Rapid Freezing of Soybeans by Liquid Nitrogen

Abstract

Direct freezing of soybeans by liquid nitrogen were tried at various moisture contents. The results obtained from the measurements of transient temperature and the observation of bubble generation during freezing were as follows:
1) An differential equation of heat balance was introduced assuming that temperature is uniform in a soybean grain and depends on the freezing ratio of Heiss formula. The equation was solved numerically by Runge-Kutta-Gill method and the obtained one agreed well with the observed one.
2) The photographs of bubbles on the soybean surfaces during freezing revealed that the boiling mode was a nucleate one. Consequently, an equation on heat balance was developed. Analyzing this equation by Runge-Kutta-Gill method and fitting the predicted curves to the observed values, the characteristic value of α on the heat transfer in nucleate boiling of soybeans was determined.