Imagine trying to weigh something you cannot see, cannot touch, and whose properties continuously change as temperatures soar to nearly 500°C. This is the real challenge scientists face when measuring the density of hydrogen, a gas widely regarded as one of the fuels of the future. Without accurate data, hydrogen storage and distribution systems cannot be designed safely or efficiently.
A study published in the June 2018 issue of SINERGI offers a solution: a density measurement method that is simpler, requires fewer experimental steps, and has demonstrated high accuracy.
Why High-Temperature Hydrogen Data Remain Limited
Hydrogen has been studied for more than a century. Its thermodynamic properties—including the relationship between pressure, volume, and temperature (PVT)—have been investigated since the 1920s, with researchers around the world collecting data across a wide range of temperatures and pressures.
However, one important gap remains. Experimental PVT data for hydrogen at temperatures above 150°C and pressures between 0.1 MPa and 1 MPa are still remarkably scarce. Yet these are precisely the operating conditions encountered in many hydrogen energy applications. The design of storage tanks, distribution pipelines, and safety systems all depends on accurate
A New Instrument, A New Approach
To address this gap, Supriatno of the Institut Teknologi Medan developed an experimental apparatus that combines the isochoric method with the expansion method.
Conventional isochoric measurements require researchers to repeatedly record pressure and temperature along an isochoric path—a time-consuming procedure that is susceptible to cumulative measurement errors. The new approach significantly simplifies the process. Rather than directly measuring the mass or volume of the gas, hydrogen is first introduced into a 250 cm³ sample cell before being expanded into a 2,500 cm³ expansion cell, which has a volume ten times larger.
"This method does not require pressure and temperature measurements along an isochoric path, as in conventional isochoric techniques, nor does it require direct measurement of the gas mass or volume."
The large difference in volume between the two chambers is intentional. Following expansion, the hydrogen pressure inside the expansion cell becomes sufficiently low that the gas behaves almost as an ideal gas, greatly simplifying density calculations. Both chambers were constructed from SUS316 stainless steel, which provides excellent resistance to high temperatures and pressures while also offering good thermal conductivity, allowing the system to reach thermal equilibrium more rapidly.
Temperature was controlled using a high-precision proportional-integral-derivative (PID) control system. During measurements, temperature stability was maintained within ±10 millikelvin (mK), reflecting the stringent accuracy requirements of the experiment.
The Results: A Maximum Deviation of Just 1.42%
Measurements were performed at three target temperatures—300°C, 400°C, and 500°C—and three target pressures: 0.3 MPa, 0.5 MPa, and 0.7 MPa. The hydrogen used in the study had a purity of 99.999%.
The measured densities were then compared with values predicted by the Leachman equation of state, the internationally recognized reference model for hydrogen thermodynamic properties available through the National Institute of Standards and Technology (NIST) database.
The maximum deviation between the experimental measurements and the reference values was 1.42%, recorded at 498.217°C and 0.2947 MPa. The smallest deviation, 0.11%, occurred at 399.461°C and 0.6981 MPa. Overall, the researchers observed that deviations tended to increase slightly as temperature increased—a pattern that is both physically consistent and scientifically expected.
One particularly intriguing phenomenon also emerged during the experiments. At elevated temperatures, the pressure inside the sample cell exhibited a slight decrease before expansion took place. Similar behavior had been reported in previous studies. Despite extensive testing, the researchers found no evidence of physical leakage within the apparatus. Interestingly, the same phenomenon was not observed when helium or nitrogen was tested using the identical experimental setup, leading the researchers to conclude that the behavior appears to be unique to hydrogen under high-temperature conditions.
A Small Step Toward Cleaner Energy
This research may not immediately transform how the world uses hydrogen, but it fills a significant gap that has persisted in the scientific literature for decades.The experimental data provide engineers designing hydrogen energy systems with valuable reference points for temperature and pressure conditions that previously relied largely on theoretical estimates.
Moreover, the combined measurement technique developed in this study may also be applicable to other gases whose PVT properties remain incompletely characterized.As the global transition toward clean energy accelerates, seemingly small improvements in measurement accuracy can make the difference between systems that operate safely and efficiently and those that fail under unexpected conditions.
Source DOI: https://doi.org/10.22441/sinergi.2018.2.006
Authors: Anny Anggraini; drg. Achmad Zam Zam Aghasy, M.Kes.
Photo: Freepik