CRYSTALLIZATION OF AMMONIUM NITRATE UNDER ORGANIZED MONOLAYERS OF VARIOUS AMPHIPHILES

This paper deals with the investigation on the influence of four amphiphile monolayers viz. arachidic acid, a mixture of dioctadecyl amine and arachidic acid (3:1(, carboxybetaine and dioleoyl-L-a-lecithin (DOPC) on ammonium nitrate crystallization. The study was carried out by means of surface pressure vs. area, surface potential vs. area and fluorescent microscopy. Results indicated a strong effect on ammonium nitrate crystallization in the presence of carboxybetaine and dioctadecylamine monolayers, whereas an inhibition in crystal growth was observed in the presence of DOPC

Numerical Simulations for Indirect and Direct Cooling of 54 V LiFePO₄ Battery Pack

In this study, three-dimensional thermal simulations for a 54 V Lithium-ion battery pack composed of 18 LiFePO4 pouch battery cells connected in series were conducted using a multi-scale electrochemical-thermal-fluid model. An equivalent circuit model (ECM) is used as a subscale electrochemical model at each cell node of the battery, which is then combined with the macro-scale thermal and fluid equations to construct a model of the battery and battery pack. With the model, the cooling effects of indirect cooling and direct cooling battery thermal management systems (BTMS) on the battery pack under rapid discharging conditions are explored. It is found that when the battery pack is discharged at 2C, indirect cooling of the bottom plate can effectively dissipate heat and control the temperature of the battery pack. Under the 10C discharging condition, the maximum temperature of the battery pack will exceed 100 °C, and the temperature uniformity will be very poor when using indirect cooling of the bottom plate for the battery pack. Direct air cooling is also unable to meet the cooling requirements of the battery pack at a 10C discharging rate. The possible reason is that the convective heat transfer coefficient of direct air cooling is small, which makes it difficult to meet the heat dissipation requirements at the 10C condition. When single-phase direct cooling with fluorinated liquid is used, the maximum temperature of the battery pack under the 10C discharging condition can be controlled at about 65 °C. Compared with air direct cooling, the pressure drop of fluorinated liquid single-phase direct cooling is smaller, and the obtained battery pack temperature uniformity is better. From the detailed study of fluorinated liquid single-phase direct cooling, it is concluded that increasing the coolant flow rate and reducing the cell spacing in the battery pack can achieve a better cooling effect. Finally, a new cooling method, two-phase immersion cooling, is investigated for cooling the battery pack. The maximum temperature of the battery pack discharged at a 10C rate can be controlled below 35 °C, and good temperature uniformity of the battery pack is also achieved at the same time. This study focuses on fluorinated liquid immersion cooling using numerical simulations, showing that it is a promising cooling method for lithium-ion battery packs and deserves further study. This paper will provide a reference for the design and selection of BTMS for electric vehicles

Three-Dimensional Thermal Simulations of 18650 Lithium-Ion Batteries Cooled by Different Schemes under High Rate Discharging and External Shorting Conditions

In this work, three-dimensional thermal simulations of single 18650 lithium-ion battery cell and 75 V lithium-ion battery pack composed of 21 18650 battery cells are performed based on a multi-scale multi-domain (MSMD) battery modeling approach. Different cooling approaches’ effects on 18650 lithium-ion battery and battery pack thermal management under fast discharging and external shorting conditions are investigated and compared. It is found that for the natural convection, forced air cooling, and/or mini-channel liquid cooling approaches, the temperature of battery cell easily exceeds 40 °C under 3C rate discharging condition. While under external shorting condition, the temperature of cell rises sharply and reaches the 80 °C in a short period of time, which can trigger thermal runaway and may even lead to catastrophic battery fire. On the other hand, when the cooling method is single-phase direct cooling with FC-72 as coolant or two-phase immersed cooling by HFE-7000, the cell temperature is effectively limited to a tolerable level under both high C rate discharging and external shorting conditions. In addition, two-phase immersed cooling scheme is found to lead to better temperature uniformity according to the 75 V battery pack simulations

One-Dimensional Numerical Simulation of Pt-Co Alloy Catalyst Aging for Proton Exchange Membrane Fuel Cells

The service life of catalysts is a key aspect limiting the commercial development of proton exchange membrane fuel cells (PEMFCs). In this paper, a one-dimensional degradation model of a Pt-Co alloy catalyst in the cathode catalytic layer (CCL) of a PEMFC is proposed, which can track the catalyst size evolution in real time and demonstrate the catalyst degradation during operation. The results show that severe dissolution of particles near the CCL/membrane leads to uneven aging of the Pt-Co alloy catalyst along the CCL thickness direction. When the upper potential limit (UPL) is less than 0.95 V, it does not affect the catalyst significantly; however, a slight change may cause great harm to the catalyst performance and service life after UPL > 0.95 V. In addition, it is found that operating temperature increases the Pt mass loss on the carbon support near the CCL/membrane side, while it has little effect on the remaining Pt mass on the carbon support near the CCL/GDL side. These uncovered degradation mechanisms of Pt-Co alloy provide guidance for its application in PEMFCs