Entropy Based Design of Fuel Cells

Naterer, G.F.; Tokarz, C. D.

doi:10.1115/1.2174065

Cited by 8 publications

(4 citation statements)

References 21 publications

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“…21 Entropy production due to heat transfer and gas friction requires additional modeling of the coupled mass and momentum equations within the fuel channel. When fuel channel and membrane electrode assembly irreversibilities are combined, the entropy-based design provides a unified formulation for characterizing all sources of effective voltage losses within a fuel cell.…”

Section: Resultsmentioning

confidence: 99%

Fuel Cell Exergy Losses of Activation Energy and Cathode Polarizaztion

Naterer

Tokarz

2006

Journal of Thermophysics and Heat Transfer

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This article investigates thermochemical irreversibilities of activation energy and concentration polarization in fuel cells. The predictive formulation uses the Butler-Volmer equation for the activation overpotential and it includes both Knudsen and self-diffusion for the concentration polarization. Entropy production of activation energy occurs due to a portion of cell voltage lost in driving the chemical reaction to transfer electrons to/from the electrode. In this article, exergy losses associated with these activation and concentration irreversibilities are formulated based on the Second Law. Unlike past studies of entropy production in solid oxide fuel cells, this article extends past methods to half-cell reactions and thermochemical irreversiblities in a proton-exchange membrane fuel cell. Voltage losses are derived based on entropy production within the fuel cell, in contrast to past methods involving polarization curves. The entropy-based method provides a useful alternative to past conventional methods, because it can encompass both electrochemical irreversibilities (such as electrode polarization) and thermofluid irreversibilities (such as fuel channel friction). NomenclatureFaraday's constant, 96,785 C/mol G = Gibbs free energy, J i = current density, A/m 2 J = flux, mol/s K = equilibrium constant l = thickness, m M = molar masṡ m = mass flow rate, kg/s N = number of moles per mole H 2 n d = electro-osmotic drag coefficient n e = moles of electrons per half-cell reaction P = pressure, Pȧ P s = entropy production rate, W/mol K Q = heat transfer rate, W R = universal gas constant, 8.314 J/mol K s = molar entropy, J/mol K T = temperature, K v = specific volume, m 3 /kġ W = power, W X dest = exergy destruction rate, W/mol β = transfer coefficient γ = stoichiometric ratio η = polarization, V ρ = density, kg/m 3 a, c = anode, cathode eff = effective fc = fuel cell H 2 = hydrogen H 2 O = water vapor m = membrane/electrolyte O 2 = oxygen P, R = products, reactants 0 = exchange Superscripts I = inlet conditions rev = reversible

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Section: Resultsmentioning

confidence: 99%

Fuel Cell Exergy Losses of Activation Energy and Cathode Polarizaztion

Naterer

Tokarz

2006

Journal of Thermophysics and Heat Transfer

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“…The predicted entropy production (per unit area) in the streamwise direction (x * = x/L) for a slip-flow case with ζ 1 = 5.1 × 10 −8 is shown in figure 6. Since the gas density remains constant and pressure decreases, the temperature falls in the x-direction, so equation (9) indicates that ζ 2 rises through the channel. The entropy production (per unit area) is calculated based on the integrated y-profile of equation (27) across the channel at each x * point.…”

Section: Resultsmentioning

confidence: 99%

“…An optimal design of a cryogenic system was developed analytically by a heat-leak function that minimizes an entropy generation integral, subject to finitesize constraints and a Lagrange multiplier [6]. In complex systems such as fuel cells, entropy production occurs from combined friction, thermal and chemical transport phenomena [9]. Microfluidic transport may involve additional effects of electromagnetic irreversibilities [10], which involve coupled velocity and magnetic fields in the momentum equations.…”

Section: Introductionmentioning

confidence: 99%

Slip-flow irreversibility of dissipative kinetic and internal energy exchange in microchannels

Ogedengbe

Naterer

Rosen

2006

J. Micromech. Microeng.

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The mechanisms of near-wall velocity slip and their effects on energy conversion of fluid motion in microchannels are investigated. Unlike large-scale channels with no-slip boundary conditions, this paper predicts how streamwise temperature gradients and transverse velocity gradients contribute to velocity slip during intermolecular interactions near a microchannel wall. A numerical formulation is developed with a mass-weighted convection scheme (called NISUS; non-inverted skew upwind scheme) in a SIMPLEC finite volume method. The new convection scheme provides accurate upstream interpolation of convection variables, including robust pressure/velocity coupling near the slip-flow boundary. Numerical predictions of entropy production characterize the near-wall dissipation of kinetic energy. Effects of varying pressure ratios, accommodation coefficients, flow rates and channel aspect ratios are presented for nitrogen gas flows between Re = 0.001 and 0.003. This paper gives new insight regarding dissipative kinetic and internal energy exchange in microchannels, due to slip-flow behavior.

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“…Which validates the voltage output from the entropy production [12]. Since in the past the energy loss in the fuel cell was determined by means of models from "overpotential" and "polarization" [11].…”

Section: Figure 3 Voltage Profile In Pemfc (T = 373k) [11]mentioning

confidence: 99%

Entropic Performance of Proton-Exchange Membrane through Current Density, Temperature, Pressure, Membrane Thickness and Humidity

Dib

Takei

Shing

et al. 2017

PAMR

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The fuel cell is a renewable technology which utilizes the hydrogen fuel via oxidation to generate electricity. The development of the technology is being focused on the most effective configurations of these processes to balance availability, efficiency and capacity. A meta-study has been conducted with the aim to analyze fuel cell performance was analysed of different materials such as; Solid Oxide fuel cells, Nafion and Peresulfuric acid under a series of variables: current density, temperature, pressure, membrane thickness and humidity. The reaction kinetics at high temperatures allow for greater hydrogen and oxygen permeability and solubility but are limited by proton conductivity of membrane at high temperature. From meta-study outcome, the largest improvement in current density is achieved by improving cathode polarity and membrane permeability. Optimizing H+ ion concentration is done by increasing humidity through increased pressure.

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Entropy Based Design of Fuel Cells

Cited by 8 publications

References 21 publications

Fuel Cell Exergy Losses of Activation Energy and Cathode Polarizaztion

Fuel Cell Exergy Losses of Activation Energy and Cathode Polarizaztion

Slip-flow irreversibility of dissipative kinetic and internal energy exchange in microchannels

Entropic Performance of Proton-Exchange Membrane through Current Density, Temperature, Pressure, Membrane Thickness and Humidity

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