201 201 103 203 103 207 101 209 211 205 201 Figure 5. Liquid cooling system designed by Tesla for Model S. (Source: Wu et al., 2019; used with permission.) TABLE 1. Comparison among cooling strategies. (Source: Kumar et al., 2020.) Performance Criteria Initial cost of setup Maintenance Simplicity Heat transfer rate Ease of integration Viscosity of coolant Life Indirect Liquid Cooling High Medium Medium Medium Difficult Medium (e.g., water) About 20 years Direct Liquid Cooling High Difficult Difficult High Difficult High (e.g., mineral oils) 3-5 years Forced Air Low Easy Easy Low Easy Low PCM Moderate Easy Easy High Easy Medium About 20 years About 20 years Fins Li-Ion Battery Box PCM Air Coolant Figure 6. Combined PCM and air cooling. (Source: Kumar et al., 2020.) increased by 40% with the addition of carbon nanofiber. The thermal conductivity of PCMs can also be improved by impregnating them with porous metal foam and carbon foam matrixes. It was found that the impregnation of paraffin with graphite foam leads to an increment in thermal conductivity by around 576%. When expanded graphite was added in the paraffin with a 20% weight concentration, the increment in thermal conductivity was observed to be 41%. Similarly, with the use of porous carbon foam, the thermal conductivity of paraffin increased from 0.796 to 1.284 Wm−1K−1. The concentration of metal foam and carbon foam also plays an important role in the thermal performance enhancement of the base fluid. The thermal conductivity of a PCM composite with metal foam increases on decreasing the porosity of the metal foam. This impregnation also improves other thermophysical properties, such as stability and thermal IEEE Electrification Magazine / DECEMBER 2022 81