• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.45-50
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• 2004

Two phenomena often encountered in liquid flow, which were completely absent in gas or vapor flow, were cavitation and flashing. These phenomena were of significant interest in any comprehensive discussion of control valves or contracted devices since their occurrence would affect the device sizing procedures, might introduce noise and vibration, and also may limit the life expectancy of device components and the immediate downstream piping. Thus, this study aimed to find the reduction method of occurred cavitation in system by the computer simulation. A derivative six model with different dimensions of cavity were adopted. From the results, it was found that the length of the cavity was mote important factor to reduce the pressure drop over the control valves or contracted devices than the depth of the cavity. And the pressures along the centerline of the contracted devices were dropped two times in the case of haying the large length (Lc=1.5D) of cavity.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.176-180
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• 2003

To obtain superconducting state, a reliable cryocooler system is required. Structural and thermal design have been performed to design cryocooler system operated with reverse Brayton cycle using gas neon as refrigerant. This cryocooler system consists of compressor recuperator, coldbox, control valves and has 1 ㎾ cooling capacity. Heat loss calculation was conducted for the given cryocooler system by considering the conduction and radiation through the multi-layer insulation (MLI) and high vacuum. The results can be summarized as; conduction heat loss is 7 W in valves and access port and radiation heat loss is 18 W through the surface of cryocooler. The full design specifications were discussed.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.124-130
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• 1999

Flow characteristics of a compressible gas flow through a rotating disc-type rotary valve are investigated experimentally under various conditions. It is known that the mass flow rate through poppet valves of 4-stroke cycle engines and through piston valves of 2-stoke cycle engines decrease with increase in engine speed. Rotary valve is one means by which air may be made to flow inter-mittently through a pipe. In this paper an exhaust system simulator of engine was used to experi-mentally analyze the decrease in flow rate at high rotation speeds and to determine what variables other than rotational speed give rise to the observed behaviour. These variables have been included in an empirical equation which is representative of the measured flow characteristics.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.579-584
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• 2005

Unsteady state free natural gas jets injected from several types of injectors were numerically simulated. Simulations showed good agreements with the schlieren experimental results. Moreover, injections of natural gas in intake manifolds of a single-valve engine and a double-valve engine were predicted as well. Predictions revealed that large volumetric injections of natural gas in intake manifolds led to strong impingement of natural gas with the intake valves, which as a result, gave rise to pronounced backward reflection of natural gas towards the inlets of intake manifolds, together with significant increase in pressure in intake manifold. Based on our simulations, we speculated that for engines with short intake manifolds, reflections of the mixture of natural gas and air were likely to approach the inlets of intake manifolds and subsequently be inbreathed into other cylinders, resulting in non-uniform mixture distributions between the cylinders. For engines with long intake manifolds, inasmuch as the degrees of intake interferences between the cylinders were not identical in light of the ignition sequences, non-uniform intake charge distributions between the cylinders would occur.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.797-803
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• 2012

Proportional solenoid valves are a modulating type that can control the displacement of valves continuously by means of electromagnetic forces proportional to the solenoid coil current. Because the solenoid-type modulating valves have the advantages of fast response and compact design over air-operated or motor-operated valves, they have been gaining acceptance in chemical and power plants to control the flow of fluids such as water, steam, and gas. This paper deals with the auto tuning of the position controller that can provide the proportional and integral gain automatically based on the dynamic system identification. The process characteristics of the solenoid valve are estimated with critical gain and critical period at a stability limit based on implemented relay feedback, and the controller parameters are determined by the classical Ziegler-Nichols design method. The auto-tuning algorithm was verified with experiments, and the effects of the operating point at which the relay control is activated as well as the relay amplitude were investigated.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.73-78
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• 2011

When a liquid rocket engine - specifically for the gas-generator cycle engine has throttle valves to control the thrust level and mixture ratio of the engine, it is possible to adjust the inherent flow characteristics of the control valves in order to secure a linearized correlation between the control-process-parameters like the thrust or mixture ratio of an engine and the throttle angle of valve. These linearities can reduce the complexity of the control process and make the process more explicit by ensuring the intuitive control. In this point, we proposed an algorithm within the frame of the in-house-developed program to obtain the control valves' inherent flow characteristics which satisfy the linearity, and calculated the sensitivities of control valves with respect to the throttle angle. Also, we compared the obtained inherent flow characteristics with the existed data and concluded the results are satisfactory.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.5
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• pp.431-438
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• 2023

Recently, study on hydrogen is being conducted due to environmental pollution and fossil fuel depletion. High-pressure gas hydrogen commonly used is applied to vehicle and tube trailers. In particular, high-pressure hydrogen storage tank for vehicles must comply with the guidelines stipulated in SAE J2601. There is a charging temperature limitation condition for the safety of the storage tank material. In this study, numerical analysis method were verified based on previous studies and the nozzle angle was changed for thermal management to analyze the increase in forced convection effect and energy uniformity due to the promotion of circulation flow. The previously applied high-pressure hydrogen storage tank has a length/diameter ratio of about 2.4 and was analyzed by comparing the length/diameter ratio with 8. As a result, the circulation flow of hydrogen flowing into the high-pressure hydrogen storage tank is promoted at a nozzle angle of 30° than the straight nozzle and accordingly, the effect of suppressing temperature rise by energy uniformity and forced convection was confirmed.

• Tribology and Lubricants
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• v.37 no.6
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• pp.246-252
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• 2021

Among the engine components of an internal combustion engine, the valve train is a series of systems that supply intake gas to the combustion chamber and operate intake and exhaust valves that discharge exhaust gas. If excessive wear occurs in the valve train system, the suction and exhaust valves do not open and close on time, which leads to abnormal combustion and exhaust gas. In this study, we conduct experiments and analyses on friction and wear characteristics of the valve train system. Moreover, we experimentally study the correlation between the pinball and pinball cap on engine oil lubrication, friction experiment, wear amount analysis, and surface analysis. Specifically, we experiment using Ball on reciprocating tribo-tester and apply commercial engine oil sold on the market engine oil. We construct the experimental conditions for each new oil and oil. Accordingly, the completed specimen was subjected to a confocal microscope to check the wear volume, observe the surface of the specimen, and confirm the elemental components using a scanning microscope (SEM) and an energy dispersion X-ray spectrometer (EDS). Through this experiment, we analyze the friction and wear characteristics of valve train components according to engine oil grade, and the obtained data serve as an effective engine oil management method.

• Journal of the Korean Institute of Gas
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• v.19 no.3
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• pp.9-17
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• 2015

Almost all of the natural gas consumed in South Korea is compressed into very high pressure for the transportation through the underground pipelines, then reduced in pressure regulation stations before delivery to the consumer. For pressure reduction, expansion valves have been used due to the simple and effective installation, but recover none of the energy in the gas during compression. Hence, turbo-expanders are proposed instead of the valves to accomplish the same pressure letdown function and recover some of the compression energy in the form of shaft work converting into electric powers. Here we have theoretically calculated the electric powers at the pressure reduction from 68.7 bar to 23 bar (which are the average values taken at the inlet and outlet points of the expansion valve in medium-pressure regulation stations) according to the inlet conditions of temperature and flow rate. The natural gas is considered as two cases of a pure methane and the mixture of hydrocarbons with a very small amount of nitrogen, and the Peng-Robinson equation of state is employed for the calculation of required thermodynamic properties. The electric energy is recovered as much as 1596 MW(methane) and 1567 MW(mixture) based on the total supply of natural gas in 2013.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.05a
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• pp.277-284
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• 1998

LPG refueling include a lot of risk done by human beings, dealing with highly combustible gas, so, during the refueling, the leakage initiated by human errors can result in a catastrophic accident. Therefore, this research tried to show what kind of tasks would include the high probability of the human errors and what should be considered for effective safety management in the LPG refueling. At first, 4 typical cases were taken through surveying various accident cases, and then a prototype of the refueling task was presented. And each task was analysed by FTA and ETA. The results showed that overpressure occupies 64.64% of the major reasons for gas leakage, and its probability was approximately 6.62E-06. Among the tasks, gas leakage resulted from mal-assembly of lorry hoses had the highest rate, and human errors related to opening and closing valves of pipe lines were most frequent. Also, the effects of confirming tasks were analyzed quantitatively.