Air Liquefaction

This example models a Linde-Hampson air liquefaction cycle using the two-phase fluid components. The compressor drives the vapor air through two heat exchangers, recuperator, expansion valve, and storage tank. The first heat exchanger contains water at atmospheric temperature, while the second heat exchanger contains refrigerant. The pressure drops as the cooled air passes through the expansion valve which results in condensation. The air and entrained condensation then pass through a receiver tank where the condensation separates from the air. The liquid air is stored in a receiver tank while the vapor air is circulated back to the compressor.

Model

The figure shows the model of an air liquefaction cycle with its subcomponents.

Fluid Properties

This example uses air as the working fluid, which is modeled as pseudo-pure.

p-h Diagram of the Linde-Hampson Cycle

This figure shows the state of the fluid at the four points on the air liquefaction p-h diagram: at the compressor inlet, compressor outlet, expansion valve inlet, and expansion valve outlet. The black contour is the saturation dome of the air. Note that the lines joining the four states in the p-h diagram do not represent the fluid process.

Simulation Results from Simscape Logging

This figure shows the compressor parameters over the time. The output pressure of the compressor increases to ~110 bar initially and settles around ~62 bar. The pressure output of the compressor can be varied by changing the area of the throttle valve.

This figure shows the figure of merit of the compressor over the time. Figure of merit is the ratio of the ideal work done per unit mass of the air liquefied to the actual work done per unit mass of the air liquefied. It is a measurement of the efficiency of the compressor.

This figure shows the input and output temperatures for the throttle valve and vapor fraction of the fluid at the outlet of the throttle valve. The temperature drop obtained across the throttle valve is ~70K and the vapor fraction is ~0.87. The liquid fraction of the air gets accumulated in the receiver tank while the gas fraction of the air goes to the inlet of the compressor.