Temperature Distribution Of Stack Research Articles

Effect of defective cells on the temperature distribution of a proton exchange membrane fuel cell stack

Proton exchange membrane fuel cell (PEMFC) stacks may encounter performance degradation or even damage during long-term operations, while the influence of defective cells on the stack performance still remains inadequately understood. In this study, the effect of defective cells on the stack temperature distribution was experimentally investigated. Two defective cells of different defect degrees were prepared by controlling hydrogen starvation time and quantitively characterized by the polarization curves, electrochemical impedance spectroscopy (EIS), and galvanostatic charge method (GCM) tests. Results show that the presence of defective cells reduces the stack performance and the temperature distribution uniformity. The increment of stack temperature and decrement of stack temperature uniformity is more prominent (with 0.9 °C and 0.31 °C at 0.8 A cm−2, respectively) when the defective cell is located at central stack. The peak sub-cell regional temperature rise can even reach 2.9 °C. For defective cells with a relatively low degree of defect, the reverse current density is high, thus leading to an increased heat generation with the average sub-cell regional temperature increment of 0.5 °C and causing adjacent normal cells to operate at higher temperature. For defective cells with an excessive degree of defect, polarization reverse occurs at low current densities, resulting in significant voltage losses and reduced performance of the stack. The present results are insightful for developing thermal management strategies for the long-term operation of PEMFC stacks.

Experimental Results of a 10/40 kW-Class Reversible Solid Oxide Cell Demonstration System at Forschungszentrum Jülich

In 2018, a 5/15 kWDC reversible solid oxide cell system was developed and successfully operated by Forschungszentrum Jülich. Based on the knowledge gained with this first system, an optimized system in the power class of 10/40 kWAC was developed afterwards in 2019 that uses the well-established Integrated Module. This module consists of four 20-layer sub-stacks, two heat exchangers and five heating plates. It represents the main components of the system. The basic system layout was retained in general from the previous system and adjusted in accordance with the higher power level, as well as the supporting balance of plant components. The layout of the demonstrator system and its results are described. During the experimental evaluation in fuel cell mode, the system could provide an electrical output power from 1.7 to 13 kWAC. The maximum system efficiency of 63.3% based on the lower heating value (LHV) could be reached at a system power of 10.4 kWAC. This operating point was also analyzed regarding the temperature distribution in the stack and efficiency losses. In electrolysis mode, a maximum efficiency of 71.1% (LHV) was achieved with an electrical power input of −49.6 kWAC. At this operating point, about 11.7 Nm3 h−1 of hydrogen are generated. The stack temperature distribution and the efficiency losses are also analyzed for the electrolysis mode. Finally, the potential for the efficiency optimization through higher heat integration in this mode is experimentally evaluated and discussed.

Influence of hydrogen fuel cell temperature safety on bus driving characteristics and stack heating mode

Hydrogen fuel cells have developed rapidly in bus because of their cleanliness. The driving parameters of hydrogen fuel cell bus and the internal temperature distribution of hydrogen fuel stack are investigated in this study. The 1-D model of hydrogen fuel cell bus and the 2-D model of hydrogen fuel cell stack are established based on AMESim. In the cooling process, for the existing typical thermal management system, the influence of ambient temperature on the fuel cell bus driving parameters is analyzed by the 1-D model. In the heating process, the internal temperature distribution of the stack is analyzed under three heating modes by the 2-D model. As the ambient temperature increases, to ensure the safe operating temperature of the fuel cells, the bus top speed should be reduced, and the acceleration time should be extended. When the stack needs to be heated, the gas-liquid heating mode can supply a more uniform temperature distribution inside the stack. • The 1-D vehicle model and 2-D stack model of hydrogen fuel cell are established. • The effect of ambient temperature on driving parameters is analyzed. • The internal temperature distribution of the stack is analyzed under three heating modes. • Gas-liquid heating mode can give a more uniform stack temperature distribution.

Highly Efficient SOFC System with Mk35x-Stack Module Operated with Gasified Biomass - HieffBioPower -

A stationary SOFC system utilizing gas from a biomass updraft gasifier is under development within the project “HiEffBioPower” by MAWERA, BIOS, Bosal, AVL, Calida Cleantech, Fraunhofer IKTS, Wuppertal Institute and University Utrecht (European Union Horizon2020 No. 727330). The system is based on Mk352-CFY-stack with Chromium based (CFY) interconnects and electrolyte supported cells. These stacks are robust, redox stable and demonstrated low degradation rates. The stacks are arranged to modules of eight 30-cell stacks and are electrically connected in series. The stack module was pre-tested at the test rig at IKTS and showed performance in accordance with system requirements. Stationary power points were measured to compare the behaviour of the stack module with the system tests at MAWERA. AVL designed and installed the overall SOFC system (heat exchangers, stack, catalytic afterburner, process control and visualisation) with a nominal capacity of 6 kWel. After shipping all parts of the SOFC system to MAWERA in Hard (AT), the coupling of the biomass gasifier, the gas cleaning unit and the SOFC system was conducted. The system is operated by an automated process control. The highest efforts needed the novel gas cleaning unit, consisting of a high temperature filter, a desulphurisation unit as well as a novel catalytic gas reforming stage developed by BIOS.The biomass gasifier has been operated with wood chips of different quality. The high tar contents of the product gas make a tar cracking essential to reach a high calorific value of the gas for the SOFC system. The novel gas cleaning system shows good performance and reaches the defined SOFC requirements. The SOFC system developed and operated by AVL reached stable conditions for several days. The operating results of the stack module at lab conditions and at the real system are in a good agreement. The SOFC stack module performance in terms of cell voltages, stack temperature distribution and fuel utilization under biomass reformate fuel will be shown and supported by several simulation to get an overall energy balance. Examples of optimization for several components by CFD simulation and component tests will be given.

Machine learning based soft sensor and long-term calibration scheme: A solid oxide fuel cell system case

To quickly and accurately obtain the multi-dimensional state in a sealing reactor is critical for the safety and high performance of industrial system. In this work, a generic machine learning based multi-dimensional soft sensor and a long-term calibration scheme is proposed by using the case of steam reforming solid oxide fuel cell (SR-SOFC) system. Firstly, based on a validated SR-SOFC system model, the temporal-spatial temperature distribution (TSTD) characteristics are analyzed and a TSTD characteristic model is constructed by Multivariable Linear Regression. Then, the central node temperature of the stack is estimated by applying the Least Square Support Vector Machine and the SR-SOFC stack temperature distribution is accurately obtained by explaining the TSTD characteristics model with the central node temperature. In addition, the temperature distribution is calibrated by Stochastic Gradient Descent algorithm to eliminate the estimation error resulting from stack degradation in a long term. The simulation results show that the proposed method can obtain the SR-SOFC stack temperature distribution in time and effectively, the average error is less than 1 K. The proposed estimation strategy can be easily expanded to other scenarios with similar operation conditions.

Thermoelectrical-based fuel adaptability analysis of solid oxide fuel cell system and fuel conversion rate prediction

Solid oxide fuel cell (SOFC) has attracted more and more attention for its advantages of high efficiency, low emission, and strong fuel adaptability. However, the fuel adaptability also brings issues for thermoelectric cooperative optimization of SOFC system because different fuel compositions can result in different thermal stresses and system performances. In this paper, the temperature distribution and electrical characteristics of a 1 kW external steam-reforming SOFC system at different power stages are studied based on the 200-hour experimental data obtained from the system fed by hydrogen and methane respectively. The thermoelectric characteristics of SOFC system using hydrogen and methane as fuels with the same output power are further compared. Furthermore, the influences of methane conversion rate (MCR) on the thermoelectric characteristics in SOFC system are analyzed through a mathematical SOFC system model and a Gaussian process regression (GPR) model is constructed to predict the MCR. The results show that, the stack voltage of the SOFC system fed by methane (CH4-SOFC) is lower than that of the SOFC system fed by hydrogen (H2-SOFC) by 0.59–4.35 V for the hydrogen concentration at the anode is relatively low in the CH4-SOFC system. Meanwhile, the electrical efficiency of the CH4-SOFC system is lower than that of the H2-SOFC system by 0.85–6.08% in the power range of 300–600 W. In terms of thermal characteristics, the stack temperature gradient on the fuel direction of the CH4-SOFC system is much larger than that of the H2-SOFC system. Different methane conversion rates (MCRs) in the CH4-SOFC system can shift the stack temperature distribution significantly, and properly increasing the MCR can effectively increase the stack voltage and electrical efficiency. Finally, the GPR model can accurately predict the MCR and the MAPE is 0.030%, which can prevent the deformation and fracture of cells caused by the excessive temperature gradient in the stack when the MCR is too low. This work lays a foundation for system control strategy design in the future, especially SOFC stack thermal management, improving the fuel adaptability of the system and ensuring the safety of the stack temperature.

Two-Dimensional Temperature Distribution Estimation for a Cross-Flow Planar Solid Oxide Fuel Cell Stack

The uniform temperature distribution of a cross-flow planar solid oxide fuel cell stack is important to stack thermal safety and electrical performance. However, due to the stack’s strict sealing requirement, it is difficult to install thermo-couples to directly measure the stack internal temperature, thus accurately estimating the stack temperature distribution is crucial for stack’s temperature management. In this paper, a two-dimensional mechanism model of the stack is built to reflect its internal temperature states. Then, experimental data is utilized to validate the model and ensure its reliability. Finally, a temperature distribution estimator based on unscented kalman filter algorithm is designed to achieve fast and accurate stack temperature distribution estimation. Simulation results show that the estimator can fast converge and has a maximum estimated error rate of less than 0.015% while there is an input disturbance, which indicates it has good performance in both static and dynamic estimation.

Use of infrared matrix sensor for temperature measurement and monitoring of PEM/FC stacks

Cells composing FC stacks can be subject to distinct operating conditions, resulting in different temperatures between them. This procedure establishes a non-homogeneous distribution along the stack profile. For a more precise monitoring and control purposes, the location of the cell’s temperature measurements has to be right on the surface of the stack profile. Thus, the greater the number of temperature measurement points on the stack profile, the greater is its control reliability and safer the operating conditions. As the fuel cell composition is almost entirely made of graphite and constantly subjected to an electrical potential difference, the direct contact of a temperature sensor with the stack must be avoided. The purpose of this paper is to propose a method to monitor the FC stack temperature distribution by an infrared matrix sensor. This procedure will obtain an increased number of measuring points avoiding any physical contact with the cells. This paper deals with information obtained from an infrared matrix sensor with its calibration handled by software. After processing the sensor's temperature data, they are displayed as a thermal image. With this, the temperature control of the stack can act in such a way that it does not reach critical levels that could compromise its useful life. In this text, a sensor calibration procedure is presented together with data validation through experimental results. In the tests using this technique was verified that about 84% of the normal error distribution around the maximum temperature was kept between ± 2 °C, therefore within tolerable limits.

Experimental validation of the polarization curve and the temperature distribution in a PEMFC stack using a one dimensional analytical model

This paper presents the experimental validation of a one dimensional analytical model developed for a Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack. The analytical model is developed to simulate a stack formed by N cells, where the experimental validation has been carried out for a stack formed by 3, 5 and 7 cells. The main physical phenomena in a PEMFC such as electrochemistry, mass transfer (hydrogen, oxygen and water – both liquid and gas) have been modeled. The experimental validation has been done with two different variables in order to provide good quality results. The polarization curve and the stack temperature distribution have been selected as validation variables. In order to compare the experimental and the numerical results, a set of experimental tests modifying the main operating conditions such as the cathode stoichiometric, relative humidity in anode and cathode and operating pressure have been performed. The model results show a good agreement also for the different configurations of the stack (3, 5 and 7 cells). The average error is always less than 2% for the polarization curve and for the stack temperature distribution, so the accuracy of the one dimensional analytical model is verified.

9000 Hours Operation of a 25 Solid Oxide Cells Stack in Steam Electrolysis Mode

Hydrogen production through water electrolysis is one of the key processes required in the conversion of electricity to fuels. Carbon free hydrogen produced through water electrolysis can be used as a fuel for hydrogen powered applications (such as fuel cell cars) or grid injection, or as a reactant in downstream processes to produce synthetic fuels such as SNG or methanol. Among available technologies, high temperature electrolysis potentially offers significantly higher electrical to chemical conversion efficiencies compared to alkaline and PEM electrolysers, with values in excess of 100% achievable if additional thermal energy is supplied to the system. High temperature electrolysers are essentially solid oxide fuel cells operated in reverse. Hence, the development of solid oxide electrolysers (SOE) has hugely benefited from the intensive research carried out for the development of Solid Oxide Fuel Cells (SOFCs) in the past decades. A 25 cells stack manufactured by Topsoe Fuel Cells has been tested at EIFER in high temperature electrolysis mode at about 750°C and current densities of 0.57 and 0.72 A/cm2. The applied steam conversion rate was 50%, with a 90 % absolute humidity gas feed. The total duration of the test was almost 9100 hours, split between 8300 current hours and 800 standby hours induced by incidents that occurred during the test. Incidents included losses of the steam and current supplies. After each incident, the stack performance was recovered, indicating a good robustness of the stack towards unexpected and potentially damaging conditions. The main issue during the test has been the considerable increase of the voltage drop between the positive end plate and the bottom stack repeat unit (SRU), before a sharp improvement occurred after about 2000 hours of operation, which has influenced the stack temperature distribution and in turn individual SRU degradation. The maximum observed voltage drop culminated at 2.73 V, before stabilising around 0.6V. The stack has shown an overall voltage degradation of 2% per thousand hours, as can be seen on Figure 1. The corresponding voltage losses were 613 mV and 678 mV per thousand hours, for 0.57 and 0.72 A/cm2 current densities, respectively. This in turn corresponds to an average degradation in the range 0.24 – 0.27 mV per thousand hours per SRU. Moreover, the stack temperature has been adjusted on a few occasion during the test, which highlighted the possibility of using the wide operating temperature range of the solid oxide technology to counter balance the stack degradation and increase the lifetime. Indeed, allowing the stack to increase at a rate of 3°C per thousand hours produced a reduced degradation rate of 1.80 % per thousand hours. Figure 1

Three-Dimensional Numerical Simulations of Heat and Mass Transfer and Degradation in a SOFC Cell Stack

We developed a three dimensional (3-D) mathematical model for a cell stack to perform comprehensive CFD analyses of degradation over a long period of time. The constructed 3-D CFD model consists of complete components in a practical SOFC stack. We calculated the concentration of the chemical species, the temperature distribution, the potential distribution, and the current density for each part of the stack. We also calculated the incremental electrical resistance using empirical formulas and predicted the change of electrical output and stack temperature distribution caused by degradation.

Design and experimental characterization of a 350 W High Temperature PEM fuel cell stack

High Temperature Proton Exchange Membrane (HT PEM) fuel cell based on polybenzimidazole (PBI) polymer and phosphoric acid, can be operated at temperature between 120 °C and 180 °C. Reactants humidification is not required and CO content up to 2% in the fuel can be tolerated, affecting only marginally performance. This is what makes HT PEM very attractive, as low quality reformed hydrogen can be used and water management problems are avoided. Till nowadays, from experimental point of view, only few studies relate to the development and characterization of high temperature stacks. The aim of this work is to present the main design features and the performance curves of a 25 cells HT PEM stack based on PBI and phosphoric acid membranes. Performance curves refer to the stack operating with two type of fuels: pure hydrogen and a gas mixture simulating a typical steam reformer output. The stack voltage distribution analysis and the stack temperature distribution analysis suggest that cathode air could be used as coolant leading to a better thermal management. This could simplify stack design and system BOP, thus increasing system performance

Modeling and Performance Analysis of the Rolls-Royce Fuel Cell Systems Limited: 1 MW Plant

This paper is focused on the performance of the 1 MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector, and off-gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behavior is determined by many parameters. In particular, two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole, and each physical component is modeled in detail as a subsystem. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the solid oxide fuel cell (SOFC) stack and reformer. In order to characterize the system behavior, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure, as described in the paper. Given the complexity of the system, various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures, and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.

Hydrogen production through steam electrolysis: Model-based steady state performance of a cathode-supported intermediate temperature solid oxide electrolysis cell

Hydrogen production via steam electrolysis may involve less electrical energy consumption than conventional low temperature water electrolysis, reflecting the improved thermodynamics and kinetics at elevated temperatures. The present paper reports on the development of a one-dimensional dynamic model of a cathode-supported planar intermediate temperature solid oxide electrolysis cell (SOEC) stack. The model, which consists of an electrochemical model, a mass balance, and four energy balances, is here employed to study the steady state behaviour of an SOEC stack at different current densities and temperatures. The simulations found that activation overpotentials provide the largest contributions to irreversible losses while concentration overpotentials remained negligible throughout the stack. For an average current density of 7000 A m −2 and an inlet steam temperature of 1023 K, the predicted electrical energy consumption of the stack is around 3 kW h per normal m 3 of hydrogen, significantly smaller than those of low temperature stacks commercially available today. However, the dependence of the stack temperature distribution on the average current density calls for strict temperature control, especially during dynamic operation.

PEM Fuel Cell Stack Cold Start Thermal Model

AbstractFor passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick‐starting fuel cell systems are impeded by two problems: (i) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (ii) temperature‐dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub‐freezing startup conditions. Existing models lack the following features: (i) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (ii) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a model considering individual cell layers can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect. This paper presents and discusses results from simulations performed with a new, layered model.

Polymer electrolyte fuel cell stack thermal model to evaluate sub-freezing startup

For passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick-starting fuel cell systems are impeded by two problems: (1) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (2) temperature-dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub-freezing startup conditions. Existing models lack the following features: (1) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (2) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. The focus of this research is the development and use of a sub-freezing thermal model for a polymer electrolyte fuel cell stack. Specifically, the work has focused on the generation of a model in which the fuel cell is separated into layers to determine an accurate temperature distribution within the stack. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a layered model can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect.

C08 熱音響冷凍機におけるスタック温度分布に及ぼす熱交換器の影響

C08 熱音響冷凍機におけるスタック温度分布に及ぼす熱交換器の影響

Contemplative stance for chemical process control: An IFAC report

To quickly and accurately obtain the multi-dimensional state in a sealing reactor is critical for the safety and high performance of industrial system. In this work, a generic machine learning based multi-dimensional soft sensor and a long-term calibration scheme is proposed by using the case of steam reforming solid oxide fuel cell (SR-SOFC) system. Firstly, based on a validated SR-SOFC system model, the temporal-spatial temperature distribution (TSTD) characteristics are analyzed and a TSTD characteristic model is constructed by Multivariable Linear Regression. Then, the central node temperature of the stack is estimated by applying the Least Square Support Vector Machine and the SR-SOFC stack temperature distribution is accurately obtained by explaining the TSTD characteristics model with the central node temperature. In addition, the temperature distribution is calibrated by Stochastic Gradient Descent algorithm to eliminate the estimation error resulting from stack degradation in a long term. The simulation results show that the proposed method can obtain the SR-SOFC stack temperature distribution in time and effectively, the average error is less than 1 K. The proposed estimation strategy can be easily expanded to other scenarios with similar operation conditions.