Two-Phase Pressure Drop Characteristics During Low Temperature Transients in PEMFCs

2014 ◽  
Author(s):  
Rupak Banerjee ◽  
Satish G. Kandlikar
Keyword(s):  
Fuel Cells ◽  
Steady State ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Transient Behavior ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Four Levels ◽  
Phase Pressure

Proton Exchange Membrane fuel cells are being considered as the powertrain of choice for automotive applications. Automotive fuel cells experience transients during start-up, shut-down and changing load conditions, which constitute a significant part of the drive cycle. Transient behavior of PEMFCs can be classified into three categories: electrochemical, thermal and two-phase flow. Two-phase transients require a longer time to return to steady state than the electrochemical transient (which typically requires less than 1 second). Experiments have shown two-phase transients to be more prominent at the lower temperatures due to the increased presence of liquid water. Overshoot / undershoot behavior of current and voltage has been observed during investigations of electrochemical transients. This study investigates similar overshoot / undershoot behavior in the two-phase pressure drop in the reactant channels. An increase in the current drawn from the PEMFC is accompanied by larger air flow rates and greater water generation. An in situ setup is utilized to measure the pressure drop in the reactant channels across the length of the channel, when the electrical load drawn from the PEMFC is changed. This pressure drop measurement along the length of the reactant channels is used to characterize the overshoot / undershoot behavior. A parametric study is conducted to identify the factors which influence the overshoot / undershoot in two-phase flow pressure drop. The transient behavior is explored at the temperatures of 40, 60 and 80°C. Transient behavior is more pronounced at the lower temperature. Five different ramp rates have been used to show that faster ramp rates results in larger overshoot. The effect of magnitude of current change is investigated using four levels of load change. It was observed that increased magnitude of change results in increased overshoot behavior. However, no direct relationship has been observed between the magnitude of overshoot and the time required to return to steady state.

An Analysis of Two-Phase Flow Pressure Drop in Operating Proton Exchange Membrane Fuel Cell Channels With the Lockhart-Martinelli Approach

2014 ◽  
Author(s):  
Ryan Anderson ◽  
Lifeng Zhang ◽  
David P. Wilkinson
Keyword(s):  
Fuel Cells ◽  
Pressure Drop ◽  
Proton Exchange Membrane ◽  
Two Phase Flow ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Current Densities ◽  
Flow Pressure ◽  
Exchange Membrane

Proton exchange membrane fuel cells (PEMFCs) are considered one of the most promising alternatives for the automotive industry owing to their high energy efficiency, zero emission at the vehicle use stage, and low temperature operation. Water as a byproduct plays a complex role in fuel cell operation. In particular, the inevitable occurrence of liquid water leads to gas-liquid two-phase flows in various components of PEMFCs including flow channels of which diameters range from micrometers to millimeters. In conventional minichannels and microchannels, the Lockhart-Martinelli (LM) approach has been employed to predict the two-phase pressure drop of gas-liquid systems. This approach has previously been updated by our group to more accurately reflect the introduction of liquid water into the flow channels of a PEMFC i.e. from a porous media perpendicular to the gas flow. Importantly, the LM method normalizes the data independent of the flow field design and operating conditions like temperature, pressure, and relative humidity. This paper analyzes the increasing amount of experimental data on two-phase flow pressure drops/two-phase flow multipliers in the literature with these approaches. The focus is the cathode side (therefore an air/water system), and data is collected from multiple research groups using active fuel cells (electrochemically produced water). The traditional LM approach greatly under-predicts the two-phase pressure drop at low current densities. However, the analysis is applied over a range of current densities, and it better predicts results at higher current densities (>600 mA cm−2). Literature correlations for the Chisholm parameter C, a flow regime dependent parameter in the LM equation, have been proposed for non-active (external water injection) fuel cells but do not match the results from operating fuel cells. C is shown here to vary with current density, flow stoichiometry (gas velocity), gas diffusion layer, and slightly with relative humidity.

Pressure Drop in a Capillary Tube in Boiling Two-Phase Flow

2003 ◽  
Author(s):  
Fumito Kaminaga ◽  
Baduge Sumith ◽  
Kunihito Matsumura
Keyword(s):  
Pressure Drop ◽  
Vapor Phase ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Capillary Tube ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
System Pressure ◽  
Phase Pressure

Two-phase pressure drop is experimentally examined in a flow boiling condition in a tube of diameter 1.45 mm using water in ranges of pressure from 10 to 100 kPa, mass flux from 18 to 152 kg/m2s, heat flux from 13 to 646 kW/m2, and exit quality from 0.02 to 0.77. Also, pressure drop in an adiabatic air-water two-phase flow is measured at atmospheric pressure using the same test section and mass flux ranges of liquid and gas as those in the flow boiling. Decreasing system pressure the pressure drop significantly increases at a given mass flux. Influence of vapor phase on the pressure drop is found to be large both in the adiabatic and the diabatic conditions. The frictional pressure drop correlation for the adiabatic two-phase flow is developed and applied to predict pressure drop in the flow boiling. But it cannot give satisfactory predictions. The Chisholm correlation calculating a two-phase pressure drop multiplier is modified to account the influence of vapor phase in a capillary tube and the modified correlation can predict the pressure drop in the flow boiling within an error of 20%.

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