30 kW metal diaphragm pressure wave generator

Abstract

Abstract. Callaghan Innovation has been developing a metal-diaphragm pressure wave generator technology for pulse tube or Stirling cryocoolers since 2005. A series of successful pressure wave generators have been designed, fabricated and demonstrated ranging in swept volume from 20 to 240 cc driven by commercially available induction motors of powers from 0.5 kW to 7.5 kW respectively. A number of pulse tubes have also been design and successfully trialed with these pressure wave generators. Cooling powers up to 600 W at 120 K have been achieved. We have now scaled the pressure wave generator technology to 1000cc swept volume, powered by a 30 kW induction motor with the intention of providing over 20 kW of acoustic power to either pulse tube or Stirling expanders. The aim is to develop a cryocooler with more than 1000 W of refrigeration at 77 K. Target applications include liquefaction and High Temperature Superconducting devices. Initial results from testing the 1000 cc pressure wave generator are presented and we will discuss the challenges and advantages involved in scaling the metal diaphragm technology to higher acoustic powers.

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.…”

Commercialisation of Pulse Tube cryocoolers to produce 330 W and 1000 W at 77 K for liquefaction

“…The design of the 330 cc DPWG was based on the successful 90 cc DPWG [7], which had counter-rotating shafts and a hydraulic lifter to move the diaphragms. Features from the 1000 cc DPWG prototype [3] were incorporated into the 330 cc design such as: improved lifter details and water cooling, and an external oil sump. The result was a production-ready DPWG with 330 cc of swept volume, capable of producing 7 kW of PV power from ~12 kW of motor input power.…”

“…Three identical PTC330 pulse tubes were manufactured for mounting on a single 1000 cc DPWG [3] to create the PTC1000 cryocooler. The area of the DPWG's compression diaphragm was divided into three equal segments with the pulse tubes positioned at the centroids of their respective area segments.…”

“…The ideal cryocooler unit size for these systems is 1 to 2 kW. For these reasons Callaghan Innovation developed the 1000 cc DPWG [3] as a key enabler for industrial cryocoolers of over 1000 W at 77 K capacity. The DPWG has been designed for manufacture in small batches, therefore not requiring high production numbers to reduce cost.…”

“…The DPWG has the simplicity and low cost of a lubricated crank system with the diaphragms providing a non-rubbing hermetic seal to maintain a clean cryocooler working gas. To date, 15 pressure wave generators have been made with swept volumes from 20 cc to 1000 cc [1]- [3]. These have all been coupled to pulse tube [4]- [7] or Stirling [8], [9] cold heads.…”