Thermal Coupling Studies of a High Temperature Proton Exchange Membrane Fuel Cell Stack and a Metal Hydride Hydrogen Storage System (original) (raw)
Related papers
2012
A proper thermal management strategy is needed to maintain uniform temperature distribution and derive optimal performance in high temperature proton exchange membrane fuel cells (HT-PEMFC). In HT-PEMFCs, more than half of the chemical energy is converted into thermal energy during the electrochemical generation of electrical power. We investigate the viability of three heat removal strategies: (a) using cooling plates through which cathode air is passed in excess of stoichiometric requirement for the purpose of heat removal, (b) using forced convection partly in conjunction with cooling plates, and (c) using forced convection alone for heat removal. Calculations, partly done using computational fluid dynamics simulations, for a 1 kWe HT-PEMFC stack, which is suitable for scooter type of transport applications, show that a combination of excess stoichiometric factor and forced draft appears to provide the optimal strategy for thermal management of high temperature PEM fuel cells. With proper cooling strategy, the temperature variations within the cell may be reduced to about 20 K over most of the cell and to about 50 K in isolated spots.
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. K E Y W O R D S airflow simulation, coolant temperature, fuel cell vehicles, PEM fuel cells, stack temperature, thermal management
Thermal management of edge-cooled 1 kW portable proton exchange membrane fuel cell stack
• Lumped model and real-time transient CFD model are compared during a load profile. • Influence of bipolar plate material on temperature is determined. • Influence of operating delta pressure on relative humidity inside the stack. • Significant influence of cooling fin redesign on heat transfer is outlined. • Heat transfer between the stack and metal hydride tank is analyzed.
Energy Conversion and Management, 2019
A fuel cell power system integrating proton-exchange-membrane fuel cell (PEMFC) and metal hydride (MH)based hydrogen storage tank presents great potential in transportation applications. The embedded PEMFC and MH tank are thermally coupled through a heat ex-changer and control system. The hydrogen generating and supplying rate from the MH tank to PEMFC is strongly influenced by the transferred heat, which affects the performance of long-term operation as well. In this work, the dynamic behavior of the fuel cell system is simulated with a mathematical model set and validated using a database from the real operation vehicles. Thanks to the heat ex-changer combined by fan, radiator and circulation water, the hydrogen flow rate from MH tank to PEMFC is well controlled to meet the requirement of power load. The simulated model describes the response of each component including the power and heat generated by PEMFC, the hydrogen desorption kinetics and the heat transfer in the system. A thermal management strategy with a PID controller is proposed to reduce the degradation and extend the lifespan of PEMFC. The results demonstrate that an optimized performance of PEMFC after 1000 h is realized. In spite of the MH tank degradation rate has been raised 0.3%, 2.5% of voltage degradation of PEMFC is reduced. Meanwhile, for the integration fuel cell system, more than 3% of fuel efficiency and 10% of fuel economy is saved.
Journal of the Energy Institute, 2017
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 Ae90 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.
Numerical Modeling of the Proton Exchange Membrane Fuel Cell for Thermal Management
2006
A thermal model of the Proton Exchange Membrane Fuel Cell (PEMFC) was developed to investigate the performance of a large active area fuel cell with the water cooling thermal management system. The model includes three sub-models: water transport model, electrochemical reaction model and heat transfer model. The water transport model calculates water distribution and the electric resistance of the membrane electrolyte. The electrochemical reaction model for the agglomerate structure cathode catalyst layer predicts the cathode overpotentials including mass transport limitation effect at high current density region. Two-dimensional heat transfer model incorporated with coolant and gas channels predicts the temperature distribution within the fuel cell. By integrating those sub-models, local electric resistance and overpotentials depending on the water and temperature distribution can be predicted. The model was calibrated with published experimental data and sensitivity studies were p...
Analysis of Heat Transport in a Proton Exchange Membrane (PEM) Fuel Cell
American Journal of Applied Sciences, 2009
In this study a two-phases, single-domain and non-isothermal model of a Proton Exchange Membrane (PEM) fuel cell has been studied to investigate thermal management effects on fuel cell performance. A set of governing equations, conservation of mass, momentum, species, energy and charge for gas diffusion layers, catalyst layers and the membrane regions are considered. These equations are solved numerically in a single domain, using finite-volume-based computational fluid dynamics technique. Also the effects of four critical parameters that are thermal conductivity of gas diffusion layer, relative humidity, operating temperature and current density on the PEM fuel cell performance is investigated. In low operating temperatures the resistance within the membrane increases and this could cause rapid decrease in potential. High operating temperature would also reduce transport losses and it would lead to increase in electrochemical reaction rate. This could virtually result in decreasing the cell potential due to an increasing water vapor partial pressure and the membrane water dehydration. Another significant result is that the temperature distribution in GDL is almost linear but within membrane is highly non-linear. However at low current density the temperature across all regions of the cell dose not change significantly. The cell potential increases with relative humidity and improved hydration which reduces ohmic losses. Also the temperature within the cell is much higher with reduced GDL thermal conductivities. The numerical model which is developed is validated with published experimental data and the results are in good agreement.
Tools for designing the cooling system of a proton exchange membrane fuel cell
2012
Proton exchange membrane fuel cell (PEMFC) requires a careful management of the heat distribution inside the stack. The proton exchange membrane is the most sensitive element of this thermal management and it must operate under specific conditions in order to increase the lifetime and also the output power of the fuel cell. These last decades, the enhancement of the output power of the PEMFC has led the manufacturers to greatly improve the heat transfer effectiveness for cooling such systems. In addition, homogenizing the bipolar plate temperature increases the lifetime of the system by limiting the occurrence of strong thermal gradients. In this context, using a fluid in boiling conditions to cool down the PEMFC seems to be very suitable for this purpose. In order to compare the thermal performances between a coolant used in single-phase flow or in boiling flow conditions, we have built an experimental set-up allowing the investigation of cooling flows for these two conditions. Mor...
Proton exchange membrane fuel cell has many distinctive features that made it an attractive alternative clean energy source, including low start-up, high power density, high efficiency, portability and remote applications. Commercial application of this energy source had been greatly hindered by series of technical issues ranging from inadequate water and heat management, intolerance to impurities such as CO, slow electrochemical kinetics at electrodes, and relatively high cost. An approach to stem the thermal build-up within the fuel cell structure that could lead to degradation of the system components is by integrating cooling channels as part of flow structure of the PEM fuel cell system. In this study, a numerical investigation was carried out to investigate the impact of cooling channel geometry in combination with temperature dependent operating parameters on thermal management and overall performance of a PEM fuel cell system. The evaluation is performed using a CFD code based on a finite volume approach. The systems net power and polarization curves are presented as a function of the system temperature, operating parameters and geometry. In addition, the parameters studied were optimized using a mathematical optimization code integrated with the commercial computational fluid dynamics code.