MINIATURE ENGINEERING SYSTEMS GROUP

MINIATURE CENTRIFUGAL COMPRESSOR TESTING

Presented by

Dipjyoti Acharya

Miniature Centrifugal Compressor Testing

Problems The compressor could run only upto 98,000 rpm.

The factors hindering to achieve our desired speed of 150 K rpm :-

1)The existing Teflon Coupler is not able to transmit power from the motor and causing Bearing Loss as well as failure.2)Three components namely the Motor Shaft, Compressor Shaft and the Coupler are bringing in Vibrations due to MISALIGNMENT .

Solution 1)Eliminate the coupler 2) Compressor and Motor Shafts to be machined to act as male-female joint and acts as a single shaft.

3) Assemble both Motor part and Compressor part by REDESIGNING the whole

HOUSING in SINGLE PIECE.

4) Assembled Part to be LASER ALIGNED.

Compressor and Motor Shaft

Motor Shaft

Compressor Shaft

New Housing

Motor Cooling Jacket

One Bearing to be eliminated

Miniature Motor Issues

The Shaft ( Titanium Alloy) and Magnet (Samarium Cobalt)

Calculated

Stress due to Centrifugal Force

Thermal Analysis

The Magnet and the Shaft have to be assembled at room temperature

The shaft SHRINKS more than the magnet. Hence at room temperature the magnet will be loose fit.

Thermal Stress analysis were based on assumption that Maximum Stress developed in the shaft will be transmitted to magnet.

Maximum Stress due to Centrifugal Force = 1553 MPa

Maximum Thermal Stress developed =388 MPa

Problems with Titanium Shaft Material

The GRADES of Titanium Alloy conveniently available in the market have Yield Strength = 1400 MPa

Our Calculations show Total Stress = 1553 +388 = 1941 MPa

Solution

Feedback from motor group Gap can be increased between the magnet and outer diameter of Shaft.

REDESIGNING AND ANALYSING with GAP = 1.0 mm

Shaft Centrifugal Stress = 728 MPa

Shaft Thermal Stress = 329 MPa

Magnet Centrifugal Stress=251.2 MPa

Magnet Thermal Stress=130 MPa

Total Stress = 1308.2 MPa

728 MPa (Shaft Centrifugal) + 329MPa (Shaft Thermal)+ 251.2 MPa (Magnet Centrifugal)

We can find Titanium Grades for our application !! Yield Strength >1400 MPa

Thermal Stress 130 MPa < Magnet UTS = 833 MPa (Compressive)

Magnet is safe !!

Conclusion

Future WorkTo look for

1) Available GRADES of Titanium and its suppliers

TIMET has Grades with Yield Strength > 1400 MPa

2) Possible ways of machining the section,

SOMEC can do the machining

3) Bearings to operate at 200 K rpm.

Available with Barden Corporation = DN # = 1.5 million

4) Calculating the Critical Speeds of the whole system