Small scale cryogenic refrigeration technology

Issued as final reportVirtual Aerosurface Technologie

Z-inertial fusion energy: power plant final report FY 2006.

This report summarizes the work conducted for the Z-inertial fusion energy (Z-IFE) late start Laboratory Directed Research Project. A major area of focus was on creating a roadmap to a z-pinch driven fusion power plant. The roadmap ties ZIFE into the Global Nuclear Energy Partnership (GNEP) initiative through the use of high energy fusion neutrons to burn the actinides of spent fuel waste. Transmutation presents a near term use for Z-IFE technology and will aid in paving the path to fusion energy. The work this year continued to develop the science and engineering needed to support the Z-IFE roadmap. This included plant system and driver cost estimates, recyclable transmission line studies, flibe characterization, reaction chamber design, and shock mitigation techniques

Thermal Dispersion and Convection Heat Transfer during Laminar Transient Flow in Porous Media

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.Solid-fluid thermal interactions during unsteady flow in porous media play an important role in the regenerators of pulse tube cryocoolers. Pore-level thermal processes in porous media under unsteady flow conditions are poorly understood. The objective of this investigation was to study the pore-level thermal phenomena during pulsating and unidirectional sinusoidal flow through a generic, two-dimensional porous medium by numerical analysis. Furthermore, an examination of the effects of flow pulsations on the thermal dispersion and heat transfer coefficient that are encountered in the standard, volume-average energy equations for porous media were carried out. Pulsating and unidirectional sinusoidal inlet flow rates were chosen as an intermediate step towards the more difficult problem of periodic flow. The investigated porous media are periodic arrays of square cylinders. Detailed numerical data for the porosities of 0.75 and 0.84, with flow pulsation frequencies of 0 - 80 Hz, were obtained at Reynolds numbers of 560 and 980. Based on these numerical data, the instantaneous as well as cycle-average thermal dispersion and heat transfer coefficients, to be used in the standard unsteady volume-average energy conservation equations for flow in porous media, were derived

Simulation of Boundary Layer Effects in the Pulse Tube of a Miniature Cryocooler

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.As pulse tube cryocoolers are miniaturized, boundary layer effects in the pulse tube may become more important than they are for larger refrigerators. Nearly uniform flow in the pulse tube is necessary for efficient cooling, and this condition is compromised as the pulse tube diameter becomes smaller relative to the thermal and viscous boundary layer thicknesses. As a result, miniature pulse tube cryocoolers are likely to experience enhanced acoustic streaming losses compared to larger PTC’s. This acoustic streaming results from thermal and viscous interactions between the working fluid and the pulse tube walls. The thermal and viscous penetration depths and their magnitudes relative to the pulse tube diameter and wall thickness are therefore important parameters for this phenomenon. A parametric study of the effects of the pulse tube diameter, scaled to a non-dimensional value by the relevant boundary layer thicknesses, on acoustic streaming in the pulse tube was performed using CFD modeling. The effect of the operating frequency was also considered through the frequency dependence of the viscous and thermal penetration depths. Temperature dependant material properties were included in the CFD models because they play an important role in acoustic streaming. Results indicated that close attention must be paid to the sizes of the boundary layers relative to the pulse tube physical dimensions when designing miniature pulse tube cryocoolers