كرار تكليف عبد الزهرة العيفاري

Proper water management in Proton Exchange Membrane (PEM) fuel cell is important to achieve high performance. Understanding the percolation of the produced water at the cathode catalyst layer (CL) is critical for any robust water management technique. In this study, an ex-situ experimental setup is used to study percolation in the CL at different injection rates and relative humidity (RH) conditions. The results show that increasing the flow rate force the liquid to flow through the bulk of the pores due to the dominant viscous effect. On the other hand, at low injection rates, the capillary becomes dominant and liquid flow along the roughness of pores surfaces. At low flow rates, a big wetted area is captured, compared to high flow rates tests, but the liquid saturation is lower. Another set of testing was done at a fixed flow rate and a varied RH conditions, where permeability is calculated based on the steady percolation pressure. The permeability of the CL for both gas and liquid decreases as RH increases, and that more likely related to ionomer swelling. A correlation between the permeability and water content is derived. A sharp decrease in the permeability is observed at low water content ($\lambda<3$), beyond that there are no significant changes. Moreover, low and high RH condition shows a significant effects on the structure of CL and flow regime. Static contact angle measurements at a range of RH also indicate possible morphological changes in the CL. In addition, fractional flow theory (FFT) model is adapted to study immiscible displacement of two-phase flow in a porous medium. The resulting model accurately predicts trapped saturation that occurs during imbibition and drainage of incompressible fluids for any capillary number. It also accurately predicts the fluid-fluid front displacement and critical capillary number at which trapped saturation begins to decrease. The unique aspect of this model is incorporation of a scaling factor, suggested by [12], that captures the propensity for gas or liquid holdup for any porous media and fluid pair.

This research presents the development and experimental evaluation of an automated control system designed to minimize the power consumption of air conditioning units by regulating airflow from duct diffusers based on occupancy. The system employs a heat-sensing occupancy sensor to detect human presence. When an occupant is detected, a signal triggers a motor to open the corresponding diffuser gate, directing conditioned air only to that occupied zone; the gate closes when the area is vacated. An experimental, rectangular glass air duct (16cm x 20cm) was constructed and fitted with four diffusers to visually demonstrate the mechanism. A comprehensive case study was conducted at the Najaf Post Office, a building with 13 rooms cooled by a 40-ton AC unit, to quantify energy savings. The analysis compared the baseline energy consumption with three simulated scenarios using the control system.