• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1542-1547
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• 2003

Air entrainment can become a significant problem in a web handling process. The development of air film between a web and an idle roller can cause a reduction of traction and traction coefficient, by which a slip is occurrred. Computational and experimental study was carried out to describe the slippage of an idle roller for given operating conditions, tension and web velocity. An extended mathematical model to find out a slip condition was developed by using the models of air film height, dynamic traction coefficient, and torque balance of a rotational roller. And by using the extended model, a mechanism to define the slippage between the roller and the moving web was suggested. The results of simulation and experiment showed that the extended dynamic model could properly characterize the rotational motion of the idle roller by considering dynamic traction coefficient. By examining the rotational motion of the idle roller with web dynamics(speed), the mechanism to define al slip condition between the roller and the web was found to be effective.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.608-613
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• 2003

In this paper, the effect of interconnected boundary between journal and thrust bearings on the performance of self-acting air-lubricated bearings is investigated. When journal and thrust bearings have common boundary, conventional boundary condition which assumes that the boundary pressure is equal to atmosphere is no more valid. Instead, new boundary condition by mass conservation at interconnected boundary is needed. To do this, a duct model satisfying mass conservation at interconnected boundary is developed. Using this model, pressure distribution at interconnected boundary is numerically analyzed with changing the volume of interconnecting part. As a result, it is shown that load capacity of thrust bearing can be greatly increased when journal and thrust have a common boundary.

• Tribology and Lubricants
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• v.12 no.2
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• pp.65-73
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• 1996

Rapid increase of Refrigeration and Air conditioning system in modem industries brings attention to the urgency of core technology development in the area. This paper presents theoretical investigation of the lubrication characteristics of rotary compressor for refrigeration and air conditioning. In order to analyze the lubrication characteristics of the main & sub bearing of rotary compressor, the bearing force and locus of shaft center are analyzed by the dynamic analysis of rotary compressor and numerical analysis of Reynolds equation as the operating condition is changed in various ways. In this paper, we used the Runge-Kutta method for the dynamic analysis of rotary compressor and the SOR (Successive OverRelaxation) method for the numerical analysis of Reynolds equation. The result shows that the operating condition of sub bearing is severer than that of main bearing, and eccentricity ratio grows as the bearing force increases. It is believed that the result can be applied to the design of alternative refrigerant rotary compressor.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.5
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• pp.66-72
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• 1999

It is necessary to discuss lightening engine parts and reducing the friction of sliding parts to improve fuel consumption and combustion stability at idling condition. Lean best torque combustion which produce maximum power at a lean air-fuel ratio is effective for the reduction of exhaust gas emission and the improvement of fuel consumption. Accordingly, this study deals with the expansion of lean combustible limitation, the combustion stability and the reduction of idle speed through the analysis of combustion characteristics on the base of the control technique of precise air-fuel ratio because it does not need to maximum power at idling condition. The idle speed is increased proportional to ISC(Idle Speed Control) duty ratio. On the other hand the idle speed decreased by lean air-fuel ratio. The COV in engine speed is stable within maximum two percent up to 17.6 mixture ratio by the control of ISC duty ratio.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.183-190
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• 2006

For continuously regenerative PM collecting system which adopted thermally stable SiC DPF and electrical heater which was placed upstream of the filter and driven by well constructed control logic, PM oxidation characteristics were investigated varying air flow rate, amounts of PM accumulated on the DPF and filter inlet temperature in order to get optimized PM regeneration performance. This study showed that the operating condition of air flow rate 70 lpm, high PM loading around 30g and filter inlet temperature $700^{\circ}C$ with heat insulation was effective in achieving high regeneration efficiency. Also, in this condition, we could decrease the electric energy consumption by reducing the regeneration time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.3
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• pp.321-331
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• 1999

A numerical study is carried out for increasing heat removal using indirect cooling system. Computation is performed for nine cases as variation of flow condition in the lower channel. As the result of this study, water is more effective than air at the same pressure loss in spite of the lower inlet velocity. In channel configuration, the vertical channel is more effective than horizontal channel because of the buoyancy effect. Under the condition that heat generation is the same, counter flow effectively decreases the temperature difference among blocks. Parallel flow is more effective than counter flow when average temperature of all blocks is considered. In the case of installing obstacles in the lower channel, it is desirable to install obstacles in the bottom of lower channel. Heat transfer rate increases as the height of obstacles increases.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.559-567
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• 2018

In this paper, we propose a new load forecasting method for smart air conditioning (A/C) based on the modified thermodynamics of indoor temperature and the unbiased finite memory estimator (UFME). Based on modified first-order thermodynamics, the dynamic behavior of indoor temperature can be described by the time-domain state-space model, and an accurate estimate of indoor temperature can be achieved by the proposed UFME. In addition, a reliable A/C load forecast can be obtained using the proposed method. Our study involves the experimental validation of the proposed A/C load forecasting method and communication construction between DR server and HEMS in a test bed. Through experimental data sets, the effectiveness of the proposed estimation method is validated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.111-116
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• 2004

An experiment was carried out to confirm the validity of time series evaluation of supersonic mixing condition by using catalytic reaction on a platinum wire. Geseous hydrogen was injected parallel to supersonic freestream (M$\infty$ $\approx$ 1.81) from a slit injector, which was located at backward facing step. Time series condition of supersonic mixing was evaluated by using W-type probe which has a platinum wire and reference wire (nickel wire). The evaluation was by simultaneously measuring each electric circuit which kept the temperature of wire constant. Investigations were also conducted for helium, air and no secondary injectant cases to compare with the hydrogen injectant case. The results indicated that it was possible to measure the time series behavior of air and hydrogen supersonic mixing layer or coherent motion of turbulence by using this evaluation.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.14 no.2
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• pp.108-117
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• 1985

In this study, a numerical analysis was performed for the natural convection heat transfer in a vertical channel which was consisted of two finite-thickness vertical walls with heat source. The ratio of the thermal conductivity of wall to air played an important role in the analysis. The case for which one side wall has protrusion resistances was also examined. The governing equations for the system was discretized by control volume formulation and solved by SIMPLE method. As the result of this study, it was found that the uniform heat flux boundary condition could be applied when the conductivity ratio was below approximately 50 and the uniform temperature boundary condition could be used when the conductivity rat io was over approximately 15,000. However, when the conductivity ratio was between 50 and 15,000, the thermal conductivity ratio value should be considered for the analysis. It was also found that the existence of protrusion resistance influenced the thermal field up to the distance of 3-4 times of the protrusion length.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.998-1004
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• 2005

Recently natural ventilation rate is decreased due to the airtightness of apartment building. Therefore the use of heat recovery ventilator (HRV) has been greatly increased as an alternative method to supply fresh air and save energy in the building. In this research the experiment standard of HRV is compared between KS and JIS and the sensitivity analyses are experimented by both standards. Under cooling experiment condition indoor and outdoor wet-bulb temperature difference of JIS is 2 to 3 times higher than that of KS. It shows that the efficiency measurement of HRV by KS is expected to have greater sensitivity than by JIS and thus accurate measurement of web-bulb temperature is required. The experimental results provide that the efficiency of thermal exchange is resemblance to each others between KS and JIS. Under cooling experiment condition the efficiency of humidity exchange by KS presents higher than by JIS, however, under heating experiment condition the efficiency by KS shows lower than by JIS, reversely.