Emf, Maximum Power and Efficiency of Fuel Cells

1993 ◽  
Vol 115 (2) ◽  
pp. 100-104 ◽  
Author(s):  
R. A. Gaggioli ◽  
W. R. Dunbar
Keyword(s):  
Free Energy ◽  
Fuel Cells ◽  
Gibbs Free Energy ◽  
Flow Rate ◽  
Power Output ◽  
Local Characteristic ◽  
Work Output ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
The Ideal

The ideal voltage of steady-flow fuel cells is usually expressed by Emf = −ΔG°/nF where ΔG° is the “Gibbs free energy of reaction” for the oxidation of the fuel at the supposed temperature of operation of the cell. Furthermore, the ideal power of the cell is expressed as the product of the fuel flow rate with this emf. Such viewpoints are flawed in several respects. While it is true that if a cell operates isothermally, the maximum conceivable electrical work output is equal to the difference between the Gibbs free energy of the incoming reactants and that of the leaving products; nevertheless, even if the cell operates isothermally, the use of the conventional ΔG° of reaction (a) assumes that the products of reaction leave separately from one another (and from any unused fuel); and (b) when ΔS of reaction is positive, it assumes that a free heat source exists at the operating temperature, whereas if ΔS is negative, it neglects the potential power which theoretically could be obtained from the heat released during oxidation. Moveover, (c) the usual cell does not operate isothermally, but (virtually) adiabatically. Comment (a) is often accounted for by employing the Nernst equation to correct for the dilution of reactants and/or products. Nevertheless, comments (b) and (c) remain pertinent. Rather than with emf, the proper starting place is with power output. The ideal power is that which would be obtained if the fuel were oxidized without irreversible entropy generation. Among other factors, this ideal power output depends upon the ratio of oxidant to fuel flow rate (e.g., air-fuel ratio) and the percentage of fuel oxidation. The ideal voltage is deduced from the ideal power, because it is defined as electrical work output per unit of charge delivered. It is a local characteristic which varies with the percent of fuel oxidized. Therefore, (d) ideal power is not equal to the product of emf with current (unless the amount of fuel utilized is infinitesimal). Examples are presented which illustrate such affects and their importance for the evaluation of ideal power and of efficiency.

Current distribution in PEM fuel cells. Part 1: Oxygen and fuel flow rate effects

AIChE Journal ◽  
2005 ◽  
Vol 51 (9) ◽  
pp. 2587-2598 ◽  
Author(s):  
Dilip Natarajan ◽  
Trung Van Nguyen
Keyword(s):  
Fuel Cells ◽  
Flow Rate ◽  
Current Distribution ◽  
Pem Fuel Cells ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Rate Effects

Thermodynamic Optimization of a Gas Turbine Power Plant With Pressure Drop Irreversibilities

1998 ◽  
Vol 120 (3) ◽  
pp. 233-240 ◽  
Author(s):  
V. Radcenco ◽  
J. V. C. Vargas ◽  
A. Bejan
Keyword(s):  
Power Plant ◽  
Gas Turbine ◽  
Flow Rate ◽  
Power Output ◽  
Pressure Ratio ◽  
Plant Size ◽  
Fuel Flow Rate ◽  
Flow Area ◽  
Fuel Flow ◽  
Gas Turbine Power Plant

In this paper we show that the thermodynamic performance of a gas turbine power plant can be optimized by adjusting the flow rate and the distribution of pressure losses along the flow path. Specifically, we show that the power output has a maximum with respect to the fuel flow rate or any of the pressure drops. The maximized power output has additional maxima with respect to the overall pressure ratio and overall temperature ratio. When the optimization is performed subject to a fixed fuel flow rate, and the power plant size is constrained, the power output and efficiency can be maximized again by properly allocating the fixed total flow area among the compressor inlet and the turbine outlet.

Dynamic Simulation of a HRSG System for a Given Start-Up/Shut Down Curve

2011 ◽  
Author(s):  
Hun Cha ◽  
Yoo Seok Song ◽  
Kyu Jong Kim ◽  
Jung Rae Kim ◽  
Sung Min KIM
Keyword(s):  
Dynamic Analysis ◽  
Gas Turbine ◽  
Flow Rate ◽  
Exhaust Gas ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Start Up ◽  
Gas Turbine Exhaust ◽  
Main Steam ◽  
Duct Burner

An inappropriate design of HRSG (Heat Recovery Steam Generator) may lead to mechanical problems including the fatigue failure caused by rapid load change such as operating trip, start-up or shut down. The performance of HRSG with dynamic analysis should be investigated in case of start-up or shutdown. In this study, dynamic analysis for the HRSG system was carried out by commercial software. The HRSG system was modeled with HP, IP, LP evaporator, duct burner, superheater, reheater and economizer. The main variables for the analysis were the temperature and mass flow rate from gas turbine and fuel flow rate of duct burner for given start-up (cold/warm/hot) and shutdown curve. The results showed that the exhaust gas condition of gas turbine and fuel flow rate of duct burner were main factors controlling the performance of HRSG such as flow rate and temperature of main steam from final superheater and pressure of HP drum. The time delay at the change of steam temperature between gas turbine exhaust gas and HP steam was within 2 minutes at any analysis cases.

Model Analysis of Syngas Combustion and Emissions for a Micro Gas Turbine

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Chi-Rong Liu ◽  
Hsin-Yi Shih
Keyword(s):  
Gas Turbine ◽  
Flow Rate ◽  
Heat Input ◽  
Emission Characteristics ◽  
Nox Emissions ◽  
Fuel Flow Rate ◽  
Micro Gas Turbine ◽  
Fuel Flow ◽  
Temperature Distributions ◽  
Flame Structures

The purpose of this study is to investigate the combustion and emission characteristics of syngas fuels applied in a micro gas turbine, which is originally designed for a natural gas fired engine. The computation results were conducted by a numerical model, which consists of the three-dimension compressible k–ε model for turbulent flow and PPDF (presumed probability density function) model for combustion process. As the syngas is substituted for methane, the fuel flow rate and the total heat input to the combustor from the methane/syngas blended fuels are varied with syngas compositions and syngas substitution percentages. The computed results presented the syngas substitution effects on the combustion and emission characteristics at different syngas percentages (up to 90%) for three typical syngas compositions and the conditions where syngas applied at fixed fuel flow rate and at fixed heat input were examined. Results showed the flame structures varied with different syngas substitution percentages. The high temperature regions were dense and concentrated on the core of the primary zone for H2-rich syngas, and then shifted to the sides of the combustor when syngas percentages were high. The NOx emissions decreased with increasing syngas percentages, but NOx emissions are higher at higher hydrogen content at the same syngas percentage. The CO2 emissions decreased for 10% syngas substitution, but then increased as syngas percentage increased. Only using H2-rich syngas could produce less carbon dioxide. The detailed flame structures, temperature distributions, and gas emissions of the combustor were presented and compared. The exit temperature distributions and pattern factor (PF) were also discussed. Before syngas fuels are utilized as an alternative fuel for the micro gas turbine, further experimental testing is needed as the modeling results provide a guidance for the improved designs of the combustor.

scholarly journals A Method to Measure the Fuel Distribution and the Fuel Captured by V–Gutter Flameholder in High Speed Airstream

1985 ◽  
Author(s):  
Gu Shan-Jian ◽  
Yang Mao-Lin ◽  
Li Xiang-Yi
Keyword(s):  
Flow Rate ◽  
Experimental Error ◽  
High Speed ◽  
Fuel Flow Rate ◽  
Fuel Distribution ◽  
Fuel Flow ◽  
Sampling Condition ◽  
Detailed Determination

A method to measure the fuel distribution and the percentage of fuel flow rate captured by a V-gutter flameholder in a high speed airstream has been developed. The effects of configuration and size of the probe and temprature of the sample mixture in the probe on measurement have been investigated. The detailed determination of isokinetic sampling condition is described. The effects of V-gutter geometry on flowfield have been considered. The total experimental error is of the order ±5%.

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.

System Level Analysis of Acoustically Forced Nonpremixed Swirling Flames

2014 ◽  
Vol 6 (3) ◽  
Author(s):  
Uyi Idahosa ◽  
Saptarshi Basu ◽  
Ankur Miglani
Keyword(s):  
Heat Release ◽  
Flow Rate ◽  
Ccd Camera ◽  
Time Dependent ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Flame Response ◽  
Rate Oscillations ◽  
Swirling Flames ◽  
Flame Sheet

This paper reports an experimental investigation of dynamic response of nonpremixed atmospheric swirling flames subjected to external, longitudinal acoustic excitation. Acoustic perturbations of varying frequencies (fp = 0–315 Hz) and velocity amplitudes (0.03 ≤ u′/Uavg ≤ 0.30) are imposed on the flames with various swirl intensities (S = 0.09 and 0.34). Flame dynamics at these swirl levels are studied for both constant and time-dependent fuel flow rate configurations. Heat release rates are quantified using a photomultiplier (PMT) and simultaneously imaged with a phase-locked CCD camera. The PMT and CCD camera are fitted with 430 nm ±10 nm band pass filters for CH* chemiluminescence intensity measurements. Flame transfer functions and continuous wavelet transforms (CWT) of heat release rate oscillations are used in order to understand the flame response at various burner swirl intensity and fuel flow rate settings. In addition, the natural modes of mixing and reaction processes are examined using the magnitude squared coherence analysis between major flame dynamics parameters. A low-pass filter characteristic is obtained with highly responsive flames below forcing frequencies of 200 Hz while the most significant flame response is observed at 105 Hz forcing mode. High strain rates induced in the flame sheet are observed to cause periodic extinction at localized regions of the flame sheet. Low swirl flames at lean fuel flow rates exhibit significant localized extinction and re-ignition of the flame sheet in the absence of acoustic forcing. However, pulsed flames exhibit increased resistance to straining due to the constrained inner recirculation zones (IRZ) resulting from acoustic perturbations that are transmitted by the co-flowing air. Wavelet spectra also show prominence of low frequency heat release rate oscillations for leaner (C2) flame configurations. For the time-dependent fuel flow rate flames, higher un-mixedness levels at lower swirl intensity is observed to induce periodic re-ignition as the flame approaches extinction. Increased swirl is observed to extend the time-to-extinction for both pulsed and unpulsed flame configurations under time-dependent fuel flow rate conditions.

scholarly journals A new generation of F1 race engines – hybrid power units

2016 ◽  
Vol 167 (4) ◽  
pp. 22-37 ◽  
Author(s):  
Zbigniew STĘPIEŃ
Keyword(s):  
Flow Rate ◽  
Regulatory Framework ◽  
Fuel Flow Rate ◽  
Maximum Performance ◽  
Engine Efficiency ◽  
Hybrid Power ◽  
Fuel Flow ◽  
New Generation ◽  
Technical Regulations

The paper aims at reviewing the evolution of the F1 engine technology and the associated regulatory framework governing the sport over the last 10 years. Technical regulations, in force since 2014, replaced the 2.4-liter V8 naturally aspirated engines with sophisticated hybrid units such as the 1.6-liter V6 turbocharged engines supported with energymanagement and recovery systems. Since 2014 the fundamental trend in the development of powertrains has been the advancement of their efficiency. Due to the fact that the fuel flow rate has been restricted, the maximum performance is now entirely dependent on the engine efficiency.

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