• 동력기계공학회지
• /
• 제20권5호
• /
• pp.37-45
• /
• 2016

Exhaust gas recirculation has the advantage of being low-cost and easy to control of NOx emission. Therefore, it is most generally used to reduce NOx emission according to strengthen regulation. In the case of a non-road engine, such as the agricultural engine, since it mainly operate a middle or high-load state, NOx emission is decreased in accordance with the mapping range of the EGR rate, but results in an increase in the particulate matter which is caused to deposit and fouling problem of the EGR system. This problem has become an important issue for maintaining the performance of the engine, as well as emission performance. This study had examined the effects of cooler aging on the performance of heat transfer efficiency and NOx emission in non-road diesel engine. As a result of the EGR cooler aging during 200 hours engine operation, the cooling performance decreased about 25% compared with that of fresh cooler and the NOx emission increased about 14.6% on NRSC(non-road steady cycle) and 20% on NRTC(non-road transient cycle) compared with that of fresh cooler respectively.

• Nuclear Engineering and Technology
• /
• 제48권4호
• /
• pp.1022-1035
• /
• 2016

A double-tube once-through steam generator (DOTSG) consisting of an outer straight tube and an inner helical tube is studied in this work. First, the structure of the DOTSG is optimized by considering two different objective functions. The tube length and the total pressure drop are considered as the first and second objective functions, respectively. Because the DOTSG is divided into the subcooled, boiling, and superheated sections according to the different secondary fluid states, the pitches in the three sections are defined as the optimization variables. A multi-objective optimization model is established and solved by particle swarm optimization. The optimization pitch is small in the subcooled region and superheated region, and large in the boiling region. Considering the availability of the optimum structure at power levels below 100% full power, we propose a new operating scheme that can fix the boundaries between the three heat-transfer sections. The operation scheme is proposed on the basis of data for full power, and the operation parameters are calculated at low power level. The primary inlet and outlet temperatures, as well as flow rate and secondary outlet temperature are changed according to the operation procedure.

• 한국연초학회지
• /
• 제18권2호
• /
• pp.145-149
• /
• 1996

The experiment was carried out to study the effect of dry ice expanded tobacco (DIET) blending ratio on the physical properties of cigarettes. Vnencapsulated pressure drop (UPD) of the cigarette decreased from 85 mmWG to 78 mWG when the DIET blending ratio increased from 0% to 60%, but it increased in the range of over 60% blending ratio. But the overall UPD/EPD ratio of these cigarettes showed a decreasing tendency. Cigarette ventilation rate increased from 55% to 66% with the increased blending ratio of expanded tobacco and loose ends also showed the same tendency. The higher the blending ratio of expanded tobacco, the faster became the static burning time from 7' 34" to 5' 02". However, the cigarette hardness was almost not affected by the blending ratio.ing ratio.

• 한국연소학회지
• /
• 제14권4호
• /
• pp.1-6
• /
• 2009

Analysis of the internal state of the blast furnace is necessary to predict and to control the operating conditions. Especially, it is important to develop models of the blast furnace to predict the cohesive zone because shape of the cohesive zone influences overall operating conditions of blast furnace such as gas flow, chemical reactions and temperature. Because many previous blast furnace models have assumed cohesive zone to be fixed, it was not possible to evaluate the shape change of cohesive zone in relation with operating conditions such as PCR, blast condition, and production rate. In this study, an axi-symmetric 2-dimensional steady state model is proposed to simulate blast furnace processes. In this model, cohesive zone is determined by the solid temperature. Finite volume method is employed for numerical simulation. To find location of the cohesive zone, entire calculation procedure is iterated until converged. Through this approach, shape of the cohesive zone, velocity and temperature within the furnace are predicted from the model.

• Journal of Advanced Marine Engineering and Technology
• /
• 제23권5호
• /
• pp.687-694
• /
• 1999

This study was conducted to develop new drying process for automatic control and marine engi-neering system. Air-water tests were carried out to investigate dryer performance. The dispersed flow in he dryer test apparatuses was also simulated by using a numerical code which solves the Dittus-Boelter equation for continuous liquid phase and the Reynolds equation of droplet motion for continuous liquid phase and the Reynolds equation of droplet motion for dispersed phase to predict droplet removal efficiency. Proper conditions for dehumidification were optimized by response ambient conditions. When the selected indexes were constrained in the range of 85-98% moisture content above $15^{\circ}$ and more than mass flow rates of moist air 750kg/h. The numerical results were compared with the experimental data pertaining to the removal effi-ciency at chamber stage and overall pressure drop along concentric tubes Good agreement was obtained as for the efficiency while relatively poor agreement was obtained for the relative humidity. The results also showed that the efficiency depended strongly on the relative humidity at the inlet condition which indicated the importance of estimating the heat exchanger length. Effects of some design parameters in both removal efficiency and breakthrough onset condition are discussed.

• 설비공학논문집
• /
• 제26권4호
• /
• pp.163-168
• /
• 2014

The plate heat exchanger has been widely used in water heating systems due to high efficiency, simple structure, and easy maintenance. However, the studies on the effects of fouling on the heat transfer performance under various operation and maintenance conditions are very limited in the open literature. The objective of this study is to investigate the effects of fouling with calcium carbonate ($CaCO_3$) on the heat transfer characteristics of the plate heat exchanger under various operating and geometric conditions. The heat transfer coefficient and pressure drop in the plate heat exchangers were measured under accelerated fouling conditions with $CaCO_3$ by varying geometric and operational parameters. The fouling resistance increased with the decrease in the flow rate, and the increase in the chevron angle and the concentration.

• Elastomers and Composites
• /
• 제22권3호
• /
• pp.213-218
• /
• 1987

고무중에서 polymer melt와 가장 유사한 유변학적 거동을 보이는 EPDM을 택하여, 가황반응속도를 조사하였으며, 이에 따라 부분적으로 가교도를 달리한 시편의 유변학적 특성을 capillary rheometer를 사용하여 검토하였다. 가교도가 0, 1.5, 3, 6%로 증가함에 따라 die 입구 및 출구에서의 압력 손실은 커지고, melt fracture가 일어나는 전단속도는 낮아지며 특히 die swell은 거의 직선적으로 증가하였다. 본 연구를 통하여 die swell, melt fracture, end effects등의 근원이 고분자 사슬의 탄성변형에 있음을 확인하였으며, 또한 압출, 압연등에서 흔히 관측되는 die swell의 요동이 가공중 발생할 수 있는 가황반응에 기인할 수도 있음을 보여준 것이다.

• 한국CDE학회논문집
• /
• 제3권3호
• /
• pp.201-209
• /
• 1998

To develop timely an optimal fan, a design system and a new manufacturing process used step by step have to be integrated. A small sized optimal fan for refrigerators, that was the goal on this project, was developed by the following principal processes. All processes are technologically linked in many directions: The existing fan was measured through reverse engineering. The measured data was used for the basic source of 3D design. The performance tests were carried and used as the data for the evaluation of the existing fan. Flow analysis by FANS-3D/sup [1]/ was performed at the given information (pressure drop and flow rate) to find out the configuration of optimal fan design. The flow patterns were investigated to measure the performance of fan through numerical experiment. The grid point data obtained by the above analysis turned into 3D high efficiency fan model by using CATIA. The product was manufactured by RP process (SLS, SLA) and tested the characteristic curves of the developed fan to compare with the existing fan. The modification of fan design were all examined to see any change in performance and checked to find any deficiency in assembling the fan into a duct. After the plastics flow analysis of the injection molding cycle to ensure acceptable quality fan, an optimal mold was processed by using tool-path for the newly designed fan.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1807-1812
• /
• 2004

Sinusoidal wavy channel is one of the most commonly used devices in the industry for achieving mixing and heat transfer. Here we report on results obtained from the DNS of flow inside the wavy channel performed using the finite volume technique. As a primary stage to obtain the optimal design for heat transfer and mixing, this study observed the basic flow structures in a wavy channel. The mass flow rate is kept constant with friction Reynolds number of $Re_{\tau}$ = 140 . Time- and space-averaged and instantaneous flow fields are illustrated to observe the flow structures. Although the direct comparison of results between turbulent wavy and flat channel is somehow difficult due to the different flow phenomena derived from different configuration, here the mean streamwise velocity and RMS of velocities at same $Re_{\tau}$ of two different channels are compared. The basic difference between wavy and flat channel flow is the existence of small scale wall vortices along the walls in a wavy channel. These vortices make flow more complex, which will accompany the increase of heat transfer, pressure drop and drag.

• 대한기계학회논문집B
• /
• 제33권1호
• /
• pp.60-68
• /
• 2009

The steam reformer for hydrogen production from methane is studied by a numerical method. Langmuir- Hinshelwood model is incorporated for catalytic surface reactions, and the pseudo-homogeneous model is used to take into account local equilibrium phenomena between a catalyst and bulk gas. Dominant chemical reactions are Steam Reforming (SR) reaction, Water-Gas Shift (WGS) reaction, and Direct Steam Reforming (DSR) reaction. The numerical results are validated with experimental results at the same operating conditions. Using the validated code, parametric study has been numerically performed in view of the steam reformer performance. As increasing a wall temperature, the fuel conversion increases due to the high heat transfer rate. When Steam to Carbon Ratio (SCR) increases, the concentration of carbon monoxide decreases since WGS reaction becomes more active. When increasing Gas Hourly Space Velocity (GHSV), the fuel conversion decreases due to the heat transfer limitation and the low residence time. The reactor shape effects are also investigated. The length and radius of cylindrical reactors are changed at the same catalyst volume. The longer steam reformer is, the better steam reformer performs. However, system energy efficiency decreases due to the large pressure drop.