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Wang S.F.,South China University of Technology | Hu Y.X.,South China University of Technology | Zhou Y.,South China University of Technology | Zhang W.,Novark Technology Inc.
ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2015, collocated with the ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels | Year: 2015

Self-rewetting fluids (SRWFs) are non-azeotropic solutions enjoy a particular surface tension behavior-an increase in the surface tension with increasing temperature. Due to the unique property, the SRWF can spontaneously wet hotter region and enhance heat transfer. The interesting behavior makes the SRWF become the research hotspot in phase change heat transfer research field. To clarify the heat transfer characteristics of SRWF, a series of boiling experiments have been carried out by employing dilute heptanol aqueous solution as SRWF. It is found out that, the bubble size of the SRWF is much smaller than that of pure water, and the critical heat flux of SRWF is much higher than that of water, which is beneficial for application in heat pipes. To find out the heat transfer performance of SRWF in heat pipes, experimental studies are performed on oscillating heat pipe (OHP) consisting of 4 meandering turns, with heat transfer length (L) of 150 mm and inner diameter (Di) of 1.3 mm. Compared with the water, the SRWF exhibits much better thermal performance, which indicates that SRWF is a promising and useful working liquid for the application in high efficient cooling devices with micro structure. Copyright © 2015 by ASME. Source

Lin Z.,South China University of Technology | Wang S.,South China University of Technology | Chen J.,South China University of Technology | Huo J.,South China University of Technology | And 2 more authors.
Applied Thermal Engineering | Year: 2011

A series of experiments were performed to investigate the effect of heat transfer length and inner diameter on the heat transport capability of miniature oscillating heat pipes (MOHPs). In the experiments, MOHPs with heat transfer length (L) of 100, 150 and 200 mm, consisting of 4 meandering turns and inner diameter of 0.4, 0.8, 1.3 and 1.8 mm were adopted, and pure water was used as the working fluid. The results show that increasing inner diameter or decreasing heat transfer length is beneficial to MOHPs startup. An effective range of MOHPs has been identified. The recommended inner diameter of MOHPs should be bigger than 0.8 mm in vertical bottom heating mode, while the heat transfer length should be controlled less than approximately 100 mm in horizontal heating mode. For high heating power, the thermal performance of MOHPs can only approach that of sintered heat pipes in horizontal heating mode, while exceed it in vertical bottom heating mode. Finally, the dominating dimensionless parameters, including Di/L, Ja, Bo and Wa, are used to predict the heat transport capability of MOHPs. The correlation prediction agrees with the experimental results fairly well. © 2010 Elsevier Ltd. All rights reserved. Source

Lin Z.,South China University of Technology | Wang S.,South China University of Technology | Shirakashi R.,University of Tokyo | Winston Zhang L.,Novark Technology Inc.
International Journal of Heat and Mass Transfer | Year: 2013

In order to study the heat transfer mechanism of miniature oscillating heat pipes (MOHPs) and predict the heat transport capability of MOHPs, a comprehensive mathematical and physical model of MOHP was built to simulate the two-phase flow behavior in vertical bottom heating mode. Water was used as the working fluid. The volume of fluid (VOF) and mixture model in FLUENT were used for comparison in the simulations. The phase change process in a MOHP was deal with by adding a user-defined function (UDF) source term in each phase. The continuum surface force (CSF) model was used to consider the effect of surface tension. The result showed that the mixture model was more suitable for the two-phase flow simulation in a MOHP. Having agreed with the flow visualization, the simulation with unsteady model was successful in reproducing the two-phase flow process in a MOHP, including the bubble generation in evaporation section and the oscillations caused by the pressure difference. The quasi periodic thermal oscillation with the same characteristic frequency for both evaporation section and condensation section indicated that the heat was transferred by the oscillations. The simulation results of MOHPs with different heat transfer lengths (L) and inner diameters (Di) at different heating powers, were compared with the experimental results at the same condition. This showed that the inner diameter had a greater impact on the thermal performance of MOHPs than the heat transfer length. Increasing the inner diameter was beneficial to improve the thermal performance of MOHPs. © 2012 Elsevier Ltd. All rights reserved. Source

Saw L.H.,National University of Singapore | Tay A.A.O.,National University of Singapore | Zhang L.W.,Novark Technology Inc.
Annual IEEE Semiconductor Thermal Measurement and Management Symposium | Year: 2015

Electric Vehicles (EVs) are projected as the most sustainable solutions for future transportation. EVs have many advantages over conventional hydrocarbon internal combustion engines including energy efficiency, environmental friendliness, noiselessness and less dependence on fossil fuels. However, there are also many challenges which are mainly related to the battery pack, such as battery cost, driving range, reliability, safety, battery capacity, cycle life, and recharge time. The performance of EVs is greatly dependent on the battery pack. Temperatures of the cells in a battery pack need to be maintained within its optimum operating temperature range in order to achieve maximum performance, safety and reliability under various operating conditions. Poor thermal management will affect the charging and discharging power, cycle life, cell balancing, capacity and fast charging capability of the battery pack. Hence, a thermal management system is needed in order to enhance the performance and to extend the life cycle of the battery pack. In this study, the effects of temperature on the Li-ion battery are investigated. Heat generated by LiFePO4 pouch cell was characterized using an EV accelerating rate calorimeter. Computational fluid dynamic analyses were carried out to investigate the performance of a liquid cooling system for a battery pack. The numerical simulations showed promising results and the design of the battery pack thermal management system was sufficient to ensure that the cells operated within their temperature limits. © 2015 IEEE. Source

Lin Z.R.,Novark Technology Inc. | Lee Z.Y.,Novark Technology Inc. | Zhang L.W.,Novark Technology Inc. | Wang S.F.,South China University of Technology | And 2 more authors.
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011 | Year: 2011

Loop heat pipe (LHP) is a highly efficient cooling device. It has gained great attention in the electronics cooling industry due to its superior heat transport capability - that is, its ability to carry heat over long distances. For this article, a miniature flat loop heat pipe (MFLHP) with rectangular-shaped evaporator was developed. The LHP's evaporator was combined with the compensation chamber. MFLHPs with different diameters and lengths for the connecting pipeline were selected for a series of experimental studies on their heat transfer characteristics. In these experiments, pure water was used as the working fluid. The studies showed that the heat transport capability of a MFLHP with 4 mm diameter was better than that a MFLHP with 3 mm diameter. At a low thermal resistance of 0.04°C/W (at 200W), an optimal length for the connecting pipeline for a particular MFLHP with 4 mm diameter was identified. Finally, a heat sink attached to a MFLHP was developed for cooling a graphics processing unit (GPU), the thermal design power (TDP) of which was 200 W. The results showed the GPU heat sink with MFLHP had good performance and satisfied GPU cooling requirements. Compared to the conventional heat pipe solutions, only one MFLHP was able to cope with high power dissipation, offering the potential to make a lighter heat sink. © 2011 by ASME. Source

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