Simulation of a Refrigerated Sea Water (RSW) Based Cooling System for a 30 GT Purse Seine Fishing Boat

Abstract

The use of block ice by traditional fishermen at Muncar Port, Banyuwangi, presents technical and economic limitations, such as increased vessel weight leading to higher fuel consumption and reduced cargo hold capacity. This thesis research aims to design and analyze the performance of a Refrigerated Sea Water (RSW) cooling system using a closed-loop recirculation method for the hold of a 30 GT purse seine vessel (KM Kota Abadi). The system is designed to cool 11,144 kg of pelagic fish from an initial temperature of 30 °C down to −5 °C within a target time of 3 hours. Based on analytical calculations, the total cooling load required is 4,094 MJ, necessitating a design refrigeration capacity of 436 kW using R404A refrigerant and a semi-hermetic screw compressor. The chilled seawater circulation system requires a flow rate of 100 m³/h, evenly distributed through 8 spray nozzles per hold at a spray velocity of 8 m/s.

Cooling performance evaluation was conducted through 3D transient Computational Fluid Dynamics (CFD) simulations using ANSYS Fluent across 90% and 70% hold filling rate variations. The numerical model was validated against the transient analytical results at the 30th second, demonstrating high agreement with a percentage error in Area-Weighted Average Wall Heat Flux of only 3.22% (7,989.13 W/m² for the numerical model versus 7,740.00 W/m² for the analytical method). Simulation results revealed that although the air temperature distribution inside the hold was relatively similar for both variations (~271 K to ~307 K), the wall heat flux parameter on the fish surface showed significant differences in cooling effectiveness. A 70% filling rate proved to be faster and more effective due to lower thermal load and minimal shadowing effect, whereas a 90% filling rate resulted in slower heat dissipation with a maximum heat flux peaking at 6,687 W/m² (18.3% higher than the 70% variation).