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Thermophysical properties of hydrogen at high temperature and high pressure

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100MPa vessel for
PVT measurements


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A capillary tube
viscometer apparatus


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Short wire probe for thermal
conductivity measurements

The development of hydrogen fuel cell vehicles and the potential for hydrogen to play a key role as an energy carrier in the foreseeable future has intensified interest in the properties of hydrogen over a wide range of conditions. For safe hydrogen energy use, it is of special importance to assure reliability and safety in the design of practical equipment and systems.

We need to understand the thermophysical properties of hydrogen at high pressures and high temperatures to provide reliable designs, and extensive efforts are needed to collect accurate data in this regard.

The current status of thermophysical property data for hydrogen is insufficient. To improve on this, we especially need data covering PVT properties (the relationship between pressure, volume and temperature), viscosity, thermal conductivity, isobaric specific heat and the solubility of hydrogen at high temperatures and high pressures. To obtain this data, we will first develop equipment that is capable of accurately measuring hydrogen properties over a wide range of temperatures and pressures, and then develop an Equation of State (EOS) for hydrogen.

1. PVT property measurements of hydrogen.
PVT properties of fluids are of great importance in many fields. PVT property data of hydrogen at high temperatures and high pressures is required, as accurate experimental data is rare. New measurements are especially desired for high temperature and high pressure environments. The Burnett method is one of the most useful ways of measuring PVT properties in a gas phase, such as hydrogen above room temperature, because this method derives the PVT properties from sample temperatures and pressure measurements, without measuring sample mass. We have measured the PVT properties of hydrogen from 350 K to 473 K and up to 100 MPa using the Burnett method, and a virial EOS was developed based on the measured data with the existing data at low temperatures. The virial EOS is available from 220 K to 473 K and up to 100 MPa, and represents the primary PVT property data within 0.1%, with normal behavior of the second and third virial coefficients. PVT property measurements for hydrogen of up to 773 K are now in progress.

2. Viscosity measurements of hydrogen.
The viscosity of hydrogen, one of its transport properties, is a basic property that must be known when developing any device in which hydrogen gas flows. An accurate collection of viscosity data for hydrogen is needed for a hydrogen society. We constructed a capillary tube viscometer for use in high pressure and high temperature conditions. Obtaining measurements of a pressure drop with high accuracy in extreme conditions is one of the main challenges in this method. A differential pressure sensor that can be used at high pressures of up to 100 MPa is not available commercially, so we examined a pair of accurate absolute pressure transducers for use as differential pressure sensors. The pressure drop through the capillary tube was obtained by subtracting the outlet pressure from the inlet. By using this instrument, we can measure pressure drops with a relative uncertainty of within 1%. Hydrogen gas viscosity has been measured for ranges of temperature and pressure from 295 to 400 K and up to 100 MPa. Viscosity measurements for hydrogen of up to 773 K are now in progress.

3. The study of hydrogen thermal conductivity
The study of hydrogen thermal conductivity has a history of over 140 years, probably beginning in the days of Maxwell, when he correctly anticipated that it should be about seven times that of air. The high thermal conductivity of hydrogen relative to other gases has been used as a characteristic for gas analysis in detectors for gas chromatography. It is also useful when measuring relative concentrations of ortho- and para-hydrogen and for making distinctions among the different hydrogen isotopes. Moreover, its high thermal conductivity makes hydrogen an effective heat carrier in cooling processes. The purpose of this study is to present some new measurements of hydrogen thermal conductivity at pressures of up to 99 MPa, which to the best knowledge of the authors, is 29 MPa higher than any other available measurement. We employ the transient short-hot-wire method, which was used to measure thermal conductivity in the present study. This technique is a variation of the usual transient hot-wire method in that it employs only one short wire instead of two long wires of differing lengths. This simplifies the apparatus and makes it ideal for high pressures and high temperatures, since only a small pressure vessel is required. The challenge with the short-hot-wire method is the need to compensate for the effect of heat conduction through the ends of the wire. This effect is factored in through a high-precision numerical solution using the two-dimensional unsteady heat conduction equation.

Thermofluid Physics Lab.,
Department of Mechanical Engineering, Faculty of Engineering, Kyushu University
Professor Yasuyuki Takata
Associate Professor Masamichi Kohno
Assistant Professor Naoya SAKODA
Technical Staff Sumitomo HIDAKA
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