• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.96-102
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• 1999

Cross flow fans are used in various applications, especially in industrial ventilation applications and in room air conditioners, due to their superior performance characteristics. Unlike radial and/or axial fans, the design of cross flow fans have been mostly based on earlier experiences and experiments. In the present study, numerical computations of flow fields through a cross flow fan used in room air conditioner are performed to investigate the detailed flow fields and to study the effect of the blade shape on performance curves to aid better design of the fan. Despite some discrepancies between the two results, it is seen from the present study that the computational results agree quite well with the qualitative experimental results. It is also shown from the present study that by having a different shape of blade, it is possible to achieve about $15\%$ increase in flow rates. The stimulating results of the present study can be used in the design of high performance cross flow fans with the use of optimal design algorithm and experimental verifications.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.480-507
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• 2019

This paper aims at optimizing the auxiliary ventilation system in large-opening limestone mines with unducted fans. An extensive CFD and also site study were carried out for optimization at the blind entries. The fan location, operating mode, and layout are the parameters for optimization. Since the jet stream discharged from the auxiliary fan is flowing faster than 15 m/s in most of the cases, the stream collides with floor, sides or roof and even with the jet stream generated from the other fan placed upstream. Then, it is likely to lose a large portion of its inertial force and then its ventilation efficiency drops considerably. Therefore, the optimal fan installation interval is defined in this study as an interval that maximizes the uninterrupted flowing distance of the jet stream, while the cross-sectional installation location can be optimized to minimize the energy loss due to possible collision with the entry sides. Consequently, the optimization of the fan location will improve ventilation efficiency and subsequently the energy cost. A number of different three-dimensional computational domains representing a full-scale underground space were developed for the CFD study. The velocity profiles and the CO concentrations were studied to design and optimize the auxiliary ventilation system without duct and at the same time mine site experiments were carried out for comparison purposes. The ultimate goal is to optimize the auxiliary ventilation system without tubing to provide a reliable, low-cost and efficient solution to maintain the clean and safe work environment in local large-opening underground limestone mines.

• Journal of the Korean Solar Energy Society
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• v.21 no.2
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• pp.35-43
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• 2001

The results of numerical simulation on the performance of a solar chimney system in building are described. The inside surface temperature of four walls within the solar chimney arc calculated with solar radiation and outdoor temperature in summer. The air within the solar chimney is heated by conduction, convection and radiation. Air temperature distribution from the bottom to the top and outlet air temperature can be obtained by solving energy balance equation. Since the buoyance or stack effect is affected by temperature difference between the bottom and the top within the solar chimney. It is evaluated using inlet and outlet temperatures. It is expected that natural ventilation by the solar chimney of witch the height is 7.8m and the cross sectional area is $4.93m^2$ can provide about $6400m^3/h$ on sunny day.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.2
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• pp.111-120
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• 2004

The optimal design method of indoor thermal environment using CFD coupled simulation and genetic algorithms (GA) is developed in this study. CFD could analyze the thermal environment considering the distribution of temperature, velocity, etc. in a room. Therefore, It would be appropriate to use CFD for the optimal design method considering their distribution. In this paper, the optimal design means the most appropriate boundary conditions of the room among the conditions where the design target of indoor therm environment is achieved. Two step optimal indoor thermal environment design method is proposed. It includes the GA for searching the optimal indoor thermal environment design. To examine the performance of this method, the optimal design of hybrid ventilation system, which uses the natural cross ventilation and the radiation-cooling panel is conducted. The optimal design which satisfies the design target (thermal comfort, minimum cooling load, minimum vertical temperature difference) is found using two step optimal design method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.779-793
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• 2019

The ventilation rate (Qreq) requirement in road tunnels is not just a basic information for determining the tunnel cross-sectional area, but also a major factor for the ventilation system selection. The Qreq is predominantly dependent on the vehicle traffic volume, while among others, the vehicle exhaust emissions and permissible standards are critical. This paper analyzes the changes in the Qreq designing criteria and/or recommendations suggested by World Road Association and local authorities over the last 20 years, since the first local designing criteria was established in 1997 by Korea Expressway Corporation. Additionally, based on the updated vehicle emission standards of Ministry of Environment and recent recommendations of the World Road Association (WRA), changes in the Qreq and its effects are studied in terms of the length and grade of the tunnel.

• Journal of The Korean Society of Clinical Toxicology
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• v.4 no.2
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• pp.113-121
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• 2006

Purpose: Previous studies have reported that plasma cholinesterase (AchE) concentration can serve as a useful prognostic parameter in cases of acute organophosphate (OP) poisoning. However, there has been considerable disagreement regarding the degree of its prognostic value. Earlier cross-sectional and one- time point studies were plagued with methodologic flaws, making it difficult to interpret their results. The purpose of this study was to clarify the prognostic value of time-variable cholinesterase levels and their relationship with clinical outcomes in OP poisoning. Methods: We reviewed medical and intensive care records of patients with acute OP poisoning admitted to our emergency department between March 1998 and Sep 2006. We collected patient information regarding poisoning, clinical, and demographic features. Patients were assessed for clinical outcomes and AchE concentrations on days 1, 2, 3, 5, and 7 and on the final day. Results: During the study period, 58 patients were enrolled in this study. There was a statistically significant difference in the AchE differentials on 1-3 days for patients requiring mechanical ventilation and for patients with mild poisoning (p<0.05). Also, the decrease in the log AchE concentration correlated with longer durations of mechanical ventilation (r=-0.411, p=0.002). Conclusion: In severe OP poising, measurements of time-variable AchE concentrations can be helpful in the prediction of mortality, the development of intermediate syndrome, and duration of mechanical ventilation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.213-229
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• 2017

Recently, in urban areas there is a tendency to construct more complex network-type tunnels including entrance and exit ramps. At the same time, various one-dimensional programs based on the network theory have been proposed for tunnel ventilation analysis. This paper aims at developing a program that can analyze the ventilation flow rate and pollutants concentration in complex network-type tunnels based on the none hardy-cross method. The flow analysis in the branch was carried out on the basis of the Gradient method, while for the concentration analysis a new logic has been developed to calculate the inflow and outflow concentration automatically in a complex network-type structure. Additionally, in the tunnel segments showing low flow rate, proper grid interval sizes were proposed to reduce numerical error. To verify the applicability of the program, flow rates predicted in the straight tunnels were compared with the classical velocity-diagram method by Stokic and the TVSDM program. The results showed that the errors were within 1%. In addition, the program was applied to the recent ventilation system adopted in the complex network-type urban tunnels.

• Proceedings of the SAREK Conference
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• 2007.06a
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• pp.97-97
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• 2007

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.39-53
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• 2018

Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.375-388
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• 2017

In order to solve the traffic congest and environmental issues, small-cross section tunnel for small car only is increasing, but there is not standard for installation of disaster prevention facility. In this study, in order to investigate the behavioral characteristics of thermal environment and smoke in a small cross section tunnels with a large port exhaust ventilation system, the A86, the U-Smartway and the Seobu moterawy tunnel, Temperature and CO concentration in case of fire according to cross sectional area, heat release rate and exhaust air flow rate were analyzed by numerical analysis and the results were as follows. As the cross-sectional area of the tunnel decreases, the temperature of the fire zone increases and the rate of temperature rise is not significantly affected by heat release rate. However, there is a difference depending on the change of the exhaust air flow rate. In the case of applying the exhaust air flow rate $Q_3+2.5Ar$ of the large port exhaust ventilation system, the temperature of the fire zone was 7.1 times for A86 ($Ar=25.3m^2$) and 5.4 time for U-smartway ($Ar=37.32m^2$) by Seobu moterway tunnel ($Ar=46.67m^2$). The CO concentration of fire zone also showed the same tendency. The A86 tunnels were 10.7 times and the U-Smartways were 9.5 times more than the Seobu moterway. Therefore, in the case of a small section tunnel, the thermal environment and noxious gas concentration due to the reduction of the cross-sectional area are expected to increase significantly more than the cross-sectional reduction rate.