Heat Transfer Characterization Inside a Rotating Rib Roughened Cooling Channel With Multiple Heated Walls

Abstract This work experimentally investigates the effects of walls heating conditions on the heat transfer coefficient distribution inside a rotating cooling channel. The model has a square cross-section with a hydraulic diameter of 50 mm and one ribbed side. The ribs are perpendicular to the main flow direction, the rib pitch-to-height ratio is 10, and the blockage ratio is 10%. Detailed heat transfer measurements were performed employing the liquid crystals thermography in steady-state approach under two thermal boundary conditions: only ribbed wall heated or equal heat fluxes set to ribbed wall and sidewalls. Inlet Reynolds number was 20000 and the tests were conducted in both static and rotating conditions up to a rotation number of 0.18, with the ribbed wall acting as trailing edge side. The results show that the wall heating conditions have a negligible effect on the heat transfer distribution for the stationary case, whereas, they lead to a modification of the heat transfer distribution under rotation with an overall enhancement when three walls are heated.

Pressure Loss and Heat Transfer in Channels Roughened on Two Opposed Walls

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/89-gt-86 ◽

1989 ◽

Author(s):

R. E. Mayle

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Pressure Loss ◽

Flow Direction ◽

Height Ratio ◽

Cooling Effectiveness ◽

Rectangular Channels ◽

Logarithmic Law ◽

In order to selectively increase cooling effectiveness, coolant channels in gas turbine components are often only roughened on one or two walls of the channel. A model is presented for flow in rectangular channels having two opposed roughened walls and a theory is developed for both the pressure loss and heat transfer. The theory allows one to calculate the heat transfer coefficient on each wall separately in addition to the overall friction factor and heat transfer coefficient. Comparisons are made to data for similarly configured channels, tubes and surfaces roughened by regularly spaced transverse ribs placed normal to the flow direction. Correlations for the displacement velocity in the logarithmic law and the roughness Stanton number in terms of the rib pitch-to-height ratio and roughness Reynolds number are also presented.

Pressure Loss and Heat Transfer in Channels Roughened on Two Opposed Walls

Journal of Turbomachinery ◽

10.1115/1.2927738 ◽

1991 ◽

Vol 113 (1) ◽

pp. 60-66 ◽

Cited By ~ 8

Author(s):

R. E. Mayle

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Pressure Loss ◽

Flow Direction ◽

Height Ratio ◽

Cooling Effectiveness ◽

Rectangular Channels ◽

Logarithmic Law ◽

In order to increase cooling effectiveness selectively, coolant channels in gas turbine components are often only roughened on one or two walls of the channel. A model is presented for flow in rectangular channels having two opposed roughened walls and a theory is developed for both the pressure loss and heat transfer. The theory allows one to calculate the heat transfer coefficient on each wall separately in addition to the overall friction factor and heat transfer coefficient. Comparisons are made to data for similarly configured channels, tubes, and surfaces roughened by regularly spaced transverse ribs placed normal to the flow direction. Correlations for the displacement velocity in the logarithmic law and the roughness Stanton number in terms of the rib pitch-to-height ratio and roughness Reynolds number are also presented.

Systematic heat transfer measurements in highly viscous binary fluids

Heat and Mass Transfer ◽

10.1007/s00231-021-03087-w ◽

2021 ◽

Author(s):

Ann-Christin Fleer ◽

Markus Richter ◽

Roland Span

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Volatile Component ◽

Test Tube ◽

Heat Fluxes ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Low Viscosity ◽

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Study the flow direction and number of tubes in cross-flow heat exchanger to improve the heat transfer coefficient.

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1076/1/012075 ◽

2021 ◽

Vol 1076 (1) ◽

pp. 012075

Author(s):

Shatha Ali Merdan ◽

Zena khalefa Kadhim

Keyword(s):

Heat Transfer ◽

Heat Exchanger ◽

Transfer Coefficient ◽

Flow Direction ◽

Cross Flow ◽

Flow Heat ◽

ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels ◽

Effect of Open Micro-Channels on External Condensation Heat Transfer

10.1115/icnmm2016-8062 ◽

2016 ◽

Author(s):

Brandon Hulet ◽

Andres Martinez ◽

Melanie Derby ◽

Amy Rachel Betz

Keyword(s):

Heat Transfer ◽

Film Thickness ◽

Transfer Coefficient ◽

Heat Fluxes ◽

Condensation Heat Transfer ◽

Dropwise Condensation ◽

Micro Channels ◽

Lower Heat ◽

This research experimentally investigates the heat transfer performance of open-micro channels under filmwise condensation conditions. Filmwise condensation is an important factor in the design of steam condensers used in thermoelectric power generation, desalination, and other industrial applications. Filmwise condensation averages five times lower heat transfer coefficients than those present in dropwise condensation, and filmwise condensation is the dominant condensation regime in the steam condensers due to a lack of a durable dropwise condensation surface. Film thickness is also of concern because it is directly proportional to the condenser’s overall thermal resistance. This research focuses on optimizing the channel size to inhibit the creation of a water film and/or to reduce its overall thickness in order to maximize the heat transfer coefficient of the surface. Condensation heat transfer was measured in three square channels and a plane surface as a control. The sizes of the square fins were 0.25 mm; 0.5 mm; and 1 mm, and tests were done at a constant pressure of 6.2 kPa. At lower heat fluxes, the 0.25mm fins perform better, whereas at larger heat fluxes a smooth surface offers better performance. At lower heat fluxes, droplets are swept away by gravity before the channels are flooded. Whereas, at higher heat fluxes, the channels are flooded increasing the total film thickness, thereby reducing the heat transfer coefficient.

Entropy Generation and Heat Transfer Performance in Microchannel Cooling

Entropy ◽

10.3390/e21020191 ◽

2019 ◽

Vol 21 (2) ◽

pp. 191 ◽

Cited By ~ 5

Author(s):

Jundika Kurnia ◽

Desmond Lim ◽

Lianjun Chen ◽

Lishuai Jiang ◽

Agus Sasmito

Keyword(s):

Heat Transfer ◽

Entropy Generation ◽

Heat Transfer Performance ◽

Second Law Of Thermodynamics ◽

High Heat ◽

Heat Fluxes ◽

Transfer Performance ◽

Cooling Channel ◽

High Heat Transfer ◽

Microchannel Cooling

Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250–1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.

Inverse BEM Method to Identify Surface Temperatures and Heat Transfer Coefficient Distributions at Inaccessible Surfaces

Volume 3: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68873 ◽

2005 ◽

Author(s):

Alain J. Kassab ◽

Eduardo A. Divo ◽

Minking K. Chyu ◽

Frank J. Cunha

Keyword(s):

Heat Transfer ◽

Inverse Problem ◽

Transfer Coefficient ◽

Field Variable ◽

Quadratic Functional ◽

Two Dimensional ◽

Additional Information ◽

Coefficient Distribution ◽

The purpose of the inverse problem considered in this study is to resolve heat transfer coefficient distributions by solving a steady-state inverse problem. Temperature measurements at interior locations supply the additional information that renders the inverse problem solvable. A regularized quadratic functional is defined to measure the deviation of computed temperatures from the values under current estimates of the heat transfer coefficient distribution at the surface exposed to convective heat transfer. The inverse problem is solved by minimizing this functional using a parallelized genetic algorithm (PGA) as the minimization algorithm and a two-dimensional multi-region boundary element method (BEM) heat conduction code as the field variable solver. Results are presented for a regular rectangular geometry and an irregular geometry representative of a blade trailing edge and demonstrate the success of the approach in retrieving accurate heat transfer coefficient distributions.

Low-Aspect-Ratio Rib Heat Transfer Coefficient Measurements in a Square Channel

Journal of Turbomachinery ◽

10.1115/1.2841796 ◽

1998 ◽

Vol 120 (4) ◽

pp. 831-838 ◽

Cited By ~ 16

Author(s):

M. E. Taslim ◽

G. J. Korotky

Keyword(s):

Heat Transfer ◽

Aspect Ratio ◽

Transfer Coefficient ◽

Flow Direction ◽

Turbine Blades ◽

Transfer Coefficients ◽

Square Channel ◽

Low Aspect Ratio ◽

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of round-corner, low-aspect-ratio (ARrib = 0.667) ribs. Twelve rib geometries, comprising three rib height-to-channel hydraulic diameters (blockage ratios) of 0.133, 0.167, and 0.25 as well as three rib spacings (pitch-to-height ratios) of 5, 8.5, and 10 were investigated for two distinct thermal boundary conditions of heated and unheated channel walls. A square channel, roughened with low-aspect-ratio ribs on two opposite walls in a staggered manner and perpendicular to the flow direction, was tested. An instrumented copper rib was positioned either in the middle of the rib arrangements or in the furthest upstream location. Both rib heat transfer coefficient and channel friction factor for these low-aspect-ratio ribs were also compared with those of square ribs, reported previously by the authors. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared.

Heat Transfer in an Airfoil Trailing Edge Configuration With Shaped Pedestals Mounted Internal Cooling Channel and Pressure Side Cutback

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2006-91019 ◽

2006 ◽

Cited By ~ 10

Author(s):

Shuping P. Chen ◽

Peiwen W. Li ◽

Minking K. Chyu ◽

Frank J. Cunha ◽

William Abdel-Messeh

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Transfer Coefficient ◽

Internal Cooling ◽

Hybrid Technique ◽

Pressure Side ◽

Cooling Channel ◽

Trailing Edge ◽

Described in this paper is an experimental study of heat transfer over a trailing edge configuration preceded with an internal cooling channel of pedestal array. The pedestal array consists of both circular pedestals and oblong shaped blocks. Downstream to the pedestal array, the trailing edge features pressure side cutback partitioned by the oblong shaped blocks. The local heat transfer coefficient over the entire wetted surface in the internal cooling chamber has been determined by using a “hybrid” measurement technique based on transient liquid crystal imaging. The hybrid technique employs the transient conduction model in a semi-infinite solid for resolving the heat transfer coefficient on the endwall surface uncovered by the pedestals. The heat transfer coefficient over a pedestal can be resolved by the lumped capacitance method with an assumption of low Biot number. The overall heat transfer for both the pedestals and endwalls combined shows a significant enhancement compared to the case with thermally developed smooth channel. Near the downstream most section of the suction side, the land, due to pressure side cutback, is exposed to the stream mixed with hot gas and discharged coolant. Both the adiabatic effectiveness and heat transfer coefficient on the land section are characterized by using the transient liquid crystal technique.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

Journal of Turbomachinery ◽

10.1115/1.2841122 ◽

1997 ◽

Vol 119 (2) ◽

pp. 381-389 ◽

Cited By ~ 55

Author(s):

M. E. Taslim ◽

C. M. Wadsworth

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Thermal Performance ◽

Blockage Ratio ◽

Transfer Coefficients ◽

Height Ratio ◽

Average Heat ◽

Heat Transfer Coefficients ◽

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.