Lithium-ion batteries are well-suited for fully electric and hybrid electric vehicles due to their high specific energy and energy density relative to other rechargeable cell chemistries. However, these batteries have not been widely deployed commercially in these vehicles yet due to safety, cost, and poor low temperature performance, which are all challenges related to battery thermal management. In this paper, a critical review of the available literature on the major thermal issues for lithium-ion batteries is presented. Specific attention is paid to the effects of temperature and thermal management on capacity/power fade, thermal runaway, and pack electrical imbalance and to the performance of lithium-ion cells at cold temperatures. Furthermore, insights gained from previous experimental and modeling investigations are elucidated. These include the need for more accurate heat generation measurements, improved modeling of the heat generation rate, and clarity in the relative magnitudes of the various thermal effects observed at high charge and discharge rates seen in electric vehicle applications. From an analysis of the literature, the requirements for lithium-ion thermal management systems for optimal performance in these applications are suggested, and it is clear that no existing thermal management strategy or technology meets all these requirements. Thomas-Alyea (kethomas@alumni.princeton.edu) and Kandler Smith (kandler.smith@gmail.com). This article was reviewed by KarenElectric and hybrid electric vehicles ͑EV and HEV͒ may present the best near-term solution for the transportation sector to reduce our dependence on petroleum and to reduce emissions of greenhouse gases and criteria pollutants. Rechargeable lithium-ion batteries are well-suited for these vehicles because they have, among other things, high specific energy and energy density relative to other cell chemistries. For example, practical nickel-metal hydride ͑NiMH͒ batteries, which have dominated the HEV market, have a nominal specific energy and energy density of 75 Wh/kg and 240 Wh/L, respectively. In contrast, lithium-ion batteries can achieve 150 Wh/kg and 400 Wh/L, 1 i.e., nearly 2 times the specific energy and energy density.Whereas lithium-ion batteries are rapidly displacing NiMH and nickel-cadmium secondary batteries for portable and hand-held devices, they have not yet been widely introduced in automotive products. The main barriers to the deployment of large fleets of vehicles on public roads equipped with lithium-ion batteries continue to be safety, cost ͑related to cycle and calendar life͒, and low temperature performance 2 -all challenges that are coupled to thermal effects in the battery. Since the recent introduction of HEV fleets, the industry trend is toward larger batteries required for plug-in hybrids, extended-range hybrids, and all-electric vehicles. These larger battery designs impose greater pressure to lower costs and improve safety.Furthermore, most of the research on these types of batteries has been related to fin...

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Heat transfer and fluid flow in microchannels have been topics of intense research in the past decade. A critical review of the current state of research is presented with a focus on the future research needs. After providing a brief introduction, the paper addresses six topics related to transport phenomena in microchannels: single-phase gas flow, enhancement in single-phase liquid flow and flow boiling, flow boiling instability, condensation, electronics cooling, and microscale heat exchangers. After reviewing the current status, future research directions are suggested. Concerning gas phase convective heat transfer in microchannels, the antagonist role played by the slip velocity and the temperature jump that appear at the wall are now clearly understood and quantified. It has also been demonstrated that the shear work due to the slipping fluid increases the effect of viscous heating on heat transfer. On the other hand, very few experiments support the theoretical models and a significant effort should be made in this direction, especially for measurement of temperature fields within the gas in microchannels, implementing promising recent techniques such as molecular tagging thermometry (MTT). The single-phase liquid flow in microchannels has been established to behave similar to the macroscale flows. The current need is in the area of further enhancing the performance. Progress on implementation of flow boiling in microchannels is facing challenges due to its lower heat transfer coefficients and critical heat flux (CHF) limits. An immediate need for breakthrough research related to these two areas is identified. Discussion about passive and active methods to suppress flow boiling instabilities is presented. Future research focus on instability research is suggested on developing active closed loop feedback control methods, extending current models to better predict and enable superior control of flow instabilities. Innovative high-speed visualization and measurement techniques have led to microchannel condensation now being studied as a unique process with its own governing influences. Further work is required to develop widely applicable flow regime maps that can address many fluid types and geometries. With this, condensation heat transfer models can progress from primarily annular flow based models with some adjustments using dimensionless parameters to those that can directly account for transport in intermittent and other flows, and the varying influences of tube shape, surface tension and fluid property differences over much larger ranges than currently possible. Electronics cooling continues to be the main driver for improving thermal transport processes in microchannels, while efforts are warranted to develop high performance heat exchangers with microscale passages. Specific areas related to enhancement, novel configurations, nanostructures and practical implementation are expected to be the research focus in the coming years.