Design and Analysis of a Nested Halbach Permanent Magnet Magnetic Refrigerator
Date
2013-08-19
Authors
Tura, Armando
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Abstract
A technology with the potential to create efficient and compact refrigeration devices is
an active magnetic regenerative refrigerator (AMRR). AMRRs exploit the
magnetocaloric effect displayed by magnetic materials whereby a reversible temperature
change is induced when the material is exposed to a change in applied magnetic field. By
using the magnetic materials in a regenerator as the heat storage medium and as the
means of work input, one creates an active magnetic regenerator (AMR). Although
several laboratory devices have been developed, no design has yet demonstrated the
performance, reliability, and cost needed to compete with traditional vapor compression
refrigerators. There are many reasons for this and questions remain as to the actual
potential of the technology.
The objective of the work described in this thesis is to quantify the actual and potential
performance of a permanent magnet AMR system. A specific device configuration
known as a dual-nested-Halbach system is studied in detail. A laboratory scale device is
created and characterized over a wide range of operating parameters. A numerical model
of the device is created and validated against experimental data. The resulting model is
used to create a cost-minimization tool to analyze the conditions needed to achieve
specified cost and efficiency targets.
Experimental results include cooling power, temperature span, pumping power and
work input. Although the magnetocaloric effect of gadolinium is small, temperature
spans up to 30 K are obtained. Analysis of power input shows that the inherent magnetic
work is a small fraction of the total work input confirming the assumption that potential
cycle efficiencies can be large. Optimization of the device generates a number of areas
for improvement and specific results depend upon targeted temperature spans and cooling
powers. A competitive cost of cooling from a dual-nested-Halbach configuration is
challenging and will depend on the ability to create regenerator matrices with near-ideal
adiabatic temperature change scaling as a function of temperature.
Description
Keywords
magnetic refrigeration, magnetocaloric effect, optimization, active magnetic regenerator, exergetic analysis