Обґрунтування умов швидкого заморожування харчових продуктів

Abstract

Запропоновано методику технологічного розрахунку тривалості швидкого заморожування, яка повинна складатися з двох етапів. На першому визначають умови, за яких можливе швидке заморожування, тобто розраховують потрібний коефіцієнт тепловіддачі для заданого розміру продукту, а на другому етапі – безпосередньо загальну тривалість процесу заморожування, з урахуванням його теплофізичних характеристик, що забезпечують задану лінійну швидкість заморожування.

The well-known Plank formula for calculating freezing duration is the most simple and quite universal formula. It well describes the duration of freezing front advancing from the surface to the center of the product. However, this formula cannot be used under rapid freezing conditions since it does not consider the further cooling of the product which is being frozen. The further advancement of this formula is the one considering terminal heat capacity of frozen part and body shape coefficient of the product. Authors made the same assumptions as in the case of Plank formula. However, the integral equation of energy conservation and transfer with phase transitions for arbitrary volume which consists of freezing front and layer of frozen product was used. Based on these calculations there exists the maximal characteristic product size for which the rapid freezing mode is applicable. Thus, in order to provide rapid freezing mode it is necessary to determine the relationship between the characteristic product size and the intensity of external heat transfer. According to the authors, the method of calculating the duration of rapid freezing should consist of two stages. On the first stage the conditions under which the fast freezing is possible are defined. Also the necessary heat transfer coefficient for a given amount of product is defined. On the second stage the overall duration of the freezing process is calculated considering the time required for cooling and final freezing.