scholarly journals A New Model for Constant Fuel Utilization and Constant Fuel Flow in Fuel Cells

2019 ◽  
Vol 9 (6) ◽  
pp. 1066 ◽  
Author(s):  
Uday Chakraborty
Keyword(s):  
Fuel Cells ◽  
Fuel Utilization ◽  
Rate Condition ◽  
New Model ◽  
Constant Flow Rate ◽  
Fuel Flow ◽  
Gain Term ◽  
Loss Term ◽  
Utilization Condition ◽  
Control Constant

This paper presents a new model of fuel cells for two different modes of operation: constant fuel utilization control (constant stoichiometry condition) and constant fuel flow control (constant flow rate condition). The model solves the long-standing problem of mixing reversible and irreversible potentials (equilibrium and non-equilibrium states) in the Nernst voltage expression. Specifically, a Nernstian gain term is introduced for the constant fuel utilization condition, and it is shown that the Nernstian gain is an irreversibility in the computation of the output voltage of the fuel cell. A Nernstian loss term accounts for an irreversibility for the constant fuel flow operation. Simulation results are presented. The model has been validated against experimental data from the literature.

Pumpless Fuel Supply Using Pressurized Fuel Regulated by Autonomous Flow-Rate Regulation Valves

2012 ◽  
Vol 9 (3) ◽  
Author(s):  
Il Doh ◽  
Young-Ho Cho
Keyword(s):  
Fuel Cells ◽  
Flow Rate ◽  
Electrical Power ◽  
Initial Pressure ◽  
Flow Regulation ◽  
Present System ◽  
Constant Flow ◽  
Constant Flow Rate ◽  
Fuel Supply ◽  
Fuel Flow

A pumpless fuel supply using pressurized fuel with autonomous flow regulation valves is presented. Since micropumps and their control circuitry consume a portion of the electrical power generated in fuel cells, fuel supply without micropumps makes it possible to provide more efficient and inexpensive fuel cells than conventional ones. The flow regulation valves in the present system maintain the constant fuel flow rate from the pressurized fuel chamber even though the fuel pressure decreases. They autonomously adjust fluidic resistance of the channel according to fuel pressure so as to maintain constant flow rate. Compared to previous pumpless fuel supply methods, the present method offers more uniform fuel flow without any fluctuation using a simple structure. The prototypes were fabricated by a polymer micromolding process. In the experimental study using the pressurized deionized water, prototypes with pressure regulation valves showed constant flow rate of 5.38 ± 0.52 μl/s over 80 min and 5.89 ± 0.62 μl/s over 134 min, for the initial pressure in the fuel chamber of 50 and 100 kPa, respectively, while the other prototypes having the same fluidic geometry without flow regulation valves showed higher and gradually decreasing flow rate. The present pumpless fuel supply method providing constant flow rate with autonomous valve operation will be beneficial for the development of next-generation fuel cells.

scholarly journals Numerical investigation and optimization of vapor-feed microfluidic fuel cells with high fuel utilization

2018 ◽  
Vol 261 ◽  
pp. 127-136 ◽  
Author(s):  
Yifei Wang ◽  
Dennis Y.C. Leung ◽  
Hao Zhang ◽  
Jin Xuan ◽  
Huizhi Wang
Keyword(s):  
Fuel Cells ◽  
Numerical Investigation ◽  
Fuel Utilization

High-efficiency fuel utilization innovation in microfluidic fuel cells: From liquid-feed to vapor-feed

Energy ◽  
2021 ◽  
pp. 122484
Author(s):  
Tiancheng Ouyang ◽  
Jie Lu ◽  
Peihang Xu ◽  
Xiaoyi Hu ◽  
Jingxian Chen
Keyword(s):  
Fuel Cells ◽  
High Efficiency ◽  
Fuel Utilization ◽  
Liquid Feed

Modeling of a Direct Carbon Fuel Cell System

2005 ◽  
Author(s):  
K. Hemmes ◽  
M. Houwing ◽  
N. Woudstra
Keyword(s):  
Fuel Cells ◽  
Exergy Analysis ◽  
Cell System ◽  
System Model ◽  
System Level ◽  
Anode Side ◽  
Fuel Utilization ◽  
Fuel Cell System ◽  
Bench Scale ◽  
Direct Carbon Fuel Cell

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO2 produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study the performance of a CO2-producing DCFC system model. The theoretically predicted advantages that are confirmed on a bench scale are also confirmed on a system level, except for the production of pure CO2. Net system efficiencies of around 78 % were found for the developed system. An exergy analysis of the system shows where the losses in the system occur. If the cathode of the DCFC must be operated as a standard MCFC cathode the required CO2 at the cathode is the reason why a large part of the pure CO2 from the anode is recycled and mixed with the incoming air and cannot be used directly for sequestration. Bench scale studies should be performed to test the minimum amount of CO2 needed at the cathode. This might be lower than in standard MCFC operation due to the pure CO2 at the anode side that enhances diffusion towards the cathode.

Effects of Operating Conditions on the Heat Management of a Microscale Fuel Cell

2019 ◽  
Author(s):  
Liyong Sun ◽  
Adam S. Hollinger ◽  
Jun Zhou
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Waste Heat ◽  
Heat Removal ◽  
Current Collector ◽  
Ambient Air ◽  
Operating Conditions ◽  
Heat Management ◽  
Fuel Flow ◽  
Fuel Stream

Abstract Higher energy densities and the potential for nearly instantaneous recharging make microscale fuel cells very attractive as power sources for portable technology in comparison with standard battery technology. Heat management is very important to the microscale fuel cells because of the generation of waste heat. Waste heat generated in polymer electrolyte membrane fuel cells includes oxygen reduction reaction in the cathode catalyst, hydrogen oxidation reaction in the anode catalyst, and Ohmic heating in the membrane. A novel microscale fuel cell design is presented here that utilizes a half-membrane electrode assembly. An ANSYS Fluent model is presented to investigate the effects of operating conditions on the heat management of this microscale fuel cell. Five inlet fuel temperatures are 22°C, 40°C, 50°C, 60°C, and 70°C. Two fuel flow rate are 0.3 mL/min and 2 mL/min. The fuel cell is simulated under natural convection and forced convection. The simulations predict thermal profiles throughout this microscale fuel cell design. The exit temperature of fuel stream, oxygen stream and nitrogen stream are obtained to determine the rate of heat removal. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air by the exposed current collector surfaces. The top and bottom current collector removes almost the same amount of heat. The model also shows that the heat transfer through the oxygen channel and nitrogen channel is minimal over the range of inlet fuel temperatures. Increasing fuel flow rate and ambient air flow both increase the heat removal by the exposed current collector surfaces. Ultimately, these simulations can be used to determine design points for best performance and durability in a single-channel microscale fuel cell.

SOFC Stack Model for Integration Into a Hybrid System: Stack Response to Control Variables

2015 ◽  
Vol 12 (3) ◽  
Author(s):  
Michael M. Whiston ◽  
Melissa M. Bilec ◽  
Laura A. Schaefer
Keyword(s):  
Flow Rate ◽  
Current Density ◽  
Cell Model ◽  
Control Strategies ◽  
Negative Electrode ◽  
Open Loop ◽  
Fuel Utilization ◽  
Tight Coupling ◽  
Fuel Flow ◽  
Energy And Momentum

Due to the tight coupling of physical processes inside solid oxide fuel cells (SOFCs), efficient control of these devices depends largely on the proper pairing of controlled and manipulated variables. The present study investigates the uncontrolled, dynamic behavior of an SOFC stack that is intended for use in a hybrid SOFC-gas turbine (GT) system. A numerical fuel cell model is developed based on charge, species mass, energy, and momentum balances, and an equivalent circuit is used to combine the fuel cell's irreversibilities. The model is then verified on electrochemical, mass, and thermal timescales. The open-loop response of the average positive electrode-electrolyte-negative electrode (PEN) temperature, fuel utilization, and SOFC power to step changes in the inlet fuel flow rate, current density, and inlet air flow rate is simulated on different timescales. Results indicate that manipulating the current density is the quickest and most efficient way to change the SOFC power. Meanwhile, manipulating the fuel flow is found to be the most efficient way to change the fuel utilization. In future work, it is recommended that such control strategies be further analyzed and compared in the context of a complete SOFC-GT system model.

Sign in / Sign up

Export Citation Format

Share Document