Role of Random Roughness on Thermal Performance of Micro-Fins

2005 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Technical Conference ◽  
Electronic Systems ◽  
Cross Sectional ◽  
Random Roughness ◽  
Surface Areas ◽  
Isotropic Distribution ◽  
Developed Surface

Heat transfer in rough circular cylinder microfins is studied and a novel analytical model is developed. Surface roughness is assumed to posses a Gaussian isotropic distribution. It is shown that, as a result of roughness, both cross-sectional and surface areas are increased. As a result, an enhancement is observed in the heat transfer rate and thus the thermal performance of microfins. The present model can be implemented to analyze other geometries such as rectangular and tapered microfins.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Convective Heat Transfer of Laminar Single-Phase Flow in Randomly Rough Microtubes

2005 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Single Phase ◽  
Phase Flow ◽  
Wall Roughness ◽  
Single Phase Flow ◽  
Cross Sectional ◽  
Surface Areas

Convective heat transfer of laminar, single-phase flow in rough microtubes is studied. Wall roughness and slope are assumed to possess Gaussian, isotropic distributions. Fractal concepts are used to model the rough microtube. It is shown that due to the existence of wall roughness, both cross-sectional and inside surface areas are increased. A new concept is defined as a figure of merit for assessing thermal performance of rough microtubes. As a result of increasing roughness, an enhancement is observed in the thermal performance of microtubes. The present model can be extended to analyze other geometries such as rectangular and trapezoidal microchannels.

Effect of Conjugate Heat Transfer on MEMS-Based Thermal Shear Stress Sensor

2005 ◽  
Author(s):  
Jianghui Chao ◽  
Wei Shyy ◽  
Siddharth S. Thakur ◽  
Mark Sheplak ◽  
Renwei Mei
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Conjugate Heat Transfer ◽  
Stress Measurement ◽  
State Of The Art ◽  
Technical Conference ◽  
Flow Structures ◽  
Thermal Conductivity Ratio ◽  
Electronic Systems ◽  
Physical Mechanisms

The effect of conjugate heat transfer resulting from a Micro-electromechanical Systems (MEMS)-based thermal shear stress is investigated. Due to the length scale disparity and large solid-fluid thermal conductivity ratio, a two-level computation is used to examine the relevant physical mechanisms and their influences on wall shear stress. The substantial variations in transport properties between the fluid and solid phases and their interplay in regard to heat transfer and near-wall fluid flow structures are investigated. It is demonstrated that for the state-of-the-art sensor design, the buoyancy effect can noticeably affect the accuracy of the shear stress measurement.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Role of Random Roughness on Thermal Performance of Microfins

2007 ◽  
Vol 21 (1) ◽  
pp. 153-157 ◽  
Author(s):  
Majid Bahrami ◽  
M. Michael Yovanovich ◽  
J. Richard Culham
Keyword(s):  
Thermal Performance ◽  
Random Roughness

Thermo-hydraulic assessment of non-Newtonian MWCNT nanofluid flows inside microchannels with different cross-sections

2021 ◽  
pp. 095440622110560
Author(s):  
AR Ramezan ◽  
A Ahmadpour ◽  
MR Hajmohammadi
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Thermal Performance ◽  
Cross Sections ◽  
Volume Fraction ◽  
Thermal Conditions ◽  
Geometrical Shape ◽  
Newtonian Viscosity ◽  
Two Phase ◽  
Cross Sectional

In the present study, the convective heat transfer of MWCNT/water nanofluid was investigated along microchannels with different cross-sectional geometries. This class of carbon-based nanofluid exhibited a notable non-Newtonian shear-thinning behavior, which made them suitable for different heat transfer applications. A two-phase mixture model with a well-tuned non-Newtonian viscosity function was adapted. The effects of the volume fraction of nanoparticles, Reynolds number, and the geometrical shape of the cross-section were examined on the pressure drop and heat transfer rate across various microchannels. The obtained results showed that the microchannel cross-section geometry had a significant effect on the thermal performance of MWCNT/water nanofluids under certain thermal conditions. Moreover, it was deduced that for all Reynolds numbers and nanoparticle volume fractions considered, the flattened geometry exhibited the most superior thermal performance, which is around 19.03% larger than the circle geometry at Re = 1000 and volume fraction of 2%.

scholarly journals Experimental implementation of thermal enhancement performance of air heat exchanger’s pipes utilizing unconventional turbulator

2021 ◽  
pp. 35-44
Author(s):  
Ali Abdulwahab Ismaeel ◽  
Nassr Fadhil Hussein ◽  
Kadhim H. Suffer ◽  
Zuradzman M Razlan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Heated Surface ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Practical Implementation ◽  
Cross Sectional

Heat exchangers are widely used in industry, however, raising their performance are important for the variety of applications. Consequently, efficiency improvement associated with low production cost is considered in this experimental work. The current study aims to enhance the rate of heat transfer in pipe-type heat exchangers experimentally by using a novel nozzle as a turbulator. The cross-sectional shape of the nozzle is hexagonal, and the diameter ratio DR is equal to 0.5. Constant heat flux was maintained in the vicinity of the section of the test tube, while the working fluid was pumped into the open system at six discrete Reynolds number values ranging from 6000 to 19500. To investigate the effect of distance among the pieces, three turbulators with different numbers were assigned and named as (N=4, 5 and 6). The results indicated an increase of 172 %, 194 % and 216 % of the heat transfer rate for cases 4, 5 and 6 respectively comparing to the benchmark tube. On the other hand, the friction factor values increased remarkably due to the inserting of turbulators by about of 722.9 % for N=4, 823.9 % for N=5 and 886.7 % for N=6 compared to a plain tube case. Moreover, it has been established that with the insertion of 6 pieces two enhancements was observed; heat transfer rate and thermal performance, where, thermal performance of all cases exceeds unity (maximum thermal performance of 1.62 has been obtained by inserting 6 pieces of hexagonal nozzles turbulators). A comparison with another types of vortex generators shows the gap between the turbulator and heated surface offers a solution for problems occurred in the pipes of heat exchanger. The study therefore suggests a wider practical implementation of the turbulators

Heat Transfer in Porous Graphite Foams

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Brian E. Thompson
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Pressure Loss ◽  
Average Diameter ◽  
Cross Sectional ◽  
Pressure Losses ◽  
Porous Graphite ◽  
Order Of Magnitude ◽  
Measured Pressure

Measured values of heat transfer and pressure loss are presented for a variety of porous graphite foams in subsonic turbulent airflow. These foams were developed over the last decade to find combinations of high conductivity, porosity, strength, and low density suitable for application to rapid cooling of electronics and to corrosionless heat-exchangers. Measured maxima in the thermal performance that is the ratio of heat transfer to pressure loss, were correlated the pore structure obtained from scanning electron microscopy, to show a linear dependence of thermal performance on the average diameter of interpore windows representative of the cross-sectional area through which cooling air flows. For the same heat transfer, measured pressure losses were reduced by over two orders of magnitude by increasing pore and window diameters. However, the best thermal performance of porous graphite foams that were strong enough for industrial application, had measured pressure losses that were more than an order of magnitude greater than losses in conventional finned heat exchangers.

Novel Process Techniques to Reduce Voids in Solder Thermal Interface Materials Used for Flip-Chip Package Applications

2005 ◽  
Author(s):  
M. Montano ◽  
J. Garcia ◽  
W. Shi ◽  
M. T. Reiter ◽  
U. Vadakkan ◽  
...  
Keyword(s):  
Process Parameters ◽  
Thermal Performance ◽  
Flip Chip ◽  
Technical Conference ◽  
Thermal Interface Material ◽  
Electronic Systems ◽  
Thermal Interface ◽  
Cure Time ◽  
Materials Used ◽  
The Impact

In the present study, the thermal performance of flip chip electronics packages was evaluated by characterizing the amount of voiding present in the Solder Thermal Interface Material (STIM) which is placed between the die and Integrated Heat Spreader (IHS). The study found that the thermal resistance, Rjc (resistance between the Si die and IHS), is dependent upon the amount of voiding present as well as the location of the voiding in the STIM. The study also described the techniques to reduce the STIM voids in flip chip packages and identified the key process parameters to improve the thermal performance. The process parameters varied in this study consisted of STIM thickness, dwell time and temperature, flux weight, and many others. A detailed DOE and statistical analysis were carried out to determine the impact of the parameters mentioned above toward reducing the quantity of voids in the STIM. The analysis showed that for the packages under consideration, the primary process parameters that affect the STIM voiding are cure time, flux weight and TIM thickness.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

scholarly journals Spray Cooling Trajectory Angle Impact Upon Heat Flux Using a Straight Finned Enhanced Surface

2005 ◽  
Author(s):  
Eric A. Silk ◽  
Jungho Kim ◽  
Ken Kiger
Keyword(s):  
Heat Flux ◽  
Flat Surface ◽  
Spray Cooling ◽  
Technical Conference ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Electronic Systems ◽  
Cross Sectional ◽  
Enhanced Surface ◽  
Trajectory Angle

Experiments were conducted to study the effects of spray trajectory angles on heat flux for flat and enhanced surface spray cooling. The surface enhancement consisted of straight fins machined on the top surface of a copper heater block. Spray cooling curves were obtained with the straight fin surface aligned both parallel (axial) and perpendicular (transverse) to the spray axis. Measurements were also obtained on a flat surface heater block for comparison purposes. Each copper block had a cross-sectional area of 2.0 cm2. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) conditions. Results show that the highest CHF in all cases was attained for a trajectory angle of 30° from the surface normal. Also, straight finned surfaces can enhance critical heat flux (CHF) as much as 75% (heat flux value of 140 W/cm2) relative to the vertical spray orientation for the analogous flat surface case.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Thermal Performance of the Realistic Leading Edge Cooling Passage of a Turbine Blade

2018 ◽  
Author(s):  
Inhwan Song ◽  
Changmin Son ◽  
Jangsik Yang ◽  
Changyong Lee ◽  
Kidon Lee
Keyword(s):  
Heat Transfer ◽  
Experimental Model ◽  
Thermal Performance ◽  
Leading Edge ◽  
Surface Heat ◽  
Test Model ◽  
Cross Sectional ◽  
Friction Factors ◽  
Rib Turbulators ◽  
Cooling Passage

The present study focuses on evaluating the thermal performance of the realistic leading edge cooling passage of a turbine blade, experimentally. The detailed heat transfer distributions and pressure loss of the cooling passage are measured with and without rib turbulators for direct comparison. The experimental model is representing the realistic leading edge cooling passage, which has a converging duct with triangular cross sectional shape. Therefore, the aspect ratio and the cross sectional area of the triangular passage vary significantly along the coolant flow direction. A Perspex test model is designed at 1.3 times large scale to meet Reynolds number similarity. The test model is installed with 45-degree rib turbulators at constant space-to-height ratio of P/e = 10. The experiments are carried out at the Reynolds numbers of 20,000, 40,000 and 80,000. The transient heat transfer test technique using thermochromic liquid crystals (TLCs) was applied to measure the detailed surface heat transfer distributions. The local mixed bulk temperatures (Tmb) are defined using the air thermocouples positioned in the centerline along the cooling passage. The static pressures are measured from the pressure taps machined as a part of the test model so that friction factors of the ribbed cooling passage are also evaluated. The friction factors are influenced by the characteristics of 3 dimensional converging duct of the experimental model. The full surface heat transfer coefficients, friction factors, and overall thermal performance of the cooling passage are reported for the comparison with the other cooling configurations.

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