RESEARCH ARTICLE Passive thermal management of the lithium‐ion battery unit for a solar racing car Acar Celik | Hüseyin Coban | Sinan Göcmen | Mehmet Akif Ezan | Aytac Gören | Aytunc Erek Faculty of Engineering, Department of Mechanical Engineering, Dokuz Eylül University, Buca, Turkey Correspondence Mehmet Akif Ezan, Faculty of Engineering, Department of Mechanical Engineering, Dokuz Eylül University, Buca, Izmir, Turkey. Email: mehmet.ezan@deu.edu.tr Summary In this study, a three‐dimensional numerical model is developed to investigate the thermal and electrical characteristics of 18 650 lithium‐ion battery cells that are used in the solar racing car of Dokuz Eylül University, i.e., SOLARIS. The Newman, Tiedemann, Gu, and Kim (NTGK) battery model of ANSYS Fluent software is implemented to resolve the coupled multiphysics problem. In the analysis, only the discharging period of the battery is considered. Before going through parametric studies under variable weather conditions, time‐wise vari- ations of the cell temperature and the battery voltage are evaluated both exper- imentally and numerically under two different ambient conditions of 0°C and 25°C. Comparative results revealed that reasonable predictions are achieved with the current battery model, and the difference between the predicted bat- tery surface temperature and experimental data is less than 1°C. Following the model validation, the battery performance is numerically examined by applying the battery model to a real race procedure of SOLARIS. Phase change materials (PCMs) with different amounts and melting temperatures are imple- mented around the batteries, and transient analyses are conducted under real weather conditions. The current study aims to keep the battery temperature of a solar racing car above a certain limit to prevent the overcooling and main- tain higher charging capacity. Implementation of PCM with a melting temper- ature of 26°C yields 3.15% of capacity increment, and such a performance improvement corresponds to 15.51 Wh of extra energy that can be extracted from an individual battery. KEYWORDS CFD, experimental, lithium‐ion battery, PCM, solar racing car Nomenclature: _ q, volumetric heat generation (W/m 3 ); A PV , surface area of photovoltaic panels (m 2 ); C, discharge rate; C battery , charge capacity (%); D, battery cell diameter (m); H, battery cell height (m) or volumetric enthalpy (J/m 3 ); h, convective heat transfer coefficient (W/m 2 K); I solar , solar radiation (W/m 2 ); k, thermal conductivity (W/mK); T, temperature (°C); t, time (s); T ∞ , ambient temperature (°C); x i , global coordinate of the system (m); Δt, time interval (s); η PV , efficiency of photovoltaic panels Abbreviations: ARC, accelerating rate calorimetry; BTMS, battery thermal management system; EV, electric vehicle; FEM, finite element method; HEV, hybrid electric vehicle; NTGK, Newman, Tiedemann, Gu, and Kim; PCM, phase change material; RMSE, root mean square error; SOC, state of charge Received: 29 November 2018 Revised: 26 February 2019 Accepted: 26 February 2019 DOI: 10.1002/er.4521 Int J Energy Res. 2019;1–11. © 2019 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/er 1