• 대한기계학회논문집B
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• 제21권1호
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• pp.165-173
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• 1997

The present study investigates heat/mass transfer for flow through perforated plates for application to combustor wall and turbine blade film cooling. The experiments are conducted for hole length to diameter ratios of 0.68 to 1.5, for hole pitch-to-diameter ratios of 1.5 and 3.0, for gap distance between two parallel perforated plates of 1 to 3 hole diameters, and for Reynolds numbers of 60 to 13, 700. Local heat/mass transfer coefficients near and inside the cooling holes are obtained using a naphthalene sublimation technique. Detailed knowledge of the local transfer coefficients is essential to analyze thermal stress in turbine components. The results indicate that the heat/mass transfer coefficients inside the hole surface vary significantly due to flow separation and reattachment. The transfer coefficient near the reattachment point is about four and half times that for a fully developed circular tube flow. The heat/mass transfer coefficient on the leeward surface has the same order as that on the windward surface because of a strong recirculation flow between neighboring jets from the array of holes. For flow through two perforated plate layers, the transfer coefficients on the target surface (windward surface of the second wall) affected by the gap spacing are approximately three to four times higher than that with a single layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1442-1446
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• 2004

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is employed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiments are carried out for two free-stream turbulence intensities of 1.2% and 14.7%. The high free-stream turbulence results in more uniform distributions of heat load on the both pressure and suction surfaces and in an early boundary-layer separation on the suction surface. The heat (mass) transfer enhancement on the suction surface due to the endwall vortices is found to be relatively small under the high free-stream turbulence.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1096-1105
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• 1996

A theoretical model of the frost formation has been presented to investigate the characteristics of the growth of frost layer by considering molecular diffusion of water vapor and heat generation caused by sublimation of water vapor in the frost layer. The present model was compared with existing experimental data as well as a previous model. The difference between the present model and existing experimental data was found to be about 6 percent. An analysis for the behavior of frost formation using present model shows a good agreement with the trend for a number of experimentally observed features. The present analysis can also provide the physical understanding on the phenomena of the frost formation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.436-441
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• 2003

The present study investigates heat/mass transfer characteristics in rotating two-pass ducts of three different aspect ratios with 90-ribbed surfaces. The results show that the flows generated by the 180-turn, rib turbulators, and duct rotation. The curvature of the 180-turn produces Dean vortices causing high heat/mass transfer in the turning region and in the upstream region of the second-pass. The rib turbulators disturb the main flow by producing reattachment and separation near the ribbed surfaces, and increase heat/mass transfer in the region between the ribs. As the rotation number increases, the heat/mass transfer discrepancy between the leading and the trailing surfaces become larger.

• 대한기계학회논문집B
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• 제24권6호
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• pp.870-879
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• 2000

An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.125-131
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• 2000

The local heat/mass transfer coefficients for arrays of impinging circular air jets on a plane surface are determined by means of the naphthalene sublimation method. Spent fluid makes a crossflow in the confined space. The crossflow reduces heat/mass transfer at the small gap distance between the jet plate and impingement surface because of reentrainment of the spent fluid. The present study suggests a new exhaust system having effusion holes in the impinging jet plate. The spent air flow out after impingement just through effusion holes located in the upper plate. This system increases heat/mass transfer coefficients and uniformity for small gap distances$(H/d{\leq}2)$

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.173-177
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• 2005

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat/mass transfer coefficient is measured for four tip clearance height-to-chord ratios of h/c = 1.0%, 2.0%, 3.0%, and 4% at the Reynolds number of $2.09{\times}105$. The result shows that at lower h/c, there exists a strong flow separation/re-attachment process, which results in severe thermal load along the pressure-side comer. As h/c increases, the re-attachment is occurred further downstream of the pressure-side comer with lower thermal load. At higher h/c, a pair of vortices on the tip surface near the leading edge are found along the pressure-side and suction-side comers, and the pressure-side tip vortex have significant influence even on the mid-chord local heat transfer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1092-1097
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• 2004

The heat (mass) transfer characteristics on the endwall surface of a first-stage linear turbine rotor cascade at off-design conditions has been investigated by employing the naphthalene sublimation technique. The experiments are carried out at the Reynolds number of $2.78{\times}10^{5}$ for two incidence angles of -5% and +5%. The positive incidence angle results in intensification of the pressure-side leg of a leading-edge horseshoe vortex, which delivers higher heat transfer along its trace. On the other hand, the negative incidence angle show an opposite tendency.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2029-2032
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• 2008

In this study, we have investigated the effects of upstream rectangular winglet pair (RWP) on the heat/mass transfer coefficients in a dimple. Dimple print diameter was fixed at 20mm and the dimple depth was 4.0mm (0.4H). The dimple surface was coated with naphthalene for mass transfer experiment and the test plate was positioned at a rectangular straight duct whose aspect ratio (W/H) was 20. A rectangular winglet pair was positioned at y/d=-2.5. The RWP angle ($\beta$) was varied from $15^{\circ}$ to $60^{\circ}$. The Reynolds number, based on the duct height (H), was 5,000. with changing the RWP angle ($\beta$), the induced vortices had different flow characteristics; longitudinal or transversal vortices. These variation of induced vortices affected on the heat/mass transfer characteristics in the dimple.