A Theoretical and Experimental Study for A humidification-Dehumidification (HDD) Solar Desalination Unit
A humidification-dehumidification (HD) solar desalination unit was designed. It seems to be suitable to provide drinking water for population or remote arid areas. Solar water and solar air collectors were designed to provide the hot water and air to the desalination chamber. The desalination chamber was divided into humidifier and dehumidifier towers. The circulation of air in the two towers was maintained by the forced convection. Theoretical and experimental works were done at different environmental conditions. A mathematical model was formulated, in which the thermodynamic relations were used to study the flow, heat and mass transfer inside the humidifier and dehumidifier. Such a technique was performed in order to increase the unit performance. Heat and mass balance was done and a set of governing equations was solved using the finite difference technique. The solar intensity was measured along the working day during the summer and winter months and a comparison between the theoretical and experimental results were performed. The average accumulative productivity of the system in November, December and January was ranged between 2 to 3.5 kg / m day while the average summer productivity was found between 6 to 8 kg/m day in June and 7.26 to 11 22
Performance and cost assessment of a solar HDH desalination system integrated with thermal storage: a case study
Solar desalination systems often have limited operating hours and their operation is significantly affected by the variation of solar radiation intensity. A model of a humidification–dehumidification (HDH) desalination system integrated with evacuated tube solar collectors and thermal storage is developed and validated against available data in the literature. Operating parameters such as the maximum temperature of water heater and the mass flow rate ratio of the HDH component are optimized. The thermal storage unit consists of separate hot and cold-water storage tanks, which allow control of the water temperature leaving the storage unit. Furthermore, performance of the system for six different geographical locations in Saudi Arabia, namely Riyadh, Jeddah, Dhahran, Qassim, Sharurah, and Tabuk, is studied. The system is evaluated for four different scenarios as follows: (i) 24-h operation; (ii) with the ideal flow rate; (iii) with the average flow rate; and (iv) with the maximum flow rate. The effect of flow rate on the number of operating hours and the rate of freshwater production is also evaluated. The maximum freshwater production is 9.346 L/h and the minimum is 3.01 L/h. For a service life of 20 years, the cost of freshwater produced varies from 0.021 to 0.034 $/L considering interest rate of 2%.
A Public Health Approach to Child Protection: Why Data Matter
In Australia, many researchers and policy makers believe that statutory child protection systems are overburdened and ineffective. The way forward, they suggest, is a public health model of child protection. A public health approach comprises four steps: (1) collecting surveillance data; (2) establishing causes and correlations; (3) developing and evaluating interventions; and (4) disseminating information about the effectiveness of intervention activities to the public health community. However, in Australia there are no reliable surveillance data. There is no information about ‘person’. Information is not collected about the characteristics of children (e.g., ethnicity) and parents (e.g., mental illness) reported to child protection services. Data are not comparable across place. This is because the states and territories have their own child protection legislation, definitions and data recording methods. Data are not comparable over time. This is because many jurisdictions have introduced new data recording systems over recent years. This paper concludes that it is essential to develop an effective child protection surveillance data system. This will ensure that services are located in areas and targeted towards populations in greatest need. It will enable large-scale evaluation of the effectiveness of prevention and intervention activities.