• 설비공학논문집
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• 제24권5호
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• pp.409-414
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• 2012

A theoretical investigation to optimize thermoelectric elements for thermoelectric coolers was performed using a new one-dimensional analytic model. Mathematical expressions for the optimum current and the optimum length of a thermoelectric element, which maximize the coefficient of performance of thermoelectric coolers, were obtained. The optimum current is expressed in terms of the cooling load for a thermoelectric element, the hot and cold side temperatures and thermoelectric properties, but not the length of a thermoelectric element. The optimum current is proportional to the cooling load and decreases as the temperature difference between the hot and cold sides decreases. It is also shown that the optimum length of a thermoelectric element decreases as the cooling load increases.

• 산업경영시스템학회지
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• 제33권4호
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• pp.38-44
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• 2010

We investigated the effects of trunk twist on postural stability during manually handling flat ties. Ten male subjects participated in this study. While handling 5kgf and 10kgf bundles of flat ties respectively, their centers of pressure (COPs) were measured under two levels of body position (twisted and fixed), two levels of direction (left and right), and three levels of object position ($30^{\circ}$, $45^{\circ}$, and $60^{\circ}$). Subjects' postural stability was quantified by calculating the sway length. Results showed that the effect of different object position was significant on postural sway length in subject's medio-lateral axis. Post-hoc multiple comparions revealed that, under the 5kgf load condition, the sway length was increased significantly as the object position increased to $45^{\circ}$. Under the 10kgf load condition, however, the sway length was increased significantly at the object position of $60^{\circ}$. Actual or potential applications of this research include guidelines for the design of working posture evaluation techniques.

• 대한의용생체공학회:의공학회지
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• 제41권2호
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• pp.84-93
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• 2020

Despite of a lot of studies about proprioception tests, there are little study results to investigate the relationship between the functional movement and proprioception level. In this study, we tried to perform quantitative analysis for the effect of ankle joint proprioception level on the one leg standing postural control ability. Nine healthy people volunteered for this study. Force and position aspects of proprioception were evaluated using the electromyography system (EMG) and mobile clinometer application, respectively. The center of pressure (COP) trajectories, measured by a pressure mat sensor, were used for quantitative analysis of balance for each subject. We computed indices and errors of force and position aspects of proprioception from the EMG and ankle angle. Mean velocity of total and anterior-posterior direction (Vm and Vm_ap), root mean squared distance in anterior-posterior direction (RDap), travel length (L), and area (A) of COP trajectories were also calculated as indices of postural control ability of subjects. Two aspects of proprioception showed the low correlation from each other as previous studies. However, the EMG error of gastrocnemius lateral activation showed a high correlation coefficient with COP variables such as Vm (ρ=0.817, p=0.007), Vm_ap (ρ=0.883, p=0.002), RDap (ρ=0.854, p=0.003), L (ρ=0.817, 0.007) and A (ρ=0.700, p=0.036). Within our knowledge, this is almost the first study that investigated the relationship between proprioception level and functional movement. These study results could support that the ankle joint proprioception facilitation exercise would have positive effects on functional balance rehabilitation interventions.

• 설비공학논문집
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• 제28권5호
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• pp.202-207
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• 2016

Experimental studies for an indirect R404A-$CO_2$ refrigeration system and a direct R404A refrigeration system were conducted. The configurations of the indirect R404A-$CO_2$ refrigeration system are a R404A refrigeration system as a top cycle and a circulating $CO_2$ system as a bottom cycle. The direct R404A system was modified from indirect R404A-$CO_2$ refrigeration system by removing circuit for $CO_2$ circulation. Various tests for both systems were conducted by changing load side brine temperature from 0 to 5 and $10^{\circ}C$ with cooling brine temperatures for R404A system at 15, 20, or $25^{\circ}C$. The indirect R404A-$CO_2$ refrigeration system showed the highest COP when load side brine temperature was at $10^{\circ}C$ in the evaporator and at cooling brine temperature of $15^{\circ}C$. The COP of 3.04 under that condition was the highest. This indirect R404A-$CO_2$ refrigeration system showed 9.02% higher COP than the direct R404A system that had increased pipeline length of 15 m, which simulated actual installation in a supermarket.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.579-585
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• 2009

Recently, Vertical-Closed Loop system using geothermal which is the most efficient among the building cooling and heating systems is coming into wide spread due to assistance of domestic policies. However, there is a limitation that a design of ground heat exchanger taking 60% of construction cost is done by GLD and GLHEPRO programs without specific guidelines and consideration on Entering Water Temperature(EWT). For getting an optimal EWT, we analyzed the costs for construction of ground heat exchanger and cooling and heating for 15 years. In the results, reduction of construction costs as the length of ground heat exchanger shortens was much greater than increase of the electrical power consumption as COP gets low. EWT that COP of heat pump can be 3.76 or above was below $31^{\circ}C$ in cooling and was over $5^{\circ}C$ in heating.

• Journal of Advanced Marine Engineering and Technology
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• 제31권5호
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• pp.543-551
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• 2007

The performance characteristics of water-chilling heat pump using $CO_2$ with respect to variation of inlet temperature and mass flow rate of secondary fluid was investigated experimentally. An experimental apparatus is consisted of a compressor, a gas cooler, an expansion valve, an evaporator and a liquid receiver. All heat exchangers used in the test rig are counter-flow-type heat exchangers with concentric dual tubes, which ate made of copper. The gas cooler and the evaporator consist of 6 and 4 straight sections respectively arranged in parallel, each has 2.4 m length. The experimental results were summarized as the followings : As inlet temperature of secondary fluid in the gas cooler increases from $10^{\circ}C$ to $40^{\circ}C$, the compressor work, heating capacity and heating COP were varied to 37.8%, -13%, -35.9%, respectively. The heating capacity, compressor work, heating COP were turned into 23.3%, 6.42%, 13.1%, respectively when ass flow rate of secondary fluid in the evaporator increases from 70 g/s to 150 g/s. The above tendency is similar with performance variation with respect to temperature variation of secondary fluid in the conventional vapor compression cycle.

• 대한물리의학회지
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• 제15권4호
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• pp.37-45
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• 2020

PURPOSE: The purpose of this study was to identify the effects of neck stabilization exercise combined with trunk stabilization exercise on balance and gait function in patients with chronic stroke. METHODS: Twenty-two chronic stroke patients were included in this study. The experimental group subjects (n = 11) performed neck stabilization (15 min) and trunk stabilization (15 min) exercises, while the control group subjects (n = 11) performed trunk stabilization exercise only for 30 min. Before and after the intervention, the subjects underwent static balance and gait testing. RESULTS: The 95% confidence ellipse area, center of pressure (COP) path length, and COP average velocity were significantly lower in both groups after the intervention compared to before intervention (p < .05). The average stance force on the affected side increased significantly in both groups after the intervention (p < .05). The changes in the static balance variables were larger in the experimental group than in the control group. The cadence, gait velocity, and single leg support increased significantly in both groups after intervention (p < .05). The changes in the gait variables were larger in the experimental group than in the control group. CONCLUSION: Trunk stabilization is a beneficial intervention, but the combination of neck stabilization with trunk stabilization is a more effective method to increase the gait and static balance in chronic stroke patients.

• 대한물리의학회지
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• 제16권1호
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• pp.17-22
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• 2021

PURPOSE: This study examined the correlations between gait, static balance, and pelvic inclination in patients with chronic stroke. METHODS: Twenty-two chronic stroke patients were included in this study. The subjects participated in gait, static balance, and pelvic inclination tests. In the gait measurement, the cadence and gait velocity were measured, and the average of three trials was calculated and recorded. The static balance was measured using a force platform. The data was captured for ten seconds, and five successful trials were recorded. Pelvic inclination in the sagittal plane was measured using a palpation meter. For data processing, a KolmogorovSmirnov test was used to determine the type of distribution for all variables. Pearson's correlation coefficient was used for correlation analysis. The correlations among the gait, static balance, and pelvic inclination was calculated. The level of significance was .05. RESULTS: Significant negative correlations were observed between the gait variables (cadence, velocity) and static balance variables (COP path length, COP average velocity, and 95% confidence ellipse area) (p < .05). On the other hand, there was no significant correlation between pelvic inclination and gait or between the pelvic inclination and static balance variables. CONCLUSION: Significant correlations were observed between the gait function and static balance. On the other hand, there were no significant correlations between the pelvic inclination and gait and static balance. These results suggest that the pelvic inclination is not an important consideration for increasing the gait function and static balance.

• 대한물리의학회지
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• 제15권2호
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• pp.101-108
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• 2020

PURPOSE: The purpose of this study was to investigate the effect of treadmill walking training using the metronome on the gait pattern. METHODS: A total of 33 healthy persons were studied consisting of 17 female and 16 male in the 20-30 age group. A gait analysis program was installed on a treadmill with a built - in gait analysis sensor and laptop. After 9 minutes of treadmill walking, gait analysis was performed for 1 minute. The mean values of the differences in the step length, angle of COP, separation line standard deviation and step force of the lower legs affecting walking symmetry were calculated for treadmill walking and treadmill walking using the metronome. The Shapiro-Wilk test was used to test the normality of the collected data and a paired t-test was performed to analyze the difference in walking before and after using the metronome. RESULTS: As a result of the analysis, the mean of difference between the measured values of the bilateral lower extremity for step length, angle of COP, separation line standard deviation and step force were statistically significant before and after treadmill walking using the metronome. CONCLUSION: Therefore, the treadmill walking training using the metronome is effective in decreasing the difference in the foot width, gait angle, gait distribution, and foot pressure. Because of this, the treadmill walking training using the metronome has a significant effect on walking symmetry among the elements for correct walking, which is a means for enabling efficient and continuous walking.

• PNF and Movement
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• 제18권2호
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• pp.183-194
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• 2020

Purpose: Functional ankle instability (FAI) causes tension in the joints, ligaments, and tendons, and the impact on visual and vestibular organs leads to imbalance. This study compared the effects of a traditional balance training program to virtual reality training to improve FAI. Methods: Twenty-four participants with FAI (CAIT score < 24) were assigned to a virtual reality training group (n = 13) and a traditional balance training group (n = 11). Both groups pursued their respective training program for four weeks. After a ten-minute warm-up, participants completed a 30-minute training session, three times per week. The traditional balance training group underwent static and dynamic training using a balance board and a stability trainer pad while the virtual reality group underwent balance training using a virtual reality program. Biorescue was used to measure changes in the speed and length of center of pressure (COP) for single-leg stance pre- and post-training. Results: The speed and length of COP improved significantly in both groups after training as compared to before (p < 0.05). However, there were no significant differences in these outcomes between the virtual reality training group and the traditional balance training group (p>0.05). Conclusion: The study findings confirm the effectiveness of both virtual reality training and traditional balance training in reducing ankle instability, with no difference in treatment effects.