APPLICATION OF A NEW SELECTION ALGORITHM TO THE DEVELOPMENT OF A WIDE-RANGE EQUATION OF STATE FOR REFRIGERANT R134A

Refrigerant R134a (1,1,1,2-tetrafluoroethane) is a leading substitute for refrigerant R12. As such, there has been worldwide activity to dev elop accurate wide-range equations of state for this fluid. In this st udy, we have developed a new selection algorithm for determining high- accuracy equations of state in the Helmholtz representation. This meth od combines least-squares regression analysis with simulated annealing optimization. Simulated annealing, unlike stepwise regression, allows for the controlled acceptance of random increases in the objective fu nction. Thus, this procedure produces a computationally efficient sele ction algorithm which is not susceptible to the function-space local-m inima problems present in a purely stepwise regression approach. Two e quations are presented in this work and compared against experimental data and other high-accuracy equations of state for R134a. One equatio n was produced strictly by using stepwise a regression algorithm, whil e the other was produced using the simulated-annealing selection algor ithm. In both cases the temperature dependence of the equations was re stricted to have no terms whose exponents were greater than five.