Two identical prototype solar dryers (direct and indirect) having the same dimensions were used to dry whole mint. Both prototypes were operated under natural and forced convection modes. In the case of the later one the ambient air was entered the dryer with the velocity of 4.2 m s(-1). The effect of flow mode and the type of solar dryers on the drying kinetics of whole mint were investigated. Ten empirical models were used to fit the drying curves; nine of them represented well the solar drying behavior of mint. The results indicated that drying of mint under different operating conditions occurred in the falling rate period, where no constant rate period of drying was observed. Also, the obtained data revealed that the drying rate of mint under forced convection was higher than that of mint under natural convection, especially during first hours of drying (first day). The values of the effective diffusivity coefficient for the mint drying ranged between 1.2 × 10(-11) and 1.33 × 10(-11) m(2) s(-1).

Conducting physical attendance exams during pandemics is a challenge facing many educational institutes and universities. Our study’s main objective is to numerically simulate the expected transmission of the harmful exhaled droplets of aerosols from an infected instructor to students in an exam room ventilated by a number of spiral diffusers. Several critical parameters, including the droplet size, the ventilation rate, and status of the entrance door were considered in the analysis. Two dimensionless indices, i.e., the specific normalized average concentration (SNAC) and the exceedance in exposure ratio (EER), were introduced to examine the effect of the said parameters on student exposure to the harmful droplets. The study revealed that the 5 μm droplets were less hazardous as they resulted in an 87% reduction in exposure when compared with the small 1 μm size droplets. We also found that when the ventilation rate ratio (VRR) increased above unity, an upward entrainment process, due to the swirl diffuser, of the aerosol droplets took place, and consequently the risk of student exposure was reduced. The results also demonstrated that increasing VRR from zero to 1 and then to 2 decreased the exceedance in the student exposure from 3.5 to 2.15 and then to less than zero, respectively. The study also showed that keeping the lecture room’s main door open is recommended as this reduced the risk of exposure by 26% in the case of a VRR equal to 2.

The Arab region is characterized by arid and semi-arid conditions with very limited renewable water resources. Most of the surface water comes from transboundary streams and most of the groundwater resources are fossil in nature. Water quality degradation and excessive use of pesticides and herbicides in agriculture pose severe environmental and health risks. The underlying research is a joint effort between Cairo University and the Technical University of Berlin to develop technologies and strategies for sustainable pesticide-free agriculture using saline or brackish water. This project builds on a previously implemented project in Spain by the German research partner that introduced the concept of Watergy, which presents an integrated desalination horticulture solar greenhouse. In this current research, the Watergy greenhouse is further developed to meet more arid climate requirements, reduce construction costs, and increase resource utilization efficiency. Several lab-scale experiments and a 100 m2 prototype were built in Egypt to optimize the process and answer research questions. Lessons learned from this project provided guidelines on the development of the most efficient approach of desalination and water management in the system, devised a cost-effective and efficient heat exchanger using low-cost local material, and established the feasibility of the system in the arid climate together with prospects for wider applications. The proposed greenhouse was estimated to be able to save in irrigation water 40% for cherry tomatoes and cucumbers, and 50% for bell peppers. Maximum crop yield can be achieved at extended upper salinity levels using the proposed greenhouse as follows: from 1,000 to 1,700 mg/L for cherry tomatoes; from 960 to 2,000 mg/L for bell peppers; and from 1,600 to 2,700 mg/L for cucumbers.

The effect of microwave power, sample thickness, and diameter on drying kinetics, effective moisture diffusivity, and activation energy of apple cylinders for microwave drying were investigated. Also, the effect of the microwave power on the quality of the dried apples was studied by measuring the surface color change and scanning the surface structure. The same mass of fresh apples was dried at different power levels. Two diameters and three thicknesses were studied. Aghbashlo model showed the best fitting for the drying kinetics of apple. The drying time was reduced by increasing the power and the diameter, but the thickness had no clear effect. The effective diffusivity values ranged between 1.47 × 10-7 and 24.4 × 10-7 m2/s. The effective diffusivity increased by increasing the three studied parameters. The parameters' effects on the drying time and the diffusivity were studied using a full factorial experimental design. The power and the diameter had the highest effect on the drying time. However, the thickness had the highest effect on the effective diffusivity.