Technology
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• v.21 no.2
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• pp.203-211
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• 1989

During hot air drying of root vegetables such as radish and sweet potatoes, shrinkage and casehardening occurred, and thereby the quality change appeared. Therfore the hot air drying apparatus in which air temperature, relative humidity and air velocity could be controlled was designed, and the drying and shrinking characteristics of radish and sweet potatoes were studied. Also the external factors that affected these characteristics were investigated. The whole drying process of radish and sweet potatoes could be divided into four different drying rate periods, namely constant rate period, first falling rate period, second falling rate period (a) and (b). The shrinking rate curve consisted of four periods nearly corresponding to drying rate periods. The shrinking rate slowly increased in the constant rate period, rapidly increased in the first falling rate period, and reached the highest value in the early period of the second falling rate period. The surface shrinkage was greatly affected by the thickness of sample, relative humidity and initial moisture content. The shrinking ratio was increased with decreasing thickness and increasing relative humidity and initial moisture content.

• Physical Therapy Korea
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• v.8 no.3
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• pp.107-117
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• 2001

Falls are the most serious health problems in elderly population. They are a major cause of premature death, physical injury, immobility, psychosocial dysfunction, and nursing home placement. To reduce the alarming rate of falls and related excessive mortality and morbidity, efforts must be made to detect persons at risk of falling and to prevent or reduce the frequency of falls. To facilitate such approaches, it is essential to find the cause of falling (and under what conditions) of the elderly and the factors that are associated with risk of falling. This study was aimed at designing interventions that minimize risk of falling by ameliorating contributing factors while maintaining or improving patient's mobility.

• Clean Technology
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• v.7 no.2
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• pp.151-159
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• 2001

Mathematical modeling and numerical simulation studies have been conducted for a falling film type absorber of the ammonia absorption heat pump. A rigorous absorber model has been developed by considering temperature effects on physical properties and its predictability proved far superior to that of existing models, which has been confirmed by the experimental data. Using the developed model, effects of cooling water condition - temperature and flow rate - on the efficiency of absorber has been examined. As the result of simulation, the efficiency of absorber has increased as the cooling water temperature has decreased and flow rate has increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.996-1003
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• 2002

Heat transfer characteristics were investigated for the falling film flowing down the outside of an electrically heated vertical tube. Water was used for the falling film, and its Reynolds number was varied in the range of 70～500. Because water is heated and evaporated as it flows down, both sensible and latent heat transfer should be considered. The effect of the surrounding air movement was investigated by changing the direction of the air injection; without air injection, parallel-flow, and counter-flow. For all cases, sensible teat transfer rate was almost linearly increased with the increasing film flow rate. It was found that the film heat transfer coefficient was hardly influenced by the parallel air flow. However, the counter-flow of air reduced the heat transfer coefficient, which might be caused by the uneven distribution or flooding of the film. At high heat flux, a sudden change of the film heat transfer coefficient was detected as the film flow rate reached the transition value. It is supposed that this phenomenon was caused by the change in the film flow pattern.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.7
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• pp.642-648
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• 2000

Falling film heat transfer analyses with aqueous lithium bromide solution were peformed to investigate the transfer characteristics of the copper tubes. Finned(knurled) tube and a smooth tube were selected as test specimens. Averaged generation fluxes of water and the heat transfer performances(heat flux, heat transfer coefficient) were obtained. The results of this work were compared with the data reported previously. As the film flow rate of the solution increased, the generation fluxes of water decreased for both tubes. The reason is estimated by the fact that the heat transfer resistance with the film thickness increased as the film flow rate increased. The effect of the enlarged surface area at the knurled tube was supposed to be dominant at a small flow rate. The generation fluxes of water increased with the increasing degree of tube wall superheat. Nucleate boiling is supposed to occur at a wall superheat of 20 K for a smooth tube, and at 10 K for a knurled tube. The heat transfer performance of the falling film was superior to pool boiling at a low wall superheat below 10 K for both tubes tested. The knurled tube geometry showed good performance than the smooth tube, and the increased performance was mainly came from the effect of the increased heating surface area.

• Journal of the Korean Society of Safety
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• v.34 no.3
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• pp.83-88
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• 2019

The 7,993 cases of Survey Report of Fatal Industrial Accidents conducted jointly by the MEOL and the KOSHA for the recent seven years(2007-2013) were categorized according to personal and occupational characteristics, industry types, business sizes, job types, activities at the time accident, types of accidents, material agents(assailing materials), unsafe conditions, and unsafe acts. And it is found that among the 72.2 percent of fatal occupational accidents in the construction and manufacturing industries are caused by falling, sticking, bumping and being caught under objects & overturning. For this study, through the empirical analysis on causes of fatal industrial accidents, was used to identity high risk groups based on total data of 7,993 victims of occupational accidents. An annual fatal occupational injury (FOI) rate per 10,000 workers was about 0.47‱. The middle-aged group and the elderly group showed the highest FOI rates per 10,000 workers (0.73‱, 0.80‱), and the daily workers showed the highest FOI rate (1.46‱), and the craft and related trades workers showed the highest FOI rate (2.17‱). In case of industry type the mining industry (7.26‱) showed the highest FOI rate, followed by the sewerage, waste management, materials recovery and remediation activity industry (3.91‱) and the construction industry (2.71‱). The primary high risk target group that requires a strategy designed to reduce fatal occupation injuries caused by falling and bumping & contact(collision) is the construction industry, and the secondary high risk target group in the construction industry is classified as the equipment, machine operating and assembling workers in the construction industry, those aged 50 years old and above need the prevention measures against bumping & contact(collision) and being caught under an object & falling(objects), while those aged less than 50 years old need prevention measures against falling(persons).

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.241-250
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• 1990

Characteristic relaxation time and characteristic diffusion time of viscoelastic fluids are determined experimentally by measuring the zero-shear-rate viscosity by falling ball viscometer and the infinite-shear-rate viscosity by capillary tube viscometer. Fluids used in experiments are aqueous solutions of polyacrylamide Separan AP-273 and the polymer concentrations range from 300 to 2000 wppm. A newly designed laser beam and timer system is employed to overcome the difficulty in measuring terminal velocities of the low concentration solutions. Ball removal device is prepared to remove the dropped ball from the bottom of cylinder without disturbing the testing fluid. In order to measure the zero-shear-rate viscosity, densities of hollow aluminium balls are adjusted very close to the densities of testing fluids. Characteristic diffusion time, which is ball viscometer. However, terminal velocity of a needle by falling ball viscometer is not affected by the time interval of dropping needles and characteristic diffusion time is not measured with a dropping needle. Powell-Eyring model predicts the highest values of the characteristic relaxation times among models used for heat transfer experimental works for a given polymer solution. As degradation of a polymer solution continues, the zero-shear-rate viscosity decreases more seriously than the infinite-shear-rate viscosity. Characteristic relaxation times of polymer solutions decreases as degradation continues.

• Journal of Biosystems Engineering
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• v.41 no.4
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• pp.342-356
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• 2016

Purpose: The drying of a thin layer of native cassava starch in a tray dryer was modeled to establish an equation for predicting the drying behavior under given conditions. Methods: Drying tests were performed using samples of native cassava starch over a temperature range of $40-60^{\circ}C$. We investigated the variation in the drying time, dynamic equilibrium moisture content, drying rate period, critical moisture content, and effective diffusivity of the starch with temperature. The starch diffusion coefficient and drying activation energy were determined. A modification of the model developed by Hii et al. was devised and tested alongside fourteen other models. Results: For starch with an initial moisture content of 82% (db), the drying time and dynamic equilibrium moisture content decreased as the temperature increased. The constant drying rate phase preceded the falling rate phase between $40-55^{\circ}C$. Drying at $60^{\circ}C$ occurred only in the falling rate phase. The critical moisture content was observed in the $40-55^{\circ}C$ range and increased with the temperature. The effective diffusivity of the starch increased as the drying temperature increased from 40 to $60^{\circ}C$. The modified Hii et al. model produced randomized residual plots, the highest $R^2$, and the lowest standard error of estimates. Conclusions: Drying time decreased linearly with an increase in the temperature, while the decrease in the moisture content was linear between $40-55^{\circ}C$. The constant drying rate phase occurred without any period of induction over a temperature range of $40-55^{\circ}C$ prior to the falling rate period, while drying at $60^{\circ}C$ took place only in the falling rate phase. The effective diffusivity had an Arrhenius relationship with the temperature. The modified Hii et al. model proved to be optimum for predicting the drying behavior of the starch in the tray dryer.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.745-748
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• 2002

Many malfunctions take place in container crane spreader due to impact. So we designed a 2DOF hydraulic impact absorbing system and studied the change of impulse with respect to the variation of falling height and weight. The falling height becomes higher than 1m and the falling weight goes up heavier than 100kg, the impact absorbing rate was lower. When spreader is bumped against container and impulse force concentrates on one point, impact absorbing equipment would not be operated properly and make some trouble.

• Korean Journal of Food Science and Technology
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• v.27 no.3
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• pp.358-364
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• 1995

In order to determine the moisture content level for safe storage of wild vegetables, drying characteristics and water vapor sorption characteristics of four vegetables, i.e., zucchini slice, sweet potato stem, taro stem, and platycodon, were investigated. The drying curves of these vegetables were consisted of three characteristic stages which were the initial settling down period, the constant drying rate period, and the falling drying rate period. And the falling rate period of the vegetables showed 2 or 3 parts of falling rate. All of the falling rate curves of the vegetables showed upwardly convex shape which is known as a characteristic pattern for the drying of fibrous food materials. The critical moisture contents of the vegetables were $8.29{\sim}9.75,\;10.40{\sim}15.08,\;9.51{\sim}14.52\;and\;3.29{\sim}3.56g\;H_2O/g$ dry solids for zucchini slice, sweet potato stem, taro stem, and platycodon, respectively. Activation energy values of drying rate during falling rate period were 2.30, 2.11, 4.97, and 2.80 kcal/mol for zucchini slice, sweet potato stem, taro stem, and platycodon respectively. The BET monolayer moisture contents of the vegetables were $10.05{\sim}13.59,\;9.49{\sim}12.69,\;9.50{\sim}16.48\;and\;5.01{\sim}5.44g\;H_2O/g$ dry solids for zucchini slice, sweet potato stem, taro stem, and platycodon, respectively. And these values were found to be very compatible with the values of the critical moisture content. Consequently, it was found that the moisture of these vegetables should be removed below the BET monolayer moisture content or below the critical moisture content for the long term storage.