Experimental Study of a Single Microchannel Flow Under Nonuniform Heat Flux

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Ahmed Eltaweel ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Dissipation ◽  
Hot Spot ◽  
Management Strategies ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Nonuniform Heating ◽  
Maximum Heat ◽  
Microchannel Heat Sinks

Abstract Nonuniform heat fluxes are commonly observed in thermo-electronic devices that require distinct thermal management strategies for effective heat dissipation and robust performance. The limited research available on nonuniform heat fluxes focus mostly on microchannel heat sinks while the fundamental component, i.e., a single microchannel, has received restricted attention. In this work, an experimental setup for the analysis of variable axial heat flux is used to study the heat transfer in a single microchannel with fully developed flow under the effect of different heat flux profiles. Initially, a hot spot at different locations, with a uniform background heat flux, is studied at different Reynolds numbers, while varying the maximum heat fluxes in order to compute the heat transfer in relation to its dependent variables. Measurements of temperature, pressure, and flow rates at a different locations and magnitudes of hot spot heat fluxes are presented, followed by a detailed analysis of heat transfer characteristics of a single microchannel under nonuniform heating. Results showed that upstream hotspots have lower tube temperatures compared to downstream ones with equal amounts of heat fluxes. This finding can be of importance in enhancing microchannel heat sinks effectiveness in reducing maximum wall temperatures for the same amount of heat released, by redistributing spatially fluxes in a descending profile.

Experimental Study of a Single Microchannel Flow Under Non-Uniform Heat Flux

2017 ◽  
Author(s):  
Ahmed Eltaweel ◽  
Abdulla Baobeid ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Dissipation ◽  
Hot Spot ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Uniform Heat Flux ◽  
Maximum Heat ◽  
Uniform Heat ◽  
Microchannel Heat Sinks

Non-uniform heat fluxes are commonly observed in thermo-electronic devices that require distinct thermal management strategies for effective heat dissipation and robust performance. The limited research available on non-uniform heat fluxes focus mostly on microchannel heat sinks while the fundamental component, i.e. a single microchannel, has received restricted attention. In this work, an experimental setup for the analysis of variable axial heat flux is used to study the heat transfer in a single microchannel with fully developed flow under the effect of different heat flux profiles. Initially a hot spot at different locations, with a uniform background heat flux, is studied at different Reynolds numbers while varying the maximum heat fluxes in order to compute the heat transfer in relation to its dependent variables. Measurements of temperature, pressure, and flow rates at a different locations and magnitudes of hot spot heat fluxes are presented, followed by a detailed analysis of heat transfer characteristics of a single microchannel under non-uniform heating. Results showed that upstream hotspots have lower tube temperatures compared to downstream ones with equal amounts of heat fluxes. This finding can be of importance in enhancing microchannel heat sinks effectiveness in reducing maximum wall temperatures for the same amount of heat released, by redistributing spatially fluxes in a descending profile.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

Bubble Injection to Enhance Heat Transfer in Microchannel Heat Sinks

2009 ◽  
Author(s):  
Amy Rachel Betz ◽  
Daniel Attinger
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Single Phase ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Segmented Flow ◽  
Liquid Cooling ◽  
Microchannel Heat Sinks ◽  
Convective Resistance ◽  
Parallel Microchannels

Liquid cooling is an efficient way to remove heat fluxes with magnitude of 1 to 10,000 W/cm2. One limitation of current single-phase microchannel heat sinks is the relatively low Nusselt number, because of laminar flow. In this work, we experimentally investigate how to enhance the Nusselt number in the laminar regime with the periodic injection of non-condensable bubbles in a water-filled array of microchannels in a segmented flow pattern. We designed a polycarbonate heat sink consisting of an array of parallel microchannels with a low ratio of heat to convective resistance, to facilitate the measurement of the Nusselt Number. Our heat transfer and pressure drop measurements are in good agreement with existing correlations, and show that the Nusselt number of a segmented flow is increased by more than a hundred percent over single-phase flow provided the mass velocity is within a given range.

Evaporative Thermal Performance of Vapor Chambers Under Nonuniform Heating Conditions

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Je-Young Chang ◽  
Ravi S. Prasher ◽  
Suzana Prstic ◽  
P. Cheng ◽  
H. B. Ma
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Hot Spots ◽  
Hot Spot ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Nonuniform Heating ◽  
Test Results ◽  
Uniform Heating

This paper reports the test results of vapor chambers using copper post heaters and silicon die heaters. Experiments were conducted to understand the effects of nonuniform heating conditions (hot spots) on the evaporative thermal performance of vapor chambers. In contrast to the copper post heater, which provides ideal heating, a silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The vapor chambers were tested for hot spot heat fluxes as high as 746 W/cm2. The experimental results show that evaporator thermal resistance is not sensitive to nonuniform heat conditions, i.e., it is the same as in the uniform heating case. In addition, a model was developed to predict the effective thickness of a sintered-wick layer saturated with water at the evaporator. The model assumes that the pore sizes in the sintered particle wick layer are distributed nonuniformly. With an increase of heat flux, liquid in the larger size pores are dried out first, followed by drying of smaller size pores. Statistical analysis of the pore size distribution is used to calculate the fraction of the pores that remain saturated with liquid at a given heat flux condition. The model successfully predicts the experimental results of evaporative thermal resistance of vapor chambers for both uniform and nonuniform heat fluxes.

Heat Transfer Enhancement in Microchannels Incorporating Slanted Grooves

2008 ◽  
Author(s):  
Poh-Seng Lee ◽  
Chiang-Juay Teo
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fluid Temperature ◽  
Additional Energy ◽  
Pressure Drops ◽  
Microchannel Heat Sinks ◽  
Significant Temperature

The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques. Microchannel heat sinks have the potential to satisfy these requirements. However, significant temperature variations across the chip persist for conventional single-pass parallel flow microchannel heat sinks since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. To accommodate higher heat fluxes, enhanced microchannel designs are needed. The present work presents an idea to enhance the single-phase convective heat transfer in microchannels. The proposed technique is passive, and does not require additional energy to be expended to enhance the heat transfer. The idea incorporates the generation of a spanwise or secondary flow to enhance mixing and hence decrease fluid temperature gradients across the microchannel. Slanted grooves can be created on the microchannel wall to induce the flow to twist and rotate thus introducing an additional component to the otherwise laminar flow in the microchannel. Numerical results are presented to demonstrate the effectiveness of such an enhanced microchannel heat sink. The heat transfer was found to increase by up to 12% without incurring substantial additional pressure drops.

Enhanced Heat Transfer in Radial Heat Sinks for LED Lamps

2018 ◽  
Author(s):  
Fernando Cano-Banda ◽  
Ana Gallardo-Gutierrez ◽  
Jesus Garcia-Gonzalez ◽  
Abel Hernandez-Guerrero ◽  
Luis Luviano-Ortiz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Output Analysis ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Longitudinal Orientation ◽  
Radial Heat

A radial design of a passive heat sink for cooling LED illumination devices is analyzed numerically in order to identify the geometric shape that promotes better heat dissipation rates. Natural convection with the surrounding is considered during the operation of the heat sink. Due to the fact that natural convection is the main mechanism of heat transfer, the shape of the heat sink has a high influence in the heat dissipated. An analysis of the influence of different parameters of a heat sink is conducted in the presented study. The radial heat sink under analysis consists in a flat disc with rectangular fins on it, and the fins are distributed with a radial longitudinal orientation in a circular row arrangement. The number of rows can vary but there is a constant relation of two times the number of fins between the number of fins in an inner row and the next outer row. In order to find a correct configuration to improve the dissipation of heat, parameters like the number of fins, the length of the fins and the separation between fins are studied. The average Nusselt number and thermal resistance for each geometric configuration are compared. The output analysis provides the best shape for a maximum heat transfer.

scholarly journals Numerical Optimization of a Microchannel Geometry for Nanofluid Flow and Heat Dissipation Assessment

2021 ◽  
Vol 11 (5) ◽  
pp. 2440
Author(s):  
Inês M. Gonçalves ◽  
César Rocha ◽  
Reinaldo R. Souza ◽  
Gonçalo Coutinho ◽  
Jose E. Pereira ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Jet Impingement ◽  
Experimental Tests ◽  
Heat Sinks ◽  
Working Fluid ◽  
Optimized Design ◽  
Nanofluid Flow ◽  
Microchannel Heat Sinks

In this study, a numerical approach was carried out to analyze the effects of different geometries of microchannel heat sinks on the forced convective heat transfer in single-phase flow. The simulations were performed using the commercially available software COMSOLMultiphysics 5.6® (Burlington, MA, USA) and its results were compared with those obtained from experimental tests performed in microchannel heat sinks of polydimethylsiloxane (PDMS). Distilled water was used as the working fluid under the laminar fluid flow regime, with a maximum Reynolds number of 293. Three sets of geometries were investigated: rectangular, triangular and circular. The different configurations were characterized based on the flow orientation, type of collector and number of parallel channels. The main results show that the rectangular shaped collector was the one that led to a greater uniformity in the distribution of the heat transfer in the microchannels. Similar results were also obtained for the circular shape. For the triangular geometry, however, a disturbance in the jet impingement was observed, leading to the least uniformity. The increase in the number of channels also enhanced the uniformity of the flow distribution and, consequently, improved the heat transfer performance, which must be considered to optimize new microchannel heat sink designs. The achieved optimized design for a heat sink, with microchannels for nanofluid flow and a higher heat dissipation rate, comprised a rectangular collector with eight microchannels and vertical placement of the inlet and outlet.

Measurement of Condensation Curves for Dropwise Condensation of Steam at Atmospheric Pressure

1983 ◽  
Vol 105 (3) ◽  
pp. 633-638 ◽  
Author(s):  
I. Tanasawa ◽  
Y. Utaka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Heat Fluxes ◽  
Dropwise Condensation ◽  
Maximum Heat ◽  
Transfer Block ◽  
Peak Heat Flux ◽  
The One ◽  
The Heat Transfer Coefficient

Condensation curves for dropwise condensation of steam at atmospheric pressure were measured for the range of surface subcooling between 0.5 and 180 K using a heat transfer block having a concave spherical condensing surface. The heat transfer coefficient remained constant with the increase of surface subcooling up to about 10 K, and then it decreased. The maximum heat fluxes were found to be between 9.3 and 12.2 MW/m2. Dropwise condensation could be observed at a surface subcooling larger than the one corresponding to the peak heat flux, but shortly the mode of condensation shifted to pseudo-film or on-ice condensation.

Enhanced Pool Boiling With HFE7000 Over Selectively Sintered Microchannels

2017 ◽  
Author(s):  
Travis S. Emery ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Fold Increase ◽  
High Heat ◽  
Heat Fluxes ◽  
Dielectric Fluid ◽  
Maximum Heat ◽  
Maximum Heat Transfer

As the need for efficient thermal management grows, pool boiling’s ability to dissipate high heat fluxes has gained significant interest. The objective of this work was to study the performance of pool boiling at atmospheric pressure using a dielectric fluid, HFE7000. Both plain and enhanced copper surfaces were tested, and these results were then compared to similar testing performed with water and FC-87. The enhanced surfaces utilized microchannels with porous coatings selectively located on different regions of the heat transfer surface. A maximum critical heat flux (CHF) of 41.7 W/cm2 was achieved here, which translated to a 29% CHF increase in comparison to a plain chip. A maximum heat transfer coefficient (HTC) of 104.0 kW/m2°C was also achieved, which translated to a 6-fold increase in HTC when compared to a plain copper chip. More notably, this HTC was achieved at a wall temperature of 38.4 °C. This HTC enhancement was greater than that of water and FC-87 when using the same enhanced surface. The effect of sintering location was found to have a similar effect on CHF with HFE7000 in comparison with water. The effect of microchannel size was shown to have similar effects on CHF when compared with FC-87 and water. From the results found here, it is concluded that the employment of selectively sintered open microchannels with HFE7000 has significant potential for enhanced heat dissipation in electronics cooling applications.

scholarly journals Numerical Research on Thermal Variations along SSF Pin Fins Shaped with SSM Processing

2019 ◽  
Vol 8 (12) ◽  
pp. 504-507
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Stainless Steel ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Pin Fin ◽  
Temperature Distributions ◽  
Pin Fins ◽  
Numerical Research

Fins or heat sinks are meant for boosting heat transfer. Therefore, planned computations remain fortified for examining the impacts of SSF pin fin on thermal dispersal concerning constant thermal value 6 W/cm2 . For that SSF pin fins materials of stainless steel and aluminum are preferred. Usual convective equations are solved to foretell thermal apprehensions. As anticipated, for both the stated SSF pin fins, temperature and heat flux declines for increasing length scales. Additionally, temperature distributions on SSF aluminum pin fin lays beneath SSF stainless steel pin fin. Hence, heat dissipation from SSF aluminum pin fin is relatively higher. Obviously, it may be owing to quite higher thermal conductivity of SSF aluminum pin fin. Consequently, it delivers higher, gregarious and remarkable thermal behaviors. Nevertheless, both simulation forecasts remain analogous with one another.

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