• 설비공학논문집
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• 제17권2호
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• pp.101-109
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• 2005

The purpose of this study is to investigate the performance of outdoor heat exchanger for heat pump using carbon dioxide. Two types of fin and tube heat exchangers (2 rows for type A and 3 rows for B) are tested. Both heat exchangers have counter-cross flow and 1-circuit arrangement. Test results such as heat transfer rate, pressure drop characteristics and temperature distribution in the heat exchanger are shown with respect to mass flow rate of refrigerant and frontal air velocity For cooling mode, the minimum temperature difference between air and refrigerant of type B is smaller than that of type A by $1^{circ}C$, but the pressure loss of air side is much higher for type B by $29\%$. It is found that a large temperature gradient of carbon dioxide during gas cooling Process Promotes thermal conduction through tube wall and fins which results in degradation of heat transfer performance. For heating mode operation, type B heat exchanger shows higher heat transfer performance compared to type A. However, because pressure loss of refrigerant side of type B is much greater than that of type A, the refrigerant outlet pressure of type B becomes lower than that of type A.

• 한국식품저장유통학회지
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• 제6권3호
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• pp.255-259
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• 1999

EPS 포장상자가 도마토를 포장시 기존의 골판지 상자에 비해 어느정도 신선도 유지효과 기능이 있는지의 여부를 분석하고 일반적인 MA 포장재인 LDPE 포장과도 비교하고자 도마토를 포장하여 $25^{\circ}C$에 저장하면서 골판지상자와 0.02와 0.04mm 두께의 LDPE 필름, EPS 상자로 포장한 것들과 신선도 유지효과를 비교하였다. 저장 7일 후 중량감소는 대조구는 5.9%, EPS 상자는 1.1%의 중량감소가 나타났고, 비타민C도 EPS 포장구가 대조구 보다 20% 높게 유지되고 있었고 산도와 가용성 고형물함량도 EPS와 LDPE 포장구가 대조구보다는 변화가 적은 것으로 나타났으며, 대조구는 위조현상과 도마토의 표면 색상이 붉게 변하여 상품성이 떨어지는 것으로 나타났다. EPS 포장구는 LDPE 포장구와는 신선도가 비슷하게 유지되고 있었고 대조구인 골판지 상자보다는 품질이 잘 유지되고 있어 EPS 포장상자를 도마토 포장상자로 활용가능성이 확인되었다.

• 한국식품저장유통학회지
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• 제6권3호
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• pp.260-263
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• 1999

EPS 포장상자가 포도의 신선도 유지효과 기능이 있는지의 여부를 조사하고자 'Sheridan' 포도를 포장하여 $25^{\circ}C$에 저장하면서 골판지상자와 0.02와 0.04mm 두께의 LDPE필름, EPS 상자로 포장한 것들과 신선도 유지효과를 비교하였다. 저장 10일후 중량감소는 대조구는 5.7%, EPS 상자는 0.9%의 중량감소가 나타났다. 비타민C는 EPS 포장구가 대조구 보다 15.5%, 산도는 24.4% 높게 유지되고 있었다. 당도는 EPS와 LDPE 포장구가 대조구 보다 약간 낮게 유지되고 있었으며, 곰팡이 발생 등의 부패는 대조구에서는 일부 송이에서 발생했으나 EPS 포장구에서는 발생하지 않았고 품질도 양호해, EPS 포장상자는 일반적인 MA포장재인 LDPE포장과는 신선도가 비슷하게 유지되었으나 대조구인 골판지 상자보다는 품질이 잘 유지되고 있어 EPS 상자를 포도 포장상자로 활용할 수 있을 것으로 확인되었다.

• 한국식품저장유통학회지
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• 제11권2호
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• pp.233-239
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• 2004

발효식품 담금 용기로 사용되고 있는 유리, PP, PET, 스테인레스 용기와 흙으로 제작된 옹기에 간장을 각각의 용기에서 발효하는 과정에 나타나는 물리, 화학적인 변화를 분석하여 발효식품 담금 용기에 따른 품질 특성을 분석, 평가하였다. 발효조건은 3$0^{\circ}C$ 발효실에서 4개월 동안 진행되었다. 저장 중 수분손실은 기공이 있는 옹기에서 높게 나타났으며, 염 함량은 용기별 차이는 미미하였다. pH의 경우 옹기를 제외한 다른 용기는 초기부터 끝까지 거의 일정한 상태를 유지하였으나 옹기는 3개월 째 급격하게 낮아졌다. 이는 기공율에 의해 미생물의 활발한 증식과 이에 따른 산도의 증가로 인한 것으로 판단되며, 이러한 현상은 발효식품에 긍정적인 영향을 미치는 것으로 나타났다. 산도는 초기 0.6%에서 최고 0.9%까지 약간의 증가를 보였다. 총질소량은 다른 용기에 비해 옹기에서 높게 나타났고, 핵산은 옹기에서 높은 함량을 나타내고 있으며 이는 맛과 관련이 있는 것으로 실제 관능검사 결과와 거의 일치함을 알 수 있었다. 미생물군의 변화는 호기성 세균인 총균수는 높은 균수를 보였으며 발효 2개월째 가장 높은 균수를 보이다 그 이후 감소하였다. 젖산균과 효모는 3개월 이후 가장 높은 균수를 보였다. Protease 활성 역시 옹기발효 처리구에서 강한 활성을 보이고 있다. 이는 아미노산의 분석에서도 같은 경향을 보이고 있다. 아미노산 분석에서는 맛에 관여하는 glutamic acid의 함량이 옹기발효에서 월등히 높게 나타나고 있고 이러한 결과는 관능검사 결과와 일치하고 있다.

• 한국해양공학회지
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• 제25권5호
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• pp.15-20
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• 2011

This study carried out a series of experiments involving impact tests (Drop Weight type & Charpy type with a standard specimen and newly designed I-type specimen), hardness tests, and fracture surface observations of French-made roll shell steel (F), abnormal roll shell steel (M), reheated roll shell steel (R), and S25C steel under heat treatment conditiAn experimental study was carried out to study the solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with a rotating inner cylinder. The lift forces acting on a fluidized particle play a central role in many important applications such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs, sediment transport, the cleaning of particles from surfaces, etc. In this study a clear acrylic pipe was used to observe the movement of solid particles. Annular velocities varied from 0.4 to 1.2 m/s. The effect of the annulus inclination and drill pipe rotation on the carrying capacity of a drilling fluid, particle rising velocity, and pressure drop in a slim hole annulus were measured for fully-developed flows of water and aqueous solutions of CMC (sodium carboxymethyl cellulose) and bentonite. The rotation of the inner cylinder was efficient at carrying particles to some degree. For a higher particle volume concentration, the hydraulic pressure loss of the mixture flow increased because of the friction between the wall and solids or between solids.

• 대한기계학회논문집B
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• 제24권5호
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• pp.744-752
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• 2000

The influence of arrangement and length of discrete ribs on heat/mass transfer and friction loss is investigated. Mass transfer experiments are conducted to obtain the detailed local heat/mass transfer information on the ribbed wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of the rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs were made by dividing each continuous rib into 2, 3 or 5 pieces and attached periodically to the top and the bottom walls of the duct with a parallel orientation The combined effects of rib angle and length of the discrete ribs on heat/mass transfer ae considered for the rib angles $({\alpha})\;of\;90^{\circ}\;and\;45^{\circ}$. As the number of the discrete ribs increases, the uniformity of the heat/mass transfer distributions increases. For $(\alpha})=90^{\circ}$, the heat/mass transfer enhancement with the discrete ribs is remarkable, while the heat/mass transfer performances are slightly higher than that of the transverse continuous ribs due to the accompanied high friction loss penalty. For $(\alpha})=90^{\circ}$, the average heat/mass transfer coefficients and the heat/mass transfer performances decrease slightly with the discrete ribs compared to the case of the angled continuous ribs.

• 한국컴퓨터정보학회논문지
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• 제22권1호
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• pp.63-69
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• 2017

In this paper, we propose a method to optimize the geometry and installation position of the mixer in the selective catalytic reduction (SCR) system by computational fluid dynamic(CFD). Using the commercial CFD software of CFD-ACE+, the flow dynamics of the flue gas was numerically analyzed for improving the injection uniformity of the reduction agent. Numerical analysis of the mixed gas heat flow into the upstream side of the primary SCR catalyst layer was performed when the denitrification facility was operated. The characteristics such as the flow rate, temperature, pressure loss and ammonia concentration of the mixed gas consisting of the flue gas and the ammonia reducing gas were examined at the upstream of the catalyst layer of SCR. The temperature difference on the surface of the catalyst layer is very small compared to the flow rate of the exhaust gas, and the temperature difference caused by the reducing gas hardly occurs because the flow rate of the reducing gas is very small. When the mixed gas is introduced into the SCR reactor, there is a slight tendency toward one wall. When the gas passes through the catalyst layer having a large pressure loss, the flow angle of the exhaust gas changes because the direction of the exhaust gas changes toward a smaller flow. Based on the uniformity of the flow rate of the mixed gas calculated at the SCR, it is judged that the position of the test port reflected in the design is proper.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.75-78
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• 2004

Various jet engines (Turbine engine family and RAM Jet engine) have been developed for high speed aircrafts. but their application to hypersonic flight is restricted by principle problems such as increase of total pressure loss and thermal stress. Therefore, the development of next generation propulsion system for hypersonic aircraft is a very important subject in the aerospace engineering field, SCRAM Jet engine based on a key technology, Supersonic Combustion. is supposed as the best choice for the hypersonic flight. Since Supersonic Combustion requires both rapid ignition and stable flame holding within supersonic air stream, much attention have to be given on the mixing state between air stream and fuel flow. However. the wider diffusion of fuel is expected with less total pressure loss in the supersonic air stream. So. in this study the direction of fuel injection is inclined 30 degree to downstream and the total pressure of jet is controlled for lower penetration height than thickness of boundary layer. Under these flow configuration both streams, fuel and supersonic air stream, would not mix enough. To spread fuel wider into supersonic air an aerodynamic force, baroclinic torque, is adopted. Baroclinic torque is generated by a spatial misalignment between pressure gradient (shock wave plane) and density gradient (mixing layer). A wedge is installed in downstream of injector orifice to induce an oblique shock. The schlieren optical visualization from side transparent wall and the total pressure measurement at exit cross section of combustor estimate how mixing is enhanced by the incidence of shock wave into supersonic boundary layer composed by fuel and air. In this study non-combustionable helium gas is injected with total pressure 0.66㎫ instead of flammable fuel to clarify mixing process. Mach number 1.8. total pressure O.5㎫, total temperature 288K are set up for supersonic air stream.

• 대한조선학회논문집
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• 제48권1호
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• pp.49-55
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• 2011

Sound insulation performance of a unit cabin mock-up is studied, where two identical rooms simulating cruise ship cabin are installed. STL (Sound Transmission Loss) measurement in the mock-up shows that STL of the partition between rooms is degraded by imperfect door ceiling and gap between wall and floor. It is also observed that gap around lighting and electrical outlet slightly affect the STL in high frequency ranges, since lighting and electrical outlet are supported by mineral wool in the back side due to fire-resistance requirement. Even after all possible gaps are sealed, STL of the partition is found to be lower than that measured in the laboratory by 9 dB. Measurement of SBN (Structure-Borne Noise) reveals that flanking transmission of SBN along the steel deck floor can severely deteriorate STL of the partition. Statistical energy analysis (SEA) of the mock-up confirms importance of the floor SBN control, in which increasing damping is essential to ensure high STL.

• Journal of Communications and Networks
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• 제18권3호
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• pp.476-483
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• 2016

Super Wi-Fi is a Wi-Fi-like service exploiting TV white space (WS) which is expected to achieve larger coverage than today's Wi-Fi thanks to its superior propagation characteristics. Super Wi-Fi has been materialized as an international standard, IEEE 802.11af, targeting indoor and outdoor applications, and is undergoing worldwide field tests. This paper demonstrates the true potential of indoor Super Wi-Fi, by experimentally comparing the signal propagation characteristics of Super Wi-Fi and Wi-Fi in the same indoor environment. Specifically, we measured the wall and floor attenuation factors and the path-loss distribution at 770MHz, 2.401 GHz, and 5.540 GHz, and predicted the downlink capacity of Wi-Fi and Super Wi-Fi. The experimental results have revealed that TVWS signals can penetrate up to two floors above and below, whereas Wi-Fi signals experience significant path loss even through a single floor. It has been also shown that Super Wi-Fi mitigates shaded regions of Wi-Fi by providing almost-homogeneous data rates within its coverage, performs comparable to Wi-Fi utilizing less bandwidth, and always achieves better spectral efficiency than Wi-Fi. The observed phenomena imply that Super Wi-Fi is suitable for indoor applications and has the potential of extending horizontal and vertical coverage of today's Wi-Fi.