The application of vacuum cooling technology has caused a revolution in the green vegetables cold chain distribution system. In summer time, vegetables tend to deteriorate very fast after harvest from the field under high temperature.
It is therefore, necessary to cool the vegetables down to about 0°C within a short time to preserve its freshness.The most effective method to cool down vegetables is under vacuum through self-evaporation of water.The “main principle is when a vacuum chamber is filled with green vegetables and evacuated, the free water in the cell tissues of the vegetables begins to evaporate at a pressure and the vegetables cool themselves due to the latent heat of the evaporating water.Since 597 Cal is required to vaporize 1 gram of water at 0°C, the vegetables are cooled to 0°C in about 20-30 minutes when the chamber is maintained ~t a pressure of about 4.6 Torr. The large amount of water vapor generated inside the chamber is condensed on the surface of the cold trap and removed from the chamber. The system uses a refrigerator to keep the cold trap at a low temperature.