scholarly journals Sensitivity analysis of heat transfers in an asymmetrically heated turbulent channel flow

2021 ◽  
Vol 321 ◽  
pp. 03001
Author(s):  
Martin David ◽  
Adrien Toutant ◽  
Françoise Bataille
Keyword(s):  
Heat Flux ◽  
Sensitivity Analysis ◽  
Channel Flow ◽  
Wall Temperature ◽  
Turbulent Channel Flow ◽  
Uncertainty Management ◽  
Bulk Temperature ◽  
Cold Wall ◽  
Heat Transfers ◽  
Global Uncertainty

A sensitivity analysis of heat transfers in an asymmetrically heated turbulent channel flow is performed using a dedicated heat transfer correlation. The investigated correlation is developed to study the heat transfers between the fluid and the wall in gas-pressurized solar receivers of concentrated solar power tower. The working conditions correspond to high-temperature levels and high heat fluxes. The correlation of the Nusselt number depends on five parameters: the Reynolds number, the Prandtl number, the fluid temperature, the hot and cold wall temperatures. We investigate the sensitivity of the heat flux to the wall and fluid temperatures. The results obtained with the global uncertainty management are compared to direct computations of the errors of measurement. In the global uncertainty management, the heat flux sensitivity is studied with the Taylor expansion of the function. This method assumes the quasilinearity and the quasi-normality of the function; therefore, only small variations of parameters are computed. The study points out the importance of the temperature measurement accuracy for the heat flux evaluation in asymmetrically heated turbulent channel flow. In particular, the results show that the cold wall heat flux is very sensitive to the variations of the cold wall temperature and the bulk temperature of the fluid. The hot wall is less influenced by the temperature variations than the cold wall. The global uncertainty management produces satisfying results on the prediction of the error linked to the uncertainties on bulk temperature. Nevertheless, the hot and cold wall temperature uncertainty propagation are poorly estimated by the method.

Water droplet condensation and evaporation in turbulent channel flow

2014 ◽  
Vol 749 ◽  
pp. 666-700 ◽  
Author(s):  
E. Russo ◽  
J. G. M. Kuerten ◽  
C. W. M. van der Geld ◽  
B. J. Geurts
Keyword(s):  
Mass Transfer ◽  
Nusselt Number ◽  
Size Distribution ◽  
Water Vapour ◽  
Channel Flow ◽  
Droplet Size ◽  
Droplet Size Distribution ◽  
Turbulent Channel Flow ◽  
Phase Changes ◽  
Cold Wall

AbstractWe propose a point-particle model for two-way coupling of water droplets dispersed in the turbulent flow of a carrier gas consisting of air and water vapour. We adopt an Euler–Lagrangian formulation based on conservation laws for the mass, momentum and energy of the continuous phase and on empirical correlations describing momentum, heat and mass transfer between the droplet phase and the carrier gas phase. An incompressible flow formulation is applied for direct numerical simulation of differentially heated turbulent channel flow. The two-way coupling is investigated in terms of its effects on mass and heat transfer characteristics and the resulting droplet size distribution. Compared to simulations without droplets or those with solid particles with the same size and specific heat as the water droplets, a significant increase in Nusselt number is found, arising from the additional phase changes. The Nusselt number increases with increasing ambient temperature and is almost independent of the heat flux applied to the walls of the channel. The time-averaged droplet size distribution displays a characteristic dependence on position expressing the combined effect of turbophoresis and phase changes in turbulent wall-bounded flow. In the statistically steady state that is reached after a long time, the resulting flow exhibits a mean motion of water vapour from the warm wall to the cold wall, where it condenses on average, followed by a net mean mass transfer of droplets from the cold wall to the warm wall.

Heat transfer in a turbulent channel flow with square bars or circular rods on one wall

2015 ◽  
Vol 776 ◽  
pp. 512-530 ◽  
Author(s):  
S. Leonardi ◽  
P. Orlandi ◽  
L. Djenidi ◽  
R. A. Antonia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Prandtl Number ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Smooth Wall ◽  
Roughness Elements ◽  
Smooth Channel

Direct numerical simulations (DNS) are carried out to study the passive heat transport in a turbulent channel flow with either square bars or circular rods on one wall. Several values of the pitch (${\it\lambda}$) to height ($k$) ratio and two Reynolds numbers are considered. The roughness increases the heat transfer by inducing ejections at the leading edge of the roughness elements. The amounts of heat transfer and mixing depend on the separation between the roughness elements, an increase in heat transfer accompanying an increase in drag. The ratio of non-dimensional heat flux to the non-dimensional wall shear stress is higher for circular rods than square bars irrespectively of the pitch to height ratio. The turbulent heat flux varies within the cavities and is larger near the roughness elements. Both momentum and thermal eddy diffusivities increase relative to the smooth wall. For square cavities (${\it\lambda}/k=2$) the turbulent Prandtl number is smaller than for a smooth channel near the wall. As ${\it\lambda}/k$ increases, the turbulent Prandtl number increases up to a maximum of 2.5 at the crests plane of the square bars (${\it\lambda}/k=7.5$). With increasing distance from the wall, the differences with respect to the smooth wall vanish and at three roughness heights above the crests plane, the turbulent Prandtl number is essentially the same for smooth and rough walls.

Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using Finite Difference Method and Its Assessment on the Thermally Stratified Turbulent Channel Flow

2005 ◽  
Vol 73 (3) ◽  
pp. 382-390 ◽  
Author(s):  
Makoto Tsubokura
Keyword(s):  
Heat Flux ◽  
Finite Difference ◽  
Channel Flow ◽  
A Priori ◽  
Turbulent Channel Flow ◽  
Eddy Diffusivity ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Scale Modeling ◽  
Subgrid Scale Modeling

Previously proposed methods for subgrid-scale (SGS) stress modeling were re-investigated and extended to SGS heat-flux modeling, and various anisotropic and isotropic eddy viscosity/diffusivity models were obtained. On the assumption that they are used in a finite-difference (FD) simulation, the models were constructed in such a way that they are insensitive to numerical parameters on which calculated flows are strongly dependent in the conventional Smagorinsky model. The models obtained, as well as those previously proposed, were evaluated a priori in a stably stratified open channel flow, which is considered to be a challenging application of large eddy simulation and suitable for testing both SGS stress and heat-flux models. The most important feature of the models proposed is that they are insensitive to the discretized test filtering parameter required in the dynamic procedure of Germano et al. (1991, Phys. Fluids, 3, pp. 1760–1765) in FD simulation. We also found in SGS heat-flux modeling that the effect of the grid (resolved)-scale (GS) velocity gradient plays an important role in the estimation of the streamwise heat flux, and an isotropic eddy diffusivity model with the effect of the GS velocity is proposed.

Logarithmic Expansions for Reynolds Shear Stress and Reynolds Heat Flux in a Turbulent Channel Flow

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Abu Seena ◽  
A. Bushra ◽  
Noor Afzal
Keyword(s):  
Heat Flux ◽  
Shear Stress ◽  
Channel Flow ◽  
Intermediate Layer ◽  
Reynolds Shear Stress ◽  
Turbulent Channel Flow ◽  
Closure Models ◽  
Fully Developed Turbulent Flow ◽  
Logarithmic Functions ◽  
Heat And Fluid Flow

The heat and fluid flow in a fully developed turbulent channel flow have been investigated. The closure model of Reynolds shear stress and Reynolds heat flux as a function of a series of logarithmic functions in the mesolayer variable have been adopted. The interaction between inner and outer layers in the mesolayer (intermediate layer) arising from the balance of viscous effect, pressure gradient and Reynolds shear stress (containing the maxima of Reynolds shear stress) was first proposed by Afzal (1982, “Fully Developed Turbulent Flow in a Pipe: An Intermediate Layer,” Arch. Appl. Mech., 53, 355–377). The unknown constants in the closure models for Reynolds shear stress and Reynolds heat flux have been estimated from the prescribed boundary conditions near the axis and surface of channel. The predictions are compared with the DNS data Iwamoto et al. and Abe et al. for Reynolds shear stress and velocity profile and Abe et al. data of Reynolds heat flux and temperature profile. The limitations of the closure models are presented.

Incipient-boiling superheat for sodium in turbulent, channel flow: Effects of heat flux and flow rate

1973 ◽  
Vol 16 (5) ◽  
pp. 971-984 ◽  
Author(s):  
O.E. Dwyer ◽  
G. Strickland ◽  
S. Kalish ◽  
P. Hlavac ◽  
G.A. Schoener
Keyword(s):  
Heat Flux ◽  
Channel Flow ◽  
Flow Rate ◽  
Turbulent Channel Flow ◽  
Flow Effects

Investigation of Convective Heat Transfer of Aqueous Nanofluids in Microchannels Integrated With Temperature Nanosensors

2011 ◽  
Author(s):  
Jiwon Yu ◽  
Seok-won Kang ◽  
Saeil Jeon ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wall Temperature ◽  
Pure Water ◽  
Bulk Temperature ◽  
Inlet Temperature ◽  
Experimental Conditions ◽  
Forced Convective Heat Transfer

Forced convective heat transfer experiments were performed for internal flow of de-ionized water (DIW) and aqueous nanofluids (ANF) in microchannels that were integrated with a calorimeter apparatus and an array of temperature nanosensors. The heat flux and wall temperature distribution was measured for the different test fluids as a function of fluid inlet temperature, wall temperature, heat flux, nanoparticles concentration, nanoparticle materials (composition, nanoparticle size and shape) and flow rates. Anomalous behavior of the nanofluids in convective heat transfer was observed where the heat flux varied as a function of flow rate and bulk temperature. The heat exchanging surfaces were characterized using electron microscopy (SEM, TEM) to monitor the change in surface characteristics both before and after the experiments. Precipitation of nanoparticles on the walls of the microchannels can lead to the formation of “nano-fins” at low concentrations of the nanoparticles while more rampant precipitation at high concentration of the nanoparticles in the nanofluids can lead to scaling (fouling) of the microchannel surfaces leading to degradation of convective heat transfer — compared to that of pure water under the same experimental conditions. Also, competing effects resulting from the decrease in the specific heat capacity as well as anomalous enhancement in the thermal conductivity of aqueous nanofluids can lead to counter-intuitive behavior of these test liquids during forced convective heat transfer.

Laminar Forced Convection in Transversely Corrugated Microtubes

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
F. Talay Akyildiz ◽  
Dennis A. Siginer
Keyword(s):  
Heat Flux ◽  
Analytical Solution ◽  
Forced Convection ◽  
Wall Temperature ◽  
Wall Heat Flux ◽  
Bulk Temperature ◽  
Straight Tube ◽  
Computational Domain ◽  
Constant Wall Temperature ◽  
Constant Wall Heat Flux

Forced convection heat transfer in fully developed laminar flow in transversely corrugated tubes is investigated for nonuniform but constant wall heat flux as well as for constant wall temperature. Epitrochoid conformal mapping is used to map the flow domain onto the unit circle in the computational domain. The governing equations are solved in the computational domain analytically. An exact analytical solution for the temperature field is derived together with closed form expressions for bulk temperature and Nusselt number for the case of the constant heat flux at the wall. A variable coefficient Helmholtz eigenvalue problem governs the case of the constant wall temperature. A novel semi-analytical solution based on the spectral Galerkin method is introduced to solve the Helmholtz equation. The solution in both constant wall heat flux and constant wall temperature case is shown to collapse onto the well-known results for the circular straight tube for zero waviness.

Effect of viscous dissipation on forced convection for laminar flow through a straight regular polygonal duct using BEM method

2018 ◽  
Vol 28 (1) ◽  
pp. 220-238 ◽  
Author(s):  
Tomasz Janusz Teleszewski ◽  
Slawomir Adam Sorko
Keyword(s):  
Heat Flux ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Forced Convection ◽  
Viscous Dissipation ◽  
Wall Temperature ◽  
Bulk Temperature ◽  
Brinkman Number ◽  
Content Type ◽  
Flow Through

Purpose The purpose of this paper is to investigate the effect of the viscous dissipation of laminar flow through a straight regular polygonal duct on forced convection with constant axial wall heat flux with constant peripheral wall temperature using the boundary element method (BEM). Design/methodology/approach Both the wall heating case and the wall cooling case are considered. Applying the velocity profile obtained for the duct laminar flow and the energy equation with the viscous dissipation term is solved exactly for the constant wall heat flux using the BEM. The numerical values are obtained by means of a computer program, written by the authors in Fortran. The results of the BEM approach are verified by analytic models. Nusselt numbers are obtained for flows with a different number of sides of a regular polygonal duct and Brinkman numbers. Findings When the difference in temperature between the wall temperature and the fluid bulk temperature changes the sign, then the functions of the Nusselt number with the Brinkman number generated some singularities (BrqLs). For the Brinkman number referring to the total wall linear power, with the increasing value of the number of sides of a regular polygonal duct, BrqLs decreases in the range of 3 ≤ n < ∞. If the BrqL < BrqLs, it is possible to note that, in general, the Nusselt number is higher for cross-sections having a lower value of the number of sides of a regular polygonal duct. For BrqL > BrqLs, this rule is reversed. Originality/value This paper illustrates the effects of viscous dissipation on laminar forced convective flow in regular polygon ducts with a different number n of sides. A compact relationship for the Nusselt number vs the Brinkman number referring to the temperature difference between the wall temperature and the fluid bulk temperature and the Brinkman number, which is based on the total wall linear power, have been proposed.

scholarly journals DNS of turbulent channel flow subject to oscillatory heat flux

2014 ◽  
Vol 18 ◽  
pp. 02001
Author(s):  
Anastasia Bukhvostova ◽  
J.G.M. Kuerten ◽  
B.J. Geurts
Keyword(s):  
Heat Flux ◽  
Channel Flow ◽  
Turbulent Channel Flow
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