Marcus Keding

Development of a µ-Scale Turbine Expander for Energy Recovery

Waste heat is a primary source of energy loss in many applications. A number of developments around a micro rocket engine at the Austrian Research Centers (ARC) promise innovative energy recovery and micro power generation solutions. Here we focus on the investigation of micro technologies for application in HVAC (heating, ventilating, and air conditioning) systems. The use of μ-scale turbine expanders for work recovery in transcritical CO2 heat pump processes has been identified as most interesting and promising for the application in HVAC cases. One of the main drawbacks of transcritical CO2 heat pumps is the lower COP (coefficient of performance) compared to conventional heat pump systems which originates from the non isothermal heat rejection in the gas cooler. This drawback can be compensated by utilizing the pressure difference between the high pressure and low pressure part of the heat pump for work recovery. This is feasible as the pressure difference is considerably larger in case of CO2 heat pumps compared to conventional systems. Work recovery can be realized by substituting the expansion valve between the high and low pressure side by an expansion machine. Due to the low flow rate of the working fluid, the turbine type is based on the Pelton turbine with specific two phase flow turbine blades. In addition to the turbine part a magnetic coupling, miniature bearings and a small scale generator are important parts of the system. Thermodynamic simulations showed an absolute microturbine power yield between 60 W and 150 W for a 2 kW heating system.Copyright

Development of Innovative Hydrogen and Micro Energy Solutions at the Austrian Research Centers

Hydrogen technologies are increasingly important for a number of future aerospace and terrestrial applications. The Austrian Research Centers (ARC) are presently developing an innovative hydrogen tank system based on a combination of hollow microspheres and chemical hydrides, promising very high storage densities up to 10 weight % (wt%) at ambient pressures and temperatures. ARC is also active in developing micro energy converters based on micro turbines and Stirling engines to use waste heat and exhaust for improving the overall efficiency for a number of applications. Furthermore the present paper discusses a concept that utilizes a micro energy converter together with a micro combustion module that enables a micro power generator with very high power-to-weight ratios. In addition an overview of energy-related developments is presented that is specifically suitable for aerospace and demanding terrestrial applications.

Development of Innovative Micro Power Converter Technologies at the Austrian Institute of Technology

Waste heat is a primary source of energy loss in many aerospace and terrestrial applications. The Austrian Institute of Technology (AIT) is presently developing two different types of micro power converters, promising high efficiencies in their respective application areas. The first converter is based on an innovative thermoacoustic Stirling engine concept without moving parts. Such a maintenance-free engine system would be particularly suitable for advanced Stirling radioisotope space power systems. The second converter is based on microturbines to use exhaust-gases for improving the overall efficiency for a number of applications. This paper will summarize our efforts on micro power converter technologies. Nomenclature y0 = half gap width �k = thermal penetration depth � = wavelength � = angular frequency � = efficiency �c = efficiency relative to Carnot

IMPROVED µ-SCALE TURBINE EXPANDER FOR ENERGY RECOVERY

Micro power converters for energy recovery are increasingly important for a number of future applications. The Austrian Institute of Technology (AIT) is presently developing an innovative μ-scale turbine expander for work recovery in transcritical CO2 heat pumps. The main drawback of a lower COP (coefficient of performance) of transcritical CO2 heat pumps compared to conventional heat pump systems can be compensated by utilizing the pressure difference between the high pressure and low pressure part of the pump for work recovery. Work recovery can be realized by substituting the expansion valve between the high and low pressure side by a Pelton turbine with specific two phase flow turbine blades. In order to increase the power output, the generator was integrated into the turbine to reduce the friction losses and hence increase the overall efficiency. An important aspect is that the generator is directly connected with the high pressure part of the turbine. One part of the project is the optimization of the turbine geometry via simulation tools. The paper will give an overview about our microturbine development as well as a comparison of the power output of each turbine generation. Furthermore the present paper discusses a concept that utilizes our microturbine together with a micro combustion module that enables a micro power generator with very high power-to-weight ratios based on green fuels.Copyright