• 상하수도학회지
• /
• 제35권2호
• /
• pp.163-174
• /
• 2021

Heatwaves are one of the most common phenomena originating from changes in the urban thermal environment. They are caused mainly by the evapotranspiration decrease of surface impermeable areas from increases in temperature and reflected heat, leading to a dry urban environment that can deteriorate aspects of everyday life. This study aimed to calculate daily maximum ground surface temperature affecting heatwaves, to quantify the effects of urban thermal environment control through water cycle restoration while validating its feasibility. The maximum surface temperature regression equation according to the impermeable area ratios of urban land cover types was derived. The estimated values from daily maximum ground surface temperature regression equation were compared with actual measured values to validate the calculation method's feasibility. The land cover classification and derivation of specific parameters were conducted by classifying land cover into buildings, roads, rivers, and lands. Detailed parameters were classified by the river area ratio, land impermeable area ratio, and green area ratio of each land-cover type, with the exception of the rivers, to derive the maximum surface temperature regression equation of each land cover type. The regression equation feasibility assessment showed that the estimated maximum surface temperature values were within the level of significance. The maximum surface temperature decreased by 0.0450℃ when the green area ratio increased by 1% and increased by 0.0321℃ when the impermeable area ratio increased by 1%. It was determined that the surface reduction effect through increases in the green area ratio was 29% higher than the increasing effect of surface temperature due to the impermeable land ratio.

• 대한기계학회논문집
• /
• 제18권11호
• /
• pp.3046-3056
• /
• 1994

To design and develop a turbocharged engine, it needs that many studies must be preceded about the characteristics of engine performance and thermal flow. To accomplish this purpose, turbocharger was equipped to 1.3 liter naturally aspirated gasoline engine. The temperature probe of plate type was designed and it was installed into the combustion chamber wall to measure unsteady temperature. The unsteady heat flux at combustion chamber wall was evaluated using one dimensional unsteady conduction equation with the wall temperature and temperature gradient.

• 대한기계학회논문집
• /
• 제17권10호
• /
• pp.2574-2581
• /
• 1993

A Shadow mask in C. R. T. (Cathod Ray Tube) undergoes a temperature increase due to impinging electron beams emitted from guns, and thermal deformation from such temperature rise may cause the electron beams to island on the panel, and thus give rise to depolarization. Hence the analysis of temperature distribution for a shadow mask is an important procedure for designing the shadow mask. In this paper, we are concerned with nonlinear finite element analysis of the temperature distribution on a shadow mask. First of all, we replace shadow mask, containing numerous apertures of a slit type, by an orthotropic shell without apertures, and calculate the apparent thermal conductivities. Because of thermal radiation, which is one of the major heat transfer mechanism for shadow masks, the resulting finite element equation is nonlinear and solved by the Newton method. Finally numerical examples are illustrated for a 21" FST(Full Square Tube) shadow mask, and followed by discussion.sion.

• 대한설비공학회지:설비저널
• /
• 제12권2호
• /
• pp.71-80
• /
• 1983

The passive type solar energy heating system for the classroom was investigated. A classroom in a primary school located at Gangnam-ku, Seoul was taken as a model classroom the heat balance equation was established. The temperature in the classroom and solarium were calculated from the heat balance. at clear days, the temperature in the classroom and solarium were measured and compared with the calculated values. The calculated and measured values for the temperature agreed with, in general, in the increasing of $20\%$ range. It was found that the smaller size of solarium could Provide the increasing of energy efficiency for the classroom temperature.

• 한국자동차공학회논문집
• /
• 제5권4호
• /
• pp.70-83
• /
• 1997

We made a selection of engine operating conditions in the natural aspiration type diesel engine as load and speed. The effects on the power, smoke emission and cylinder pressure characteristics of these variations in operating conditions were observed experimentally. Also, the smoke emission was predicted by using the Arrhenius equation and empirical equation of the smoke emission was made. At the same time, the correlations, between the combustion and smoke emission characteristic were examined. From the above results, it is clear that to prevent power dropping and to decrease exhaust fume whin the conditions are changed, one should improve the intake system. To do this, the best way is to lower the air-fuel mixing ratio. We found that the parameters of the indicated mean effective pressure, maximum pressure and its location and combustion duration, etc. change the motion in accordance with the conditions described above. Also, we found that the variation of the pressure cycle comes from an amplified variation of the early part of process. From the analysis of comparing combustion and exhaust fume, the exhaust fume is produced at the latter time of combustion and decreased when the combustion ratio is higher. Also, we developed a special formula which can predict the exhaust fume value according to the engine load and speed.

• 대한기계학회논문집B
• /
• 제27권7호
• /
• pp.963-972
• /
• 2003

Performance characteristics of the planar-type solid oxide fuel cell (SOFC) are investigated by the analysis of flow fields coupled with heat and mass transfer phenomena in anode and cathode channels. For these purposes, performance analysis of the SOFC is conducted based on electrochemical reaction phenomena in electrodes and electrolyte coupled with flow fields in anode and cathode channels. In the present study, the isothermal model adopted in the previous paper prepared by the same authors is extended to the non-isothermal model by solving energy equation additionally with momentum and mass transfer equations using CFD technique. It is found that the difference between isothermal and non-isothermal models come from non-uniform temperature distribution along anode and cathode electrodes by solving energy equation in non-isothermal model. Non-uniform temperature distribution in non-isothermal model contributes to the increase of average temperature of the fuel cell and influences its performance characteristics.

• 한국산학기술학회논문지
• /
• 제14권11호
• /
• pp.5317-5322
• /
• 2013

본 연구에서는 ${\epsilon}$-NTU 방법을 사용하여 $CO_2$ 히트펌프 가스쿨러의 열전달 성능을 해석하였고, 공개된 실험결과와 비교하였다. $CO_2$ 히트펌프 가스쿨러의 열전달률, 냉매측/순환수측 출구온도를 EES로 계산하였다. 해석은 시험부를 하나의 구간으로 설정하여 냉매와 순환수측 입출구의 평균온도를 물성치로 적용한 평균해석과 시험부를 50구간으로 나누어 각 구간에서의 출구온도를 다음 구간의 입구온도로 사용한 국소해석으로 진행되었다. 실험결과로부터 평균해석보다는 국소해석의 결과가 실험값을 더 만족하였으며, 열전달률은 0.3~1.1%, 순환수측 출구온도는 1.31~1.88%, 냉매측 출구온도는 3.12~5.18% 정도의 오차를 보였다.

• 한국화재소방학회논문지
• /
• 제30권1호
• /
• pp.49-56
• /
• 2016

본 논문에서는 동절기 소방배관의 동파방지를 위한 열선의 직선 시공과 감기 시공의 효과를 수치해석을 통하여 분석하였다. 두 시공법들의 효과 분석을 위하여 3차원 에너지방정식과 비정상 비압축성 Navier-Stokes 방적식의 비정상 해를 구하였다. 수치해석에서 물의 자연대류와 소방 배관의 열전도 방정식이 상호작용을 하므로 복합열전달 해석을 상용코드 ANSYS-FLUENT에서 제공하는 압력-속도 연성기법들 중의 하나인 SIMPLE 알고리즘을 이용하여 수행하였다. 수치해석을 통하여 시간에 따른 배관 내의 유동장 및 온도분포와 배관 내 물의 최대 및 최소온도 변화를 고찰하였다. 수치해석 결과 배관 단위 길이 당 투입열량이 동일한 경우에 감기 시공과 직선 시공의 동파방지 효과는 거의 동일함을 확인하였다. 따라서, 열선 손상과 단락 등을 고려하면 직선 시공이 더 나은 시공법이라 판단된다.

• 한국정밀공학회지
• /
• 제32권2호
• /
• pp.167-172
• /
• 2015

In order to prevent crack in thick weld zones, the preheating process such as induction and gas torch heating needs to be applied. Among them induction heating is the most effective heat source because it has rare thermal effect and very rapid heating characteristics. In this paper, when the induction heating method is used to improve arc welding, the temperature distribution and magnetic field density of the welding zones are analyzed by simultaneously solving heat transfer and electromagnetic field equation. In particular, cone and flat type coils are designed and induction heating effects of each type are compared to identify heating characteristics on a V-groove weld joint. As a result, a cone shape coil is more efficient in the preheating process. When induction heating and arc welding system is designed for thick plate with V-groove weld joint, the results in this paper could be applied.

• Journal of Welding and Joining
• /
• 제28권4호
• /
• pp.33-40
• /
• 2010

The purpose of this study is to establish a predictive equation of transverse residual stress at the thick FCA butt weldment of large container vessel. The variables used were restraint degree, yield strength of base material, thickness of weldment and welding heat input. Restraint degree at the thick weldment of container ship having the various welding sequence was calculated using FEA. From the result, the H-type specimen was designed to reproduce the level of restraint degree at the actual weldment of containership. Based on the results, the predictive equations of the mean value and the distribution of transverse residual stress at each location of the weldment were established using dimensional analysis and multiple-regression method. The predictive equations were verified by comparing with those measured by XRD in the actual weldment of the ship.