• Energy Research

Machining operation and presence of water droplets cause increase the surface roughness of wet steam ejector walls and change its performance in the refrigeration cycle. The purpose of this work is to investigate the influences of the primary nozzle surface roughness on wet steam ejectors in the refrigeration cycle with steam water as a working flow. The Eulerian-Eulerian model is validated by a comparison of numerical results with experimental data. Moreover, different surface roughness has been successfully applied to the primary nozzle, and its effect on the entire flow is shown. Six properties of wet steam are selected, including pressure, temperature, Mach number, average droplet radius, droplet growth rate, and liquid mass fraction. The result shows increasing roughness resulted in a shift of the shock chain to the primary nozzle, damping shock strength, and rising temperature in the diffuser. In addition, increment of the primary nozzle surface roughness decreases ER and COP of the refrigeration cycle by 3.67% and 3.8%, respectively. The designers and operators should be considered the roughness effects in the design and operation of wet steam ejectors due to the vital impact of the roughness on the liquid mass fraction, average droplet radius, droplet growth rate, ER, and COP. Post-print / Final draft

Abstract Nowadays, the presence of droplets in industrial devices such as ejectors, turbine blades, and nozzles causes the reduction of efficiency and reduces the life-cycle of the device by the erosion of walls. The wet steam model is validated by the experimental data. The purpose of this study is to dehumidify and increase the power-saving via the suction technique. To create suction, a hole has been used in the divergent section of the nozzle. The effects of the hole locations and angles are studied using the criteria of wetness loss, power-saving, and erosion rate. Furthermore, another nozzle is applied to the validation of the suction technique, due to lack of experimental data about suction technique. It is shown that the modified model has less wetness loss up to 6.5 % compared to the original mode. The modified model has also been numerically analyzed, showing that it has also led to a 1.22 kW increase in power-saving. In addition, it has caused a reduction of 6 %, 1.52 %, 0.41 % and 6.9 % in the erosion rate ratio, droplets radius, max nucleation rate and liquid mass fraction ratio compared to the original mode, respectively.

Abstract The maneuver-induced liquid cargo motion in the partly-filled tanks called, sloshing poses a serious threat to the stability and controllability of this phenomenon. The entropy generation in the sloshing phenomenon is obtained for the first time in the rectangular storage tank. In this paper, a numerical model is developed to simulate the sloshing phenomenon by using coupled RANS solver and VOF method. The RANS equations are discretized and solved using the staggered grid finite difference and SMAC methods. The entropy generation distribution provides designers with useful information about the causes of the energy losses. As an objective, the total entropy generation is introduced as a design criterion parameter for rectangular storage tanks and is compared with the tank perimeter ( TP ) criterion. In order to do this, the horizontal periodic sway motions with different amplitudes, angular frequencies, and aspect ratios ( AR ) are applied to the rectangular storage tanks. The results show that the optimal AR is about 2.9 for TP criterion and is about 3.2 for the entropy generation criterion.

In the steam turbine, the wetness loss due to vapor condensation is one of the most crucial losses at low-pressure stage. This study focused on entropy generation and exergy destruction of condensing steam flow in turbine blade with the roughness. The governing equations including entropy transport equation combined with condensation model, transition SST model and roughness correlation were established and verified by experiments and theory. Flow field behaviors, such as wetness fraction, intermittency and turbulent viscosity distributions, controlled by the deviation angle were obtained to evaluate effects of back pressure ratio and surface roughness. The mass-averaged wetness fraction at outlet was also extracted considering the influence of uneven mass flux. Finally, each part of entropy generation derived from viscous, heat conduction, phase change and aerodynamic losses and exergy destruction ratio were analyzed. Research shows that roughness plays an important part in the intermittency and turbulent viscosity. The mass-averaged wetness fraction at outlet sharply drops with back pressure ratio but slightly decreases with the roughness. With the roughness rising or back pressure dropping, the entropy generation grows resulting in more exergy destruction. The maximum value of the total entropy generation is 84.520 J·kg−1·K−1, corresponding exergy destruction is 25.187 kJ·kg−1 and exergy destruction ratio is 4.43%.

Injecting hot steam into the cascade flow is one of the procedures for resisting losses and damages caused by condensation. In the current study, utilizing a 3D (three-dimensional) geometry for steam turbine blades, the hot steam has been injected into the steam cascade via the embedded channel. In the power plant industry, the hot steam injection process is done in two ways: constant pressure with a reservoir or constant mass flow rate utilizing a control valve. Therefore, considering these two methods and the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) optimization method, the best temperature for injecting hot steam into non-equilibrium steam in a constant steam turbine blade has been gained. At the optimal temperature of 540 K at the constant pressure mode, Er (erosion rate ratio) and Lr (condensation loss ratio) were obtained as 66.6% and 30.7%, respectively, and Kr (kinetic energy ratio) showed a 0.6% growth in the hot steam injection mode, in comparison with the original mode. In addition, the economic cost of hot steam injection was calculated as 0.457 ($/hour). By the TOPSIS optimization method, the optimal temperature of hot steam injection, utilizing the constant mass flow rate method, has been obtained as 460 K, and the Er, Lr, and Kr values were 31.2%, 66.1%, and 88.48%, respectively at the optimal temperature. Moreover, the economic cost was 0.43 ($/hour). It is easier to control the steam injection by the constant mass flow rate method utilizing a control valve; therefore, the 460 K temperature and constant mass flow rate method are introduced as the optimal method.

The heat transfer enhancement in the latent heat thermal energy storage system through dispersion of nanoparticle is reported. The resulting nanoparticle-enhanced phase change materials exhibit enhanced thermal conductivity in comparison to the base material. Calculation is performed for nanoparticle volume fraction from 0 to 0.08. In this study rectangular and cylindrical containers are modeled numerically and the effect of containers dimensions and nano particle volume fraction are studied. It has been found that the rectangular container requires half of the melting time as for the cylindrical container of the same volume and the same heat transfer area and also, higher nano particle volume fraction result in a larger solid fraction. The increase of the heat release rate of the nanoparticle-enhanced phase change materials shows its great potential for diverse thermal energy storage application.

Abstract The present paper focuses on exergoeconomic optimization of a proposed system with the goal of cogenerating freshwater and power, simultaneously. The cogeneration system includes Internal Combustion Engine, Organic Rankine Cycle, and Reverse Osmosis desalination unit. The thermodynamic model of the cogeneration system is investigated from energy, exergy, and exergoeconomic viewpoint. In addition, the variation of some key parameters including the engine speed, turbine inlet pressure, the number of the active vessels, freshwater mass flow rate, and the unit cost of freshwater to obtain optimum working condition is analyzed. The results show that the optimum value of the unit cost of power generation and freshwater occurs when the engine speed is 4000 rpm. Based on the optimization, the optimal condition does not occurred at the speed that exergy destruction becomes minimum. Furthermore the optimum value of the turbine inlet pressure was obtained respect to the maximum exergy efficiency and minimum unit cost of fresh water. The result showed that the optimum value of the turbine inlet pressure is 2690 k P a . There is an optimum value for the number of the active vessels that is achieved when 3 pressure vessels exist in the stage. In addition, the multi-objective optimization of the system based on the Pareto method revealed that at the optimum working condition, the exergy efficiency and freshwater mass flow rate are 30.7% and 2.926 kg/s, respectively. As a final result, it can be stated that the optimal values are not achieved in the minimum exergy destruction.

The isogeometric finite volume analysis is utilized in this research to numerically simulate the two-dimensional viscous wet-steam flow between stationary cascades of a steam turbine for the first time. In this approach, the analysis-suitable computational mesh with ‘‘curved’’ boundaries is generated for the fluid flow by employing a non- uniform rational B-spline (NURBS) surface that describes the cascade geometry, and the governing equations are then discretized by the NURBS representation. Thanks to smooth and accurate geometry representation of the NURBS formulation, the employed isogeometric framework not only resolves issues concerning the conventional mesh generation techniques of the finite volume method in steam turbine problems, but also, as validated against well-established experiments, significantly improves the accuracy of the numerical solution. In addition, the shock location in the cascade is predicted and tracked with a sufficient accuracy.