09:00
Session 6C: Volumetric Expanders (2)
Chair: RIchard Aumann
09:00
20 mins
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Experimental Evaluation of R1336mzz(Z) as Low GWP Replacement for R245fa in a Scroll Expander
Matthias Welzl, Florian Heberle, Theresa Weith, Dieter Brüggemann
Abstract: Hydrofluoroolefin (HFO) refrigerants are promising low global warming potential (GWP) alternatives to the currently used hydrofluorocarbons (HFCs) in Organic Rankine Cycle (ORC) systems. This study led the focus on the experimental evaluation of the novel HFO R1336mzz(Z) as a low GWP replacement for the HFC R245fa. The investigated scroll expander is a semi-hermetic oil-free expander with a rated power of 1 kW and a built-in volume ratio of 3.5, which is magnetically coupled with a 1 kW permanently excited synchronous generator. For the determination of the expander mechanical power output, a contactless torque sensor is integrated. The experimental investigation involved measurements at eight different operating conditions for the working fluids R245fa and R1336mzz(Z), varying the saturation temperature, the scroll expander rotational speed, and the pressure ratio. The maximum mechanical isentropic efficiencies of 58.9 % for R245fa and 57.0 % for R1366mzz(Z) were obtained at a saturation temperature of 90 °C. For all variations, the mechanical isentropic efficiency for R1366mzz(Z) is between 0.9 % and 6.2 % lower compared to R245fa. The experimental evaluation indicates, that R1336mzz(Z) is a suitable low GWP replacement for R245fa with slightly lower scroll expander efficiencies.
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09:20
20 mins
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Developement and Demonstration on Single Screw Expander in Organic Rankine Cycle
Yu Ting Wu, Wei Wang, Biao Lei, Rui Ping Zhi, Chong Fang Ma
Abstract: Single screw expander is a machine which can realize volume change by means of a screw and two gaterotors. Single screw expander was recognized as the best volumetric expanders for the advantages of ideal force balance, low leakage, low noise, low vibration, long life , low maintenance cost , hige pressure ratio, etc.
Based on the gear theory and spatial relationship between single screw rotor and gate rotor, mathematical models on the profile of CP-type, PP-type, CC-type and PC-type structure are established. The groove volume of the four types of structure are derived. And the unwrapped helix of single screw rotor deciding the suction size and discharge position are obtained. Moreover, the changing rules of groove volume and volume ratio are quantitatively analyzed.Developed a generating processing technology and 2 sets of special machine tools to massive manufacture screw rotors from Φ20 to Φ450mm at high precision and low cost. The cutting tool and moulds for machining the gate rotor have been successfully designed and machined.
Thermo- fluid dynamic models and performance testing system of single screw expander were established. Influences of clearance height, lubrication oil. rotating speed, pressure and temperature on single screw expander were investigation by experiments and numerical simulations. Compound slide valve adjusting capacity and internal volume ratio regulation simultaneously were proposed to improve the single screw expander performance under different operating conditions. Developed six module single screw expander prototypes in wide power range from 5kW to 172 kW. A double-stage single screw expander by utilizing the discharge velocity of screw grooves was developed. Experimental result indicates that the developed single screw expander performed well under different expansion ratio conditions. The coefficient of discharge velocity utilization achieved 0.42.
An optimized single screw expander ORC system working with R123 was developed, the maximum efficiency achieved 9.3%. Four demonstration projects were established respectively with solar and internal combustion engine waste heat.
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09:40
20 mins
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Study of a Waste Energy Driven Organic Rankine Cycle Using Linear Piston Expander for Marine Applications
ChunWee Ng, Ivan CK Tam, Dawei Wu
Abstract: Installation of Organic Rankine Cycle (ORC) waste heat recovery systems have been reported on at least six sea-going ships since 2012 and is expected to gain more interest as a means to reduce fuel consumption to meet increasing stringent environmental regulations. In contrast with land-based ORC systems for biomass and geothermal applications, wide-spread application of ORC onboard ships can only be possible if it is optimised for weight, volume, power output to meet actual electrical demands and importantly address concerns of the shipowner in return on capital. Previous studies by the authors have explored the economic aspects by looking at potential fuel savings and payback time of such a system onboard a ship. Selection of expander type for the ORC system is very important and linear piston expanders are expected to yield economic and thermodynamic advantages due to their simpler design and high isentropic efficiency. This paper presents the feasibility of the application of ORC using a linear piston expander onboard a sea-going ship. The proposed ORC system using both thermal waste heat from main engines and waste cryogenic energy from Liquefied Natural Gas fuel considers the ship’s actual design like general arrangement plan and operational data like operational profile. A dynamic simulation method using a Siemens Simcenter Amesim will be used for the design and optimisation process. Results from the study show that the free piston linear generator to provide stable output suitable for electrical generation. However, the mechanical efficiency is found to be low which indicates that various parts of the expander design needs to be optimized. Due to this, the economics of an earlier study needs to be reduced from 7% to 5.9% for fuel savings and 2.7 years to 3.1 years for payback period which could impact project viability if the dynamics of the expander is considered.
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10:00
20 mins
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Model Based Design of a Dual Intake Port Sliding Vane Rotary Expander for Small Scale ORC-based Power Units
Fabio Fatigati, Marco Di Bartolomeo, Davide Di Battista, Roberto Cipollone
Abstract: Volumetric expanders are the most suitable technological solution for small scale ORC power units thanks to their compactness, flexibility, capacity to manage two-phase working fluid and low operating revolution speed. Among the positive displacement expanders, sliding vane rotary expanders (SVRE) is one of the most reliable and cheaper alternative. Nevertheless, volumetric and friction losses affect their performances more than other volumetric technologies. Moreover, some design choices introduced to reduce the volumetric losses such as the increase of the number of the vanes, lead to an increase of the mechanical power losses due to viscous and friction effects.
A way to improve the performances of SVRE is be represented by the dual intake port technology, which involves a further intake phase after the end of the main one. Indeed, keeping constant the mass flow rate provided by the pump, the dual intake expander produces a mechanical power close to the single intake machine with a lower intake pressure. The machine, in fact, is more permeable and this reduces, for a given flow rate imposed by the pump, the upstream pressure at the expander’s inlet. This aspect ensures the reduction of both volumetric and friction losses as they are proportional to pressure difference between consecutive vanes. Moreover, the dual intake expander operating at lower intake pressure allows to preserve the sealing components integrity, increasing reliability.
This novel design option was analyzed in this paper through a 1-D CFD model, validated on a wide set of experimental data collected on an ORC-based power unit test bench. The analysis opens the way to a model based design approach which aim to develop a new technological concept of SVRE.
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10:20
20 mins
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Development and Testing of a Free Piston Linear Expander for Organic Rankine Cycle Based Waste Heat Recovery Application
Muhammad Usman, Apostolos Pesyridis, Sam Cockerill, Thomas Howard
Abstract: The global community has agreed to limit global warming well below 2oC (COP21) . Automotive internal combustion engines (ICE) generally convert 40% of fuel energy into useful power and discharge the remaining to environment. Disruptive ideas are needed to achieve the set goals for improvement of energy conversion efficiency. Organic Rankine cycle systems appear to be favourable for waste heat recovery from the automotive exhaust, but the technology readiness levels are still low for mobile applications particularly due to non-availability of suitable and cost-effective expansion machines in mini-scale (<20kW) power scale.
The work is focussed on the development and experimental testing of linear free piston expander. Free piston expanders are suitable and have smaller leakage losses. The expander also has a passive inlet port which controlled by bounce pressure due to small recompression and thus complex valve mechanisms can be avoided. The generator also encompasses a linear electrical machine on the piston of the expander to generate electricity directly. Multi-physics models were used to understand the gas expansion characteristics, valve dynamics, leakage losses and heat losses using Mathworks Simscape. The models helped to size the equipment (ports/plenum/chambers etc.) and also provided the control schemes for the control expansion machine
The work also presents details of adaptation/retrofitting of an organic Rankine cycle (ORC) rig originally used for testing of a turbo-generator. The currently, the proposed expander is based on R1233zde so the balance of plant was re-iterated along with the specific expander integration equipment details. The expander was tested at 8 bar inlet pressure and 1 bar discharge pressure, the machine under investigation is the downsized version to generate 2.5kWe power.
The results concluded that the proposed expander is an effective solution for waste heat recovery applications for 10kWe scale output. Despite, lower efficiencies compared to a turbo-expander, the design and shape permits integration of pump and high-temperature heat exchanger to the expander to form a compact unit, thus saving cost and weight.
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