The operating parameters considered in this study include evaporating and condensing temperature, degree of subcooling and degree of superheating. in R744-R717 cascade refrigeration system and R744 two-stage compression refrigeration system with the range of low temperature -50℃∼-30℃. The coefficient of performance(COP) of R744-R717 cascade refrigeration system is about 16∼20% greater than that of R744 two-stage compression refrigeration system in the range of evaporation temperature of -50℃∼-30℃. R744 two-stage compression refrigeration system is unstable because its coefficient of performance changes significantly depending on the evaporating temperature and total compression work, and compression efficiency decreases. In this case, not efficient for long-term use. Whereas R744-R717 R744-R717 is a cascade refrigeration system using eco-friendly refrigerants. And this system is a high-efficiency refrigeration system that performs well even under various operating conditions. This is why it can be configured by selecting a refrigerant suitable for the high temperature side and the low temperature side.

PURPOSES : The number of snowfall and the amount of snowfall are gradually increasing, and due to the characteristics of Seoul, which has a lot of traffic, it is difficult to respond quickly with a snow removal method that relies on snow removal vehicles. Therefore, it is necessary to develop an IoT based eco-friendly snow removal system that can respond to unexpected heavy snow in winter. In this study, the low temperature operation and snow removal performance of the IoT road condition snow removal detector and the snow removal system using CNT and PCM are evaluated in the climatic environment chamber. METHODS : To make artificial snow, it consists of an climatic environment chamber that can simulate a low temperature environment and equipment that can supply compressed air and cold water. Depending on the usage characteristics of the climatic environment chamber, use an air-water type snow maker. In order to make artificial snow, wet temperature, which takes into account the actual air temperature and the amount of moisture in the air, acts as the most important variable and is suitable for making snow, below –1.5 ℃. The lower the water temperature, the easier it is to freeze, so the water source was continuously supplied at 0 ℃ to 4 ℃. One of the two different pipes is connected to the water tank to supply water, and the other pipe is connected to the compressor to supply high-pressure air. Water is dispersed by compressed air in the form of many small droplets. The sprayed microscopic water particles freeze quickly in the low temperature environmental climatic chamber air and naturally fall to the floor, forming snow. Based on the KS C IEC 60068-2-1 cold resistance test standard, an integrated environmental test procedure was prepared to apply to IoT-based snow removal systems and performance evaluation was performed accordingly. The IoT based eco-friendly snow removal system is needed to in winter, so visual check and inspect the operation at the climatic chamber before setting up it to the actual site. In addition, grid type equipment was manufactured for consistent and reliable snow removal performance evaluation under controlled environmental conditions. RESULTS : The IoT-based eco-friendly snow removal system normally carried out the task of acquiring data and images without damaging the appearance or freezing in a low temperature environment. It showed clear snow removal performance in areas where PCM and CNT heating technology were applied to the concrete slab. This experiment shows that normal snow removal tasks can be carried out in low temperature environments in winter. CONCLUSIONS : The integrated environmental test procedures and grid type evaluation equipment are applied to low temperature operation and snow removal performance evaluation of snow removal systems. In the climatic environment chamber, where low temperature environments can be simulated, artificial snow is created regardless of the season to derive quantitative experimental results on snow removal performance. PCM and CNT heating technology showed high snow removal performance. The system is expected to be applied to road site situations to preemptively respond to unexpected heavy snow in winter.

Cars using diesel have always had problems with reducing exhaust fumes, and have been studied steadily in this regard. There were studies on the remanufacturing effect of DOC catalyst deactivated by diesel vehicle smoke reduction device, analysis of vehicle fire accident cases caused by damage to diesel vehicle smoke reduction device, and related studies on the remanufacturing effect of diesel vehicle smoke reduction device DPF. This study also developed a burner system in a smoke reduction device suitable for exhaust engines to completely burn smoke generated by institutions using diesel engines in low-temperature exhaust gases. The main systems to be developed are high-performance heaters, burner structures that can maintain ignition in exhaust flows, and exhaust flow control units that reduce exhaust gas backflow effects caused by diesel engines.

PURPOSES : The numeric-based Highway Pavement Management System (HPMS), along with an advanced three-dimensional pavement condition monitoring profiler vehicle (3DPM), in South Korea has presented remarkable advancements in pavement management since the early 2000. Based on these results, visual distress on pavement surfaces can be easily detected and analyzed. Additionally, the entire expressway pavement surface conditions in South Korea can be easily monitored using the current graphical user interface-based advanced information graphic (AIG) approach. Therefore, a critically negative pavement section can be detected and managed more easily and efficiently. However, the actual mechanical performance of the selected pavement layer still needs to be investigated in a more thorough manner not only to provide more accurate pavement performance results but also to verify the feasibility of the current 3DPM and AIG approaches. In this study, the low-temperature performance of the selected asphalt pavement layer section was evaluated to further verify and strengthen the feasibility of the current 3DPM and AIG approaches developed by the Korea Expressway Corporation. METHODS : Based on 3DPM and AIG approach, the positive and negative-riding-quality road sections were selected, respectively. The asphalt material cores were extracted from each section then bending beam rheometer mixture creep test was performed to measure their low-temperature properties. Based on the experimental results, thermal stress results were computed and visually compared. RESULTS : As expected, the asphalt material from the negative driving performance section presented a poorer low-temperature cracking resistance than that from the positive driving performance section. CONCLUSIONS : Current 3DPM equipment can successfully evaluate expressway surface conditions and the corresponding material performance quality. However, more extensive experimental studies are recommended to verify and strengthen the findings of this study

대표적인 비구조요소인 배관의 지진에 의한 손상은 관성력과 두 지지점 사이의 위상차에 의해 작용하는 반복하중 그 리고 허용변형량을 초과하는 상대변위 등에 의해 발생할 수 있다. 특히 주요 손상모드는 큰 반복하중에 의한 저주기피로임이 많은 실험적 연구를 통하여 알려졌다. 따라서 과도한 지진변위에 의한 배관의 손상을 방지하기 위하여 지진상대변위가 발생할 수 있는 위치에 지진분리이음 또는 지진분리장치의 적용이 요구된다. 신축관이음 중 하나인 벨로우즈는 지진분리이음으로 적용 할 수 있다. 본 논문에서는 3ply 금속 벨로우즈 신축관이음의 온도차에 의한 내진성능의 변화를 분석하기 위한 실험적 연구를 수행하였다. 상온환경에서 점진증폭 반복하중재하실험을 수행하였으며, -20°C의 저온조건에서 동일한 실험을 수행하고 그 결과 를 비교하였다. 실험 결과로부터, -20°C의 저온환경에서 금속벨로우즈의 변위성능은 약 10% 저하될 수 있음을 확인하였다.

In this paper, cycle performance analysis of two-stage compression two-stage expansion refrigeration system using eco-friendly refrigerants is presented to offer the basic design data for the operating parameters of the system. Eco-friendly refrigerant R600a(Isobutane) for freon refrigerant R22 were used working fluids in this study. The coefficient of performance(COP) of R600a is about 5% greater than that of R22 two-stage compression refrigeration system in the range of evaporation temperature –30℃∼-60℃. The coefficient of performance of two-stage compression and two-stage expansion refrigeration system decreases with the increasing condensation temperature and superheating degree but increases with the increasing evaporation temperature, subcooling degree and mass flow rate ration of intercooler.

PURPOSES: Using recyclable materials in asphalt pavement industry is one of the essential tasks not only for saving construction budgets but also for mitigating environmental pollutions. Over the past decades, several efforts have been made by road maintenance agencies to incorporate various recyclable materials into virgin asphalt paving mixtures. As a result, reclaimed asphalt pavement (RAP), which consists of old pavement material was selected as one of most widely used recyclable materials. In this paper, the effects of using different amounts of single-recycled RAP (SRRAP) and double-recycled RAP (DRRAP) on the low-temperature characteristics of asphalt mixtures were investigated. METHODS: To evaluate the low-temperature characteristics of SRRAP and DRRAP mixtures, two experiments, the bending beam mixture creep test and semicircular bending fracture test were performed. The experimental parameters: creep stiffness, m-value, thermal stress, critical cracking temperature, fracture energy, and fracture toughness were computed then compared. RESULTS : RAP mixtures (SRRAP or DRRAP) showed lower mechanical performance compared with conventional asphalt mixtures. The differences became distinct with increased RAP addition. However, the performance differences between SRRAP and DRRAP mixtures were not significant in all cases, which indicate the possible application of re-recycling technology (DRRAP) in the asphalt pavement industry. CONCLUSIONS : The addition of RAP to virgin asphalt can mitigate low-temperature performance despite the improvement in fracture performance observed in some cases. Therefore, using RAP (SRRAP or DRRAP) mixtures on inter or sublayer construction, but not on the surface layer, is recommended. Moreover, the possibility of applying double-recycling technology in asphalt pavement industry can be introduced in this study because not significant performance differences were found between SRRAP and DRRAP mixtures especially at low temperature.

PURPOSES: Using recycled asphalt materials (called Reclaimed Asphalt Pavement: RAP) from existing asphalt pavement layers in newly constructed asphalt pavement is an essential option not only for lowering the construction budget but also for mitigating environmental pollution for society. For this reason, many pavement agencies in South Korea, the USA, and Canada have observed the effect of RAP on conventional asphalt pavement to evaluate and set proper material specifications and addable amounts. In this paper, effect of recyclable material on low-temperature performance of asphalt materials was investigated with two different mechanical tests. Among the recyclable material sources, RAP and Taconite Aggregate (TA), which is mainly produced in northern Minnesota (USA), were considered. METHODS : To evaluate the low-temperature mechanical performance of a RAP mixture, two different experimental tests (In-Direct Tensile (IDT) low temperature creep test and Semi-Circular Bending (SCB) test) were considered. The mechanical parameters creep-stiffness, relaxation modulus, fracture energy, and fracture toughness were computed then compared. RESULTS: More brittle characteristics were observed with RAP-added asphalt mixtures compared to the conventional asphalt mixtures, as expected. However, the differences of computed mechanical performances were not significantly distinct for RAP mixtures compared to conventional mixtures when the RAP proportion was around 20%, and with the addition of TA up to 20%. CONCLUSIONS : It can be concluded that up to 20% of RAP addition (along with TA up to 20%) in a virgin asphalt mixture does not provide significant performance reduction. This addable proportion can be viewed as a successful minimum level when considering the addition of RAP to hot-mix asphalt (HMA). Moreover, applying TA with RAP could offer a successful alternative for asphalt recycling and the materials industry.

본 연구에서는 저온소성 코팅을 적용한 SUS 304 판을 사용하여 고가의 티타늄 판 대체에 대한 성능평가를 수행하였다. 전산유 동해석 결과, 저온소성 코팅을 적용한 SUS 304 판은 100 마이크론 두께의 코팅까지는 티타늄 판에 비해 더 뛰어난 열전달 성능을 보이는 것으로 나타났다. 실제 열교환기를 이용하여 열전달 성능에 대한 실험을 한 결과, 코팅을 적용한 SUS 304 판이 티타늄 판에 비해 더 우수 한 열전달 성능을 나타냄을 확인하였다. 또한 개방검사를 통해서 판의 부식 및 스케일 생성 정도를 확인하였을 때, 코팅을 적용한 SUS 304 판의 내부식 성능은 티타늄 판과 거의 동등하게 나타났으며, 해수에 의한 스케일의 생성 억제 효과는 코팅을 적용한 SUS 304 판에서 더욱 우수하게 나타났다.

Transparent conducting oxides (TCOs) were fabricated using solution-based ITO (Sn-doped In2O3) nanoinks with nanorods at an annealing temperature of 200 oC. In order to optimize their transparent conducting performance, ITO nanoinks were composed of ITO nanoparticles alone and the weight ratios of the nanorods to nanoparticles in the ITO nanoinks were adjusted to 0.1, 0.2, and 0.5. As a result, compared to the other TCOs, the ITO TCOs formed by the ITO nanoinks with weight ratio of 0.1 were found to exhibit outstanding transparent conducting performance in terms of sheet resistance (~102.3 Ω/square) and optical transmittance (~80.2%) at 550 nm; these excellent properties are due to the enhanced Hall mobility induced by the interconnection of the composite nanorods with the (440) planes of the short lattice distance in the TCOs, in which the presence of the nanorods can serve as a conducting pathway for electrons. Therefore, this resulting material can be proposed as a potential candidate for solution-based TCOs for use in optoelectronic devices requiring large-scale and low-cost processes.

In this paper, cycle performance characteristics of a cascade refrigeration system with internal heat exchanger for cascade heat exchanger using alternative freon refrigerants is presented to offer the basic design data for the operating parameters of the system. This system considered in this study is consisted of a high temperature cycle using Freon refrigerant R23, R508B and low temperature cycle using Freon refrigerants R22, R507A. The operating parameters of this system include subcooling and superheating degree, evaporating temperature, compressor efficiency, and so on. The main results were summarized as follows : The COP of cascade refrigeration system using R23/R507A is the highest results in this study. The COP of cascade refrigeration system with internal heat exchanger only in high temperature cycle is the highest value among three cycle, such as only low temperature cycle, only high temperature cycle and all the cycle

국내 벼 건조기간의 기상조건에 적합한 열펌프를 설계, 제작하여 기본 성능을 측정하고, 건조온도 20-50oC 범위에서 벼 건조실험을 통하여 건조특성 및 소요에너지를 분석하였다. 열펌프는 건압축 냉동 사이클에서 냉동효과는 173.8 kJ/kg이었으며, 냉매순환량은 49.6 kg/hr이었다. 따라서, 성능계수는 5.5로 표준냉동사이클에서 냉매 R-22의 성능계수 4.0에 비해 높은 값을 나타내었으며, 목표 건조공기의 온도 30oC 및 상대습도 40%에 도달하는 시간은 6분 및 7분으로 만족할 만한 수준이었다. 건조온도와 곡온과의 온도차이는 건조온도 21.9oC에서는 약 1.5oC, 건조온도 48.7oC에서는 약 8.5oC로서, 건조실에서 상승한 곡온은 템퍼링실에서 충분한 냉각이 이루어지는 것으로 판단되었다. 건조온도 21.9, 30.7 38.8 및 48.7oC에서 건조속도는 0.29, 0.61, 0.85 및 1.25%/hr로 나타나 상용건조기와 유사한 수준이었다. 건조온도 21.9oC에서 소요에너지는 325 kJ/kg, 건조온도 30.7, 38.8 및 48.7oC에서는 667, 692 및 776 kJ/kg로 나타나 외기조건에 따라 건조소요에너지의 차이가 발생했지만, 화석연료를 사용하는 상용 화력건조기의 벼 건조 소요에너지 4,000-5,000 kJ/kg에 비해 평균 86% 절감되는 것으로 나타났다.