• 한국환경과학회지
• /
• 제26권12호
• /
• pp.1363-1374
• /
• 2017

Global climate change caused by industrialization has caused abnormal weather conditions such as urban temperatures and tropical nights, urban heat waves, heat waves, and heavy rains. Therefore, the study tried to analyze climate conditions and weather conditions in the streets and analyze climate factors and meteorological factors that lead to inconvenience to citizens. In the case of trees, the overall temperature, surface temperature, solar irradiance, and net radiation were measured low, and the temperature was lower in the Pedestrian road than in roads. The dry bulb temperature, the black bulb temperature, and the wet bulb temperature for the thermal evaluation showed the same tendency. In the case of thermal evaluation, there was a similar tendency to temperature in WBGT, MRT, and UTCI, and varied differences between types. Although the correlation between the meteorological environment and the thermal environment showed a statistically significant significance, the difference between the measured items was not significant. The study found that the trees were generally pleasant to weather and thermal climate in the form of trees, and the differences were mostly documented.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.623-627
• /
• 2001

Suppression of very low-frequency noise from an automobile exhaust system is difficult due mainly to its large wave length. Therefore, the configuration of total exhaust system, i,e., piping and muffler layout, is important at low frequencies. In this paper, an optimal layout technique of exhaust systems has been developed for reducing low-frequency exhaust noise. For this purpose, system insertion loss and virtual attenuation coefficient have been defined by considering the effects of mean flow and temperature gradient in the pipe. The applicability of present method is investigated with an actual automobile exhaust system and an optimized layout of pipes and mufflers is suggested.

• 한국자동차공학회논문집
• /
• 제3권1호
• /
• pp.1-12
• /
• 1995

Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at $600^{\circ}C$ and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to $600^{\circ}C$ were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at $600^{\circ}C$ showed that the fatigue life decreased as the strain rate and frequency decreased,especially for the low strain ranges.

• Asian-Australasian Journal of Animal Sciences
• /
• 제23권7호
• /
• pp.937-945
• /
• 2010

This study aimed to investigate the effects of dietary zinc (Zn), environmental temperatures and Zn${\times}$temperature interaction on growth, feathering score and mineral composition of broilers. A total of 256 d-old Avian male broiler chicks were randomly allocated to a $4{\times}2$ factorial arrangement with four corn-soybean meal basal diets (containing 44 mg Zn/kg) supplemented with 0, 40, 60 mg/kg Zn (Diets 1, 2 and 3, respectively; 0.8% Ca for these three diets) and non-Zn supplementation, 1.6% Ca (Diet 4) and two temperature conditions (low: 26, 24, $22^{\circ}C$ vs. high: 30, 28, $26^{\circ}C$). All birds were given feathering coverage scores for back, breast, wing, under-wing and tail. The wing and tail were further evaluated for the occurrence and severity of defect feathers. Feathers were then pooled for mineral composition analysis. The results showed that in high temperature conditions, broilers fed Zn-unsupplemented, 0.8% Ca ration (Diet 1) had significantly (p<0.05) lower ADFI and ADG (wk 1-6) than birds under low temperature conditions. However, when the birds were fed 40 and 60 mg/kg Zn supplementation (Diets 2 and 3), the ADFI and ADG in both temperature conditions were not significantly different. In low temperature conditions, the ADFI, ADG (p<0.05), all feather coverage (p<0.01) and tail defect scores (p<0.001) of birds fed Diet 4 (excess Ca) were significantly poorer than those fed Diet 1. More Ca (p<0.05) was retained in the feathers of broilers fed Diet 4 under high temperature conditions. Broilers fed the Zn-unsupplemented ration (Diet 1) had significantly higher feather phosphorus (p<0.01) and potassium (p<0.05) concentrations than those fed the 60 mg/kg Zn-supplemented ration (Diet 3). A reduction of feather phosphorus (p<0.01) and potassium (p<0.05) and higher manganese (p<0.05) concentrations were observed in Diet 4 broilers as compared to those fed Diet 1. Under high temperature conditions, broilers had lower iron (p<0.05) and higher manganese (p<0.05) concentrations in feathers. Broilers kept in high temperature conditions had a higher Zn requirement and 40 mg/kg Zn supplementation was sufficient for the birds to achieve optimum growth. Supplemental Zn ameliorated the adverse effect of high temperature on growth and occurrence of tail feather defects. Excess Ca disrupted Zn metabolism to exert a detrimental effect on growth performance and normal feathering and this was elucidated in the birds kept in low temperature conditions.

• 한국재료학회지
• /
• 제15권4호
• /
• pp.217-223
• /
• 2005

Thermal, electrical and mechanical properties of high purity niobium and tantalum refractory rare metals were investigated tn evaluate the physical purity. Higher purity niobium and tantalum metals showed lower hardness due to smaller solution hardening effect. Temperature dependence of electrical resistivity showed a typical metallic behavior. Remarkable decrease in electrical resistivity was observed for a high purity specimen at low temperature. However, thermal conductivity increased for a high purity specimen, and abrupt increase in thermal conductivity was observed at very low temperature, indicating typical temperature dependence of thermal conductivity for high purity metals. It can be known that reduction of electron-phonon scattering leads to increase in thermal conductivity of high purity niobium and tantalum metals at low temperature.

• 한국물환경학회지
• /
• 제35권4호
• /
• pp.299-307
• /
• 2019

The purpose of this study was to investigate the effect of low temperature thermal pre-treatment on biodegradation of waste activated sludge for anaerobic digestion as a countermeasure for increasing sludge generation. The experimental condition was accomplished in 2 %, 4 %, and 6 % TS concentration, and $70^{\circ}C$, $80^{\circ}C$, $90^{\circ}C$ of temperature for a maximum of 120 minutes retention time. Then, it was followed by analysis of physical/chemical properties, BMP test and composition of biogas. The biogas characteristic was evaluated by applying the modified Gomperz model. As a result, solubility of dissolved substrate, such as $SCOD_{Cr}$, soluble carbohydrate, and soluble protein, and biogas production increased as temperature increased. Solubilization efficiency at $90^{\circ}C$ was 18.4 %, 17.03 % and 16.88% in 2 %, 4 %, and 6 % TS concentration respectively. Also, solubilization rates of carbohydrate and protein similarly increased. BMP test results also showed that methane production in excess sludge increased to 0.194, 0.187 and $0.182m^3/kg$ VS. respectively, and lag phase decreased to 0.145, 0.220, 0.351 day due to acceleration of the hydrolysis step. Consequently, low-temperature thermal pre-treatment could increase biodegradability of sludge, positively affecting biogas production and sludge reduction.

• Journal of the Korean Wood Science and Technology
• /
• 제42권1호
• /
• pp.49-57
• /
• 2014

최종함수율은 예비천연건조를 수행한 시험재에서 더 균일하게 건조가 가능하였으며, 예비천연건조 후 고온저습건조시 최종함수율은 초기함수율에 영향을 받는 것으로 사료된다. 재면할렬 억제 효과는 예비천연건조를 수행한 시험재에서 더 효과적인 것으로 조사되었으나, 예비천연건조 중 발생된 재면할렬에 의한 영향이 크기 때문에 예비천연건조 중할렬발생 억제가 중요할 것으로 판단된다. 부분엔드코팅은 내부할렬, 표면경화율, 비틀림, 수축율에 미치는 영향이 없는 것으로 조사되었다. 예비천연건조는 고온저습건조 중 내층에 발생하는 인장응력을 감소시켜 내부할렬의 발생을 매우 효과적으로 억제하고 표면경화율을 감소시키는 것으로 조사되었다. 비틀림의 경우 함수율감소에 따른 수축으로 인하여 비틀림의 정도가 증가되었다.

• 한국지리정보학회지
• /
• 제26권2호
• /
• pp.42-54
• /
• 2023

우리나라 대도시 지역에 인구가 집중되고 이에 따른 수요를 충족시키기 위하여 저밀도 주거지가 재개발·재건축을 통하여 고밀도 주거지화 되고 있다. 그러나 단시간에 이루어진 대규모의 재건축은 도시녹지 면적 감소에 의한 열섬현상을 발생시키는 등 도시 기후에 부정적인 영향을 끼치게 된다. 본 연구에서는 Landsat 8 위성영상을 활용하여 서울특별시 강동구 고덕동, 둔촌동 재건축 지역의 2013년에서 2022년까지의 지표 온도의 변화를 분석하였다. 고덕동 지역에서는 재건축이 진행되는 대상지와 산림지역, 산림과 시가지가 혼재된 지역, 저층주거지역에 대한 지표 온도의 차이를 분석하였으며, 둔촌동 지역에서는 대상지와 산림지역, 저층주거지역에 대한 지표 온도의 차이를 분석하였다. 분석은 지표 온도 차이에 대한 다중회귀분석을 통하여 진행되었다. 고덕동 지역과 둔촌동 지역에서 공통적으로 재건축 전단계까지 전반적으로 지표 온도가 산림보다 높고 저층주거지역보다 낮게 나타났다. 이러한 특징들은 고덕동, 둔촌동의 저층주거지역이 대상지보다 녹지율이 낮고 건폐율이 높기 때문에 발생하였음을 알 수 있다. 본 연구를 통해 저밀도 지역이 고밀도화가 되더라도 녹지와 건폐율을 적절하게 관리한다면 도시열섬현상을 완화시킬 수 있음을 알 수 있다.

• 공업화학
• /
• 제22권6호
• /
• pp.658-663
• /
• 2011

SNCR-SCR hybrid system은 SNCR에서 NOx를 제거한 뒤, SCR로 NOx를 추가 제거하는 시스템으로 NOx 제거 효율을 향상시키는 경제적인 시스템이다. 본 연구에서는 SNCR-SCR hybrid system에서 운전 변수가 질소산화물 저감 효율에 미치는 영향을 고찰하였다. SNCR을 optimum temperature ($900{\sim}950^{\circ}C$)보다 낮은 온도에서 운전할 경우, 추가적인 암모니아 주입 없이도 $NH_3$ slip을 이용한 NO의 추가적인 제거의 효과가 있었으나 $NH_3$ slip이 높은 것으로 나타났다. 그러나 그 이상의 온도에서는 고온에 의한 암모니아의 분해로 SCR에 의한 추가 제거의 효과를 얻지 못했다. 따라서 SNCR 공정을 optimum temperature에서 운전하는 것이 NO 제거 효율과 $NH_3$ slip 농도를 고찰하였을 때 가장 적절하였으며, $SR_{RES}$가 적정 수준으로 유지되도록 NSR을 조절하는 것이 중요한 운전 변수인 것으로 나타났다.

• 청정기술
• /
• 제24권4호
• /
• pp.307-314
• /
• 2018

본 연구에서는 NMO (Natural Manganese Ore), $MnO_2$, $Mn_2O_3$ 촉매를 산소 존재 하에 저온에서 $NH_3$를 환원제로 이용하여 질소산화물(NOx)을 제거하는 선택적 촉매 환원법에 사용되었다. NMO의 경우, 안정성 실험에서 질소산화물 전환율이 423 K에서 100시간 후에도 변하지 않는 것을 확인하였다. 동력학 실험의 경우, 열 및 물질전달이 영향을 주지 않는 영역에서 수행하였다. 정상상태에서의 반응속도 연구는 저온 SCR반응에서 암모니아에 대하여 0차이고 일산화질소에 대해서는 0.41 ~ 0.57차였으며 산소에 대해서는 0.13 ~ 0.26차인 것을 확인하였다. 온도가 증가할 때, 암모니아와 산소 농도의 결과에 따라 반응차수가 감소함을 확인하였다. 촉매 표면에 해리흡착 된 암모니아와 가스상 일산화질소(E-R 모델)와의 반응 및 흡착 된 일산화질소(L-H 모델)와의 반응을 확인하였다.