Test rig for organic vapour: design and simulation of operation

A blow-down wind tunnel for real gas applications has been designed and the main processes involved in its operation has been simulated in order to verify its behaviour. The facility is aimed to characterize an organic vapour stream, representative of expansions taking place in Organic Rankine Cycles (ORC) turbines, by independent measurements of pressure, temperature and velocity. ORC turbine performances are expected to strongly benefit of flow description and design tools validation provided by experimental data. This paper discusses how the facility has been designed and presents its final layout. The dynamic models of plant components are also described and the facility operation is discussed via the simulation results. A straight axis planar convergent-divergent nozzle represents the test section for early tests, but the test rig can also accommodate linear blade cascades. High fluid densities and temperatures to be reached resulted in an unaffordable thermal power to be provided in case of continuous loop, therefore a blow down operating scheme has been adopted. A wide variety of working fluids can be tested with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar. The test rig operational mode is unsteady, but the inlet nozzle pressure can be kept constant by a control valve. In order to estimate the duration of both set-up and experiments and to evaluate the time trend of fluid properties during the main processes, the plant operation has been dynamically simulated using Dymola®, an object oriented simulation code, able to treat both fluid-dynamic and automation components; they have been either selected in a database or created through Modelica routines. Design and simulation have been performed with a lumped parameter approach using Siloxane MDM and Hydrofluorocarbon R245fa as reference compounds and FluidProp® for properties calculation. Depending on the fluid and test pressure, experiments may last from 12 seconds to several minutes while the plant set-up requires a few hours. The design calculation and dynamic simulation shown how the set-up and test duration make the facility suited to perform the desired experiments. INTRODUCTION Organic Rankine Cycles (ORC) represent a viable technology for the exploitation of energy from low/medium temperature sources, such as renewable or heat-recovery sources, with applications to low/medium electrical power generation and Combined Heat and Power (CHP) plants. An Organic Rankine Cycle consists in a Rankine Cycle employing an organic compound as working fluid [1]. For the above cited applications, the ORC technology is usually preferred over steam cycle due to the simplicity of plant components, the high reliability and the low operational costs [2, 3], exhibiting at the same Figure 1 : Left: Typical regenerative Organic Rankine Cycle power plant. Right: Corresponding Regenerative Organic Rankine Cycle XX Biannual Symposium on Measuring Techniques in Turbomachinery Transonic and Supersonic Flow in Cascades and Turbomachines