1. Numerical Analysis of Inertance Pulse Tube Cryocooler with a Modified Reservoir
Derick Abraham1, Damu C2, Biju T Kuzhiveli1
1Centre for Advanced Studies in Cryogenics(CASC), National Institute of Technology Calicut, India.
2Sambhram Institute of Technology, Bangalore, India.
INTRODUCTION
ELECTRICAL CIRCUIT ANALOGY
COAXIAL CRYOCOOLER DESIGN
RESULTS
ABSTRACT
In the harmonic approximation, in which the oscillatory pressures and velocities are considered to be essentially sinusoidal in time, a simple AC electrical circuit illustrates the principle. Oscillating pressure is analogous to AC electric voltage, and oscillatory volumetric velocity is analogous to AC electric current.
Cryocooler Structure: The structure of a coaxial PTC with modified reservoir driven by a linear motor is as shown in Figure 1.
Modelling: Modelling of the cryocooler was done with the help of Sage v11 software and Ansys Work bench.
The appropriate length and inner diameter of the Pulse Tube are then determined to be 79.3 mm and 15 mm respectively.
The appropriate length of regenerator is selected as 74.3 mm, the best compromise length.
For regenerator the inner diameter is 15mm and outer diameter is 25mm.
The phase difference between pressure and mass obtained at cold tip is 49º.
The cooling capacity obtained at 80K is 2.43W
The COP obtained is 9.13% of COPcarnot.
The reservoir volume is reduced to 200cc.
Cryocoolers are increasingly employed in areas such as cooling superconducting devices, basic scientific research, space and military applications. Among various types of cryocoolers, the pulse tube cryocooler (PTC) is considered as an ideal candidate for miniaturised coolers. The absence of any moving component at the cold end brought to the PTC several attractive advantages such as simplicity in fabrication, potential long life and reliability in operation.
Pulse tube cryocoolers are used for cooling applications, where very high reliability is required as in space applications. The Pulse tube cryocooler requires a buffer volume depending on the temperature and cooling load. A miniature single stage coaxial Inertance Pulse Tube Cryocooler is proposed which operates at 80K to provide a cooling effect of at least 2W. In this pulse tube cryocooler a modified reservoir is suggested, where the reverse fluctuation in compressor case is used instead of a steady pressure in the reservoir to bring about the desired phase shift between the pressure and the mass flow rate in the Cold Heat Exchanger. Therefore, the large reservoir of the cryocooler is replace by the crank volume of the hermetically sealed linear compressor, and hence the cryocooler is simplified and compact in size. The components of the cryocooler consisting of a connecting tube, aftercooler, regenerator, acceptor, flow straightener, pulse tube, warm heat exchanger, inertance tube and the modified reservoir along with the losses were designed and analysed. Each part of the cryocooler was analysed using Sage v11 and Ansys Fluent. The simulation results clearly show that there is about 50% reduction in the reservoir volume.
Pm Mean pressure
γ Ratio of specific heat
ω Angular frequency
ρ Density
A Area of cross section
µ Dynamic viscosity
δv Viscous penetration depth
ϕ Porosity
L Length
Capacitance(C) =
Inductance(L) =
Resistance(R) =
Figure 3. 2D axis symmetric CFD model of the modified inertance pulse tube cryocooler (figure not to scale).
INERTANCE PULSE TUBE CRYOCOOLER
WITH MODIFIED RESERVOIR
A miniaturised single-stage coaxial pulse tube cryocooler with a modified reservoir operating at 80K has been proposed to provide appropriate cooling of infrared focal plane arrays. For this application, a typical design might call for at least 2W of net cooling power at 80K at no load with Helium as refrigerant. This Inertance pulse tube cryocooler uses an inertance tube and a modified reservoir to control the phase difference.
Features
Coaxial type pulse tube cryocooler occupies less space.
Reverse fluctuation of pressure in the compressor case is utilized instead of the steady pressure in the reservoir.
Reservoir volume is reduced considerably.
Equivalent performance comparable to other cryocoolers.
CONCLUSIONS
Figure 4. CFD Mesh file (Coaxial head)
The performance of a pulse tube cryocooler depends on the phase angle between the pressure and flow rate phasors.
Electrical circuit analogy supports the fact that the modified reservoir cryocooler could work effectively.
Using the crankcase volume as Reservoir volume creates the potential for DC flow circulation, which can reduce cooling power.
The Sage model analysis consider the effect of DC flow circulation.
The results shows the designed cryocooler has 9.13% Carnot efficiency considering DC flow involved.
Figure 2(a). An IPTC Electrical circuit model. (b). Modified reservoir model, fluctuation pressure represented as P2.
Working Fluid
Helium
Mean Pressure
3.0 MPa
Temperature
80K
Reject
300K
Compression ratio of
compressor
1.18
Volume of Compressor
5cc
Reservoir volume
200cc
COP/COPcarnot
9.13%
Figure 5. Variation of COP/COPcarnot
and cooling capacity at 80 K with regenerator length.
Figure 6. Pressure variation in the compression
space volume and reservoir volume .
REFERENCES
Figure 1. Schematic diagram of a inertance pulse tube cryocooler with a modified reservoir driven by linear motor (figure is not to the scale).
[1]R. Radebaugh, Low Temperature and Cryogenic Refrigeration, pp , 2003.
[2]D. L. Gardner and G. W. Swift, Cryogenics, vol. 37, no. 2, pp. 117–121, Jan
[3]Wang X, Luo E, Dai W, Hu J, Zhou Y. AIP; 2012; Available from:
[4]H. Dang and Y. Zhao, Cryogenics, vol. 78, pp. 40–50, Sep
CONTACT
Derick Abraham,
National Institute of Technology Calicut, Kerala, INDIA, Pin:
Figure 7. Variations of COP/COPcarnot
and cooling capacity at 80 K with reservoir volume.
Figure 8. Phase diagram of pressure and mass
for the modified coaxial pulse tube cryocooler.
Table 1. Parameters of the Modified IPTC.