• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.873-876
• /
• 2002

It has been reported that discrepancies exist in the case of double panels with an air layer when the measured sound transmission loss is compared with the calculated values. It has been known that the cause of this discrepancy is in major from the unavoidable dips associated with the double wall resonances. In this work, several correction methods to make up for such resonances are studied. In particular, the ‘boundary damping’concept is revisited and its effects are discussed by comparing with measured values. It is shown that the correction methods are necessary for the sound insulation analysis of double partitions with an air layer, in order to ascertain the quantitative correlation between measured and predicted values.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.51 no.9
• /
• pp.493-498
• /
• 2002

Double-side linear pulse motor(DSLPM) has more advantages than single-side linear pulse motor because noise and vibration can be considerably decreased by countervailing the normal forces, which is generated between two stators and mover. However, DSLPM has more complicated magnetic flux path and layout of stator pole toot/mover tooth rather than single-side linear pulse motor In this paper, DSLPM is designed and fabricated by considering the air gap magnetic density, shape of tooth and slot. In order to verify the characteristics of DSLPM, the air gap magnetic flux density is analyzed by 2D FEM and the magnetic flux path is analyzed by 3D FEM. Also the static thrust forces is obtained with the analyzed results.

• Membrane and Water Treatment
• /
• v.5 no.2
• /
• pp.109-122
• /
• 2014

Polyvinylidene fluoride (PVDF) hollow fiber membrane is widely used for water treatment. However, the weak mechanical strength of PVDF limits its application. To enhance its tensile strength, a double-layer composite hollow fiber membrane, with PVDF and polyetherimide as the external and inner layers, respectively, was successfully prepared through phase inversion technique. The effects of additive content, air gap distance, N,N-dimethyl-acetamide content in the inner core liquid, and the temperature of external coagulation bath on the membrane structure, permeation flux, rejection, tensile strength, and porosity were determined. Experimental results showed that the optimum preparation conditions for the double-layer composite hollow fiber membrane were as follows: PEG-400 and PEG-600, 5 wt%; air gap distance, 10 cm; inner core liquid and the external coagulation bath should be water; and temperature of the external coagulation bath, 40 C. A single layer PVDF hollow fiber membrane (without PEI layer) was also prepared under optimum conditions. The double-layer composite membrane remarkably improved the tensile strength compared with the single-layer PVDF hollow fiber membrane. The permeation flux, rejection, and porosity were also slightly enhanced. High-tensile strength hollow fiber PVDF ultrafiltration membrane can be fabricated using the proposed technique.

• Current Optics and Photonics
• /
• v.5 no.4
• /
• pp.375-383
• /
• 2021

We present a simulation method to design antireflection coating (ARCs) for fiber-coupled superconducting nanowire single-photon detectors. Using a finite-element method, the absorptance of the nanowire is calculated for a defined unit-cell structure consisting of a fiber, ARC layer, nanowire absorber, distributed Bragg reflector (DBR) mirror, and air gap. We develop a method to evaluate the uncertainty in absorptance due to the uncontrollable parameter of air-gap distance. The validity of the simulation method is tested by comparison to an experimental realization for a case of single-layer ARC, which results in good agreement. We show finally a double-layer ARC design optimized for a system detection efficiency of higher than 95%, with a reduced uncertainty due to the air-gap distance.

• Journal of the Korean Magnetics Society
• /
• v.26 no.6
• /
• pp.206-212
• /
• 2016

The shape of a iron bed supporting a permanent magnet in a large-sized motor is a important factor for determining the coupling strength with the yoke. In a large-sized motor, there is a difference in electromagnetic force with the yoke depending on the shape of the iron bed. In this paper, we show the differences and problems by calculating the electromagnetic force between the double bed and the single bed through the virtual air gap, and show that the single bed is superior in terms of the binding force. It is also shown that the binding force between the bed and the yoke is improved by carving the groove shape under the bed.

• Journal of Energy Engineering
• /
• v.1 no.1
• /
• pp.66-75
• /
• 1992

The performance of heat transfer through double pane window has been investigated using experimental and numerical methods. The range of the gap distance between glasses are 0.5-10 cm. The convection heat transfer plays the dominant role for the case of the wide gap distance together with the large Rayleigh number and thereby, reduces the enhanced thermal resistance due to the increased air gap, while the conduction heat transfer does the major role for the case of small gap distance. In order to enhance the thermal insulation of the double pane window, the heat transfer of triple pane window, which is constructed to put one more glass at the middle of the double pane, is investigated to check the reduction of the convection heat transfer together with the effect of the radiation shield due to the presence of the additional glass. Further, a spacer is installed at the middle height of the double pane, and the effect of which on the suppression of the convective heat transfer is analyzed carefully, using experimental and numerical methods. For the case of the spacer-installation, the amount of energy saving is considered about 10%, but the energy saving increases a lot to 30-50% for the case of triple pane window, due to the substantial radiation shield effect of the presence of the additional glass.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.3
• /
• pp.1028-1039
• /
• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• Journal of Bio-Environment Control
• /
• v.22 no.3
• /
• pp.270-278
• /
• 2013

The objective of the present study is to provide data needed to decide covering method to be able to increase the thermal insulation and light transmittance efficiency of commercial greenhouse. The thermal insulation effect, PPF transmittance and quantity of condensation water were estimated in experimental tomato greenhouses covered with three types of coverings of single layer, air inflated and conventional double layers covering. The overall heat flow of air inflated double layers greenhouse was similar to that of conventional double layers greenhouse, but the temperature between covering material and thermal screen in air inflated double layers greenhouse was lower than that in conventional double layers greenhouse at the same outside temperature condition due to air leakage through the gap of roof vent. The overall heat transfer coefficients acquired by experiment that was performed in single layer and conventional double layers greenhouses were close to those obtained from model experiment. Even though the PPF transmittance of air inflated double layers greenhouse was lower than that of single layer greenhouse, which was greater than that of conventional double layers greenhouse. The quantity of condensation water on covering surface of single layer greenhouse was greater than that of air inflated double layers greenhouse due to lower covering surface temperature.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.12
• /
• pp.2427-2433
• /
• 2015

A high-gain circularly-polarized patch antenna with a double-layered superstrate is proposed operating at a wireless LAN frequency. A superstrate has an array of metallic periodic unit cells and is located above the patch antenna with an air-gap. The designed antenna has a high gain of over 9.59dBi, which is the gain enhancement of 6.48dB compared to the patch antenna without superstrate. And it has a low axial ratio of under 3dB, so that it maintains the circular polarization of the patch antenna. The optimum air-gap height at the superstrate of $4{\times}4$ arrays is 25mm, which is equivalent to about $0.2{\lambda}$ at the frequency of 2.45GHz. We confirmed that the double-layered stacking of a superstrate increases the effective aperture size and hence it leads to enhance a gain of the patch antenna.

• Proceedings of the SAREK Conference
• /
• 2006.06a
• /
• pp.866-871
• /
• 2006

Recently according to the fashion of well-being, the case study of under floor heating system type for residential space is increasing. Specially double slab floor system can make several roles as reducing the acoustic noises and also supplying fresh air through the gap. So in present study floor heating performance was examined with various location of the space in the case of floor supply air and ceiling supply air. In both cases return air went out through ceiling opening. As one of the result is that when using the heat pipe type floor heating system the temperature difference between supply and return water was $15.2^{\circ}C$, but in case of commercial type floor heating system the temperature difference was $5.3^{\circ}C$ when the supply water temperature was $50^{\circ}C$.