The inertance tube is a relatively new phase shifter that can avoid the DC-flow loss that commonl... more The inertance tube is a relatively new phase shifter that can avoid the DC-flow loss that commonly occurs in a pulse tube refrigerator with a double-inlet loop. The impedance of an inertance tube is a result of its resistance, inertance, and compliance effects. Previously, simple lumped-parameter models have been used to predict the phase shifting performance, but with limited accuracy. Other realistic effects, such as turbulent flow and heat transfer between gas and solid wall must be considered in improved models. Verification of inertance tube models has been difficult because systematic experimental data on inertance tubes are very limited. This paper presents a laminar-flow thermoacoustic transmission-line model and a turbulent-flow thermoacoustic model that accounts for both turbulent flow and heat transfer. The laminar-flow transmission-line model is solved analytically whereas the turbulent thermoacoustic model must be solved numerically. To verify the accuracy of the models, experimental measurements were conducted with frequencies between 20 and 90 Hz and with acoustic power flows less than about 50 W. The turbulent-flow model agrees reasonably with the experimental results for most of the experimental conditions investigated here.
The present state of the art is such that the greatest cost in using small superconducting device... more The present state of the art is such that the greatest cost in using small superconducting devices, in many applications, is the expense and inconvenience of the associated cryogenic system. The practicality of such devices would be greatly enhanced, therefore, if a practical and economical self-contained, closed-cycle cryocooler could be made compatible with such devices. An experimental cryocooler has been
Previously we have shown that the lower volumetric heat capacity and more ideal behavior of heliu... more Previously we have shown that the lower volumetric heat capacity and more ideal behavior of helium-3 compared with helium-4 at 4 K results in an improved performance for packed sphere regenerators operating with helium-3 between 4 K and 0 K. In this paper we use the NIST numeri- cal software REGEN3.3 to calculate the regenerator loss and the coefficient of
Previously measured and calculated impedances of inertance tubes were compared at frequencies bel... more Previously measured and calculated impedances of inertance tubes were compared at frequencies below 70 Hz and average pressures below 3 MPa. In this paper we present similar comparisons for frequencies up to 150 Hz and average pressures up to 3.5 MPa. Measurements were made on inertance tube diameters from 1.0 mm to about 3.0 mm, as well as on a
Growing interest in larger scale pulse tubes has focused attention on optimizing their thermodyna... more Growing interest in larger scale pulse tubes has focused attention on optimizing their thermodynamic efficiency. For Stirling-type pulse tubes, the performance is governed by the phase difference between the pressure and mass flow, a characteristic that can be conveniently adjusted through the use of inertance tubes. Unfortunately, data describing the optimized inertance geometry as a function of desired phase-shifts and
The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K devia... more The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K deviates considerably from an ideal gas. As a result, losses in the regenerator, given by the time-averaged enthalpy flux, are increased and are strong functions of the operating pressure and temperature. Helium-3, with its lower boiling point, behaves somewhat closer to an ideal gas in
The low heat capacity of regenerator materials near 4 K and the real gas properties of helium at ... more The low heat capacity of regenerator materials near 4 K and the real gas properties of helium at this temperature give rise to anomalous temperature profiles and behavior not seen at higher temperatures. This paper describes the behavior of regenerators calculated from the NIST computer code REGEN3.2 when the cold end is at 4 K. The results show that the regenerator loss is independent of the regenerator volume over a wide range and does not increase until the volume is decreased below some critical value, at which point the loss increases very rapidly. The transition occurs when the gas displacement amplitude at the warm end approaches the length of the regenerator. The model shows that reducing the porosity leads to a decreased regenerator loss at the plateau. The paper also describes the effect of the temperature at the warm end and the matrix heat capacity on the regenerator loss. The calculated temperature profiles agree with experimental measurements on regenerators in 4 K Gifford-McMahon refrigerators. .
The inertance tube is a relatively new phase shifter that can avoid the DC-flow loss that commonl... more The inertance tube is a relatively new phase shifter that can avoid the DC-flow loss that commonly occurs in a pulse tube refrigerator with a double-inlet loop. The impedance of an inertance tube is a result of its resistance, inertance, and compliance effects. Previously, simple lumped-parameter models have been used to predict the phase shifting performance, but with limited accuracy. Other realistic effects, such as turbulent flow and heat transfer between gas and solid wall must be considered in improved models. Verification of inertance tube models has been difficult because systematic experimental data on inertance tubes are very limited. This paper presents a laminar-flow thermoacoustic transmission-line model and a turbulent-flow thermoacoustic model that accounts for both turbulent flow and heat transfer. The laminar-flow transmission-line model is solved analytically whereas the turbulent thermoacoustic model must be solved numerically. To verify the accuracy of the models, experimental measurements were conducted with frequencies between 20 and 90 Hz and with acoustic power flows less than about 50 W. The turbulent-flow model agrees reasonably with the experimental results for most of the experimental conditions investigated here.
The present state of the art is such that the greatest cost in using small superconducting device... more The present state of the art is such that the greatest cost in using small superconducting devices, in many applications, is the expense and inconvenience of the associated cryogenic system. The practicality of such devices would be greatly enhanced, therefore, if a practical and economical self-contained, closed-cycle cryocooler could be made compatible with such devices. An experimental cryocooler has been
Previously we have shown that the lower volumetric heat capacity and more ideal behavior of heliu... more Previously we have shown that the lower volumetric heat capacity and more ideal behavior of helium-3 compared with helium-4 at 4 K results in an improved performance for packed sphere regenerators operating with helium-3 between 4 K and 0 K. In this paper we use the NIST numeri- cal software REGEN3.3 to calculate the regenerator loss and the coefficient of
Previously measured and calculated impedances of inertance tubes were compared at frequencies bel... more Previously measured and calculated impedances of inertance tubes were compared at frequencies below 70 Hz and average pressures below 3 MPa. In this paper we present similar comparisons for frequencies up to 150 Hz and average pressures up to 3.5 MPa. Measurements were made on inertance tube diameters from 1.0 mm to about 3.0 mm, as well as on a
Growing interest in larger scale pulse tubes has focused attention on optimizing their thermodyna... more Growing interest in larger scale pulse tubes has focused attention on optimizing their thermodynamic efficiency. For Stirling-type pulse tubes, the performance is governed by the phase difference between the pressure and mass flow, a characteristic that can be conveniently adjusted through the use of inertance tubes. Unfortunately, data describing the optimized inertance geometry as a function of desired phase-shifts and
The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K devia... more The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K deviates considerably from an ideal gas. As a result, losses in the regenerator, given by the time-averaged enthalpy flux, are increased and are strong functions of the operating pressure and temperature. Helium-3, with its lower boiling point, behaves somewhat closer to an ideal gas in
The low heat capacity of regenerator materials near 4 K and the real gas properties of helium at ... more The low heat capacity of regenerator materials near 4 K and the real gas properties of helium at this temperature give rise to anomalous temperature profiles and behavior not seen at higher temperatures. This paper describes the behavior of regenerators calculated from the NIST computer code REGEN3.2 when the cold end is at 4 K. The results show that the regenerator loss is independent of the regenerator volume over a wide range and does not increase until the volume is decreased below some critical value, at which point the loss increases very rapidly. The transition occurs when the gas displacement amplitude at the warm end approaches the length of the regenerator. The model shows that reducing the porosity leads to a decreased regenerator loss at the plateau. The paper also describes the effect of the temperature at the warm end and the matrix heat capacity on the regenerator loss. The calculated temperature profiles agree with experimental measurements on regenerators in 4 K Gifford-McMahon refrigerators. .
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Papers by Ray Radebaugh