CONDENSATION OF AMMONIA VAPOR DURING RAPID EXPANSION

The report presents an experimental study, through pressure distributions, of the homogeneous nucleation and condensation of initially super-heated ammonia vapor during its expansion in a low Mach number supersonic nozzle. The results of the experiments are compared with the classical nucleation theory of Becker and Doring or Frenkel-Zeldovich, on the basis of the predicted pressure and temperature at which condensation would occur starting from a given stagnation condition. It is found that ammonia shows far less supersaturation than this theory predicts. The effect of arbitrary corrections to the surface tension showed that a further reduction in surface tension of the drop relative to the flat-film value gives better agreement between measured and predicted pressure distributions. Even better agreement is obtained without a surface tension correction if we assume that the nucleation rate is greater by a factor of 10 to the 17th power.