HEAT AND MASS TRANSFER ANALYSIS DURING PRECOOLING OF FOOD PRODUCTS IN COLD STORAGE

Abstract

Heat and mass transfer behaviour during precooling of fruits and vegetables exposed to cold air has been widely investigated and reported in literature and studies. However, the variation in heat and mass transfer behaviour while fruits and vegetables are placed in sufficient number inside a package has not been investigated in any systematic manner. This variation of temperature inside will depend upon the type of fruits and vegetables, the sizes of the packages and the cooling medium. In present investigations main emphasis is given€othe study of temperature variation of different fruits and vegetables on packaging. An experimental setup is used which s :mulates the precooling process to obtain the time-temperature variations inside individual and packed fruits and vegetables. Packages taken were made of common card board which is normally used in commercial packaging. These package were taken in different sizes and freely suspended inside the duct where cold air was forced upon it at a speed of 6.4-6.6 m/s. Investigations were conducted on apple, orany,e, sapota, ,rapes and ladyfinger. Measured Time-Temperature histories are used to calculate the thermal diffusivity by comparing them with Gurnie-Lurie charts. Thermal conductivity values for calculating above values of thermal diffusivity were taken from literature in case of individual food commodity, but in case of packages a scheme of calculation is proposed to calculate thermal conductivity on the basis of air column inside package. Thermal conductivity value are also calculated on the basis of the measured thermal diffusivity and specific heat of packages. These values of thermal conductivity and the calculated thermal diffusivities are fed to the computer programmes written in FORTRAN-77 language to calculate back time temperature characteristics. The calculated time temperature characteristics have been found to agree well with the measured data. ***