Isobaric heat capacity (Cp) measurements of supercritical fluids using flow calorimetry: equipment design and experimental validation with carbon dioxide, methanol, and carbon dioxide-methanol mixtures

Abstract

Accurate thermodynamic property data of dense fluids and supercritical fluids are important in many scientific investigations and engineering applications. A flow calorimeter has been constructed to measure the isobaric heat capacity of pure fluids and fluid mixtures over a range of temperatures, 25-150 °C, and pressures, 1-300 bar. Base measurement accuracy approaches ±1% and is limited by precise equipment calibration and refinement of the measurement technique. Validation of the calorimeter's operation was achieved with supercritical carbon dioxide, methanol, and carbon-dioxide-methanol mixtures, over a range of conditions from sub-critical to supercritical temperatures and densities, demonstrating the calorimeter's robustness.

Thermodynamics analysis of S-CO<sub>2</sub> recompression-reheating cycle for coal fired power plant

“…Yang 等人 [18] 针对π式煤粉炉构建了与Mecheri等人相似的 热 力 循 环 , 循 环 采 用 一 次 再 热 布 置 , 并 构 建 了 300 MW煤粉炉模型, 分析了受热面的吸热特性. [19] 计算得出, REFPROP 内置了CO 2 的状态方程, 该方程是由Span等人 [20] 基 于实验数据拟合得到的, 具有较高的精度 [21] , 被广…”

Isobaric Heat Capacity Measurements of Supercritical R1234yf

“…The isobaric heat capacity of R1234yf was measured using a custom-made flow calorimeter developed in our research group. The design of the apparatus and its operating principles are described in detail in our earlier publication and are only briefly summarized here. The accuracy of the calorimeter has been validated using carbon dioxide, methanol, and CO 2 –methanol mixtures at temperatures up to 423 K and pressures up to 30 MPa. , …”

“…The calorimeter cell (B) consists of a small-diameter U-tube placed in a vacuum chamber, which is submerged in a temperature-controlled sand bath to reduce the heat loss from the calorimeter. A detailed description of the apparatus including specifications of individual subcomponents and design solutions used to improve measurement accuracy is provided in our earlier publication …”

“…Both the careful design of the calorimeter and performing blank experiments reduced the experimental heat capacity error. To account for the remaining sources of systematic error, such as the heat loss, calorimeters measuring absolute c P typically require calibration. ,− In this work, physical calibration using R134a was performed prior to making c P measurements of R1234yf. R134a was chosen as a reference fluid because it has similar thermodynamic properties to R1234yf and its heat capacity has been accurately measured ,, and quantified using highly accurate, multiparameter EOS .…”

“…The accuracy of the calorimeter has been validated using carbon dioxide, methanol, and CO 2 −methanol mixtures at temperatures up to 423 K and pressures up to 30 MPa. 12,13 The flow calorimeter approximates the definition of the isobaric heat capacity of a pure fluid by performing a c P measurement over a small but measurable temperature difference:…”