• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.4
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• pp.177-183
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• 2002

A pulsed tracer gas technique is applied to measure the distributions of local mean age and local mean residual-life-time of air in a half-scale experimental chamber, The airflow patterns in the chamber are visualized by a Helium bubble generator for three different exhaust locations. A supply slot is located at the top of a right wall, and an exhaust slot is at either bottom-left (Case 1), bottom-right (Case 2), or top-left (Case 3) location. Results show that the distributions of local mean age and local mean residual-life-time are different from each other, but both of them are closely related to the airflow pattern in the space. Included are discussions on explaining the variations of overall room ventilation effectiveness depending upon airflow rates for three different supply-exhaust configurations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.736-745
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• 2005

This study is undertaken to evaluate the relationship between the indoor $CO_2$ concentration and the local mean air-age in the lecture room with the occupants. We conducted the experiments to examine the indoor $CO_2$ concentration and the local mean air-age with respect to the supply airflow of the ventilation system and the discharge angle and air-flow of the system air conditioner. Through the experiments, we found out that indoor $CO_2$ concentrations calculated by the prediction equation of Seidel are about 350 ppm lower than those measured by the experiments. The indoor $CO_2$ concentration is not related with the air-flow and the discharge angle of the system air-conditioner, but with the ventilation airflow. From the numerical calculation, the indoor $CO_2$ concentration is not related with the ventilation effectiveness, but strongly with the local mean air-age. In case of our model, the indoor $CO_2$ concentration is likely to fall within the acceptable air quality when the local mean air-age is averagely predicted under 400 seconds.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.853-859
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• 2001

A pulsed tracer gas technique is applied to measure distributions of local mean age and residual life time of air in a half-scale experimental chamber. The room airflow patterns are flow-visualized by a Helium bubble generator for three different exhaust locations. A supply slot is located at the top of a right wall, and an exhaust slot is either at bottom-left(Case 1), bottom-right(Case 2), or top-left(Case 3) location. Results show that the distribution of LMA and LMR are different from each other, but both of them are closely related to the airflow pattern in the space. Results on overall room ventilation effectiveness are provided depending upon ventilation airflow rates for three different supply-exhaust configurations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.253-262
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• 1992

A numerical procedure is introduced to calculate local ventilation effectiveness using the definitions of local decay rate and local mean age. A low Reynolds number $k-{\varepsilon}$ model is implemented to calculate steady state turbulent velocity distributions, and a step-down method is used to calculate transient concentration distributions. Simulations are carried out for several different values of air change rates and several different diffuser angles in a two-dimensional model of a half scale office room. The results show that the local ventilation effectiveness within a room could vary significantly from one location to another. The nominal air change rate based on the assumption of complete mixing of room air does not provide the local ventilation effectiveness information. It is numerically proved that the local mean age distribution obtained from the transient calculation is equivalent to the steady state concentration distribution with homogeneously distributed contaminant sources.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.5
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• pp.457-466
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• 2007

A numerical and experimental study on the evaluation and the prediction of cleanliness level in the mini-environment system was carried out. Using the concept of local mean air-age (LMA) and effective flow rate, the new direct method for estimating the mini-environment was developed and compared with the previous performance index of airflow pattern characteristics. It was found out that the airflow pattern analysis is a restricted method to estimate the real performance of the mini-environment. The reason is that the airflow pattern cannot predict the effect of the increment of the ventilation rate on the cleanliness level in the mini-environment. While LMA is capable of showing the effects of the contaminant accumulation caused by turbulent intensity, eddy, and the increment of the effective flow rate. This result showed that LMA is more exact and effective performance index than the previous one like the airflow pattern characteristics.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.5
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• pp.206-211
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• 2014

The objective of the present study was to identify ventilation problems, and also to suggest new axial fan systems for the improvement of IAQ in the underground parking lots. Numerical results for air mean-velocity, local mean age, and sound power level are presented along with some of fan angles. The results showed the influence of airflow patterns on the fan performances installed in the underground parking lots. Discharge air volume is increased with the angle of the blade. And also, the main factors affecting the noise of the ventilation fan was found to be a rotational speed.

• ALGAE
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• v.37 no.1
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• pp.63-74
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• 2022

Perennial stipitate kelps are globally distributed and individual species can inhabit broad latitudinal ranges, expressing notably longevous persistence. Despite the foundational role kelps provide to their communities, little is known about the variability in persistence of the stipitate kelps at local spatial scales. We studied the population persistence of Eisenia arborea, a heat- and wave force-tolerant perennial stipitate kelp with a distributional range extending from British Columbia to south of the range limit of all other northeast Pacific kelps, in Baja California Sur, Mexico. Persistence characteristics for E. arborea among sites were compared and used to test the hypothesis that stand persistence varied at local spatial scales around Isla Natividad, a Pacific island off the Baja California peninsula with documented spatiotemporal environmental heterogeneity. Collected individuals around the island were "aged" using the previously validated age estimation technique of counting annual cortical dark rings. After detecting no significant differences among sites in the covariation between estimated ages for collected individuals and stipe length, we utilized in-situ population-level stipe length measurements to more rapidly predict age structures within six stands around the island. Predicted age structures, and associated stand densities, revealed persistence characteristics and density varied at local scales and a strong positive relationship existed between stand density and stand mean and maximum ages. We speculate that stands responded differently to deterministic influences (e.g., the 2014-2016 marine heatwave and / or competition with Macrocystis) resulting in heterogenous local persistence of this foundation species.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.658-665
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• 1998

This paper investigates local exhaust effectiveness in a room with a supply and an exhaust slots on the ceiling. The mean age of air is an indicator of supply effectiveness, while the mean residual life time can be used as an indicator of exhaust effectiveness. The distribution of local mean residual life time in a space is calculated by four different numerical procedures. The reverse-flow calculation method has been proved to show quite accurate results while it can save considerable amount of computation time and efforts, compared to the method by its original definition. It is concluded that the diffusion term in the equation of mean residual life time can be neglected. The spatial and temporal diffusion characteristics of the contaminant are also discussed.

• The Korean Journal of Community Living Science
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• v.15 no.2
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• pp.55-64
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• 2004

The purpose of this study was to examine the differences in skin temperature and thermal comfort of participants in a $19^\circ{C}$ room (the recommended room temperature in the winter) depending on age, sex and clothing weight. Subjects were divided into four groups (6 young males, 5 young females, 6 old males, 6 old females) and experimental trials consisted of three conditions: wearing underwear in a $19^\circ{C}$ room (19CUW), without underwear in a $19^\circ{C}$ room (19C), and without underwear in a $24^\circ{C}$ room (24C). The results indicated the following: 1) There were no significant differences in mean skin temperature based on age or sex, and the mean skin temperatures of the four groups were in the range of 32.4∼$34.0^\circ{C}$. 2) In the 19C condition, the skin temperatures of the hands and feet of old females were higher than those of the other three groups. 3) In terms of perceived thermal comfort, young females showed a tendency to feel the most uncomfortable. Both old and young groups agreed that the 24C condition was the most comfortable. 4) Relational coefficients between thermal comfort and skin temperatures were higher in the young group than in the old group. Furthermore, the perceived thermal comfort had a stronger relationship with mean skin temperatures than with local skin temperatures. 5) The mean skin temperatures of subjects who indicated they were 'comfortable' were in the range of 31∼$36^\circ{C}$ regardless of age or sex.

• Korean Journal of Applied Biomechanics
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• v.27 no.1
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• pp.45-52
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• 2017

Objective: The aim of this study was to investigate the periodicity of the lower extremity joint flexion/extension angle to compare the local stability between young and elderly women during walking on a treadmill. Method: Eighteen young women (mean $age=21.2{\pm}1.6y$; mean $mass=57.1{\pm}6.1kg$; mean $height=1.61{\pm}0.04m$) and 18 elderly women (mean $age=66.4{\pm}1.2y$; mean $mass=55.4{\pm}8.3kg$; mean $height=1.56{\pm}0.04m$) participated in this study. Approximate entropy (ApEn) was used to determine the periodicity in the lower limb joint angles. Results: The ApEn values of the two groups were statistically greater in the surrogate data test than in the original time series data (p<.05). The periodicity of the hip and ankle flexion/extension angles decreased in the elderly women group compared with the young women group (p<.05). The periodicity of the lower extremity joint flexion/extension angle showed that the ankle joint increased dominatingly in both groups (p<.05); the hip joint decreased compared with the knee joint in the young women group; and the knee joint decreased compared with the hip joint in the elderly women group (p<.05). Conclusion: These results suggest that the lower extremity joint flexion/extension angles of the young and elderly women during walking contained random noises as well as biological signals. In addition, the differences in the periodicity in the lower extremity joint between the young and elderly women may provide some insight in predicting potential falls and be used as a characteristic indicator for determining local stability in elderly women during walking.