scholarly journals Revisited analysis of gas convection and heat transfer in micro channels: Influence of viscous stress power at wall on Nusselt number

2018 ◽  
Vol 134 ◽  
pp. 565-584 ◽  
Author(s):  
Xavier Nicolas ◽  
Eric Chénier ◽  
Chahinez Tchekiken ◽  
Guy Lauriat
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Viscous Stress ◽  
Convection And Heat Transfer ◽  
Micro Channels

Numerical Simulation of Pressure Loss and Heat Transfer Characteristics for Additively Manufactured Channels

2020 ◽  
Author(s):  
Bryan Arko ◽  
Chad Iverson ◽  
Nicholas Staudigel
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Measured Data ◽  
Transfer Effects ◽  
Micro Channels ◽  
Heat Transfer Effects

Abstract This body of work provides an initial study of modeling both surface roughness and heat transfer concurrently in a numerical simulation of micro-channels representative of those that might be found in a turbine cooling application. Increased use of additive manufacturing (AM) or 3D printing techniques for turbomachinery components enable the manufacture of complex features to achieve higher operational performance. Accurate modeling of flow losses and heat transfer effects are critical to designing parts which achieve optimal efficiency paired with durability. Surface finish is rougher with AM compared to more traditional manufacturing techniques; therefore enhancing the pressure loss and heat transfer effects. Proper implementation of surface roughness within the computational model and correct modeling of the near wall boundary mesh must be maintained to produce accurate results. This study focuses on the comparison of near wall mesh treatment coupled with surface roughness to determine a practice for obtaining accurate pressure loss and heat transfer within a cooling passage, as compared to measurements. Steady-state computational fluid dynamics (CFD) models consisting of a wind tunnel inlet nozzle and outlet diffuser, along with internal cooling passages represented using micro-channels, has been run for a range of Reynolds numbers and simulated roughness levels. Analysis of a baseline configuration with aerodynamically smooth walls is first compared to the measured data to verify the assumption of aerodynamically smooth walls. Surface roughness is then added to the channel walls, from published test coupon measurements, and compared to published experimental data for a range of Reynolds numbers. The metal surrounding the passages is also included as a conjugate heat transfer model providing heat addition to the fluid. Pressure loss and heat transfer is compared to the measured data as a friction factor and Nusselt number for the range of Reynolds numbers. Since surface roughness units and measurements vary, an effect of surface roughness values on pressure loss and heat transfer will also be investigated to determine the importance of using and converting to the correct units for the numerical model. This serves as a starting point for a guideline that will help when both heat transfer and surface roughness are included in a CFD model. Further study is recommended to understand the diminishing levels of increase in friction factor and Nusselt number observed as surface roughness was continually increased in the numerical simulation.

Heat Transfer Enhancement in Wavy Micro-Channels Through Multiharmonic Surfaces

2018 ◽  
Author(s):  
Justin Moon ◽  
J. Rafael Pacheco ◽  
Arturo Pacheco-Vega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Numerical Solutions ◽  
Cold Water ◽  
Bottom Surface ◽  
Transfer Enhancement ◽  
Cross Sectional ◽  
Single Wave ◽  
Micro Channels

In this study, three-dimensional numerical simulations are performed to investigate heat transfer enhancement in multi-harmonic micro-scale wavy channels. The focus is on the influence of channel surface-topography, modeled as multi-harmonic sinusoidal waves of square cross-sectional area, on the enhancing mechanisms. A single-wave device of 0.5 mm × 0.5 mm × 20 mm length, is used as baseline, and new designs are built with harmonic-type surfaces. The channel is enclosed by a solid block, with the bottom surface within the sinusoidal region being exposed to a 47 W/cm2 heat flux. The numerical solutions of the governing equations for an incompressible laminar flow and conjugate heat transfer are obtained via finite elements. By using the ratio of the Nusselt number for wavy to straight channels, a parametric analysis — for a set of cold-water flowrates (Re = 50, 100, and 150) — shows that the addition of harmonic surfaces enhances the transfer of energy and that such ratio achieves the highest value with wave harmonic numbers of n = ±2. Use of a performance factor (PF), defined as the ratio of the Nusselt number to the pressure drop, shows that, surprisingly, the proposed wavy multi-harmonic channels are not as efficient as the single-wave geometries. This outcome is thought to be, primarily, due to the uncertainty associated with the definition of the Nusselt number used in this study, and establishes a direction to investigate the development of a more accurate definition.

Evaluation of Nusselt number and pressure drop in hexagonal and rectangular micro-channels in the presence of nano-fluids

2020 ◽  
Vol 234 (6) ◽  
pp. 665-672
Author(s):  
S Emami ◽  
MH Dibaei Bonab ◽  
M Mohammadiun ◽  
H Mohammadiun ◽  
M Sadi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Heat Sinks ◽  
Nano Particles ◽  
Geometrical Parameters ◽  
Micro Channels ◽  
Nano Fluids

Few papers investigated the effect of different nano-fluids and geometrical parameters of the micro channels on the performance of heat sinks. In this study, Nusselt number and pressure drop are investigated in differential geometry and Reynolds numbers. Then the effect of the micro-channel is studied for different heat flux. The results show that hexagonal micro-channels represents a better performance than the rectangular and the heat transfer of without using nano-particles in the hexagonal cross-section is about 9% higher than the rectangular cross-section and with the presence of nanoparticles (Al2O3 - CUO- TiO2, φ  =  4%), heat transfer is about 30 to 40% higher than the base liquid.

Natural Convection in a Cavity Partially Filled with a Vertical Porous Medium

2011 ◽  
Vol 321 ◽  
pp. 15-18 ◽  
Author(s):  
Fang Liu ◽  
Bao Ming Chen
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Boundary Condition ◽  
Porous Medium ◽  
Nusselt Number ◽  
Free Fluid ◽  
Stress Jump ◽  
Convection And Heat Transfer ◽  
Flow And Heat Transfer ◽  
Stress Jump Boundary Condition

The shear stress jump boundary condition that must be imposed at an interface between a porous medium and a free fluid in an enclosure is investigated. Two-domain approach is founded and finite element method is used to solve the problem. Three stress jump coefficients 0, 1, -1 are analyzed for different Rayleigh number, permeability and thickness of porous layer. Variation of Maximum stream function and Nusselt number show stronger convection and heat transfer when the stress jump coefficient is positive. There is little distinctive in flow and heat transfer when the value of coefficient is equal to 0 and -1.

Numerical Investigation of Flow and Heat Transfer in Microchannels

2008 ◽  
Author(s):  
Emrah Deniz ◽  
I. Yalcin Uralcan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Experimental Studies ◽  
Numerical Results ◽  
Turbulent Regime ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Micro Channels

Mini and microchannel applications have become an important and attractive research area during the past decades. For micro systems design purposes, numerical and experimental studies have been conducted on flow and heat transfer characteristics of mini and microchannels and various friction factor and Nusselt number correlations have been proposed. Some researchers have tried to apply conventional tube correlations to mini and micro channels, rather than deriving new correlations. In this study, using commercial CFD software, flow and heat transfer characteristics in laminar and turbulent flow through circular channels are analyzed numerically. The applicability of conventional correlations in calculating the friction factor and Nusselt number is investigated. It is concluded that, in laminar regime conventional correlations can be used to calculate the friction factor for the channel sizes considered. In turbulent regime, however, numerical results for friction factor yielded greater values than those calculated by the conventional correlations. Numerical Nusselt numbers are found to be closer to the conventional values in laminar and turbulent regimes. In turbulent regime, on the other hand, Nusselt number values calculated with the microchannel correlations are determined to be greater than the numerical results and the values calculated with the conventional correlations.

Forced Convection Heat Transfer of a Giesekus Fluid in Circular Micro-Channels Subjected to a Constant Wall Temperature

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
M. Norouzi ◽  
M. R. Rezaie
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Constitutive Equation ◽  
Wall Temperature ◽  
Micro Channel ◽  
Slip Coefficient ◽  
Constant Wall Temperature ◽  
Mobility Factor ◽  
Micro Channels ◽  
Giesekus Fluid

Abstract In this paper, an exact analytical solution for forced convective heat transfer of nonlinear viscoelastic fluid in isothermal circular micro-channel is presented. The nonlinear Giesekus constitutive equation is used to model the Giesekus fluid heat transfer in micro-channel with constant wall temperature, which is the main innovative aspect of the current study. This constitutive equation is a powerful tool and able to model the fractional viscometric functions, extensional viscosity, and elastic property. The solution of temperature profile and Nusselt number is obtained based on the Frobenius method. The effects of Weissenberg number, mobility factor, slip coefficient, and Navier index on temperature distribution, velocity profile, and Nusselt number are investigated in detail. The results show that the increases in both slip coefficient and Navier index cause the increases in slip velocity and maximum dimensionless temperature at the wall and the micro-channel center, respectively. Moreover, the Nusselt number has an upward trend with increases in slip coefficient and Navier index parameters. The results are indicated that the flow and temperature fields have a complex relation with mobility factor which controls the level of the nonlinearity of the Giesekus model. Additionally, three correlations for Nusselt number of Giesekus flow in micro-channel are presented.

scholarly journals Effect of Taper Manifolds with Different Slopes in Microchannel Heat Sink

2019 ◽  
Vol 8 (12) ◽  
pp. 3988-3992
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Sink ◽  
Microchannel Heat Sink ◽  
Micro Channel ◽  
Flow And Heat Transfer ◽  
Micro Channels ◽  
Upward Direction ◽  
Degree Slope

In this analysis, the liquid flow and heat transfer in micro channel heat sink (MCHS) to find the pressure drop are experimentally investigated by three degree slope in manifolds in addition to the arrangement of micro channels. This experimental analysis is executed with respect to the Nusselt Number and Heat transfer characteristics for three manifolds with different arrangement. We are working on this experiment at three different arrangement manifolds: Arrangement (A) is the three-degree slope in manifolds downward and upward, Arrangement (B) is the three-degree slope in manifolds upward and downward and Arrangement (C) is the three-degree slope in upward direction of the manifolds are selected. In this investigation we are using the Reynolds number ranging from 705-1411 for micro channel heat sink. The Arrangement (A) is the greater heat transfer coefficient within the increase Nusselt number and velocity and low pressure drop in comparison to Arrangement (B) and (C) type manifolds

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