Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Crossflow

2005 ◽  
Author(s):  
Zhihua Li ◽  
Jane Davidson ◽  
Susan Mantell
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Circular Cylinder ◽  
Average Nusselt Number ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Published Data ◽  
Transfer Coefficients ◽  
Axis Ratio

The use of streamlined tubes to reduce pressure drop across polymer tube bundles is considered because of the relative ease of fabrication. The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 are determined numerically for cross-flow Reynolds numbers from 500 to 10,000. An isothermal surface is assumed. The two-dimensional, unsteady Navier-Stokes equations and energy equation are solved using the finite volume method. Laminar flow is assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake is resolved using the shear stress transport k-omega model. Local heat transfer, pressure and friction coefficients as well as a total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Reductions in drag may be increased by making the streamlined cylinders more slender. Over the range of Reynolds number considered, an elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30 to 40 percent compared to that of a circular cylinder. The lenticular and elliptical geometries have nearly identical average of Nusselt number. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15 to 35% lower than that of a circular cylinder. A case study for an automotive radiator is presented to illustrate comparison of shaped and circular tubes in terms of both heat transfer and pressure drop.

Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Cross Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 564-570 ◽  
Author(s):  
Zhihua Li ◽  
Jane H. Davidson ◽  
Susan C. Mantell
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Average Nusselt Number ◽  
Stokes Equations ◽  
Cross Flow ◽  
Published Data ◽  
Transfer Coefficients ◽  
Axis Ratio ◽  
Elliptical Cylinders

The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 were determined numerically for cross-flow Reynolds numbers from 500 to 104. The two-dimensional, unsteady Navier-Stokes equations and energy equation were solved using the finite volume method. Laminar flow was assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake was resolved using the shear stress transport k-ω model. Local heat transfer, pressure and friction coefficients as well as the total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Drag can be reduced by making the streamlined cylinders more slender. Drag is relatively insensitive to Reynolds number over the range studied. An elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30–40% compared to that of a circular cylinder. The Nusselt numbers of lenticular and elliptical cylinders are comparable. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15–35% lower than that of a circular cylinder.

Experimental Investigation of the Effect of Synthetic Jets in Minichannels With Subcooled Boiling Flow

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. The experimental range extends from transitional to turbulent flows. Local wall temperature measurements indicate that increases of heat transfer coefficient of over 20% can occur directly below the synthetic jet with low exit qualities. In this study, the heat transfer augmentation by using synthetic jets was dictated by the momentum ratio of the synthetic jet to the bulk fluid flow. As local quality was increased, the heat transfer augmentation dropped from 23% to 10%. Surface tension variations had a large effect on the Nusselt number, while variations in inertial forces had a small effect on Nusselt number in this operating region.

Inverse Determination of the Local Heat Transfer Coefficients for Nucleate Boiling on a Horizontal Cylinder

2003 ◽  
Vol 125 (6) ◽  
pp. 1087-1095 ◽  
Author(s):  
H. Louahlia-Gualous ◽  
P. K. Panday ◽  
E. A. Artioukhine
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pool Boiling ◽  
Gradient Methods ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Nucleate Boiling ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Iterative Regularization

This article treats the local heat transfer for nucleate pool boiling around the cylinder using the inverse heat conduction analysis. The physical model considers a half section of a cylinder with unknown surface temperature and heat flux density. The iterative regularization and the conjugate gradient methods are used for solving the inverse analysis. The local Nusselt number profiles for nucleate pool boiling are presented and analyzed for different electric heat. The mean Nusselt number estimated by IHCP is closed with the measured values. The results of IHCP are compared to those of Cornewell and Houston (1994), Stephan and Abdelsalam (1980) and Memory et al. (1995). The influence of the error of the measured temperatures and the error in placement of the thermocouples are studied.

Comparison of Pressure Drop and Endwall Heat Transfer Measurements to Flow Visualization Testing of Solid and Porous Pin Fin Arrays

2009 ◽  
Author(s):  
Jared M. Pent ◽  
Jay S. Kapat ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Visualization ◽  
Local Heat Transfer ◽  
Ccd Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Porous Aluminum ◽  
Pin Fins ◽  
A Charge

This paper examines the local and averaged endwall heat transfer effects of a staggered array of porous aluminum pin fins with a channel blockage ratio (blocked channel area divided by open channel area) of 50%. Two sets of pins were used with pore densities of 0 (solid) and 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates using each set of pins. Local heat transfer coefficients on the endwall were measured using Thermochromatic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. The heat transfer and pressure data was then compared to flow visualization tests that were run using a fog generator. Results are presented for the two sets of pins with Reynolds numbers between 25000 and 130000. Local HTC (heat transfer coefficient) profiles as well as spanwise and streamwise averaged HTC plots are displayed for both pin arrays. The thermal performance was calculated for each pin set and Reynolds number. All experiments were carried out in a channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72.

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

Experimental and Numerical Investigation of Natural Convection Heat Transfer in Horizontal Elliptic Annuli

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Ramadan Y. Sakr ◽  
Nabil S. Berbish ◽  
Ali A. Abd-Aziz ◽  
Abdalla Said Hanafi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Orientation Angle ◽  
Elliptic Cylinder ◽  
Major Axis ◽  
Radius Ratio ◽  
Hydraulic Radius ◽  
Axis Ratio

Experimental and numerical studies for natural convection in two dimensional regions formed by a constant flux heat horizontal elliptic tube concentrically located in a larger, isothermally cooled horizontal cylinder were investigated. Both ends of the annulus are closed. Experiments were carried out for the Rayleigh number based on the equivalent annulus gap length ranges from 1.12x107 up to 4.92x107; the elliptic tube orientation angle varies from 0o to 90o and the hydraulic radius ratio, HRR, was 6.4. These experiments were carried out for the axis ratio of an elliptic tube (minor/major=b/c) of 1:3. The numerical simulation for the problem is carried out by using commercial CFD code. The effects of the orientation angle as well as other parameters such as elliptic cylinder axis ratio and hydraulic radius ratio on the flow and heat transfer characteristics are investigated numerically. The numerical simulations covered a range of elliptic tube axis ratios from 0.1 to 0.98 and for the hydraulic radius ratios from 1.5 to 6.4. The results showed that the average Nusselt number increases as the orientation angle of the elliptic cylinder increases from 0o (the major axis is horizontal) to 90o (the major axis is vertical) and with the Rayleigh number as well. Also, the average Nusselt number decreases with the increase of the hydraulic radius ratio. An increase up to 1.75 and further increases in the hydraulic radius ratio leads to an increase in the average Nusselt number. The axis ratio of the elliptic cylinder has an insignificant effect on the average Nusselt number. Both the average and local Nusselt number from the experimental results are compared with those obtained from the CFD code.Both the fluid flow and heat transfer characteristics for different operating and geometric conditions are illustrated velocity vectors and isotherm contours that were obtained from the CFD code. Also, two correlation equations that relate the average Nusslet number with the Rayleigh number, orientation angle, and hydraulic radius ratio and axis ratio are obtained.

Measurements of Developing and Fully Developed Heat Transfer Coefficients along a Periodically Interrupted Surface

1979 ◽  
Vol 101 (2) ◽  
pp. 211-216 ◽  
Author(s):  
N. Cur ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Plate Thickness ◽  
Turbulent Regime ◽  
Duct Flow ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Interrupted Surface

The heat transfer and pressure drop characteristics for an array of colinear, equally spaced plates aligned parallel to the flow in a flat rectangular duct have been studied experimentally. The periodic interruptions (i.e., the gaps between the plates) preclude the attainment of hydrodynamic and thermal development of the type that is encountered in conventional duct flows, but a periodic fully developed regime can exist. Measurements of the heat transfer coefficients for the successive plates of the array affirmed the periodically developed regime and demonstrated the developmental pattern leading to its attainment. The thickness of the plates in the array was varied parametrically. In general, the Nusselt number increases with plate thickness. Thickness-related increases in the fully developed Nusselt number of up to 65 percent were encountered. The presence of the interruptions serves to augment the heat transfer coefficients. In the fully turbulent regime, the heat transfer coefficients are on the order of twice those for a conventional duct flow. The pressure drop also increases with the plate thickness.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
M. R. Salem ◽  
K. M. Elshazly ◽  
R. Y. Sakr ◽  
R. K. Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Average Nusselt Number ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Fanning Friction Factor ◽  
Coil Heat

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

Local Heat Transfer Coefficients Under an Axisymmetric, Single-Phase Liquid Jet

1991 ◽  
Vol 113 (1) ◽  
pp. 71-78 ◽  
Author(s):  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Single Phase ◽  
Radial Distance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Plate Spacing

The purpose of this investigation was to characterize local heat transfer coefficients for round, single-phase free liquid jets impinging normally against a flat uniform heat flux surface. The problem parameters investigated were jet Reynolds number Re, nozzle-to-plate spacing z, and jet diameter d. A region of near-constant Nusselt number was observed for the region bounded by 0≤r/d≤0.75, where r is the radial distance from the impingement point. The local Nusselt number profiles exhibited a sharp drop for r/d > 0.75, followed by an inflection and a slower decrease there-after. Increasing the nozzle-to-plate spacing generally decreased the heat transfer slightly. The local Nusselt number characteristics were found to be dependent on nozzle diameter. This was explained by the influence of the free-stream velocity gradient on local heat transfer, as predicted in the classical analysis of infinite jet stagnation flow and heat transfer. Correlations for local and average Nusselt numbers reveal an approximate Nusselt number dependence on Re1/3.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

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