Analysis of thermal flow around heat sink with ionic wind for high-power LED

Shin, Dong Ho,Sohn, Dong Kee,Ko, Han Seo Elsevier 2018 Applied thermal engineering Vol.143 No.-

<P><B>Abstract</B></P> <P>This paper presents a new method of active cooling for a Light Emitting Diode (LED) application using the ionic wind which is a flow induced by a corona discharge at a tip of a curved electrode. Thermal flow around a heat sink for a high-power LED was analyzed and the ionic wind was investigated for the heat sink application in this study. Details of a numerical investigation of natural convection around the heat sink for the 200 W-LED were studied. The reliability of the computational fluid dynamics (CFD) was verified by experimental data of temperatures. A particle image velocimetry (PIV) test was performed to analyze the behavior of the ionic wind around the heat sink. The thermal flow around the heat sink fins was analyzed and it was concluded that the center pole of the cylindrical heat sink was unnecessary for the cooling performance. And, the ionic wind from a wire to cylinder electrode was applied to the heat sink to enhance the cooling performance. As a result, the optimum radius of the wire curvature and input voltage for the ionic wind were found to be 110 mm and 7.5 kV, respectively. The heat transfer coefficient of the heat sink increased by 37% from 96.7 to 133 W/m<SUP>2</SUP> K by the ionic wind, which was confirmed experimentally. And, the cooling performance of the heat sink was enhanced by 148% in maximum by the ionic wind compared with that of the original heat sink for 0.6 W of the applied power. The result of this study can be used for the wide variety of the ionic wind application as a promising technology for the LED cooler.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The ionic wind using the wire and cylinder electrode was applied to the heat sink. </LI> <LI> The radial heat sink without the center pole was suggested for 200 W-LED. </LI> <LI> The optimum radius of wire curvature was 110 mm at 7.5 kV. </LI> <LI> The heat transfer coefficient of the heat sink increased by 37% by the ionic wind. </LI> <LI> The cooling performance was enhanced by 148% in maximum by the ionic wind. </LI> </UL> </P>

전자부품 냉각을 위한 Vapor chamber heat sink의 열성능 연구

김윤호(Yoon-Ho Kim),전현수(Hyeon-Soo Jeon),배수호(Soo-Ho Bae),차호진(Hojin Cha),구홍모(Hong-Mo Koo) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

As the electronic devices is more accelerated the compact size, the light-weight and the high integrated trend of electronic components, the most increasingly the heat generation problem rises. Recently, there are growing interests in developing alternative heat sink devices. Vapor chamber heat sinks are heat-spreading systems that develop phase change to spread heat and are of increasing interest in the electronics industry. Vapor chambers are increasingly being investigated as a way to spread the heat generated by an electronic component to the base of a heat sink for typical heat sink applications. In this study, vapor chamber heat sinks have been performed to investigate the thermal performances under the natural convection and forced convection conditions and to compare their performance against copper base heat sink. It is fabricated to be used a real telecommunication equipment specifications. The thermal characteristics of vapor chamber heat sinks are studied according to various input power using dummy heater, test jig and fan. The study shows that vapor chamber heat sinks can thermally perform better than a copper block heat sink. The thermal conductivity of the vapor chamber is also numerically analyzed using CFD simulation and is compared to the experiment results. Thus vapor chamber heat sinks provide good performance alternative to typical heat sinks.

Heat transfer and flow characteristics of forced convection in PDMS microchannel heat sink

Jung, Sung Yong,Park, Jun Hong,Lee, Sang Joon,Park, Hanwook Elsevier 2019 Experimental thermal and fluid science Vol.109 No.-

<P><B>Abstract</B></P> <P>Recently, microfluidic devices are being widely used in various heat transfer applications and, thermal management in microchannels is a challenging issue. As a solution, different types of microchannel heat sinks have been employed to enhance the heat transfer. The flow characteristics in the microchannel heat sink have influence on the heat transfer rate and thermal management performance. Therefore, the simultaneous measurement of temperature and velocity fields is highly required to understand the single-phase heat transfer phenomena in the PDMS microchannel heat sink. In this study, μPIV-μLIF technique which can provide the velocity and temperature field information of micro-scale thermofluid flow was newly developed to analyze the heat transfer of forced convection in PDMS microchannel heat sink. Especially, flow characteristics in the microchannel heat sink were systematically investigated. At a high <I>Re</I> flow (<I>Re</I> = 10) with heating, a high-speed crossflow occurs in the microchannel heat sink. Spanwise vorticity and Reynolds shear stress, which contribute to heat transfer in the microchannel, exhibit higher values at <I>Re</I> = 10 with heating compared to the non-heating case. Variations in velocity and local <I>Nu</I> number were also compared to explain heat transfer enhancement in the microchannel heat sink. Temporal variations in the temperature field were evaluated to demonstrate the effect of flow on heat transfer. The results presented herein would be helpful for understanding heat transfer in microscale thermofluid flows and for designing microscale heat transfer devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Velocity and temperature fields in microchannels were measured by μPIV and μLIF. </LI> <LI> Flow characteristics near the heat sink were systematically investigated. </LI> <LI> High-speed crossflow occurs in the heat sink of the microchannel when <I>Re</I> = 10. </LI> <LI> Velocity fluctuations and local <I>Nu</I> number were compared to explain heat transfer. </LI> <LI> Temporal variations in temperature were evaluated to analyze the heat transfer. </LI> </UL> </P>

자연대류 조건에서 크로스컷 히트싱크의 열전달 특성

조재영(Jaeyeong Jo),김성진(Jin Kim) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.6

In the present study, we investigate heat transfer characteristics of a cross-cut heat sink and how the cross-cut changes the flow fields, which is strongly related to the heat transfer coefficient. The effects of the input heat flux, fin height, and difference of base thicknesses of upper and bottom heat sink on thermal performance are investigated. The tested heat sink system consists of 4 heat sinks. The heat sink base thickness of upper part is lower than that of bottom part. The flow characteristics in the heat sink system are investigated by numerical simulation tools and it is validated by experiments. The thermal performance of the cross-cut heat sink is approximately 10% better than that of the plate fin heat sink when the cross-cut is located at the point where the difference between the heat sink base thickness occurs. The effect of the cross-cut is significant when fin height is low. In conclusion, the cross-cut improves the thermal performance in the natural convection when the base thickness difference exists.

1-D two-phase flow analysis for interlocking double layer counter flow mini-channel heat sink

Lim, Kihoon,Lee, Jaeseon Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.135 No.-

<P><B>Abstract</B></P> <P>Mini and micro-channel heat sinks with two-phase flow boiling are considered as one of the promising cooling methods due to their ability to efficiently manage high heat flux heat dissipation. However, it is characterized by a significant decrease in the heat transfer coefficient of the liquid deficient portion where the quality of flow is increased by the boiling in the channel. The heat transfer coefficient at which the wall dry-out occurs sharply decreases, which can cause a large temperature gradient in the direction of flow. Such a dry-out condition may correspond to the critical heat flux state, and a drastic decrease in cooling performance is inevitable. To alleviate the temperature gradient increase and to improve the cooling performance, the two-phase counter flow mini-channel heat sink with interlocking double layer structure has been proposed. The proposed mini-channel heat sink was designed based on the commercial IGBT module size and numerically analyzed by applying 1-D two-phase flow in each counter flow direction. Two-phase boiling heat transfer correlation and momentum equation were solved to calculate the pressure drop and analyze the cooling performance benefits of proposed counter flow heat sink. The applied analysis method was extended to the single-phase counter flow situation and the results were compared with two-phase flow case. From the results of the analysis, it was confirmed that the counter flow heat sink can obtain a more uniform temperature distribution than the conventional unidirectional heat sink. The non-uniformity of the temperature distribution due to the uneven flow rate of the parallel channels can be improved by applying the counter flow configuration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An interlocking double layer counter flow channel heat sink for IGBT is proposed. </LI> <LI> The heat sink performance predicted by the 1-D flow boiling model for counter flow. </LI> <LI> The model analysis is performed by iterative operations by genetic algorithm. </LI> <LI> The benefits of counter flow are uniform surface temperature and low thermal resistance. </LI> </UL> </P>

ANSYS에 의한 에어컨용 공진형 전력변환기 방열 시스템의 열 분포 해석

한근우(Keun-Woo Han),정영국(Young-Gook Jung) 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.6

This study deals with the heat distribution analysis of the heat dissipation system of the resonant power converter for a non starting air conditioner compressor in commercial vehicles using ANSYS. The heat sink and the peripheral parts of the power converter were set as the thermal analysis model. The external temperature under natural convection condition was set at 25℃ and the heat flux value corresponding to the exothermic parts such as MOSFET was inputted. As a result of the ANSYS simulation with the above thermal analysis condition, the heat sink of the power converter showed a maximum heat distribution of 28.4℃, and the maximum temperature of the power converter including the heat sink was about 59.2℃. From this result, the size (L) 250mm in the horizontal direction of the heat sink selected at the beginning of the development was reduced to 210mm by the simulation result. Experiments were conducted under maximum load conditions (2.5kW) using a reduced 210mm heat sink and two original 250mm heat sinks. There was little temperature difference between the two cases except for the wire part. Looking at the heat distribution, the temperature is high in the busbar and switching device, and is measured at about 51℃ for MOSFET and 33℃ for heat sink. Without ANSYS simulation, it was possible to predict about 30℃ for the heat sink and about 55℃ for the MOSFET. Finally, the resonant current of the transformer with respect to the 2.5kW resistive load, the converter output voltage and the output current were obtained, and the output voltage of 250V could be stably maintained even at the battery voltage of 24V.

엔지니어링 플라스틱의 LED조명 방열판 적용

조영태(Young-Tae Cho) 한국기계가공학회 2013 한국기계가공학회지 Vol.12 No.4

As an advance study for the development of a heat sink for special purpose high power illumination, an investigation was made to find feasibility for the application of copper plated EP to a heat sink of small LED light of less than 10W installed in commercial product. In this study, the plated heat sink with EP copper was fabricated for the conventional LED light. It was used actually for finding heat radiation property and effectiveness of the heat sink accompanied with measurement of luminous intensity. The heat is radiated by transfer and dissipation only through the copper plated surface due to extremely low heat conductivity of EP in case of EP heat sink; however the total area of the plate plays the function of heat transfer as well as heat radiation in case of the aluminum heat sink. It seems that the volume difference of heat radiating material is so big that the temperature P₁ is 9.0~12.3% higher in 3W and 42.7~54.0% higher in case of 6W volume difference of heat radiating material is so big that the temperature P₁ is 9.0~12.3% higher in 3W and 42.7~54.0% higher in case of 6W even though heat transfer rate of copper is approximately 1.9 times higher than that of aluminum. It was thought that this is useful to utilize for heat sink for low power LED light with the low heating rate. Also, the illumination could be greatly influenced by the surrounding temperature of the place where it is installed. Therefore, it seems that the illumination installation environment must be taken into consideration when selecting illumination. Further study was expected on order to aims at development of an exterior surface itself made into heat radiation plate by application of this technology in future.

Thermal performance and orientation effect of an inclined cross-cut cylindrical heat sink for LED light bulbs

Park, S.J.,Jang, D.,Lee, K.S. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.103 No.-

An inclined cross-cut cylindrical heat sink was investigated in an attempt to improve the energy conversion and management of LED light bulbs. The thermo-flow characteristics were studied to enhance the cooling performance of a cylindrical heat sink, which is the cooling apparatus used for LED light bulbs. In the inclined cross-cut heat sink, the natural convection flow with an incidence angle had a flow path length that was more stretched in comparison to the flow path length of a straight cross-cut heat sink. Accordingly, the heat transfer rate between the air and fins was increased. When the fins had an inclined angle of 25-30<SUP>o</SUP>, the thermal resistance was the smallest. However, when the inclined angle increased to greater than 50<SUP>o</SUP>, only the blocking effect was increased and the flow path length was not stretched. Hence, cooling performance was decreased with inclined angles greater than 50<SUP>o</SUP>. A correlation predicting the degree of improvement in cooling performance relative to a baseline straight cross-cut heat sink was suggested as a function of heat sink design variables and the installation angle of the heat sink. Finally, a contour map was developed, which can be used to select the optimum heat sink type, with respect to the installation angle of the heat sink and the inclined angle of the fins.

Laser transformation hardening of carbon steel sheets using a heat sink

Ki, H.,So, S.,Kim, S. Elsevier 2014 Journal of materials processing technology Vol.214 No.11

A heat-sink assisted laser transformation hardening method is presented as a way to enhance the hardenability of carbon steel sheets. In this study, the thermal conductivity of the heat sink and the thermal contact resistance between the steel sheet and the heat sink were identified as the two primary parameters for the process. Using a process map approach, the heat-treatability of steel sheets was studied theoretically focusing on carbon diffusion and cooling time characteristics. For validation purposes, 2mm thick DP 590 and boron steel sheets were laser-hardened using four types of heat sink: stainless steel, steel, copper, and no heat sink. Surface hardness, hardening width and depth were measured and analyzed over a wide range of process parameters. From this study, it was revealed that, when a heat sink is used, both cooling and carbon diffusion characteristics become roughly on par with those of the thick plate case, but the heat treatable region remains similar to that of the no heat sink case. The use of a heat sink was found to be an effective way of enhancing the hardenability of steel sheets and the amount of enhancement is largely proportional to the heat sink thermal conductivity.

Topology optimization of heat sinks in natural convection considering the effect of shape-dependent heat transfer coefficient

Joo, Younghwan,Lee, Ikjin,Kim, Sung Jin Pergamon Press 2017 International journal of heat and mass transfer Vol. No.

<P><B>Abstract</B></P> <P>Heat sinks in natural convection are thermally optimized by using the topology optimization method. To investigate the shape-dependent effect in natural convection, a new surrogate model accounting for the variation of the heat transfer coefficient within the computational domain is proposed. In order to validate the surrogate model, the result from topology optimization with the proposed surrogate model is compared to the plate-fin heat sink optimized using the existing correlation. From the comparison, it is found that the optimum channel spacing for the plate-fin heat sink is successfully reproduced by applying the surrogate model. With the validated surrogate model, a new conceptual design for a heat sink is obtained in the physical domain for which a conventional heat sink has been designed. To reflect the manufacturing constraints for mass production, guidelines for design simplification are suggested and applied to the conceptual design. Through the numerical simulation, it is found that the topology-optimized heat sink has 15% lower thermal resistance and 26% less material mass than the conventional heat sink.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A surrogate model for topology optimization in natural convection was developed. </LI> <LI> The surrogate model reproduced optimum channel spacing for plate-fin heat sink. </LI> <LI> The newly proposed design had 15% lower thermal resistance than conventional HS. </LI> <LI> Guidelines for design simplification were suggested and applied. </LI> </UL> </P>