In some applications, an expander is used to achieve maximum refrigeration in a low-flow process stream. The potential energy recovered from the gas expansion is not sufficient to justify the investment of an attached generator, or it may not be feasible to attach a booster compressor. In this situation, the energy is absorbed by a dynamometer wheel rotating in a liquid system. A dynamometer is sometimes referred to as a brake. The dynamometer dissipates the energy into the liquid through a pumping action. The liquid is normally contained in a closed loop system that incorporates a cooler to keep the liquid at a predictable viscosity. Both Oil and Hydraulic systems are available.
The sizes 10-40 and 20-70 as indicated above can be combined with a dynamometer to form a turbo-expander / generator package.