Numerical Simulation of Heat Transfer Process of Viscoelastic Fluid Flow at High Weissenberg Number by Log-Conformation Reformulation

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Hong-Na Zhang ◽  
Dong-Yang Li ◽  
Xiao-Bin Li ◽  
Wei-Hua Cai ◽  
Feng-Chen Li
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Viscoelastic Fluid ◽  
Transfer Process ◽  
Viscoelastic Fluids ◽  
Heat Transfer Process ◽  
Weissenberg Number ◽  
Transfer Enhancement ◽  
Working Medium

Viscoelastic fluids are now becoming promising candidates of microheat exchangers’ working medium due to the occurrence of elastic instability and turbulence at microscale. This paper developed a sound solver for the heat transfer process of viscoelastic fluid flow at high Wi, and this solver can be used to design the multiple heat exchangers with viscoelastic fluids as working medium. The solver validation was conducted by simulating four fundamental benchmarks to assure the reliability of the established solver. After that, the solver was adopted to study the heat transfer process of viscoelastic fluid flow in a curvilinear channel, where apparent heat transfer enhancement (HTE) by viscoelastic fluid was achieved. The observed heat transfer enhancement was attributed to the occurrence of elastic turbulence which continuously mix the hot and cold fluids by the twisting and wiggling flow motions.

Heat Transfer Asymptote in Laminar Tube Flows of Non-Linear Viscoelastic Fluids

2010 ◽  
Author(s):  
Dennis A. Siginer
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Cross Section ◽  
Viscoelastic Fluids ◽  
Weissenberg Number ◽  
Secondary Flows ◽  
Asymptotic Independence ◽  
Transfer Enhancement ◽  
Elasticity Number

The fully developed thermal field in constant pressure gradient driven laminar flow of a class of nonlinear viscoelastic fluids with instantaneous elasticity in straight pipes of arbitrary contour ∂D with constant wall flux is investigated. The nonlinear fluids considered are constitutively represented by a class of single mode, non-affine constitutive equations. The driving forces can be large. Asymptotic series in terms of the Weissenberg number Wi are employed to expand the field variables. A continuous one-to-one mapping is used to obtain arbitrary tube contours from a base tube contour ∂D0. The analytical method presented is capable of predicting the velocity and temperature fields in tubes with arbitrary cross-section. Heat transfer enhancement due to shear-thinning is identified together with the enhancement due to the inherent elasticity of the fluid. The latter is to a very large extent the result of secondary flows in the cross-section but there is a component due to first normal stress differences as well. Increasingly large enhancements are computed with increasing elasticity of the fluid as compared to its Newtonian counterpart. Order of magnitude larger enhancements are possible even with slightly viscoelastic fluids. The coupling between inertial and viscoelastic nonlinearities is crucial to enhancement. Isotherms for the temperature field are discussed for non-circular contours such as the ellipse and the equilateral triangle together with the behavior of the average Nusselt number Nu, a function of the Reynolds Re, the Prandtl Pr and the Weissenberg Wi numbers. Analytical evidence for the existence of a heat transfer asymptote in laminar flow of viscoelastic fluids in non-circular contours is given for the first time. Nu becomes asymptotically independent from elasticity with increasing Wi, Nu = f (Pe,Wi) → Nu = f(Pe). This asymptote is the counterpart in laminar flows in non-circular tubes of the heat transfer asymptote in turbulent flows of viscoelastic fluids in round pipes. A different asymptote corresponds to different cross-sectional shapes in straight tubes. The change of type of the vorticity equation governs the trends in the behavior of Nu with increasing Wi and Pe. The implications on the heat transfer enhancement is discussed in particular for slight deviations from Newtonian behavior where a rapid rise in enhancement seems to occur as opposed to the behavior for larger values of the Weissenberg number where the rate of increase is much slower. The asymptotic independence of Nu from elasticity with increasing Wi is related to the extent of the supercritical region controlled by the interaction of the viscoelastic Mach number M and the Elasticity number E, which mitigates and ultimately cancels the effect of the increasingly strong secondary flows with increasing Wi to level off the enhancement. The physics of the interaction of the effects of the Elasticity E, Viscoelastic Mach M, Reynolds Re and Weissenberg Wi numbers on generating the heat transfer enhancement is discussed.

Effects of Guide Vanes on the Tip Heat Transfer Enhancement of a Turbine Blade

2011 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Turbine Blade ◽  
Pressure Loss ◽  
Transfer Enhancement ◽  
Guide Vanes ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Blade Tip

Gas turbine blade tips encounter large heat load as they are exposed to the high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip life time. This paper presents numerical predictions of turbulent fluid flow and heat transfer through two-pass channels with and without guide vanes placed in the turn regions using RANS turbulence modeling. The effects of adding guide vanes on the tip-wall heat transfer enhancement and the channel pressure loss were analyzed. The guide vanes have a height identical to that of the channel. The inlet Reynolds numbers are ranging from 100,000 to 600,000. The detailed three-dimensional fluid flow and heat transfer over the tip-walls are presented. The overall performances of several two-pass channels are also evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide vanes are 10∼60% higher than that of a channel without guide vanes, while the pressure loss might be reduced when the guide vanes are properly designed and located, otherwise the pressure loss is expected to be increased severely. It is suggested that the usage of proper guide vanes is a suitable way to augment the blade tip heat transfer and improve the flow structure, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip-wall directly.

Application of Different Conductive Substrate Materials for Heat Transfer Enhancement in Cooling of Electronic Components

2014 ◽  
Vol 1082 ◽  
pp. 327-331
Author(s):  
Thiago Antonini Alves ◽  
Murilo A. Barbur ◽  
Felipe Baptista Nishida
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Pure Aluminum ◽  
Rectangular Channel ◽  
Electronic Components ◽  
Transfer Enhancement ◽  
Cooling Process ◽  
Conductive Substrate

In this research, a study of the heat transfer enhancement in electronic components mounted in channels was conducted by using different materials in the conductive substrate. In this context, a numerical analysis was performed to investigate the cooling of 3D protruding heaters mounted on the bottom wall (substrate) of a horizontal rectangular channel using the ANSYS/FluentTM 15.0 software. Three different materials of the conductive substrate were analyzed, polymethyl methacrylate (PMMA), fiberglass reinforced epoxy laminate (FR4), and pure aluminum (Al). Uniform heat generation rate was considered for the protruding heaters and the cooling process happened through a steady laminar airflow, with constant properties. The fluid flow velocity and temperature profiles were uniform at the channel entrance. For the adiabatic substrate, the cooling process occurred exclusively by forced convection. For the conductive substrate, the cooling process was characterized by conjugate forced convection-conduction heat transfer through two mechanisms; one directly between the heaters surfaces and the flow by forced convection, and the other through conduction at the interfaces heater-substrate in addition to forced convection from the substrate to the fluid flow at the substrate surface. The governing equations and boundary conditions were numerically solved through a coupled procedure using the Control Volumes Method in a single domain comprising the solid and fluid regions. Commonly used properties in cooling of electronics components mounted in a PCB and typical geometry dimensions were utilized in the results acquisition. Some examples were presented, indicating the dependence of the substrate thermal conductivity related to the Reynolds number on the heat transfer enhancement. Thus, resulting in a lower work temperature at the electronic components.

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