Optimization of heat-transfer rate into time-periodic two-dimensional Stokes flows

Experimental investigations of the flow and the associated heat transfer were conducted in two-dimensional microchannels in order to test possible size effects on the laws of hydrodynamics and heat transfer and to infer optimal conditions of use from the measurements. The test section was designed to modify easily the channel height e between 1 mm and 0.1 mm. Measurements of the overall friction factor and local Nusselt numbers show that the classical laws of hydrodynamics and heat transfer are verified for e > 0.4 mm. For lower values of e, a significant decrease of the Nusselt number is observed, whereas the Poiseuille number continues to have the conventional value of laminar developed flow. The transition to turbulence is not affected by the channel size. For fixed pressure drop across the channel, a maximum of heat transfer rate density is found for a particular value of e. The corresponding dimensionless optimal spacing and heat transfer rate density are in very good agreement with the predictions of Bejan and Sciubba (1992). This paper is the first time that the optimal spacing between parallel plates is determined experimentally.

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Numerical Simulation of Natural Convection in a Two-Dimensional Enclosure Filled with Nanofluids

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.560-561.1184 ◽

2012 ◽

Vol 560-561 ◽

pp. 1184-1187

Author(s):

Su Fen Zhao ◽

Xin Fang Li

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Heat Transfer Rate ◽

Transfer Process ◽

Transfer Rate ◽

Mass Fraction ◽

Heat Transfer Process ◽

Two Dimensional ◽

Grashof Number ◽

Transfer Properties

The natural convection of nanofluids in a two-dimensional enclosure is numerically simulated with Fluent software. The effect of copper particle concentration and Grashof number on heat transfer properties is investigated. The results indicate that the suspended copper nanoparticles substantially increase the heat transfer rate at any given Grashof number, and the heat transfer rate of the nanofluid increases remarkably with the mass fraction of nanoparticles. For a given initial Grashof number, as the mass fraction increases, the velocity components of nanofluid increase as a result of an increase in the energy transport through the fluid. In addition, the intensity of the streamline increase with the increases of the Grashof number, which indicate the heat transfer properties are enhanced. The heat transfer process is dominant with the heat exchange at low Gr, while the heat transfer process is dominant with the natural convection at high Gr.

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Flow Instabilities and Heat Transfer in Buoyancy Driven Flows of Inelastic Non-Newtonian Fluids in Inclined Rectangular Cavities

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30243 ◽

2010 ◽

Author(s):

Dennis Siginer ◽

Lyes Khezzar

Keyword(s):

Heat Transfer ◽

Prandtl Number ◽

Heat Transfer Rate ◽

Power Law ◽

Transfer Rate ◽

Newtonian Fluids ◽

Two Dimensional ◽

Aspect Ratios ◽

Flow Configurations ◽

Rayleigh Numbers

Steady two-dimensional natural convection in rectangular two dimensional cavities filled with non-Newtonian power law-Boussinesq fluids is numerically investigated. The conservation equations of mass, momentum and energy are solved using the finite volume method for varying inclination angles between 0° and 90° and two cavity height based Rayleigh numbers, Ra = 104 and 105, a Prandtl number of Pr = 102 and two cavity aspect ratios of 1, 4. For the vertical inclination of 90°, computations were performed for two Rayleigh numbers Ra = 104 and 105 and three Prandtl numbers of Pr = 102, 103 and 104. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. A comprehensive comparison between the Newtonian and the non-Newtonian cases is presented based on the dependence of the average Nusselt number Nu on the angle of inclination together with the Rayleigh number, Prandtl number, power law index n and aspect ratio dependent flow configurations which undergo several exchange of stability as the angle of inclination O̸ is gradually increased from the horizontal resulting in a rather sudden drop in the heat transfer rate triggered by the last loss of stability and transition to a single cell configuration. Despite significant differences in the heat transfer rate and flow configurations both Newtonian and non-Newtonian fluids of the power law type exhibit qualitatively similar behavior.

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FREE CONVECTION FROM A HORIZONTAL HEATED CYLINDER LOCATED BELOW A CEILING

Transactions of the Canadian Society for Mechanical Engineering ◽

10.1139/tcsme-1999-0002 ◽

1999 ◽

Vol 23 (1A) ◽

pp. 19-35 ◽

Cited By ~ 1

Author(s):

G.B. Lawrence ◽

G.E. Jardin ◽

D. Naylor ◽

A.D. Machin

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Free Convection ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Average Nusselt Number ◽

Two Dimensional ◽

Number Range ◽

Heated Cylinder ◽

Made In

Steady two-dimensional laminar free convection from a horizontal heated cylinder located beneath a wide ceiling at ambient temperature has been studied. A finite element numerical solution has been obtained for a Prandtl number of Pr = 0.7 and a Rayleigh number range (based on the cylinder diameter) of 102 ≤ Ra ≤ 105. Numerically predicted temperature field and local Nusselt number distributions were compared to experimental measurements made in air using a Mach-Zehnder interferometer. For cylinder- to-ceiling spacings greater than about one diameter, the ceiling was found to have almost no influence on the heat transfer rate from the cylinder. At very close cylinder-to-ceiling spacings, the average Nusselt number increased substantially because of conduction effects. However, for 103 ≤ Ra ≤ 105, the effect of the ceiling on the numerically predicted overall heat transfer rate was less than ±10%, provided the cylinder was more than about one quarter of a diameter away form the ceiling.

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Unsteady Heat Transfer Measurements on a Rotating Gas Turbine Blade

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/90-gt-175 ◽

1990 ◽

Cited By ~ 8

Author(s):

M. A. Hilditch ◽

R. W. Ainsworth

Keyword(s):

Heat Transfer ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Turbine Blades ◽

Digital Signal ◽

Two Dimensional ◽

Unsteady Heat Transfer ◽

Frequency Spectra ◽

Dimensional Simulation ◽

Transfer Signal

Heat transfer measurements made on the rotor blade of a full stage model turbine operating at engine representative conditions are presented. The measurement technique of mounting thin film heat transfer gauges on enamel coated turbine blades enables the heat transfer rate to be measured across a frequency range of d.c. to 100kHz. The output is amplified using electronic circuits housed inside the shaft before transmission through a slipring and digital signal processing routines are used to calculate the heat transfer rate. A calibration experiment in which the gauge is pulsed with a laser beam is described in detail. The results are compared with data from a previous two-dimensional simulation of wake-passing flow on the midheight section of the same blade. The mean heat transfer rate recorded in the two experiments shows reasonable agreement. Fluctuations in the unsteady heat transfer signal at NGV passing frequency are seen at the same locations in data from both experiments, however the magnitude of the fluctuations seen on the rotor are much smaller than those recorded in the two-dimensional simulation. Frequency spectra and correlation analysis of heat transfer traces recorded on the rotor are also presented.

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Thermal Analysis and Optimization of Orthotropic Pin Fins: A Closed-Form Analytical Solution

Journal of Heat Transfer ◽

10.1115/1.4000059 ◽

2009 ◽

Vol 132 (3) ◽

Cited By ~ 14

Author(s):

Syed M. Zubair ◽

A. F. M. Arif ◽

Mostafa H. Sharqawy

Keyword(s):

Heat Transfer ◽

Boundary Condition ◽

Temperature Distribution ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Two Dimensional ◽

Fin Efficiency ◽

Pin Fin ◽

Special Cases ◽

Pin Fins

Analytical solutions for temperature distribution, heat transfer rate, and fin efficiency and fin effectiveness are derived and presented for orthotropic two-dimensional pin fins subject to convective-tip boundary condition. The generalized results are presented and discussed in terms of dimensionless variables such as radial and axial Biot numbers (Bir,Biz), fin aspect ratio, L/R, and radial-to-axial conductivity ratio k∗. Several special cases are derived from the general solution, which includes the insulated-tip boundary condition. It is also demonstrated that the classical temperature distribution and heat transfer rate from the two-dimensional isotropic pin fin introduced earlier in literature can easily be recovered from the general solutions presented in this paper. Furthermore, dimensionless optimization results are presented for orthotropic pin fins that can help to solve many natural and forced convection pin fin problems.

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Natural Convective Heat Transfer From an Inclined Narrow Isothermal Flat Plate

Heat Transfer: Volume 1 ◽

10.1115/ht2008-56190 ◽

2008 ◽

Cited By ~ 4

Author(s):

Patrick H. Oosthuizen ◽

Abdulrahim Kalendar

Keyword(s):

Heat Transfer ◽

Prandtl Number ◽

Flat Plate ◽

Convective Heat Transfer ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Two Dimensional ◽

Two Dimensional Flow ◽

Adiabatic Surface ◽

Plate Width

Natural convective heat transfer rate from an isothermal flat plate inclined at moderate angles to the vertical has been numerically studied. When the plate is wide compared to its height the flow can be adequately modeled by assuming two-dimensional flow. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be considerably greater than that predicted by these two-dimensional flow results. The heat transfer from a narrow isothermal plate embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the heated plate and inclined at an angle to the vertical has been numerically considered. Results for both positive and negative inclination angles have been numerically determined here. Attention was restricted to results for a Prandtl number of 0.7; this being approximately the value existing in the application that originally motivated this study. It has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in dimensionless form. The solution was obtained using a commercial finite element method based code, FIDAP. The solution has the Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Results have been obtained for Rayleigh numbers between 103 and 107 for ratios of the plate width to the plate height of between 0.3 and 1.5 and for angles of inclination between +45° and −45°.

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