Generally, the actual cooling capacity of expander is always less than the theoretical cooling capacity. Under the same inlet and outlet pressure and inlet gas temperature, the lower the efficiency of expander, the smaller the unit refrigerant cooling capacity and the smaller the temperature drop efficiency of expander.
The efficiency of expander depends on the size of various losses inside the expander. Due to the existence of various losses, the ability of gas to do external work is reduced in varying degrees. To sum up, the losses mainly include the following aspects:
1.When the air flow passes through the work wheel and the deflector, the loss caused by friction and air flow impact on the runner surface is called flow loss.
2.When the impeller is rotating, the friction heat generated by the gas around the wheel disc will increase the temperature of the gas, which is called friction blast loss.
3.When the gas passes through the deflector, the leakage from the gap between the working wheel and the casing is called the internal leakage loss; the leakage along the axial clearance through the rear of the wheel disc is called the external leakage loss.
4.When the gas passing through the expander still has a certain speed at the outlet of the expander, it is called residual velocity. The larger the residual velocity is, the greater the energy loss is. This part of the loss is called residual velocity loss or exhaust loss.
