Applications of heat transfer and fluid flow through porous media are very capacious, so they have drawn great attention and research. Acoustics, filtrations, and heat storage are examples of the wide application. The technique of the thermal energy storage (TES) to stock heat energy for later use is applied in many applications. Reliable stable low cost can be provided by storage solar thermal energy and undue heat from non-natural sources. A simple low-cost design that can fluently be constructed which uses the available porous media founded in nature is considered in the present study. The present study analytically investigated the effect of faction void of porous media (silicon rubber) on the process of heat transfer through heat storage and on the storage system. The study develops a numerical model to investigate the effect of several parameters, e.g. mass flow rate, bed length, particle diameter and different values of porosity during charging and discharge. The results depict that the amount of thermal energy stored, and the time of storage are affected by the working fluid, its porosity, and mass flow rate. The present model uses water as working fluid and the silicon rubber as storage medium. It is governed by two partial differential equations for these two substances. The conservation equations are applied on the present system for each of them separately. The storage medium and the working fluid are in case of heat exchange process all over.

The aim of this work is to develop dual purposes solar heating system using heat pipe evacuated tube solar collector. The heat transfer fluid between the thermal loads and the solar collector loop was heating oil. The study provided two thermal loads; solar water heating system and solar baking/cooking system that had experimentally investigated under various weather conditions. The experimental pilot unit was installed in Solar Energy Department, National Research Centre, Giza, Egypt. Several test runs were performed to measure all assigned parameters that affect the system performance. The system is designed to provide high thermal energy through hot oil surrounding the inner vessel of the baker while the raw food can be baked/cooked and the outlet thermal energy can be used for heating water via immersed coil in the hot water storage tank; then the relatively cooled oil is returned to the solar collector via hot oil circulating pump. The water tank heat exchanger is designed with the following design parameters; specific heat of oil and water were 1.67 kJ/kg o C and 4.186 kJ/kg o C respectively; density of oil and water were 850 kg/m 3 and 1000 kg/m 3 respectively; mass flow rate of oil and water were 12 liters/min and 6 liters/min respectively. It is clear that the system in addition to provide thermal energy for baking/cooking unit, it can provide thermal energy for water heating purposes. The tested system can be positively contributed in baking and cooking purposes and providing hot water as well. It is found that, for the same flow rates of hot oil and water, as the hot oil temperature difference increased, the outlet hot water increased. The system is capable to produce hot water temperature up to 85 o C if the hot oil temperature difference was 100 o C while it can produce hot water temperature about 60 o C if the hot oil temperature difference was 60 o C during the day which is suitable for residential purposes and industrial process as well. Based on the resultant data, it is found that the system solar fraction was estimated as 54%. The auxiliary heating system can be electric source in case of using in urban areas and can be renewable energy source like biogas or hydrogen fuels in rural and isolated areas.

<p>Over the last few decades, Greater Cairo Megacity has experienced rapid population growth and expansion of its industrial activity. Hosting more than 20 million people, Cairo is considered one of the most polluted megacities in the world. Concentration levels of fine particulate matter (PM<sub>2.5</sub>) are several times higher than those recommended by the World Health Organization (WHO). Although actions have been designed recently to improve air quality in the framework of a “Pollution Management and Environmental Health program” (PMEH) supported by the World Bank, observational studies assessing the main sources leading to this PM pollution are missing, making difficult to implement and monitor the efficiency of local mitigation strategies.</p><p>The aim of our study is to investigate atmospheric concentrations levels, temporal variability, as well as major sources, and atmospheric aging of PM in Cairo megacity with a focus on the submicron aerosol fraction (PM<sub>1</sub>) to better assess human-made activities with lower interference from natural (dust) emissions. A comprehensive suite of on-line and off-line instruments has been set-up to monitor PM<sub>1</sub> chemical composition and reactive trace gases (i.e. Volatile Organic Compounds) as a part of the POLCAIR campaign that took place during winter 2019-2020, at an urban background site in Greater Cairo. Chemical composition of PM<sub>1</sub> and source apportionment analysis via Positive Matrix Factorization (PMF) on both Q-ACSM (Aerosol Chemical Speciation Monitor, Aerodyne, US) organic mass spectra and co-located filter samples, attributed exceptionally high concentrations of compounds to traffic emissions and diverse combustion sources with pronounced diurnal variability. Two severe pollution episodes were recorded, with hourly mean PM<sub>1</sub> concentrations reaching values as high as 300 μg/m<sup>3</sup> and lasting for 2 consecutive days favored by low dispersion conditions. Pollutant variability is directly associated with the meteorological conditions, including wind patterns and air mass origins. This helps in recognizing emission hot spots of major anthropogenic PM<sub>1</sub> sources. Additionally, the effects of the relative humidity and the role of heterogeneous oxidation reaction mechanisms was investigated. Finally, the multi-variable analyses performed, helped us to better investigate the complex urban atmospheric chemistry in Cairo megacity and to highlight the dynamics of Secondary Organic Aerosol formation.</p>