Laminar forced convective slip flow in a microduct with a sinusoidally varying heat flux in axial direction

Aydın, Orhan; Avcı, Mete

doi:10.1016/j.ijheatmasstransfer.2015.05.056

Cited by 17 publications

(7 citation statements)

References 39 publications

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“…Recently, Altun et al [22] worked on a transient conjugated heat transfer problem in thick walled pipes, under time-wise periodically changing outer wall temperature boundary condition. Similar problems under different boundary conditions were taken into consideration by [23][24][25]. The general findings from the above works can be summarized as given below.…”

Section: Introductionmentioning

confidence: 97%

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Transient conjugated heat transfer in thick walled pipes with axially periodic surface temperature in downstream region

Ateş

2019

Sādhanā

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Thermal entrance region transient conjugate heat transfer is investigated involving fluid axial heat conduction for laminar pipe flows. Constant outer wall temperature boundary condition is assumed in the upstream region of a thick walled, two regional pipe. In the downstream region, the outer wall temperature is considered changing spatially in a periodical manner. The problem is solved numerically by a finite difference method. A parametric analysis is conducted in order to determine the effects of Peclet number, wall thickness ratio, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio and axial frequency on heat transfer characteristics. It is seen that, the results are highly dependent on the parameter values and the most effective ones are the Peclet number and the wall thickness ratio. It is observed that heat is transferred towards upstream due to the axial conduction in the wall and in the fluid and with increasing values for high axial frequency. Keywords. Axially periodic temperature; transient conjugate heat transfer; laminar flow in pipes; thick walled pipe.

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Section: Introductionmentioning

confidence: 97%

“…Some numerical solutions have been developed to the problem for thick walled pipes where two-dimensional wall conduction is taken into consideration. Problems having axially changing periodical boundary condition were studied by [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] under various circumstances.…”

Section: Introductionmentioning

confidence: 99%

Transient conjugated heat transfer in thick walled pipes with axially periodic surface temperature in downstream region

Ateş

2019

Sādhanā

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“…The use of microchannel heat sinks belonging to the so-called MFDs (micro-flow devices) ranges from the integrated cooling of small electronic components to much larger assemblies, such as those for HVAC, and the trend seems to keep steadily increasing [1][2][3][4]. Advanced manufacturing techniques, often pioneered in the semiconductor industry, have opened up new possibilities for creating unique structures and channels with varying cross-sections, allowing the miniaturisation of geometries previously restricted to much larger dimensions [1,[5][6][7][8][9]. This, in turn, has led to renewed interest in exploring laminar forced convection through channels of different shapes, as evidenced by numerous research studies [10][11][12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Combined Geometrical Optimisation of a Square Microchannel with Smoothed Corners

Lorenzini,

Suzzi

2024

Energies

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Several engineering systems currently use microchannel heat sinks. In order to increase the performance of these devices, optimisation according to the first and second law of thermodynamics is employed. One way to achieve the goal is to modify the geometry of the cross-section, as is done in this paper for square ducts, having the walls at a uniform temperature which is higher than that of the bulk fluid at the inlet. The effects of both the thermal entry region of the duct and the heat generation due to viscous dissipation are considered. The resulting Graetz–Brinkman problem is solved numerically to obtain the velocity and temperature fields. It is demonstrated that non-negligible viscous heating eventually causes the heat flux to reverse (from fluid to walls), and that, only after this condition is achieved, can the flow become fully developed, which makes the entry region the only useful stretch for real-life applications. The length after which the direction of the heat flux reverses due to viscous heating in the fluid is obtained as a function of the Brinkman number and of the smoothing radius. Optimisation with performance evaluation criteria and entropy generation minimisation was carried out separately, and the results were combined into a single objective function. A comparison with published models highlights how neglecting the entry region and viscous heating yields misleading results. It turns out that smoothing the corners is always profitable in the case of the constrained heated perimeter or area of the cross-section but seldom when the characteristic length or the hydraulic diameter is fixed. With few exceptions, viscous heating amplifies the trends experienced for zero-Brinkman flows. The results are in non-dimensional form, yet they have been obtained starting from plausible dimensional values and are applicable to real-life devices.

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“…All these articles have neglected the effect of axial conduction. In our very recent study [30], we included this effect for the problem of laminar forced slip flow in a microduct with a sinusoidally varying heat flux in an axial direction.…”

Section: Introductionmentioning

confidence: 99%

Analysis of extended micro-Graetz problem in a microtube

Avcı

Aydın

2018

Sādhanā

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In this numerical study, hydrodynamically developed but thermally developing forced convection in a microtube subjected to a step change in the wall heat flux is analysed using a finite-volume method. The slip velocity and temperature jump conditions at the wall and the axial conduction in the fluid are included in the analysis. The combined effects of the Peclet number and the Knudsen number on the local Nusselt numbers as well as on the wall and bulk temperatures are determined in the continuum and slip flow regimes (0 B Kn B 0.1). In the entrance region, large reductions are observed in the Nusselt number with decreasing Peclet number or increasing Knudsen number. The results also show that the thermal length increases with decreasing Peclet number.

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Laminar forced convective slip flow in a microduct with a sinusoidally varying heat flux in axial direction

Cited by 17 publications

References 39 publications

Transient conjugated heat transfer in thick walled pipes with axially periodic surface temperature in downstream region

Transient conjugated heat transfer in thick walled pipes with axially periodic surface temperature in downstream region

Combined Geometrical Optimisation of a Square Microchannel with Smoothed Corners

Analysis of extended micro-Graetz problem in a microtube

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