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MINIATURE ENGINEERING SYSTEMS GROUP. MINIATURE JOULE-THOMSON CRYOCOOLERS FOR PROPELLENT MANAGEMENT. TASK I: Thermodynamic Cycle Analysis and System Optimization Presented by K.V.Krishna Murty MMAE. Compressor : Pressure Ratio = 10, Efficiency = 85%,
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MINIATURE ENGINEERING SYSTEMS GROUP MINIATURE JOULE-THOMSON CRYOCOOLERS FOR PROPELLENT MANAGEMENT TASK I: Thermodynamic Cycle Analysis and System Optimization Presented by K.V.Krishna Murty MMAE
Compressor: • Pressure Ratio = 10, Efficiency = 85%, • Working Fluid = Neon, Operating pressure range = 3 bar to 30 bar, • Electric Power required to run the motor for compressor = 11.7 kW. • Recuperative Heat Exchanger: • Temperature drop/rise = 263.16 K, Effectiveness = 95 %, • Pressure difference between Hot side and Cold side = 27 bar. • JT Valve: • JT coefficient = 0.63, Temperature drop across JT Valve = 17 K. • Heat Sink: • Heat Load = 9927 W, Working pressure = 30 bar. • Cold Head: • Cooling power = 20 W, Working pressure = 3 bar. • Overall system: • Working Fluid = Neon, Working pressure range = 3 bar to 30 bar, • Mass flow rate/cold head = 3.81 g/s, • System COP = 0.0069. Optimized Cycle Specifications
Companies from which the price quotes for the required compressor were received • Hydro-Pac, Inc. $ 9,000 .00 Model – Li’l Critter High Pressure Gas Compressor Maximum discharge pressure = 30 bar Inlet pressure = 3 bar Inlet temperature = 300 K Volumetric flow rate = 1.0 scfm Cooling water required = 1.0 gpm • Fluitron, Inc. $ 11,300.00 Model – Fluitron S1-35 Type – Metal diaphragm types, water-cooled., Suction pressure = 3 bar Discharge pressure = 30 bar Volumetric flow rate = 1.0 scfm Cooling water required = 0.25 gpm
Other considerations for cycle optimization • Nitrogen was considered as a working fluid instead of Neon. But it showed that the system turns into a 2 phase system if nitrogen is used. With N2, we cannot use high pressures as the melting point of N2 increases with pressure. For example, at 10 bar, N2 is still a liquid at 90 K (LOX M.P). So, we cannot use 30 bar pressure. • The requirement of the high HEX effectiveness becomes very prominent. So, we cannot use Nitrogen as the working fluid.
Future Work • Continue with the development of High Effectiveness Recuperative Micro Heat Exchanger. An option of using a turbo expander instead of JT valve is under consideration. Commercially available turbo expanders for the system are being actively searched for. • Start designing the Miniature High Effective Cold Head.