• Title/Summary/Keyword: Very low specific speed range

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Flow Analysis in Positive Displacement Micro-Hydro Turbine and Development of Low Pulsation Turbine

  • Kurokawa, Junichi;Matsui, Jun;Choi, Young-Do
    • International Journal of Fluid Machinery and Systems
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    • v.1 no.1
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    • pp.76-85
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    • 2008
  • In order to extract micro hydropower in the very low specific speed range, a Positive Displacement Turbine (PDT) was proposed and steady performance was determined experimentally. However, the suppression of large pressure pulsation is inevitable for practical application of PDT. The objective of the present study is to reveal the mechanism and the characteristics of pressure pulsation in PDT by use of CFD and to suppress the pressure pulsation. Unsteady CFD analysis has revealed that large pressure pulsation is caused by large variation of rotational speed of the following rotor, while the driving rotor, which is output rotor, keeps constant speed. Here is newly proposed a 4-lobe helical type rotor which can reduce the pressure pulsation drastically and the performance prediction of new PDT is determined.

A New Concept of Hydraulic Design of Water Turbine Runners

  • Vesely, Jindrich;Pochyly, Frantisek;Obrovsky, Jiri;Mikulasek, Josef
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.4
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    • pp.383-391
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    • 2009
  • Vibrations at different frequencies with a different intensity as well as a pressure pulsation with different parameters are two phenomena which can be observed at different water turbines. Due to the vibration and the pressure pulsation some restrictions of water turbine operation range are applied. Similar problems with the efficiency level in a wide water turbine operation range are the basic problems which are solved for ages. A theoretical and practical solution of the above mentioned problems is very much time and money consuming. The paper describes a new theoretical solution of the excitation and pressure pulsation decrease as well as extension of the operational range with high efficiency level. The new concept to decrease the vibrations and pressure pulsations is based on a heterogeneous runner blade geometry generation. The new concept of the runner geometry design was numerically tested at a low specific speed pump turbine, see Fig. 1, and basic points of the concept are presented in this paper.

Performance Prediction Method of n Positive Displacement Turbine with 4-Lobe Helical Type Rotor (4-로브 헬리컬형 로터를 가진 용적형수차의 성능예측법)

  • Choi, Young-Do
    • Journal of Advanced Marine Engineering and Technology
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    • v.31 no.5
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    • pp.522-530
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    • 2007
  • In order to extract small hydropower in the very low specific speed range of $n_s<10$, a Positive Displacement Turbine (PDT) has been proposed and steady performances have been determined experimentally. However, the suppression of large pressure fluctuation is inevitable for practical application of PDT. Therefore, present study adopted 4-lobe helical type robe to reduce the pressure fluctuation. The results show that 4-lobe helical type robe can be adopted to suppress the pressure fluctuation drastically. Moreover, efficiency and unit power of the turbine with newly proposed 4-lobe helical type lobe are higher than those of the turbine with 3-lobe straight type robe.

A study on the Frequency Analysis Function of the Auricle Using A Notch Filter

  • Park, Dong-Cheol
    • International journal of advanced smart convergence
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    • v.10 no.4
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    • pp.241-255
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    • 2021
  • The human auricle is the first part to receive sound from the outside. In this part, the frequency range of human recognizable form is divided and organized. In this study, we propose modeling by applying a single sound source to the surface of the human auricle. This means that when the sound pressure of a low frequency (low frequency) sound enters the pinna, the impedance felt at the tip of a part of the non-linear surface of the pinna is mainly due to the tensile force at the end of the part of the non-linear surface of the pinna. By expressing the situation of moving at a very small speed, the characteristic impedance of the pinna was confirmed to be negative infinity, and it was also confirmed that the speed at the tip of a part of the non-linear surface of the pinna was 0 in the anti-resonance state. It was found that the wave propagation phenomenon that determines the characteristics of the filter is determined by how large the wavelength, kL, is compared to the length of the tip of a part of the non-straight surface of the pinna. Humans first receive sounds from outside through their ears. The auricle is non-linear and has a curved shape, and it is known that it analyzes frequencies while receiving external sounds. The human ear has an audible frequency range of 20Hz - 20,000Hz. Through the study, we applied the characteristics of the notch filter to hypothesize that the human audible frequency range is separated from the auricle, and applied filter theory to analyze it, and as a result, meaningful results were obtained. The curved part and the inner part of the auricle function as a trumpet, collecting sounds, and at the same time amplifying the weak sound of a specific band. The point was found and the shape of the envelope detected in the auricle was found. Selectivity for selecting sounds coming from the outside is the formula of the pinna that implements the function of Q. The function of distinguishing human-recognizable sound from the pinna from low to high through frequency analysis is performed in the pinna, and the 2-3kHz area, where human hearing threshold is the most sensitive, is also the acoustic impedance of the most recessed area of the pinna. It can be seen that starting from.

The Fabrication of Porous Nickel Oxide Thin Film using Anodization Process for an Electrochromic Device

  • Lee, Won-Chang;Choe, Eun-Chang;Hong, Byeong-Yu
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.407.1-407.1
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    • 2016
  • Electrochromism is defined as a phenomenon which involves persistently repeated change of optical properties between bleached state and colored state by simultaneous injection of electrons and ions, sufficient to induce an electrochemical redox process. Due to this feature, considerable progress has been made in the synthesis of electrochromic (EC) materials, improvements of EC properties in EC devices such as light shutter, smart window and variable reflectance mirrors etc. Among the variable EC materials, solid-state inorganics in particular, metal oxide semiconducting materials such as nickel oxide (NiO) have been investigated extensively. The NiO that is an anodic EC material is of special interest because of high color contrast ratio, large dynamic range and low material cost. The high performance EC devices should present the use of standard industrial production techniques to produce films with high coloration efficiency, rapid switching speed and robust reversibility. Generally, the color contrast and the optical switching speed increase drastically if high surface area is used. The structure of porous thin film provides a specific surface area and can facilitate a very short response time of the reaction between the surface and ions. The large variety of methods has been used to prepare the porous NiO thin films such as sol-gel process, chemical bath deposition and sputtering. Few studies have been reported on NiO thin films made by using sol-gel method. However, compared with dry process, wet processes that have the questions of the durability and the vestige of bleached state color limit the thin films practical use, especially when prepared by sol-gel method. In this study, we synthesis the porous NiO thin films on the fluorine doped tin oxide (FTO) glass by using sputtering and anodizing method. Also we compared electrical and optical properties of NiO thin films prepared by sol gel. The porous structure is promised to be helpful to the properties enhancement of the EC devices.

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Desorption characteristics of Activated Carbon and Activated Carbon Fiber by Development of Sorbent Tube for Measurement of Organic Solvent (유기용제 측정용 흡착관 개발을 위한 AC 및 ACF의 흡착특성)

  • 원정일;김기환;신창섭
    • Journal of environmental and Sanitary engineering
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    • v.17 no.3
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    • pp.99-109
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    • 2002
  • Charcoal $tube/CS_2$ method are more popularly used than any other in the measurement of the working environment for the exposure evaluation of organic solvent, but it is some weak points that the lower accuracy can be obtained on the polar materials and within the range of the low concentration. Thus solvent desorption method has been developed to make accuracy higher and to overcome some weak points. However, because of high price of adsorption tube for thermal desorption and the short of study on its application to the working environment, it is not popularly used in the domestic industrial hygiene fields. This dissertation aims to develop thermal desorption and adsorption tubes for measuring organic solvents in the working environment, by comparing and analyzing breakthrough condition and adsorption capacity with ACF. Specific surface area of ACF used in this study is wider than the one of AC and micropore of ACF related with adsorption has been developed, and adsorption velocity and adsorption amount are very excellent by linking a pore of surface and an inside well into micropore. 1. Result of analysis on physical characteristics of adsorbent, the specific surface area of ACF was 1.3 times higher than that of AC. Distribution ratio of micropore related to adsorption was 94% on ACF and AC. Result of SEM, micropore of the AC is opened to the surface. In contrast, ACF shows that extremely fast adsorption speed. Because of micropore are exposed on the surface and penetrate through each other. 2. Breakthrough characteristics of adsorbents was not different from slop of breakthrough curve. The effluent concentration reaches 10% of initial concentration($C_{out}/C_{in}=0.1$, break point) of ACF was 30~316min longer than that of AC. Therefore, the adsorption capacities of ACF was 1.1~4.6 times higher than that of AC. ACF can be used as a proper adsorbent for measurement of organic solvent.

Problems in the Korean National Family Planning Program (한국가족계획사업(韓國家族計劃事業)의 문제점(問題點))

  • Hong, Jong-Kwan
    • Clinical and Experimental Reproductive Medicine
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    • v.2 no.2
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    • pp.27-36
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    • 1975
  • The success of the family planning program in Korea is reflected in the decrease in the growth rate from 3.0% in 1962 to 2.0% in 1971, and in the decrease in the fertility rate from 43/1,000 in 1960 to 29/1,000 in 1970. However, it would be erroneous to attribute these reductions entirely to the family planning program. Other socio-economic factors, such as the increasing age at marriage and the increasing use of induced abortions, definitely had an impact on the lowered growth and fertility rate. Despite the relative success of the program to data in meeting its goals, there is no room for complacency. Meeting the goal of a further reduction in the population growth rate to 1.3% by 1981 is a much more difficult task than any one faced in the past. Not only must fertility be lowered further, but the size of the target population itself will expand tremendously in the late seventies; due to the post-war baby boom of the 1950's reaching reproductive ages. Furthermore, it is doubtful that the age at marriage will continue to rise as in the past or that the incidence of induced abortion will continue to increase. Consequently, future reductions in fertility will be more dependent on the performance of the national family planning program, with less assistance from these non-program factors. This paper will describe various approaches to help to the solution of these current problems. 1. PRACTICE RATE IN FAMILY PLANNING In 1973, the attitude (approval) and knowledge rates were quite high; 94% and 98% respectively. But a large gap exists between that and the actual practice rate, which is only 3695. Two factors must be considered in attempting to close the KAP-gap. The first is to change social norms, which still favor a larger family, increasing the practice rate cannot be done very quickly. The second point to consider is that the family planning program has not yet reached all the eligible women. A 1973 study determineded that a large portion, 3096 in fact, of all eligible women do not want more children, but are not practicing family planning. Thus, future efforts to help close the KAP-gap must focus attention and services on this important large group of potential acceptors. 2. CONTINUATION RATES Dissatisfaction with the loop and pill has resulted in high discontinuation rates. For example, a 1973 survey revealed that within the first six months initial loop acceptance. nearly 50% were dropouts, and that within the first four months of inital pill acceptance. nearly 50% were dropouts. These discontinuation rates have risen over the past few years. The high rate of discontinuance obviously decreases the contraceptive effectiveness. and has resulted in many unwanted births which is directly related to the increase of induced abortions. In the future, the family planning program must emphasize the improved quality of initial and follow-up services. rather than more quantity, in order to insure higher continuation rates and thus more effective contraceptive protection. 3. INDUCED ABORTION As noted earlier. the use of induced abortions has been increase yearly. For example, in 1960, the average number of abortions was 0.6 abortions per women in the 15-44 age range. By 1970. that had increased to 2 abortions per women. In 1966. 13% of all women between 15-44 had experienced at least one abortion. By 1971, that figure jumped to 28%. In 1973 alone, the total number of abortions was 400,000. Besides the ever incre.sing number of induced abortions, another change has that those who use abortions have shifted since 1965 to include- not. only the middle class, but also rural and low-income women. In the future. in response to the demand for abortion services among rural and low-income w~men, the government must provide and support abortion services for these women as a part of the national family planning program. 4. TARGET SYSTIi:M Since 1962, the nationwide target system has been used to set a target for each method, and the target number of acceptors is then apportioned out to various sub-areas according to the number of eligible couples in each area. Because these targets are set without consideration for demographic factors, particular tastes, prejudices, and previous patterns of acceptance in the area, a high discontinuation rate for all methods and a high wastage rate for the oral pill and condom results. In the future. to alleviate these problems of the methodbased target system. an alternative. such as the weighted-credit system, should be adopted on a nation wide basis. In this system. each contraceptive method is. assigned a specific number of points based upon the couple-years of protection (CYP) provided by the method. and no specific targets for each method are given. 5. INCREASE OF STERILIZA.TION TARGET Two special projects. the hospital-based family planning program and the armed forces program, has greatly contributed to the increasing acceptance in female and male sterilization respectively. From January-September 1974, 28,773 sterilizations were performed. During the same time in 1975, 46,894 were performed; a 63% increase. If this trend continues, by the end of 1975. approximately 70,000 sterilizations will have been performed. Sterilization is a much better method than both the loop and pill, in terms of more effective contraceptive protection and the almost zero dropout rate. In the future, the. family planning program should continue to stress the special programs which make more sterilizations possible. In particular, it should seek to add the laparoscope techniques to facilitate female sterilization acceptance rates. 6. INCREASE NUMBER OF PRIVATE ACCEPTORS Among the current family planning users, approximately 1/3 are in the private sector and thus do not- require government subsidy. The number of private acceptors increases with increasing urbanization and economic growth. To speed this process, the government initiated the special hospital based family planning program which is utilized mostly by the private sector. However, in the future, to further hasten the increase of private acceptors, the government should encourage doctors in private practice to provide family planning services, and provide the contraceptive supplies. This way, those do utilize the private medical system will also be able to receive family planning services and pay for it. Another means of increasing the number of private acceptors, IS to greatly expand the commercial outlets for pills and condoms beyond the existing service points of drugstores, hospitals, and health centers. 7. IE&C PROGRAM The current preferred family size is nearly twice as high as needed to achieve a stable poplation. Also, a strong boy preference hinders a small family size as nearly all couples fuel they must have at least one or more sons. The IE&C program must, in the future, strive to emphasize the values of the small family and equality of the sexes. A second problem for the IE&C program to work. with in the: future is the large group of people who approves family planning, want no more children, but do not practice. The IE&C program must work to motivate these people to accept family planning And finally, for those who already practice, an IE&C program in the future must stress continuation of use. The IE&C campaign, to insure highest effectiveness, should be based on a detailed factor analysis of contraceptive discontinuance. In conclusion, Korea faces a serious unfavorable sociodemographic situation- in the future unless the population growth rate can be curtailed. And in the future, the decrease in fertility will depend solely on the family planning program, as the effect of other socio-economic factors has already been maximumally felt. A second serious factor to consider is the increasing number of eligible women due to the 1950's baby boom. Thus, to meet these challenges, the program target must be increased and the program must improve the effectiveness of its current activities and develop new programs.

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