Combined Natural and Forced Convective Heat Transfer In Spherical Annuli

1984 ◽  
Vol 106 (4) ◽  
pp. 811-816 ◽  
Author(s):  
S. Ramadhyani ◽  
M. Zenouzi ◽  
K. N. Astill
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Outer Sphere ◽  
Reynolds Numbers ◽  
Numerical Work ◽  
Low Reynolds Numbers ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers ◽  
Different Temperatures

This paper presents numerical finite difference solutions of combined natural and forced convective heat transfer in spherical annuli. The flow is assumed to enter the annulus through a port in the bottom of the outer sphere and exit through a diametrically opposite port. The spheres are isothermal and at different temperatures. The governing conservation equations are reduced to dimensionless form and the nondimensional parameters of the problem are identified. The influence of these parameters of the problem are identified. The influence of these parameters on the solution is studied. Details of the flow field and temperature field are presented by means of velocity vector and isotherm maps. Circumferential average and local Nusselt numbers are presented and compared with earlier numerical work in which the effects of natural convection were ignored. It is shown that the buoyancy effects can have a very significant impact on the heat transfer and fluid flow, particularly at low Reynolds numbers.

Free Convection Effects on Laminar Forced Convective Heat Transfer in a Horizontal Isothermal Tube

1982 ◽  
Vol 104 (1) ◽  
pp. 145-152 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Free Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Reynolds Numbers ◽  
Transfer Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers

The influence of free convection due to buoyancy on forced laminar flow of air in the entrance region of a horizontal isothermal tube was investigated. The Graetz numbers ranged form 2.5 to 110.0, 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 up to 46. The average Nusselt numbers based on the log-mean temperature difference, ranged from 2.0 to 25.9. The heat transfer data were correlated according to the influence of free convection which was found to have a significant effect at points close to the entrance to the tube.

scholarly journals Effect of Thermal Creep on Heat Transfer for a Two-Dimensional Microchannel Flow: An Analytical Approach

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Barbaros Çetin
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Slip Flow ◽  
Reynolds Numbers ◽  
Thermal Creep ◽  
Thermal Systems ◽  
Low Reynolds Numbers ◽  
Nusselt Numbers ◽  
Fundamental Understanding

In this paper, velocity profile, temperature profile, and the corresponding Poiseuille and Nusselt numbers for a flow in a microtube and in a slit-channel are derived analytically with an isoflux thermal boundary condition. The flow is assumed to be hydrodynamically and thermally fully developed. The effects of rarefaction, viscous dissipation, axial conduction are included in the analysis. For the implementation of the rarefaction effect, two different second-order slip models (Karniadakis and Deissler model) are used for the slip-flow and temperature-jump boundary conditions together with the thermal creep at the wall. The effect of the thermal creep on the Poiseuille and Nusselt numbers are discussed. The results of the present study are important (i) to gain the fundamental understanding of the effect of thermal creep on convective heat transfer characteristics of a microchannel fluid flow and (ii) for the optimum design of thermal systems which includes convective heat transfer in a microchannel especially operating at low Reynolds numbers.

Study on Forced Convective Heat Transfer of FC-72 in Vertical Small Tubes

2019 ◽  
Author(s):  
Yantao Li ◽  
Yulong Ji ◽  
Katsuya Fukuda ◽  
Qiusheng Liu ◽  
Hongbin Ma
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Inlet Temperature ◽  
Experiment Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers ◽  
Mini Channels ◽  
Heat Transfer Correlations

Abstract In this paper, the forced convective heat transfer of FC-72 was experimentally investigated for various of parameters like velocity, inlet temperature, tube size, and exponential period of heat generation rate. Circular tubes with different inner diameters (1, 1.8 and 2.8 mm) and heated lengths (30–50 mm) were used in this study. The experiment data suggest that the single-phase heat transfer coefficient increases with increasing flow velocity as well as decreasing tube diameter and ratio of heated length to inner diameter. The experiment data were nondimensionalized to study the effect of Reynolds number (Red) on forced convection heat transfer. The results indicate that the relation between Nusselt numbers (Nud) and Red for d = 2.8 mm show the same trend as the conventional correlations. However, the Nud for d = 1 and 1. 8 mm depend on Red in a different manner. The conventional heat transfer correlations are not adequate for prediction of forced convective heat transfer in mini channels. The heat transfer correlations for FC-72 in vertical small tubes with diameters of 1, 1.8 and 2.8 mm were developed separately based on the experiment data. The differences between experimental and predicted Nud are within ±15%.

scholarly journals Experimental Investigation into the Forced Convective Heat Transfer of Aqueous Fe3O4 Nanofluids under Transition Region

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Jie Ma ◽  
Yinchen Xu ◽  
Wenlie Li ◽  
Jiantao Zhao ◽  
Shuping Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Transition Region ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Forced Convective Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Initial Expectation

The forced convective heat transfer (FCHT) properties of nanofluids, made of Fe3O4 nanomaterials and deionized water, are firstly measured by a self-made forced convective heat transfer apparatus. The nanofluid flows through a horizontal copper tube in the transition region with Reynolds numbers in the range of 2500–5000. Some parameters including Reynolds number, axial distance, and mass concentration are also investigated. The preliminary results are firstly presented that the heat transfer coefficients of Fe3O4 nanofluids systematically decrease with increasing concentration of nanoparticles under transition region which contradicts the initial expectation.

Numerical investigation of nanofluid particle migration and convective heat transfer in microchannels using an Eulerian–Lagrangian approach

2019 ◽  
Vol 878 ◽  
pp. 62-97 ◽  
Author(s):  
Omar Z. Sharaf ◽  
Ashraf N. Al-Khateeb ◽  
Dimitrios C. Kyritsis ◽  
Eiyad Abu-Nada
Keyword(s):  
Heat Transfer ◽  
Brownian Motion ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Particle Distribution ◽  
Reynolds Numbers ◽  
Streamwise Direction ◽  
Nanofluid Flow ◽  
Low Reynolds Numbers ◽  
Low Reynolds

An Eulerian–Lagrangian modelling approach was employed in order to investigate the flow field, heat transfer and particle distribution in nanofluid flow in a parallel-plate microchannel, with a focus on relatively low Reynolds numbers ($Re\leqslant 100$). Momentum and thermal interactions between fluid and particle phases were accounted for using a transient two-way coupling algorithm implemented within an in-house code that tracked the simultaneous evolution of the carrier and particulate phases while considering timescale differences between the two phases. The inaccuracy of assuming a homogeneous particle distribution in modelling nanofluid flow in microchannels was established. In particular, shear rate and thermophoresis were found to play a key role in the lateral migration of nanoparticles and in the formation of particle depletion and accumulation regions in the vicinity of the channel walls. At low Reynolds numbers, nanoparticle distribution near the walls was observed to gradually flatten in the streamwise direction. On the other hand, for relatively higher Reynolds numbers, higher particle non-uniformities were observed in the vicinity of the channel walls. Furthermore, it was established that convective heat transfer between channel walls and the bulk fluid can either improve or deteriorate with the addition of nanoparticles, depending on whether the flow exceeded a critical Reynolds number of enhancement. It was also established that Brownian motion and thermophoresis had a major role in nanoparticle deposition on the channel walls. In particular, Brownian motion was the main deposition mechanism for nano-sized particles, whereas due to thermophoresis, nanoparticles were repelled away from channel walls. The result of the competition between the two is that deposition gradually increased along the streamwise direction.

Enhanced Heat Transfer Through the Use of Nanofluids in Forced Convection

2004 ◽  
Author(s):  
Daniel J. Faulkner ◽  
David R. Rector ◽  
Justin J. Davidson ◽  
Reza Shekarriz
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Forced Convection ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Enhanced Heat Transfer ◽  
Low Reynolds Numbers ◽  
Turbulent Flow Regime

Much attention has been paid in recent years to the use of nanoparticle suspensions for enhanced heat transfer. The majority of this work has focused on the thermal conductivity of these nanofluids, which can be as much as 2.5 times higher than that of the plain base fluid. The present work moves beyond measurements of non-flowing liquids, to explore the role that nanofluids can play in enhancing convective heat transfer within microscale channels. A unique pseudo-turbulent flow regime is postulated, which simulates turbulent behavior at very low Reynolds numbers, in what are nominally laminar flows. The resulting fluid mixing has the potential to raise the average convective heat transfer coefficient within the channel. Numerical modeling, using the lattice Boltzmann method, confirms the existence of the pseudo-turbulent flow regime. Finally, experimental results are presented which demonstrate a significant heat transfer enhancement when using nanofluids in forced convection. The current results are especially relevant to microchannel heatsinks, where the low Reynolds numbers impose limitations on the maximum Nusselt number achievable.

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