Combined Free and Forced Convection in a Horizontal Circular Tube

1966 ◽  
Vol 88 (2) ◽  
pp. 147-152 ◽  
Author(s):  
S. T. McComas ◽  
E. R. G. Eckert
Keyword(s):  
Free Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Forced Flow ◽  
Appreciable Effect ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Grashof Number ◽  
Free And Forced Convection ◽  
Flow Heat

The effect of free convection on laminar forced flow heat transfer in a horizontal uniformly heated tube was investigated. The Grashof number was varied from 1000 down to the order of one, the low Grashof number runs agreeing with the prediction for pure forced convection within ±8 percent. The effect of the secondary flow created by free convection was observed as a decrease in the wall to bulk fluid temperature difference required to transfer heat as compared to the pure forced flow case in the region far from the tube inlet. This effect was found to increase as the ratio of Grashof number to Reynolds numbers increased. No appreciable effect of free convection was found in the thermal development region.

An Interferometric Study of Combined Free and Forced Convection in a Horizontal Isothermal Tube

1981 ◽  
Vol 103 (2) ◽  
pp. 249-256 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk
Keyword(s):  
Nusselt Number ◽  
Free Convection ◽  
Forced Convection ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Free And Forced Convection

A Mach-Zehnder interferometer was employed to determine the three-dimensional temperature field, and the circumferential and average Nusselt numbers for laminar flow of air in the entrance region of an isothermal horizontal tube where the velocity and the temperature profiles were developing simultaneously. The influence of free convection due to buoyancy on forced convection heat transfer was investigated. The Reynolds numbers ranged from 120 to 1200, the Grashof numbers ranged from 0.8 × 104 to 8.7 × 104, and the ratio L/D was varied from 6 to 46. The free convection increases, substantially, the average Nusselt number, by up to a factor of 2.0 from the analytical predictions, which account for forced convection only, near the tube inlet. Far from the tube inlet the free convection tends to decrease the average Nusselt number below the analytical predictions.

Combining Forced and Free Convective Equations to Represent Combined Heat-Transfer Coefficients for a Horizontal Cylinder

1971 ◽  
Vol 93 (2) ◽  
pp. 247-248 ◽  
Author(s):  
Thomas W. Jackson ◽  
Howard H. Yen
Keyword(s):  
Free Convection ◽  
Forced Convection ◽  
Horizontal Cylinder ◽  
Forced Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Simplified Method ◽  
Analytical Correlation ◽  
Free And Forced Convection ◽  
Simple Systems

An analytical correlation of superposed free and forced convection for air for a horizontal cylinder in which the forced convection and free convection forces act in the same direction is considered. A simplified method by which the ordinary formulas for forced convection and for free convection can be used together to give the Nusselt number is presented. The method proposed herein can easily be modified to work for other combinations of free and forced flow systems. The method, therefore, may have wide application because standard formulas for simple systems are easily combined to obtain formulas which are valid for complicated systems.

Forced Convection Heat Transfer From a Cylinder in Carbon Dioxide Near the Thermodynamic Critical Point

1971 ◽  
Vol 93 (3) ◽  
pp. 290-296 ◽  
Author(s):  
J. R. Green ◽  
E. G. Hauptmann
Keyword(s):  
Heat Transfer ◽  
Critical Temperature ◽  
Forced Convection ◽  
Temperature Difference ◽  
Forced Flow ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Transfer Rates ◽  
Heated Cylinder ◽  
Increasing Temperature

In an attempt to determine the heat transfer rates in forced flow normal to a heated cylinder and to provide some insight into the mechanisms in heat transfer in the critical region, heat transfer rates have been measured for both free and forced flow of supercritical carbon dioxide normal to a horizontal heated cylinder. The 0.006-in-dia cylinder was held at various constant temperatures by a feedback circuit. The effects of bulk fluid temperature, bulk fluid pressure, and surface temperature were studied for a range of bulk fluid temperatures and pressures from 0.8 to 1.4 times the critical temperature and pressure, and free-stream velocities from 0 to 3 fps. The temperature difference between the heated cylinder and the bulk fluid was varied from 1 to 300 deg F. Several photographs of the flow field are presented. In a supercritical fluid the heat transfer rate increases smoothly and monotonically with increasing temperature difference, increasing velocity, and increasing pressure. In fluid with the bulk temperature below the pseudo-critical temperature the heat transfer coefficient shows large peaks when the cylinder temperature is near the pseudo-critical temperature. The heat transfer coefficient decreases with increasing temperature difference when the bulk fluid temperature is above the pseudo-critical temperature. Supercritical forced convection does not exhibit the characteristic maximum in heat transfer rate shown in forced-flow nucleate boiling. Heat transfer rates at larger temperature differences are very similar in forced-flow film boiling and supercritical forced-flow heat transfer. With this horizontal constant-temperature cylinder, no “bubble-like” or “boiling-like” mechanisms of heat transfer were observed in supercritical free or forced convection.

Influence of free convection on the diffusion current to a sphere in a laminar forced flow regime

1985 ◽  
Vol 50 (12) ◽  
pp. 2697-2714
Author(s):  
Arnošt Kimla ◽  
Jiří Míčka
Keyword(s):  
Asymptotic Expansion ◽  
Free Convection ◽  
Boundary Value Problem ◽  
Concentration Gradient ◽  
Empirical Formula ◽  
Convective Diffusion ◽  
Forced Flow ◽  
Diffusion Current ◽  
Wide Range ◽  
Free And Forced Convection

The formulation and solution of a boundary value problem is presented, describing the influence of the free convective diffusion on the forced one to a sphere for a wide range of Rayleigh, Ra, and Peclet, Pe, numbers. It is assumed that both the free and forced convection are oriented in the same sense. Numerical results obtained by the method of finite differences were approximated by an empirical formula based on an analytically derived asymptotic expansion for Pe → ∞. The concentration gradient at the surface and the total diffusion current calculated from the empirical formula agree with those obtained from the numerical solution within the limits of the estimated errors.

Effects of Free Convection and Axial Conduction on Forced-Convection Heat Transfer Inside a Vertical Channel at Low Peclet Numbers

1984 ◽  
Vol 106 (2) ◽  
pp. 297-303 ◽  
Author(s):  
L. C. Chow ◽  
S. R. Husain ◽  
A. Campo
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Reynolds Numbers ◽  
Convection Heat ◽  
Constant Property ◽  
Axial Conduction ◽  
Forced Convection Heat Transfer

A numerical investigation was conducted to study the simultaneous effects of free convection and axial conduction on forced-convection heat transfer inside a vertical channel at low Peclet numbers. Insulated entry and exit lengths were provided in order to assess the effect of upstream and downstream energy penetration due to axial conduction. The fluid enters the channel with a parabolic velocity and uniform temperature profiles. A constant-property (except for the buoyancy term), steady-state case was assumed for the analysis. Results were categorized into two main groups, the first being the case where the channel walls were hotter than the entering fluid (heating), and the second being the reverse of the first (cooling). For each group, heat transfer between the fluid and the walls were given as functions of the Grashof, Peclet, and Reynolds numbers.

Turbulent Flow Characteristics Over Offset Wall Confined Columns in a Channel at Low Reynolds Numbers

2018 ◽  
Author(s):  
Kira Toxopeus ◽  
Kamran Siddiqui
Keyword(s):  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Turbulent Energy ◽  
Narrow Channel ◽  
Thermal Regulation ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Mean Flow ◽  
Bulk Fluid ◽  
Flow Characterization

The current study is focused on the flow through offset, wall confined vertical inserts in a channel. The columns are intended to act as the thermal storage media, which continuously exchange heat with the channel fluid to regulate it thermally. These columns could, for example, be filled with a phase change material (PCM) for passive thermal regulation, or have hot or cold fluid pumped through them for active thermal regulation. The current study has two parts: (1) the flow characterization without heat transfer, and (2) flow characterization during thermal exchange with a PCM used for regulation of bulk fluid temperature. The work presented here is focused only on the first part of the study. The experiments were conducted in a narrow channel, with water as the working fluid. Two geometries of the vertical columns (circular and square) and two offset lengths were considered. For each configuration, experiments were conducted at Reynolds numbers of 20, 50 and 90 (based of the column’s characteristic length). Particle image velocimetry was used to measure the two-dimensional velocity field in a horizontal plane at multiple regions of interest along the length of the channel to characterize the flow passing over columns. The results indicate vortex shedding at the two higher Reynolds numbers. The generation, magnitude and decay rate of turbulent energy is shown to have an offset dependency at Re = 90, but a column shape dependency at Re = 50. The mean flow has a shape dependency due to the difference in separation point over the square and circular columns.

Pseudoboiling Heat Transfer to Supercritical Pressure Water in Smooth and Ribbed Tubes

1970 ◽  
Vol 92 (3) ◽  
pp. 490-497 ◽  
Author(s):  
J. W. Ackerman
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heated Surface ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Pressure Water ◽  
Supercritical Pressure Water

Investigations of heat transfer to supercritical pressure fluids have been going on for some time, and correlations have been developed for both free and forced-convection conditions. In these investigations, unpredictable heat transfer performance has sometimes been observed when the pseudocritical temperature of the fluid is between the temperature of the bulk fluid and that of the heated surface. The unusual performance has been attributed to many causes, but one for which more evidence is being collected is that of a pseudofilm-boiling process similar to film boiling which occurs at subcritical pressures. This paper, which is an extension of work reported earlier on forced-convection heat transfer to supercritical pressure water, presents experimental evidence which suggests that a pseudofilm-boiling phenomenon can occur in smooth-bore tubes. During the period from 1963–1966, tubes with ID’s from 0.37 to 0.96 in. were tested at pressures from 3300–6000 psia and at heat fluxes and mass velocities in the range of interest in steam-generator design. The effects of heat flux, mass velocity, tube diameter, pressure, and bulk fluid temperature on both the occurrence and characteristics of pseudofilm boiling are discussed. Results of a second series of tests conducted in 1967, which show that ribbed tubes suppress pseudofilm boiling at supercritical pressure much like they do film boiling at subcritical pressures, are also discussed.

scholarly journals Skin-friction for unsteady free convection MHD flow between two heated vertical parallel plates

2006 ◽  
Vol 33 (4) ◽  
pp. 259-280 ◽  
Author(s):  
Gopal Singha ◽  
P.N. Deka
Keyword(s):  
Free Convection ◽  
Skin Friction ◽  
Mhd Flow ◽  
Reynolds Numbers ◽  
Magnetic Reynolds Number ◽  
Convection Flow ◽  
Fluid Temperature ◽  
Parallel Plates ◽  
Electrically Conducting ◽  
Induced Field

Unsteady viscous incompressible free convection flow of an electrically conducting fluid between two heated vertical parallel plates is considered in the presence of a uniform magnetic field applied transversely to the flow. The induce field along the lines of motion varies transversely to the flow and the fluid temperature changing with time. An analytical solution for velocity, induced field and the temperature distributions are obtained for small and large magnetic Reynolds numbers. The skin-friction at the two plates is obtained. Velocity distribution, induced field and skin-friction are plotted against the distance from the plates. It has been observed that with the increase in Rm, the magnetic Reynolds number, at constant M, the Hartmann number, leads to an increase in the skin-friction gradually. But with the increase in M, at constant Rm, the skin-friction decreases.

Heat Transfer by Free Convection From a Horizontal Wire to Carbon Dioxide in the Critical Region

1968 ◽  
Vol 90 (1) ◽  
pp. 51-55 ◽  
Author(s):  
R. J. Goldstein ◽  
Win Aung
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Free Convection ◽  
Critical Region ◽  
Convection Heat Transfer ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Free Convection Heat ◽  
Temperature And Pressure ◽  
Convection Correlation

The free-convection heat transfer from a 0.015-in-dia horizontal platinum wire to carbon dioxide in its critical region is experimentally investigated. The bulk fluid temperature and pressure are varied from 48 deg F to 136 deg F and 1000 psia to 1300 psia, respectively. Wire temperatures up to 1600 deg F are used. The results do not show the sharp rise in the heat flux curves that has been reported in a recent investigation. From the present measurements it appears that the usual free-convection correlation can be used even near the critical state, providing the properties are suitably evaluated.

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