Mehrdad Khamooshi

A Review of Solar Photovoltaic Concentrators

Throughout the recent centuries, the limits of using energy resources due to the cost and environmental issues became one of the scientists’ concerns. Because of the huge amount of energy received by the Earth from the sun, the application of photovoltaic solar cells has become popular in the world. The photovoltaic (PV) efficiency can be increased by several factors; concentrating photovoltaic (CPV) system is one of the important tools for efficiency improvement and enables for a reduction in the cell area requirement. The limits of the PV area can reduce the amount of absorbing irradiation; CPV systems can concentrate a large amount of sunlight into a smaller one by applying lenses or curved and flat mirrors. However, the additional costs on concentrating optics and cooling systems made CPV less common than nonconcentrated photovoltaic. This paper reviews the different types of PV concentrators, their performance with advantages and disadvantages, concentration ratio, acceptance angle, brief comparison between their efficiencies, and appropriate cooling system.

Overview of Ionic Liquids Used as Working Fluids in Absorption Cycles

The cycle performance of refrigeration cycles depends not only on their configuration, but also on thermodynamic properties of working pairs regularly composed of refrigerant and absorbent. The commonly used working pairs in absorption cycles are aqueous solutions of either lithium bromide water or ammonia water. However, corrosion, crystallization, high working pressure, and toxicity are their major disadvantages in industrial applications. Therefore, seeking more advantageous working pairs with good thermal stability, with minimum corrosion, and without crystallization has become the research focus in the past two decades. Ionic liquids (ILs) are room-temperature melting salts that can remain in the liquid state at near or below room temperature. ILs have attracted considerable attention due to their unique properties, such as negligible vapor pressure, nonflammability, thermal stability, good solubility, low melting points, and staying in the liquid state over a wide temperature range from room temperature to about 300°C. The previously mentioned highly favorable properties of ILs motivated us for carrying out the present research and reviewing the available ILs found in the literature as the working fluids of absorption cycles. Absorption cycles contain absorption heat pumps, absorption chillers, and absorption transformers.

Applications of innovative configurations of double absorption heat transformers in water purification technology

AbstractIn this study, first law of thermodynamics has been employed to analyze the performances of two different configurations of double absorption heat transformers (DAHTs) in water purification system. The upgraded heat in the absorber of the absorption heat transformers provides the heat for desalination process. The first investigated configuration is the most efficient DAHT according to the literature, and the second one is a novel configuration proposed by the authors. The aim of this research was to investigate the effects of different parameters on the studied configurations of DAHTs and the desalination system and to compare their performances in detail. Additionally by considering the quantity of the produced water, both the configurations were optimized. The results revealed that the proposed configuration is capable of producing freshwater for 806 residual units.

Unsteady Darcian Natural Convection within Porous Media of Square Enclosure at Various Rayleigh Numbers

Transient natural convection within a 2D square cavity filled with a porous medium is numerically investigated. The left wall is suddenly heated to a constant temperature Th, while the right wall is suddenly cooled to a constant temperature Tc. Both the horizontal walls are insulated. The Finite Volume numerical method is used to solve the dimensionless governing equations. The results are obtained for the initial transient state assuaging to the steady state, and for Rayleigh number values of 102–104. It is indicated that the average Nusselt number showing an undershoot during the transient period and that the time needed to reach the steady state is longer for low Rayleigh number and shorter for high Rayleigh number.