ArticlePDF Available

Effect of Jet Position on Cooling an Array of Heated Obstacles

Authors:
Hussein M Maghrabie at South Valley University
Hussein M Maghrabie
M. Attalla at South Valley University
M. Attalla
H.E. Fawaz
H.E. Fawaz
H.E. Fawaz
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Mohamad Khalil Khalil at Sohag University
Mohamad Khalil Khalil
Download full-text PDF
Read full-text
Download citation

Abstract

Numerical study of the effect of jet position on cooling process of an array of heated obstacles simulating electronic components has been investigated based on Realizable k-ε model. Jet positions have been changed to impinge each row of obstacles consecutively. The experiments have been achieved at three different values of jet-to-channel Reynolds number ratio, Rej/Rec=1, 2, and 4. In the present study, a comparison between two different cooling processes; cross flow only (CF) and jet impingement with cross flow (JICF) has been achieved. The flow structure, heat transfer characteristics, and the pumping power have been investigated for different jet positions. The results show that the jet position affects significantly the flow structure, as well as the heat transfer characteristics. According to the results of average heat transfer coefficient and the pumping power, the more effective jet position for all values of jet-to-channel Reynolds number ratio (1, 2, and 4) is achieved when the jets impinge the third row of obstacles (JP3).
Content uploaded by Hussein M Maghrabie
Author content
All content in this area was uploaded by Hussein M Maghrabie on Nov 29, 2017
Content may be subject to copyright.
Hussein M. Maghrabie
1
Mem. ASME
Department of Mechanical Engineering,
Faculty of Engineering,
South Valley University,
Al Shoban Al Moslemin Street,
Qena 83521, Egypt
e-mail: Hussein_mag@eng.svu.edu.eg
M. Attalla
Department of Mechanical Engineering,
Faculty of Engineering,
South Valley University,
Al Shoban Al Moslemin Street,
Qena 83521, Egypt
e-mail: moha_attalla@yahoo.com
H. E. Fawaz
Department of Mechanical Engineering,
National Research Centre,
33 El Buhouth Street, Dokki,
Cairo 12311, Egypt
e-mail: ehf20012001@hotmail.com
M. Khalil
Department of Mechanical Engineering,
Faculty of Engineering,
Sohag University,
Shark District,
Sohag 82514, Egypt
e-mail: mohamed_ramadan@eng.sohag.edu.eg
Effect of Jet Position on Cooling
an Array of Heated Obstacles
Numerical study of the effect of jet position (JP) on cooling process of an array of heated
obstacles simulating electronic components has been investigated based on realizable
k–emodel. Jet positions have been changed to impinge each row of obstacles consecu-
tively. The experiments have been achieved at three different values of jet-to-channel
Reynolds number ratio, Re
j
/Re
c
¼1, 2, and 4. In this study, a comparison between two
different cooling processes, cross flow only (CF) and jet impingement with cross flow
(JICF), has been achieved. The flow structure, heat transfer characteristics, and the
pumping power have been investigated for different jet positions. The results show that
the jet position affects significantly the flow structure, as well as the heat transfer charac-
teristics. According to the results of average heat transfer coefficient and the pumping
power, the more effective jet position for all values of jet-to-channel Reynolds number
ratio (1, 2, and 4) is achieved when the jets impinge the third row of obstacles (JP3).
[DOI: 10.1115/1.4036788]
Keywords: heated obstacle, cross flow, jet impingement, jet position, realizable k–e
model, average heat transfer coefficient
1 Introduction
Recently, growing utilization of electronic devices to perform
many processes is accompanied by an increase in heat dissipation
that has an adverse effect on the device performance as well as on
its lifetime. There are many cooling techniques for electronic devi-
ces, such as air cooling, spray cooling, phase change material
cooling, and heat pipe cooling. Air cooling is considered an effec-
tive way due to its simplicity in design, operation, and size
requirements.
Cooling an array of heated obstacles simulating electronic com-
ponents using air with CF has been investigated widely in the last
decades. The flow structure and the distribution of convective heat
transfer coefficient have been investigated by Meinders et al. [1].
The flow structure around the first obstacle subjected to CF is
characterized as: LHV, which is produced before the lower part of
the front face; side vortices (SV) that are generated on both sides;
top vortex (TV) that is produced on the top face; and arch-shaped
wake vortex (WV) that is generated behind the rear face as shown
in Fig. 1(a). However, the other obstacles are rounded only by
WV. The interobstacles distance (S) has a significant effect on
flow structure and heat transfer distribution [2,3]. For larger S, the
flow structure and the heat transfer distribution around each obsta-
cle were similar [4,5]. Furthermore, obstacle geometry has a sig-
nificant effect on heat transfer characteristics; the wider the
obstacle, the higher the heat removal rates [6,7]. The placement of
obstacles, the thermal wake effect, and the flow inlet and outlet
location have been found as important parameters in the thermal
management [8–10].
In the area of cooling of electronic components, the use of jet
cooling only is not effective, especially for higher power density
components. However, using only jet impingement where the
impinged face of the obstacle is cooled effectively while the other
vertical side faces have bad cooling characteristics due to vortex
formation. Among an array of obstacles, the interobstacles space
occupied by secondary flow reduces heat transfer due to its recir-
culation and settling time. By installing the components in a chan-
nel with cross flow, the side faces are cooled by the CF, which
could drag most of the secondary flow produced in free jet cooling
process.
Recently, cooling a single electronic component as well as
array of components using JICF has a significant contribution.
The flow structure around a single cubical obstacle cooled by
JICF at Re
j
/Re
c
¼0.5, 1, and 1.5 has been investigated experimen-
tally [11]. The main flow features were LHV, upper horseshoe
vortex (UHV), SV, and WV. Moreover, the Re
j
/Re
c
affects the
location of stagnation point (SP) on the top face of obstacle. In
addition, the absence of UHV was observed for the lower values
of Re
j
/Re
c
. Sketch of the flow structure around an obstacle sub-
jected to JICF obtained by Masip et al. [11] is shown in Fig. 1(b).
The effects of channel height, jet diameter, and the shift of the jet
from the center of the obstacle on the heat transfer and pressure
drop have been investigated numerically [12]. The obstacle height
and jet-to-channel Reynolds number ratio have a significant effect
on the heat transfer rate, whereas the jet diameter and shifted dis-
tance have inconsiderable effect.
The variations of flow structure and heat transfer characteristics
of a single cubical obstacle of an in-line array due to changing
Reynolds number ratio, jet diameter and its shifted centerline, and
channel height have been studied experimentally and numerically
1
Corresponding author.
Contributed by the Heat Transfer Division of ASME for publication in the
JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received
September 15, 2016; final manuscript received January 12, 2017; published online
July 6, 2017. Assoc. Editor: Qingang Xiong.
Journal of Thermal Science and Engineering Applications FEBRUARY 2018, Vol. 10 / 011005-1
Copyright V
C2018 by ASME
Downloaded From: https://thermalscienceapplication.asmedigitalcollection.asme.org/ on 08/30/2017 Terms of Use: http://www.asme.org/about-asme/terms-of-use
... The study's objective was to reduce the unfavorable effect of crossflow on cooling performance by changing jet diameters, and they found that the configuration of first increasing and then decreasing jet diameter offered better thermal performance. Maghrabie et al. [29,30] performed numerical works examining the role of the Reynolds number ratio of jetto-crossflow (Re j /Re c ) on thermohydraulic performance in the cooling of discrete heating modules representing the electronic components. They also discussed the role of nozzle position on the parameters mentioned above, and revealed that increasing the jet Reynolds number significantly increased the thermal enhancement factor. ...
... where f 0 is the friction coefficient in the reference case. The thermal enhancement factor is calculated as follows [29,30,34,61]: ...
The Role of Jet-to-Crossflow Velocity Ratio on Convective Heat Transfer Enhancement in the Cooling of Discrete Heating Modules
Article
  • Nov 2022
This study aims to investigate the role of jet-to-cross flow velocity ratio on convective heat transfer and flow characteristics in a channel with discrete heating modules simulating electronic components. Three-dimensional numerical simulations are performed using the finite volume method. The findings obtained for different velocity ratios of the jet-to-crossflow are compared with the reference case (crossflow solely). While keeping the crossflow velocity and the crossflow Reynolds number (Rec=5000) constant, numerical calculations are performed for six different velocity ratios (Ur=1.0,2.0,4.0,6.0,8.0 and 10.0). The focus is on the role of the velocity ratio (Ur) on the mean Nusselt number (Num) on the modules’ surfaces, the Nusselt number ratio (Nur), the friction coefficient ratio (fr) obtained throughout the channel and the thermal enhancement factor (TEF). As a result of the study, it is revealed that the momentum of jet flow becomes dominant over crossflow, the influence of jet flow on convective heat transfer increases, and the thermal enhancement factor increases depending on the increasing jet-to-cross flow velocity ratio.
View
... Studies on more complex assembles with multiple heat sources and obstacles are also available, however even these works include some simplifications to the geometry. Two examples are the works of Maghrabie et al. [5] and Baudoin et al. [6] where a number of electronic components are positioned inside a cabinet and fluid flow and heat transfer effects are evaluated. Both studies accounted for the interactions among the components, but geometry and positioning are simplified, i.e., components are rectangular and positioned in aligned rows and columns. ...
Natural and mixed convection cooling evaluation of a hybrid photovoltaic inverter
Preprint
Full-text available
  • May 2024
Temperature control of embedded systems have become a key factor for the design of more thermal efficient electronic devices. They are becoming smaller and more powerful, what results in a large heat dissipation which must be removed from the system. Heat sinks and forced convection are the usual alternatives used to keep components temperature bellow critical values. In this work, a commercial hybrid photovoltaic inverter is numerically simulated and its thermal behavior is investigated for natural, forced and mixed flow conditions. Experimental results, for a forced convection case, were also reported and used do verify the numerical results. The 3D model accounts for all equipment with high heat dissipation and most of the less important (for thermal analysis) electronic devices, as well as, the fluid regions. A finite volume solution is obtained using the OpenFOAM software, more specifically the chtMultiRegionFoam solver. Flow modeling uses the Boussinesq approximation to account for the natural convection effects, while the k-e formulation was used to close the turbulence model. Results have shown that with current computational capacity, such complex systems (in terms of geometry) can be modeled with just a few simplifications. The inverter could work using only natural convection to cool down the system, however the operating temperatures would be close to the limiting values. In terms of forced convection, it is highlighted the importance of the correct design for the cooling system, avoiding oversizing the overall systems.
View
... The arrangement involving increasing-decreasing jet diameter provided greater convective heat transfer. The effect of jet-to-crossflow Reynolds number ratio on thermohydraulic efficiency in the cooling of electronic modules was analyzed numerically by Maghrabie et al. [37,38]. The authors also examined the influence of nozzle position and found that a rise in the jet Reynolds number led to a significant rise in the thermal enhancement factor. ...
View
... Larraona et al. [10] evaluated numerically the critical cooling parameters of heating modules subjected to crossflow and jet flow, and demonstrated that the combination of jet and channel flows were more effective for cooling than channel flow alone. Maghrabie et al. [11,12] conducted computational studies to determine the effect of the jet-to-crossflow Reynolds number ratio on thermohydraulic performance in the cooling of electronic modules. Masip et al. [13,14] investigated the flow pattern and heat transfer for various Reynolds numbers, and found that raising the jet velocity increased the cooling effectiveness of the module's top surface. ...
Jet Impingement Cooling of Electronic Modules: Effect of the Nozzle Position
Conference Paper
  • Jun 2023
In this study, jet impingement cooling of electronic modules with a series of jet nozzles is studied numerically. Three-dimensional numerical simulations are conducted for two alternative jet Reynolds numbers (Re ! =8568 and 14023) at various dimensionless nozzle positions (s ! b ⁄ =0.166-0.5) and validated with experimental data. The study focuses on evaluating the influence of nozzle position on the temperature distribution and local and average heat transfer characteristics on the module surfaces. As a consequence of the study, it is determined that the position of the nozzles has a substantial influence on the local and average heat transfer characteristics, and the convective heat transfer is always greater in the impingement region than in the other regions of the modules.
View
... Hence, as a result of the high turbulence of interaction flow issued from the jet and faced the fronted wall, the distribution of convective heat transfer coefficients is unlike that for a free jet [8]. Confined jets are frequently employed for cooling electronic components [9,10], gas turbine blades [11], photovoltaic cells [12], etc. The jet flow in the confined jet is divided into four regions, i.e., free, stagnation, wall regions, and a confinement recirculation region in which the jet flows away from the surface forming a subatmospheric pressure region that is created on the confinement plate [13,14]. ...
Heat Transfer Intensification of a Confined Impinging Air Jet Via a Guiding Baffle
Article
  • Mar 2023
The heat transfer intensification of a confined imping jet was achieved using rough surface, pin fines as well as using modified nozzle such as chamfering, chevron, sweeping, swirling, etc. In the current work, the enhanced cooling process utilizing a single confined air jet impinged on a flat plate using a guiding baffle is implemented. The impacts of Reynolds number (Re) ranged from 500 to 5000, guiding baffle diameter-to-nozzle diameter (D/d) of 2, 4, and 6, and guiding baffle height-to-nozzle to impinging plate distance (h/H) of 1/3, 1/2, and 3/4 on the cooling process are studied. The distributions of surface temperature are acquired experimentally using the thermal infrared camera. As well, the local Nusselt number,(Nu) stagnation Nusselt number (Nu¯st), average Nusselt number,(Nu¯) and average Nusselt number ratio (Nur¯) are evaluated. The results reveal that the enhancement of heat transfer is achieved due to installing a baffle with a D/d of 2 for all values of baffle height and Reynolds number. In addition, the (Nur¯) is increased with increasing the Re in the range from 500 to 2500, then it is decreased by a further increase in in Re. Moreover, based on the experimental results, an empirical correction is proposed to compute (Nu¯) the average Nusselt number depending on Re, D/d, and h/H with a ± 2.65% standard deviation.
View
... This study of the jet impingement flow field is performed at moderate Reynolds turbulent flow. The two-equation turbulence models such as standard k-e, realizable k-e, standard k-x, renormalization group (RNG) k-e, and shear stress transport (SST) k-x are widely employed for solving the applications of moderate Reynolds turbulent flow [37]. The SST k-x is utilized to predict the turbulent flow structure and the heat transfer characteristics for similar engineering applications [11,12,24]. ...
Cooling of Gas Turbine Blade Leading Edge Via an Array of Air Jets With Variable Diameters
Article
  • Oct 2022
In this study, the cooling of a gas turbine (GT) blade leading edge using a single row of five impinging air jets was numerically and experimentally investigated. The inner surface of the blade leading edge was depicted as a semicircle profile. The numerical study was performed using a shear stress transport (SST) k-x turbulence model. On the other side, the experimental work was conducted using the infrared (IR) thermal camera. Additionally , the heat transfer characteristics were investigated with changing the Reynolds number (Re) from 5000 to 40,000. The study was carried out for different cases based on the jet diameter (d), named as fixed diameter (FD) and variable jet diameter in the streamwise flow direction, i.e., ascending diameter (AD) and descending diameter (DD). The local and average Nusselt numbers and heat transfer uniformity were studied at different operating and design parameters. The results revealed that for FD, increasing the jet diameter decreased the average Nusselt number while it enhanced the heat transfer uniformity. Furthermore, for all values of Re, the thermal performance of the AD was better than the DD, which has the worst heat transfer uniformity. Finally, predicted developed correlations to estimate the average Nusselt number, surface heat transfer uniformity, and performance evaluation factor (PEF) for all cases of jet diameter were introduced.
View
... The conventional cooling CF method has been shown to have lower performance on electronic systems [13], [14]. Therefore, investigations conducted to obtain acceptable values in heat transfer have been necessary to increase the performance of fans that move the more excellent air flow used. ...
Parametric Study of Electronic Cooling by Means of a Combination of Crossflow and an Impinging Jet
Article
Full-text available
  • Jan 2022
This paper reports a parametric study’s experimental results based on the experiments’ design. No works in the literature have investigated parametrically experimental effects on electronic component cooling by combining an impinging jet and a channel flow configuration on the cooling of electronic components. This study analyzed five parameters experimentally to enhance the cooling process using statistical techniques. Additionally, the optimal configuration determined for the conventional cooling method using only the channel flow was compared. Three parameters are associated with the geometric configuration (height of the electronic component h/H = 1/6, 1/3, 1/2, jet diameter D/H = 0.3, 0.4, 0.5 and jet-component eccentricity S/H = 0, 1/8, 1/4), and the other two are related to the fluid flow (the Reynolds number based on the channel height and mean velocity of the stream ReH = 3410, 4205, 5000 and the ratio between the jet and the channel mean velocities Uj/Um = 2.5, 3.75, 5). The results show that the main parameters are statistically significant relative to heat transfer, with ReH , Uj/Um and h/H displaying the most significant amplitude of variation in response and increasing the Nusselt number by approximately 60%. The surface response models have shown a satisfactory fit with the experimental data, allowing, in a preliminary way, the minimum mechanical energy loss requirement to be identified to maximize up to 160% of the heat transfer. Specifically, the heat transfer enhancement is more significant for components of considerable height than other components. Heat transfer enhancement occurs at low mechanical energy loss when the velocity ratio decreases at the minimum channel Reynolds number at the maximum jet diameter and jet-component eccentricity.
View
Numerical study on natural, forced and mixed convection of a hybrid photovoltaic inverter
Article
  • Oct 2024
  • J BRAZ SOC MECH SCI
Temperature control of embedded systems has become a key factor for the design of more thermally efficient electronic devices. These devices are becoming smaller and more powerful, dissipating a larger amount of energy which must be removed from the system. Heat sinks and forced convection are the usual alternatives used to keep components temperature below critical values. There are many investigations in literature about heat sinks performance; however, a very limited number of them model the whole system. In this work, a commercial hybrid photovoltaic inverter is numerically simulated and its thermal behavior is investigated for natural, forced and mixed flow conditions. Experimental results, for a forced convection case, were also reported and used to verify the numerical results. The 3D model takes into account all equipment with high heat dissipation and most other electronic components, as well as the two fluid regions. A finite volume solution is obtained using the OpenFOAM software, more specifically the chtMultiRegionFoam solver. Flow modeling uses the Boussinesq approximation to account for the natural convection effects, while the κ-ε formulation was used to close the turbulence model. Results have shown that with current computational capacity, such complex systems (in terms of geometry) can be modeled with just a few simplifications. The inverter could work using only natural convection to cool down the system; however, the operating temperatures would be close to the limiting values. In terms of forced convection, it is highlighted the importance of the correct design for the cooling system, avoiding oversizing the heat sink and the fans sizes.
View
Microchannel heat sinks with nanofluids for cooling of electronic components: Performance enhancement, challenges, and limitations
Article
  • Dec 2022
Nowadays, the cooling of electronic components that are widely spread globally is considered a critical issue. Designers and engineers alike confront major obstacles in electronic devices, the main one being how to find a reliable method to overcome the issues of dissipating high heat flux and ensuring the acceptable limit of operating temperature. The current work attempts to study fluid flow, heat transfer, and thermal performance to avoid hot spots in electronic devices. To intensify the heat rate of electronic components in sophisticated applications with minimum size, the utilization of specified working nanofluids (NFs) rather than traditional ones was promoted. The thermal behavior of a microchannel heat sink (MCHS) utilizing different nanofluids depends essentially on the thermophysical properties of nanoparticles (NPs). In the current study, the aspects related to the cooling of electronics using nanoparticles in microchannels (MCs) are deeply discussed. Regarding the distinctive characteristics of the nanoparticles, researchers have noted noteworthy progress in the cooling of electronics, including the use of hybrid nanoparticles, electronics with rough surfaces, utilizing phase change material (PCM), employment of modified channels, and other effects. The thermophysical properties, behaviors, performance, challenges, application, limitations, and future prospects of nanofluids in electronic components are also presented.
View
Cooling of Gas Turbine Blade Leading Edge Via an Array of Air Jets With Variable Diameters
Article
  • Sep 2022
In the present study, the cooling of a gas turbine blade leading edge by a single row of five impinging air jets was investigated numerically and experimentally. The inner surface of a blade leading edge was simulated by a semi-circle profile. The numerical study was performed using a Shear Stress Transport (SST) k-? turbulence model while the experimental work was conducted using the infrared (IR) thermal camera. Additionally, the heat transfer characteristics were investigated by varying the Reynolds number (Re) from 5,000 to 40,000. The experiments were carried out for different cases based on jet diameter (d), namely, fixed diameter (FD) and variable jet diameter in the streamwise flow direction i.e., ascending diameter (AD) and descending diameter (DD). The local and average Nusselt number and heat transfer uniformity were studied at different operating and design parameters. The results revealed that for FD, increasing the jet diameter decreased the average Nusselt number, whereas it enhanced the heat transfer uniformity. Whereas, the worst heat transfer uniformity occurred for DD. Furthermore, for all values of Re, the thermal performance of AD was better than that of DD. Finally, proposed correlations to estimate the average Nusselt number, surface heat transfer uniformity, and performance evaluation factor for all cases of jet diameter as functions of Re, jet diameter, and diameter increment/decrement in the examined range were introduced.
View
Thermal wakes measurement in electronic modules in the presence of heat transfer enhancement devices
Article
Full-text available
  • Oct 1999
  • APPL THERM ENG
This paper reports the thermal wake measurements in electronic modules in the presence of heat transfer enhancement devices. The enhancement devices consist of various sizes and shapes of ribs, secondary air flow injections through cylinders and “film cooling-like” injection devices. The effects of such devices on the thermal wake and the pressure drop characteristics of an array of rectangular modules at different values of Reynolds number in the range 4.0×103–1.6×104 have been investigated. Generally, it was found that using sizes and shapes of ribs as well as the presence of secondary air flow injection cylinders and film cooling-like injection hole devices tends to results in a significant attenuation in the thermal wake, in particular in the region downstream of the enhancement devices, depending on the location of the active module in the array. A maximum attenuation in the thermal wake of 33%, 30% and 25% for the rectangular, triangular and cylindrical ribs occurs at the sixth row, respectively, when the active module is located just upstream of the rib-enhancement devices. The film cooling-like enhancement devices tend to have higher attenuation in the thermal wake than the rib enhancement devices for the same location of the active module downstream of these devices, but with very much smaller pressure drop.
View
Simulation of steady-state operation of an ejector-assisted loop heat pipe with a flat evaporator for application in electronic cooling
Article
  • Dec 2015
  • APPL THERM ENG
This paper proposes an ejector-assisted copper-water loop heat pipe with a flat evaporator (ELHP) for applications in electronic cooling. In the ELHP, the ejector is used to remove the generated vapor in the compensation chamber due to heat leaks through the wick, which could eliminate the need for the subcooling liquid supplied to the compensation chamber and improve the loop heat pipe performances. The steady-state performance of ELHP is simulated based on an established mathematical model and compared with the basic loop heat pipe with a flat evaporator (BLHP). The simulation results show that the operating temperature of the ELHP can be lower than that of the BLHP under the same heat load condition. Since the working fluid subcooling zone in the ELHP condenser is not required, the total length of the pipe-in-pipe type condenser also can be decreased by 24.4-34.8% when compared with that of the BLHP under given operating conditions. In addition, the effects of the thickness of the wick, the total length of the condenser, the inner diameter of the vapor line and the mass flow rate and inlet temperature of the cooling water on the performances of the ELHP are also evaluated in this study. These simulation results indicate that the ELHP can achieve a better performance than BLHP, which could be beneficial to the applications in electronic cooling.
View
CFD study of constructal microchannel networks for liquid-cooling of electronic devices
Article
  • Nov 2015
  • APPL THERM ENG
The heat transfer performance of liquid-cooled heat sinks with a constructal design of the flow field configurations is assessed in the present investigation. Y- and Ψ-shaped microfluidic networks embedded on a silicon substrate are numerically analyzed and compared in order to propose an alternative cooling layer for integrated circuits (ICs). The shape, path and geometric dimensions of the flow channels are designed with the Phi number and Allometric scaling laws based on constructal networks, resulting in tree-shaped flow paths with variable hydraulic diameter. The thermal and hydraulic performances of eight different configurations are discussed in terms of the average surface temperature and pressure drop, respectively. Results indicate that the Ψ-shaped heat sink designs offer a higher degree of temperature uniformity than Y-shaped designs, with the penalty of a slightly higher flow restriction. It was observed that the Phi number ratio has a strong effect on thermal performance, with enhanced results for higher ratios. Discussions about heat transfer area, temperature uniformity and pressure drop are given for the different cases, proposing an enhanced design for electronics cooling applications.
View
View
View
Experimental comparison between different configurations of PCM based heat sinks for cooling electronic components
Article
  • May 2015
  • APPL THERM ENG
The thermal control of electronic components is aimed at ensuring their use in a temperature range compatible with their performances. This paper presents an experimental study of the behavior of phase change materials (PCMs) as the cooling system for electronic devices. Four configurations are used to control the increase in the system temperature: pure PCM, PCM in a silicone matrix, PCM in a graphite matrix and pure PCM in a system of fins. Thermo-physical properties of different PCMs are determined and found to be desirable for application in this study. Solid liquid interface visualization and temperature evolution are employed to understand the mechanism of heat transfer during the different stages. Results indicated that the inclusion of PCM can lower component increase temperature and extends twice the critical time of the heat sink. The use of Graphite matrix filled by PCM showed more improvement on system thermal performance than silicon matrix. Also, for the same fraction of copper, it was found by incorporating long copper fins with suitable spacing into PCM, can enhance heat distribution into PCM leading to longer remain component temperature below the critical limit. This work therefore shows that the combination of PCM and long, well-spaced fins presents an effective means for thermal control of electronic devices.
View
A novel flat polymer heat pipe with thermal via for cooling electronic devices
Article
  • Aug 2015
  • ENERG CONVERS MANAGE
The efficiency and heat transfer characteristics of a newly designed flat polymer heat pipe that uses copper micro thermal via was investigated using a fabricated laboratory model to measure the amount of heat that could be removed from a given heat source (a heater or a light emitting diode (LED) module) under a range of different operating conditions. The heat pipe consists of a copper frame 1 mm thick which is sandwiched between top and bottom sheets of FR4 polymer to form a vapor chamber. Copper meshes were used for the wick structure in the vapor chamber. The design also includes an array of thermal via, formed by 0.5 mm holes drilled through the polymer, which are copper plated and filled with resin similar to the FR4 polymer. This novel design enhances heat conduction through the wall of the polymer heat pipe. A transient dual interface method (TDIM) was used to measure the thermal resistance of the LED module mounted on the flat heat pipe. Experimental results showed that use of the thermal via design reduced the lateral thermal resistance by 20–25%. The thermal resistance of the flat heat pipe was also affected by the filling ratio of working fluid and the tilt angle. When the flat heat pipe with thermal via was used as a mounting substrate with the LED module located in the center of the top surface, experimental results showed the thermal resistance of the substrate was reduced by 57%.
View
View
Experimental study of the turbulent flow around a single wall-mounted cube exposed to a cross-flow and an impinging jet
Article
  • Dec 2012
  • INT J HEAT FLUID FL
The air flow around a cubic obstacle mounted on one wall of a rectangular channel was studied experimentally. The obstacle represents an electronic component and the channel the space between two parallel printed circuit boards (PCBs). The flow was produced by the combination of a channel stream and a jet which issued from a circular nozzle placed at the wall opposite from where the component is mounted. With this aim, a test rig was designed and built to carry out experiments with both the above mentioned configurations and other cooling arrangements. Planar Particle Image Velocimetry (PIV) was employed to measure the instantaneous flow velocity on several planes covering the space around the component. The mean velocity and the Reynolds stresses were obtained from averaging the instantaneous velocity, and the mean flow showed a complex pattern with different features such as recirculation bubbles, vortices, detachment and reattachment zones. The influence of two parameters, namely the channel Reynolds number and the jet-to-channel Reynolds number ratio, on these flow features was studied considering nine cases that combined three values of the channel Reynolds number (3410, 5752 and 8880) and three values of the ratio (0.5, 1.0 and 1.5). The results show that the Reynolds number ratio determines the drag produced on the jet and the deflection from its geometric axis due to the channel stream. In all the cases corresponding to the lowest value of the ratio, the jet was dragged and did not impact the component. This fact accounts for the non-existence of the Upper Horseshoe Vortex and changes in the flow characteristics at the region over the component.
View
Computational parametric study of an impinging jet in a cross-flow configuration for electronics cooling applications
Article
  • Apr 2013
  • APPL THERM ENG
A parametric study based on design of experiments (DoE) techniques was carried out by computational simulation in order to evaluate the effect that design parameters have on heat transfer and pressure loss of an impinging jet in a cross-flow configuration. The main effects of each parameter and the interactions between parameters were analyzed in detail through the Response Surface Methodology (RSM). Additionally, the potential of the impinging jet in a cross-flow configuration was assessed by calculating the optimal values of the parameters and comparing the cooling efficiency of the resulting configuration with the efficiency of the conventional cross-flow configuration. It was found that the degree to which the average heat transfer coefficient is enhanced as the result of adding an impinging jet depends on the height of the cooled component. Specifically, it was found that the higher the component, the more significant the enhancement.
View