A system comprising: an electric heat source; a first heat exchanger having a first portion and a second portion; a first fluid circuit in substantial thermal contact with the heat source and configured to circulate a first thermal management fluid between the heat source and the first portion of the first heat exchanger, wherein the first fluid circuit is configured such that the first thermal management fluid can absorb heat from the heat source and can dissipate heat in the first heat exchanger; and a second fluid circuit configured to pass a second thermal management fluid over the second portion of the first heat exchanger and absorb heat therefrom, wherein (a) the first thermal management fluid comprises: one or more dielectric fluids present in a total amount in the range of 65 wt% to 99.9 wt%; and one or more halocarbons each having a boiling point in the range of 30 °C to 150 °C, present in a total amount in the range of 0.1 wt% to 35 wt%, wherein the one or more halocarbons are homogeneously dispersed in the first thermal management fluid; wherein the dielectric thermal management fluid has a dielectric constant of at least 1.5 at 25 °C; and wherein a flash point of the first thermal management fluid is above the boiling point of the one or more halocarbons; and/or (b) the second thermal management fluid comprises: an aqueous carrier fluid; and a dispersion of micelles within the aqueous carrier fluid, wherein each micelle comprises a solid hydrophobic core particle comprising a phase change material having a melting point in the range of 30 °C to 100 °C and one or more emulsifiers forming a micellar shell around the solid hydrophobic core particle. an electric heat source; a first heat exchanger having a first portion and a second portion; a first fluid circuit in substantial thermal contact with the heat source and configured to circulate a first thermal management fluid between the heat source and the first portion of the first heat exchanger, wherein the first fluid circuit is configured such that the first thermal management fluid can absorb heat from the heat source and can dissipate heat in the first heat exchanger; and a second fluid circuit configured to pass a second thermal management fluid over the second portion of the first heat exchanger and absorb heat therefrom, wherein (a) the first thermal management fluid comprises: one or more dielectric fluids present in a total amount in the range of 65 wt% to 99.9 wt%; and one or more halocarbons each having a boiling point in the range of 30 °C to 150 °C, present in a total amount in the range of 0.1 wt% to 35 wt%, wherein the one or more halocarbons are homogeneously dispersed in the first thermal management fluid; wherein the dielectric thermal management fluid has a dielectric constant of at least 1.5 at 25 °C; and wherein a flash point of the first thermal management fluid is above the boiling point of the one or more halocarbons; and/or (b) the second thermal management fluid comprises: an aqueous carrier fluid; and a dispersion of micelles within the aqueous carrier fluid, wherein each micelle comprises a solid hydrophobic core particle comprising a phase change material having a melting point in the range of 30 °C to 100 °C and one or more emulsifiers forming a micellar shell around the solid hydrophobic core particle. (a) the first thermal management fluid comprises: one or more dielectric fluids present in a total amount in the range of 65 wt% to 99.9 wt%; and one or more halocarbons each having a boiling point in the range of 30 °C to 150 °C, present in a total amount in the range of 0.1 wt% to 35 wt%, wherein the one or more halocarbons are homogeneously dispersed in the first thermal management fluid; wherein the dielectric thermal management fluid has a dielectric constant of at least 1.5 at 25 °C; and wherein a flash point of the first thermal management fluid is above the boiling point of the one or more halocarbons; and/or one or more dielectric fluids present in a total amount in the range of 65 wt% to 99.9 wt%; and one or more halocarbons each having a boiling point in the range of 30 °C to 150 °C, present in a total amount in the range of 0.1 wt% to 35 wt%, wherein the one or more halocarbons are homogeneously dispersed in the first thermal management fluid; wherein the dielectric thermal management fluid has a dielectric constant of at least 1.5 at 25 °C; and wherein a flash point of the first thermal management fluid is above the boiling point of the one or more halocarbons; and/or (b) the second thermal management fluid comprises: an aqueous carrier fluid; and a dispersion of micelles within the aqueous carrier fluid, wherein each micelle comprises a solid hydrophobic core particle comprising a phase change material having a melting point in the range of 30 °C to 100 °C and one or more emulsifiers forming a micellar shell around the solid hydrophobic core particle. an aqueous carrier fluid; and a dispersion of micelles within the aqueous carrier fluid, wherein each micelle comprises a solid hydrophobic core particle comprising a phase change material having a melting point in the range of 30 °C to 100 °C and one or more emulsifiers forming a micellar shell around the solid hydrophobic core particle.