Highlights• CFD-based shape optimization of a nozzle and a turbine blade regarding nucleating steam flow is performed.• Nucleation rate and droplet radius are the best suited objective functions for the optimization p rocess.• Maximum 34% reduction in entropy generation rate is reported for turbine cascade.• A maximum 10% reduction in Baumann factor and a maximum 2.1% increase in efficiency is achieved for a turbine cascade. Abstract:In this study CFD-based shape optimization of a 3D nozzle and a 2D turbine blade cascade is undertaken in the presence of non-equilibrium condensation within the considered flow channels.A two-fluid formulation is used for the simulation of unsteady, turbulent, supersonic and compressible flow of wet steam accounting for relevant phase interaction between nucleated liquid droplets and continuous vapor phase. An in-house CFD code is developed to solve the governing equations of the two phase flow and was validated against available experimental

solar collectors, evaporators, condensers and relevant energy storage schemes during thermal charging and discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.

No abstract

No abstract

No abstract

No abstract

The purpose of this study was to present the heat transfer coefficients and flow patterns during the condensation of R134a inside an inclined smooth tube at low mass fluxes and different temperature differences (the temperature differences were between the saturation temperature and wall temperature). Condensation experiments were conducted at different inclination angles ranging from −90° (vertically downwards) to +90° (vertically upwards), at low mass fluxes of 50, 75, and 100 kg/m 2 s, and temperature differences from 1 °C to 10 °C. Measurements were taken at different mean vapour qualities between 0.1 to 0.9 in a smooth tube test section with an internal diameter of 8.38 mm and length of 1.5 m. The average saturation temperature was kept constant at 40 °C. It was found that inclination significantly influenced the flow patterns and the heat transfer coefficients. Downwards flows accounted for an increase in heat transfer coefficient with the maximum heat transfer coefficient found at inclinations of −15° and −30° (downwards flow) at the corresponding minimum temperature difference was tested for in each case. The maximum inclination effect was approximately 60% and was obtained at the lowest mass flux of 50 kg/m 2 s. In general, it was concluded that the heat transfer coefficients were more sensitive to the temperature difference for downwards flows than for upwards flows. Furthermore, there was no significant effect of temperature difference on the heat transfer coefficients for upwards flows. It was also found that the downwards and upwards vertical orientations were almost independent of the temperature difference. With respect to the inclination effect, it was found that in general, it decreased with an increase in temperature difference but decreased with an increase in mass flux and vapour quality.

In this study, the effect of the tube inclination angle on simultaneous condensation inside and pool boiling outside a smooth tube is investigated numerically. Such conjugate phase-change phenomena happen in many heat exchangers, particularly in passive heat removal systems. The simulated domain is a pool filled with water liquid at atmospheric pressure, with a submerged tube with inner and outer diameters of 19 mm and 25 mm respectively. The fluid inside the tube is considered to be the steam at the saturation temperature of 250 °C, which is a very common operating condition in many heat removal systems. The flow field is considered to be turbulent, unsteady and three dimensional. The effect of conduction through the tube thickness is also taken into account. The Eulerian-Eulerian multiphase flow approach is utilized to express the governing equation of the problem. ANSYS FLUENT 17.1 is also used to solve the governing equations. The effects of various parameters, such as tube orientation, steam mass flux and inlet steam quality on the condensation and pool boiling heat transfer coefficients, are investigated. The results show good agreement with the available experimental data. The condensation heat transfer coefficient is found to increase with an increase in the inlet steam quality and steam mass flow rate. The results of the effect of inclination on the heat transfer coefficient are also compatible with the previous experimental works. Moreover, the results show that there is a partial maximum point for the total heat transfer coefficient at an inclination angle between θ = -60° and θ = -30°.