Abstract
A self-seeding particle method is proposed for particle image velocimetry measurements in closed cycles such as Organic Rankine Cycles. Condensed droplets of vapor are used as tracers in a ...closed cycle for both subsonic and supersonic regimes. A free jet of R245fa in the vapor phase is examined in a case study with two different nozzle pressure ratios of 5.1 and 2.1 to evaluate the tracer particles in both supersonic and subsonic conditions. A simple turbulent jet in subsonic conditions and an under-expanded jet are observed in high supersonic conditions. The flow structures of the under-expanded jet are captured using the proposed method, and vivid images of the Mach disk and shock cells are obtained. A series of Schlieren photography experiments are performed to validate the proposed method. The results show that the method can be a good candidate for tracer particles in the closed cycles where condensation of the working fluid is possible.
Real-gas effects should be considered in ORC expanders, particularly in a supersonic flow. This study deals with the numerical evaluation of cubic real gas models in a supersonic R245fa flow over a ...wedge-shaped cascade. The NIST Refprop real gas model was selected as a benchmark model, and four other cubic real gas equations of state (EoS) were evaluated with respect to the reference model. The four cubic real gas EoS are studied. The results show that the Peng-Robison EoS is the most accurate model with an average error of less than 1.1 % for Mach number prediction for 3 different sections, and its computational cost is 39 % lower than NIST. However, the Aungier-Redlich-Kwong EoS model shows better performance accuracy and the computational cost with an average error of 1.7 % for Mach number prediction and a 17 % computational cost lower than NIST. Therefore, using this model is recommended for modeling R245fa in the supersonic regime.
Open-cell metal foams are porous medium for thermo-fluidic systems. However, their complex geometry makes it difficult to perform time-resolved (TR) measurements inside them. In this study, a TR ...particle image velocimetry (PIV) method is introduced for use inside open-cell metal foam structures. Stereolithography 3D printing methods and conventional post-processing methods cannot be applied to metal foam structures; therefore, PolyJet 3D printing and post-processing methods were employed to fabricate a transparent metal foam replica. The key to obtaining acceptable transparency in this method is the complete removal of the support material from the printing surfaces. The flow characteristics inside a 10-pore-per-inch (PPI) metal foam were analyzed in which porosity is 0.92 while laminar flow condition is applied to inlet. The flow inside the foam replica is randomly divided and combined by the interconnected pore network. Robust crosswise motion occurs inside foam with approximately 23% bulk speed. Strong influence on transverse motion by metal foam is evident. In addition, span-wise vorticity evolution is similar to the integral time length scale of the stream-wise center plane. The span-wise vorticity fluctuation through the foam arrangement is presented. It is believed that this turbulent characteristic is caused by the interaction of jets that have different flow directions inside the metal foam structure. The finite-time Lyapunov exponent method is employed to visualize the vortex ridges. Fluctuating attracting and repelling material lines are expected to enhance the heat and mass transfer. The results presented in this study could be useful for understanding the flow characteristics inside metal foams.
Mixing is an inseparable part of many industries. Static mixers are motionless inserts that are widely used for mixing. In this study, planar laser-induced fluorescence (PLIF) was used to study the ...mixing characteristics of a multilayer static mixer. The effects of the arrangement angle of layer elements of the static mixer were examined. Arrangement angles of 0°, 45°, and 90° were investigated at four different flow-rate ratios of two mixing fluids. The mixing performance of each angle was evaluated with both qualitative and quantitative approaches. The volume fractions of the flows were obtained from the PLIF results, and the mixing index was calculated. The friction factor was measured to assess the pressure loss of each arrangement angle. The results show that the arrangement angles do not affect the mixing index for higher flow ratios. However, at the lowest flow ratio, the angle of 45° resulted in the highest mixing index of 74.9%, while at 0° and 90°, the values reached 66.4% and 69.8%, respectively. In regard to pressure loss, 45° also resulted in the lowest friction factor.
Graphic abstract
Airfoils are mostly inefficient in their off-design conditions. In order to improve the aerodynamic performance of airfoils in these conditions, using an optimized cavity on airfoils as a passive ...method can be useful. In this study, a cavity on a Risø_B1_18 airfoil, which is used as a wind turbine airfoil, was optimized at an off-design angle of attack by incorporating a genetic algorithm into a RANS flow solver. For the cavity optimization, the geometry and downstream suction surface were defined by 16 parameters, and the lift-to-drag ratio was considered as the cost function at 14° angle of attack. The numerical solution showed that the optimized cavity traps a vortex, which postpones the stall. Due to the uncertainty of CFD especially at off-design conditions, it was necessary to evaluate the performance of the optimized cavity in a wide range of angles of attack. This study used the particle image velocimetry (PIV) measurement method to evaluate the improved flow structures over the optimized cavity. Two models of airfoils with and without the cavity were made of aluminum and installed inside the test section of an open-jet wind tunnel with an air speed of 30 m/s and a cross section of 30 × 30 cm
2
. The air flow on the suction side of the airfoils was measured at 7°–15° angles of attack by PIV. A comparison between the measured flow fields over the two airfoils showed that the optimized cavity postpones the stall angle by 3°. Furthermore, the cavity increases the momentum behind the airfoil at the angles of attack greater than 9°. After this angle, a further increase in the angle of attack increases the difference between the momentums behind the airfoils with and without cavity. The Risø_B1_18 airfoil with the optimized cavity can be used as a wind turbine airfoil at high angles of attack to increase the stall angle and decrease the instability and fluctuation at off-design conditions.
Graphic abstract
Organic Rankine Cycles (ORC) are one of the most notable methods for waste heat recovery at low to medium temperatures which leads to a cleaner environment. Organic vapors with high molecular weight ...are the working fluid of the ORC. Using such substances leads to non-ideal or non-classical gas dynamics inside the expander, where transonic and supersonic regimes occur. This paper presents a comprehensive review of the literature related to the real-gas effects with applications of ORCs. The review includes numerical simulations and experimental approaches. It is shown that the main gap in this field is quantitative experimental results for the flow field. However, recently a free jet of such flows investigated by particle image velocimetry but, this experiment is done for a specific substance. Therefore, a number of research opportunity in this field will be remained for future studies.
•An extensive review has been made on the real-gas effects with application in ORC.•Real-gas effects have been discussed with the effects on ORC expanders.•Both numerical and experimental approach have been investigated.•There is a lack of quantitative results for CFD simulation validation.•Experimental line is still open for further investigation.
The energy security and supplies of energy are the key components for progressing countries. Renewable energy resources are rapidly being recognized as clean sources of energy to withstand damages to ...environment and to avoid future crisis. In this study, energy consumption and energy demands in the progressing Middle East countries are reviewed. First, the growth of energy consumption of the region through recent years is presented which show the rapidly growing energy demand in the Middle East countries. Second, by using RETScreen software data, the potential of the main renewable energies of solar and wind resources are evaluated. Results showed that the Middle East region have a very good potential for using renewable energies. Results are presented as GIS maps of wind speed, wind power density and solar radiation intensity. With using the GIS maps, the great locations for utilizing solar or wind energies are identified. The presented GIS maps may facilitate development of hybrid solar and wind systems within the Middle East region.
Nowadays, renewable energies are more preferable to fossil fuels because of being free, widely available and producing minimal pollution. One of the disadvantages of renewable energy systems is that ...using only one type of renewable energy cannot guarantee a continuous power generation. To overcome this problem, two or more renewable energy systems should be used simultaneously to compensate for times when one of them is not available or the renewable system should be used aligned with the generator. In addition, another weakness is that they are not accessible in every geographical position and location. It is clear that renewable energy systems can be exploited to their fullest capacity when used in the proper place. Therefore, given the importance of finding suitable places for co-utilization of several renewable energies, present paper attempted to find the ideal locations for construction of hybrid solar-wind power stations in Middle-East using Boolean model in GIS software. The Boolean method is, in a way, a more stringent method compared to the other positioning methods. Therefore, the selected locations will definitely have greater energy potential by using the Boolean method. Data obtained by RETScreen4 software from 400 stations in Middle-East were used for collecting monthly weather information. Results of the current paper may be helpful in creating prospects for sustainable energy development for systems based on natural resources and facilitating the national power transmission and sustainable environmental policies.
Identifying potential locations for installation of solar power plants is a critical step in utilizing sustainable energy resources. In this study, a GIS-based Multi-Criteria Decision Analysis ...(GIS-MCDA) technique is used to generate maps that represent potential areas for solar power plants in four provinces with different climate conditions in Iran. The concept of risk is included in the GIS-MCDA process using the Ordered Weighted Averaging (OWA) model. The OWA model can provide various risk-taking (optimistic) and risk-aversion (pessimistic) scenarios to determine the suitable power plant areas. The results of this study indicate that provinces located in an arid climate such as Yazd contain a more suitable area for the solar power plants compared to wet climate provinces (e.g., Mazandaran). The sensitivity analysis of results show that the criterion “fault” has the minimum effect while the criteria “slope” and “road network” have the maximum effects on the area of the highly desirable class.
•The GIS-MCDA is used to evaluate the locations for establishment of solar power plants.•The evaluation process involves the locations in different climate conditions.•An OWA-based technique is utilized to incorporate risk in solar energy assessment.•The sensitivity of results to each criterion is evaluated.
Solar energy is one of the important energy sources and countries have realized the important role of renewable energies due to the depletion of conventional energy sources. In this study, a ...GIS-based analysis is utilized for investigating the feasibility of solar energy in Iran. To evaluate the concept of risk into the GIS-based analysis for determining optimal areas for installation of solar power plants an Ordered Weighted Averaging (OWA) approach is used for the first time. Integration of OWA-based approach and GIS analysis provide models that determine the priority of regions from risk-free decision to risky decision strategies. The results show that Kerman, Yazd, Fars, Khuzestan, Sistan and Baluchistan, South Khorasan and Isfahan provinces have a good capacity to invest in solar energy projects. The GIS-based analysis indicates that the values of installed solar power plants percentages in high chosen areas for the most pessimistic and optimistic strategies are 7% and 64%, respectively.
•A new model is used to evaluate the solar energy in Iran.•To evaluate solar energy potential a risk analysis is added to GIS-based method.•An Order Weight Averaging is utilized for first time in solar energy assessment.•A location analysis is done for currently working solar plants.•A maximum of 498 W/m2 solar radiation is achievable yearly.
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