• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.5-11
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• 2014

The purpose of this paper is to investigate an analytical approach for opening performance evaluation of the nuclear pressure safety valve based on standard codes such as ASME or KEPIC. It is well-known that safety valve is considered as one of pressure relief valves for protecting a boiler or pressure vessel from exceeding the maximum allowable working pressure. When pressure in a container reaches its set pressure, the safety valve commences discharging the internal fluid by a sudden opening called as popping. Safety valve is usually evaluated by set pressure, full open, blow-down, leakage and flow capacity. The test procedure and technical requirement for performance evaluation is described in international code of ASME code such as BPVC. The opening characteristics of steam safety valve can be analyzed by computational fluid dynamics (CFD) and steam shaft dynamics. First, the flow analysis along opening process is simulated by running the CFD models of the ten types of opening steps from 0 to 100%. As a analysis result, the various CFD outputs of flow pattern, pressure, forces on the disc and mass flow at each simulation step is demonstrated. The lift force is calculated by using the forces applied on disc from static pressure and secondary flow. And, the effect of huddle chamber or control chamber is studied by dynamic analysis based on CFD simulation results such as lift force. As a result, dynamics analysis shows opening features according to the sizes of control chamber.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.9
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• pp.56-62
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• 1999

The disintegration of transient diesel spray in early was investigated at different opening pressure and chamber pressure by measns of shadowgraph method using nanolite and still camera. Diesel spary was injected into the spray chamber which was charged with high pressure nitrogen gas. Atthe begining of injection, a liquid column that was almost the same diameter as the nozzle hole was observed . Spray tip penetration and spray angle were always increased with an increase in opening pressure.

• KIEAE Journal
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• v.11 no.6
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• pp.37-42
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• 2011

This Paper aims for analyzing the effect of opening types on wind-driven ventilation performance in basement parking lots of apartment. The scale model of basement parking lot was made, wind tunnel tests conducted. Wind pressure of three opening types was measured, wind pressure coefficient calculated. As the result, it showed that the air flow pattern of stack type opening was strongly changed by wind direction, but it was almost not at scuttle vent type. But, as for the difference of wind pressure coefficient, stack type opening was more than the other two types.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1299-1306
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• 2005

The suitable pressure regulator modeling at each opening ratio and pressure ratio is very important to obtain reliable results, especially in small scale pipeline network analysis such as a pressure regulator system. And it is needed to confirm both whether temperature recovery is achieved after passing by the pressure regulator's narrow neck and how much amount of low temperature area that can cause condensate accumulation is distributed by various PCV models and driving conditions. In this research, the numerical model resembling P company pressure regulator that is used widely for high pressure range in commercial, is adopted as the base model of CFD analysis to investigate pressure regulator's flow characteristics at each pressure ratio and opening ratio. And it is also introduced to examine pressure regulator's critical flow characteristics and possibility of condensation or freezing at each pressure ratio and opening ratio. Additionally, the comparison between the results of CFD analysis and the results of analytic solution obtained by compressible fluid-dynamics theory is attempted to validate the results of CFD modeling in this study and to estimate the accuracy of theoretical approach at each pressure ratio and opening ratio too.

• Journal of Environmental Science International
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• v.27 no.6
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• pp.359-369
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• 2018

A model has been developed to predict natural ventilation in a single zone building with large openings. This study first presents pressure-based equations on natural ventilation, that include the combined effect of wind and thermal buoyancy. Moreover, the concept of neutral pressure level(NPL) is introduced to consider the two-way flow through a large opening. The total pressure differences across the opening and the NPL are calculated, and nonlinear equations are solved to find the zonal pressure to satisfy mass conservation. For this analysis, an iterative technique of successively approximating the zonal pressure is used. The results of applying this study model to several simple cases are as follows. When there is no wind and only the stack effect is caused, a one-way flow occurs in both the top and bottom openings in the case of two openings of equal-area, and a one-way flow occurs in the top opening; however, a two-way flow occurs in the bottom opening in the case of two openings of unequal-area. When there is a wind effect, regardless of whether the outside air temperature is lower or higher than the indoor air temperature, air flows into the room through the bottom opening and out of the room through the top opening. As the wind velocity increases, the wind effect appears to be more influential than the stack effect owing to the temperature difference.

• Journal of Korean Neurosurgical Society
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• v.46 no.4
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• pp.370-377
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• 2009

Objective : There is no definite adjustment protocol for patients shunted with programmable valves. Therefore, we attempted to find an appropriate method to adjust the valve, initial valve-opening pressure, adjustment scale, adjustment time interval, and final valve-opening pressure of a programmable valve. Methods : Seventy patients with hydrocephalus of various etiologies were shunted with programmable shunting devices (Micro Valve with $RICKHAM^{(R)}$ Reservoir). The most common initial diseases were subarachnoid hemorrhage (SAH) and head trauma. Sixty-six patients had a communicating type of hydrocephalus, and 4 had an obstructive type of hydrocephalus. Fifty-one patients had normal pressure-type hydrocephalus and 19 patients had high pressure-type hydrocephalus. We set the initial valve pressure to $10-30\;mmH_2O$, which is lower than the preoperative lumbar tapping pressure or the intraoperative ventricular tapping pressure, conducted brain computerized tomographic (CT) scans every 2 to 3 weeks, correlated results with clinical symptoms, and reset valve-opening pressures. Results : Initial valve-opening pressures varied from 30 to $180\;mmH_2O$ (mean, $102{\pm}27.5\;mmH_2O$). In high pressure-type hydrocephalus patients, we have set the initial valve-opening pressure from 100 to $180\;mmH_2O$. We decreased the valve-opening pressure $20-30\;mmH_2O$ at every 2- or 3-week interval, until hydrocephalus-related symptoms improved and the size of the ventricle was normalized. There were 154 adjustments in 81 operations (mean, 1.9 times). In 19 high pressure-type patients, final valve-opening pressures were $30-160\;mmH_2O$, and 16 (84%) patients' symptoms had nearly improved completely. However, in 51 normal pressure-type patients, only 31 (61%) had improved. Surprisingly, in 22 of the 31 normal pressure-type improved patients, final valve-opening pressures were $30\;mmH_2O$ (16 patients) and $40\;mmH_2O$ (6 patients). Furthermore, when final valve-opening pressures were adjusted to $30\;mmH_2O$, 14 patients symptom was improved just at the point. There were 18 (22%) major complications : 7 subdural hygroma, 6 shunt obstructions, and 5 shunt infections. Conclusion : In normal pressure-type hydrocephalus, most patients improved when the final valve-opening pressure was $30\;mmH_2O$. We suggest that all normal pressure-type hydrocephalus patients be shunted with programmable valves, and their initial valve-opening pressures set to $10-30\;mmH_2O$ below their preoperative cerebrospinal fluid (CSF) pressures. If final valve-opening pressures are lowered in 20 or $30\;mmH_2O$ scale at 2- or 3-week intervals, reaching a final pressure of $30\;mmH_2O$, we believe that there is a low risk of overdrainage syndromes.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.27-32
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• 2005

This paper investigates the effects of outdoor pressure fluctuations on natural ventilation through openings of a building envelope. The ventilation airflow rate depends on the magnitude and the period of the pressure fluctuations, the size of the opening compared to the space volume, and the resistance characteristics of the opening. Non-dimensional parameters have been derived, which determine indoor pressure responses due to outdoor pressure fluctuations. The flow regions are categorized into synchronized region, opening resistance region, and transition region depending on the non-dimensional parameters.

• Wind and Structures
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• v.16 no.1
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• pp.117-136
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• 2013

A field study of wind-induced internal pressures in a flexible and porous industrial warehouse with a single dominant opening, of various sizes for a range of moderate wind speeds and directions, is reported in this paper. Comparatively weak resonance of internal pressure for oblique windward opening situations, and hardly discernible at other wind directions, is attributed to the inherent leakage and flexibility in the envelope of the building in addition to the moderate wind speeds encountered during the tests. The measured internal pressures agree well with the theoretical predictions obtained by numerically simulating the analytical model of internal pressure for a porous and flexible building with a dominant opening. Ratios of the RMS and peak internal to opening external pressures obtained in the study are presented in a non-dimensional format along with other published full scale measurements and compared with the non-dimensional design equation proposed in recent literature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1134-1141
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• 2006

This paper presents the model for evaluating restraint effect of pressure induced bending (PIB) on the circumferential through-wall crack opening displacement (COD), which considers plastic behavior of crack. This study performed three-dimensional elastic-plastic finite element (FE) analyses for different crack angle, restraint length, pipe geometry, stress level, and material conditions, and evaluated the influence of each parameter on the PIB restraint effect on COD. Based on these evaluations and additional perfectly-plastic FE analyses, a closed-form model to evaluate the restraint effect of PIB on the plastic crack opening of circumferential through-wall crack, was proposed as functions of crack angle, restraint length, radius to thickness ratio, axial stress corresponding to an internal pressure, and normalized COD evaluated from linear-elastic crack opening condition.

• Wind and Structures
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• v.24 no.1
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• pp.79-93
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• 2017

Wind-induced fluctuating internal pressures in a building with a dominant opening can be described by a second-order non-linear differential equation. However, the accuracy and efficiency of the governing equation in predicting internal pressure fluctuations depend upon two ill-defined parameters: inertial coefficient $C_I$ and loss coefficient $C_L$, since $C_I$ determines the un-damped oscillation frequency of an air slug at the opening, while $C_L$ controls the decay ratio of the fluctuating internal pressure. This study particularly focused on the value of loss coefficient and its influence factors including: opening configuration and location, internal volumes, as well as wind speed and approaching flow turbulence. A simplified formula was presented to predict loss coefficient, therefore an approximate relationship between the standard deviation of internal and external pressures can be estimated using Vickery's approach. The study shows that the loss coefficient governs the peak response of the internal pressure spectrum which, in turn, will directly influence the standard deviation of the fluctuating internal pressure. The approaching flow characteristic and opening location have a remarkable effect on the parameter $C_L$.