A new type of streaming in pulse tubes

By numerical simulation a new type of streaming in pulse tubes has been found. The geometry in the simulation consists of the pulse tube with its flow straighteners. The straighteners are described as a porous medium. Viscous effects are taken into account, but heat transfer with the wall is not considered. The gas flow in the pulse tube is periodic. Positive and negative boundary conditions are imposed which result in flow fields with opposing directions. The net flow field is obtained by the superposition of these two flow fields. It turns out that two loops are formed in the tube. This paper analyzes this phenomenon and explains how the flow resistance of the straightener and the viscous effect of the tube wall result in this type of streaming

One-dimensional analytical and numerical models of the pulse-tube cooler

Three one-dimensional models describing the fluid dynamics and thermodynamics in the tube section of a pulse-tube refrigerator have been developed: numerical, analytical and harmonic. The numerical model concerns a finite-difference scheme that is second-order accurate in space and time. The analytical model is exact and based on the method of characteristics. The harmonic model is approximate and assumes sinusoidal variations of all variables. Some typical results for a single-stage Stirling type pulse-tube refrigerator are presented

One-dimensional analytical and numerical models of the pulse-tube cooler

Three one-dimensional models describing the fluid dynamics and thermodynamics in the tube section of a pulse-tube refrigerator have been developed: numerical, analytical and harmonic. The numerical model concerns a finite-difference scheme that is second-order accurate in space and time. The analytical model is exact and based on the method of characteristics. The harmonic model is approximate and assumes sinusoidal variations of all variables. Some typical results for a single-stage Stirling type pulse-tube refrigerator are presented

Cryogenic challenges for different superconductive motor topologies

Numerous studies and prototypes have proven the potential benefi t of supercon- ducting material being used in motors and generators. The electromagnetic system used in the motor or generator offers already for normal conductive systems a large variety of topologies, with the superconduc- tor being introduced completely new compositions can be realized. This presentation will give an overview of selected rotor and stator topologies being suitable for integrating superconducting material to improve the performance. The specifi c requirements of each system will be discussed, focusing on the potential application range. Besides the electromagnetic layout it is also important to completely integrate necessary cryogenic components into the motor or generator. Depending on the topology the specifi cations for the cryogenic components will be listed and characteristical constraints are mentioned. Complementary to the theoretical discussion of the topologies some representative demonstrators of the past will be selected and presented

One-Dimensional Simulation of a Stirling Three-Stage Pulse-Tube Refrigerator

A one-dimensional mathematical model is derived for a three-stage pulse-tube refrigerator (PTR) that is based on the conservation laws and the ideal gas law. The three-stage PTR is regarded as three separate single-stage PTRs that are coupled via proper junction conditions. At the junctions there are six fluid flow possibilities each defining its own boundary conditions for the adjacent domains. Each single stage cools down the gas in the regenerator to a lower temperature such that the system reaches its lowest temperature at the cold end of the third stage. The velocity and pressure amplitudes are decreasing towards the higher stages and there is an essential phase difference between them at different positions. The system of coupled PTRs is solved simultaneously first for the temperatures and then for the velocities and the regenerator pressures. The final result is a robust and accurate simulation tool for the analysis of multi-stage PTR performance