• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.804-809
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• 2009

The present study measured frost pattern on a cylinder to propose empirical correlation equations for the local and average frost thickness, frost density and frost mass. The key parameters were diameter of the cylinders (7mm, 20mm), cooling surface temperature of the circular tube, absolute humidity of air, air temperature and air velocity. A 50% ethylene glycol aqueous solution was applied as a coolant. The frost thicknesses at both front and rear were larger than those at the other parts, while they were increased as diameter of the cylinder was increased. The local frost thicknesses at high air velocity were more uniform than those at low air velocity. The values predicted by Kim et al. under the freezer condition showed larger by the maximum of $30{\sim}50%$ than the measured data under heat pump condition. The empirical correlations for the local and average frost thickness and frost mass were proposed. The correlation equations for the frost thickness and frost mass under the heat pump condition in the present study might predict more accurate than the other correlation equations. The proposed correlations might be applied for the freezer condition within the maximum 15% deviation from the previous correlations under freezer condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1086-1091
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• 2003

The problem of residual stresses and fatigue behavior in welded structures is the main concern of welding research fields. The residual stresses and distortions of structures by welding exert negative effect on the safety of mechanical structures. Postweld heat treatment is usually carried out to relieve this residual stresses of welded joints. In this paper the influence of postweld heat treatment on fatigue life of butt-welded joint was investigated. To predict the effect of PWHT, an analytical model is developed by finite element and local strain approach and the result of fatigue life analysis is compared to experimental results. It is demonstrated that fatigue life estimates closely approximate the experimental results and PWHT provides some increase of fatigue lives in long-life fatigue region and no increase in short-life fatigue region because of the residual stress relaxation under tensile loads.

• Advances in aircraft and spacecraft science
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• 제9권1호
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• pp.59-68
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• 2022

The physical and mathematical foundations of the heat-shielding composite materials functioning under the conditions of aerodynamic heating of aircraft, as well as under the conditions of the point effect of high-energy radiation are considered. The problem of deformation of a thin shallow shell under the action of a local temperature field is approximately solved. Such problems arise, for example, in the case of local destruction of heat-protective coatings of aircraft shells. Then the aerodynamic heating acts directly on the load-bearing shell of the structure. Its destruction inevitably leads to the death of the entire aircraft. A methodology has been developed for the numerical solution of the entire complex problem on the basis of economical absolutely stable numerical methods. Multiple results of numerical simulation of the thermal state of the locally heated shallow shell under conditions of its thermal destruction at high temperatures have been obtained.

• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.105-110
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• 2018

The flow boiling heat transfer of water was experimentally investigated on plain and sintered microporous surfaces in a mini-channel. The effects of microporous coating on flow boiling heat transfer of subcooled water were investigated in a 300 mm long mini-channel with a cross section of $20{\times}10mm^2$. The test section has sufficiently long entrance length of 300 mm which provides a fully-developed flow before the channel inlet. The bottom side of the channel was heated by a copper block assembled with a high-density cartridge heater and other sides of the channel were insulated. The microporous surface was fabricated by sintering copper particles with the average particle size of $50{\mu}m$ on the top side of the copper block. Heat transfer measurement was conducted at the mass flux of $208kg/m^2s$ and the heat flux up to $500kW/m^2$. Microporous coated surface showed an earlier boiling incipience compared with plain surface regardless of the mass flux. Microporous coating were significantly attributed to local wall temperature and local heat transfer coefficient for flow boiling.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1115-1125
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• 1997

Experiments have been conducted to obtain local and average heat transfer coefficients associated with impingement of a row of circular, free surface-water jets on a constant heat flux surface. Nozzle arrays are a row of 3 jets (nozzle dia.=4.6 mm) and a row of 5 jets (nozzle dia.=3.6 mm), and the nozzle configuration is Reverse cone type revealed good performance in heat transfer. Nozzle-to-plate spacings ranging from 16 mm to 80 mm were investigated for two jet center to center spacings 25 mm and 37.5 mm in the jet velocity of 3 m/s (R $e_{D}$=27000) to 8 m/s (R $e_{D}$=70000). For a row of 3 jets and a row of 5 jets, the stagnation heat transfer of the central jet is lower than that of adjacent jets. In the wall jet region between jets, for small nozzle-to-plate spacing and large jet velocity, the local maximum in the Nusselt number was observed, however, for small jet velocity or large nozzle-to-plate spacing, the local maximum was not observed. Except for the condition of $V_{O}$=8 m/s and H/D=10, the average Nusselt number reveals the following ranking: a row of 5 jets, a row of 3 jets, single jet. For a row of 3 jet, the maximum average Nusselt number occurs at H/D=8 ~ 10, and for a row of 5 jets, it occurs at H/D=2 ~ 4. Compared with the single jet, enhancement of average heat transfer for a row of 3 jets is approximately 1.52 ~ 2.28 times, and 1.69 ~ 3.75 times for a row of 5 jets.ets.s.

• 대한기계학회논문집
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• 제15권1호
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• pp.323-327
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• 1991

본 연구에서는 로켓노즐로 부터 분출되는 고온의 초음속제트가 45˚로 경사진 평판으로 분사되는 경우의 열전달을 측정하였다.고온의 제트가 충돌하는 평판표면 의 고온과 열유속을 측정하는 것이 거의 불가능하므로, 국소적열전달은 국소적 준 1차 원 열전도모형을 평판표면 아래에서 측정한 온도자료에 적용하여 구하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.382-389
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• 2001

In the present study, local heat transfer rates for co-rotating disks with two modified hubs having ventilation holes are investigated for Rossby number of 0.04, 0.1 and 0.35 to evaluate the influence of incoming flows through hub holes. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using Laser Doppler Anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by the disk rotation. The basic flow structure in a cavity between co-rotating disks consists of three regions; the solid-body rotating inner region, the outer region with turbulence vortices and the shroud boundary layer region. The heat/mass transfer. rates on the co-rotating disks are very low near the hub due to the solid-body rotation and those increase rapidly in the outer region due to turbulence mixing. The modified hubs with ventilation holes enhances significantly the heat/mass transfer rates on the region near the hub. The results also show that the heat transfer of Hub-2 is superior to that of Hub-1, but Hub-1 is more profitable for destructing the solid-body rotating inner region.

• 대한기계학회논문집B
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• 제22권1호
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• pp.50-60
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• 1998

As a method to develop an enhanced heat transfer fluid, the fine particles of a phase-change material were mixed with a conventional heat transfer fluid. Paraffin, which can be obtained easily in domestic market, was used for the phase-change material and water was used as a carrier fluid. Fine liquid particles of paraffin were formed in water as an emulsion by using an emulsifier, and they were cooled rapidly to become solid particle, resulting in paraffin slurry. The average diameter of produced solid particles was inversely proportional to the amount of the added emulsifier, which was theoretically proved. The produced paraffin slurry was tested thermally in heat transfer test section having a constant-heat-flux boundary condition. The test section was made of a circular stainless-steel pipe, which was directly heated by the power supply having a maximum of 50 Volts-500 Amperes. DSC(Differential scanning calorimeter) tests showed that two kinds of phase change were involved in the melting of paraffin, and it was explained in two different ways. A five- region-melting model was developed by extending the conventional three-region-melting model, and was used to obtain the local bulk mean temperatures of paraffin slurry in the heating test section. The local heat transfer coefficient showed a maximum where the bulk mean temperature of the paraffin slurry reached at the melting temperature of paraffin.

• 대한기계학회논문집
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• 제12권2호
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• pp.338-348
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• 1988

본 연구는 환상휜에서 휜 바탕의 온도가 조기적으로 변화할 때, 휜 바탕의 온도가 주기적으로 변화할 때, 휜 주변 뿐만 아니라 휜 선단에서의 대류현상을 고려한 과도 전열에 대한 해석이다.

• 설비공학논문집
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• 제18권8호
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• pp.656-663
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• 2006

The convective heat transfer on the outer surface of tube arrays perpendicular to the flow direction was experimentally investigated. The test sections which include the aligned and staggered arrangements were made and the local heat transfer coefficients on the outer surface of the tube were measured after the flow has been fully developed. The results showed that the local heat transfer coefficients of the staggered arrangement, which has transverse pitch of 0.075 m and longitudinal pitch of 0.08 m, were about 15% greater than that of the aligned arrangement. Also, the overall mean Nusselt number of the former was greater than that of the latter. It is verified that the results obtained by using the simulation show the same tendency with those of experiment.