Dimple plate heat exchangers for a sea-water chiller using CO2 as refrigerant, design and testing.

To ensure proper quality of high value product, cooling is a critical process in the fishing industry. Traditionally, on board pelagic fish cooling is achieved using Refrigerated Sea Water (RSW) refrigeration plants with halocarbon HCFC 22 as working fluid. According to EU-regulations, refilling of this fluid is not allowed from 2015. HFC alternatives have considerable greenhouse warming potential and are heavily taxed in some countries, thus only a short time solution. The main natural alternative, ammonia, has significant drawbacks that can be unacceptable particularly for smaller vessels and for rebuilding of existing ships. Carbon Dioxide (CO2) is an environmental friendly, inexpensive, non-toxic, non-flammable alternative. One drawback is the high operating pressure which could give heavy, bulky and expensive components. In this project a novel dimple plate type evaporator and condenser were developed and tested in a 300 kW cooling capacity RSW plant using CO2 as refrigerant. Optimal geometry was simulated and verified in laboratory tests. Then, new full size heat exchangers and refrigeration racks were mounted in a fishing boat replacing an existing R22 system. Measurements on-board boat showed promising results and the first mackerel catch cooling fulfilled the boat owner's expectations. The heat exchangers are smaller, lighter and cheaper than comparable shell and tube units designed for CO2. Preliminary calculations show that the production cost could be about equal to ammonia units.