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T White, Martin
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T White
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Martin
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Martin T White
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Pressure profile optimisation of a nozzle for wet-to-dry expansionOgrodniczak, Pawel; Sayma, Abdulnaser; T White, MartinWet-to-dry expansion within the nozzle guide vane of an ORC turbine has been proposed as a means to improve the power output of ORC systems for waste-heat recovery (< 250 °C). However, given the rapid fluid acceleration in the stator, the phases can develop significant velocity and temperature disparity due to the density difference and finite rate of interphase heat transfer. Since these factors can significantly affect the phase-change process, wet-to-dry nozzle design techniques must account for non-equilibrium effects. The first part of this paper aims to further validate a previously developed quasi-1D inviscid nozzle design tool that accounts for non-equilibrium effects. The interphase mass, momentum and energy exchange models have been updated using correlations better tailored to evaporating droplet flows, while the drag equation and vapour mass fraction definition have been updated. The validation is performed using nonequilibrium CFD simulations, which, unlike the design model, account for lateral flow variations, viscous and turbulence effects, and secondary momentum forces. The results showed that these effects delay the evaporation, with CFD-predicted outlet vapour mass fraction being about 10 to 15% smaller than predicted by the quasi-1D tool. However, the overall flow behaviour and phase-change pattern were in satisfactory agreement, justifying the use of the design tool for 1D optimisation. In the second part of the paper, the quasi-1D tool is coupled to a gradient-based optimiser to optimise the nozzle pressure profile and enhance evaporation of siloxane MM for expansions with inlet pressure ranging from 450 to 650 kPa, and inlet quality of 0.3. The design variables are the control points of a Bezier curve that defines the shape of the intended nozzle pressure profile. CFD simulations of the optimised geometries indicate a 5.5 to 6.6% increase in the outlet vapour mass fraction, which was raised from 84.9, 88.2 and 90.7% to 90.4, 94.8 and 97.2% for the 450, 550 and 650 kPa inlet pressures respectively. More abrupt expansion in the optimised nozzles resulted in the development of a shock and led to nozzle efficiency deterioration compared to the baseline. This emphasises the need for multi-objective optimisation, which will be conducted in future studies.- pocketORC: A BROWSER-BASED CALCULATOR FOR TEACHING ORGANIC RANKINE CYCLE POWER SYSTEMST White, MartinThis paper presents a steady-state design model for an organic Rankine cycle (ORC) power plant that is completely web-browser based and does not rely on any external libraries (e.g., for the computation of thermodynamic properties). This means the tool can be easily accessed by students via any electronic device with a web browser and used as a teaching aid to teach basic principles relating to ORC power systems. Therefore, ORC power cycles can be introduced interactively without requiring any programming knowledge or the distribution and installation of source files. This allows ORC power systems to be introduced earlier in the curriculum, and to a wider variety of students, than might otherwise be possible. The current version of the model combines the Peng-Robinson equation of state with a thermodynamic model of a recuperated ORC system and discretised heat exchanger sizing models. The model is written in the Python programming language and the PyScript framework is used to call Python code directly from HTML. The user can vary cycle variables such as the condensation temperature, pressure ratio, degree of superheat, recuperator effectiveness and heat-source temperature drop via the graphical-user interface which returns key indicators of cycle performance such as thermal efficiency and power output amongst others. The tool enables single-point calculation and parametric studies of a single variable and includes introductory self-paced lessons. This allows students to develop an understanding of the influence of different cycle variables on cycle performance. This paper provides an overview of the tool and its capabilities, alongside discussing its potential role as a teaching aid to support the introduction of ORC power systems into the curriculum.
