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The storage of hydrogen is one of the main problems that needs to be solved before hydrogen can become a real alternative to oil in mobile applications. Physisorption of hydrogen in an adsorbate is one of the possible solutions to this problem. This thesis studies the adsorption of hydrogen in Single-Walled Carbon Nanotubes (SWNTs). Neutron scattering techniques are used to probe the possible adsorption sites and the interaction between the hydrogen and the nanotubes at those sites.

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A test rig was developed in an effort to perform droplet evaporation and combustion experiments at high levels of turbulent intensity under elevated pressures and temperatures. The detailed explanation of the design and operation of the various components that are part of the testing apparatus is presented. Once the apparatus was completed, 2D Laser Doppler Velocimetry measurements were used to fully characterize the turbulent field inside the chamber. The results showed that the test rig was capable of producing homogenous isotropic turbulence with a 40 mm central region of the chamber at turbulent kinetic energy levels of up to 5.0 m/s. From the characterization data a correlation of turbulent kinetic energy vs fan speed was produced. The produced correlation is valid at standard conditions as well as elevated pressures and temperatures. After determination of the turbulent field, droplet evaporation experiments were performed, first at standard conditions and then elevated temperature and pressure. The results show that turbulence continued to enhance droplet evaporation at elevated temperature and pressures, 298-348°K and 1-21 bar respectively. Broad conclusions are then drawn from the work performed in the study and recommendations are made for future work and improvements to the test apparatus.

Transport phenomena in high porosity open-cell fibrous structures have been the focus of many recent industrial and academic investigations. Unique features of these structures such as relatively low cost, ultra-low density, high surface area to volume ratio, and the ability to mix the passing fluid make them excellent candidates for a variety of thermofluid applications including fuel cells, compact heat exchangers and cooling of microelectronics. This thesis contributes to improved understanding of thermal transport phenomena in fuel cell gas diffusion layers (GDLs) and metal foams and describes new experimental techniques and analytic models to characterize and predict effective transport properties. Heat transfer through the GDL is a key process in the design and operation of a proton exchange membrane (PEM) fuel cell. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance (TCR) associated with the interface between the GDL and adjacent surfaces/ layers. The effective thermal conductivity significantly differs in through-plane and in-plane directions due to anisotropy of the GDL micro-structure. Also, the high porosity of GDLs makes the contribution of TCR against the heat flow through the medium more pronounced. A test bed was designed and built to measure the thermal contact resistance and effective thermal conductivity in both through-plane and in-plane directions under vacuum and ambient conditions. The developed experimental program allows the separation of effective thermal conductivity and thermal contact resistance. For GDLs, measurements are performed under a wide range of compressive loads using Toray carbon paper samples. To study the effect of cyclic compression, which may happen during the operation of a fuel cell stack, measurements are performed on the thermal and structural properties of GDL at different loading-unloading cycles. The static compression measurements are complemented by a compact analytical model that achieves good agreement with experimental data. The outcomes of the cyclic compression measurements show a significant hysteresis in the loading and unloading cycle data for total thermal resistance, TCR, effective thermal conductivity, thickness, and porosity. It is found that after 5 loading/unloading cycles, the geometrical, mechanical, and thermal parameters reach a“steady-state”condition and remain unchanged. A key finding of this study is that the TCR is the dominant component of the GDL total thermal resistance with a significant hysteresis resulting in up to a 34 % difference between the loading and unloading cycle data. Neglecting this phenomenon may result in significant errors in evaluating heat transfer rates and temperature distributions. In-plane thermal experiments were performed using Toray carbon paper samples with different polytetrafluoroethylene (PTFE) content at the mean temperature of 65−70◦C. The measurements are complemented by a compact analytical model that achieves good agreement with experimental data. Results show that the in-plane effective thermal conductivity remains approximately constant, k ≈ 17.5W/mK, over a wide range of PTFE content, and it is approximately 12 times higher than the through-plane conductivity. Using the test bed designed for the through-plane thermal conductivity measurement, the effective thermal conductivity and thermal contact resistance of ERG Duocel aluminum foam samples were measured under varying compressive loads for a variety of porosities and pore densities. Also, an experimental program associated with an image analysis technique is developed to find the size and distribution of contact spots at different compressive loads. Results show that the porosity and the effective thermal conductivity remain unchanged with the variation of pressure in the range of 0 to 2 MPa; but TCR decreases significantly with pressure due to an increase in contact area. Moreover, the ratio of contact area to cross-sectional area is 0-0.013, depending upon the compressive force, porosity, and pore density. This study clarifies the impact of compression on the thermal and structural properties of GDLs and metal foams and provides new insights on the importance of TCR which is a critical interfacial transport phenomenon. / Graduate

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