Geometrical investigation of microchannel with two trapezoidal blocks subjected to laminar convective flows with and without boiling

Microchannels are important devices to improve the heat exchange in several engineering applications as heat, ventilation and air conditioning, microelectronic cooling, power generation systems and others. The present work performs a numerical study of a microchannel with two trapezoidal blocks subjected to laminar flows, aiming to analyze the influence of the boiling process on the geometric configuration of the microchannel. Constructal Design and Exhaustive Search are used for the geometrical evaluation of the blocks. The Mixture multi-phase model and the Lee phase change model were both employed for the numerical simulation of the boiling process. In this study, the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate and pressure drop for different magnitudes of the ratio between the lower width and higher width (L12/L11) was investigated. It is considered water in monophase cases and water/vapor mixture for multiphase flow. Two different Reynolds numbers (ReH = 0.1 and 10.0) were investigated. Results indicated that, for the present thermal conditions, the consideration of boiling flows were not significant for prediction of optimal configurations. Results also showed that in the cases where the boiling process was enabled, the multi-objective performance was higher than in the cases without boiling, especially for ReH = 0.1.

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Constructal Design of Rectangular Fin Intruded Into Mixed Convective Lid-Driven Cavity Flows

Journal of Heat Transfer ◽

10.1115/1.4033378 ◽

2016 ◽

Vol 138 (10) ◽

Cited By ~ 9

Author(s):

G. Lorenzini ◽

B. S. Machado ◽

L. A. Isoldi ◽

E. D. dos Santos ◽

L. A. O. Rocha

Keyword(s):

Nusselt Number ◽

Aspect Ratio ◽

Convective Flow ◽

Numerical Study ◽

Reynolds Numbers ◽

Lower Surface ◽

Driven Cavity ◽

Constructal Design ◽

Mixed Convective Flow ◽

Forced Convective Flow

The present work shows a numerical study of laminar, steady, and mixed convective flow inside lid-driven square cavity with intruded rectangular fin in its lower surface. The main purpose here is to maximize the heat transfer between the rectangular fin and the surrounding mixed convective flow inside a lid-driven cavity by means of constructal design. The problem is subject to two constraints, the lid-driven cavity and intruded fin areas. The ratio between the fin and cavity areas is kept fixed (ϕ = 0.05). The investigated geometry has one degree-of-freedom (DOF), the fin aspect ratio (H1/L1), which is varied in the range 0.1 ≤ H1/L1 ≤ 10. The aspect ratio of the cavity is maintained fixed (H/L = 1.0). The effect of the fin geometry over the Nusselt number is investigated for several Rayleigh (RaH = 103, 104, 105 and 106) and Reynolds numbers (ReH = 10, 102, 3.0 × 102, 5.0 × 102, 7.0 × 102 and 103). For all simulations, the Prantdl number is fixed (Pr = 0.71). The conservation equations of mass, momentum, and energy are numerically solved with the finite volume method. Results showed that fin geometry (H1/L1) has strong influence over the Nusselt number in the fin. It was also observed that the effect of H1/L1 over Nusselt number changes considerably for different Rayleigh numbers and for the lowest magnitudes of Reynolds numbers, for example, differences of nearly 770% between RaH = 106 and forced convective flow were observed for the lowest Reynolds number studied (ReH = 10).

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Numerical Study of Newtonian Fluid Flows in T-Shaped Structures with Impermeable Walls

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.396.177 ◽

2019 ◽

Vol 396 ◽

pp. 177-186

Author(s):

Vinicius da Rosa Pepe ◽

Luiz Alberto Oliveira Rocha ◽

Flavia Schwarz Franceschini Zinani ◽

Antonio Ferreira Miguel

Keyword(s):

Steady State ◽

Newtonian Fluid ◽

Numerical Study ◽

Three Dimensional ◽

Fluid Flows ◽

Reynolds Numbers ◽

Geometric Constraints ◽

Constructal Theory ◽

3D Structures ◽

Constructal Design

This article presents the results of flows in "T" shaped duct bifurcations. The problem is to find the resistance to flow in three-dimensional (3D) structures with different homothetic relationships between sizes (diameters and lengths) of parent and daughter ducts. The method used is the Constructal Design, which is based on the Constructal Theory. The minimization of the global resistance to flow, subjected to geometric constraints of volume and area occupied by the ducts, is the key to search for optimum configurations. The flows investigated were three-dimensional, laminar, incompressible, in steady state, with uniform and constant properties. The results obtained numerically were verified via comparison with analytical results available in the literature. In this work, ranges of length and ratio of diameterss from 0.5 to 1 and 0.1 to 1, respectively, were investigated, for Reynolds numbers equal to 102 and 103. The main results indicate that the T-shaped structure with impermeable walls, agree with Hess-Murray's law.

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Towards a Numerical Study of Two-Phase Flow Exhaust Plume Jet

Volume 1: Fora, Parts A and B ◽

10.1115/fedsm2002-31028 ◽

2002 ◽

Author(s):

C. Devals ◽

J.-L. Estivalezes ◽

G. Jourdan ◽

L. Houas

Keyword(s):

Shock Tube ◽

Two Phase Flow ◽

Numerical Study ◽

Reynolds Numbers ◽

Spherical Particles ◽

Phase Flow ◽

Two Phase ◽

Set Up ◽

Solid Rocket ◽

Multi Phase

The aim of the present work is to determine experimental drag coefficients for spherical particles accelerated in shock-tube. Then, validations of two phase flow calculations dealing with solid propulsion rocket in supersonic flight are undertaken. First, experiments in the multi-phase vertical-horizontal shock-tube have been set up at IUSTI in Marseille. The drag coefficient is determinated for particle Reynolds numbers less than 50000 and for particle Mach numbers less than 1.14 and is compared with those found in literature. Second, calculation of two phase flow in solid rocket plume has been performed. The particles are tracked with a stochastic one-way coupling lagrangian method.

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CONSTRUCTAL DESIGN OF A X-SHAPED CAVITY COOLED BY CONVECTION

Revista de Engenharia Térmica ◽

10.5380/reterm.v13i1.62070 ◽

2014 ◽

Vol 13 (1) ◽

pp. 54

Author(s):

F. B. Link ◽

L. A. O. Rocha ◽

E. D. Dos Santos ◽

L. A. Isoldi

Keyword(s):

Heat Transfer ◽

Solid Body ◽

Convection Heat Transfer ◽

Thermal Conditions ◽

Optimal Distribution ◽

Convection Heat ◽

Cavity Volume ◽

Constructal Design ◽

And Performance ◽

Optimal Configurations

This paper applies Constructal design to study the geometry of a X-shaped cavity that penetrates into a solid conductive wall. The objective is minimizing the dimensionless maximal excess of temperature between the solid body and the cavity. There is uniform heat generation on the solid body. The cavity surfaces are cooled by convection heat transfer while the solid body is subjected to adiabatic conditions on its outer surfaces. The total volume and the cavity volume are fixed, but the lengths and thickness of the X-shaped cavity can vary. The emerged optimal configurations and performance are reported. The effect of the area fraction φ which denotes the ratio between the cavity area and the total area of the geometry, and the ratio between the length and thickness of the branch cavity, H1/L1, on the dimensionless maximal excess of temperature is numerically investigated. The results show that the dimensionless maximal excess of temperature θmax,min decreases approximately 60% when the cavity fraction increases from φ = 0.05 to 0.25. The results also show that the X-shaped cavity performs approximately 45% better when compared to a C-shaped cavity under the same thermal conditions. The optimal X-shaped cavity is also in accordance with the optimal distribution of imperfections principle.

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

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2006-90006 ◽

2006 ◽

Cited By ~ 3

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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Numerical study on swirl cooling flow, heat transfer and stress characteristics based on fluid-structure coupling method under different swirl chamber heights and Reynolds numbers

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2021.121228 ◽

2021 ◽

Vol 173 ◽

pp. 121228

Author(s):

Hong-Wei Li ◽

Yin-Feng Gao ◽

Chang-He Du ◽

Wen-Peng Hong

Keyword(s):

Heat Transfer ◽

Numerical Study ◽

Reynolds Numbers ◽

Coupling Method ◽

Fluid Structure ◽

Cooling Flow ◽

Swirl Chamber ◽

Flow Heat

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Thermal comfort analysis of a high-speed train cabin considering the solar radiation effects

Indoor and Built Environment ◽

10.1177/1420326x19876082 ◽

2019 ◽

Vol 29 (8) ◽

pp. 1101-1117

Author(s):

Lin Yang ◽

Xiangdong Li ◽

Jiyuan Tu

Keyword(s):

Solar Radiation ◽

Thermal Comfort ◽

High Speed ◽

Radiation Effects ◽

Numerical Study ◽

Thermal Conditions ◽

Long Distance ◽

High Speed Rail ◽

Hot Weather ◽

Cabin Environment

Due to the fast development of high-speed rail (HSR) around the world, high-speed trains (HSTs) are becoming a strong competitor against airliners in terms of long-distance travel. Compared with airliner cabins, HST cabins have much larger window sizes. When the big windows provide better lighting and view of the scenery, they also have significant effects on the thermal conditions in the cabins due to the solar radiation through them. This study presents a numerical study on the solar radiation on the thermal comfort in a typical HST cabin. The effect of solar radiation was discussed in terms of airflow pattern, temperature distribution and thermal comfort indices. Parametric studies with seven different daytime hours were carried out. The effect of using the roller curtain was also studied. The overall cabin air temperature, especially near passengers, was found to have significantly increased by solar radiation. Passengers sitting next to windows were recorded to have an obvious thermal comfort variation at different hours of the day. To improve the passengers’ comfort and reduce energy consumption during hot weather, the use of a curtain could effectively reduce the solar radiation effect in the cabin environment.

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NUMERICAL STUDY OF EFFECTS OF PULSATILE AMPLITUDE ON UNSTEADY LAMINAR FLOWS IN RIGID PIPE WITH RING-TYPE CONSTRICTIONS

International Journal for Numerical Methods in Fluids ◽

10.1002/(sici)1097-0363(19970215)24:3<275::aid-fld491>3.0.co;2-1 ◽

1997 ◽

Vol 24 (3) ◽

pp. 275-290 ◽

Cited By ~ 2

Author(s):

T. S. Lee ◽

T. W. Ng ◽

Z. D. Shi

Keyword(s):

Numerical Study ◽

Laminar Flows ◽

Ring Type

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A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

Journal of Heat Transfer ◽

10.1115/1.3245674 ◽

1983 ◽

Vol 105 (4) ◽

pp. 862-869 ◽

Cited By ~ 15

Author(s):

R. S. Amano ◽

M. K. Jensen ◽

P. Goel

Keyword(s):

Heat Transfer ◽

Numerical Solutions ◽

Numerical Study ◽

Separated Flow ◽

Flow Region ◽

Reynolds Numbers ◽

Turbulent Heat ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

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