Forced Convective Heat Transfer for Partially-Confined Compact PPF Heat Sinks With Top-Bypass Effect

2005 ◽  
Author(s):  
T. Y. Wu ◽  
M. P. Wang ◽  
J. T. Horng ◽  
S. F. Chang ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Steady State ◽  
Convective Heat ◽  
Average Nusselt Number ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Nusselt Numbers ◽  
Transient Period ◽  
State Average

A series of experimental investigations with a stringent measurement method on the study of the fluid flow and heat transfer for confined compact heat sinks in forced convection have been successfully conducted. From the results, the thermal capacity of the heat sink and the convective heat dissipation play the major roles for dominating the transient thermal behavior in the beginning of power-on transient period; while, the convective heat dissipation finally becomes the solely dominating term at the end of power-on transient period. The transient/steady-state local and average Nusselt numbers increase with increasing Grs, H/Hc ratio or Re. As compared with the steady-state average Nusselt number for non-compact heat sink (Fin-Al/ Base-Al), the steady-state heat transfer enhancement for compact heat sinks (Fin-Al/Base-Al) is 185.74%. Furthermore, a new correlation of steady-state average Nusselt number in terms of relevant influencing parameters for confined compact PPF heat sinks in forced convection is proposed. As compared with two existing correlations of steady-state average Nusselt numbers for unconfined and confined non-compact PPF heat sinks, the heat transfer enhancements for the present confined compact PPF heat sinks of H/Hc = 0.47 are 423.29% and 219.93%, respectively.

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%.

Convective Heat Transfer From Confined Heated Surfaces With Slot Jet Impingement

2005 ◽  
Author(s):  
L. K. Liu ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Steady State ◽  
Convective Heat ◽  
Local Nusselt Number ◽  
Jet Impingement ◽  
Experimental Investigations ◽  
Surface Center ◽  
Nusselt Numbers ◽  
Extended Surface

A series of experimental investigations with a stringent measurement method on the transient-/steady-state heat transfer behavior for confined smooth surfaces with slot jet impingement have been successfully conducted. From the results, a generalized correlation is proposed to represent the distributions of normalized transient convective heat flux. The highest heat transfer during the transient period occurs at the surface center of confined heated smooth or extended surface. The transient local Nusselt number decreases along the distance from the surface center toward the surface edge. The transient-/steady-state local and average Nusselt numbers are almost independent of Grs, and they are more significantly affected by ReD as compared with H/W. They will increase with increasing ReD. Maximum local and average Nusselt numbers can be found between H/W = 3 and H/W = 5. The effects of Grs and H/W on the dimensionless local Nusselt number distribution are insignificant; and the distribution can be expressed as a generalized bell-shaped profile, which is only dependent of ReD. Finally, a new composite correlation of steady-state average Nusselt number for mixed convection from confined smooth due to slot jet impingement and buoyancy are presented.

scholarly journals Influence of Ambient Temperature on Radiative and Convective Heat Dissipation Ratio in Polymer Heat Sinks

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2286
Author(s):  
Jan Kominek ◽  
Martin Zachar ◽  
Michal Guzej ◽  
Erik Bartuli ◽  
Petr Kotrbacek
Keyword(s):  
Heat Transfer ◽  
Ambient Temperature ◽  
Convective Heat ◽  
Heat Dissipation ◽  
High Surface ◽  
Heat Sinks ◽  
Fourth Power ◽  
Molding Process ◽  
Ambient Temperatures ◽  
University Of Technology

Miniaturization of electronic devices leads to new heat dissipation challenges and traditional cooling methods need to be replaced by new better ones. Polymer heat sinks may, thanks to their unique properties, replace standardly used heat sink materials in certain applications, especially in applications with high ambient temperature. Polymers natively dispose of high surface emissivity in comparison with glossy metals. This high emissivity allows a larger amount of heat to be dissipated to the ambient with the fourth power of its absolute surface temperature. This paper shows the change in radiative and convective heat transfer from polymer heat sinks used in different ambient temperatures. Furthermore, the observed polymer heat sinks have differently oriented graphite filler caused by their molding process differences, therefore their thermal conductivity anisotropies and overall cooling efficiencies also differ. Furthermore, it is also shown that a high radiative heat transfer leads to minimizing these cooling efficiency differences between these polymer heat sinks of the same geometry. The measurements were conducted at HEATLAB, Brno University of Technology.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
M. R. Salem ◽  
K. M. Elshazly ◽  
R. Y. Sakr ◽  
R. K. Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Average Nusselt Number ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Fanning Friction Factor ◽  
Coil Heat

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

Localized Heat Transfer in Buoyancy Driven Convection in Open Cavities

2006 ◽  
Vol 129 (2) ◽  
pp. 167-178 ◽  
Author(s):  
Wilson Terrell ◽  
Ty A. Newell
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Ambient Air ◽  
Nusselt Numbers ◽  
Transient Nature ◽  
Inclination Angles ◽  
Buoyancy Driven Convection ◽  
The Heat Transfer Coefficient

Background. An experimental study of buoyancy driven convection heat transfer in an open cavity was conducted. Method of Approach. Test cavities were constructed with calorimeter plates bonded to Styrofoam insulation. The inside of the cavities was heated and then exposed to ambient air for approximately thirty minutes. Different size cavities were examined at inclination angles of 0, 45, and 90deg. The heat transfer coefficient was determined from an energy balance on each calorimeter plate. The cavity’s plate temperatures varied spatially due to the transient nature of the tests. A parameter describing the nonisothermal cavity wall temperature variation was defined in order to compare with isothermal cavity heat transfer results. Results. Results showed that the cavity Nusselt number, based on a cavity averaged temperature, was insensitive to the transient development of nonisothermal conditions within the cavity. Comparison of cavity-average Nusselt number for the current study, where the Rayleigh number ranged from 5×106 to 2×108, to data from the literature showed good agreement. Cavity-average Nusselt number relations for inclination angles of 0, 45, and 90deg in the form of NuH,cav=CRa1∕3 resulted in coefficients of 0.091, 0.105, 0.093, respectively. The 45deg inclination angle orientation yielded the largest Nusselt numbers, which was similar to previous literature results. Trends in the local plate Nusselt numbers were examined and found similar to data from the literature.

Effect of Vertical Baffle Installation on Forced Convective Heat Transfer in Channel Having a Backward Facing Step

2013 ◽  
Vol 388 ◽  
pp. 169-175 ◽  
Author(s):  
Amirhossein Heshmati ◽  
Hussein A. Mohammed ◽  
Mohammad Parsazadeh ◽  
Farshid Fathinia ◽  
Mazlan A. Wahid ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Convective Heat Transfer ◽  
Skin Friction ◽  
Convective Heat ◽  
Average Nusselt Number ◽  
Skin Friction Coefficient ◽  
Expansion Ratio ◽  
Forced Convective Heat Transfer

In this study, forced convective heat transfer is considered in channel over a backward facing step having a baffle on the top wall. Four different geometries with different expansion ratios and different type of baffles are numerically investigated. The study clearly shows that the geometry with expansion ratio 2 and solid baffle has the highest Nusselt number compared to other geometries. Considering both Nusselt number and skin friction coefficient for all four geometries clearly illustrated an increase in average Nusselt number by increasing the expansion ratio. This study clearly shows that mounting a slotted baffle at the top wall instead of a solid baffle caused a decline in average Nusselt number. It is also found that for geometry with expansion ratio of 3 and a slotted baffle on the top of the channel, skin friction coefficient in both bottom wall and step wall has its minimal compared to other geometries.

Optimization of Heat Transfer Rate in the Rectangular Microchannel of Different Aspect Ratios With Constant Cross Sectional Area

2008 ◽  
Author(s):  
F. Kowsary ◽  
N. Noroozi ◽  
M. Rezaei Barmi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Cross Sectional Area ◽  
Heat Sinks ◽  
Sectional Area ◽  
Cross Sectional ◽  
Aspect Ratios

The increased power dissipation and reduced dimensions of microelectronics devices have emphasized the need for highly efficient compact cooling technologies. Microchannel heat sinks are of particular interest due to the very high rates of heat transfer they enable in conjunction with greatly reduced heat sink length scales and coolant mass flow rate. Therefore, in the present work, optimization of laminar convective heat transfer in the microchannel heat sinks is investigated for uniform heat flux and different cross sectional areas of different aspect ratios. Three-dimensional numerical simulations of general form of energy equation were performed to predict Nusselt number in the laminar flow regime. Using these results, an optimum forced convective heat transfer coefficient was computed for several cross sectional areas and Reynolds numbers, utilizing the univariable search method. Different aspect ratios have different influences on Nusselt number in thermally developing and fully developed regions for different cross sectional areas and Reynolds numbers. There exists an optimum Nusselt number for each Reynolds number and cross sectional area by varying aspect ratio. Thus, optimized state is computed and related graphs are presented.

Transient Thermal Management Using a Confined Jet Impingement of Liquid Ammonia

2003 ◽  
Author(s):  
Ryan M. Mead ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Average Nusselt Number ◽  
Liquid Ammonia ◽  
Plate Thickness ◽  
Average Heat Transfer Coefficient ◽  
Steady State Condition ◽  
Average Heat

This paper introduces the results of transient heat transfer involving a jet of liquid ammonia perpendicularly on a solid substrate of finite thickness containing discrete electronic sources on the opposite surface. The jet was confined by using a cover plate to prevent any evaporation or loss of ammonia during the heat transfer process. The numerical simulation considered both the solid and fluid regions as a conjugate problem. The equations solved in the liquid region included the conservation of mass, conservation of energy, and conservation of momentum. For the solid region, only the heat conduction equation was solved. Computed results included the temperature distribution, local and average heat transfer coefficient, and local and average Nusselt number at the solid-fluid interface. Some of the parameters such as the jet velocity, plate thickness, and plate material were altered to examine the effect that they had on the problem. It was found that the average heat transfer coefficient and a average Nusselt number were high at the initial stages of the transient process and decreased steadily with time until it reached the steady condition. As the plate thickness decreased, and as the jet velocity increased, it was observed that the time it took to reach the steady state condition declined. The time it took to reach steady state condition did not change significantly for different plate materials. However, it did change noticeably for different plate thickness and different Reynolds number.

Microchannel Optimization for Heat Dissipation From a Solid Substrate

2008 ◽  
Author(s):  
C. B. Sobhan ◽  
P. S. Anoop ◽  
Kuriyan Arimboor ◽  
Thomas Abraham ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Thermal Resistance ◽  
Computational Model ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Dissipation ◽  
Three Dimensional ◽  
Solid Substrate ◽  
Nusselt Numbers

A computational model was developed to analyze and optimize the convective heat transfer for water flowing through rectangular microchannels fabricated in a silicon substrate. A baseline case was analyzed by solving the nondimensional governing equations. Using a quasi three-dimensional computational model, the velocity and temperature distributions were obtained and the numerical results were then used to determine the overall dimensionless thermal resistance for the convective heat transfer from the substrate to the fluid. To validate the numerical model, the average Nusselt numbers as determined by the numerical model were compared with experimental results available in the literature, for channels with comparable hydraulic diameters. The procedure for arriving at an optimum geometric configuration and arrangement of microchannels on the substrate, subject to given design constraints, so that the thermal resistance is at a minimum, is described and demonstrated using the computational model.

scholarly journals Free convection of a nanofluid in a square cavity with a heat source on the bottom wall and partially cooled from sides

2014 ◽  
Vol 18 (suppl.2) ◽  
pp. 283-300 ◽  
Author(s):  
Mostafa Mahmoodi ◽  
Arani Abbasian ◽  
Sebdani Mazrouei ◽  
Saeed Nazari ◽  
Mohammad Akbari
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Heat Sinks ◽  
Square Cavity ◽  
Flow And Heat Transfer ◽  
Rayleigh Numbers

The problem of free convection fluid flow and heat transfer in a square cavity with a flush mounted heat source on its bottom wall and two heat sinks on its vertical side walls has been investigated numerically. Via changing the location of the heat sinks, six different arrangements have been generated. The cavity was filled with Cu-water nanofluid. The governing equations were discretized using the finite volume method and SIMPLER algorithm. Using the developed code, a parametric study was undertaken, and effects of Rayleigh number, arrangements of the heat sinks and volume fraction of the nanoparticles on fluid flow and heat transfer inside the cavity were investigated. Also for the middle-middle heat sinks arrangement, capability of five different water based nanofluids on enhancement of the rate of heat transfer was examined and compared. From the obtained results it was found that the average Nusselt number, for all six different arrangements of the heat sinks, was an increasing function of the Rayleigh number and the volume fraction of the nanoparticles. Also it was found that at high Rayleigh numbers, maximum and minimum average Nusselt number occurred for middle-middle and top-bottom arrangement, respectively. Moreover it was found that for the middle-middle arrangement, at high Rayleigh numbers, maximum and minimum rate of heat transfer was obtained by Cu-water and TiO2-water nanofluids respectively.

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