Diaphragm Pressure Wave Generator Developments at Industrial Research LTD

Abstract

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.

A free-piston Stirling cryocooler using metal diaphragms

“…Diaphragm pressure wave generators (DPWG) developed by Industrial Research Ltd, now called Callaghan Innovation [1][2][3][4], have matured over the last decade to become a useful alternative to linear motor pressure wave generators for Stirling and pulse tube cryocoolers [5][6][7][8]. To date, 15 metal diaphragm pressure wave generators have been made and operated with swept volumes from 20 cc to 1000 cc and with 500 W to 30 kW input power, respectively.…”

Co-Axial pulse tube for oxygen liquifaction

“…Pulse tube technology was chosen to provide the expansion, and therefore the coldhead, part of the cryocooler. Two previous inline pulse tubes [2,3] of different sizes and one U-tube pulse tube have been designed, built and run at IRL with varying degrees of success. Most of the previous designs have been used as loads for PWG development.…”