The refrigeration system in use aboard today's modern tuna seiners was developed in the late 1930's for use aboard bait boats. Since that time, fishing methods have changed, vessel carrying capacities have increased tenfold, catch rates have increased fivefold, and individual fishwell sizes have increased fourfold. As a result, although catch rates have 9one up, the refrigeration effect per ton of tuna per well has actually gone down. Despite these trends, the current refrigeration system works remarkably well. This is due partly to its inherent flexibility and partly to the durability of the tuna with respect to its intended canned market. Nevertheless, because of the increase in well sizes and catch rates, a small percentage of fish is currently being lost due to inadequate refrigeration. This results in an economic loss to the fishing fleet. These losses seem to occur when many fish are caught at a time and loaded into large fishwells. While part of the solution is operational changes, some of which have been recommended elsewhere [1], 3 it has been suggested that increasing the refrigeration effect per well will also help overcome problems observed in the present system. Of the many alternatives which could increase the refrigeration effect per well, this paper discusses the addition of an external heat exchanger, called a chiller, to augment the refrigeration effect per well provided by the existing coil evaporators lining the fishwell bulkheads. Available data on refrigeration effectiveness of modern tuna seiners are analyzed and a computer simulation of the system is presented. Other computer results deal with augmentation of the present system by the addition of additional refrigeration capacity through an external chiller. In addition, a new model for the heat transfer involved in freezing fish such as tuna is presented.
Cop Enhancement of Vapour Compression Refrigeration System