• Journal of Energy Engineering
• /
• v.9 no.2
• /
• pp.102-108
• /
• 2000

난류상태로 유동중인 고분자 수용액은 순수 용매만의 경우에 비교할 때 동일유량에서 초기에 높은 마찰 저항감소효과를 보이며, 이러한 마찰저항감소효과는 펌프의 펌핑능력 증대로 큰 경제적 이익을 가져다준다. 그러나, 고분자 수용액은 그 극적인 마찰저항감소효과에도 불구하고 유동중에 가해지는 기계적 에너지, 열에너지 등에 의해서 초기의 높은 마찰저항감소효과를 점차적으로 상실하게 되기 때문에, 고분자 수용액의 퇴화를 완화시키기위한 연구가 필요하다. 따라서 본 연구에서는 기계적 퇴화특성이 비교적 강한 합성고분자와 계면활성제의 농도합계를 100wpm 으로 고정하고 비율을 11가지로 세분화하여 , 1$0^{\circ}C$의 온도에서 유속 1.5m/sec , 3.0m/sec 및 4.5m/sec 에 대한 퇴화경향을 알아보는 실험을 수행하였으며, 각 조건에서 합성고분자와 계면활성제의 적정비율을 관찰하였다. 실험 결과, 각 속도에서 시간에 따른 퇴화경향은 고속에서 기계적 에너지에 대한 퇴화를 볼 수 있었고, 계면활성제와 합성고분자를 혼합하여 첨가했을 경우 저온에서도 퇴화완화효과가 있음을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.23 no.5
• /
• pp.679-686
• /
• 1999

This study is to investigate the effect of a substantial drag reduction caused by the polymer(A611P) when the working fluids flow to the vertical direction in the vertical cylindrical equipment of closed flow system. The drag reduction is associated with the mechanical degrada-tion thermal degradation and heat transfer. By ignore the heat fluxs within the closed system the pressure drop due to the polymer concentration the flow velocity and flow time have been mea-sured. By taking into account the mechanical and thermal degradation in the closed system an experiment has been focused on the determination of the condition which could improve the pump capacity in the heat union electric power plant. Under the condition of non-boiling it has been found out that the change of heat flux has little influence on the drag reduction.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.10
• /
• pp.1908-1914
• /
• 1992

A significant drag reduction in the turbulent flow of CWM(coal Water Mixture) adding minute amounts of high molecular weight polymer additives has been obtained and it was compared with pure CWM.However, the rate of drag reduction could come down with flow time, which is caused by polymer degradation, The rate of drag reduction and polymer degradation is affected by polymer type, concentration, molecular weight, and flow velocity. In the present investigation, these important parameters were evaluated for their influences on polymer degradation in order to find out stable conditions for CWM transportation with time. It was necessary to determine the more effective type of polymer additives to guarantee the optimum conditions for CWM transport. Experiments were undertaken with a test section of pipe diameter 9.8mm and pipe length 3500mm(L/D=357) in a closed loop, and polyacrylamide and polyetylene oxide were utilized as polymer additives. The tests were carried out under the conditions of 200, 400, 700ppm of polymer concentrations. CWM concentrations utilized were 5% and 10% with flow velocities of 4.9m/s and 6.1m/s. Experimental data show that polyehylene oxide degraded faster than polyacrylamide in CWM transport, and polyacryamide is considered to be a more effective candidate as additive for long time-CWM transport. Polymer degradation is also found to be more likely at lower polymer concentrations, at higher flow velocities, and higher CWM concentrations.

• Journal of Energy Engineering
• /
• v.7 no.2
• /
• pp.163-171
• /
• 1998

Degradation of polymer additives is enhanced at higher temperature of the test solutions. The degradation of Co-polymer solution was investigated experimentally in a closed loop at the temperature of 6$0^{\circ}C$ and 8$0^{\circ}C$ with various polymer concentrations of 100, 200, 400, 600 ppm in order to see the effect of temperature and polymer concentration with time. The degradation effect were found to be more dependent on temperature than mechanical shear. The friction factor versus Reynolds number curves show that in the range of Reynolds number number 50,000~150,000 the friction was decreased as Reynolds number increased and the friction of solution at low temperature approached to Virk's maximum drag reduction asymptote. For constant flowrates and temperatures the degradation effect was found to be less likely in higher polymer concentration. For constant flowrates and polymer concentrations the degradation rates are affected mainly by temperature. At the temperature of 8$0^{\circ}C$ and polymer concentration of 100 ppm, drag reduction effect was disappeared after 4 hours. However, this thermal degradation could be avoided with additional materials such as surfactants which are supposed to enhance the bonding forces between polymer molecules.

• 한국전기화학회:학술대회논문집
• /
• 1999.10a
• /
• pp.51-51
• /
• 1999

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.4
• /
• pp.505-514
• /
• 1998

Flow pattern of air-water two phase flow depends on the conditions of pressure void fraction and channel geometry. We classify the flow pattern by measuring the output signal of the conductivity probe. under the classified flow pattern we mount a visualization equipment on the test section and take pictures. We vary the concentration of pure solvent and polymer to measure local void fraction. We know that the maximum point position of local void fraction distribution move from the center of the pipe to the wall of the pipe as JSL increase when JSA is constant in two phase flow. But we find that the maximum point position of local void friction move from the wal of the pipe to the center of the pipe when polymer concentration increase.

• Electrical & Electronic Materials
• /
• v.5 no.1
• /
• pp.111-121
• /
• 1992

본 연구는 Pb( $Co_{1}$3/Nb$_{2}$3/) $O_{3}$-PbTi $O_{3}$-PbZr $O_{3}$계 압전세라믹스의 조성에 따른 착화소자특성과 기계적응력 인가시의 압전열화현상에 대하여 조사하였다. 그 결과 상경계 조성에서 소결밀도, $K_{33}$ 및 출력전압이 최고치를 나타내었으며 능방정계조성에서는 조성의 변화에 따른 소결 및 전기적특성의 변화는 정방정계조성에 비하여 작았다. 기계적 응력 인가시의 압전퇴화현상은 분역의 재배열로 설명할 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.6 no.4
• /
• pp.285-290
• /
• 2005

Mechanical properties of rubber mat are influenced by many factors such as compounding ingredients and states of cure, process of rubber, and fillers. Our study aim is to investigate influence of N-isopropyl-N'-chloro-P-phenylene diamine antioxidant on the thermal aging and ozone cracking. In this work, the degradation of antiblastic rubber mat was studied and suggested mechanism to involve two-types of degradation, thermal-aging and ozone-cracking both of which can be contained antioxidant or non-antioxidant.

• Korean Journal of Materials Research
• /
• v.11 no.4
• /
• pp.294-299
• /
• 2001

Effects of the surface fluorination on the electrochemical charge-discharge properties of $Mg_2$Ni electrode in Ni-MH batteries fabricated by mechanical alloying were investigated. After 20h ball milling, Mg and Ni powder formed nanocrystalline $Mg_2$Ni. Discharge capacity of this alloy increased greatly at first one cycle, but due to the formation of Mg(OH)$_2$ passive layer, it showed a rapid degradation in alkaline solution within 10cyc1es. In case of 6N KOH +xN KF electrolyte (x = 0.5, 1, 2), a continuous and stable fluorinated layer formed by adding excess F$^{[-10]}$ ion, increased durability of $Mg_2$Ni electrode greatly and high rate discharge capability(90-100mAh/g). 2N KF addition led to the highest durability of all tested here. The reason of the improvement is due to thin MgF$_2$, which can prevent the $Mg_2$Ni electrode from forming Mg(OH)$_2$layer that is the main cause of degradation.

• Journal of Biomedical Engineering Research
• /
• v.25 no.6
• /
• pp.519-523
• /
• 2004

This study investigates micro-structural and mechanical properties of trabecular bone in human femoral head with and without osteoporosis using Micro-CT and finite element-model. 15 cored trabecular bone specimens with 20min of diameter were obtained from femoral heads with osteoporosis (T-score > -2.5 ) resected for total hip arthroplasty, and 5 specimens were removed from femoral head of cadavers, which has no history of musculoskeletal diseases. A high-resolution micro-CT system was used to scan each specimen to obtain histomorphometry indices. Based on obtained micro-images(pixel size=21.31㎛), a FE-model was created to determine mechanical property indices. While non-osteoporosis group had increases trabecular thickness, bone volume, bone volume fraction, degree of anisotropy and trabecular number compared with those of non-osteoporotic group, the non-osteoporotic group showed decreases in trabecular separation and structure model index. Regarding the mechanical property indices, reaction force, apparent stress and young's modulus were 1ower in osteoporotic group than in non-osteoporotic group. Our data shows salient deteriorations in trabecular micro-structural and mechanical properties in human femoral head with osteoporosis.