Cooling of a compressor shaft gas bearing
A heat transfer circuit includes a compressor, a condenser, an expander, and an evaporator. The compressor includes a shaft that is rotated to compress a working fluid and a gas bearing to support the shaft. A conduit is configured to supply a portion of the working fluid to the compressor to cool the gas bearing. A method of controlling a heat transfer circuit includes directing a working fluid through a main flow path of the heat transfer circuit that directs the working fluid through a compressor, a condenser, an expander, an evaporator, and back to the compressor. The method also includes suppling supplying a portion of the working fluid in the main flow path to the compressor to cool a gas bearing of the compressor.
1 . A heat transfer circuit, comprising:
a compressor including:
a housing,
a shaft rotatable relative to the housing to compress a working fluid, and
a radial gas bearing including an outer radial surface of the shaft and a radial support surface of the housing, the outer radial surface having grooves that direct gas between the outer radial surface and the radial support surface when the shaft is rotated to form a layer of the gas between the radial support surface and the outer radial surface, the layer of gas configured to radially support the shaft, the shaft having a radius r at the radial gas bearing, and a radial clearance in the radial gas bearing between the outer radial surface and the radial support surface is at or less than 0.0011 of the radius r of the shaft;
a condenser to cool the working fluid,
an expander to expand the working fluid;
an evaporator to heat the working fluid with a process fluid;
a main flow path traveling through the compressor, the expander, and the evaporator, and back to the compressor;
a conduit extending from the condenser, the evaporator, or between the condenser and the evaporator in the main flow path and to the compressor, the conduit configured to supply a portion of the working fluid to the compressor to cool the radial gas bearing; and
a controller configured to control a flowrate of the portion of the working fluid supplied through the conduit to the compressor based on preventing heat in the radial gas bearing from exceeding a predetermined amount, and the controller being configured to control the compressor to rotate the shaft such that a speed of the outer radial surface of the shaft is at or greater than 25 m/s.
2 . The heat transfer circuit of claim 1 , wherein the conduit selectively supplies the portion of the working fluid.
3 . The heat transfer circuit of claim 1 , wherein the outer radial surface of the shaft is a material with a thermal expansion coefficient that is at or less than 20×10 −6 m/(m*k).
4 . The heat transfer circuit of claim 1 , wherein the outer radial surface of the shaft is a material with a thermal expansion coefficient that is at or less than 15×10 −6 m/(m*k).
5 . The heat transfer circuit of claim 1 , wherein the outer radial surface of the shaft comprises one or more of silicon nitride, tungsten carbide, kovar, and alumina.
6 . The heat transfer circuit of claim 1 , wherein the portion of the working fluid cools the radial gas bearing while remaining separate from the layer of the gas.
7 . The heat transfer circuit of claim 1 , wherein the radial support surface includes two or more apertures each respectively fluidly connected to the conduit, the portion of the working fluid flowing through the two or more apertures and between the radial support surface of the housing and the outer radial surface of the shaft to cool the radial gas bearing.
8 . The heat transfer circuit of claim 1 , further comprising:
a second conduit extending within and from the compressor, wherein
the compressor includes a suction inlet and a discharge outlet, the working fluid in the main flow path entering the compressor through the suction inlet and exiting the compressor through the discharge outlet, and
the portion of the working fluid entering the compressor through the first conduit and exiting the compressor through the second conduit.
9 . A method of operating a heat transfer circuit, the heat transfer circuit including a compressor with a radial gas bearing and a shaft, a condenser, an expander, and an evaporator, the method comprising:
directing a working fluid through a main flow path of the heat transfer circuit, the main flow path directing the working fluid through the compressor, the condenser, the expander, the evaporator, and back to the compressor, the directing of the working fluid through the main flow path includes rotating the shaft of the compressor to compress the working fluid, the radial gas bearing including an outer radial surface of the shaft and a radial support surface of a housing, the rotating of the shaft causing grooves in the outer radial surface of the shaft to direct gas between the outer radial surface and the radial support surface to form a layer of the gas between the outer radial surface and the radial support surface that radially supports the shaft while rotating, wherein the rotating of the shaft of the compressor to compress the working fluid includes controlling, with a controller, the compressor to rotate the shaft such that a speed of the outer radial surface of the shaft is at or greater than 25 m/s; and
supplying a portion of the working fluid in the main flow path at the condenser, at the evaporator, or between the condenser and the evaporator to the compressor to cool the radial gas bearing, wherein the supplying of the portion of the working fluid to the compressor to cool the radial gas bearing includes controlling, with the controller, a flowrate of the portion of the working fluid supplied to the compressor based on preventing heat in the radial gas bearing from exceeding a predetermined amount,
wherein the shaft has a radius r at the radial gas bearing, and a radial clearance in the radial gas bearing between the outer radial surface and the radial support surface is at or less than 0.0011 of the radius r of the shaft.
10 . The method of claim 9 , wherein the supplying of the portion of the working fluid to the compressor to cool the radial gas bearing is selectively supplying of the portion of the working fluid to the compressor to cool the radial gas bearing.
11 . The method of claim 9 , wherein the outer radial surface of the shaft is a material with a thermal expansion coefficient that is at or less than 20×10 −6 m/(m*k).
12 . The method of claim 9 , wherein the outer radial surface of the shaft is a material with a thermal expansion coefficient that is at or less than 15×10 −6 m/(m*k).
13 . The method of claim 9 , wherein the outer radial surface of the shaft comprises one or more of silicon nitride, tungsten carbide, kovar, and alumina.