Numerical analysis of small scale axial and radial turbines for solar powered Brayton cycle application

In the current work two types of turbines, axial and radial turbine, with their three configurations, Single Stage Axial, Dual Stage Axial and Single Stage Radial turbines, for solar Brayton cycle applications have been parametrically investigated with the aim of figuring out their performance in terms of efficiency and power output. The mean line design for each turbine was effectively completed in order to figure out the initial guess for the dimensions, the power output and the efficiency. Consequently, the Computational Fluid Dimension CFD analysis was employed for the sake of visualising the 3-Dimentions behaviour of the fluid inside the turbine as well as determining the main output like the power output and the efficiency at different boundary conditions. These boundary conditions were selected to be compatible with a small scale solar powered Brayton cycle. An evaluation for some types of losses such as tip clearance and trailing edge losses as well as the total loss coefficient of the rotor of each configuration, in terms of pressure losses, has been established as well. The current paper deals with Small Scale Turbines SST ranged from 5 to 50 kW as a power output. The outcomes showed that the Dual stage axial turbine performances better at the off design conditions. By contrast, the single stage radial turbine achieved higher power output during the same operating conditions. The results of the CFD analysis have been successfully validated against the experimental work done by the researchers for small scale (axial) compressed air turbine in the lab

Development of efficient small scale axial turbine for solar driven organic rankine cycle

Recently, the increase in fossil fuel consumption and associated adverse impact on the environment led to significant interest in renewable energy sources like solar. This paper presents a new methodology that integrates the ORC cycle analysis with modeling of an efficient small scale subsonic axial turbine at low temperature heat sources using wide range of organic working fluids like R123, R134a, R141b, R152a, R245fa, R290 and isobutene. The work involves detailed turbine analysis including 1D mean line approach, extensive 3D CFD simulations and ORC cycle analysis at inlet total pressure ranging from 2–5 bar corresponding to temperature range from 275K–365K to achieve the best turbine and cycle performance. This work provides a more reliable data base for small scale organic working fluids instead of using the map of large scale gas turbine. The numerical simulation was performed using 3D RANS with SST turbulence model in ANSYS-CFX. Using iterative CFD simulations with various working fluids with subsonic inlet conditions, Mach number ranging from 0.6–0.65, results showed that using working fluid R123 for a turbine with mean diameter of 70mm, the maximum isentropic efficiency was 82% and power output 5.66 kW leading to cycle efficiency of 9.5%.</jats:p

Impact of skin friction, tip clearance and trailing edge losses on small scale cryogenic axial turbine performance

Cryogenic Energy Storage (CES) technology which uses liquid air/nitrogen as energy carrier has attracted considerable attention recently due to its high exergy density (762kJ/kg) compared to other energy storage technologies. Liquid air/nitrogen occupies about 1/700 of the volume of its gaseous phase making it easier to store and transport. The stored energy can be recovered through a direct expansion process where the expander design and performance have a major effect on the efficiency of the energy conversion process. In this work the effects of surface roughness, tip clearance and trailing edge thickness on the performance of a small scale (tip diameter 40mm, mass flow rate 0.3 kg/s) axial cryogenic turbine have been investigated using mean line 1D analysis and ANSYS CFX 3D modelling where limited data available in the literature. Results showed that stator surface roughness has the highest impact on the turbine performance, where power output and turbine efficiency were significantly reduced as the roughness increased. For example at 20000RPM (design point) with stator roughness value of 0.5mm the efficiency and power output were 87.2% and 1197.7 W while for the same roughness on rotor blade the efficiency and power output were 89.34% and 1198.59 W. Regarding the effect of tip clearance, the efficiency decreases by 2% as the tip clearance increases from 0.35mm to 1mm.</jats:p