Heat Transfer Enhancement in a High Aspect Ratio Channel with System Optimization

2013 ◽  
Vol 63 (8) ◽  
pp. 604-622 ◽  
Author(s):  
Haseung Chung ◽  
Seungwon Shin
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
System Optimization ◽  
Transfer Enhancement

Heat Transfer Enhancement Induced by Cube- and Diamond-Shaped Block Arrays in Two-Pass High-Aspect Ratio Channels With a 180-Degree Turn

2010 ◽  
Author(s):  
Pavin Ganmol ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
Local Heat Transfer ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Smooth Channel ◽  
Sharp Turn ◽  
First Pass

Described in this paper is an experimental investigation of the heat transfer and pressure characteristics in a high aspect ratio, (4.5:1 width-to-height), two-pass channel, with cube-shaped and diamond-shaped block arrays placed in both passes before and after a 180-degree sharp turn. Transient liquid crystal technique was applied to acquire detailed local heat transfer data on both the channel surfaces and the block elements. Reynolds number tested varies between 13000 and 28000. To further explore potential design alternatives for enhancement cooling, the effects of block height, ranging from 1/4, 1/2, 3/4 and full span of the channel height were also evaluated. Present results suggest that a staggered cube-array can enhance heat transfer rate up to 3.5 fold in the first pass and about 1.9 fold in the second pass, relative to the fully-developed smooth channel counterpart. For the corresponding diamond-shaped block array, the enhancement is 3.4 and 1.9 fold respectively. Even though the post-turn turbulence transport in the second pass is generally higher than that in the first pass, the effects of surface-block induced heat transfer enhancement in fact are less prominent in the post-turn region of the second pass. Pressure loss for diamond block arrays is generally higher than that of the corresponding cube-block arrays.

Heat Transfer and Pressure Drop Measurements in a High Aspect Ratio Channel With Circular Pins and Strip Fins

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Metapun Nuntakulamarat ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
Thickness Effect ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pin Fin

Abstract This paper focuses on the measurements of heat transfer enhancement and pressure drop of different pin or fin configurations in a high aspect ratio (AR = 9.57/1.2) channel. Two different pin-fin shapes including circular pins and strip fins were studied. Different pin-fin spacings for circular pins (S/D = 2, 4) and strip fins (S/W = 8, 16) were investigated, respectively. In addition, the thickness effect of the strip fin was included in this study. The regionally averaged heat transfer measurement method was used to acquire the heat transfer coefficients on two opposite featured surfaces within the test channel. For each configuration, the tested Reynolds number was ranging from 20,000 to 80,000. The results indicate that the channel with circular pins has better heat transfer enhancement and higher pressure loss than their strip fins counterparts. However, the strip fins are considered better designs in terms of thermal performance. For the gas turbine designers aim at developing an improved internal cooling feature, this work demonstrates the great potential of the strip fins as a novel and effective cooling design compared with the conventional circular pins.

Heat Transfer in a Rotating, Two-Pass, Variable Aspect Ratio Cooling Channel With Profiled V-Shaped Ribs

2020 ◽  
Author(s):  
I-Lun Chen ◽  
Izzet Sahin ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Channel Modeling ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Rotation Numbers ◽  
First Pass ◽  
Rib Turbulators

Abstract The thermal performance of two V-type rib configurations is measured in a rotating, two-pass cooling channel. Modeling modern, high pressure, turbine blades, the cross-section of the cooling channel varies from the first pass to the second pass. The coolant travels radially outward in the rectangular first pass with an aspect ratio of 4:1. Near the tip region, the coolant turns 180°, and travels radially inward in a 2:1 rectangular channel. The serpentine passage is positioned such that both the first and second passes are oriented 90° to the direction of rotation. The leading and trailing surfaces of both the first and second pass of the channel are roughened with V-type rib turbulators. The thermal performance of two V-type configurations is measured in this two-pass channel. The first V-shaped configuration is similar to a traditional V-shaped turbulator with a narrow gap at the apex of the V. The configuration is modified by off-setting one leg of the V to create a staggered discrete, V-shaped configuration. The ribs are oriented 45° relative to the streamwise coolant direction. In both passes, the rib spacing is P/e = 10 and the rib height – to – channel height is e/H = 0.16. The heat transfer enhancement and frictional losses are measured for both rib configurations with varying Reynolds and rotation numbers. The Reynolds number varies from 10,000 to 45,000 in the AR = 4:1 first pass; this corresponds to 16,000 to 73,500 in the AR = 2:1 second pass. Considering the effect of rotation, the rotational speed of the channel varies from 0–400 rpm with maximum rotation numbers of 0.39 and 0.16 in the first and second passes, respectively. The heat transfer enhancement on both the leading and trailing surfaces of the first pass of the 45° V-shaped channel is slightly reduced with rotation. In the second pass, the heat transfer increases on the leading surface while it decreases on the trailing surface. The 45° staggered, discrete V-shaped ribs provide increased heat transfer and thermal performance compared to the traditional V-shaped and standard, 45° angled rib turbulators.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

Effect of Rib Spacing on Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) With a Sharp Entrance at High Rotation Numbers

2008 ◽  
Author(s):  
Michael Huh ◽  
Yao-Hsien Liu ◽  
Je-Chin Han ◽  
Sanjay Chopra
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
Sharp Bend ◽  
Buoyancy Parameter ◽  
First Pass ◽  
Rib Turbulators

The focus of the current study was to determine the effects of rib spacing on heat transfer in rotating 1:4 AR channels. In the current study, heat transfer experiments were performed in a two-pass, 1:4 aspect ratio channel, with a sharp bend entrance. The channel leading and trailing walls in the first pass and second pass utilized angled rib turbulators (45° to the mainstream flow). The rib height-to-hydraulic diameter ratio (e/Dh) was held constant at 0.078. The channel was oriented 90° to the direction of rotation. Three rib pitch-to-rib height ratios (P/e) were studied: P/e = 2.5, 5, and 10. Each ratio was tested at five Reynolds numbers: 10K, 15K, 20K, 30K and 40K. For each Reynolds number, experiments were conducted at five rotational speeds: 0, 100, 200, 300, and 400 rpm. Results showed that the sharp bend entrance has a significant effect on the first pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement based on total area, whereas the P/e = 2.5 had the highest heat transfer enhancement based on the projected area. The current study has extended the range of the rotation number (Ro) and local buoyancy parameter (Box) for a ribbed 1:4 aspect ratio channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement, due to rotation, in the ribbed (P/e = 2.5, 5, and 10) 1:4 aspect ratio channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.

Effects of Variable Viscosity and Thermal Conductivity of CuO-Water Nanofluid on Heat Transfer Enhancement in Natural Convection: Mathematical Model and Simulation

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Eiyad Abu-Nada
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Variable Viscosity ◽  
Cylinder Surface ◽  
Transfer Enhancement

Heat transfer enhancement in horizontal annuli using variable thermal conductivity and variable viscosity of CuO-water nanofluid is investigated numerically. The base case of simulation used thermal conductivity and viscosity data that consider temperature property dependence and nanoparticle size. It was observed that for Ra≥104, the average Nusselt number was deteriorated by increasing the volume fraction of nanoparticles. However, for Ra=103, the average Nusselt number enhancement depends on aspect ratio of the annulus as well as volume fraction of nanoparticles. Also, for Ra=103, the average Nusselt number was less sensitive to volume fraction of nanoparticles at high aspect ratio and the average Nusselt number increased by increasing the volume fraction of nanoaprticles for aspect ratios ≤0.4. For Ra≥104, the Nusselt number was deteriorated everywhere around the cylinder surface especially at high aspect ratio. However, this reduction is only restricted to certain regions around the cylinder surface for Ra=103. For Ra≥104, the Maxwell–Garnett and the Chon et al. conductivity models demonstrated similar results. But, there was a deviation in the prediction at Ra=103 and this deviation becomes more significant at high volume fraction of nanoparticles. The Nguyen et al. data and the Brinkman model give completely different predictions for Ra≥104, where the difference in prediction of the Nusselt number reached 50%. However, this difference was less than 10% at Ra=103.

Effect of 45-Deg Rib Orientations on Heat Transfer in a Rotating Two-Pass Channel With Aspect Ratio From 4:1 to 2:1

2019 ◽  
Author(s):  
Izzet Sahin ◽  
Andrew F. Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Rotation Number ◽  
Pressure Loss ◽  
Heat Transfer Analysis ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
First Passage

Abstract The internal cooling passages of gas turbine blades mostly have varying aspect ratios from one passage to another. However, there are limited data available in the open literature that used a reduced cross-section and aspect ratio, AR, after the tip turn. Therefore, the current study presents heat transfer and pressure drop of three different α = 45° profiled rib orientations, typical parallel (usual), reversed parallel (unusual), and criss-cross patterns in a rotating two-pass rectangular channel with AR = 4:1 and 2:1 in the first radially outward flow and second radially inward flow passages respectively. For each rib orientation, regional averaged heat transfer results are obtained for both the flow passages with the Reynolds number ranging from 10,000 to 70,000 for the first passage and 16000 to 114000 for the second passage with a rotational speed range of 0 rpm to 400 rpm. This results in the highest rotation number of 0.39 and 0.16 for the first and second passage respectively. The effects of rib orientation, aspect ratio variation, 180° tip turn, and rotation number on the heat transfer and pressure drop will be addressed. According to the results, for usual, unusual and criss-cross rib patterns, increasing rotation number causes the heat transfer to decrease on the leading surface and increase on the trailing surface for the first passage and vice versa for the second passage. Overall heat transfer enhancement of the usual and unusual rib patterns is higher than criss-cross one. In terms of the pressure losses, the criss-cross rib pattern has the lowest and the usual rib pattern has the highest-pressure loss coefficients. When pressure loss and heat transfer enhancement are both taken into account together, the criss-cross or unusual rib pattern might be an option to use in the internal cooling method. Therefore, the results can be useful for turbine blade internal cooling design and heat transfer analysis.

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