Hydrogen Mass Flow Rate Research Articles

Active disturbance rejection control of metal hydride hydrogen storage

Metal hydride (MH) hydrogen storage is used in both mobile and stationary applications. MH tanks can connect directly to high-pressure electrolyzers for on-demand charging, saving compression costs. To prevent high hydrogen pressure during charging, hydrogen generation needs to be controlled with consideration for unknown disturbances and time-varying dynamics. This work presents a robust control system to determine the appropriate mass flow rate of hydrogen, which the water electrolyzer should produce, to maintain the gaseous hydrogen pressure in the tank for the hydriding reaction. A control-oriented model is developed for MH hydrogen storage for control system design purposes. A proportional-integral (PI) and an active disturbance rejection control (ADRC) feedback controllers are investigated, and their performance is compared. Simulation results show that both the PI and ADRC controllers can reject both noises from the output measurements and unknown disturbances associated with the heat exchanger. ADRC excels in eliminating disturbances produced by the input mass flow rate, maintaining the pressure of the tank at the charging pressure with little oscillations. Additionally, the parameters estimated by the ADRC's extended state observer was used to predict the state-of-charge (SOC) of the MH.

Influence of propagation direction on operation performance of rotating detonation combustor with turbine guide vane

Due to the pressure gain combustion characteristics, the rotating detonation combustor (RDC) can enhance thermodynamic cycle efficiency. Therefore, the performance of gas-turbine engine can be further improved with this combustion technology. In the present study, the RDC operation performance with a turbine guide vane (TGV) is experimentally investigated. Hydrogen and air are used as propellants while hydrogen and air mass flow rate are about 16.1 g/s and 500 g/s and the equivalence ratio is about 1.0. A pre-detonator is used to ignite the mixture. High-frequency dynamic pressure transducers and silicon pressure sensors are employed to measure pressure oscillations and static pressure in the combustion chamber. The experimental results show that the steady propagation of rotating detonation wave (RDW) is observed in the combustion chamber and the mean propagation velocity is above 1650 m/s, reaching over 84% of theoretical Chapman-Jouguet detonation velocity. Clockwise and counterclockwise propagation directions of RDW are obtained. For clockwise propagation direction, the static pressure is about 15% higher in the combustor compared with counterclockwise propagation direction, but the RDW dominant frequency is lower. When the oblique shock wave propagates across the TGV, the pressure oscillations reduces significantly. In addition, as the detonation products flow through the TGV, the static pressure drops up to 32% and 43% for clockwise and counterclockwise propagation process respectively.

Parametric analysis on the combustion and thermal performance of a swirl micro-combustor for micro thermophotovoltaic system

A swirl micro-combustor which has strong capability to stabilize the flame has been developed and is promising to be used in micro thermophotovoltaic power generators in this work. Heat recirculation plays a requisite role in flame stability and thermal performance of micro combustors. Thus, the effects of three parameters (center inlet radius w1, swirler width w2, and step height w3) that determine the size and location of the recirculation zones in a premixed hydrogen/air flame are investigated numerically. The results show that inner recirculation zone and corner recirculation zone generated by a swirler are critical for stabilizing the flame. The parameter w1 has an insignificant influence on the thermal performance. Enlarging the inner recirculation zone by decreasing w2 provokes enhanced heat transfer, and increases the temperature level and temperature non-uniformity of combustor walls. The size of corner recirculation zone is increased by increasing w3, which raises the outer wall temperature uniformity. Based on the parametric analysis, the newly designed micro combustor possesses a high wall temperature level. Additionally, the energy output increment is between 9.1% and 14.2% at hydrogen mass flow rate of 0.0006 g/s when stoichiometric hydrogen/air ratio ranges from 0.6 to 1.4.

Dynamic simulations of medium-sized hydrogen liquefiers based on EcosimPro simulation software

Dynamic simulations of medium-sized hydrogen liquefiers have been performed using process simulation software EcosimPro. Two hydrogen liquefier process flows have been simulated. One process flow is a helium refrigerator with one helium turbine providing cooling power for hydrogen liquefier, the other one is a helium refrigerator with two helium turbines providing cooling power for hydrogen liquefier. Control logics and control strategies for these two hydrogen liquefiers have been proposed. The cooling down simulations have been performed separately. One turbine hydrogen liquefier, pressure ratio is 2/16 bara, helium mass flow rate is 111 g/s, hydrogen mass flow rate is 4.3 g/s, the liquefaction rate of hydrogen is about 191 L/h. Two turbines hydrogen liquefier, pressure ratio is 1/14 bara, helium mass flow rate is 110 g/s, hydrogen mass flow rate is 5.2 g/s, the liquefaction rate of hydrogen is about 184 L/h. Comparison and discussion have been proposed.

Effect of shock structure on stabilization and blow-off of hydrogen jet flames

Under-expanded hydrogen jet has characteristic shock structure immediately downstream of the nozzle exit. The shock structure depends on the ratio pEX/pA, i.e. the ratio of nozzle exit to ambient pressure, and the distributions of velocity and concentration in an under-expanded hydrogen jet depend on characteristics of the shock structure. Therefore, the shock structure should affect the blow-off behaviour of under-expanded hydrogen jet flame. Since this issue has not been investigated in detail, this study aims to close this knowledge gap. The effect of changes in shock structure on lift-off length and blow-off conditions for non-premixed turbulent hydrogen free jet flame has been experimentally investigated. The shock structure was varied by using three types of nozzles: convergent, straight and divergent nozzles. Inlet diameters of nozzles change from 0.31 to 1.04 mm and outlet diameters from 0.34 to 1.7 mm. The static pressure and the ratio of cross-section area at the nozzle inlet to that at the outlet were varying parameters in this study. Hydrogen was horizontally spouted through a nozzle to atmosphere. The maximum static pressure in a nozzle was 13.2 MPa. The experiments revealed that when the hydrogen jet had sequential shock cell structures, which occurred in the range of pEX/pA smaller than 2.45, a higher mass flow rate of hydrogen was needed for the stabilization of a jet flame than that for pEX/pA larger than 2.45 and that when closed to the ideal expansion (pEX/pA = 1), the mass flow rate for stable flame became maximum. In addition, it was observed that the lift-off length of stable flames followed with sequential shock cell structures were almost the same when the minimum cross-section area of used nozzles was constant. However, when hydrogen jet had a shock structure with single Mach disk, the lift-off lengths and the minimum mass flow rate required for the stable jet flame were decreasing with the decrease of the cross-sectional area ratio of the nozzle exit to inlet.

Effects of rectangular rib on exergy efficiency of a hydrogen-fueled micro combustor

In order to further optimize the working performance of micro-cylindrical combustor, the combustion chamber of the micro-cylindrical combustor is inserted in a rectangular rib. Extensive numerical investigations are conducted to compare the exergy efficiency of non-ribbed and rectangular-ribbed micro combustors under various hydrogen mass flow rates and hydrogen/air equivalence ratios. Moreover, the effects of dimensionless rib positions and heights on the exergy efficiency of micro-cylindrical combustor are also widely investigated. Results suggest that the exergy efficiency of the rectangular-ribbed micro combustor is significantly higher than that of the non-ribbed micro combustor under different inlet conditions. Moreover, the exergy efficiency of the rectangular-ribbed micro combustor is significantly affected by the dimensionless positions l. The optimum dimensionless l is increased with the increase of hydrogen mass flow rate. This work offers us significant reference for optimizing the micro combustor in energy utilization.

Hydrogen circulation system model predictive control for polymer electrolyte membrane fuel cell-based electric vehicle application

Polymer electrolyte membrane fuel cell (PEMFC) is one of the promising solutions overcoming future energy crisis and environment pollution in the automotive industry. However, PEMFC is vulnerable to the circulation of hydrogen mass flow rate and pressure, which may cause the degradation of the PEMFC's anode components and reduction of output performance over time. Thus, the control of the hydrogen supply system draws attention currently and is critical for the durability and stability of the PEMFC system. In this study, a model predictive control (MPC) approach for hydrogen circulation system is developed to regulate the hydrogen flow circulating. A model of the hydrogen supply system that contains a flow control valve, a supply manifold, a return manifold and a hydrogen circulating pump is firstly developed to describe the behavior of the hydrogen mass flow dynamics in the PEMFC. Subsequently, a hydrogen circulating pump MPC scheme is designed based on the piecewise linearized model of hydrogen circulation as well as the switched MPC controllers. By predicting the pressure of the return manifold and the angle velocity of the pump, the proposed MPC approach can manipulate the hydrogen circulating pump to achieve efficient and stable operation of the PEMFC.

Numerical investigations on thermal performance enhancement of hydrogen-fueled micro planar combustors with injectors for micro-thermophotovoltaic applications

In order to address the issue about the low output power of the micro-thermophotovoltaic system, in this work, the inlets of the traditional micro planar combustor are modified into injectors for better thermal performance and higher output power of the micro-thermophotovoltaic system. The thermal performance of traditional and modified micro planar combustors is numerically investigated and compared. It is found that the thermal performance of the modified micro planar combustor is greatly enhanced with the help of the injectors. This is due to that the reduction of the step diameter leads to the rise of the velocity of the inlet flow, resulting in the chemical reaction zone is closer to the center of the combustion chamber in the micro planar combustor. Furthermore, the positive effects and negative effects on thermal performance enhancement brought by the reduction of the step diameter of injectors are vividly discussed under different hydrogen mass flow rate, hydrogen/air equivalence ratio and solid wall material. Finally, some guidelines are proposed for the applications of the micro planar combustors with injectors in the micro-thermophotovoltaic system. This work provides us a simple and practical way to address the issue about the low output power of the micro-thermophotovoltaic system.

Parametric study on dynamic heat and mass transfer response in polymer electrolyte membrane fuel cell for automotive applications

Numerical study on dynamic responses of a polymer electrolyte fuel cell vehicle was performed to understand the effect of operating parameters on heat and mass transfer. We developed a system-level model to analyze dynamic behavior of fuel cell car applied with a variable pressure system consisting blower and back pressure control valve at cathode. Increased hydrogen mass flow rate increased both the anode pressure and relative humidity; when the stoichiometric number increased from 1.5 to 2.5, the pressure increased from 1.6 bar to 3.4 bar and the relative humidity increased from 32% to 62%, respectively. Although pressure increased with air mass flow rate from the blower, relative humidity decreased because blower outlet temperature increased; the relative humidity is 90% at 1.9 bar, but 30% at 1.4 bar. For back pressure control valve, pressure changed without altering mass flow rate or temperature. Therefore, relative humidity is proportional to pressure; the relative humidity is 70% at 1.6 bar, but 98% at 1.9 bar. The operating temperature was changed by controlling the fan speed. Relative humidity was inversely proportional while vehicle performance was proportional to temperature; the relative humidity is 95% at 55 °C, but 58% at 70 °C. Under drastic load variations, changes in pressure by blower and pressure regulator affected dynamic behavior differently; changing the pressure by controlling blower resulted in over/under-shoot, but that by controlling pressure regulator resulted in smooth variation. This analysis can help to understand the dynamic behavior of fuel cell vehicles at the system level and provide the proper direction for the operating strategy of fuel cell vehicles.

Dynamic modelling and controlling strategy of polymer electrolyte fuel cells

A comprehensive dynamic control oriented model of a polymer electrolyte fuel cell (PEFC) is developed, considering the mixed effects of temperature, gas flow and capacitance. The fractional relationship between the dynamic output voltage and the capacitance, which escaped the attention in most previous studies is also addressed. Moreover, based on the developed PEFC model, a proportional integral and derivative (PID) controller is designed to stabilize the output voltage at a determined value by regulating the input hydrogen mass flow rate under a series of disturbance in the input. The dynamic PEFC model and controller are simulated in Matlab/Simulink. The simulation results illustrate that the PEFC system model is capable of characterizing dynamic properties of PEFCs. Additionally, the developed PID controller is effective in stabilizing the output voltage with a rather small overshoot and rather faster response, which also proves that the developed model is suitable for PEFC control algorithms development.

Effect of Channel Diameter on the Combustion and Thermal Behavior of a Hydrogen/Air Premixed Flame in a Swirl Micro-Combustor

Improving the flame stability and thermal behavior of the micro-combustor (MC) are major challenges in microscale combustion. In this paper, the micro combustions of an H2/air premixed flame in a swirl MC with various channel diameters (Din = 2, 3, 4 mm) were analyzed based on an established three-dimensional numerical model. The effects of hydrogen mass flow rate, thermal conductivity of walls, and the preferential transport of species were investigated. The results indicated that the flame type was characterized by the presence of two recirculation zones. The flame was anchored by the recirculation zones, and the anchoring location of the flame root was the starting position of the recirculation zones. The recirculation zones had a larger distribution of local equivalence ratio, especially in the proximity of the flame root, indicating the formation of a radical pool. The combustion efficiency increased with an increasing Din due to the longer residence time of the reactants. Furthermore, the MC with Din = 2 mm obtained the highest outer wall temperature distribution. However, the MC with Din = 4 mm had a better uniformity of outer wall temperature and large emitter efficiency due to the larger radiation surface. An increase in thermal conductivity boosts the thermal performance of combustion efficiency, emitter efficiency, and wall temperature uniformity. But there is a critical point of thermal conductivity that can increase the thermal performance. The above results can offer us significant guidance for designing MC with high thermal performance.

Analysis of a clean hydrogen liquefaction plant integrated with a geothermal system

Abstract Hydrogen is attracting a lot of attention because of its high-energy content and lower weight and volume, making it a promising replacement of fossil fuels. Hydrogen liquefaction is an energy-intensive process that requires high electrical power. This paper presents a novel approach of a large-scale hydrogen liquefaction system combined with geothermal and isobutene power plant. The hydrogen liquefaction system uses a hydrogen Claude refrigeration system and a nitrogen precooling system to produce 335 ton/day of liquefied hydrogen. The mass flow rate of hydrogen in the refrigeration system and nitrogen precooling system were 14 kg/s and 52 kg/s, respectively, to produce specific energy consumption of 6.41 kWh/kg-LH2. The overall power consumption of the liquefaction system was 107 MW. This requires constructing three geothermal and isobutene power plants to produce 130 MW of electrical power. Some parametric studies were conducted to reduce the specific energy consumption (SEC). It is found that reducing the hydrogen mass flow rate to 9 kg/s and the high pressure to 20 bar results in the reduction of the SEC to 4.7 kWh/kg-LH2. However, increasing the steam and isobutene mass flow and high pressure in the system results in an increase in the electric power delivered to 225 MW from 130 MW.

A modified micro reactor fueled with hydrogen for reducing entropy generation

In order to reduce the entropy generation of premixed hydrogen/air flame in the micro combustion chamber, the combustion chamber of the old micro reactor is modified by gradually varying the diameter of the combustion chamber. Extensive numerical investigations about the entropy generation of premixed hydrogen/air flame in old and modified micro reactors are conducted under various hydrogen mass flow rates, hydrogen/air equivalence ratios, solid materials and inlet/outlet diameter ratios. Results suggest that the modified micro reactor has lower total entropy generation than that of the old micro reactor. This is attributed to that the temperature gradient of the burned gas in the modified micro reactor is lower than that in the old micro reactor after chemical reactions. Finally, the largest descent percentages of total entropy generation are achieved under various conditions, which provide significant reference values for hydrogen energy usage under micro scale combustion.

The Net Radial Flow Velocity of the Neutral Hydrogen in the Oval Distortion of NGC 4736

Abstract The net radial flow velocity of gas is an important parameter for understanding galaxy evolution. It is difficult to measure in the presence of the elliptical orbits of an oval distortion because the mathematical model describing the observed velocity is degenerate in the unknown velocity components. A method is developed in this paper that breaks the degeneracy using additional information about the angular frequency of the oval distortion. The method is applied to the neutral hydrogen in the oval distortion of NGC 4736. The neutral hydrogen is flowing inward at a mean rate of −6.1 ± 1.9 km s−1. At this rate, it takes 400 Myr, or 1.7 rotations of the oval distortion, for the neutral hydrogen to travel the 2.5 kpc from the end to the beginning of the oval distortion. The mean mass flow rate of the neutral hydrogen in this region is −0.25 ± 0.11 M ⊙ yr−1, which is similar to estimates for the star formation rate reported in the literature.

Comparative study of combustion and thermal performance in a swirling micro combustor under premixed and non-premixed modes

A swirling micro combustor fueled by hydrogen/air has been proposed based on the concept of swirling flow stabilization. The effects of premixed and non-premixed combustion modes on the combustion efficiency, flame stability, and thermal performance of the micro combustor at various hydrogen/air mass flow rates and equivalence ratios are discussed and compared. The results show that premixed mode has a lower flame location than non-premixed mode, and the flame location of non-premixed mode is more susceptible to changes of hydrogen/air mass flow rate and equivalence ratio than premixed mode. When the hydrogen mass flow rate is lower, the non-premixed mode is more suitable for micro thermophotovoltaic (MTPV) system because the wall temperature is more uniform. However, the premixed mode has a higher and more uniform wall temperature distribution at high hydrogen mass flow rate. Moreover, the hydrogen/air equivalence ratio has a significant effect on the thermal performance in the swirling micro combustor, and the advantage of a high and uniform wall temperature distribution of premixed mode is more obvious at small equivalence ratio. This work provides a reference for the choice of micro combustor combustion modes under different hydrogen/air mass flow rates and equivalence ratios in the MTPV system.

Modeling and Control Strategies of Proton Exchange Membrane Fuel Cells

In this work, comprehensive mathematical models for polymer electrolyte fuel cells (PEFCs) with three different controllers (PID, FOPID and fuzzy + PID) are developed. The models are designed to control the PEMFCs’ output voltage at a determined value by indirectly regulating the input hydrogen mass flow rate. The simulation results show that the developed model is well suitable for characterizing the performance a PEFC. The developed controllers are effective in stabilizing the voltage, the fuzzy + PID controller exhibits superior performance with smaller overshoot and faster response.

Combustion analysis of hydrogen-diesel dual fuel engine with water injection technique

In this paper, the effect of direct diesel injection timing and engine speed on the performance and emissions of CI engine operating on RCCI (H2/diesel mixture) coupled with water injection have been numerically investigated and validated. The simulation have been carried out using GT-Power professional software. A single cylinder dual fuel compression ignition model has been built. The diesel fuel was injected directly to the cylinder. The hydrogen and water were injected to the engine intake manifold and engine port with constant mass flow rate and constant temperature for all engine speed. During the simulation the engine speed was varied from 1000 to 5000 rpm and the diesel injection timing was varied from (−5° to −25° CAD). In addition, the optimized diesel injection timing for specific engine operation parameters has also been performed.The results show that, for specific injection timing and constant hydrogen and water mass flow rate, the increase of engine speed results in an increase in the cylinder temperature, engine brake power, brake specific fuel consumption and NO emissions; but decreases brake thermal efficiency. Moreover, the analysis performed shows that, the advanced injection timing decreases the engine power, brake thermal efficiency and CO emissions; but increases NO emissions.

Dynamic simulation of different transport options of renewable hydrogen to a refinery in a coupled energy system approach

Three alternative transport options for hydrogen generated from excess renewable power to a refinery of different scales are compared to the reference case by means of hydrogen production cost, overall efficiency, and CO2 emissions. The hydrogen is transported by a) the natural gas grid and reclaimed by the existing steam reformer, b) an own pipeline and c) hydrogen trailers. The analysis is applied to the city of Hamburg, Germany, for two scenarios of installed renewable energy capacities. The annual course of excess renewable power is modeled in a coupled system approach and the replaceable hydrogen mass flow rate is determined using measurement data from an existing refinery. Dynamic simulations are performed using an open-source Modelica® library. It is found that in all three alternative hydrogen supply chains CO2 emissions can be reduced and costs are increased compared to the reference case. Transporting hydrogen via the natural gas grid is the least efficient but achieves the highest emission reduction and is the most economical alternative for small to medium amounts of hydrogen. Using a hydrogen pipeline is the most efficient option and slightly cheaper for large amounts than employing the natural gas grid. Transporting hydrogen by trailers is not economical for single consumers and realizes the lowest CO2 reductions.

Evaluation of the effect of reactant gases mass flow rates on power density in a polymer electrolyte membrane fuel cell

In this study it was experimentally investigated the effect of mass flow rates of reactant gases which is one of the most important operational parameters of polymer electrolyte membrane (PEM) fuel cell on power density. The channel type is serpentine and single PEM fuel cell has an active area of 25 cm2. Design-Expert 8.0 (trial version) was used with four variables to investigate the effect of variables on the response using. Cell temperature, hydrogen mass flow rate, oxygen mass flow rate and humidification temperature were selected as independent variables. In addition, the power density was used as response to determine the combined effects of these variables. It was kept constant cell and humidification temperatures while changing mass flow rates of reactant gases. From the results an increase occurred in power density with increasing the hydrogen flow rates. But oxygen flow rate does not have a significant effect on power density within determined mass flow rates.

Numerical investigations on different configurations of a four-channel meso-scale planar combustor fueled by hydrogen/air mixture

Multiple single-channel meso-scale combustors assembling into a multi-channel meso-scale planar combustor is a good solution for elevating the output power of the micro-thermophotovoltaic system. Consequently, how to assembly a multi-channel meso-scale planar combustor for achieving higher output power comes to be an interesting issue. In this work, four representative four-channel meso-scale planar combustors, namely, combustor A, combustor B, combustor C and combustor D are designed. Extensive numerical investigations are conducted to compare the wall temperature of the four combustors under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. Two variables, namely, mean wall temperature and nonuniformity coefficient of wall temperature are defined for comparing the wall temperature of the four meso-scale combustors. It is found that the purely counterflow four-channel meso-scale planar combustor D has more uniform and higher wall temperature compared with other combustors. Furthermore, the detailed heat transfer mechanisms of four different four-channel meso-scale planar combustors are analyzed and presented. In addition, some critical values are proposed for keeping high and uniform wall temperature on the purely counterflow four-channel meso-scale planar combustor. This work offers us great reference value for the design of multi-channel meso-scale planar combustor.