Gas-Grain Simulation Facility (GGSF). Volume 2: Conceptual design definition

This document is Volume 2 of the Final Report for the Phase A Study of the Gas-Grain Simulation Facility (GGSF), and presents the GGSF Conceptual Design. It is a follow-on to the Volume 1 Facility Definition Study, NASA report CR 177606. The development of a conceptual design for a Space Station Freedom (SSF) facility that will be used for investigating particle interactions in varying environments, including various gas mixtures, pressures, and temperatures is delineated. It's not possible to study these experiments on earth due to the long reaction times associated with this type of phenomena, hence the need for extended periods of microgravity. The particle types will vary in composition (solids and liquids), sizes (from submicrons to centimeters), and concentrations (from single particles to 10(exp 10) per cubic centimeter). The results of the experiments pursued in the GGSF will benefit a variety of scientific inquiries. These investigations span such diverse topics as the formation of planets and planetary rings, cloud and haze processes in planetary atmospheres, the composition and structure of astrophysical objects, and the viability of airborne microbes (e.g., in a manned spacecraft)

Gas-grain simulation experiment module conceptual design and gas-grain simulation facility breadboard development

This report delineates the Option portion of the Phase A Gas-Grain Simulation Facility study. The conceptual design of a Gas-Grain Simulation Experiment Module (GGSEM) for Space Shuttle Middeck is discussed. In addition, a laboratory breadboard was developed during this study to develop a key function for the GGSEM and the GGSF, specifically, a solid particle cloud generating device. The breadboard design and test results are discussed and recommendations for further studies are included. The GGSEM is intended to fly on board a low earth orbit (LEO), manned platform. It will be used to perform a subset of the experiments planned for the GGSF for Space Station Freedom, as it can partially accommodate a number of the science experiments. The outcome of the experiments performed will provide an increased understanding of the operational requirements for the GGSF. The GGSEM will also act as a platform to accomplish technology development and proof-of-principle experiments for GGSF hardware, and to verify concepts and designs of hardware for GGSF. The GGSEM will allow assembled subsystems to be tested to verify facility level operation. The technology development that can be accommodated by the GGSEM includes: GGSF sample generation techniques, GGSF on-line diagnostics techniques, sample collection techniques, performance of various types of sensors for environmental monitoring, and some off-line diagnostics. Advantages and disadvantages of several LEO platforms available for GGSEM applications are identified and discussed. Several of the anticipated GGSF experiments require the deagglomeration and dispensing of dry solid particles into an experiment chamber. During the GGSF Phase A study, various techniques and devices available for the solid particle aerosol generator were reviewed. As a result of this review, solid particle deagglomeration and dispensing were identified as key undeveloped technologies in the GGSF design. A laboratory breadboard version of a solid particle generation system was developed and characterization tests performed. The breadboard hardware emulates the functions of the GGSF solid particle cloud generator in a ground laboratory environment, but with some modifications, can be used on other platforms

The effects of compression on single and multiphase flow in a model polymer electrolyte membrane fuel cell gas diffusion layer

A two-dimensional study of an idealised fibrous medium representing the gas diffusion layer of a PEMFC is conducted using computational fluid dynamics. Beginning with an isotropic case the medium is compressed uni-directionally to observe the effects on single and multiphase flow. Relations between the compression ratio and the permeability of the medium are deduced and key parameters dictating the changes in flow are elucidated. The main conclusions are that whilst compression reduces the absolute permeability of an isotropic medium, the creation of anisotropic geometry results in preferential liquid water pathways. The most important parameter for capillary flow, in uniformly hydrophobic media, is the minimum fibre spacing normal to the flow path. The effect is less pronounced with decreasing contact angle and non-existent for neutrally wettable media

Effective diffusivity of polymer electrolyte fuel cell gas diffusion layers: An overview and numerical study

Published experimental and theoretical investigations conducted to estimate the effective diffusivity of the gas diffusion layers (GDLs) and other porous layers in polymer electrolyte fuel cells (PEFCs) have been reviewed. The main observations are that most of the diffusivity investigations were on the Toray carbon papers and that fewer studies have been conducted to estimate the effective diffusivity of the microporous layers (MPLs) and the catalyst layers. The main finding set by most of the reviewed investigations is that the Bruggeman relation significantly overestimates the effective diffusivity of the GDL. In order to evaluate how this overestimation is reflected on the performance of the fuel cell, a numerical study has been conducted. The outputs of this numerical study have shown that the Bruggeman relation significantly overestimates the performance of the fuel cell; this overestimation may be up to a factor of 2 or more. It is therefore recommended that empirical relations are used rather than the Bruggeman relation to calculate the effective diffusivity of the GDL materials. Also, the results suggest that a distinction between the GDL and the MPL in the single-phase modelled fuel cell should be made if the difference between the porosities of the two layers is significant