Analysis of buoyancy-aided convection heat transfer from a horizontal cylinder in a vertical duct at low Reynolds number

1990 ◽  
Vol 25 (6) ◽  
pp. 337-343 ◽  
Author(s):  
C. J. Ho ◽  
M. S. Wu ◽  
J. B. Jou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Horizontal Cylinder ◽  
Convection Heat ◽  
Low Reynolds ◽  
Vertical Duct

Numerical Study of Deteriorated Convection Heat Transfer of Supercritical Fluid Flowing Through Vertical Mini Tube at Relatively Low Reynolds Numbers

2018 ◽  
Author(s):  
Chen-Ru Zhao ◽  
Zhen Zhang ◽  
Qian-Feng Liu ◽  
Han-Liang Bo ◽  
Pei-Xue Jiang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Convection Heat ◽  
Flow Acceleration ◽  
Heat Transfer Deterioration ◽  
Low Reynolds

Numerical investigations are performed on the convection heat transfer of supercritical pressure fluid flowing through vertical mini tube with inner diameter of 0.27 mm and inlet Reynolds number of 1900 under various heat fluxes conditions using low Reynolds number k-ε turbulence models due to LB (Lam and Bremhorst), LS (Launder and Sharma) and V2F (v2-f). The predictions are compared with the corresponding experimentally measured values. The prediction ability of various low Reynolds number k-ε turbulence models under deteriorated heat transfer conditions induced by combinations of buoyancy and flow acceleration effects are evaluated. Results show that all the three models give fairly good predictions of local wall temperature variations in conditions with relatively high inlet Reynolds number. For cases with relatively low inlet Reynolds number, V2F model is able to capture the general trends of deteriorated heat transfer when the heat flux is relatively low. However, the LS and V2F models exaggerate the flow acceleration effect when the heat flux increases, while the LB model produces qualitative predictions, but further improvements are still needed for quantitative prediction. Based on the detailed flow and heat transfer information generated by simulation, a better understanding of the mechanism of heat transfer deterioration is obtained. Results show that the redistribution of flow field induced by the buoyancy and flow acceleration effects are main factors leading to the heat transfer deterioration.

Performance of a variety of low Reynolds number turbulence models applied to mixed convection heat transfer to air flowing upwards in a vertical tube

2004 ◽  
Vol 218 (11) ◽  
pp. 1361-1372 ◽  
Author(s):  
W S Kim ◽  
J D Jackson ◽  
S He ◽  
J Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Vertical Tube ◽  
Convection Heat ◽  
Mixed Convection Heat Transfer ◽  
Low Reynolds

The study reported here is concerned with mixed convection heat transfer to air flowing upwards in a vertical tube. Computational simulations of experiments from a recent investigation have been performed using an ‘in-house’ code which was written specifically for variable-property, developing, buoyancy-influenced flow and heat transfer in a vertical passage. The code incorporates a selection of two-equation, low Reynolds number turbulence models. The objective of the study was to evaluate the models in terms of their capability of reproducing the effects on turbulent heat transfer of non-uniformity of fluid properties and buoyancy. Direct comparisons have been made between results from the experimental investigation and those obtained by computational modelling for a range of conditions. The trends of impairment and enhancement of heat transfer owing to the influence of buoyancy found in the experiments were captured to some extent in the simulations using each of the models. However, none reproduced observed behaviour correctly over the entire range of buoyancy influence.

scholarly journals THE EFFECT OF VIBRATION ON NATURAL CONVECTION HEAT TRANSFER IN AN ENCLOSED SQUARE CAVITY

2020 ◽  
Vol 20 (4) ◽  
pp. 282-307
Author(s):  
Baydaa Khalil Khudhair ◽  
Adel Mahmood Salh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Thermal Convection ◽  
Low Reynolds Number ◽  
Differential Forms ◽  
Convection Heat Transfer ◽  
Simple Algorithm ◽  
Square Enclosure ◽  
Low Reynolds

  A numerical investigation has been implemented to elucidate the effect of vertical and horizontal vibration at normal gravity on natural convection in a square enclosure filled with air at Rayleigh number 7×107 and 4× 108. The enclosure was comprised of two vertical and opposed surfaces (the right hot and the left cold) while the two other surfaces are adiabatic. The two-dimensional, low-Reynolds number k ? ???? turbulence model is applied to enable it to cope with low Reynolds number flows. By transforming the equation of (continuity, Navier-Stokes and energy) using finite volume method from differential forms to algebraic forms using SIMPLE algorithm with hybrid scheme dealing with the time term are adopted to solve the governing equations. A computer program in Fortran 90 was built to carry on the numerical solution. Three cases were studied in this work, case I(reaches to steady state and then begins the effect of vibration at each frequency), caseII and caseIII(begin the effect of vibration from the transient at ascending and descending frequencies respectively).After the validity of the present code by comparing results with these of previous study for similar conditions, solutions have been obtained for Prandtle number of 0.7, aspect ratio (A=1). In the high Rayleih number case (Ra=4×108), the gravitional thermal convection dominates, and the vibration motion does not enhances the heat transfer remarkably. In contrast, in low Rayleigh (Ra=7×107), the vibration thermal convection is dominant, and the vibration enhaces the heat transfer rate significantly. The effect of vertical directional vibration is more powerful in caseII(ascending frequency), when the horizontal directional vibration more effective in case III(descending frequency).  

Transient Heat Transfer From a Horizontal Cylinder in the Low-Reynolds-Number Flow of Helium Gas

2002 ◽  
Author(s):  
Qiusheng Liu ◽  
Katsuya Fukuda ◽  
Koichi Hata
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Heat Input ◽  
Low Reynolds Number ◽  
Horizontal Cylinder ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Helium Gas ◽  
Low Reynolds

The knowledge of forced convection transient heat transfer at various periods of exponentially increasing heat input to a heater is important as a database for understanding the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity. In this study, the transient heat transfer coefficients for Helium gas flowing perpendicular to a horizontal cylinder were measured in the low-Reynolds-number region. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponentially increasing heat input of Q0exp(t/τ). It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ over around 1 s, and it becomes higher for the period of τ shorter than about 1 s. The transient heat transfer shows less dependent on the gas flowing velocity when the period becomes very short. Based on the experimental data, the ratio of transient heat transfer to the quasi-steady-state one was correlated as a function of Reynolds number of the gas flow and the non-dimensional period of increasing heat input. For the non-dimensional period larger than about 300, the transient heat transfer approaches the steady-state one, and shows no dependence on the Reynolds number.

Enhanced Forced Convection Heat Transfer From a Cylinder Using Permeable Fins

2003 ◽  
Vol 125 (5) ◽  
pp. 804-811 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Cross Flow ◽  
Horizontal Cylinder ◽  
Convection Heat ◽  
Transfer Rates ◽  
Forced Convection Heat Transfer ◽  
Nusselt Numbers

The problem of cross-flow forced convection heat transfer from a horizontal cylinder with multiple, equally spaced, high conductivity permeable fins on its outer surface was investigated numerically. The heat transfer characteristics of a cylinder with permeable versus solid fins were studied for several combinations of number of fins and fin height over the range of Reynolds number (5–200). Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Reynolds number and fin height but tended to decrease with number of fins. This ratio was as high as 4.35 at Reynolds number of 150 and a single fin with a nondimensional height of 3.0. The use of 1–2 permeable fins resulted in much higher Nusselt number values than when using up to 18 solid fins. Such an arrangement has other benefits such as a considerable reduction in weight and cost.

Laminar Mixed Convection of Large-Prandtl-Number Nanofluids in Horizontal Tube: Experiment, Correlation, and Criterion

2012 ◽  
Author(s):  
Wei Li ◽  
Si-Pu Guo ◽  
Zhao-Zan Feng ◽  
Zhao-Yan Zhang ◽  
Ze-Cong Fang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Prandtl Number ◽  
Single Phase ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Forced Flow ◽  
Convection Heat

This paper describes an experimental investigation into combined forced and natural convection heat transfer for large-Prandtl-number nanofluids flow in a horizontal tube at low Reynolds number (9 < Re < 450). By the inclusion of nanoparticles, the contribution of natural convection to the overall convective heat transfer can be either deteriorated under the same heat flux or enhanced under a given Grashof number. The huge increasing of the viscosity and Prandtl number were turned out to be the major reason for the observed deterioration and enhancement, respectively. Moreover, the measured heat transfer behavior of nanofluids was illustrated to be in good agreement with the single-phase-based evaluation. However, the experimental data obtained could not be totally reconciled with existing correlations, which relate mainly to specific pure liquids or relatively higher Reynolds number. Therefore, new correlations have been derived by using single-phase fluid approach. These correlations fit our data to within ± 10 percent and also agree with the data in literature quite well. Such results verify that nanofluids can be treated as a homogeneous mixture with effective thermophysical properties. In addition, the new correlations grasp the essence of natural convection and can reduce to both normal forced convection and pure natural convection equations at limiting cases. Whether a flow can be treated as pure forced flow or not (i.e., natural convection effects cannot be neglected) is a crucial problem remains to be determined for the assessment of performance of nanofluids in low-Reynolds-number convection heat transfer application. Generally, the boundary curve function involves the variable parameter of forced main flow (Graetz number) and natural secondary flow (Rayleigh number), constituting a criterion suitable for defining transition of forced flow to mixed flow.

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