The Experts below are selected from a list of 48009 Experts worldwide ranked by ideXlab platform
Orhan Aydin - One of the best experts on this subject based on the ideXlab platform.
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forced convection Flow of viscous dissipative power law fluids in a plane duct part 1 hydrodynamically and thermally Fully Developed Flow
2008Co-Authors: Mete Avci, Orhan AydinAbstract:In this study, an analysis of laminar forced convection in a plane duct for a power-law fluid with constant thermophysical properties is performed by taking the viscous dissipation into account. This part of the study, Part 1, examines both hydrodynamically and thermally Fully Developed Flow case. Two different thermal boundary conditions are considered: the constant heat flux (H1 boundary condition) and the constant wall temperature (T boundary condition). The combined and interactive influences of the power-law index and the Brinkman number on temperature distribution and the Nusselt numbers are analytically determined both for the wall heating and cooling cases at T and H1 boundary conditions. Singularities are observed in Nu-Br-n behaviors and these are discussed in terms of the energy balance.
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effects of viscous dissipation on the heat transfer in forced pipe Flow part 1 both hydrodynamically and thermally Fully Developed Flow
Energy Conversion and Management, 2005Co-Authors: Orhan AydinAbstract:In this study, an analysis of laminar forced convection in a pipe for a Newtonian fluid with constant properties is performed by taking the viscous dissipation into account. This part of the study, Part 1, examines both hydrodynamically and thermally Fully Developed Flow. Two different thermal boundary conditions are considered: constant heat flux (CHF) and constant wall temperature (CWT). Either wall heating (the fluid is heated) or wall cooling (the fluid is cooled) is considered. The temperature distribution and Nusselt numbers are analytically determined as a function of the Brinkman number.
Subhashis Ray - One of the best experts on this subject based on the ideXlab platform.
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performance optimisation of laminar Fully Developed Flow through square ducts with rounded corners
International Journal of Thermal Sciences, 2011Co-Authors: Subhadeep Chakraborty, Subhashis RayAbstract:A study on combined first and second law based optimisation of thermal-hydraulic performance of laminar Fully Developed Flow through square ducts with rounded corners has been presented in this paper. The objective functions have been considered according to suggestions of Webb and Bergles [7]. Four specific geometric constraints have been imposed on the shape of the ducts and these ducts have also been subjected to three different thermal and (or) hydraulic constraints. Two different thermal boundary conditions have been considered and the correlations for friction factor and Nusselt numbers have been adopted from the study of Ray and Misra [21]. The results obtained from the present study clearly show that the optimal duct geometry strongly depends on geometric and thermal-hydraulic constraints, as well as, the objective functions and hence, no general comment can be made with respect to the superiority of a particular geometry of the ducts. Nevertheless, the present study also shows that although entropy generation minimisation may be considered to be an important tool, one requires being careful in using it for thermal-hydraulic optimisation since it may lead to contradictory results for some of the performance evaluation criteria.
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laminar Fully Developed Flow through square and equilateral triangular ducts with rounded corners subjected to h1 and h2 boundary conditions
International Journal of Thermal Sciences, 2010Co-Authors: Subhashis Ray, D MisraAbstract:Abstract The present paper deals with the evaluation of pressure drop and heat transfer characteristics of laminar Fully-Developed Flow through ducts of square and equilateral triangular cross sections with rounded corners, for both H1 and H2 boundary conditions. The dimensionless radius of curvature (Rc) of both type of ducts is varied from zero to the maximum possible value (1 for square duct and 1 / 3 for triangular duct). The solutions for velocity and temperature are considered in the form of a harmonic series. The constants of the series are evaluated by ‘least square technique’. From the velocity and temperature solutions, fRe and Nu are calculated. The results show that for square duct, at lower values of Rc, both fRe and Nu increase rapidly with Rc and for higher values of Rc, both fRe and Nu asymptotically assume their values corresponding to that for the circular duct. For triangular ducts, Nu shows a similar behaviour. fRe, on the other hand, shows a similar behaviour only for lower values of Rc. At moderate Rc, fRe attains its maximum value around Rc ≈ 0.35 and with further increase in Rc, fRe drops slightly and finally tends to its value corresponding that of a circular ducts in an asymptotic manner. For both type of ducts, Nu for H1 boundary condition is always higher than that for H2 boundary condition. It is also observed that the straight portion of the duct is always more effective than the circular duct, where as, the effectiveness of the rounded portion, which is always less than the circular duct, increases with the increase in Rc. Correlations, in two different forms, are obtained for all the cases and they show excellent agreement with the computed data.
Azadeh Amrollahi - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of laminar convective heat transfer and pressure drop of water based al2o3 nanofluids in Fully Developed Flow regime
Experimental Thermal and Fluid Science, 2013Co-Authors: Mohammad Mahdi Heyhat, Farshad Kowsary, Alimorad Rashidi, M H Momenpour, Azadeh AmrollahiAbstract:Abstract This article presents the heat transfer coefficient and friction factor of the nanofluids Flowing in a horizontal tube under laminar Flow conditions, experimentally. The experiments have been done on Fully Developed region under the constant wall temperature condition. Al 2 O 3 nanoparticles with diameters of 40 nm dispersed in distilled water with volume concentrations of 0.1–2 vol.% were used as the test fluid. All physical properties of the Al 2 O 3 –water nanofluids needed to calculate the pressure drop and the convective heat transfer coefficient have been measured. The results show that the heat transfer coefficient of nanofluid is higher than that of the base fluid and increased with increasing the Reynolds number and particle concentrations. The heat transfer coefficient increases by approximately 32% in the Fully Developed region at 2 vol.% nanofluid. The measured pressure loss for the nanofluids was in general much higher than for pure water. The experimental results illustrate that the single phase correlation with nanofluids properties could not predict heat transfer coefficient enhancement of nanofluids fairly.
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experimental investigation of turbulent Flow and convective heat transfer characteristics of alumina water nanofluids in Fully Developed Flow regime
International Communications in Heat and Mass Transfer, 2012Co-Authors: Mohammad Mahdi Heyhat, Farshad Kowsary, Alimorad Rashidi, Alem Varzane S Esfehani, Azadeh AmrollahiAbstract:Abstract In this paper the convective heat transfer and friction factor of the nanofluids in a circular tube with constant wall temperature under turbulent Flow conditions were investigated experimentally. Al 2 O 3 nanoparticles with diameters of 40 nm dispersed in distilled water with volume concentrations of 0.1–2 vol.% were used as the test fluid. All physical properties of the Al 2 O 3 –water nanofluids needed to calculate the pressure drop and the convective heat transfer coefficient were measured. The results show that the heat transfer coefficient of nanofluid is higher than that of the base fluid and increased with increasing the particle concentrations. Moreover, the Reynolds number has a little effect on heat transfer enhancement. The experimental data were compared with traditional convective heat transfer and viscous pressure drop correlations for Fully Developed turbulent Flow. It was found that if the measured thermal conductivities and viscosities of the nanofluids were used in calculating the Reynolds, Prandtl, and Nusselt numbers, the existing correlations perfectly predict the convective heat transfer and viscous pressure drop in tubes.
Arthur E. Bergles - One of the best experts on this subject based on the ideXlab platform.
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performance evaluation of ducts with non circular shapes laminar Fully Developed Flow and constant wall temperature
International Journal of Thermal Sciences, 2014Co-Authors: Valentin M Petkov, Ventsislav D Zimparov, Arthur E. BerglesAbstract:Abstract Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase Fully Developed laminar Flow through bundle of ducts with non-circular shape – rectangular, isosceles triangular, elliptical, trapezoidal and hexagonal. The bundle of circular tubes has been used as a reference heat transfer unit. Constant wall temperature has been selected as the thermal boundary condition. The performance characteristics of the bundles with non-circular ducts have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the hydraulic diameter of the duct has been specified. The results clearly show that the rectangular, trapezoidal or hexagonal duct configuration can compete, in some cases, with the circular tube configuration. The choice of the tube shape and geometrical details depends on the constraints imposed and the objectives pursued. The results obtained from the present study revealed that they differed from those obtained with a common constraint of specified cross sectional area.
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performance evaluation of laminar Fully Developed Flow through ducts with non circular shapes subjected to h1 boundary condition part 1
International Review of Chemical Engineering (IRECHE), 2013Co-Authors: Valentin M Petkov, Ventsislav D Zimparov, Arthur E. BerglesAbstract:Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase Fully Developed laminar Flow through heat exchangers with axial corrugated, square with rounded corners, and triangular with rounded corners ducts. The heat exchanger with circular tubes has been used as a reference heat transfer unit. The H1 boundary condition has been selected as thermal boundary condition. The performance characteristics of the heat exchangers with non-circular tubes have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the cross sectional area of the non-circular duct has been specified. As expected, the analysis of the thermal performance of heat exchangers with non-circular ducts revealed that the selection of the optimal shape of the duct strongly depends on the geometric and thermal-hydraulic constraints imposed on the unit, and the objectives pursued. The use of a general criterion connecting two objectives simultaneously permits to avoid the contradictory results that can be obtained if criteria based on first or second law analysis are implemented alone. The evaluation concerning the superiority of a particular shape of the non-circular duct depends also on the value of the irreversibility distribution ratio, . For the cases FG (fixed geometry criteria) the use of ducts with non-circular shapes is inefficient, whereas in the cases FN (fixed number of tubes) and VG (variable geometry) some benefit can be achieved according to the value of
Arun K Saha - One of the best experts on this subject based on the ideXlab platform.
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numerical study of Fully Developed unsteady Flow and heat transfer in asymmetric wavy channels
International Journal of Heat and Mass Transfer, 2016Co-Authors: Abhishek G Ramgadia, Arun K SahaAbstract:Abstract The present study aims at the numerical investigation of Fully Developed Flow and heat transfer through asymmetric wavy-walled geometry. The Flow characteristics and thermal performance of wavy-walled configuration is assessed for three different geometries generated using three phase shift angles ( φ ) between the two opposite heated walls. The function y = 2 a ·sin 2 ( πx / L ) is used to describe the walls of the wavy channel. For the symmetric geometry ( φ = 180°) considered in the present study, the ratios H min / H max and L / a are kept fixed to 0.4 and 8.0 respectively while the four asymmetric channels are created through a desired phase-shift of φ = 0°, 45°, 90° and 135° between the two opposite sine-wave walls. The finite volume method on collocated grid has been employed to solve the time dependent Navier–Stokes and energy equation. The Fully Developed Flow and heat transfer has been modeled using periodic boundary conditions. The critical Reynolds number of unsteadiness is found to be the highest for the symmetric ( φ = 180°) wavy-walled channel. The Flow in all three geometries has been found to be equally complex but the asymmetric geometry with 0° phase-shift reveals maximum Flow asymmetry about the Flow centreline. It has also been observed that the most asymmetric geometry having 0° phase-shift encourages best heat transfer over symmetric configuration with 180° phase-shift, but is accompanied by the highest friction penalty.
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numerical study of Fully Developed Flow and heat transfer in a wavy passage
International Journal of Thermal Sciences, 2013Co-Authors: Abhishek G Ramgadia, Arun K SahaAbstract:Abstract A two-dimensional numerical study of Fully Developed fluid Flow and heat transfer through a horizontal wavy surface is presented. Time dependent Navier–Stokes and energy equation have been solved using finite volume method. Numerical calculations are performed for a wavy surface described by sine function y = 2 a × sin 2 (π x / L ) with ratios H min / H max and L / a fixed to 0.4 and 8 respectively. Attempts have been made to foresee the effect of streamwise domain length, an integer multiple of periodic domain length, on the Flow and heat transfer characteristics. It is established that the Flow and heat transfer characteristics do not show any dependence on the length of the periodic domain thereby confirming that geometric and Flow periodicity are identical. The effect of Reynolds numbers, for Re in the range 25–1000, on the Flow field and heat transfer has been presented. For steady Flow the heat transfer rates are found to be very low and for unsteady Flow with increased mixing between core and near wall fluids enhanced heat transfer rates are obtained.
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Fully Developed Flow and heat transfer characteristics in a wavy passage effect of amplitude of waviness and reynolds number
International Journal of Heat and Mass Transfer, 2012Co-Authors: Abhishek G Ramgadia, Arun K SahaAbstract:Abstract The present study deals with numerical simulation of Fully Developed Flow and heat transfer through a wavy surface described by the function y = 2 a sin 2 ( πx / L ). Finite volume method on collocated grid is used to solve incompressible, time-dependent Navier–Stokes and energy equation in primitive variable form. Effect of geometry, generated by varying H min / H max ratio from 0.1 to 0.5 and keeping L / a ratio fixed to 8, on fluid Flow and heat transfer characteristics has been elaborated at a Reynolds number of 600. The critical Reynolds number of unsteadiness is found to depend on the geometrical parameters. At Re = 600, one model shows the Flow with multiple frequencies while the others reveal single frequency. It is established that geometry with H min / H max ratio 0.2 produces the highest Nusselt number and spawns the best thermal performance factor ( TPF ). With increase in Reynolds number, the steady Flow shows a decrease in TPF while an increase in TPF is noticed when the Flow is unsteady.
