Petri Sallinen

Power Limits of High-Speed Permanent-Magnet Electrical Machines for Compressor Applications

The maximum-power limits for high-speed permanent-magnet (PM) electrical machines for air compressor applications are determined in the speed range 20000-100000 r/min. For this purpose, five PM machines are designed and the electromagnetic, thermal, and mechanical designs of each machine are simultaneously performed. The critical values of the thermal and mechanical constraints are considered in order to obtain the maximum powers of the electrical machines. The electromagnetic losses generated in the machine are the output parameters of the electromagnetic design and input parameters for the thermal design. The thermal design is performed using a multiphysics method, which couples computational-fluid-dynamics equations with heat-transfer equations. The mechanical design considers the retention of the rotor elements against the huge centrifugal forces that arise during the high-speed operation and also the rotor dynamics properties of the rotor. The reliability of these design techniques is experimentally validated in the paper. The obtained maximum-power limit defines the speed-power region, in which the high-speed PM electrical machines intended for compressor applications can have a safe operation.

Thermal analysis of a high-speed PM machine using numerical and thermal-network method

Different methods for thermal analysis of a high-speed permanent-magnet machine are presented. The first implemented method is a numerical method which couples computational fluid dynamics and heat-transfer equations. This method gives simultaneous solutions for the thermal and turbulent properties of the cooling fluid in a 2D axi-symmetric geometry and a 3D solution of the temperature distribution in the solid domain of the machine. This method uses the properties of the turbulent flow from the 2D model such as the temperature rise of the fluid and the coefficients of thermal convection and implements them in the boundary conditions of the 3D model. The traditional thermal-network method that is based on analytical and empirical equations is also implemented in this paper and its results are compared with the results of the numerical method. The aforementioned methods are validated with measurements using thermocouples at different spots of the stator winding.

Computational and Experimental Comparison of Different Volute Geometries in a Radial Compressor

Two different volute geometries of a radial compressor at three different operating points have been analyzed using Computational Fluid Dynamics and detailed laboratory measurements. The performance of the volutes were compared using steady-state CFD-analysis, where the volute and the impeller with diffuser were modeled separately. In addition, a time dependent simulation of the complete compressor using the sliding mesh technique was performed for one operation point. Both volutes were manufactured and the overall performance of the compressor, the pressure distribution in the volute and the flow field in the volute inlet were measured with the respective volute geometries. The results obtained from steady, quasi-steady and time-accurate simulations are compared with experimental data.Copyright

CFD Analysis of a Centrifugal Compressor Impeller and Volute

In this study, centrifugal compressor performance was predicted using CFD. Three-dimensional time-averaged impeller and volute simulations were performed using a Navier–Stokes code. The presented performance prediction method has been divided into three phases. Firstly, the impeller was calculated with a vaneless diffuser. That gives inlet boundary conditions for the volute analysis and the pressure ratio at the diffuser exit. Next, the volute analysis was performed and a static pressure recovery coefficient obtained. Finally, that result was combined with the pressure ratio prediction from the impeller analysis, and the overall compressor performance thus obtained.Copyright

Refrigeration Process With High Speed Technology

The aim of this study was to make a computer program that simulates a standard refrigeration process, and a process provided with a bubble intercooler. A further object of the study was to establish the suitability of a turbocompressor for small refrigeration plants.Firstly the fundamentals of refrigeration machines and industrial refrigeration systems are discussed. An iteration procedure of steady state refrigeration process calculation is introduced. Fluid properties are calculated with the program units created for the modelling of an ORC power plant. Specific input files were made for 6 process fluids R134a, R123, isopentane, isobutane, toluene and ammonia. The compressor program is linked to the refrigeration process simulation program in order to model single stage and two stage radial compressors. The Turbo Pascal program made for microcomputers is modular, which makes it possible to develop and test the program unit by unit. The maximum deviations of fluid properties from those in tables was found to be less than 1 per cent.To simulate tailor-made refrigeration plants, a simple model is required. On nominal loads the program estimates an optimum intermediate pressure for the bubble process and optimum rotational speed for the radial compressor(s). The lowering of the rotational speed by an inverter gives high COP-values on partial loads of the plant. Based on the example calculation, a two stage turbocompressor calculated with isopentane as the working fluid, a cooling capacity of 1200 W seems to be feasible.Copyright

Design and Performance Measurements of a 6 kW High-Speed Micro Gas Turbine Prototype

Small portable electricity generating systems are suitable in remote locations where the access by vehicles is restricted or not even possible. These kind of places include for example catastrophic areas after earthquakes or tropical cyclones. Such machines can also be used as auxiliary power units in motor or sail boats. Gas turbine based electricity generation systems offer a good alternative for typical engine-generator units which are characterized by lower specific powers. It is suggested that the power to weight ratio of a 6 kW micro gas turbine can be more than eight times higher than that of the corresponding engine-generator unit. The biggest drawback is the higher specific fuel consumption; however, by introducing a recuperator, the specific fuel consumption can be improved.In this article, the design process and experiments of a 6 kW micro gas turbine prototype are described and discussed in detail. The built non-recuperated prototype is based on a commercial, small jet engine originally designed to give thrust to radio controlled model airplanes. The jet nozzle of the jet engine was replaced by an axial power turbine which was directly connected to a small, high speed permanent magnet generator. The experiments showed the potential of the prototype.Copyright