Thermal Characteristics in a Curved Rectangular Channel With Variable Cross-Sectional Area

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Sink ◽  
Rectangular Channel ◽  
Variable Cross ◽  
Entry And Exit ◽  
Transfer Enhancement ◽  
Curved Channel ◽  
Dean Number ◽  
Cross Sectional

Heat transfer due to steady, laminar air flow through a curved rectangular channel with a variable cross-sectional (c/s) area is investigated computationally. Such a flow passage is formed between two fin walls of a curved fin heat sink with a 90 deg bend, used in avionics cooling. Simulations are carried out for two different configurations: (a) a variable c/s area curved channel with inlet and outlet sections (entry and exit lengths) that are straight and constant c/s area—termed as the long channel and (b) a variable c/s area curved channel with no entry and exit lengths—termed as the short channel. Multiple secondary flow patterns develop in the curved section of the channel, which in conjunction with the bulk axial flow, lead to the formation of multiple vortices and separation bubbles. The complex 3-D flow structures, as well as the variable c/s area of the curved channel (diverging–converging) significantly alter the heat transfer characteristics, compared to the straight fin heat sink. Secondary flow strengthens with increasing axial (bulk) flow velocity, or Dean number in dimensionless form. This in turn improves heat transfer from all walls, particularly, the outer curvature (concave) wall and the heat sink base. At the highest Dean number condition, the local heat transfer coefficient at certain locations of the outer curvature wall is augmented by as much as 3.5 times, compared to the straight fin walls. The overall channel average heat transfer coefficient is improved by about 40% for the long channels, and about 10% for the short ones. However, the heat transfer enhancement is associated with a penalty of higher pressure drop, compared to the straight channels. To quantify the effectiveness of thermal performance enhancement a system Figure of Merit (FOM) is defined. A greater than unity FOM value is observed for all curved channel geometries and flow rate conditions. This indicates that heat transfer enhancement in the variable c/s area curved channel outweighs the penalty of additional pressure drop, compared to a straight channel of similar length.

Flow Characteristics in a Curved Rectangular Channel With Variable Cross-Sectional Area

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Pressure Drop ◽  
Rectangular Channel ◽  
Variable Cross ◽  
Entry And Exit ◽  
Curved Channel ◽  
Dean Number ◽  
Cross Sectional ◽  
Dean Vortices ◽  
Area Expansion ◽  
Expansion Effect

Laminar air flow through a curved rectangular channel with a variable cross-sectional (c/s) area (diverging-converging channel) is computationally investigated. Such a flow passage is formed between the two fin walls of a 90 deg bend curved fin heat sink, used in avionics cooling. Simulations are carried out for two different configurations: (a) a curved channel with long, straight, constant c/s area inlet and outlet sections (entry and exit lengths); and (b) a short, curved channel with no entry and exit lengths. Formation of a complex 3D flow pattern and its evolution in space is studied through numerical flow visualization. Results show that a secondary motion sets in the radial direction of the curved section, which in combination with the axial (bulk) flow leads to the formation of a base vortex. In addition, under certain circumstances the axial and secondary flow separate from multiple locations on the channel walls, creating Dean vortices and separation bubbles. Velocity above which the Dean vortices appear is cast in dimensionless form as the critical Dean number, which is calculated to be 129. Investigation of the friction factor reveals that pressure drop in the channel is governed by both the curvature effect as well as the area expansion effect. For a short curved channel where area expansion effect dominates, pressure drop for developing flow can be even less than that of a straight channel. A comparison with the flow in a constant c/s area, curved channel shows that the variable c/s area channel geometry leads to a lower critical Dean number and friction factor.

scholarly journals Numerical analysis of heat transfer enhancement with the use of γ-Al2O3/water nanofluid and longitudinal ribs in a curved duct

2012 ◽  
Vol 16 (2) ◽  
pp. 469-480 ◽  
Author(s):  
Hosseinali Soltanipour ◽  
Parisa Choupani ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Transfer Enhancement ◽  
Dean Number ◽  
Particle Volume ◽  
The Heat Transfer Coefficient

This paper presents a numerical investigation of heat transfer augmentation using internal longitudinal ribs and ?-Al2O3/ water nanofluid in a stationary curved square duct. The flow is assumed 3D, steady, laminar, and incompressible with constant properties. Computations have been done by solving Navier-Stokes and energy equations utilizing finite volume method. Water has been selected as the base fluid and thermo- physical properties of ?- Al2o3/ water nanofluid have been calculated using available correlations in the literature. The effects of Dean number, rib size and particle volume fraction on the heat transfer coefficient and pressure drop have been examined. Results show that nanoparticles can increase the heat transfer coefficient considerably. For any fixed Dean number, relative heat transfer rate (The ratio of the heat transfer coefficient in case the of ?- Al2o3/ water nanofluid to the base fluid) increases as the particle volume fraction increases; however, the addition of nanoparticle to the base fluid is more useful for low Dean numbers. In the case of water flow, results indicate that the ratio of heat transfer rate of ribbed duct to smooth duct is nearly independent of Dean number. Noticeable heat transfer enhancement, compared to water flow in smooth duct, can be achieved when ?-Al2O3/ water nanofluid is used as the working fluid in ribbed duct.

The Flow and Heat Transfer Characteristic of Curved Channel CPU Water-Cooled Heat Sinks

2013 ◽  
Vol 391 ◽  
pp. 213-216
Author(s):  
Yan Feng Liu ◽  
Xiang Hong Li ◽  
Shi Ping Li
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Rectangular Channel ◽  
Transfer Characteristic ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Curved Channel ◽  
Flow And Heat Transfer ◽  
Heat Sink Temperature ◽  
Better Than

This article conducted numerical simulation and experimental study of curved channel laminar flow and heat transfer characteristics with different Reynolds number and different heat fluxes, it also showed the comparison with straight rectangular channel of a same heat transfer area. The results showed that: cooling effect of curved channel heat sink is better than that of straight rectangular channel heat sink, temperature distribution appears to be more uniform as well; The experimental results showed that the curved channel heat sink can effectively satisfy the needs of the CPU cooling.

Flow in a Curved Rectangular Channel With Variable Cross-Section Area

2008 ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Pressure Drop ◽  
Cross Section ◽  
Rectangular Channel ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Entry And Exit ◽  
Curved Channel ◽  
Cross Section Area ◽  
Secondary Motion ◽  
Curved Section

Laminar air flow through a curved rectangular channel with a variable cross-section (c/s) area (diverging-converging) is numerically investigated. Such a flow passage is formed between the two fin walls of a 90° bend curved fin heat sink, used in avionics cooling. Simulations are carried out for two different configurations — (a) a curved channel with long, straight, constant c/s area inlet and outlet sections (entry and exit lengths), and (b) a short, curved channel with no entry and exit lengths. Formation of a complex, 3-D flow pattern and its evolution in space is studied through numerical flow visualization. Results show that a secondary motion sets in the radial direction in the curved section, which in combination with the axial (bulk) flow leads to the formation of a base vortex. In addition, under certain circumstances the axial and secondary flow separate from multiple locations on the channel walls, and create Dean vortices and separation bubbles. The role of variable c/s geometry is elucidated by comparing the results with those of a constant c/s area, curved channel. Investigation of the dimensionless friction factor reveals that the overall channel pressure drop is governed by both the curvature effect as well as the area expansion effect. Due to the combined effect pressure drop for developing flow in a short, curved channel can be even less than that of a straight channel.

scholarly journals Numerical Studies on the Thermal Performances of Electroosmotic Flow in Y-Shaped Microchannel Heat Sink

Coatings ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 380 ◽  
Author(s):  
Dalei Jing ◽  
Jian Song
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Sink ◽  
Electroosmotic Flow ◽  
Convective Heat Transfer Coefficient ◽  
Microchannel Heat Sink ◽  
Cross Sectional ◽  
Sectional Shape

This paper numerically studies the thermal performances of electroosmotic flow (EOF) in a symmetric Y-shaped microchannel heat sink (MCHS) having a constant total channel surface area, that is, constant convective heat transfer area. It is found that the average convective heat transfer coefficient of EOF increases with the increasing driven voltage, which is attributed to the increase of EOF flowrate with the increasing driven voltage. However, the maximum MCHS temperature shows an increasing after decreasing trend with the driven voltage owing to the dramatically increasing Joule heating when the voltage is large enough. Further, both the maximum MCHS temperature and average convective heat transfer coefficient are sensitive to the cross-sectional dimensions of the Y-shaped microchannels. The thermal performances of EOF in the Y-shaped MCHS show a strengthening to weakening trend with the increasing daughter-to-parent channel diameter ratio of the Y-shaped microchannel with circular cross-sectional shape, and show a similar strengthening to weakening trend with the increasing daughter-to-parent channel width ratio and the increasing microchannel height of the Y-shaped microchannel with rectangular cross-sectional shape. These cross-sectional dimension dependences of thermal performances are related to the increasing to decreasing trend of EOF flowrate changing with the microchannel cross-sectional dimensions.

Heat Transfer Enhancement of Vertical Heat Sinks with a Piezofan

2013 ◽  
Vol 284-287 ◽  
pp. 773-777
Author(s):  
Jin Cherng Shyu ◽  
Jhih Zong Syu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
High Heat ◽  
Heat Sinks ◽  
Transfer Enhancement ◽  
Vertical Heat ◽  
Pin Fins

This study examines several effects, including the piezofan positions, and piezofan arrangements, as well as piezofan height, on the heat transfer enhancement of two typical types of vertical heat sink. Either 30-mm-high or 10-mm-high heat sink having 11 plate-fins or 100 square pin-fins is tested with a running piezofan. The piezofan having Mylar blade is either vertically or horizontally placed above the heat sinks vibrating with resonant frequency of 31 Hz and tip mean-to-peak amplitude of 7.2 mm. The heat transfer coefficient is measured at five different fan locations with fan heights of 12 mm and 16 mm. Results show that the piezofan located at x/L = 0.5 usually performs the highest heat transfer enhancement for a given heat sink, while piezofan located at x/L = 1 usually shows the worst heat transfer enhancement. Depending on the fan arrangements and positions, heat transfer coefficient of the present 10-mm-high plate-fin heat sink shows 1.2 – 2.4 times higher than that under natural convection, while the enhancement factor ranges from 1.1 to 2.6 for 10-mm-high pin-fin heat sink.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

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