Thermal management studies for a high temperature proton exchange membrane fuel cell stack

High temperature proton exchange membrane fuel cells (HT-PEMFCs) operate in the temperature range of 100 to 200oC and offer several advantages compared to the better known low temperature proton exchange membrane fuel cells (LT-PEMFCs) which typically operateattemperaturesbelow100oC. During the operation of a HT-PEMFC stack, heat is generated in the electrodes and electrolyte of each cell, and this heat must be effectively removed without creating any hot or cold spots. Proper thermal management of the HT-PEMFCs stack is required to ensure that the cell temperature is neither too low (which would lead to low cell efficiency) nor too high(which would damage the materials of the stack).The high heat generation rate in HT-PEMFCs, especially at high current densities where it can exceed the total electric power output, poses a challenge to the thermal management of HT-PEMFC stacks. Against this background, the objective of the present work is to systematically study the thermal management of an HT-PEMFC stack and quantify the effect of various stack cooling strategies on the overall performance of the stack using a multi-scale computational fluid dynamics (CFD) model. The stack model couples the flow and temperature fields with the electrochemistry using an empirical cell polarization curve to capture local current density – a function of local temperature within the active regions of each cell. This approach greatly reduces computational effort and time while retaining the essential physics and the coupling between the temperature and current density fields, thus enabling studies that clarify thermal management at the stack level: the focus of this study. A specific goal of this study is to investigate stack cooling methods that enable as high an average stack temperature as possible while ensuring that the temperature does not exceed 200oC anywhere in the stack. The thermal management techniques investigated in this work are: i) integrated cathode air cooling, ii) external air flow over the hot stack, iii) coupling a H2 storage system to the cathode air cooling system, iv) the use of liquid coolants in a separate cooling circuit.Integrated cathode air cooling uses excess air directed through cooling channels between cells to remove heat from the stack before directly introducing this air into the channels feeding air to the cell

Current status of fuel cell based combined heat and power systems forresidential sector

Combined Heat and Power (CHP) is the sequential or simultaneous generation of multiple forms of usefulenergy, usually electrical and thermal, in a single and integrated system. Implementing CHP systems inthe current energy sector may solve energy shortages, climate change and energy conservation issues.This review paper is divided into six sections: thefirst part defines and classifies the types of fuel cellused in CHP systems; the second part discusses the current status of fuel cell CHP (FC-CHP) around theworld and highlights the benefits and drawbacks of CHP systems; the third part focuses on techniques formodelling CHP systems. The fourth section gives a thorough comparison and discussion of the two mainfuel cell technologies used in FC-CHP (PEMFC and SOFC), characterising their technical performance andrecent developments from the major manufacturers. Thefifth section describes all the main componentsof FC-CHP systems and explains the issues connected with their practical application. The last partsummarises the above, and reflects on micro FC-CHP system technology and its future prospects

Assessment of a novel solid oxide fuel cell tri-generation system for building applications

The paper provides a performance analysis assessment of a novel solid oxide fuel cell (SOFC) liquid desiccant tri-generation system for building applications. The work presented serves to build upon the current literature related to experimental evaluations of SOFC tri-generation systems, particularly in domestic built environment applications. The proposed SOFC liquid desiccant tri-generation system will be the first-of-its-kind. No research activity is reported on the integration of SOFC, or any fuel cell, with liquid desiccant air conditioning in a tri-generation system configuration. The novel tri-generation system is suited to applications that require simultaneous electrical power, heating and dehumidification/cooling. There are several specific benefits to the integration of SOFC and liquid desiccant air conditioning technology, including; very high operational electrical efficiencies even at low system capacities and the ability to utilise low-grade thermal energy in a (useful) cooling process. Furthermore, the novel tri-generation system has the potential to increase thermal energy utilisation and thus the access to the benefits achievable from on-site electrical generation, primarily; reduced emissions and operating costs. Using empirical SOFC and liquid desiccant component data, an energetic, economic and environmental performance analysis assessment of the novel system is presented. Significant conclusions from the work include: (1) SOFC and liquid desiccant are a viable technological pairing in the development of an efficient and effective tri-generation system. High tri-generation efficiencies in the range of 68-71% are attainable. (2) The inclusion of liquid desiccant provides an efficiency increase of 9-15% compared to SOFC electrical operation only, demonstrating the potential of the system in building applications that require simultaneous electrical power, heating and/or dehumidification/cooling. (3) Compared to an equivalent base case system, the novel tri-generation system is currently only economically viable with a government’s financial support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent. (4) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production

The role of hydrogen and fuel cells in the global energy system

Hydrogen technologies have experienced cycles of excessive expectations followed by disillusion. Nonetheless, a growing body of evidence suggests these technologies form an attractive option for the deep decarb onisation of global energy systems, and that recent improvements in their cost and performance point towards economic viability as well. This paper is a comprehensive review of the potential role that hydrogen could play in the provision of electricity, h eat, industry, transport and energy storage in a low - carbon energy system, and an assessment of the status of hydrogen in being able to fulfil that potential. The picture that emerges is one of qualified promise: hydrogen is well established in certain nic hes such as forklift trucks, while mainstream applications are now forthcoming. Hydrogen vehicles are available commercially in several countries, and 225,000 fuel cell home heating systems have been sold. This represents a step change from the situation of only five years ago. This review shows that challenges around cost and performance remain, and considerable improvements are still required for hydrogen to become truly competitive. But such competitiveness in the medium - term future no longer seems an unrealistic prospect, which fully justifies the growing interest and policy support for these technologies around the world

Advancements and prospects of thermal management and waste heat recovery of PEMFC

Despite that the Proton Exchange Membrane Fuel Cell (PEMFC) is considered to be an efficient power device; around half of the energy produced from the electrochemical reaction is dissipated as heat due to irreversibility of the cathodic reaction, Ohmic resistance, and mass transport overpotentials. Effective heat removal from the PEMFC, via cooling, is very important to maintain the cell/stack at a uniform operating temperature ensuring the durability of the device as excessive operating temperature may dry out the membrane and reduces the surface area of the catalyst hence lowering the performance of the cell. In addition to cooling, capturing the produced heat and repurposing it using one of the Waste Heat Recovery (WHR) technologies is an effective approach to add a great economic value to the PEMFC power system. Global warming, climate change, and the high cost of energy production are the main drivers to improve the energy efficiency of PEMFC using WHR. This paper presents an overview of the recent progress concerning the cooling strategies and WHR opportunities for PEMFC. The main cooling techniques of PEMFCs are described and evaluated with respect to their advantages and disadvantages. Additionally, the potential pathways for PEMFC-WHR including heating, cooling, and power generation are explored and assessed. Furthermore, the main challenges and the research prospects for the cooling strategies and WHR of PEMFCs are discussed

Parametric study of an external coolant system for a high temperature polymer electrolyte membrane fuel cell

Considerable heat is generated in a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) at high current densities which poses a challenge in the cooling of stack, especially in automobile applications which require high power densities. In the present study, we investigate the effectiveness of an external coolant system using a multiscale, stack heat transfer model on a commercially available computational fluid dynamics (CFD) computer code which takes account of the convective and conductive heat transfer occurring through various layers of the cell and stack elements of an HT-PEMFC operating at 473 K (200 °C). The model accounts for the coupling between the local cell temperature, the local current density and the local overpotential through an empirical polarization curve appropriate for the cell. Results from the simulations show that temperature variations within the stack can be kept to within 10 K by an optimal choice of the number of coolant plates, the coolant flow rate and the temperature at which it enters the stack. Specific power densities of up to 690 W kg−1 (based on the active volume of the fuel cell) have been obtained for a 1 kWe stack with graphite cooling plates located one for four cells

SOFC system development and held trials for commercial applications

At Fraunhofer IKTS, appropriate processes and methods for the development of customized, application-specific SOFC concepts and prototype systems have been established during various projects in the past, funded by public bodies and industrial customers. As an outcome of the cell and stack developments during the past years, two proprietary SOFC technology platforms for system integration are readily available at IKTS. The eneramic® technology can be utilized for SOFC devices in the power range between 50 and 300 W. CFY stacks are available in standard sizes between 10 and 40 cells with a power output between 300 W and 1.2 kW. Higher power levels can be achieved by integration of multiple stacks in joint HotBox modules. For the development of SOFC systems, a detailed plant specification and process design is prepared initially. Here, all application-specific requirements are considered and a system concept with special consideration of the proposed operating modes and fuel processing technology is derived. The proposed concept is validated afterwards by means of laboratory tests on component, HotBox and system level. Further design iterations and model-based analyses are used for the creation of optimized solutions to be implemented in prototype and demonstration systems. Two exemplary SOFC development projects are described in order to illustrate the development status and system engineering approach