An Experimental Study of Forced Heat Convection in Concentric and Eccentric Annular Channels

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
N. Kline ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Mixed Convection ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Outer Diameter ◽  
Narrow Gap ◽  
Convection Regime ◽  
Annular Channels ◽  
Internal Surfaces

An experimental study of the effect of eccentricity on forced convective heat transfer was conducted for upward flows in vertical, open-ended annular channels with a diameter ratio of 0.61, a length to outer diameter ratio of 18:1, and both internal surfaces heated uniformly. Flows with Reynolds numbers Re = 5450, 10,000, and 27,500 and eccentricities varying from 0 to 0.9 were examined. These results are deemed to be mostly in the forced convection regime with some possible overlap with the mixed convection regime at the lowest Reynolds number considered. This work complements our previous work on natural and mixed convection using the same facility. The effect of eccentricity was not significant at lower eccentricities, but, in highly eccentric cases, the wall temperature in the narrow gap was much higher than in the wide gap and the average heat transfer coefficient was as low as one-fifth of the concentric value. For Re > 10,000, the average Nusselt number for the concentric case was nearly four times higher than the value predicted by the Dittus–Boelter correlation.

Numerical Study of Mixed Convection around a Heated Circular Cylinder

2016 ◽  
Vol 836 ◽  
pp. 85-89
Author(s):  
Vivien S. Djanali ◽  
Ahmad Nurdian Syah ◽  
Syaiful Rizal
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Mixed Convection ◽  
Buoyancy Force ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Main Flow ◽  
Heat Transfer Characteristics ◽  
Convection Regime ◽  
Heated Cylinder

Wake and heat transfer characteristics around a heated circular cylinder were studied numerically in this paper. Heat transfer from a heated cylinder to the freestream flow was in mixed convection regime, with the free convection-bouyancy driven flow in opposite direction to the forced convection-main flow. Numerical simulations were performed for three Reynolds numbers of 100, 135 and 200, with the Richardson (Ri = Gr/Re2) numbers varied from 0 to 1. Results showed that buoyancy force significantly altered wake formation behind the heated cylinder, further resulted in increasing drag and decreasing Nusselt number.

An Experimental Study of Mixed Convection in Vertical, Open-Ended, Concentric and Eccentric Annular Channels

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
L. Maudou ◽  
G. H. Choueiri ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Turbulent Flows ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Annular Channel ◽  
High Eccentricity ◽  
Convection Regime ◽  
Annular Channels

The effect of eccentricity on heat transfer in upward flow in a vertical, open-ended, annular channel with a diameter ratio of 0.61, an aspect ratio of 18:1, and both internal surfaces heated uniformly has been investigated experimentally. Results have been reported for eccentricities ranging from the concentric case to the near-contact case and three inlet bulk Reynolds numbers, equal approximately to 1500, 2800, and 5700. This work complements our recently reported experimental results on natural convection in the same facility. The present results are deemed to be largely in the mixed convection regime with some overlap with the forced convection regime and likely to include cases with laminar, transitional, and turbulent flows in at least a part of the test section. Small eccentricity had an essentially negligible effect on the overall heat transfer rate, but high eccentricity reduced the average heat transfer rate by up to 60%. High eccentricity also resulted in wall temperatures in the narrow gap region that were much higher than those in the open channel. The concentric-case Nusselt number was higher than the Dittus–Boelter prediction, whereas the highly eccentric-case Nusselt number was significantly lower than that.

scholarly journals EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

2017 ◽  
Vol 60 (4) ◽  
pp. 352-366 ◽  
Author(s):  
A. B. Sukhotskii ◽  
G. S. Sidorik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Convection Flow ◽  
Single Bundle ◽  
Single Row

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

Buoyancy Effect on Heat Transfer in 5×5 Rod Bundles

2017 ◽  
Author(s):  
Da Liu ◽  
Fujun Gan ◽  
Chaozhu Zhang ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Buoyancy Force ◽  
Reynold Number ◽  
Low Flow ◽  
Buoyancy Effect ◽  
Rod Bundles ◽  
Convection Regime ◽  
Dc Power

Experiments of heat transfer at low flow rate are performed in a 5×5 square arrayed rod bundles. The diameter of the rod is 10mm with a pitch of 13.3mm, length of the test section is about 3 meters. Inlet Reynold number ranges from 2000 to 30000, Bo * ranges from 4×10−6 to 5×10−3. The rods are heated using a DC power, the heat flux ranges from 30 to 300 kW/m2. The experiment is aimed to investigate the buoyancy effect of mixed convection in rod bundles. The experimental data shows that similar with mixed convection in circular channels, buoyancy force has great effect on heat transfer at mixed convection regime in rod bundles. But the buoyancy effect appears at higher Bo* conditions. The spacer effect have also been investigated at both turbulent forced convection regime and mixed convection regime. The reconstruction of heat transfer downstream of spacers is different at different flow regimes, a reasonable explanation was provided.

Numerical and Experimental Study of Flow and Convective Heat Transfer on a Rotor of a Discoidal Machine with Eccentric Impinging Jet

2019 ◽  
pp. 1-29
Author(s):  
Chadia Haidar ◽  
Rachid Boutarfa ◽  
Mohamed Sennoune ◽  
Souad Harmand
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Steady State ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Impinging Jet ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Air Jet

This work focuses on the numerical and experimental study of convective heat transfer in a rotor of a discoidal the machine with an eccentric impinging jet. Convective heat transfers are determined experimentally in steady state on the surface of a single rotating disk. The experimental technique is based on the use of infrared thermography to access surface temperature measurement, and on the numerical resolution of the energy equation in steady-state, to evaluate local convective coefficients. The results from the numerical simulation are compared with heat transfer experiments for rotational Reynolds numbers between 2.38×105 and 5.44×105 and for the jet's Reynolds numbers ranging from 16.5×103 to 49.6 ×103. A good agreement between the two approaches was obtained in the case of a single rotating disk, which confirms us in the choice of our numerical model. On the other hand, a numerical study of the flow and convective heat transfer in the case of an unconfined rotor-stator system with an eccentric air jet impinging and for a dimensionless spacing G=0.02, was carried out. The results obtained revealed the presence of different heat transfer zones dominated either by rotation only, by the air flow only or by the dynamics of the rotation flow superimposed on that of the air flow. Critical radii on the rotor surface have been identified

Experimental Study of Mixed Convection Shell-and-Coil Heat Exchanger

2008 ◽  
Author(s):  
Nasser Ghorbani Mianroudi ◽  
Mofid Gorji ◽  
Hessam Taherian
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Mixed Convection ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Equivalent Diameter ◽  
Coil Diameter ◽  
Laminar And Turbulent Flow ◽  
Helical Coils ◽  
Coil Heat Exchanger

In this study the mixed convection heat transfer in a coil-in-shell heat exchanger for various Reynolds numbers, various tube-to-coil diameter ratios and different dimensionless coil pitch was experimentally investigated. The experiments were conducted for both laminar and turbulent flow inside coil. Effects of coil pitch and tube diameters on shell-side heat transfer coefficient of the heat exchanger were studied. Different characteristic lengths were used in various Nusselt number calculations to determine which length best fits the data and several equations were proposed. The particular difference in this study in comparison with the other similar studies was the boundary conditions for the helical coils. The results indicate that the equivalent diameter of shell is the best characteristic length.

Effects of Various Physical and Numerical Parameters on Heat Transfer in Vertical Passages at Relatively Low Heat Loading

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Amir Keshmiri
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Reynolds Numbers ◽  
Boussinesq Approximation ◽  
Low Flow ◽  
Physical Parameters ◽  
Pipe Length ◽  
Viscosity Models ◽  
Heat Loading ◽  
Fluid Properties

The present work is concerned with the modeling of buoyancy-modified mixed convection flows, such flows being representative of low-flow-rate flows in the cores of Gas-cooled Reactors. Three different eddy viscosity models (EVMs) are examined using the in-house code, “CONVERT.” All fluid properties are assumed to be constant, and buoyancy is accounted for within the Boussinesq approximation. Comparison is made against experimental measurements and the direct numerical simulations (DNS). The effects of three physical parameters including the heat loading, Reynolds number, and pipe length on heat transfer have been examined. It is found that by increasing the heat loading, three thermal-hydraulic regimes of “early onset of mixed convection,” “laminarization,” and “recovery” were present. At different Reynolds numbers, the three thermal-hydraulic regimes are also evident. The k-ε model of Launder and Sharma was found to be in the closest agreement with consistently normalized DNS results for the ratio of mixed-to-forced convection Nusselt number (Nu/Nu0). It was also shown that for the “laminarization” case, the pipe length should be at least “500× diameter” in order to reach a fully developed solution. In addition, the effects of two numerical parameters namely buoyancy production and Yap length-scale correction terms have also been investigated and their effects were found to be negligible on heat transfer and friction coefficient in ascending flows.

Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed and V-Shaped Angled Ribs

1991 ◽  
Author(s):  
J. C. Han ◽  
Y. M. Zhang ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Ratio ◽  
Side Wall ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Wall Heat Flux ◽  
Wall Heat Transfer ◽  
Square Channel ◽  
Heat Transfer Augmentation

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1 - q″r1/q″s = q″r2/q″s = 1; Case 2 - q″r1/q″s = q″r2/q″s = 3; Case 3 - q″r1/q″s = q″r2/q″s = 6; Case 4 - q″r1/q″s = 6 and q″r2/q″s = 4; Case 5 - q″r1/q″s = q″r2/q″s = ∞ and Case 6 - q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90° rib, 60° parallel rib, 60° crossed rib, and 60° ∨-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5 - q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed-side-wall heat transfer augmentation than the four-wall uniform heating (Case 1 - q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60° ∨-shaped rib and 60° parallel rib perform better than the 60° crossed rib and 90° rib, regardless of wall heat flux ratio and Reynolds number.

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