Heat transfer enhancement by external magnetic field for paramagnetic laminar pipe flow

Abstract Ferrofluid channel flows have been used for many non-invasive flow manipulation applications, including drug-delivery, heat transfer enhancement, mixing enhancement, etc. Heat transfer enhancement is one of the most coveted outcomes from novel cooling systems employed for electronic cooling. While using Ferrofluids for heat transfer enhancement, the external magnetic field usually induces Kelvin Body Force, which causes the ferrofluid to swirl or ‘mix’. This mixing process causes extra convection over what is induced through fluid inertia and is responsible for heat transfer enhancement. In order to understand the phenomenon of heat transfer enhancement, it would be logical to view it from the perspective of mixing enhancement. Moreover, channel flows are most common in liquid cooling of electronics equipment, and hence such a fundamental understanding of synergies between mixing and heat transfer enhancement can help pose design rules for advanced cooling configuration for electronics cooling. In this work, a Ferrofluid channel flow is analyzed in the presence of an external magnetic field. A 2-D 90° bend channel ferrofluid flow is considered, with a significant length scale of 0.01 m, where two external current-carrying wires provide an external magnetic field. An external inward heat flux of 1000 W/m2 is applied on the walls of the channel. The channel flow is studied numerically by varying different parameters relating to the external magnetic field and flow conditions. The ferrofluid used is considered magnetite based on water as the carrier fluid, and the properties of which are modeled using appropriate mixture models for nanofluids. The mixing induced in the flow is characterized by using two different mixing numbers based on the flow velocity. This type of characterization is analogous to characterizing flow turbulence. The heat transfer enhancement is characterized using Nusselt numbers. These non-dimensional numbers (mixing) are studied in congruence with the Nusselt number to understand the relationship between the mixing and heat transfer and draw comparative inferences with flow conditions without heat transfer enhancement. Finally, conclusions are drawn between the mixing & heat transfer intensification at local and global levels and choosing the apposite mixing numbers to characterize heat transfer enhancement.

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Numerical analysis of magnetic field effects on the heat transfer enhancement in ferrofluids for a parabolic trough solar collector

Renewable Energy ◽

10.1016/j.renene.2018.11.015 ◽

2019 ◽

Vol 134 ◽

pp. 54-63 ◽

Cited By ~ 22

Author(s):

Ali Khosravi ◽

Mohammad Malekan ◽

Mamdouh E.H. Assad

Keyword(s):

Magnetic Field ◽

Heat Transfer ◽

Numerical Analysis ◽

Heat Transfer Enhancement ◽

Solar Collector ◽

Magnetic Field Effects ◽

Transfer Enhancement ◽

Parabolic Trough ◽

Field Effects ◽

Parabolic Trough Solar Collector

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Asymmetrical Thermal Boundary Condition Influence on the Flow Structure and Heat Transfer Performance of Paramagnetic Fluid-Forced Convection in the Strong Magnetic Field

Fluids ◽

10.3390/fluids5040246 ◽

2020 ◽

Vol 5 (4) ◽

pp. 246

Author(s):

Lukasz Pleskacz ◽

Elzbieta Fornalik-Wajs ◽

Sebastian Gurgul

Keyword(s):

Magnetic Field ◽

Heat Transfer ◽

Boundary Condition ◽

Heat Transfer Enhancement ◽

Strong Magnetic Field ◽

Flow Structure ◽

Thermal Boundary Condition ◽

Solid Particles ◽

Transfer Enhancement ◽

Dimensionless Numbers

Continuous interest in space journeys opens the research fields, which might be useful in non-terrestrial conditions. Due to the lack of the gravitational force, there will be a need to force the flow for mixing or heat transfer. Strong magnetic field offers the conditions, which can help to obtain the flow. In light of this origin, presented paper discusses the dually modified Graetz-Brinkman problem. The modifications were related to the presence of the magnetic field influencing the flow and asymmetrical thermal boundary condition. Dimensionless numerical analysis was performed, and two dimensionless numbers (magnetic Grashof number and magnetic Richardson number) were defined for paramagnetic fluid flow. The results revealed the heat transfer enhancement due to the strong magnetic field influence accompanied by possible but not essential flow structure modifications. On the other hand, the flow structure changes can be utilized to prevent the solid particles’ sedimentation. The explanation of the heat transfer enhancement including energy budget and vorticity distribution was presented.

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Heat Transfer Enhancement in Turbulent Ribbed-Pipe Flow

Journal of Heat Transfer ◽

10.1115/1.4035712 ◽

2017 ◽

Vol 139 (7) ◽

Cited By ~ 1

Author(s):

Changwoo Kang ◽

Kyung-Soo Yang

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Pipe Flow ◽

Joint Probability ◽

Turbulent Heat Transfer ◽

Immersed Boundary ◽

Turbulent Heat ◽

Transfer Enhancement ◽

Maximum Heat ◽

Maximum Heat Transfer

The present study aims at explaining why heat transfer is enhanced in turbulent ribbed-pipe flow, based on our previous large eddy simulation (LES) database (Kang and Yang, 2016, “Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow,” ASME J. Heat Transfer, 138(4), p. 041901) obtained for Re = 24,000, Pr = 0.71, pitch ratio (PR) = 2, 4, 6, 8, 10, and 18, and blockage ratio (BR) = 0.0625. Here, the bulk velocity and the pipe diameter were used as the velocity and length scales, respectively. The ribs were implemented in the cylindrical coordinate system by means of an immersed boundary method. In particular, we focus on the cases of PR ≥ 4 for which heat transfer turns out to be significantly enhanced. Instantaneous flow fields reveal that the vortices shed from the ribs are entrained into the main recirculating region behind the ribs, inducing velocity fluctuations in the vicinity of the pipe wall. In order to identify the turbulence structures responsible for heat transfer enhancement in turbulent ribbed-pipe flow, various correlations among the fluctuations of temperature and velocity components have been computed and analyzed. The cross-correlation coefficient and joint probability density distributions of velocity and temperature fluctuations, obtained for PR = 10, confirm that temperature fluctuation is highly correlated with velocity-component fluctuation, but which component depends upon the axial location of interest between two neighboring ribs. Furthermore, it was found via the octant analysis performed for the same PR that at the axial point of the maximum heat transfer rate, O3 (cold wallward interaction) and O5 (hot outward interaction) events most contribute to turbulent heat flux and most frequently occur.

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