MILD 연소로에서 Coanda 노즐 효과를 이용한 배기가스 재순환에 관한 연구

하지수(Ji Soo Ha),심성훈(Sung Hoon Shim) 大韓環境工學會 2013 대한환경공학회지 Vol.35 No.12

질소산화물 저감에 큰 효과가 있는 MILD 연소는 고온의 배기가스가 연소로내에 유입되는 양에 따라 질소산화물 저 감 특성이 많은 영향을 받는다. 본 연구에서는 동심원관 형태의 MILD 연소로에서 바깥 원통의 배기가스 통로에서부터 안쪽 원통의 연소통로 사이에 연결관을 설치하고 배기가스를 유입하기 위해 coanda 노즐을 사용하였다. 이러한 coanda 노즐의 기 하학적 형상 변화에 따라 고압공기 유량, 배기가스 유입량 특성을 수치해석을 통해 살펴봄으로써 최적의 coanda 노즐 형상을 도출하는 것을 본 연구의 목적으로 하였다. 본 연구의 전산 해석의 결과는 conada 노즐의 노즐 통로 간격이 0.5 mm, 노즐 각도 4°, 노즐 확관 길이 146 mm일 때 최적의 유입량비가 되었고 노즐 통로 수직 길이는 유입량비에 무관하였다. A MILD (Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of coanda nozzle geometrical parameters, nozzle passage gap length, nozzle passage length, nozzle angle and expansion length. The optimal configuration of coanda nozzle for the best entrainment flow rate was gap length, 0.5 mm, expansion angle, 4o and expansion length, 146 mm. The nozzle passage length was irrelevant to the exhaust gas entrainement.

Design of the airflow passage structure for improving the thermal performance of the power conversion system

한장우,정승봉,오명도 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.3

In order to operate a Power conversion system (PCS) reliably, which is used for solar or wind power generation and energy storage systems, a design engineer of a PCS must evaluate that the junction temperature of power semiconductor devices, such as an Insulatedgate bipolar transistor (IGBT) module, meets the design criteria in the cooling design stage. An engineer must have evaluation procedure to design the airflow passage structure of a PCS in a way that the heat generated from inside of the system can be effectively exhausted externally. This study investigated the thermal performance of a PCS for four different airflow passage structures using the airflow rate of the heat sink attached to the IGBT module as an evaluation index. Out of the suggested airflow passage structures, the structure using the upper supply-lower exhaust type without the cooling fan for the reactor, which forms the air curtain around the airflow passage guide of the IGBT module and the louver of the maintenance door, has been found to perform the best thermal performance. In this design, the airflow rate of the heat sink was approximately 14 % larger than the required rate, with the junction temperature of the IGBT module of 132.2 °C, which satisfied the cooling design criteria. When the ventilation area of the supply is increased by approximately 2.3 times and the thickness of the filter reduced by 10 mm, the airflow rate of the heat sink can reach up to 700.4 m 3 hr -1 , and in this case, the design criteria of the IGBT module can be satisfied even in an overload condition of 106.7 % of the rated load.

The Rate Question and Special Relativity

이승일 한국과학철학회 2022 과학철학 Vol.25 No.2

Passivism is the view that time passes in a mind-independent way. Some objections to passivism are predicated on the idea that, if time passes, then there should be a coherent rate at which it passes. In this paper, I consider one of those objections, No Alternate Possibilities objection (NAP), according to which while time would pass at the rate of 1 second per second, if it passes at all, this rate is incoherent as it could not have any other value, or it is a rate of one thing to itself. I argue that NAP fails if passivism is understood in a relativistic setting; if passivism is true, then special relativistic time dilation could naturally be interpreted as implying that the rate at which time passes is a rate of distinct things with values other than 1 second per second.

STUDIES IN FIBRE DIGESTION AND PASSAGE RATE OF LIQUID AND SOLID IN CATTLE AND BUFFALOES

Abdullah, N.,Ho, Y.W.,Mahyuddin, M.,Jalaludin, S. Asian Australasian Association of Animal Productio 1991 Animal Bioscience Vol.4 No.2

Rumen liquor characteristics and disappearance rate of dry matter were studied in Kedah-Kelantan cattle and swamp buffaloes fed grass of rice straw-based diet. Cobalt-EDTA and chromium mordented fibres prepared from the faecal material were used to determine the liquid and solid particles movement in both animal species fed with rice straw. Swamp buffaloes showed a more intense rumen fermentation activity than Kedah-Kelantan cattle when both species were fed straw-based diet. The buffaloes also demonstrated faster rates of grass and straw degradation in situ. The fluid outflow rate from the rumen of buffalo ($1.06{\pm}0.19l/h$) was observed to be slower than that of cattle ($1.55{\pm}0.01l/h$). No significant differences between cattle and buffaloes were observed in rumen fluid volume and passage rate of small particles from the rumen.

Influence of Fiber Content and Concentrate Level on Chewing Activity, Ruminal Digestion, Digesta Passage Rate and Nutrient Digestibility in Dairy Cows in Late Lactation

Tafaj, M.,Kolaneci, V.,Junck, B.,Maulbetsch, A.,Steingass, H.,Drochner, W. Asian Australasian Association of Animal Productio 2005 Animal Bioscience Vol.18 No.8

The influence of fiber content of hay (low-fiber 47% NDF and high-fiber 62% NDF of DM) and concentrate level (high 50% and low 20% of ration DM) on chewing activity, passage rate and nutrient digestibility were tested on four restrict-fed (11.1 to 13.7 kg DM/d) Holstein cows in late lactation. Aspects of ruminal fermentation and digesta particle size distribution were also investigated on two ruminally cannulated (100 mm i.d.) cows of the same group of animals. All digestion parameters studied were more affected by the fiber content of the hay and its ratio to non structural carbohydrates than by the concentrate level. Giving a diet of high-fiber (62% NDF) hay and low concentrate level (20%) increased chewing activity but decreased solid passage rate and total digestibility of nutrients due to a limited availability of fermentable OM in the late cut fiber rich hay. A supplementation of high-fiber hay with 50% concentrate in the diet seems to improve the ruminal digestion of cell contents, whilst a depression of the ruminal fiber digestibility was not completely avoided. Giving a diet of low-fiber (47% NDF) hay and high concentrate level (50%) reduced markedly the chewing and rumination activity, affected negatively the rumen conditions and, consequently, the ruminal digestion of fiber. A reduction of the concentrate level from 50 to 20% in the diet of low-fiber hay improved the rumen conditions as reflected by an increase of the ruminal solid passage rate and of fiber digestibility and in a decrease of the concentration of large particles and of the mean particle size of the rumen digesta and of the faeces. Generally, it can be summarised that, (i) concentrate supplementation is not a strategy to overcome limitations of low quality (fiber-rich) hay, and (ii) increase of the roughage quality is an effective strategy in ruminant nutrition, especially when concentrate availability for ruminants is limited.

PASSAGE RATE AND TOTAL CLEARANCE RATE OF DIGESTA FROM THE RUMEN OF COWS FED GRASS SILAGES

Bosch, M.W.,Bruining, M.,van Bruchem, J. Asian Australasian Association of Animal Productio 1989 Animal Bioscience Vol.2 No.3

PASSAGE RATE OF RICE STRAW IN THE DIGESTIVE TRACT OF BUFFALOES AND CATTLE

Homma, H.,Kurata, K. Asian Australasian Association of Animal Productio 1989 Animal Bioscience Vol.2 No.3

IGBT 모듈의 냉각성능 향상을 위한 전력변환장치의 유로 설계

한창우(Chang-Woo Han),문유림(You-Lim Moon),정승붕(Seung-Boong Jeong),오명도(Myung-Do Oh) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

In the thermal design stage, a design engineer of the power conversion system (PCS) which is used in wind power, photovoltaic, and energy storage system should evaluate whether the design criterion of the junction temperature in a power semiconductor device such as an insulated-gate bipolar transistor (IGBT) is satisfied or not. Here, an engineer designs the airflow passage structure of the PCS in order to exhaust effectively the heat that is generated by electronic components in the PCS. In this paper, it was compared with different airflow passage structures of the PCS using the numerical method to thermal performance indexes that are the airflow rate of the heat sink attached at the IGBT module and the junction temperature of the IGBT module. In order to satisfy the design criterion of the junction temperature of 130℃, the structure of the airflow passage is that the appearance and the dimension of the prototype is maintained in the same manner as the design 2, and the area of supply side louvers is maintained at least 0.3 ㎡ under the rated load condition considering the numerical error of 5 percent.

Parameters Estimation of Generalized Linear Failure Rate Semi-Markov Reliability Models

A. El-Gohary,A. Al-Khedhairi 한국신뢰성학회 2010 International Journal of Reliability and Applicati Vol.11 No.1

In this paper we will discuss the stochastic analysis of a three state semi-Markov reliability model. Maximum likelihood procedure will be used to obtain the estimators of the parameters included in this reliability model. Based on the assumption that the lifetime and repair time of the system units are generalized linear failure rate random variables, the reliability function of this system is obtained. Also, the distribution of the first passage time of this system will be derived. Some important special cases are discussed.

Estimation of parameters including a quadratic failure rate semi-Markov reliability model

El-Gohary, A.,Alshamrani, A. The Korean Reliability Society 2011 International Journal of Reliability and Applicati Vol.12 No.1

This paper discusses the stochastic analysis and the statistical inference of a quadratic failure rate semi-Markov reliability model. Maximum likelihood procedure will be used to obtain the estimators of the parameters included in this reliability model. Based on the assumption that the lifetime and repair time of the system units are random variables with quadratic failure rate, the reliability function of this system is obtained. Also, the distribution of the first passage time of this system is derived. Many important special cases are discussed.