Determination of isobaric enthalpy differences of heat transfer fluids

The heat capacity of eutectic diphenyl oxide (DPO) and biphenyl (BP) was investigated with Calvet-type differential scanning calorimetry. Significant impact of the sample mass per crucible was found. With 82 mg per 130 µl lowest impact by heat of evaporation on the readings was achieved. With the linear data fit C (in J/(g*K))=0.00268 * T (in °C)+1.4917 in the range of 130 - 409 °C the calculated enthalpy difference between 300 °C and 400 °C is 0.6 - 3.7% smaller in comparison to the projections based on manufacturer's data sheets. The impact of pressure on the enthalpy difference was tested with a compression loop between 17 bar and 63 bar. It could be shown that additional mechanical pressure causes decreases of the enthalpy difference by -0.03% J/(g*bar).