Analysis of combined free and forced convection film boiling. Part I: Forced and free convection regions

AIChE Journal ◽  
1986 ◽  
Vol 32 (1) ◽  
pp. 142-145 ◽  
Author(s):  
Akira Nakayama ◽  
Hitoshi Koyama
Keyword(s):  
Free Convection ◽  
Forced Convection ◽  
Film Boiling ◽  
Free And Forced Convection

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.

Instantaneous Measurement of Heat Transfer From an Oscillating Wire in Free Convection

1970 ◽  
Vol 92 (3) ◽  
pp. 439-445 ◽  
Author(s):  
B. H. Thrasher ◽  
W. J. Schaetzle
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Free Convection ◽  
Forced Convection ◽  
Internal Resistance ◽  
Appreciable Amount ◽  
Significant Difference ◽  
Experimental Apparatus ◽  
Free And Forced Convection ◽  
The Wire

The instantaneous heat transfer properties are measured as a function of time for an oscillating wire (20 to 40 Hz) in still air. The wire is oscillated by thermal contractions and expansions which match the natural frequency based on wire mass and tension. The temperature variation results from the internal resistance heating of an alternating current. The wire temperature and velocity are measured as a function of time by photocells. This eliminates any instrumentation interference with the heat transfer. The results are plotted as a function of instantaneous and average Reynolds’ number. The oscillatory heat transfer data are divided into two regimes of free and forced convection by the critical Reynolds number. Oscillatory heat transfer rates are smaller for forced convection and greater for free convection than those for steady state conditions recommended by McAdams [2] for the respective regimes. No significant difference is found in the heat transfer for oscillations in the vertical and horizontal planes. Due to the time variation of the variables an appreciable amount of emphasis is placed on the experimental apparatus and the recording of data. The recorded data is basically corrected by assuming first order linear systems.

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.

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.

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