• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.493-502
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• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.

• Journal of Mechanical Science and Technology
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• v.15 no.9
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• Journal of Communications and Networks
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• v.17 no.4
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• pp.428-439
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• 2015

In this study, we present an approach for reducing the information inaccuracy of existing star aggregation based on bypass links when there are multi-constraint QoS parameters in asymmetric networks. In our approach, bypass links with low similarity are selected. Links that are not chosen as bypass links are included in each group depending on the star's link characteristics. Moreover, each link group is aggregated differently according to the similarity of the links that make up the group. The selection of a bypass link by using link similarity reduces the existing time complexity of O($N^3$) to O(N) by virtue of the simplification of the selection process. In addition, the adaptive integration according to the characteristics of the links in each group is designed to reduce the information inaccuracy caused by static aggregation. Simulation results show that the proposed method maintains low information distortion; specifically, it is 3.8 times lower than that of the existing method, even when the number of nodes in a network increases.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1919-1922
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• 2003

Bypass anastomosis are frequently adopted for surgical treatments. After the bypass grafting, the bypass artery is often occluded due to restenosis and/or anastomotic neointimal fibrous hyperplasia phenomena. Optimal coronary bypass anastomosis should be investigated to improve the patency for the arterial bypass techniques. The objective of this study is to investigate the influence of bypass with sequential bypass effects in the stenosed coronary artery. Numerical analyses are focused on the understanding of the flow patterns for different sequential anastomosis techniques. Blood flow field is treated as two-dimensional incompressible laminar flow. The finite volume method is adopted for discretization of the governing equations. The Carreau model is employed as the constitutive equation for blood. To find the optimal sequential bypass anastomotic configurations, the mass flow rates at the outlet of different models are compared quantitatively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.6
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• pp.326-332
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• 2009

The purpose of the study is to decrease the refrigerant temperature at the outlet of the compressor under high thermal load conditions for air cooled vapor compression refrigeration system. The subcooling bypass line called subcooling bypass technology(SBT) is installed to the window type A/C system to investigate the performance test. The standard air calorimeter test method is applied to measure the refrigerant temperature at the outlet of the compressor, cooling capacity, power consumption, and system EER. The refrigerant temperature at the outlet of the compressor decreases as the bypass rate increases. When the bypass rate is 8.2%, the refrigerant temperature at the outlet of the compressor decreases $2.8^{\circ}C$ while the cooling capacity and EER are the same as the conventional A/C unit.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.7
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• pp.1003-1011
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• 2009

This study aims at precise control of oil outlet temperature in the oil cooler system of machine tools for enhancement of working speed and processing accuracy. PID control logic is adopted to obtain desired oil outlet temperature of the oil cooler system with hot-gas bypass method. We showed that the gains of PID controller could be easily determined by using gain tuning methods to get the gain of PID controller without any mathematical model. We also investigated various gain tuning methods to design the gains of PID and compared each control performance for selecting the optimal tuning method on the hot gas bypass method through experiments. Moreover, we confirmed excellent control performance with proposed PI controller gain even though disturbances were abruptly added to the experimental system.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.241-246
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• 2001

This paper introduces modeling and solution for the dynamics of pipeline inspection gauge (PIG) flow in natural gas pipeline. Without of bypass flow, the dynamic behavior of the PIG depends on the different pressure between the rear and nose parts, which is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. With bypass flow, the PIG dynamics also depends on the amount of bypass flow across its body. The mathematical model are derived for unsteady compressible flow of the PIG driving and expelled gas, and for dynamics of the PIG. The bypass flow is assumed to be incompressible with the condition of its Mach number smaller than 0.45. The method of characteristic (MOC) and the Runge-Kutta method are used to solve the system governing equations. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical model and the proposed solution are effective for estimation the dynamics of the PIG with and without bypass flow under given operational condition.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.2
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• pp.133-138
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• 2014

This paper proposes a low power-loss averaging current mode control using a resistor and bypass switch. Generally, current sensing method using a resistor has a disadvantage of power loss which degrades the efficiency of the entire systems. On the other hand, proposed measurement technique operating with bypass-switch connected in parallel with sensing resistor can reduce power loss significantly the current sensor. An analog-circuited bypass driver is implemented and used along with an average-circuit mode controller. The bypass switch bypasses the sensing current with a small amount of power loss. In this paper, a 50[W] prototype average current mode boost converter has been implemented for the experimental verification.

• Asian-Australasian Journal of Animal Sciences
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• v.10 no.6
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• pp.571-574
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• 1997

Attempts were made in the laboratory to produce bypass fat using acid oil by precipitation and fusion methods. The degree of saponification by both of these methods was above 80 percent. Where heating facilities are not available, precipitation method could be used, otherwise, fusion method of bypass fat production is found to be more convenient, especially for commercial scale operations as handling of large volume of solutions is eliminated. Bypass fat thus produced was tested in vitro for rumen fermentation. Incorporation of acid oil in the incubation medium reduced TVFA conc. from 127.06 to 124.09 mM/l SRL and increased ammonia-N levels from 210.50 to 223 mg/l SRL indicating that the microbial activity was affected on incorporation of acid oil in the incubation medium. However, incorporation of bypass fat in the incubation medium did not significantly affect TVFA conc. as well as ammonia-N levels. In another experiment, nine rumen fistulated sheep in three groups of three each were fed bypass fat at two different levels. Dry matter disappearance in 24 h from the nylon bags suspended in the rumen of animals under different groups was found to be $47.74{\pm}1.10$, $47.55{\pm}0.21$ and $50.74{\pm}1.11$ in group I (control), group II (fed bypass fat 50 g/day) and group III (fed bypass fat 100 g/day), respectively. These studies indicated that it is possible to produce bypass fat from acid oils, a by-product of oil refining process, and its feeding did not affect rumen fermentation.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.385-390
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• 2000

In this study we propose the computational model for the coronary circulation. The bypass from left ventricle is also considered. Lumped parameter model with three compartments in the coronary circulation is implemented in this study. We connected the coronary artery compartment with left ventricle to explain the bypass procedure from left ventricle. The asymmetric resistance is assumed in the bypass line from left ventricle. The present numerical method is tested for normal coronary circulation and the results are compared with the existing computational work. The bypass simulation is conducted and the flow pattern is delineated. The effect of shunt resistance and coronary compliance to circulation is investigated for the better design of the bypass shunt.