Some design parametric considerations of cryogenic pre-cooler for spices grinding

Abstract

Some design parametric considerations of cryogenic pre-cooler for grinding of spices (fenugreek and coriander seed) were studied. In conventional or ambient grinding of spices, temperature rise causes fat malting and sieve clogging. In grinding operation, spices lose a significant portion of their volatile oil or flavouring components due to rise in temperature. To overcome these drawbacks, cryogenic grinding is employed which is referred as the grinding of spices in the presence of a cryogenic fluid. A Cryogenic spice grinding system consists a pre-cooling unit (cryogenic pre-cooler) and grinding unit (grinder). The cryogenic pre-cooler plays very important role for cryogenic grinding of spices. Some design parameters of cryogenic pre-cooler (e.g. total freezing time, screw length and capacity etc.) were computed for grinding of fenugreek and coriander seed. Total freezing time is a one of the important deciding parameter for screw length. For constant values of screw diameter and pitch, the capacity and screw length of pre-cooler were computed at different speed (3, 6, 9, 12 and 15 rpm) of cooling screw of the cryogenic pre-cooler. It was found that the screw length and capacity of cryogenic pre-cooler for fenugreek and coriander seeds increased linearly with increase in cooling screw speed from 3 to 15 rpm.