Improved performance of pulse tube refrigerators using thermoacoustics

A wide variety of science is performed at temperatures near and below 4 K. Such low temperatures are commonly achieved using the pulse tube refrigerator, a type of cryocooler that cyclically compresses and expands helium gas to pump heat from the cold end. Here, we discuss three topics demonstrating that thermoacoustic analysis enables substantial gains in the understanding and performance of these refrigerators. We begin by showing that dynamic acoustic optimization of pulse tube refrigerators can lead to a tremendous increase in their cooldown speed (up to 3.5 times the status quo speed). This is a novel technique that is currently being commercialized. Second, we discuss the development of mass flow meters for the study of pulse tube refrigerator compressor efficiency. The flow meters are used to validate a thermoacoustic expression that more simply finds the flow rate using only pressure transducers. Third, we show that a large amount of cooling power may be extracted from the regenerators of these refrigerators without impacting the cooling power available at the cold end. Thermoacoustic analysis reveals that the real-fluid properties of helium are responsible for this capability.