H2Tech - Q4 2022 - 32

REFUELING STATIONS
suring the mass flowrate directly. The
author's company has extensive experience
and knowledge in the application of
flowmeters for H2
measurements, as well
as other types of gas. In an ongoing joint
research project, the author's company is
involved in the European project of Metrology
for Hydrogen Vehicles II (MetroHyVe
II), along with several national or
designated measurement institutes and
companies from the industry.
As a part of the first MetroHyVe project,
several experiments were undertaken
on commercially available Coriolis meters
for the application in H2
dispensers (produced
by various manufacturers). Results
showed that these meters are not sensitive
to pressure effects but can be significantly
affected by temperature changes,
especially before thermal equilibrium is
reached between the flowmeter body and
the incoming gas-i.e., when pre-cooled
gas is suddenly introduced to a meter that
is at ambient temperature.
The project highlighted other major
sources of error in H2
dispenser billing.
When a customer finishes the refueling of
an FCEV, some H2 is trapped between the
meter and the head of the dispenser that
connects to the vehicle. This amount of H2
is measured by the meter but not received
by the customer. Some of the trapped H2
that is in the hose of the dispenser must
be vented for safety reasons. The rest remains
trapped between the meter and the
cutoff valve until the next customer starts
refueling. Therefore, each customer receives
some H2
metered for the previous
customer and leaves some for the next.
However, these two amounts are not always
the same as different people might
refill their vehicles to different pressures.
Hence, a different amount of H2
is trapped
each time. This effect is not related to the
flowmeter accuracy but can introduce a
significant error in the metering and billing
of H2
refueling station design considerfor
each customer, particularly
when there is a large distance between the
flowmeter outlet and the dispenser.
H2
ations and appropriate corrections can
be employed to mitigate the uncertainties
caused by the aforementioned factors.
Finding the right location for the installation
of the meter, optimizing the dispenser
to reduce the dead volume, and developing
and using proper correlations to compensate
for the remaining dead volume
and the vented H2
are some solutions. Results
of the MetroHyVe project and the author's
company's research suggest that, if
these considerations are in place, available
flowmeters produced for the application
in H2
dispensers can achieve OIML R139
Accuracy Class 2. The author's company
has also developed the UK's first mobile
primary standard for field evaluation of H2
refueling station dispensers. This primary
standard can be taken to a H2
refueling station
to test its dispensers and determine
if the metering systems can meet the requirements
of OIML R139.
MAHDI SADRI is a Clean Fuels
Consultant at TÜV SÜD National
Engineering Laboratory, a worldclass
provider of technical
consultancy, research, testing and
program management services.
Part of the TÜV SÜD Group, the
organization is also a global center of excellence
for flow measurements and fluid-flow systems and is
the UK's designated institute for flow measurement.
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