MINIATURE JOULE-THOMSON CRYOCOOLERS FOR PROPELLENT MANAGEMENT TASK I: Thermodynamic Cycle Analysis and System Optimization Presented by  K.V.Krishna Murty MMAE MINIATURE ENGINEERING SYSTEMS GROUP

Optimized Cycle Specifications Compressor:Compressor: Pressure Ratio = 10, Efficiency = 85%,Pressure Ratio = 10, Efficiency = 85%, Working Fluid = Neon, Operating pressure range = 3 bar to 30 bar,Working Fluid = Neon, Operating pressure range = 3 bar to 30 bar, Electric Power required to run the motor for compressor = 11.7 kW.Electric Power required to run the motor for compressor = 11.7 kW. Recuperative Heat Exchanger:Recuperative Heat Exchanger: Temperature drop/rise = K, Effectiveness = 95 %,Temperature drop/rise = K, Effectiveness = 95 %, Pressure difference between Hot side and Cold side = 27 bar.Pressure difference between Hot side and Cold side = 27 bar. JT Valve:JT Valve: JT coefficient = 0.63, Temperature drop across JT Valve = 17 K.JT coefficient = 0.63, Temperature drop across JT Valve = 17 K. Heat Sink:Heat Sink: Heat Load = 9927 W, Working pressure = 30 bar.Heat Load = 9927 W, Working pressure = 30 bar. Cold Head:Cold Head: Cooling power = 20 W, Working pressure = 3 bar.Cooling power = 20 W, Working pressure = 3 bar. Overall system:Overall system: Working Fluid = Neon, Working pressure range = 3 bar to 30 bar,Working Fluid = Neon, Working pressure range = 3 bar to 30 bar, Mass flow rate/cold head = 3.81 g/s,Mass flow rate/cold head = 3.81 g/s, System COP = System COP =

Companies from which the price quotes for the required compressor were received  Hydro-Pac, Inc.  $ 9, 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, 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 N 2, we cannot use high pressures as the melting point of N 2 increases with pressure. For example, at 10 bar, N 2 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.