• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.219-231
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• 2004

The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. This study focuses on the hydrodynamic behavior of bubble plumes, which is the major mechanism of destratification and their combined effect of adjacent plumes on destratification efficiency. By introducing 2-phase Computational Fluid Dynamics(CFD) technique, we could suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. Lab experiments were also carried out to verify CFD model in thermally stratified fresh water which quite differs from former researches using salts. This study showed that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is lower than 1.5 times the depth, the combined effect is stronger; as Plume Number(PN) is increased, the efficiency is strongly affected by spacing. If the distance is shorter than the depth of water, the efficiency increases linearly in proportion to PN. Otherwise, the efficiency increases non-linearly. These findings suggest that the combined effect should be more quantitatively taken into consideration for design and operation of air-diffuser destratification system, and recommend that the optimal destratification efficiency will be when plume number is 1000 and the spacing between neighboring diffusers is 1.5 times the depth.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.4
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• pp.37-46
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• 2001

This study numerically investigates thermal comfort of a space cooled by a floor-supply air-conditioning system, in which three different combinations of supply and return locations, one floor-supply/ceiling-return and two floor-supply/floor-return, are treated. A complementary experiment is performed to validate the present numerical analysis, and the prediction agrees favorably with the measured data. In the numerical procedure, a simplified model mimicking the inlet flow through a diffuser is developed for efficient simulations. The calculated results show that the ceiling-return type is far better in terms of thermal comfort than the floor-return ones within the extent of this study, which seems to be caused by effective vertical penetration of the supply air against natural convection. It is also revealed that the arrangement of port locations in the floor-supply/floor-return system has insignificant effect on the cooling performance. For selecting a proper system, other characteristics including the heating performance should be accounted for simultaneously with the present considerations.

• Proceedings of the SAREK Conference
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• 2003.07a
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• pp.6-6
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• 2003

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.147-151
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• 2002

Cross flow fan system is widely used for various applications, especially for the air-moving device of heaters, air-conditioners, and air-curtains. Although there are efforts for the optimization of cross-flow fan flow path with different methods of approach, it is still being investigated by many researchers through experimentally and/or theoretically, because the flow pattern of the cross flow fan is not stereotyped. This paper presents some results from numerical experiments for the optimization of the flow path through a cross-flow fan to be applied to indoor wall-mounted room heater. Two dimensional analysis has been applied to a specific fan system including inlet and diffuser outlet. Flow characteristics art presented and discussed for two different flow path at three different operating conditions represented by rotational speed(800, 1,000, 1,200 rpm) of the In. According to the simulated results for the specific fan system under consideration, it could be found that the flow pattern resembles each other at different rotational speed (to say from 800 rpm to 1,200 rpm) for a fixed flow path, while the secondary flows mostly absorbs the speed effects. By changing the flow path significant increase in volume flow rate is estimated upto 2.65 at the same rotational speed. According to the present experience, fan flow path design can be performed more efficiently by incorporating this type of numerical experiments combined with the model tests.

• Journal of The Korea Institute of Healthcare Architecture
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• v.14 no.4
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• pp.39-46
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• 2008

Construction and operation of Germ Free Pigs' facilities are very expensive because pigs' rooms and other major rooms of the facility require germfree environments. Especially, running the HVAC system of aseptic facilities requires a lot of expenses. However, proper location and efficient shape of outlets/inlets for the ventilation of the room can reduce the excessive running cost. In order to do that, this study proposes alternative location and shape of ventilation outlets/inlets to the existing design pattern in germfree pigs' room. The design condition of this study is the maintenance of adequate temperature(24$^{\circ}C$, $NH_3$concentration level(below 1.5 ppm), and air stream speed(below .25m/sec) in the pigs' room for the summer and the winter together. As the Software Program, FLUENT(Ver. 6.2) has been used for the analysis of proposed ventilation patterns. In conclusion, wall inlets and ceiling inlet/outlet are advisable in summer, wall inlets and ceiling outlets is advisable in winter. As far as the shape is concerned, diffuser type for the ceiling outlet is desirable.

• Journal of the Korean Solar Energy Society
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• v.31 no.6
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• pp.78-85
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• 2011

In this study, an underfloor air distribution(UFAD) system installed on the S. office building was evaluated for its indoor environmental quality performance. Field measurement and survey were conducted for the overall POE(Post Occupied Evaluation). PMV(including temperature, humidity, air velocity and globe temperature) and several environmental components were measured while thermal comfort, thermal sensation, acoustical environment and others. were investigated through survey. Except for the direct upper part of the air supply diffuser on the floor, the indoor velocity was less than 0.25m/s, which has been suggested by ASHRAES tandard 55 as the limit for thermal comfort. MRT of the perimeter zone of the room showed a higher value than that in the interior because of the introduced solar radiation through the building envelope. PMV was generally maintained in the range of thermal comfort (from -0.5 to +0.5), though it weighted to the warm side. It was reported to have 61% positive response on thermal comfort and 55% on neutral thermal sensation. The results of each survey item showed some gender-based differences. Specifically, female respondents had higher degree of dissatisfaction with indoor air cleanness and acoustical privacy. The working surface showed more than 400 lux and the equivalent noise level showed less than 50 dB(A). In conclusion, the results of the measurement and survey showed good agreement. Indoor environmental quality of the subject office room where the UFAD system was installed showed an overall excellent performance.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.15 no.1
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• pp.87-96
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• 1986

An experiment on the devices that enchance the stratification of storage tanks in a solar heat ins system has been carried out. The benefits of thermal stratification in sensible heat storage are to increase the system performance such as the collector efficiency or the fraction of the total load supplied by solar energy. Using the diffuser and the distributor as the stratification enchancement device, the expeliments were perfomed in the different condition of diameter and material of the distributor. As a result of experiments, there exists the diameter of distributor in which the stratification is made maximum under certain design and operation condition. Also it was identified that the kind of distributor material influenced the degree of stratification. Comparing the experimental result to the computational results calculated under the same conditions, the node number N(stratification index) was determined. The results of computer simulation that was performed about the actual solar heating system in Seoul for 24 hours show the relative advantage of stratified over well-mixed storage and the significant improvements in system performance.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.37-42
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• 2014

In Korea while the dam or reservoir is an important water resource, the value of this water resource is deteriorating by thermal-induced stratification. To ameliorate the water quality of reservoir by breaking stratification the use of air diffuser system is now widespread in Korea. According to the previous research, dynamics of bubble plume and destratification efficiency depended upon two dimensionless groupings; Mh and Pn suggested by Asaeda et al (1993). However, these two variables only include Q, N, H, g, u. and installed Boryeong reservior in appropriate width of water aeration, air dose and number of installations after calculating by applying these figures. This paper is performed to find out effect analysis about water aeration improvement to break thermal stratification.

• Journal of the Korean Solar Energy Society
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• v.30 no.4
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• pp.92-99
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• 2010

The purpose of this study is to apply pressurized plenum under floor air conditioning system to office areas to understand characteristics of indoor thermal environment based on forms of diffusers. For doing this, the author conducted experiment of module measurement, and based on the results, analyzed indoor temperature distribution and velocity distribution based on direction of diffusion by using Computational Fluid Dynamics(CFD), and estimated the Predicted Mean Vote(PMV) of residents based on forms of diffusers to present the optimal air conditioning of the pressurized plenum under floor air conditioning system in heating. The results of this study are as follows. First, as for forms of diffusers, distributed diffusers rather than conical and grill diffusers were favorable in maintaining $24^{\circ}C$, the established temperature in heating, were active in velocity flowing, and were wide in a radius of diffusion. Second, as for position of pressurizing, the difference between upper and lower temperature was wider in center, lateral, and dispersed pressurizing (in order). As for velocity distribution, the velocity was more increased in lateral, center, and dispersed pressurizing(in order), indicating that dispersed pressurizing maintained uniform thermal environment. Third, as for diffusion direction, mixed direction showed less difference between upper and lower temperature and the difference in velocity between center and lateral part was 0.01m/1, indicating that it maintained uniform thermal environment. Fourth, as for the PMV of residents based on the forms of diffusers, the dispersed type showed(+) values above (0) when applied variably based on the position of diffuser, presenting thermal feeling of "being comfortable" to residents.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.22-29
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• 2003

New high-speed depressurized circulating water channel was designed by using the CFD code. Flow in the channel has free surface and pressure in the test section can be depressed. In this study, Flow separation and bubble occurrence were considered in designing the contraction nozzle shape for better flow uniformity Tn the test section. To supplement velocity defect due to the free surface, nozzle injection system more effective in high-speed flow was installed instead of drum system. Necessary power and injection techniques were proposed. And guide vane arrangement was analyzed to reduce the flow resistance and keep quiet free surface from ´surging´. Wave absorber was devised to reduce the wave resistance and to prevent the entrainment of air to the diffuser.