The secondary refrigerant freezing process has been described by mathematical models of the major system components. The mathematical equations were used with the aid of a computer to study the operational-design economics of a freezing process and to predict the best operating conditions. Optimization computations showed that the economics of process operation depend largely on the temperature maintained in the freezer and the overall difference in refrigerant and equilibrium freezing temperature. The effect of departures from optimal design are assessed. An analysis of the linearized freezer dynamic equations showed the freezer to be stable and did not indicate regions of difficult control.