Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.     

Control-orientated thermal model for proton-exchange membrane fuel cell systems

A lumped parameter dynamic model is developed for predicting the stack temperature, temperatures of the exit reactant gases and coolant water outlet in a proton-exchange membrane fuel cell (PEMFC) system. A dynamic model for a water pump is also developed and can be used along with the thermal model to control the stack temperature. The thermal and water pump models are integrated with the air flow compressor and PEMFC stack current–voltage models developed by Pukrushpan et al. to study the fuel cell system under open and closed-loop conditions. The results obtained for the aforementioned variables from open-loop simulation studies are found to be similar to the experimental values reported in the literature. Closed-loop simulations using the model are carried out to study the effect of stack temperature on settling times of other variables such as stack voltage, air flow rate, oxygen excess ratio and net power of the stack. Further, interaction studies are performed for selecting appropriate input–output pairs for control purpose. Finally, the developed thermal model can assist the designer in choosing the required number of cooling plates to minimize the difference between the cooling water outlet temperature and stack temperature.     

A comparison of temperature distribution in PEMFC with single-phase water cooling and two-phase HFE-7100 cooling methods by numerical study

Thermal management has been considered as one of the critical issues in proton exchange membrane fuel cell (PEMFC). Key roles of thermal management system are maintaining optimal operating temperature of PEMFC and diminishing temperature difference over a single fuel cell and stack. Severe temperature difference causes degradation of performance and deterioration of durability, so understanding temperature distribution inside a single fuel cell and stack is crucial. In this paper, two-phase HFE-7100 cooling method is suggested for PEMFC thermal management and investigated regarding temperature change inside a fuel cell. Also, the results are compared to single-phase water cooling method. Numerical study of temperature distribution inside a single PEMFC is conducted under various conditions for the two different cooling methods. Fuel cell model considering mass transfer, electrochemical reaction and heat transfer is developed.The result indicates that two-phase HFE-7100 cooling method has an advantage in temperature maintenance and temperature uniformity than single-phase water cooling method, especially in high current density region. It is also revealed that the cell temperature is less dependent on system load change with two-phase cooling method. It indicates that the fuel cell system with two-phase cooling method has high thermal stability. In addition, the effect of coolant flow rate and coolant inlet pressure in two-phase HFE-7100 cooling method are discussed. As a result, two-phase cooling method showed reliable cooling performance even with low coolant flow rate and the system temperature increased as coolant pressure rose.     

Thermal characteristics of an air-cooled open-cathode proton exchange membrane fuel cell stack via numerical investigation

In light of stricter emissions regulations and depleting fossil fuel reserves, fuel cell vehicles (FCVs) are one of the leading alternatives for powering future vehicles. An open-cathode, air-cooled proton exchange membrane fuel cell (PEMFC) stack provides a relatively simple electric generation system for a vehicle in terms of system complexity and number of components. The temperature within a PEMFC stack is critical to its level of performance and the electrochemical efficiency. Previously created computational models to study and predict the stack temperature have been limited in their scale and the inaccurate assumption that temperature is uniform throughout. The present work details the creation of a numerical model to study the temperature distribution of an 80-cell Ballard 1020ACS stack by simulating the cooling airflow across the stack. Using computational fluid dynamics, a steady-state airflow simulation was performed using experimental data to form boundary conditions where possible. Additionally, a parametric study was performed to investigate the effect of the distance between the stack and cooling fan on stack performance. Model validation was performed against published results. The temperature distribution across the stack was identical for the central 70% of the cells, with eccentric temperatures observed at the stack extremities, while the difference between coolant and bipolar plate temperatures was approximately 10°C at the cooling channel outlets. The results of the parametric study showed that the fan-stack distance has a negligible effect on stack performance. The assumptions regarding stack temperature uniformity and measurement were challenged. Lastly, the hypothesis regarding the negligible effect of fan-stack distance on stack performance was confirmed.     

Model-based decoupling control for the thermal management system of proton exchange membrane fuel cells

As one of the most promising sustainable energy technologies available today, proton exchange membrane fuel cell (PEMFC) engines are becoming more and more popular in various applications, especially in transportation vehicles. However, the complexity and the severity of the vehicle operating conditions present challenges to control the temperature distribution in single cells and stack, which is an important factor influencing the performance and durability of PEMFC engines. It has been found that regulating the input and output coolant water temperature can improve the temperature distribution. Therefore, the control objective in this paper is regulating the input and output temperature of coolant water at the same time. Firstly, a coupled model of the thermal management system is established based on the physical structure of PEMFC engines. Then, in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack, a decoupling controller is proposed and its closed-loop stability is proved. Finally, based on the actual PEMFC engine platform, the effectiveness, accuracy and reliability of the proposed decoupling controller are tested. The experimental results show that with the proposed decoupling controller, the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line. The temperature error range is less than 0.2 °C even under the dynamic current load conditions.     

Numerical Investigation of Liquid Water Cooling for a Proton Exchange Membrane Fuel Cell Stack

The operation of proton exchange membrane fuel cell (PEMFC) stacks requires careful thermal and water management for optimal performance. Appropriate placement of cooling plates and appropriate cooling conditions are therefore essential. To study the impact of these design parameters, a two-phase model accounting for the conservation of mass, momentum, species, energy, and charge, a phenomenological model for the membrane, and an agglomerate model for the catalyst layer, is developed and solved. The model is validated for a single cell, in terms of both the local and the global current density, and good agreement is found. Four repetitive computational units are then identified for the number of single cells placed between the coolant plates: (i) one cell; (ii) two cells; (iii) three cells; and (iv) four cells. The flow fields in the single cells and the cooling plates are of a net type. The results show that there is a strong correlation between stack performance and the operating conditions/placement of the coolant plates. For the limiting case of one coolant plate between each unit cell, similar operating conditions can be achieved in every individual cell throughout the stack. As more cells are placed in between coolant plates, the stack performance drops due to an increase in temperature and decrease in water content in the membranes, unless the cooling temperature is lowered. The coolant temperature and inlet velocity need to be monitored carefully and adjusted to the operating conditions of the stack. This model can be employed for design and optimization of liquid water cooling of a PEMFC stack.     

Modeling and thermal management of proton exchange membrane fuel cell for fuel cell/battery hybrid automotive vehicle

The proton exchange membrane fuel cell (PEMFC) stack is a key component in the fuel cell/battery hybrid vehicle. Thermal management and optimized control of the PEMFC under real driving cycle remains a challenging issue. This paper presents a new hybrid vehicle model, including simulations of diver behavior, vehicle dynamic, vehicle control unit, energy control unit, PEMFC stack, cooling system, battery, DC/DC converter, and motor. The stack model had been validated against experimental results. The aim is to model and analyze the characteristics of the 30 kW PEMFC stack regulated by its cooling system under actual driving conditions. Under actual driving cycles (0–65 kW/h), 33%–50% of the total energy becomes stack heat; the heat dissipation requirements of the PEMFC stack are high and increase at high speed and acceleration. A PID control is proposed; the cooling water flow rate is adjusted; the control succeeded in stabilizing the stack temperature at 350 K at actual driving conditions. Constant and relative lower inlet cooling water temperature (340 K) improves the regulation ability of the PID control. The hybrid vehicle model can provide a theoretical basis for the thermal management of the PEMFC stack in complex vehicle driving conditions.     

Performance prediction of proton exchange membrane fuel cell engine thermal management system using 1D and 3D integrating numerical simulation

The cooling system of proton exchange membrane fuel cell (PEMFC) engine was simulated by 1D and 3D collaborative simulation method. Firstly, the resistance characteristics of the flow channel are obtained by simulating the airside flow model. A three-dimensional simulation model including dual fans and radiator is also established to simulate the airflow distribution. The one-dimensional simulation model of 30 kW PEMFC engine cooling system that are mainly composed of a thermostat, water pump, and fan and radiator model is established. Secondly, the heat dissipation performance of the cooling system is calculated by using the coupled simulation model. It is found that the simulation results of the amount of heat transferred are in good agreement with the experimental data by compromising, which proves that the model is reasonable. Finally, the thermal performance of the extreme operating conditions of the PEMFC system is simulated by means of a simulation model. By monitoring the flow of the pump and the fan speed, we can maintain the stack internal heat balances, so that the stack efficient and stable operation. The results demonstrate that the 3D simulation can get the distribution of fluid flow more accurately, while the simulation time of 1D thermal system is short and can guide the matching of heat transfer parts quickly.     

Pumpless thermal management of water-cooled high-temperature proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) have been considered for combined heat and power (CHP) applications, but cost reduction has remained an issue for commercialization. Among various types of PEMFC, the high-temperature (HT) PEMFC is gaining more attention due to the simplicity of the system, that will make the total system cost lower. A pumpless cooling concept is introduced to reduce the number of components of a HT PEMFC system even further and also decrease the parasitic power required for operating the system. In this concept, water is used as the coolant, and the buoyancy force caused by the density difference between vapour and liquid when operated above boiling temperate is utilized to circulate the coolant between the stack and the cooling device. In this study, the basic parameters required to design the cooling device are discussed, and the stable operation of the HT PEMFC stack in both the steady-state and during transient periods is demonstrated. It found that the pumpless cooling method provides more uniform temperature distribution within the stack, regardless of the direction of coolant flow.     

Numerical study for diagnosing various malfunctioning modes in PEM fuel cell systems

The proton exchange membrane fuel cell (PEMFC) is promising technology for efficient power generation and has wide applications. In PEMFC development, it is important to diagnose malfunctions in a system with defective components and a PEMFC stack can act as an effective sensor to detect the various malfunctioning modes. Hence, the focus of this study is to analyze the response of a PEMFC under various malfunction conditions including humidifier, air blower, and coolant pump, catalyst layer degradation, and membrane aging based on 3D PEMFC simulations. Except for the coolant supply malfunction, other malfunctions exhibit similar behavior in terms of voltage drop and temperature rise, requiring more detailed measurement techniques such as Electrochemical Impedance Spectroscopy to identify the cause of malfunctions. In addition, measuring the relative humidity of the outlet gas may not provide sufficient information to distinguish the malfunction of the anode or cathode humidifier. The results of the study suggest fault detection and isolation methods under these malfunction conditions to prevent more severe failure of the PEMFC stack and system. An extensive multi-dimensional contour comprising temperature, relative humidity, liquid saturation, water content, and current density is also provided for the better analyzation of system malfunctioning behaviors.     

Effect of dynamic load on the temperature profiles and cooling response time of a proton exchange membrane fuel cell

Polymer Electrolyte Membrane Fuel Cells (PEMFC) is an electrochemical device that generates electrical energy from the reactions between hydrogen and oxygen. An effective thermal management is needed to preserve the fuel cell performance and durability. Cooling by water is a conventional approach for PEMFC. Balance between optimal operating temperature, temperature uniformity and fast cooling response is a continuous issue in the thermal management of PEMFC. Various cooling strategies have been proposed for water-cooled PEMFC and an approach to obtain a fast cooling response was tested by feeding the coolant at a high temperature. In this paper, the operating behaviour was characterized from the perspectives of temperature profiles, mean temperature difference, and cooling response time. A 2.4 kW water-cooled PEMFC was used and the electrical load ranged from 40 A–90 A. The operating coolant temperature was set to 50 °C where the maximum stack operating temperature is 60 °C. The stack temperature profiles, cooling response time, mean temperature difference and cooling rates to the load variation was analysed. The analysis showed that the strategy allowed a fast cooling response especially at high current densities, but it also promotes a large temperature gradient across the stack.     

“Model-based” design of thermal management system of a fuel cell “air-independent” propulsion system for underwater shipboard

The thermal management of the fuel cell stack is critical for high-performance long-term operation. A fuel cell system of underwater vessel has a liquid-to-liquid cooling circuits which is composed of two liquid cooling pumps, two three-way valves, and a shell and tube heat exchanger. The liquid-to-liquid cooling technique makes it easier to reject the reaction heat into the surrounding but it is required refined cooling structure and control algorithm. In this study, a model-based design is applied to evaluate the control algorithm. A fuel cell system simulation model is developed and polarization curves and transient response are validated. A proportional integral controller and control strategy is developed and a nominal state feedback controller is also developed. Those control algorithms are evaluated via the dynamic response under step increases of load, and the control performance of the nominal state feedback controller is compared with the conventional controller (PI). The results show that the presented the nominal state feedback control of performs better than the PI control method with less wear and less control effort on the two circuit cooling modules. The proposed the nominal state feedback control can increase the system energy by 23.9%.     

A critical review of cooling techniques in proton exchange membrane fuel cell stacks

Effective cooling is critical for safe and efficient operation of proton exchange membrane fuel cell (PEMFC) stacks with high power. The narrow range of operating temperature and the small temperature differences between the stack and the ambient introduce significant challenges in the design of a cooling system. To promote the development of effective cooling strategies, cooling techniques reported in technical research publications and patents are reviewed in this paper. Firstly, the characteristics of the heat generation and cooling requirements in a PEMFC stack are introduced. Then the advantages, challenges and progress of various cooling techniques, including (i) cooling with heat spreaders (using high thermal conductivity materials or heat pipes), (ii) cooling with separate air flow, (iii) cooling with liquid (water or antifreeze coolant), and (iv) cooling with phase change (evaporative cooling and cooling through boiling), are systematically reviewed. Finally, further research needs in this area are identified.     

Integration of Miniature Heat Pipes into a Proton Exchange Membrane Fuel Cell for Cooling Applications

In proton exchange membrane fuel cell (PEMFC) operations, the electrochemical reactions produce a rise in temperature. A fuel cell stack therefore requires an effective cooling system for optimum performance. In this study, miniature heat pipes were applied for cooling in PEMFC. Three alternatives were considered in tests: free convection, forced convection cooling with air, and also water. An analytical model was developed to show the possibility of evoking heat from inside a fuel cell stack with different numbers of miniature heat pipes. An experiment setup was designed and then used for further analysis. The proposed experiment setup consisted of a simulated fuel cell that produced heat and a number of thermosyphon miniature heat pipes to evoke heat from the simulated fuel cell. The experiment results reported in this paper present advantages and disadvantages of each tested cooling scenario. Results show that each cooling scenario, using a different number of heat pipes, provided different heat removal rates for PEMFC cooling.     

Coolant circuit modeling and temperature fuzzy control of proton exchange membrane fuel cells

Effective temperature management is necessary for the safe and efficient operation of proton exchange membrane fuel cells (PEMFC). Generally circulating coolant can be applied in removing the excess heat of the PEMFC whose electrical power exceeds 5 kW. So a coolant circuit modeling method and a temperature fuzzy control strategy are presented in the paper in order to keep the PEMFC within the ideal operation temperature range. Firstly, a coolant circuit mathematical model is developed, which includes a PEMFC thermal model, a water reservoir model, a water pump model, a bypass valve model, a heat exchanger model and a PEMFC electrochemical model. Secondly, the incremental fuzzy control with integrator technique is designed according to the established model and control experience rule. And the PEMFC temperature and circulating coolant inlet temperature are controlled by regulating the circulating coolant flux and bypass valve factor respectively. Finally, the established model and fuzzy controllers are simulated and analyzed in Matlab software, and the simulation results demonstrate that the incremental fuzzy controller with integrator can effectively control the PEMFC temperature and the inlet coolant temperature within their objective working ranges respectively. In addition, the modeling and control process are very concise, and they can be easily applied in various power classes PEMFC temperature control in real-time.     

Sliding-mode-based temperature regulation of a proton exchange membrane fuel cell test bench

The temperature regulation of a cooling system of a PEMFC (Proton Exchange Membrane Fuel Cell) test bench is studied in this paper. Because of the unique configuration which is dedicated for cold start experiments, the operation at nominal temperature is unstable with a simple PI controller. A sliding-based control strategy is applied to suppress the temperature fluctuation. Firstly the structure of the cooling system is demonstrated and the cause of temperature fluctuation is analyzed. Then, a physics-based model of the cooling system is proposed on the Matlab/Simulink platform and validated with experimental data. Based on the model, a Sliding-mode controller with Extended Kalman Filter (EKF) is designed to regulate the temperature. The simulation results showed that the controlled system performed satisfactorily. Furthermore, when applied to the real system, the controller's real-time performance fulfills the test bench criterion. Experimental data show that the coolant temperature at the outlet of the fuel cell stack is kept in a range within ±1 °C, disregarding the heat generated at various working condition.     

High performance PEMFC stack with open-cathode at ambient pressure and temperature conditions

An open-air cathode proton exchange membrane fuel cell (PEMFC) was developed. This paper presents a study of the effect of several critical operating conditions on the performance of an 8-cell stack. The studied operating conditions such as cell temperature, air flow rate and hydrogen pressure and flow rate were varied in order to identify situations that could arise when the PEMFC stack is used in low-power portable PEMFC applications. The stack uses an air fan in the edge of the cathode manifolds, combining high stoichiometric oxidant supply and stack cooling purposes. In comparison with natural convection air-breathing stacks, the air dual-function approach brings higher stack performances, at the expense of having a lower use of the total stack power output. Although improving the electrochemical reactions kinetics and decreasing the polarization effects, the increase of the stack temperature lead to membrane excessive dehydration (loss of sorbed water), increasing the ohmic resistance of the stack (lower performance).     

Adaptive thermal control for PEMFC systems with guaranteed performance

Proton exchange membrane fuel cell (PEMFC) s are faced with dynamical load scenario in practical applications, and the resulting temperature variation will decrease the performance and consequently shorten the fuel cell lifetime. To address this problem, a control strategy for regulating the stack temperature is proposed in this paper. Firstly, a thermal management-oriented dynamic model of a water-cooled PEMFC system is built to facilitate the control design. Secondly, considering that the stack temperature should be maintained in a certain range regardless of the dynamical changing current demand, a Barrier Lyapunov function is employed to construct a feedback error of the stack temperature. Thirdly, a set of adaptation laws is designed to estimate the unknown parameters related to the gas flow rates in the flow fields. Particularly, a dynamic inversion tracking methodology is applied to design the non-affine input. A Lyapunov method based analysis demonstrates the stability and convergence of the closed-loop properties. Simulation results are provided to show that the proposed control strategy can satisfy all the control objectives and enhance the control performance compared to the proportional-integral controlled case.     

Thermodynamic analysis and assessment of novel ORC- DEC integrated PEMFC system for liquid hydrogen fueled ship application

Proton-exchange membrane fuel cell (PEMFC) and liquid hydrogen are gaining attention as a power generation system and alternative fuel of ship. This study proposes a novel PEMFC system, integrated with the organic Rankine cycle–direct expansion cycle (ORC-DEC), which exploits cold exergy from liquid hydrogen and low temperature waste heat generated by the PEMFC for application in a liquid hydrogen fueled ship. A thermodynamic model of each subsystem was established and analyzed from the economic, energy, and exergy viewpoints. Moreover, parametric analysis was performed to identify the effects of certain key parameters, such as the working fluid in the ORC, pressure exerted by the fuel pump, cooling water temperature of the PEMFC, and the stack current density on the system performance. The results showed that the proposed system could generate 221 kW of additional power. The overall system achieved an exergy and energy efficiency of 43.52 and 40.45%, respectively. The PEMFC system had the largest exergy destruction, followed by the cryogenic heat exchanger. Propane showed the best performance among the several investigated ORC working fluids and the system performance improved with the increase in the cooling water temperature of the PEMFC. The economic analysis showed that the average payback time of ORC-DEC was 11.2 years and the average net present value (NPV) was $295,268 at liquid hydrogen costing $3 to $7, showing the potential viability of the system.