scholarly journals A Complementary Experimental and Numerical Study of the Flow and Heat Transfer in Offset Strip-Fin Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 690-698 ◽  
Author(s):  
N. C. DeJong ◽  
L. W. Zhang ◽  
A. M. Jacobi ◽  
S. Balachandar ◽  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Complex Geometry ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Numerical Results ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Unsteady Numerical Simulation ◽  
Offset Strip Fin

A detailed analysis of experimental and numerical results for flow and heat transfer in similar offset strip-fin geometries is presented. Surface-average heat transfer and pressure drop, local Nusselt numbers and skin friction coefficients on the fin surface, instantaneous flow structures, and local time-averaged velocity profiles are contrasted for a range of Reynolds numbers using both prior and new experimental and numerical results. This contrast verifies that a two-dimensional unsteady numerical simulation captures the important features of the flow and heat transfer for a range of conditions. However, flow three-dimensionality appears to become important for Reynolds numbers greater than about 1300, and thermal boundary conditions are important for Reynolds numbers below 1000. The results indicate that boundary layer development, flow separation and reattachment, wake formation, and vortex shedding are all important in this complex geometry.

A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall

2018 ◽  
Author(s):  
Peng Zhang ◽  
Yu Rao ◽  
Yanlin Li
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Hybrid Structure ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Flow Mixing

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.

scholarly journals Numerical Study on Flow and Heat Transfer Mechanisms in the Heat Exchanger Channel with V-Orifice at Various Blockage Ratios, Gap Spacing Ratios, and Flow Directions

2019 ◽  
Vol 2019 ◽  
pp. 1-21 ◽  
Author(s):  
Amnart Boonloi ◽  
Withada Jedsadaratanachai
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Numerical Results ◽  
Blockage Ratio ◽  
Maximum Heat ◽  
Flow And Heat Transfer ◽  
Maximum Heat Transfer ◽  
Smooth Channel ◽  
Gap Spacing

Numerical assessments in the square channel heat exchanger installed with various parameters of V-orifices are presented. The V-orifice is installed in the heat exchanger channel with gap spacing between the upper-lower edges of the orifice and the channel wall. The purposes of the design are to reduce the pressure loss, increase the vortex strength, and increase the turbulent mixing of the flow. The influence of the blockage ratio and V-orifice arrangement is investigated. The blockage ratio, b/H, of the V-orifice is varied in the range 0.05–0.30. The V-tip of the V-orifice pointing downstream (V-downstream) is compared with the V-tip pointing upstream (V-upstream) by both flow and heat transfer. The numerical results are reported in terms of flow visualization and heat transfer pattern in the test section. The thermal performance assessments in terms of Nusselt number, friction factor, and thermal enhancement factor are also concluded. The numerical results reveal that the maximum heat transfer enhancement is found to be around 26.13 times higher than the smooth channel, while the optimum TEF is around 3.2. The suggested gap spacing for the present configuration of the V-orifice channel is around 5–10%.

Heat Transfer in a “Cover-Plate” Preswirl Rotating-Disk System

1999 ◽  
Vol 121 (2) ◽  
pp. 249-256 ◽  
Author(s):  
R. Pilbrow ◽  
H. Karabay ◽  
M. Wilson ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Cover Plate ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Cooling Air ◽  
Plate System

In most gas turbines, blade-cooling air is supplied from stationary preswirl nozzles that swirl the air in the direction of rotation of the turbine disk. In the “cover-plate” system, the preswirl nozzles are located radially inward of the blade-cooling holes in the disk, and the swirling airflows radially outward in the cavity between the disk and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder–Sharma and the Morse low-Reynolds-number k–ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disk” are compared with measured values obtained from a rotating-disk rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 X 106 to 1.5 X 106, and for 0.9 < βp < 3.1, where βp is the preswirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disk). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

Periodic Fluid Flow and Heat Transfer in a Square Cavity Due to an Insulated or Isothermal Rotating Cylinder

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
K.-H. Weng ◽  
A. Ahmed
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Flow Fields ◽  
Square Cavity ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Rotating Objects

The periodic state of laminar flow and heat transfer due to an insulated or isothermal rotating cylinder object in a square cavity is investigated computationally. A finite-volume-based computational methodology utilizing primitive variables is used. Various rotating objects (circle, square, and equilateral triangle) with different sizes are placed in the middle of a square cavity. A combination of a fixed computational grid and a sliding mesh was utilized for the square and triangle shapes. For the insulated and isothermal objects, the cavity is maintained as differentially heated and isothermal enclosures, respectively. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr=5 fluid. The Reynolds numbers were selected so that the flow fields are not generally affected by the Taylor instabilities (Ta<1750). The periodic flow field, the interaction of the rotating objects with the recirculating vortices at the four corners, and the periodic channeling effect of the traversing vertices are clearly elucidated. The simulations of the dynamic flow fields were confirmed against experimental data obtained by particle image velocimetry. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to the conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. Transient variations of the average Nusselt numbers of the respective systems show that for high Re numbers, a quasiperiodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt numbers of the insulated and isothermal object systems were correlated with the rotational Reynolds number and shape of the object. For high Re numbers, the performance of the system is independent of the shape of the object. On the other hand, with lowering of the hydraulic diameter (i.e., bigger objects), the triangle and the circle exhibit the highest and lowest heat transfers, respectively. High intensity of the periodic channeling and not its frequency is identified as the cause of the observed enhancement.

Heat Transfer in a “Cover-Plate” Pre-Swirl Rotating-Disc System

1998 ◽  
Author(s):  
Robert Pilbrow ◽  
Hasan Karabay ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Cover Plate ◽  
Swirl Ratio ◽  
Rotating Disc ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Turbine Disc ◽  
Cooling Air

In most gas turbines, blade-cooling air is supplied from stationary pre-swirl nozzles that swirl the air in the direction of rotation of the turbine disc. In the “cover-plate” system, the pre-swirl nozzles are located radially inward of the blade-cooling holes in the disc, and the swirling air flows radially outwards in the cavity between the disc and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder-Sharma and the Morse low-Reynolds-number k-ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disc” are compared with measured values obtained from a rotating-disc rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 × 106 to 1.5 × 106, and for 0.9 < βp < 3.1, where βp is the pre-swirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disc). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

Numerical Study of Nozzle Design on Cadmium Quenching Process in Thermochemical Splitting of Water

2009 ◽  
Author(s):  
Jianhu Nie ◽  
Yitung Chen ◽  
Bunsen Wong ◽  
Lloyd C. Brown
Keyword(s):  
Heat Transfer ◽  
Hydrogen Production ◽  
Gas Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Numerical Results ◽  
Nozzle Design ◽  
Flow And Heat Transfer ◽  
Quenching Process

Three-dimensional liquid-gas flow with condensation during cadmium quenching process for hydrogen production was numerically simulated in order to effectively guide the design of solar decomposer and vapor quencher. The mixture model was selected for modeling the multiphase flow, and the two-equation RNG k-ε model was used to model the turbulent flow and heat transfer. Numerical results including velocity, temperature, pressure, and mole fraction distributions were obtained for different nozzle designs. Numerical results showed that flow is relatively low in the decomposer and close to the bottom and the top inlets. The maximum velocity develops in the region near the entrance of the quenching nozzle as the nozzle angle is small. As the nozzle angle is large, the maximum velocity appears in the exit tube. Temperature, pressure and cadmium vapor distributions are also directly affected by the nozzle angle.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow

1981 ◽  
Author(s):  
L. W. Florschuetz ◽  
C. R. Truman ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Circular Jets

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

Heat Transfer Improvement in a Square Duct with Diagonal Inclined Ribs

2014 ◽  
Vol 931-932 ◽  
pp. 1144-1148
Author(s):  
Supattarachai Suwannapan ◽  
Ratsak Poomsalood ◽  
Pongjet Promvonge ◽  
Withada Jedsadaratanachai ◽  
Thitipat Limkul
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Study ◽  
Simple Algorithm ◽  
Reynolds Numbers ◽  
Square Duct ◽  
Flow And Heat Transfer ◽  
Pitch Ratio ◽  
Volume Method ◽  
Heat Transfer Improvement

This research presents a numerical study of turbulent periodic flow and heat transfer in threedimensional isothermalfluxed square duct with diagonal inclined rib inserted. The fluid flow and heat transfer characteristics are presented for Reynolds numbers in the range of 4000 to 20,000. The computations based on the finite volume method, and the SIMPLE algorithm has been implemented. Effects of rib pitch ratios (0.5 to 2) at a single blockage ratio of 0.2 and attack angle of 60o on heat transfer and friction factor in the duct are examined and their results of the inclined rib are also compared with those of the smooth duct. It is found that the inclined rib provides higher heat transfer rate and friction factor than the smooth duct for all cases. In addition, the decreasing of the pitch ratio leads to the rise in the Nusselt number and friction factor.

scholarly journals Numerical investigation of fluid flow and heat transfer around a circular cylinder utilizing nanofluid for different thermal boundary condition in the steady regime

10.30544/292 ◽  
2017 ◽  
Vol 23 (2) ◽  
pp. 131-141
Author(s):  
Rafik Bouakkaz ◽  
F. Salhi ◽  
Y. Khelili ◽  
M. Ouazzazi ◽  
K. Talbi
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Reynolds Numbers ◽  
Uniform Heat Flux ◽  
Constant Wall Temperature ◽  
Steady Regime ◽  
Volume Fractions ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Volume Method

In this work, steady flow-field and heat transfer through a copper–water nanofluid around a circular cylinder, under the influence of both the standard thermal boundary conditions i.e. uniform heat flux (UHF) and constant wall temperature (CWT) was investigated numerically by using a finite-volume method for Reynolds numbers of 10 to 40. Furthermore, the range of nanoparticle volume fractions (φ) considered is 0 ≤ φ ≤ 5%. The variation of the local and the average Nusselt numbers with Reynolds number, and volume fractions are presented for the range of conditions. The average Nusselt number is found to increase with increasing the nanoparticle volume fractions.

scholarly journals Influence of CuO nanoparticles in enhancing the overall heat transfer around a square cylinder

10.30544/435 ◽  
2019 ◽  
Vol 25 (3) ◽  
pp. 225-236
Author(s):  
Rafik Bouakkaz ◽  
Yacine Khelili ◽  
Aliouali Abdelouahed
Keyword(s):  
Heat Transfer ◽  
Particle Diameter ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Particle Volume ◽  
Volume Fractions ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Volume Method ◽  
Opposing Effect

In this study, steady flow and heat transfer through a copper–water nanofluid around a square cylinder was investigated numerically by using a finite-volume method for Reynolds numbers of 10-40. Furthermore, the range of nanoparticle volume fractions () considered is 0 ≤  ≤ 0.04, with three different nanoparticle diameters dnp = 30, 60 and 90 nm. The variation of the local and the average Nusselt numbers with Reynolds number, and volume fractions are presented for the range of above conditions. The averaged Nusselt number showed clear enhancement comparing with the base fluids. This enhancement is more apparent in flows with higher particle volume concentration, whereas the particle diameter imposes an opposing effect on the heat transfer characteristics.

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