The objectives of this study are to analyze the behavior of a pipe under different valve open and closure times and to predict water hammer-induced transient maximum pressure, deflection and frequency of vibration in a fluid filled pipe. The model that integrated a classical formulation of water hammer problem and beam vibration equation was developed and a numerical simulation including frictional losses has been carried out. The MacCormak and Runge-Kutta methods were used to solve governing partial differential equations in order to investigate water hammer induced vibration of a fluid filled pipe. The results show that fluid flow rate does not change the vibration frequency of pipe. The peak wave pressures, maximum pipe deflections at various valve open and closure times, and the frequencies of vibration with variation of fluid speed and pipe geometrical configuration are presented.
Percolation testing and contact angle measurements have been used to investigate the role of relative humidity on structure, mass transport, and wettability of a PEM fuel cell catalyst layer and membrane. Four samples were tested, two catalyst layers and two membranes. Structure and mass transport changes in the catalyst layers resulting from RH changes were studied in terms of percolation pressure. A clear change in the structure between low and high RH conditioning was observed. Relative humidity (RH) cycling also impacted percolation pressures with an indication of catalyst layer cracking. In addition, RH effect on wettability of both catalyst layers and membranes was studied by measuring contact angles of sessile drops.
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