Measurement of local heat/mass transfer coefficients on a dimple using naphthalene sublimation

2011 ◽  
Vol 54 (5-6) ◽  
pp. 1071-1080 ◽  
Author(s):  
Hyun Goo Kwon ◽  
Sang Dong Hwang ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation

Effects of Fin Shapes and Arrangements on Heat Transfer for Impingement/Effusion Cooling With Crossflow

2005 ◽  
Author(s):  
Sung Kook Hong ◽  
Dong-Ho Rhee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Flow Characteristics ◽  
Local Heat ◽  
Wall Jet ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Blowing Ratio ◽  
Transfer Characteristics ◽  
Sublimation Method

The present paper has investigated the effects of fin on the flow and heat/mass transfer characteristics for the impingement/effusion cooling with crossflow. The fins of circular or rectangular shape are installed between two perforated plates and the crossflow passes between these two plates. The blowing ratio is changed from 0.5 to 1.5 for a fixed jet Reynolds number of 10,000. A naphthalene sublimation method is used to obtain the local heat/mass transfer coefficients on the effusion plate. A numerical calculation is also performed to investigate the flow characteristics. Flow and heat/mass transfer characteristics are changed significantly due to installation of fins. In the injection region, wall jet spreads more widely than the case without fins because fin prevents the wall jet from being swept away by the crossflow. In the effusion region, higher heat/mass transfer coefficient is obtained due to the flow disturbance and acceleration by the fin. As the blowing ratio increases, the effects of fin against the crossflow become more significant and then the higher average heat/mass transfer coefficients are obtained. Especially, the cases with rectangular fins have about 40%∼45% enhancement at the high blowing ratio of M = 1.5. However, the increase of blockage effect gives more pressure loss in the channel.

Heat Transfer Characteristics of an Obliquely Impinging Circular Jet

1980 ◽  
Vol 102 (2) ◽  
pp. 202-209 ◽  
Author(s):  
E. M. Sparrow ◽  
B. J. Lovell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Local Heat ◽  
Maximum Point ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Local Coefficients ◽  
Naphthalene Sublimation

Measurements of local heat (mass) transfer coefficients were made on a surface on which a circular jet impinges at an oblique angle. The angle of inclination of the jet relative to the surface was varied from 90 deg (normal impingement) to 30 deg. The Reynolds number and the distance between the jet orifice and the impingement plate were also varied parametrically. To facilitate the experiments, the naphthalene sublimation technique was employed, and the resulting mass transfer coefficients were converted to heat transfer coefficients by the well-established analogy between the two processes. It was found that the point of maximum mass transfer is displaced from the geometrical impingement point, with the extent of the displacement increasing with greater jet inclination. The local coefficients on the uphill side of the maximum point drop off more rapidly than do those on the downhill side, thus creating an imbalance in the cooling/heating capabilities on the two sides. Neither the maximum transfer coefficient nor the surface-averaged transfer coefficient are highly sensitive to the inclination of the jet; during the course of the experiments, the largest inclination-induced decreases in these quantities were in the 15 to 20 percent range.

Effect of Rib Angle on Local Heat/Mass Transfer Distribution in a Two-Pass Rib-Roughened Channel

1988 ◽  
Vol 110 (2) ◽  
pp. 233-241 ◽  
Author(s):  
P. R. Chandra ◽  
J. C. Han ◽  
S. C. Lau
Keyword(s):  
Mass Transfer ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Test Channel ◽  
Mass Transfer Coefficients ◽  
Square Duct ◽  
Naphthalene Sublimation Technique

The heat transfer characteristics of turbulent air flow in a two-pass channel were studied via the naphthalene sublimation technique. The test section, which consisted of two straight, square channels joined by a sharp 180 deg turn, resembled the internal cooling passages of gas turbine airfoils. The top and bottom surfaces of the test channel were roughened by rib turbulators. The rib height-to-hydraulic diameter ratio (e/D) was 0.063 and the rib pitch-to-height ratio (P/e) was 10. The local heat/mass transfer coefficients on the roughened top wall, and on the smooth divider and side walls of the test channel, were determined for three Reynolds numbers of 15,000, 30,000, and 60,000, and for three angles of attack (α) of 90, 60, and 45 deg. The results showed that the local Sherwood numbers on the ribbed walls were 1.5 to 6.5 times those for a fully developed flow in a smooth square duct. The average ribbed-wall Sherwood numbers were 2.5 to 3.5 times higher than the fully developed values, depending on the rib angle-of-attack and the Reynolds number. The results also indicated that, before the turn, the heat/mass transfer coefficients in the cases of α = 60 and 45 deg were higher than those in the case of α = 90 deg. However, after the turn, the heat/mass transfer coefficients in the oblique-rib cases were lower than those in the traverse-rib case. Correlations for the average Sherwood number ratios for individual channel surfaces and for the overall Sherwood number ratios are reported.

Local Heat/Mass Transfer and Friction Loss Measurement in a Rotating Matrix Cooling Channel

2009 ◽  
Author(s):  
In Taek Oh ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Matrix Channel ◽  
Rotation Numbers ◽  
The Matrix

The present investigation provides detailed local heat/mass transfer distribution and pressure drop characteristics in a matrix cooling channel under rotating conditions. The matrix channel has cooling sub-passages with crossing angle of 45 degrees. Detailed heat/mass transfer coefficients are measured using the naphthalene sublimation method. The pressure drops are also measured. The experiments were conducted under various Reynolds numbers (10,000 to 44,000) and rotation numbers (0.0 to 0.8). For the stationary case, the heat transfer characteristics are dominated by turning, impinging and swirling flow which are induced by the matrix channel geometry. Averaged heat/mass transfer coefficients on the leading and trailing surfaces in the stationary channel are approximately 2.1 times higher than those in a smooth channel. For the rotating cases, the effect of rotation on heat/mass transfer characteristics shows different tendency compared to typical rotating channels with radially outward flow. As the rotation number increases, the Sherwood number ratios increase on the leading surface, but changed slightly on the trailing surface. The thermal performance factors increases with increasing rotation numbers due to increased Sherwood number ratios and decreased friction factor ratios.

Local Heat/Mass Transfer Measurements in a Rectangular Duct With Discrete Ribs

1999 ◽  
Author(s):  
H. H. Cho ◽  
S. J. Wu ◽  
H. J. Kwon
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Friction Loss ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Average Heat ◽  
Duct Wall ◽  
Discrete Ribs

The influence of the arrangement and the length of discrete ribs on heat/mass transfer and friction loss is investigated. The mass transfer experiments are conducted to obtain detailed local heat/mass transfer coefficients on the duct wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs are made by dividing continuous ribs into 2, 3 and 5 pieces and attached periodically to the top and bottom surfaces of the duct with a parallel orientation. After examining the effects of rib angle of attack (α) for continuous ribs, the combined effects of the rib angle and the length of discrete ribs on heat/mass transfer on the duct wall are investigated for α = 90° and 45°. As the number of broken pieces of a rib increases, the more disturbed flows affect greatly heat/mass transfer and increase the uniformity of heat/mass transfer distributions. For α = 90°, the heat/mass transfer enhancement with the discrete ribs is remarkable, so that the discrete ribs augment up to 27% of the average heat/mass transfer coefficients compared with the transverse continuous rib. However, the heat/mass transfer performances of the discrete ribs are slightly higher than that of the transverse continuous rib due to the accompanied high friction loss penalty. For α = 45°, the average heat/mass transfer coefficients are decreased slightly with the discrete ribs, and the heat/mass transfer performances of the angled discrete ribs are also decreased even though the friction losses are lower.

Effect of Blade Tip Clearance on Turbine Shroud Heat/Mass Transfer

2001 ◽  
Author(s):  
Dong Ho Rhee ◽  
Jong Hyun Choi ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Large Scale ◽  
Local Heat ◽  
Tip Clearance ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Transfer Characteristics ◽  
Blade Tip

This study investigates the local heat/mass transfer characteristics on the stationary shroud with blade tip clearances for flat tip geometry. A large scale linear cascade is used and the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the shroud surface. The geometry of blade tip used in this study is flat and the tip clearance varies from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those for no tip clearance. High heat/mass transfer region is observed along the pressure side of blade due to the entrance effect and the acceleration of the tip gap flow. Complex heat transfer patterns on the shroud are observed in the region where the blade tip and shroud are overlapped due to the flow separation and reattachment. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of blade because tip leakage vortices are generated with interacting the main flow. The experimental results show that the heat/mass transfer characteristics are changed significantly with the gap distance between the tip of turbine blade and the shroud. However, the turbulence intensity of incoming flow has little influence on the heat/mass transfer coefficients on the shroud with tip clearance.

Local Heat/Mass Transfer and Friction Loss Measurement in a Rotating Matrix Cooling Channel

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
In Taek Oh ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Rotation Number ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Matrix Channel ◽  
The Matrix

The present investigation provides detailed local heat/mass transfer and pressure drop characteristics in a matrix cooling channel, under rotating conditions. The matrix channel had cooling subpassages with crossing angles of 45 deg. The detailed heat/mass transfer coefficients were measured via the naphthalene sublimation method, and pressure drops were also obtained. The experiments were conducted for various Reynolds numbers (10,500 to 44,000) and rotation numbers (0.0 to 0.8). In the stationary case, the heat transfer characteristics were dominated by turning, impinging, and swirling flow, induced by the matrix channel geometry. Average heat/mass transfer coefficients on the leading and trailing surfaces in the stationary channel were approximately 2.1 times greater than those in a smooth channel. In the rotating cases, the effect of rotation on heat/mass transfer characteristics differed from that of typical rotating channels with radially outward flow. As the rotation number increased, the Sherwood number ratios increased on the leading surfaces but changed only slightly on the trailing surfaces. The thermal performance factors increased with rotation number due to the increased Sherwood number ratios and decreased friction factor ratios.

Influence of Injection Type and Feed Arrangement on Flow and Heat Transfer in an Injection Slot

2001 ◽  
Vol 124 (1) ◽  
pp. 132-141 ◽  
Author(s):  
Hyung Hee Cho ◽  
Jin Ki Ham
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Cooling System ◽  
Transfer Coefficients ◽  
Counter Flow ◽  
Flow Paths ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Vertical Injection ◽  
Injection Type

An experimental investigation is conducted to improve a slot film cooling system used for the cooling of a 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, inline, and counter-flow paths to the mainstream flow direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot wall with various injection types and coolant feeding directions. A numerical simulation is also conducted to help understand the flow patterns inside the slot for different injection types. 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 injection 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 dimensionless temperature distributions at the slot exits differ little with blowing rates, injection types, and secondary flow conditions. In the results of heat/mass transfer measurements, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effects of jet impingement. The lateral distributions of heat/mass transfer coefficients with the inline and counter-flow paths are more uniform than the normal-flow path. The average heat/mass transfer coefficients with the injection holes are about two to five times higher than that of a smooth two-dimensional slot path.

Effects of Bleed Flow on Heat/Mass Transfer in a Rotating Rib-Roughened Channel

2006 ◽  
Vol 129 (3) ◽  
pp. 636-642 ◽  
Author(s):  
Yun Heung Jeon ◽  
Suk Hwan Park ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Rib Turbulators ◽  
Sublimation Method

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter (Dh) of the square channel is 40.0mm. 20 bleed holes are midway between the rib turburators on the leading surface and the hole diameter (d) is 4.5mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch (p) is 10.0 times of the rib height (e) and the rib height-to-hydraulic diameter ratio (e∕Dh) is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow were fixed at 10,000 and 10%, respectively. A naphthalene sublimation method was employed to determine the detailed local heat transfer coefficients using the heat/mass transfer analogy. The results suggest that for a rotating ribbed passage with the bleed flow of BR=0.1, the heat/mass transfer on the leading surface is dominantly affected by rib turbulators and the secondary flow induced by rotation rather than bleed flow. The heat/mass transfer on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with bleed flow.

Detailed Heat/Mass Transfer Distributions in a Rotating Smooth Channel With Bleed Flow

2007 ◽  
Vol 129 (11) ◽  
pp. 1538-1545 ◽  
Author(s):  
Kyung Min Kim ◽  
Sang In Kim ◽  
Yun Heung Jeon ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Smooth Channel ◽  
Naphthalene Sublimation ◽  
Sublimation Method ◽  
Cooling Passage ◽  
Internal Cooling Passage

In this study, the effects of bleed flow on heat/mass transfer in a rotating smooth square channel were investigated. The hydraulic diameter (Dh) of the channel was 40.0mm, and the diameter of the bleed holes (d) on the leading surface was 4.5mm. Tests were conducted under various bleed flow rates (0%, 10%, 20%) and rotation numbers (0, 0.2, 0.4), while the Reynolds number was fixed at 10,000. A naphthalene sublimation method was employed to determine the detailed heat transfer coefficients using a heat and mass transfer analogy. The results suggested heat/mass transfer characteristics in the internal cooling passage to be influenced by tripping flow as well as Coriolis force induced by bleed flow and channel rotation. In cases influenced by bleed flow, the heat/mass transfer on the leading surface was higher than that without bleed flow. The heat/mass transfer on the leading surface increased with the number of rotations to Ro=0.2, after which it decreased due to rotation effects.

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