No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Experimental investigation for the operational performance improvement of cryogenic piston-type pump using subcooling effect for liquid hydrogen stations
... The results suggest that increasing the cross-sectional area of the head channel and throat can decrease the static pressure losses and mitigate the risk of cavitation. Kim et al. [10] constructed a laboratory-scale cryogenic liquid pump and performed liquid nitrogen experiments to investigate the influence of subcooling degree and discharge pressure on the duty cycle of exhaust duration. Additionally, they established a numerical model that predicts the pump operation, and the results suggest that the subcooling degree can enhance the cryogenic liquid pump performance. ...
Reciprocating liquid hydrogen pumps are essential equipment for hydrogen refueling stations with liquid hydrogen stored. The valves play a crucial role in facilitating unidirectional flow and the pressurization of liquid hydrogen within the pump. This paper establishes a comprehensive numerical model to simulate the whole working cycle of a reciprocating liquid hydrogen pump. The influence of valve parameters and pump operating conditions on the motion characteristics of valves, including lift, closing lag angle, and impact velocity, is investigated. The results indicate that with the maximum lift of the suction valve at 10 mm and the discharge valve at 5 mm, the closing lag angle is minimal, and the impact velocity of the valve falls within an acceptable range. The optimal rotation speed range is between 200 and 300 rpm, within which both the closing lag angle and impact velocity of valves are minimized. Excessive maximum lift and low rotational speed lead to significant oscillations and high impact velocity in valve movement with the effects being more pronounced in the suction valve. The effects of the subcooling degree of inflow liquid hydrogen on the valve motion are further analyzed. The findings suggest that the subcooling degree of inflow liquid hydrogen helps inhibit the vaporization in the pump operation and ensures the valves work correctly. This work would contribute to pump optimization and valve collision failure analysis in reciprocating liquid hydrogen pumps.
... On the other hand, Kim [3] analyzed the impact of subcooling degree and exhaust pressure on the performance of a high-pressure piston pump for pressurizing cryogenic liquid through an experimental study of a lab-scale cryogenic liquid pump. A new concept to measure the pump performance with the exhaust mass measure was introduced. ...
Due to the climate change effects and high fossil fuel consumption to supply the global energy demand, scientific studies have been conducted to reduce the pollutant emissions and improve the energy generation processes. In this sense, cryogenic flow transport processes for hydrogen and electrical energy generation have promoted the application of alternative fuels under complex working conditions to reduce greenhouse gas emissions. With the aim to analyze and optimize the application of mechanical devices for liquid hydrogen transport processes, this research proposes a predictive analysis of a cryogenic pumps based on numerical simulations with CFD tools in a virtual environment. To achieve accurate results, turbulence models are applied to study and predict the liquid hydrogen behavior and its interaction with impeller blades of centrifugal pumps. In consideration with the complex analysis of turbulent and cryogenic flows, a CFD tool is computed to solve and describe the workflow behavior around the blades under different working conditions. Finally, a multi-objective optimization method based on CFD simulations is proposed to improve the impeller design of the small centrifugal pump and reduce costs with computational tools.
Cryogenic piston pumps are commonly found in cryogenic systems to pressurize low-temperature liquefied fuels, such as liquified natural gas (LNG) or hydrogen, which are then gasified and stored in high-pressure vessels. The main challenges to be tackled in the design of these machines concern the low operating temperatures, high discharge pressures, and especially the need to avoid liquid evaporation, as this can lead to a reduction of volumetric efficiency or even to the shutdown of the pump. Two effects can cause the formation of vapor bubbles: cavitation, i.e., when the static pressure falls below the saturation value during the suction phase, and evaporation due to a temperature increase of the cryogenic liquid.
In this study, a numerical analysis of a cryogenic single-piston pump is carried out. In the first part of the activity, the suction phase is studied through three-dimensional, steady-state CFD simulations. The performance of the pump in terms of pressure losses is evaluated and possible improvements to the suction geometry are identified.
Then, two-phase steady-state Eulerian-Eulerian simulations are performed. The Rayleigh-Plesset model is used in order to evaluate the onset of cavitation. The minimum inlet pressure conditions that avoid cavitation are identified for two different geometries underlining the positive effect of the introduced modifications. Results show that the methodology applied in this work can lead to improvements in cryogenic pump design, reducing the static pressure losses and hence limiting the risk of cavitation.
Modeling and optimization of liquid hydrogen (LH2) pumps require accurate in-cylinder heat transfer correlations. However, the applicability of existing correlations based on gas mediums to LH2 remains to be verified. In this paper, the unsteady heat transfer and fluid flow in a closed LH2 pump cylinder are numerically studied by adopting the gas spring model. The phase shifts and temperature distribution in the closed pump cylinder are investigated. LH2 is less affected by in-cylinder heat transfer and has a more uniform temperature distribution compared to nitrogen gas, while a low-temperature zone appears near the piston face at 120 rpm. Finally, the validity of Lekic's correlation in predicting the heat flux of the LH2 compression process in the closed pump cylinder is verified, and the efficiency decrement versus rotational speed is analyzed based on the correlation. This work would be useful for selecting a proper in-cylinder heat transfer model for predicting the thermodynamic process in reciprocating LH2 pumps.
We have developed a hydrogen (H2) refueling solution capable of delivering precooled, compressed gaseous hydrogen for heavy duty vehicle (HDV) refueling applications. The system uses a submerged pump to deliver pressurized liquid H2 from a cryogenic storage tank to a dispensing control loop that vaporizes the liquid and adjusts the pressure and temperature of the resulting gas to enable refueling at 35 MPa and temperatures as low as −40 °C. A full-scale mobile refueler was fabricated and tested over a 6-month campaign to validate its performance. We report results from tests involving a total of 9000 kg of liquid H2 pumped and 1350 filling cycles over a range of conditions. Notably, the system was able to repeatably complete multiple, back-to-back 30 kg filling cycles in under 6 min each, in full compliance with the SAE J2601-2 standard, demonstrating its potential for rapid-throughput HDV refueling applications.
The experimental data accessible in the open literature related to pool boiling of liquid hydrogen (LH2), liquid methane (LCH4), and liquid oxygen (LO2) were compiled. Pool nucleate boiling of LH2 data were compiled from 17 sources, and pool film boiling of LH2 data were compiled from six sources. Pool nucleate boiling of LCH4 data were collected from eight sources, and useful data for pool film boiling of LCH4 were found from only three sources, all representing boiling on the outside surface of horizontal cylinders. For LO2, pool nucleate boiling data from 11 sources were compiled, and useful pool film boiling data could be found from only four sources, three for horizontal cylinders and one for vertical cylinders. The predictions of 19 pool nucleate and 10 pool film boiling correlations were compared with experimental data for the three cryogens. The film boiling data were only compared with appropriate models and correlations based on surface geometry and orientation.
Overall, pool nucleate boiling data for all three fluids display considerable scatter, and existing correlations are unable to effectively narrow the scatter to better than an order of magnitude. The correlations of Stephan and Abdelsalam (1980) and Forster and Zuber (1955) perform best for LH2, and can predict the bulk of the existing heat flux data within an order of magnitude. They can predict respectively, 38% and 27% of the data within a factor of two. The correlations of Bier and Lambert (1990) and Forster and Zuber (1955) perform best for nucleate boiling of LCH4 and can predict the bulk of the existing heat flux data within an order of magnitude. They can predict respectively, 58% and 49% of the data within a factor of two. For LO2, the correlations of Forster and Zuber (1955) and Bier and Lambert (1990) provide the best agreement with experimental data for nucleate pool boiling, and can predict the heat flux data within an order of magnitude. They could predict respectively, 50% and 47% of the data within a factor of two.
The film boiling data show smaller scatter in comparison with nucleate boiling, and can be predicted by existing correlations with reasonable accuracy.
Cryogenic pressurized hydrogen (H2) vessels promise maximum storage density with potential to enabling practical H2 vehicles with maximum driving autonomy and minimum cost of ownership. This paper contributes to a more complete evaluation of the benefits of cryogenic vessel technology by establishing a methodology for evaluating fill density for any initial vessel thermodynamic state. This is accomplished by analyzing 24 cryogenic pressure vessel fill experiments with a liquid hydrogen (LH2) pump manufactured by Linde and installed at the Lawrence Livermore National Laboratory (Livermore, CA) campus. The LH2 piston pump takes LH2 from the station Dewar at near ambient pressure (3 bar) and very low temperature (24.6 K) and pressurizes it to the vessel pressure in two stages of compression, up to 875 bar, although the rating of the cryogenic vessel used for these experiments limits fill pressure to 345 bar. Experiments spanned initial vessel temperatures from ambient to 22 K, enabling pump testing over a broad range of conditions. Experimental results confirm many of the virtues that make LH2 pumping a promising technology for H2 dispensing, both for filling cryogenic as well as ambient temperature vessels: high throughput (1.67 kg/min, 100 kg/h), unlimited capacity for back to back refueling, low electricity consumption at the station due to high density of LH2 minimizing compression work, and highest fill density, up to 80 g/L (estimated) when dispensing cryogenic hydrogen at 700 + bar. Analysis of the experiments shows that fill density can be predicted with reasonable accuracy (±0.7 g/L) by assuming 10 kJ/kg K cryogenic vessel inlet entropy (pump delivery hose outlet entropy). Fill lines are finally generated on a H2 phase diagram, producing charts that can be used for rapidly determining fill density for any vessel condition at the moment of fill initiation.
This paper reports the results of a comprehensive test of liquid hydrogen (LH2) pump performance and durability conducted while cycle testing a prototype thin-lined cryogenic pressure vessel 456 times to 700 bar. This extensive LH2 pump experimental data set provides a wealth of information vital for a complete evaluation of the future potential of this promising technology for ambient temperature and cryo-compressed vessel refueling. The experiment was conducted at Lawrence Livermore National Laboratory (Livermore, CA)'s hydrogen test facility, specifically built for this experiment and including a containment vessel for safe testing of the prototype vessel and a control room for efficient monitoring. Original pump and storage instrumentation was complemented with an electric power analyzer and a boil-off mass flow meter for more complete pump characterization.
The results of the experiment confirm most of the expected virtues of the LH2 pump: rapid (3 min) refueling of the 65-liter prototype vessel at high flow rate (1.55 kgH2 per minute on average), unlimited back to back refueling, low electricity consumption (1.1 kWh/kg H2), no measurable degradation, and low maintenance. High cryogenic vessel fill density is another key performance metric that was demonstrated in an earlier publication. These virtues derive from the high density of LH2 enabling pressurization to high density with relatively little energy consumption and high throughput from a small displacement pump. Boil-off losses as high as 27.7% of dispensed hydrogen were measured, at experimental conditions not representative of operation at a hydrogen refueling station. These losses drop to 15.4% for operation that may be representative of a small station (332 kg/day), while we anticipate less than 6% boil-off with the existing pump and Dewar with improved LH2 delivery truck operations and a more favorable arrangement of the LH2 pump relative to the Dewar.
A centrifugal cryogenic pump has been designed at Argonne National Laboratory to circulate liquid nitrogen (LN2) in a closed circuit allowing the recovery of excess fluid. The pump can circulate LN2 at rates of 2-10 L/min, into a head of 0.5-3 m. Over four years of laboratory use the pump has proven capable of operating continuously for 50-100 days without maintenance.
To improve performance and design of the cryogenic pump, analyze and
solve the pump fault, and ensure the reliability of design and
operating, it is highly necessary to understand the cryogenic pump
temperature profile. Regarding horizontal single cryogenic centrifugal
pump as the studied object, the flow field and structural heat transfer
is calculated and analyzed. Based on reasonable boundary condition,
three dimensional steady state of the pump mesh model is calculated by
finite-element method with the software of Fluent, the fluid pressure
field and the whole structural temperature profile is obtained. The
structural temperature profile by finite-element heat transfer
calculation indicates that: in the operating range of the cryogenic
pump, the pumping cryogenic liquid is unable to vaporize at the room
temperature, and the low temperature area is unable to interfere with
the gear case in normal operation.
Musashi's research work on hydrogen engines has demonstrated that, in respect of not only complete elimination of abnormal combustion such as knocking, pre-ignition and backfire peculiar to hydrogen engines but also high specific power brought by greater charging efficiency, hydrogen engines with high pressure hydrogen injection, spark ignition and LH2 pump are most practical and reasonable engine system. The pressure of injection to the combustion chamber has been increased up to 10 MPa aiming at rapid injection and good mixture formation. The leakage through the clearance between the piston and the cylinder of the pump has become greater with the increase of pressure of injection. To decrease the leakage, the clearance was made smaller (up to 2.5 μm) but it was found that the clearance was so small that the piston and the cylinder of the pump were more subject to contact with each other which caused heat to be generated due to the friction. As a result, LH2 in the pump was gasified and the piston compressed the hydrogen gas. This is called “gas pumping”, and results in disability of pumping.The authors have developed a LH2 pump whose piston has a cup-shaped cavity; the thin wall of which expands toward the cylinder wall of the pump only when the pressure rises. From our experiments it has been found that the leakage could be reduced to about a half that of the old type pump with the clearance of 2.5 could be operated. As a result, a desirable pump performance was obtained.