Liquid Water Movement Research Articles

Ground heat flux determination based on near-surface soil hydro-thermodynamics

Near-surface soil hydro-thermodynamics plays an important role in heat and water transfer between land and atmosphere. However, it is difficult to quantify these processes in field campaigns, such as movement of liquid water and water vapor. This has affected determination of ground heat flux, a key component of surface energy budget. This study aims to quantify soil heat and water processes utilizing in situ measurements, and to improve ground heat flux estimation and surface energy imbalance. A new model has been proposed based on three main physical processes, including thermal conduction, convection of heat by moving water, and convection of latent heat. The model was tested at a grassland site in Colorado, USA. Results show that the model can capture high values of soil water content during rain events, low values under intense solar radiation, and high-frequency fluctuations under intermittent cloudy conditions. Also, the model produces reasonable vertical velocity and mass flux of water vapor. For the estimation of ground heat flux, the method that considers vertical variation of soil thermal conductivity and the contribution of water vapor gives better energy balance ratio than methods that ignore these conditions. In spite of this, the energy balance ratio is still low. Footprint analysis further shows the seasonal variation of ground cover is a potential reason responsible for this.

Hydrologic connectivity at the hillslope scale through intra‐snowpack flow paths during snowmelt

AbstractThe seasonal snowmelt period is a critical component of the hydrologic cycle for many mountainous areas. Changes in the timing and rate of snowmelt as a result of physical hydrologic flow paths, such as longitudinal intra‐snowpack flow paths, can have strong implications on the partitioning of meltwater amongst streamflow, groundwater recharge, and soil moisture storage. However, intra‐snowpack flow paths are highly spatially and temporally variable and thus difficult to observe. This study utilizes new methods to non‐destructively observe spatio‐temporal changes in the liquid water content of snow in combination with plot experiments to address the research question: What is the scale of influence that intra‐snowpack flow paths have on the downslope movement of liquid water during snowmelt across an elevational gradient? This research took place in northern Colorado with study plots spanning from the rain‐snow transition zone up to the high alpine. Results indicate an increasing scale of influence from intra‐snowpack flow paths with elevation, showing higher hillslope connectivity producing larger intra‐snowpack contributing areas for meltwater accumulation, quantified as the upslope contributing area required to produce observed changes in liquid water content from melt rate estimates. The total effective intra‐snowpack contributing area of accumulating liquid water was found to be 17, 6, and 0 m2 for the above tree line, near tree line, and below tree line plots, respectively. Dye tracer experiments show capillary and permeability barriers result in increased number and thickness of intra‐snowpack flow paths at higher elevations. We additionally utilized aerial photogrammetry in combination with ground penetrating radar surveys to investigate the role of this hydrologic process at the small watershed scale. Results here indicate that intra‐snowpack flow paths have influence beyond the plot scale, impacting the storage and transmission of liquid water within the snowpack at the small watershed scale.

Ex-situ visualization of the wet domain in the microporous layer in a polymer electrolyte fuel cell by X-ray computed tomography under water vapor supply

The wet domain in a microporous layer (MPL) in a polymer electrolyte fuel cell (PEFC) was visualized in order to clarify water accumulation in the MPL. The performance of PEFC is affected by accumulation of liquid water in the cathode gas diffusion layer (GDL). The liquid water hinders oxygen transport to the catalyst layer, resulting in increased mass-transport loss. Although MPLs suppress water accumulation in the GDL, this mechanism has not yet been fully clarified. The present study used synchrotron X-ray micro computed tomography (CT) to visualize water accumulation in the MPL. The experiment was conducted while supplying water vapor to the MPL side of the GDL. The MPL was visualized to be wetted heterogeneously, and liquid water movement from the MPL to the GDL substrate was visualized. These observations were supported by plotting the volume fraction of either the wet domain of the MPL or the water cluster as a function of through-plane distance.

Moisture Management Properties of Seersucker Woven Fabrics of Different Structure

Moisture management is defined as the controlled movement of water vapour and liquid water (perspiration) from the surface of the skin to the atmosphere through the fabric. The ability of moisture transport is a very important feature of textile materials from the point of view of the physiological comfort of usage clothing made of these materials. Among the different textile materials (woven, knitted and nonwoven), seersucker woven fabric is considered as having good comfort-related properties. The fabrics are characterised by the occurrence of puckered and flat strips in the warp direction. The puckered effect generates air spaces between the body and the fabric, keeping the wearer cool in hot conditions as the puckered area holds the fabric away from the skin during usage. In the work presented, seersucker woven fabrics of different patterns of the puckered strips were investigated. The aim of the work was to analyse the relationship between the structure of seersucker fabrics and their moisture management properties. Measurement of the moisture transport properties of seersucker woven fabrics was made using a Moisture Management Tester M290, produced by SDL Atlas. Investigations performed showed that the properties of seersucker woven fabrics characterising their ability to transfer liquid moisture are different depending on the variant of the repeat of puckered strips.

Liquid Water Transport in Porous Metal Foam Flow-Field Fuel Cells: A Two-Phase Numerical Modelling and Ex-Situ Experimental Study

Proton exchange membrane fuel cells (PEMFCs) using porous metallic foam flow-field plates have been demonstrated as an alternative to conventional rib and channel designs, showing high performance at high currents. However, the transport of liquid product water through metal foam flow-field plates in PEMFC conditions is not well understood, especially at the individual pore level. In this work, ex-situ experiments are conducted to visualise liquid water movement within a metal foam flow-field plate, considering hydrophobicity, foam pore size and air flow rate. A two-phase numerical model is then developed to further investigate the fundamental water transport behaviour in porous metal foam flow-field plates. Both the experimental and numerical work demonstrate that unlike conventional PEMFC channels, air flow rate does not have a strong influence on water removal due to the high surface tensions between the water and foam pore ligaments. A hydrophobic foam was seen to transport liquid water away from the initial injection point faster than a hydrophilic foam. In ex-situ tests, liquid water forms and maintains a random preferential pathway until the flow-field edge is reached. These results suggest that controlled foam hydrophobicity and pore size is the best way of managing water distribution in PEMFCs with porous flow-field plates.

Upscaling the Coupled Water and Heat Transport in the Shallow Subsurface

AbstractPredicting simultaneous movement of liquid water, water vapor, and heat in the shallow subsurface has many practical interests. The demand for multidimensional multiscale models for this region is important given: (a) the critical role that these processes play in the global water and energy balances, (b) that more data from air‐borne and space‐borne sensors are becoming available for parameterizations of modeling efforts. On the other hand, numerical models that consider spatial variations of the soil properties, termed here as multiscale, are prohibitively expensive. Thus, there is a need for upscaled models that take into consideration these features, and be computationally affordable. In this paper, a multidimensional multiscale model coupling the water flow and heat transfer and its respective upscaled version are proposed. The formulation is novel as it describes the multidimensional and multiscale tensorial versions of the hydraulic conductivity and the vapor diffusivity, taking into account the tortuosity and porosity properties of the medium. It also includes the coupling with the energy balance equation as a boundary describing atmospheric influences at the shallow subsurface. To demonstrate the accuracy of both models, comparisons were made between simulation and field experiments for soil moisture and temperature at 2, 7, and 12 cm deep, during 11 days. The root‐mean‐square errors showed that the upscaled version of the system captured the multiscale features with similar accuracy. Given the good matching between simulated and field data for near‐surface soil temperature, the results suggest that it can be regarded as a 1‐D variable.

Liquid water infiltration into a layered snowpack: evaluation of a 3-D water transport model with laboratory experiments

Abstract. The heterogeneous movement of liquid water through the snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a three-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, thickness of the upper layer affected by ponding, water content profiles and wet snow fraction. Simulation results showed that the model reconstructs relevant features of capillary barriers, including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.

Analysing the mechanisms of soil water and vapour transport in the desert vadose zone of the extremely arid region of northern China

The transport of water and vapour in the desert vadose zone plays a critical role in the overall water and energy balances of near-surface environments in arid regions. However, field measurements in extremely dry environments face many difficulties and challenges, so few studies have examined water and vapour transport processes in the desert vadose zone. The main objective of this study is to analyse the mechanisms of soil water and vapour transport in the desert vadose zone (depth of ∼350 cm) by using measured and modelled data in an extremely arid environment. The field experiments are implemented in an area of the Gobi desert in northwestern China to measure the soil properties, daily soil moisture and temperature, daily water-table depth and temperature, and daily meteorological records from DOYs (Days of Year) 114–212 in 2014 (growing season). The Hydrus-1D model, which simulates the coupled transport of water, vapour and heat in the vadose zone, is employed to simulate the layered soil moisture and temperature regimes and analyse the transport processes of soil water and vapour. The measured results show that the soil water and temperatures near the land surface have visible daily fluctuations across the entire soil profile. Thermal vapour movement is the most important component of the total water flux and the soil temperature gradient is the major driving factor that affects vapour transport in the desert vadose zone. The most active water and heat exchange occurs in the upper soil layer (depths of 0–25 cm). The matric potential change from the precipitation mainly re-draws the spatio-temporal distribution of the isothermal liquid water in the soil near the land surface. The matric potential has little effect on the isothermal vapour and thermal liquid water flux. These findings offer new insights into the liquid water and vapour movement processes in the extremely arid environment.

Large scale simulation of liquid water transport in a gas diffusion layer of polymer electrolyte membrane fuel cells using the lattice Boltzmann method

A method for the large-scale simulation with the lattice Boltzmann method (LBM) is proposed for liquid water movement in a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells. The LBM is able to analyze two-phase flows in complex structures, however the simulation domain is limited due to heavy computational loads. This study investigates a variety means to reduce computational loads and increase the simulation areas. One is applying an LBM treating two-phases as having the same density, together with keeping numerical stability with large time steps. The applicability of this approach is confirmed by comparing the results with rigorous simulations using actual density. The second is establishing the maximum limit of the Capillary number that maintains flow patterns similar to the precise simulation; this is attempted as the computational load is inversely proportional to the Capillary number. The results show that the Capillary number can be increased to 3.0 × 10−3, where the actual operation corresponds to Ca = 10−5∼10−8. The limit is also investigated experimentally using an enlarged scale model satisfying similarity conditions for the flow. Finally, a demonstration is made of the effects of pore uniformity in GDL as an example of a large-scale simulation covering a channel.

Early formation of preferential flow in a homogeneous snowpack observed by micro‐CT

AbstractWe performed X‐ray microtomographic observations of wet‐snow metamorphism during controlled continuous melting and melt‐freeze events in the laboratory. Three blocks of snow were sieved into boxes and subjected to cyclic, superficial heating or heating‐cooling to reproduce vertical water infiltration patterns in snow similarly to natural conditions. Periodically, samples were taken at different heights and scanned. Results suggest that wet‐snow metamorphism dynamics are highly heterogeneous even in an initially homogeneous snowpack. Consistent with previous work, we observed an increase with time in the thickness of the ice structure, which is a measure of grain size. However, this was coupled with large temporal scatter between consecutive measurements of the specific surface area and of the statistical moments of grain thickness distributions. Because of marked differences in the right tail, grain thickness distributions did not show shape invariance with time, contrary to previous analyses. In our experiments, wet‐snow metamorphism showed two strikingly different patterns: homogeneous coarsening superimposed by faster heterogeneous coarsening in areas that were affected by preferential percolation of water. Liquid water movement in snow and fast structural evolution may be thus intrinsically coupled by early formation of preferential flow at local scale. These observations suggest that further experiments are highly needed to fully understand wet‐snow metamorphism and infiltration patterns in a natural snowpack.

Development of a Water and Enthalpy Budget‐based Glacier mass balance Model (WEB‐GM) and its preliminary validation

AbstractThis paper presents a new water and energy budget‐based glacier mass balance model. Enthalpy, rather than temperature, is used in the energy balance equations to simplify the computation of the energy transfers through the water phase change and the movement of liquid water in the snow. A new parameterization for albedo estimation and state‐of‐the‐art parameterization schemes for rainfall/snowfall type identification and surface turbulent heat flux calculations are implemented in the model. This model was driven with meteorological data and evaluated using mass balance and turbulent flux data collected during a field experiment implemented in the ablation zone of the Parlung No. 4 Glacier on the Southeast Tibetan Plateau during 2009 and 2015–2016. The evaluation shows that the model can reproduce the observed glacier ablation depth, surface albedo, surface temperature, sensible heat flux, and latent heat flux with high accuracy. Comparing with a traditional energy budget‐based glacier mass balance model, this enthalpy‐based model shows a superior capacity in simulation accuracy. Therefore, this model can reasonably simulate the energy budget and mass balance of glacier melting in this region and be used as a component of land surface models and hydrological models.

Review of Modelingfor Liquid Water Movement in the Snowpack

Review of Modelingfor Liquid Water Movement in the Snowpack

Analysis of unsaturated materials hydration incorporating the effect of thermo-osmotic flow

The geological disposal of a high level radioactive waste relies in a system composed of engineered and geological barriers. The soils and rocks involved in the design of this type of solution are generally initially unsaturated and subject to complex thermal, hydraulic and mechanical (THM) coupled phenomena triggered by the simultaneous heating and hydration of the barrier materials under confined conditions. Mathematical THM formulations are typically used to analyze the behavior and long term performance of the barriers system. These types of formulations generally do not include some coupled processes, for example thermo-osmosis (i.e. the movement of liquid water induced by gradient of temperature), because they are considered not significant when compared against the main or direct processes (e.g., Darcy’s, Fourier’s and Fick’s laws). In this work, the potential effects of thermo-osmotic phenomenon is studied in detail. Typical flow equations are modified to include thermo-osmotic flows and then they are implemented in numerical simulators. Two case studies are analyzed. The first one focuses on a simple and already proposed model to study the behavior of a geological barrier for nuclear waste when subjected to heating and hydration. The other case corresponds to the study of an engineered clay barrier material in the laboratory subjected to hydraulic and thermal gradients similar to the ones expected in real repository conditions. In both cases the analyses with and without thermo-osmotic flows are compared. From these comparisons it is observed that the effect of thermo-osmosis can be quite significant. Thermo-osmotic effects also assisted to explain the apparent low wetting observed in the hydration of a clayey barrier material.

Water and Solute Fluxes in Soils Undergoing Freezing and Thawing

Water flow and solute transport processes are more complex in frozen than in unfrozen soils. The objective of this study was to determine the effects of freezing and thawing on water flow and solute transport in field soils. Experiments were conducted at two field sites each containing soil with a distinct texture (clay loam and sandy loam). Bromide (Br−) was used as a tracer, and soil water content and tracer concentrations were measured at different depths and times. A mass balance method was proposed to estimate mean values of water and solute fluxes (apparent soil water and Br− fluxes) in frozen, transition, and unfrozen zones during a freezing period and conduction and thawed zones during a thawing period. During freezing, soil water content significantly changed below and above the freezing front. Because of the presence of solute, relatively high liquid water content was found at soil temperature below zero. Soil water fluxes were mainly affected by the phase changes during freezing and thawing periods in the clay loam soil and by changes in the hydraulic properties related to liquid water content in the sandy soil. The contribution of water flux to the change of liquid water was much larger in the frozen zones than in the transition zones. During freezing, Br− ions excluded from ice and the different directions of dispersion and convection fluxes resulted in increases and then decreases of the apparent Br− concentration to mean measured Br concentration ratios. During thawing, the movement of liquid water and the superposition of convection and dispersion fluxes resulted in Br− concentration peaks and higher variation of the ratios. The water flow process was less synchronous with the solute transport process in unfrozen soils than in frozen soils.

(Keynote) Multiscale Modeling of Polymer-Electrolyte-Fuel-Cell Components

Water management in proton-exchange membrane fuel cells plays an important role in device operation, especially at lower temperatures where liquid water exists. Key to understanding water management is determining the mechanisms of water movement through the various fuel-cell components. Traditionally, continuum-scale mathematical modeling has been used to optimize and understand fuel-cell water and thermal management. However, it is increasingly become apparent that there is a need for more detailed lower lengthscale information to feed into the models due to microscale and mesoscale heterogeneities. In this talk, we will examine these issues with a focus on liquid-water movement in fuel-cell diffusion media and in water and ion transport in fuel-cell membranes including both proton and alkaline varieties. It is well known that continuum models use a volume-averaged approach to model liquid-water transport. This strategy is suitable for higher operating temperatures and homogeneous gas-diffusion-layer (GDL) morphologies, but, such structures are not realistic. To handle the complexity of the GDL morphology and access the expected capillary-fingering type of water transport in these porous media, pore-network models (PNMs) are utilized. However, while PNMs models capture the water transport through the GDL, they do not contain suitable descriptions of the other layers, complex nonlinear transport, and electrochemical phenomena. Here, we combine the advantage of both models in an iterative scheme integrating continuum and PN models to describe the multiphase and multiscale water transport properly. The coupling is achieved through an iterative scheme wherein the 2-D continuum PEFC model passes the calculated, heat and mass fluxes to the PNM, where they act as spatially varying source terms. Subsequently, the PNM returns to the continuum model a set of effective properties, such as thermal conductivity, effective diffusivity, and permeability, which are discretized along the electrode|GDL interface. This talk will discuss the work-flow between the coupled models including utilization of X-ray CT inputs and how such an approach can explain nonintuitive experimental data. For an ion-exchange membrane, mathematical modeling is ideally suited to explore the genesis of the observed water profiles and subsequently the mechanisms of water movement. Recently, such modeling has been receiving increased attention as new knowledge on the impact and control of the membrane/environment interface is elucidated. To model such effects requires the use of a multiscale framework involving mesoscale networks and microscale ion-transport information. The linking between these scales will be discussed including appropriate ways to incorporate molecular-level information into a physically consistent framework that still allows for easy incorporation into cell-level fuel-cell models. Acknowledgement I would like to acknowledge the various graduate students, postdocs, and collaborators who have worked on this research over the years. This work was supported by The Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Erratum to: An Improved Heat Flux Theory and Mathematical Equation to Estimate Water Vapor Advection as an Alternative to Mechanistic Enhancement Factor

The current study extended the theory of heat flux which was normally used to estimate the mechanistic enhancement factor. The current improved heat flux theory included three additional phenomena that were excluded from the simplified heat flux equation. Those three phenomena were the sensible heat by liquid water movement, the sensible heat by water vapor movement, and the partial derivative of matric pressure head effects on relative humidity with respect to temperature. The first phenomenon was found to be an important factor in relatively wet porous media, whereas the third phenomenon was found important near-dry porous media condition. Moreover, mathematical descriptions derived to allow direct conversion of mechanistic enhancement factor to water vapor advection term. The study used basic mass balance equation, ideal gas law, and air advection to describe the water vapor advection mechanism. The water vapor advection equation was found to be able to describe the influence of soil moisture content and air pressure.

Diurnal pattern of liquid water and water vapor movement affected by rainfall in a desert soil with a high water table

Because arid and semi-arid regions have relatively low soil moisture, water vapor movement often occurs predominantly in the unsaturated zone, affecting the partitioning of energy among various land surface fluxes. To understand the hydrological processes of the unsaturated zone in desert areas, it is important to characterize the diurnal and spatial variations in soil water and vapor movement, which control recharge and discharge via the unsaturated zone. However, few studies have examined the pattern of soil water and vapor movement affected by rainfall in desert areas. To understand this process, field observations of desert soil physical parameters and micrometeorological variables were taken. These data were used to verify and calibrate the performance of an unsaturated–saturated zone soil water balance model, Hydrus-1D. Next, the diurnal pattern of the soil water and vapor was simulated under different climatic conditions, i.e., before, during and after rainfall. Two stages of thermal liquid and vapor movement were identified before rainfall. The thermal liquid flux fluctuates quickly and drastically, while the thermal vapor changes more moderately during and after rainfall. The changes in isothermal liquid and vapor flux differ from those of thermal liquid and vapor flux because of the change in the pressure head gradient under various wetness conditions. These findings offer insight into how water vapor affects soil water movement in the semiarid desert. They also improve our understanding of the liquid water and water vapor movement processes following rainfall.

The Design of a Modelling, Monitoring and Validation Method for a Solid Wall Structure.

Hygrothermal assessment is the combined analysis of heat, air and moisture transfer through the building fabric. The two approaches are covered by conventions known as the IS EN 5250:2011 (Glaser method) and IS EN 15026:2007 which differs from Glaser by solving the equations numerically using computer software. Results for hygrothermal analysis provide valuable information for surface and interstitial condensation risk assessment and the impact of energy upgrades. For traditional solid walled structures, conditions such as wind driven rain (WDR) and rising ground water can have a significant impact on the environmental behaviour and in particular the moisture behaviour of the building envelope. The convention IS EN 5250:2011 is still widely used to assess the moisture performance of buildings and their components, even though it is not a comprehensive assessment methodology as it fails to include the movement of liquid water and for solid wall structures in particular, it is imperative that all forms of moisture movement are assessed. This research sets out a design methodology, to establish the hygrothermal performance of rendered solid brick wall constructions to ultimately establish the optimum and most appropriate retrofit intervention. The methodology chosen establishes all material properties of a monitored wall. A weather station is used to establish all weather data for the site. The building, will be monitored initially for a 12 month period to determine its hygrothermal condition. The data logged monitoring will establish the temperature and RH profile through the wall. The data from this monitoring will be inputted to software which meets the IS EN15026:2007 convention-a dynamic model which assesses the movement of water both as a vapour and as a liquid.

Effect of Drying Temperature on the Chemical Properties and Diffusivity of belimbi (averrhoa belimbi)

In recent years, many dried fruit products have been developed in response to a strong demand by the customer. This type of fruit has a different composition and hence different moisture diffusivity (D). During drying, Fick's Law of diffusion, which describes the movement of liquid water was used to calculate this diffusivity. However diffusivity has strong effects on the material drying characteristics and these must be determined. In this paper, Fick's Law of diffusion with different kinds of boundary conditions was solve using separation of variable (SOV). In order to get the value of D, results obtained using SOV will be compared with the results from the drying of belimbi at temperature of 40°C, 50°C and 60°C. Although the results show that variation in the values of diffusivity for different temperatures is relatively small, but the variation in the total time required for drying is significantly bigger: between 3-7 hours. Its shown that diffusivity is an important measurement and should be considered in the modeling of the drying process. The chemical properties of belimbi slices in terms of vitamin C, total ash and antioxidant activity with different air temperatures and pretreatment were also investigated. Higher drying temperatures gives less drying time, a lower vitamin C and antioxidant activity but a greater total of ash, whilst pre-treatment can increased vitamin C and antioxidant activity. The results show that pre-treatment and the drying temperature are important variables to improve mass and heat transfer, as well as the belimbi chemical properties.

Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Polymer electrolyte membrane fuel cells (PEMFCs) are promising electrochemical energy conversion devices due to their high efficiency, zero-local emissions, and rapid start-up capability. Water management is a vital issue in the PEMFC, as the accumulation of water directly affects its operating efficiency. During operation the membrane must be sufficiently humidified in order to achieve high proton conductivity; however, at high current densities, accumulation of liquid water in the cathode gas diffusion layer (GDL) blocks oxygen pathways, preventing this reactant from reaching the catalyst, which in turn hinders performance. Effective water management strategies are essential to improve PEMFC performance and require a detailed understanding of liquid water transport in the GDL.In a fuel cell stack, the cell components are assembled under compressive loads to prevent gas leakage; however, high compression of the GDL may affect cell performance. The non-uniform compression of the GDL, due to its contact with the bipolar plate, significantly alters the microstructure and consequently the dynamics of liquid water transport through the GDL [1]. A number of attempts have been made in experimental visualization of liquid water transport within compressed GDLs, but more work is required to evaluate these effects quantitatively [1-3].The purpose of this study is to numerically investigate the effects of compression on liquid water transport through PEMFC GDLs. In this work, two types of carbon paper GDLs are compressed. At each compression value, volumetric X-ray tomography images of the samples are obtained. The resulting greyscale images are segmented using a novel thresholding algorithm. A watershed algorithm [4] is used to extract pore networks of the GDL. Pore network modeling with invasion percolation is employed to determine the liquid water profile within the GDL over the range of compression states. The results of this study provide a deeper knowledge of how compression and the GDL microstructure affect the movement of liquid water.