Numerical Simulation of Steady State Heat Transfer in a Microchannel With Obstruction

2007 ◽  
Author(s):  
Phaninder Injeti ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Average Nusselt Number ◽  
Isothermal Condition ◽  
Fabrication Process ◽  
Two Dimensional ◽  
Micro Electro Mechanical Systems ◽  
R 134A ◽  
Steady State Heat Transfer

Effects of obstructions on the heat transfer in a microtube and a two-dimensional microchannel were investigated. The obstructions normally arise during the fabrication process on the inner surface of the microtube or microchannel. Various shapes and sizes of the obstruction were considered. The shapes that were modeled were rectangular, triangular, and semicircular obstructions. Calculations were done for incompressible flow of a Newtonian fluid with developing momentum and thermal boundary layers. Equations governing the conservation of mass, momentum and energy were solved for an isothermal condition at the wall. Comparison with no obstruction case was made. It was found that for microtubes, the local Nusselt number increases significantly at the obstruction whereas the average Nusselt number for the whole tube comes out somewhat lower. For two-dimensional microchannels, both local Nusselt number at the obstruction as well as average Nusselt number for the entire tube came out to be higher. The working fluids that were investigated were water and refrigerant R-134a. The results presented in the paper demonstrates that in microchannels and microtubes that are widely used in micro electro mechanical systems (MEMS), small defects in the fabrication process may lead to large changes in local as well as global performance of the device.

An Experimental Investigation of Forced Convection Heat Transfer From an Isothermal V-Shaped Plate

2010 ◽  
Author(s):  
Tooraj Yousefi ◽  
Saeed Ebrahimi ◽  
Masood Bigharaz ◽  
Sajjad Mahmoodi Nezhad
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Plate Spacing ◽  
Internal Surfaces

An experimental study has been carried out to investigate heat transfer characteristics on internal surfaces of a V-shaped plate exposed to a slot jet impingement of air. A square-edged nozzle is mounted parallel with V-shaped plate axis and jet flow impinges on the bottom of the V-shaped plate. The study is focused on Rayleigh number 159000, angle of V-shaped plate ranging from 22.5 to 45 degree, low Reynolds numbers ranging from 29.05 to 60.41, and slot-to-(V-shaped plate) spacing from 17 to 21 of the slot width. A Mach-Zehnder interferometer is used for measurement of local Nusselt number on the V-shaped plate. It is observed that the local Nusselt number and average Nusselt number decrease with increasing the jet spacing and increase with increasing the Reynolds number. Also the local Nusselt number and average nusselt number increase with rising the angle of V-shaped plate.

Conjugate Heat Transfer Study of a Two-Dimensional Laminar Incompressible Wall Jet Over a Backward-Facing Step

2006 ◽  
Vol 129 (2) ◽  
pp. 220-231 ◽  
Author(s):  
P. Rajesh Kanna ◽  
Manab Kumar Das
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Flow Property ◽  
Wall Jet ◽  
Two Dimensional ◽  
Interface Boundary ◽  
Backward Facing Step ◽  
Transfer Study

Steady-state conjugate heat transfer study of a slab and a fluid is carried out for a two-dimensional laminar incompressible wall jet over a backward-facing step. Unsteady stream function-vorticity formulation is used to solve the governing equation in the fluid region. An explicit expression has been derived for the conjugate interface boundary. The energy equation in the fluid, interface boundary and the conduction equation in the solid are solved simultaneously. The conjugate heat transfer characteristics, Nusselt number are studied with flow property (Re), fluid property (Pr), and solid to fluid conductivity ratio (k). Average Nusselt number is compared with that of the nonconjugate case. As k is increased, average Nusselt number is increased, asymptotically approaching the non-conjugate value.

Natural Convective Heat Transfer From an Unconfined or a Confined Heated Surface

2005 ◽  
Author(s):  
L. K. Liu ◽  
T. W. Lin ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Steady State ◽  
Local Nusselt Number ◽  
Average Nusselt Number ◽  
Heated Surface ◽  
Nusselt Numbers ◽  
Extended Surface ◽  
Extended Surfaces ◽  
State Average

A series of experimental investigations with a stringent measurement method on the natural heat transfer from an unconfined or confined smooth and extended surface have been successfully conducted. From the results, the maximum transient-/steady-state local Nusselt number exists in the region near the edge of the heated smooth or extended surface, and the transient-/ steady-state local Nusselt number decreases along the distance from the surface edge toward the surface center. The transient-/steady-state local and average Nusselt number increases with increasing Grs, H/W or Hes/W. The effects of Grs, H/W and Hes/W on the Nus/Nus,o distribution are not significant; and the Nus/Nus,o distribution can be expressed as a generalized bowl-shaped profile, which is independent of Grs, H/W and Hes/W. By the statistical sensitivity analysis of ANOVA F-test, the steady-state average Nusselt number for unconfined/confined smooth or extended surface is significantly affected by either one of Grs, H/W and Hes/W. Among them, Grs has the most significant effect. Four new correlations of steady-state average Nusselt number in terms of relevant influencing parameters for unconfined/ confined smooth or extended surfaces are proposed, respectively. Furthermore, two normalized steady-state average Nusselt numbers for confined smooth or extended surfaces are proposed, respectively. As compared with the steady-state average Nusselt numbers for unconfined/confined smooth surface, the steady-state heat transfer enhancement for unconfined/confined extended surface can be achieved between 93.99% and 254.65%.

scholarly journals Numerical study of flow and heat transfer in differentially heated enclosures

2014 ◽  
Vol 18 (2) ◽  
pp. 451-463 ◽  
Author(s):  
Byong-Hoon Chang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Two Dimensional ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Heated Air ◽  
Side Walls ◽  
Laminar Natural Convection

Two-dimensional laminar natural convection is studied numerically for differentially heated air-filled rectangular enclosures with adiabatic side walls and aspect ratios of 1, 2, 4 and 8. The inclination angle of the enclosure was varied from 0? to 180?, and the effect of inclination on flow field and heat transfer was investigated over the range 103 ? Ra ? 106. Correlations of average Nusselt number based on the present results are presented for horizontal and vertical cases. Large discrepancies were found among published results.

FREE CONVECTION FROM A HORIZONTAL HEATED CYLINDER LOCATED BELOW A CEILING

1999 ◽  
Vol 23 (1A) ◽  
pp. 19-35 ◽  
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.

Mixed Convection in Cooling of a Surface by Two-Dimensional Confined Slot Jet Impingement

2003 ◽  
Author(s):  
Dipankar Sahoo ◽  
M. A. R. Sharif
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Transfer Process ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Heat Transfer Process ◽  
Two Dimensional ◽  
Hot Surface

The flow and heat transfer characteristics in the cooling of a heated surface by impinging confined jets have been investigated numerically through the steady state solution of laminar two-dimensional Navier-Stokes and energy equations. The principal objective of this study is to investigate the effect of buoyancy on the associated heat transfer process. Numerical computations are done for vertically downward directed two-dimensional confined slot jets impinging on a hot isothermal surface at the bottom. The computed flow patterns and isotherms for various domain aspect ratios and for a range of jet exit Reynolds numbers (100–500) and Richardson numbers (0–10) are analyzed to understand the heat transfer phenomena. The local and average Nusselt numbers at the hot surface for various conditions are compared. It is observed that for a given domain aspect ratio and Richardson number, the average Nusselt number at the hot surface increases with increasing jet exit Reynolds number. On the other hand, for a given aspect ratio and Reynolds number the average Nusselt number does not change significantly with Richardson number indicating that the buoyancy effects are not very significant on the overall heat transfer process for the range of jet Reynolds number considered in this study.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

Forced convection heat transfer study of a blunt-headed cylinder in non-Newtonian power-law fluids

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jaspinder Kaur ◽  
Roderick Melnik ◽  
Anurag Kumar Tiwari
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Power Law ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Total Drag ◽  
Shear Thinning Fluids ◽  
Power Law Fluids

Abstract In this present work, forced convection heat transfer from a heated blunt-headed cylinder in power-law fluids has been investigated numerically over the range of parameters, namely, Reynolds number (Re): 1–40, Prandtl number (Pr): 10–100 and power-law index (n): 0.3–1.8. The results are expressed in terms of local parameters, like streamline, isotherm, pressure coefficient, and local Nusselt number and global parameters, like wake length, drag coefficient, and average Nusselt number. The length of the recirculation zone on the rear side of the cylinder increases with the increasing value of Re and n. The effect of the total drag coefficient acting on the cylinder is seen to be higher at the low value of Re and its effect significant in shear-thinning fluids (n < 1). On the heat transfer aspect, the rate of heat transfer in fluids is increased by increasing the value of Re and Pr. The effect of heat transfer is enhanced in shear-thinning fluids up to ∼ 40% and it impedes it’s to ∼20% shear-thickening fluids. In the end, the numerical results of the total drag coefficient and average Nusselt number (in terms of J H −factor) have been correlated by simple expression to estimate the intermediate value for the new application.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

Investigating the effect of nanoparticles diameter on turbulent flow and heat transfer properties of non-Newtonian carboxymethyl cellulose/CuO fluid in a microtube

2019 ◽  
Vol 29 (5) ◽  
pp. 1699-1723 ◽  
Author(s):  
Ali Rahimi Gheynani ◽  
Omid Ali Akbari ◽  
Majid Zarringhalam ◽  
Gholamreza Ahmadi Sheikh Shabani ◽  
Abdulwahab A. Alnaqi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Electronic Devices ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Vlsi Circuits ◽  
Convection Heat Transfer Coefficient ◽  
Content Type ◽  
Competing Interests

Purpose Although many studies have been conducted on the nanofluid flow in microtubes, this paper, for the first time, aims to investigate the effects of nanoparticle diameter and concentration on the velocity and temperature fields of turbulent non-Newtonian Carboxymethylcellulose (CMC)/copper oxide (CuO) nanofluid in a three-dimensional microtube. Modeling has been done using low- and high-Reynolds turbulent models. CMC/CuO was modeled using power law non-Newtonian model. The authors obtained interesting results, which can be helpful for engineers and researchers that work on cooling of electronic devices such as LED, VLSI circuits and MEMS, as well as similar devices. Design/methodology/approach Present numerical simulation was performed with finite volume method. For obtaining higher accuracy in the numerical solving procedure, second-order upwind discretization and SIMPLEC algorithm were used. For all Reynolds numbers and volume fractions, a maximum residual of 10−6 is considered for saving computer memory usage and the time for the numerical solving procedure. Findings In constant Reynolds number and by decreasing the diameter of nanoparticles, the convection heat transfer coefficient increases. In Reynolds numbers of 2,500, 4,500 and 6,000, using nanoparticles with the diameter of 25 nm compared with 50 nm causes 0.34 per cent enhancement of convection heat transfer coefficient and Nusselt number. Also, in Reynolds number of 2,500, by increasing the concentration of nanoparticles with the diameter of 25 nm from 0.5 to 1 per cent, the average Nusselt number increases by almost 0.1 per cent. Similarly, In Reynolds numbers of 4,500 and 6,000, the average Nusselt number increases by 1.8 per cent. Research limitations/implications The numerical simulation was carried out for three nanoparticle diameters of 25, 50 and 100 nm with three Reynolds numbers of 2,500, 4,500 and 6,000. Constant heat flux is on the channel, and the inlet fluid becomes heated and exists from it. Practical implications The authors obtained interesting results, which can be helpful for engineers and researchers that work on cooling of electronic devices such as LED, VLSI circuits and MEMS, as well as similar devices. Originality/value This manuscript is an original work, has not been published and is not under consideration for publication elsewhere. About the competing interests, the authors declare that they have no competing interests.

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