Industrial Research Ltd (IRL) previously developed a single-stage, inline, pulse tube for use with their metallic-diaphragm pressure wave generator (PWG), achieving 45 W of cooling power at 77 K, with 19.5 % of Carnot efficiency (based on the PV input power). This paper describes the conversion of the inline pulse tube to a co-axial configuration that provides a more accessible cold finger. Sage pulse tube simulation software was used to model the modified pulse tube and predicted 105 W of cooling power at 90 K, with an indicated input power of 1350 W. The pulse tube operated at 50 Hz, with a mean helium working pressure of 2.5 MPa and was closely coupled to a 60 ml swept volume PWG. The experimental results yielded more than 100 W @ 90 K with 2.5 MPa of gas pressure, with a lowest no load temperature of 39.7 K with 1.4 MPa of gas pressure. Details of the development, experimental results and correlations to the Sage model are discussed.

Industrial Research Ltd (IRL) have been developing a unique diaphragm based pressure wave generator technology for pulse tube and Stirling cryocoolers. Our system uses a metal diaphragm to separate the clean cryocooler gas circuit from a conventionally lubricated mechanical driver, thus producing a clean pressure wave with a long life drive that does not require the precision manufacture and associated costs of large linear motors. The first successful diaphragm pressure wave generator produced 3.2kW of acoustic power at an electro-acoustic efficiency of 72% with a swept volume of 200ml and a prototype has now accumulated over 2500 hours running. This paper describes recent developments in the technology. To explore scaling, a small diaphragm pressure wave generator with a swept volume of 20ml has been constructed and has delivered 454W of acoustic power at an electro-acoustic efficiency of 60%. Improvements have been made to the hydraulic force amplifier mechanism for driving the diaphragms resulting in a cheaper and lighter mechanism than the mechanical linkage originally used. To meet a customer's specific requirements, the 200ml pressure wave generator's stroke was extended to achieve 240ml of swept volume thereby increasing its acoustic power delivery to 4.1 kW without compromising efficiency.

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