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At the present work modeling and improving the efficiency of a solar absorbing chiller system with a cylindrical phase change material (PCM) and nano-fluid is investigated. First, the absorbing chiller cycle is modeled by using the thermodynamic principles; after that, this model is changed to a standard mathematical planning model by using exergy analyses. Second, the mathematical model is optimized by a genetic algorithm and the optimum parameters of the cycle are calculated. The decision variables for optimization of the subsystem are the generator, the evaporator and the condenser temperatures. Finally, a cylindrical system of the PCM for storage of the thermal energy of the sun is designed by using the technique of thermal storage based on the enthalpy and finite volume method; the operation of the system is investigated.

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In order to achieve clean solar energy and utilize this free energy in a useful manner, current research aims at investigation of thermal performance of an evacuated U-tube solar collection, and specifying conditions that lead to development of highest thermal efficiency for the collector. The collector's efficiency is calculated in this work by introducing parameters affecting thermal efficiency including mass flow rate, collector length, and conditions that are mostly environmental factors. Finally, optimal values of decision variables to achieve maximum collector's efficiency were specified using sensitivity analysis results and genetic algorithm. The results show that the collector's efficiency would be increased by increasing thermal conductivity coefficient of filler materials at the gap between copper blade and absorbent surface. In comparison between using MWCNT nano-fluid and water as the operating fluid, as well as using air, water, Benzene and Na-k alloy fluids separately in the air gap between the copper blade and the adsorbent surface, the collector's efficiency would be increased by 10.4, 12.5, 10.8, and 10.8, respectively.

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The increased use of computed tomography (CT) and its high radiation dose have led to great concerns about its potential for radiation induced cancer risks. Breast is a radiosensitive tissue based on tissue weighting factors assigned by the International Commission on Radiological Protection (ICRP). Moreover, the dose is maximal on the surface of the patient. Therefore, strategies should be taken to reduce radiation dose to the breast. The aim of this review is to introduce methods used for reducing radiation dose to breast in thoracic CT and review related performed studies. The literature indicates that bismuth shielding increases image noise and CT numbers as well as introducing streak artifacts. Tube current modulation (TCM) technique and iterative reconstruction algorithms can provide some levels of dose reduction to radiosensitive organs and superior image quality without the disadvantages of bismuth shielding. However, they are not available on all CT scanners, especially in low-income countries. Such centers may have to continue using bismuth shields to reduce the dose until these superior techniques become available at lower costs in all CT scanners. Furthermore, design and manufacture of new shields with the lower impact on image quality are desirable.