Two-Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with eight ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10%. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state liquid crystal thermography (LCT) was employed to quantify a detailed 2D distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the sixth and eighth rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15,000, 20,000, 30,000, and 40,000. The maximum rotation number values were ranging between 0.12 (Re = 40,000) and 0.30 (Re = 15,000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case, the secondary flows are responsible for high heat transfer gradients on the investigated area.

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Two Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

Volume 5A: Heat Transfer ◽

10.1115/gt2014-26616 ◽

2014 ◽

Author(s):

Ignacio Mayo ◽

Ahmed El-Habib ◽

Tony Arts ◽

Benjamin Parres

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Convective Heat ◽

Rotation Number ◽

Reynolds Numbers ◽

Secondary Flows ◽

Operating Conditions ◽

Two Dimensional

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different Rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with 8 ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10 per cent. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state Liquid Crystal Thermography was employed to quantify a detailed two dimensional distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the 6th and 8th rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15000, 20000, 30000 and 40000. The maximum Rotation number values were ranging between 0.12 (Re = 40000) and 0.30 (Re = 15000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the Rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case the secondary flows are responsible for high heat transfer gradients on the investigated area.

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Convective Heat Transfer Coefficient and Pressure Drop of Al2O3-Water Nanofluid in a Single-Phase Microchannel for Cooling of High Heat Output Devices

ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B ◽

10.1115/mnht2008-52243 ◽

2008 ◽

Author(s):

Guillermo E. Valencia ◽

Miguel A. Ramos ◽

Antono J. Bula

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Heat Transfer Coefficient ◽

Pressure Drop ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Convective Heat ◽

Convective Heat Transfer Coefficient ◽

Heat Output ◽

Flux Boundary Condition

The paper describes an experimental procedure performed to obtain the convective heat transfer coefficient of Al2O3 nanofluid working as cooling fluid under turbulent regimen through arrays of aluminum microchannel heat sink having a diameter of 1.2 mm. Experimental Nusselt number correlation as a function of the volume fractions, Reynolds, Peclet and Prandtl numbers for a constant heat flux boundary condition is presented. The correlation for Nusselt number has a good agreement with experimental data and can be used to predict heat transfer coefficient for this specific nanofluid, water/Al2O3. Furthermore, the pressure drop is also analyzed considering the different nanoparticles concentration.

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Combustor Heat Shield Impingement Cooling and its Effect on Liner Convective Heat Transfer for a Model Annular Combustor With Radial Swirlers

Volume 5C: Heat Transfer ◽

10.1115/gt2015-42868 ◽

2015 ◽

Author(s):

David Gomez-Ramirez ◽

Deepu Dilip ◽

Bharath Viswanath Ravi ◽

Samruddhi Deshpande ◽

Jaideep Pandit ◽

...

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Gas Turbine ◽

Convective Heat ◽

Reynolds Numbers ◽

Heat Shield ◽

Impingement Cooling ◽

Annular Combustor

Increasing pressure to reduce pollutant emissions such as NOx and CO, while simultaneously increasing the efficiency of gas turbines, has led to the development of modern gas turbine combustors operating at lean equivalence ratios and high compression ratios. These modern combustors use a large portion of the compressor air in the combustion process and hence efficient use of cooling air is critical. Backside impingement cooling is one alternative for advanced cooling in gas turbine combustors. The dome of the combustor is a primary example where backside impingement cooling is extensively used. The dome directly interacts with the flame and hence represents a limiting factor for combustor durability. The present paper studies two aspects of dome cooling: the impingement heat transfer on the dome heat shield of an annular combustor and the effect of the outflow from the spent air on the liner heat transfer. A transient measurement technique using Thermochromic Liquid Crystals (TLCs) was used to characterize the convective heat transfer coefficient on the backside of an industrial heat shield design provided by Solar Turbines, Inc. for Reynolds numbers (with respect to the hole diameter) of ∼ 1500 and ∼ 2500. Reynolds-Averaged Navier Stokes (RANS) calculations using the k-ω SST turbulence model were found to be in good agreement with the experiment. A standard heat transfer correlation for impingement hole arrays overestimated the mean heat transfer coefficient compared to the experiment and computations, however this could be explained by low biases in the results. Steady state IR measurements were performed to study the effects that the spent air from the heat shield impingement cooling had on the liner convective heat transfer. Measurements were taken for three Reynolds numbers (with respect to the hydraulic diameter of the combustor annulus) including 50000, 90000, and 130000. A downstream shift in the flow features was observed due to the secondary flow introduced by the outflow, as well as a significant increase in the convective heat transfer close to the dome wall.

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Wind Induced Heat Transfer Coefficient From Flat Horizontal Surfaces Exposed to Solar Radiation

ASME 2007 Energy Sustainability Conference ◽

10.1115/es2007-36163 ◽

2007 ◽

Cited By ~ 1

Author(s):

Subhash C. Mullick ◽

Suresh Kumar ◽

Basant K. Chourasia

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Heat Loss ◽

Convective Heat ◽

Solar Collector ◽

Convective Heat Transfer Coefficient ◽

Loss Coefficient ◽

Operating Conditions

Upward heat losses have strong effect on the performance of flat plate solar collectors under different operating conditions. Suitable equations for estimation of top heat loss coefficient have already been proposed [1,2]. The top heat loss coefficient is a function of wind induced convective heat transfer coefficient in a flat plate solar collector. It is, therefore, important to choose appropriate values of this convective heat transfer coefficient for correct estimation of the top heat loss coefficient. Researchers [3–6] have suggested different wind speed based correlations for estimation of the wind induced convective heat transfer coefficient. These correlations give different values of wind heat transfer coefficient thus resulting in variation in values of the top heat loss coefficient of a solar collector under same operating conditions. In present study, an attempt has been made to measure and study the wind induced convective heat transfer coefficient from exposed flat horizontal surfaces in real wind. For this purpose, three unglazed test plates of similar construction and different sizes were employed. Experiments were conducted on the three test plates over rooftop of a building in built environment. From experimental data of the test plate, of size 925mm × 865mm × 2mm, a correlation between wind heat transfer coefficient and wind speed has been obtained by linear regression. The obtained correlation has also been compared with work of other researchers [3–6]. Results obtained from experimental data of the three test plates provide some interesting information about wind induced convective heat transfer coefficient.

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